master nanoscience and nanotechnology - ku leuven · 2013. 5. 7. · master nanoscience and...

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Master Nanoscience and Nanotechnology

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nanomaterials and nanchemistry nanoelectronic design bionanotechnology nanodevices and nanophysics

Investigation and optimization of the electrical switching properties of scaled Ta2O5-based resistive RAM memory cells

The Resistance RAM (RRAM) is a new class of memories emerging as serious candidate for future memoryreplacement. Resistance RAM cells typically consist of an insulator material sandwiched between two metalelectrodes, and exhibiting resistive-switching properties, that is to say the application of an electrical current/voltageto the cell induces reversible changes of the cell resistance, which allows thus programming different memory states.For metal/oxide/metal RRAM devices, the switching to the low resistance state (LRS) is understood as the formationof oxygen-vacancy chain through the oxide while the return to the high resistance state (HRS) is due to partialrecovery of these defects, the two operations being electrically induced.Ta2O5 materials have recently drawn a lot of attention due to excellent set of RRAM memory propertiesdemonstrated recently on scaled cells. Not only controlled memory operation, low programming power, and gooddata retention were demonstrated, but also in particular longer write-programming endurance results were obtainedon such material than on other switching oxides.

However, little is known yet with respect to the switching mechanisms and improvement potentials in Ta2O5-basedRRAM. We recently undertook the integration development of scaled Ta2O5 RRAM memory cells stacked onmemory-select transistors. The purpose of the internship will be to study the effect of processing and cell-stackmaterial combinations (including electrodes) on the electrical-switching properties. To this aim, the following methodswill be used:• Standard I-V measurements• Constant voltage stress tests• Above methods at different temperatures• Pulse programming using sub-10ns wide electrical pulses• Possible C-V measurements• Possible modeling activity

The study will be carried out within a project team consisting of experts in different fields (processing, integration,physical characterization, modeling ...), so that the understanding and modeling of the electrical results can befacilitated.

The study will also be realized in close collaboration with industrial partners. The gained understanding of theswitching will allow defining an optimum stack configuration satisfying the industrial specification for memoryoperation.

Guido Groeseneken

IMEC/CMOST/MDD

Ludovic Goux✔

electrical characterization

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Using variational calculus to solve Poisson's and Schroedinger's equationsself-consistently within a single loop: how far can we go?

Transport calculations for modern semiconductor devices heavily rely on the the local charge distribution and therelated electrostatic potential established inside a device structure. As such, one is bound to solve the Schroedingerequation self-consistently with Poisson's equation and a number of constitutive equations relating the electron andhole concentrations to the wave functions of the quantum states and their occupancies. Designing appropriatenumerical code to deal with this task, one is immediately faced with a significant computational burden due to thehighly non-linear and non-local dependence of the charge density on the potential. Moreover, the necessity offeeding back the charge density into the module that solves Poisson's equation is reflected in the conventional,double loop that handles the fully self-consistent solution.Recently, an efficient but non-linear variational principle has been developed that provides a simultaneous solution ofall equations involved, while being carried out merely within a single loop that minimizes a proper action functional.So far however, the necessary condition that the charge density be a local functional of the potential, has restrictedthe application of the principle to cases where the adiabatic approximation or local density approximation leads toan acceptable description of the quantum mechanical charge density. The purpose of this thesis is to work out thenon-linear variational principle for a number of simple test structures (e.g. planar and/or double-gate MOScapacitors or nanowires) and to explore any possible extension of the variational calculus beyond the local densityapproximation.

Mark Fannes

Wetenschappen / Instituut voor Theoretische Fysica

Wim Magnus / Bart Soree✔

Theory (quantum mechanics) and numerical programming

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flip-chip packaging for RF, mm-wave and sub-THz chips

As Moore's Law continues, the operating frequency of CMOS chips also improves. Today, the ESAT-MICASresearch group at KU Leuven has already designed several chips in the 60-200GHz frequency range. This newfrequency range enables a wide range of applications, ranging from radar, imaging, detection and communication.

However, packaging at these high frequencies remains a challenge. Flip-chip packaging on a high-frequency boardor laminate is the most promising solution. ESAT has flip-chip capabilities in-house.

This thesis will focus on the (1) the modelling of the flip-chip interface, (2) how to take this interface into accountduring circuit design and (3) perform some actual tests in our lab to investigate the yield of the flip-chip process.

The thesis can be steered more towards circuit design or towards testing depending on the interest and backgroundof the students.

Prof. Patrick Reynaert

KU Leuven ESAT-MICAS

Patrick Reynaert / Shailesh Kulkarni✔

modelling/analysis, testing and/or design

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Separation of rare earths with functionalized nanomagnets

For separation of rare earths, one cannot rely only on differences in chemical properties, but also on differences inphysical properties, such as magnetic properties. The magnetic properties of lanthanide ions are well known and notonly lead to applications as permanent magnets, but also to NMR shift reagents and MRI contrast agents. With theexception of La3+, Lu3+, Y3+ and Sc3+, the trivalent rare-earth ions are paramagnetic, due to the presence ofunpaired electrons in the 4f valence shell. The paramagnetism can be expressed by the magnetic susceptibility or bythe effective magnetic moment. In contrast to the d-block transition metals, the magnetic moment of the f-blockelements does not only depend on the number of unpaired spins, but also on the orbital angular momentum quantumnumber L (Van Vleck theory). Therefore, the highest magnetic moments are not observed for Gd3+ (7 unpairedelectrons), but for Dy3+ and Ho3+. Diamagnetic compounds have the tendency to be pushed out of a magnetic fieldand paramagnetic compounds have the tendency to be pulled into a magnetic field, these magnetic properties can beused to separate paramagnetic rare-earth ions from diamagnetic ions, and to separate ions with different magneticmoments. Magnetic core-shell particles functionalized with coordinating groups (e.g. EDTA or DTPA) will be used forthe selective extraction of rare earth ion from acidic solutions. Such nanoparticles have been used in the paste forsequestering of heavy metal ions from waste water streams. After loading of the magnetic nanoparticles with themetal ions, they can easily be removed from the solution with the aid of a permanent magnet. However, the influenceof the magnetic properties of the nanoparticles on the binding of rare-earth ions has never been investigated.Whereas Y3+ and Dy3+ have very similar chemical properties, their magnetic properties are very different (Y3+ isdiamagnetic and Dy3+ is strongly paramagnetic) so that it can be anticipated that the uptake of these ions by themagnetic particles shows differences. A main objective of the project is therefore to investigate how the uptake of therare-earth ions by the functionalized nanomagnets is influenced by their magnetic properties.

Prof. Dr. Koen Binnemans (sup.)/ Prof. Dr. Thierry Verbiest (cosup.)

Faculty of Sciences/ Molecular Design and Synthesis

David Dupont✔

Experimental work: synthesis, characterization, analytical chemistry methods

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Modeling and verification of EMC specifications for ICs for medicalapplications

Electro-Magnetic compatibility is of uttermost importance for the development of electronic systems, like for instancebrain stimulation ASICs. Just think about a mobile phone at your ear, sending out power in the 900MHz frequencyband, and the impact of this on the very sensitive analog circuitry in brain implants. There exist a wide variety ofspecifications at the system level, but more and more the specifications also arise at the IC level.However, most standards, also at the IC level, are in terms of electro-magnetic fields and are not compatible with acircuit simulator like spice or spectre.

The purpose of the thesis is to focus on one specific standard, the TEM-cell standard for electro-magneticsusceptibility. This standard has to be translated into a specification for the analog circuit designer. Field solver toolslike Fast Henry will have to be used to translate a complex 3-dimensional problem into a model that is both accurateenough and simple enough to be handled by the design environment of the analog circuit engineer. Electro-magneticcoupling to PCB tracks, bondwires, etc. will have to be investigated. High-precision analog blocks like a bandgapvoltage reference circuit can be used as a DUT for the developed models. To verify the accuracy of the model,measurements can be performed in the lab with a real-life TEM-cell.


KU Leuven ESAT-MICAS

Patrick Reynaert / Maarten Tytgat / Carolien Hermans (IC Sense)✔

modelling/analysis, testing and/or design

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Traction Force Microscopy of migrating endothelial cells

Background:Angiogenesis, the formation of new blood vessels from pre-existing ones, is crucial for any wound healing response.In addition, angiogenesis plays a major role in tumour growth and metastasis. Angiogenesis among others involvesthe migration of endothelial cells, which in turn relies on the generation of tractional forces by means of the cells ontheir surrounding extracellular matrix (ECM). These forces can be quantified by means of a technique called tractionforce microscopy (TFM). It requires the calculation of displacements fields in the ECM, as well as the retrieval of theforces that cause these displacement fields. Both steps may induce significant errors, which is among others relatedto the quality of the acquired microscopy images. At the University of Navarra (Spain) a simulator was developed toquantify error propagation, induced by different TFM algorithms.

Content:The student will apply and (if necessary) extend the TFM simulator for the study of a migrating endothelial cell on and(depending on the progress) in hydrogel substrates. To this extent, model settings will have to be adapted to ongoingin vitro experiments, requiring among others the determination and implementation of settings related to cell shapeand adhesion, hydrogel mechanical and optical properties, fluorescent beads (or labels) for tracking displacements,type of optical microscope, image resolution and noise. The goal is to provide quantitative guidelines on the accuracyof different TFM algorithms and what are the best strategies to increase this accuracy for the study of tractionalforces during endothelial cell migration.

Hans Van Oosterwyck

Engineering Science / Biomechanics

Alvaro Jorge Peñas✔

mostly computational / partly experimental

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Non-invasive monitoring of tissue-engineered construct performanceusing an in vitro bioluminescence imaging method

Background:Cellular therapies using hydrogel encapsulation have emerged as a promising treatment for many otherwiseuntreatable diseases and disorders. However, widespread clinical implementation has been hampered partiallybecause of poor long-term functionality and survival of therapeutic cells. In particular, it is not well understoodwhether graft failure may be the simple result of cell death following transplantation and, if so, when it occurs andwhat is at its origing. A non-invasive imaging method that can probe cell viability would therefore speed up humantranslation of cell therapies.A powerful and robust technique to probe cell health is by imaging reporter gene activity or bioluminescence imaging(BLI). This method makes use of the transcription and translation of reporter genes into bioactive proteins (e.g. fireflyluciferase) which are then detected with sensitive, non-invasive instrumentation (e.g. CCD cameras) usingsignal-generating probes such as D-luciferin.Content (objective and work description):Before a bioactive protein such as luciferase can interact with luciferin, this probe has to diffuse through theenvironment (extracellular matrix, hydrogel construct, …) surrounding the cell. Upon enzymatic conversion of luciferina photon is generated that also has to travel back through this cellular environment before it can be detected by theCCD camera.A crucial step in this analysis is the correlation between detected photons and viable cell numbers inside theconstruct, this requires good characterization of both substrate –luciferin - diffusion speed and the detailed reactionkinetics and the integration of this information in a useful mathematical model.In a first part of this thesis, the student will focus on developing a model that is able to capture the bioluminescenceprocess explained above. Relevant input data for this model is partially available within Prometheus, Division ofSkeletal Tissue Engineering Leuven, and/or by setting up new experiments.The second part focuses on the validation of the obtained model. To this end the student will compare resultsobtained from BLI with results from more established techniques (e.g. DNA measurement).

Hans Van Oosterwyck / Maarten Roeffaers

Engineering Science / Bioscience Engineering

Dennis Lambrechts✔

Experimental / Computational modelling

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Control of monolithic capacitive DC-DC converters: "DC goes GHz!

Scaling of the CMOS technology has made today's number of transistors that can be placed on a chip extremelylarge. It is therefore not surprising that full SoC (System on Chip) systems are more ubiquitous than ever. A goodexample are the current state-of-the-art CPUs (such as Qualcomm's Snapdragon, Nvidia's Tegra and Samsung'sExynos platform) for mobile phones that, in addition to the traditional processor circuits, also integrate fullcommunication circuits on board for GSM / EDGE / HSPA / LTE / WiFi / BlueTooth .. and other peripherals such asUSB / HDMI / cameras / audio .. In short, there are plenty of different blocks in a SoC and these blocks must besupplied in an appropriate way so that they would perform optimally. This is the task of DC-DC converters that theconvert the typical battery voltage of 3.6V to the required voltages between 0.5-1.2V.

Capacitive DC-DC converter have gained enormous popularity in recent years gained because they do not useinductors (many parasitic effects in integration), but only switches and capacitors and thus fit perfectly in the SoCconcept. The topologies that give rise to the required voltage conversion ratios have been researched extensivelyrecently. The next goal is to achieve the same for the control. The control system must be such that the convertergenerates proper in-spec supply voltage and this at smooth load variations but also even in sharp load variations(on/off switching of a subsystem -> 100mA at 20ps). In order to achieve this, control systems must be designed atmulti-GHz speeds, which will prove to be both an interesting and challenging task.

For this thesis 1 or 2 future engineers are required with interests in power electronics and mixed-signal analog /digital design to explore the options for very fast and accurate control for DC-DC converters and to implement this infully integrated chip.

Prof. Michiel Steyaert

MICAS

Aki Sarafianos ([email protected])Hans Meyvaert ([email protected])✔

10% literature study, 15% topology modeling, 20% control modeling, 40% design and simulation, 15% text and presentation

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High-speed Digital Circuits for Multi-Gbps Signal Processing

One of the most important developments in the wireless industry within the last decade was the digitization of analogand RF circuitry. This was in response to the advances of the mainstream CMOS technology in both processingspeed and circuit density. This master thesis is to investigate and design high-speed multi-bit digital circuits, such asflip-flop, adder, multiplier, digital filter, pseudo random binary sequence (PRBS) generator, etc, for multi-Gbps signalprocessing. The applicants should have good background knowledge of analog and digital integrated ciruit design.


Departement Elektrotechniek ESAT-MICAS

Dixian Zhao (91.18)✔

20% Literature study, 50% Circuit design, 30% Thesis

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40 Gbps on-chip PRBS-generator for testing purposes

Testing multi-gigabit wireless transceivers is a complex problem. One of the big challenges is to send a PRBS(pseudo random bit sequence) signal to the modulator. Due to the increase in data rate of wireless transmitterstowards 40Gbps, it is not possible anymore to generate this data externally and use a bond wire to bring this signalon a chip. Therefore an on-chip PRBS generator is essential for testing these transmitters. The second challenge isthe testing of the receiver, because the output of the receiver is also a data-signal at a high speed. Since is is notpossible to get this signal through a bond wire, other solutions need to be found. A possibility is to split a 40Gbpssignal in eight different 5Gbps signals and bring these signals at lower speed off the chip. The difficulty of thisapproach is the clock recovery and synchronization of the eight channels. This thesis starts with a brief literaturestudy. Next is the implementation of the chosen architecture and a layout will be made to take all the parasitics intoaccount.


Departement Elektrotechniek ESAT-MICAS

Wouter Volkaerts (ESAT 91.12)✔

15% Literature study, 50% Simulation, 20% Layout, 15% Text

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FLUOROCODE on chip : a super-resolution optical map of DNA

There has been an immense investment of time, effort and resources in the development of the technologies thatenable DNA sequencing in the past 10 year (nex-generation sequencing). Despite the significant advances made asa result of this effort all of the current genomic sequencing technologies suffer from two important shortcomings.Firstly, sample preparation is time-consuming and expensive, and secondly, sequence information is delivered inshort abstract fragments, which are then assembled into a complete genome. This assembly is again verytime-consuming and expensive.The research group of Prof. Hofkens recently developed a super-resolution optical DNA mapping technology, whichallows to uniquely study genetic-scale features in genomic length of DNA molecules. Labeling the DNA withfluorescent molecules at specific sites enables us to produce a map of a genomic DNA sequence with unparalleledresolution, the so-called FLUOROCODE. The sample preparation, DNA labeling and deposition for imaging will beintegrated on a digital microfluidic chip to allow simple, cost-efficient and rapid mapping of DNA molecules. In thisproject the student will be involved in the development of the FLUOROCODE digital microfluidic chip, focusing on thelabeling and stretching of the DNA on-chip. Through this topic the student will get hands-on experience withmicrofluidics, working with biological material, super-resolution fluorescence microscopy and DNA mapping.

Prof. Dr. Jeroen Lammertyn, Prof. Johan Hofkens

Bioscience Engineering, MeBioS-Biosensor group

Bram Vanspauwen (contact person), Jochem Deem✔

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Analysis of yeast cell response upon treatment at single cell level on a digital microfluidic platform

Single-cell analysis has been increasingly recognized as the key technology for the elucidation of cellular functionsthat are not accessible from bulk measurements on the population level. To date, this type of analysis is mostcommonly performed downscaling existing analysis tools to match the size of a single cell. However, noveltechnological breakthroughs are required which better respond to the requirement imposed by single cell handling.

Lab-on-a-chip (LOC) technology offers an extremely powerful and versatile platform for biochemical and biophysicalanalysis. In a LOC system, complex laboratory operations are performed in a miniaturized and automated manner ona single chip of a few centimeters size. Digital microfluidics (DMF) are a particular type of LOC in which droplets aremanipulated on an planar array of electrodes and controlled in a software-assisted manner. DMF technology holdsenormous potential in a wide range of applications in chemical biology including immunoassays, enzyme assays andcell-based assays.

In the MeBioS-Biosensors group, an innovative type of DMF has been recently described which allowsmanipulation and analysis of individual cells in micrometer-sized wells. In this thesis topic, innovative fluorescencebased detection concepts will be applied as metabolomic fingerprinting tool to describe the metabolic status ofindividual yeast cells upon exposure to different types of stimuli on a digital microfluidic chip platform. IndividualCandida albicans yeast cells will first be seeded in the microwells of pre-fabricated DMF chips through simple surfacebiofunctionalization. Then, a fluorescence-based viability study will be conducted to confirm that immobilized cellsremain viable on the chip platform. Finally, the immobilized yeast cells will be treated with stress inducing reagentsand followed using fluorescence microscopy at single cell resolution.

Prof. Jeroen Lammertyn / Co-promotors: Prof. Bruno Cammue, Dr. Karin Thevissen

Faculty of bioscience engineering/MeBioS and CMPG

Phalguni Tewari, Kim Vriens✔

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The Mother Machine: design of a microfluidic tool for monitoring growth of single bacteria

The number of microfluidic applications for testing life science research hypotheses is growing exponentially. Byusing a lab-on-a-chip technology it is possible to integrate chemical and biological interactions on an automated andminiaturized system. Due to the small dimensions the amount of reagents can be reduced to the nanoliter-scale,reactions can be carried out in a high-throughput context and studying single cell events becomes possible. The aimof this thesis is to design a microfluidic tool in PDMS (polydimethylsiloxane) to monitor bacterial growth at the singlecell level. The existing commercially available designs are not optimal with respect to nutrient supply and bacteriadeposition approaches. The master thesis student will be challenged to improve these existing designs. The chips willbe fabricated in the cleanroom facilities using soft-lithography techniques. A negative photoresist will be used togenerate a pattern of channels on the master or mold. The design of the chips will be supported by using computersimulations in Comsol multiphysics. Afterwards, this mold will be used for replica molding (PDMS). To close the chipa glass slide will be used, allowing us to follow up the bacterial growth using time laps microscopy techniques. Usingthis tool not only bacterial growth will be studied, but also the inheritance of bacterial properties upon division of thebacteria.

Prof. Jeroen Lammertyn

MeBioS – Biosensor group

Bram De Landtsheer✔

experimental (simulations)

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Boosting the potential of digital microfluidics for biochemical and biological applications

Lab-on-a-chip (LOC) technology offers extremely powerful and versatile platforms for biochemical and biophysicalanalysis. In a LOC system, complex laboratory operations are performed in a miniaturized and automated manner ona single chip of a few squared centimeters. Digital microfluidics (DMF) are a particular type of LOC in which dropletsare manipulated on an planar array of electrodes covered by a hydrophobic layer and controlled in asoftware-assisted manner. DMF technology holds enormous potential in a wide range of applications in chemicalbiology including immunoassays, enzyme assays and cell-based assays. To date, the great potential of DMF chipsfor applications that require handling of protein-containing liquids (e.g.: serum samples, enzymatic buffers, samplesolutions…) is still hindered by the absorption of proteins on the chip surface, in a phenomenon known as bio-fouling,which causes problems for assay fidelity and can make the droplets unmovable.

Within the MeBioS-Biosensors group (www.biosensors.be), a number of different projects are currently running,which leverage the miniaturization and automation provided by DMF chips for a number of different applications. Thisthesis topic will be embedded in this framework and will explore several innovative strategies with the aim of reducingthe effect of protein absorption on the chip surface and boosting the performance of the platform. First a model assaywill be selected and the student will get acquainted with the execution of the assay in a miniaturize format. Possibleassays to be examined include (i) sandwich immunoassay for biomarker detection (ii) rolling circle amplification foraptamer amplification and (iii) viability/toxicity assays on cultured cells. In a second step, different strategies will beimplemented on the model assay and their effect on the assay performance will be evaluated. Possible strategies toexplore include (i) use of different type and concentration of pluronics (ii) use of different types of protein-containingbuffer/samples (iii) use of different chip designs. Finally, the optimized conditions will be applied to the ongoingresearch projects in the group and possibly translated to other types of biological assays.


MeBioS-Biosensors group

Dr. Federica Toffalini✔

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Nanostructured surfaces for improved performance of a fiber optic biosensor

Fiber Optic - Surface Plasmon Resonance (FO-SPR) is a promising optical sensing technique successfully employedby the MeBioS – Biosensors group in diverse applications of food analysis, life science testing and medicaldiagnostics. This biosensor is particularly appealing for studying biomolecular interactions between proteins, lipids,nucleic acids, or low molecular weight molecules such as drugs. Furthermore, it provides real time information onquantification and kinetics of the binding reaction. Our current research is oriented towards further improvement ofthe performance of the FO-SPR sensing probes.In this context, the aim of this master research thesis is to improve the sensitivity of the FO-SPR system. Specialattention will be given to the morphology of the gold layer which has an important influence on the sensor response.Colloidal Lithography (CL), a high-throughput and cost-effective nanofabrication technique, will be used fornanostructuring the FO surface. Polystyrene nanoparticles self-assemble onto the FO silica core followed by Audeposition. Then, by lifting off the nanoparticles triangularly shaped Au nanostructures are created on the FO surfaceaffecting its sensitivity. Factors influencing the self-assembling process of nanoparticles will be experimentallyaddressed, for instance FO planarity, nanoparticle type and size dispersion.FO-SPR surfaces will be characterized during the different CL steps using Scanning Electron Microscopy (SEM) andAtomic Force Microscopy (AFM). Finally, one of our well-established bioassays will be implemented on thenanostructured FO-SPR sensor to compare its performance with a conventional non-structured FO-SPR sensor.

For more information, please visit our website: www.biosensors.be


Bio-Engineering/MeBioS – Biosensor group

Iulia Arghir✔

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nanomaterials and nanchemistry nanoelectronic design bionanotechnology nanodevices and nanophysics✔ ✔

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Lanthanide Doped Nanoparticles as Potential Bimodal Contrast Agents forMRI and Optical Imaging Based on

Cancer has a major impact on our society and is one of the diseases with the highest mortality rate. Diagnostics isthe first step in disease treatment and in the field of cancer diagnostics, there is still much room for developmenttowards better and earlier detection of cancer cells. The concept of bimodal contrast agents for cancer detection is anovel approach and therefore it has been intensively investigated . Combining two complementary techniques suchas Magnetic Resonance Imaging (MRI) and Optical Imaging (OI) generates high resolution images and achieves alow detection sensitivity. In this work bimodal contrast agents are developed for MRI and OI.Lanthanides are well known for their optical properties, having intense and small-band emission spectra. Anothereffect that is common among the majority of the lanthanides are their relative high paramagnetic moments, which isnecessary to act as a MRI CA. We have developed a platform for attaching CA for MRI on the surface of luminescentNaLnF4 nano-particle, giving as a result a bimodal contrast agent for magnetic resonance and optical imaging.The specific goal of this thesis is to investigate other luminescent nano-particles and vary the substitution degree ofthe lanthanide ions in the host system. These novel systems will be further examined for their optical and magneticproperties. Biochemical studies will be performed to check their compatibility with cancerous cells.

Tatjana N. Parac-Vogt

Chemistry / Lab of Bio-Inorganic Chemistry

Sophie Carron✔

Nanosynthesis, Luminescence, Relaxometry, Bio-chemistry

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Characterization of the light-sensitivity of CMOS-ICs for life science applications

For many life sciences applications, monolithic integration of analog CMOS ICs with MEMS, photonics, andmicrofluidics is essential to enable multimodal, high-performance diagnostic, therapeutic, and scientific instruments.Analog CMOS ICs are required amongst others to amplify and filter small bio-signals, multiplex large sensor arrays,and actuate and manipulate cells or other micro-objects.In most cases, such chips need to be operated under ambient light conditions or may even be exposed to laser lightfor fluorescence microscopy. On the other hand, Si CMOS is innately sensitive to light (from near IR to near UV)causing leakage currents in the transistors that alter the overall circuit performance. It is hence crucial to properlyshield the circuits.In this research project, the student will do an in-depth investigation of the light-sensitivity of implantable CMOSneural probes and multi-electrode arrays for in vitro applications. These two technology platforms have recently beendeveloped at imec. The student will do extensive IC characterization (on wafer and single die level) under variouslight conditions and, if necessary, develop appropriate experimental setups to study the observed effects in moredetail.The student will also explore and identify new solutions for light shielding or sensitivity suppression: deposition of thinmetal layers (imec processing), chip/setup packaging, layout techniques, circuit design techniques, etc. Furthermore,electrical modeling of the light effects may serve as an additional tool to further understand the observed phenomena.

Liesbet Lagae

IMEC/LST

Silke Musa/Carolina Mora Lopez✔

40% literature, 60% experimental

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Characterization & Modeling of Electrodes for In vivo and In vitro NeuralRecording

Imec develops state-of-the-art CMOS-active Si neural probes and multi-electrode arrays (MEAs) for large-scaleneural recording. One of the most important sub-components of such devices is the electrode that transduces theneural signals into measurable voltages. In addition to the wanted signal, electrodes (and integrated circuits) alsopick-up unwanted noise originating from different sources: thermal, biological, electrode-electrolyte interface,electronic, and crosstalk. Understanding the contribution of these noise sources to the overall recorded neural data iscrucial for developing better and smaller electrodes and more efficient algorithms to recover the encoded neuralinformation.In this research project, the student will perform an in-depth study of the non-biological noise recorded withelectrodes of different sizes from passive and CMOS-active Si probes and multi-electrode arrays. The student willdevelop the required setups for accurate measurements of small noise amplitudes. Hands-on experience in buildingPCBs using discrete components (low-noise amplifiers, R C components, etc.) and good understanding of theirproperties is a pre-requisite. Moreover, knowledge in handling spectrum/network/impedance analyzers & Matlab isadvantageous. The overall goal will be to identify the causal links between electrode noise and intrinsic/extrinsicelectrode properties including electrode-electrolyte impedance, area, material roughness, material composition, etc.

Liesbet Lagae

Science/Solid State Physics

Carolina Mora Lopez / Andim Stassen✔ ✔

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Heat sink thermal analysis and optimization for advanced 3D-packaging configurations

Three-dimensional (3D) integration is considered a very promising technology for integrated circuit design [1]. It offersnumerous opportunities to designers looking for more cost-effective system chip solutions. It allows further decreasein the form factor of today's systems and eases the interconnect performance limitation since the components areintegrated on top of each other instead of side by side resulting in shorter interconnect lengths. Furthermore it makesit possible to interconnect multiple heterogeneous chips (processor, GPU, memory,...), and this with much higher I/Odensity than in today's packaging solutions. Thermal management issues in these 3D stacks are considered to beone of the main remaining challenges [2,3]. The vertical integrations of the chips using polymer adhesives with lowthermal conductivity and the reduced thermal spreading due the aggressively thinned dies cause these thermalmanagement issues. An alternative to the 3D stacks is the use of an silicon interposer: this is a silicon substrate onwhich the components are mounted side by side but which is fabricated using the advanced 3D integrationtechnologies. This technique still offers many of the advantages of 3D integration but relaxes the thermal constraintscompared to the 3D chip stack.

The components integrated in these advanced 3D stacked and Si interposer packages have different power levelsand different temperature limits; a memory chip typically dissipates a few W and has a maximum operatingtemperature of 85ºC while CPU’s and GPU’s can dissipate up to 150W. The objective of this master thesis isassessing the thermal behavior in these advanced chip packages and studying the thermal coupling between thehigh power components and the temperature sensitive components. Finite element and CFD simulations will be usedto model the temperature distribution inside the chip package and to compare the cooling performance of differentheat sink configurations. More specific, the thesis is composed of the following parts:1) Extensive literature review: 3D-packaging technologies, heat sink configurations and heat sink optimizationtechniques;2) Generation of a thermal model of the chip package and heat sink, simulation of the temperature distribution andheat sink performance;3) Development of a generalized heat sink optimization methodology for multiple components with different thermalconstraints.

References1. Chanchani, R. “3D Integration Technologies – An Overview”, in Materials for Advanced Packaging edited by D.Lu, C.P. Wong, Springer (2009), pp. 1-50.2. Brunschwiler, T.; Michel, B. ; "Thermal Management of Vertically Integrated Packages," in Handbook of 3DIntegration: Technology and Applications of 3D Integrated Circuits, edited by P. Garrou, C. Bower and P. Ramm.Wiley-VCH Verlag GmbH (Weinheim, 2008) Vol. 2, Part IV, pp. 635-649.3. Agonafer, D. et al., “Thermo-Mechanical Challenges in Stacked Packaging”, Heat Transfer Engineering, Vol. 29No. 2 (2008), pp. 134 – 148.

Ingrid De Wolf

imec - Reliability, Eletrical Test and Modeling Group

Herman Oprins✔

Thermal simulations

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Multimodal integration of EEG and functional Near Infrared Spectroscopy for ambulatory brain imaging

Research on low power, portable EEG recording devices have recently gained huge momentum. These devices arealready being used for continuous monitoring of brain activity for both therapeutic and neuroscientific research.Active-electrode based, comfortable, gel-free EEG headsets have made it possible to use these in home environmentwith minimal professional supervision. Near Infrared Spectroscopy (NIRS), a brain imaging technique of growinginterest, however, lags far behind while ambulatory monitoring is concerned. It has been recently shown that EEGcombined with functional-NIRS (fNIRS) has far greater prospect in decoding brain activity. EEG measures postsynaptic potentials associated with neural activation while fNIRS measures local haemodynamic changes associatedto the same. These two modalities complement each other in their ability to resolve information about the spatial andtemporal characteristics of neural activity.

Analog circuits live at the heart of these medical systems, extracting relevant biomedical signals in presence ofvarious unwanted artifacts . As one of the key building blocks of such medical systems, constrains on these analogcircuits are strict: Low power dissipation, high signal quality, reliability, and miniature size. Combining EEG andfNIRS in a portable headset requires both electrical and optical monitoring, preferably on the same IC. These batteryoperated systems have to low power and the two modalities should have minimal interference. The sensor nodesshould be optimally placed and proper algorithms need to be developed to extract maximal information on neuralactivity.

The focus of this MS topic will be to first start with literature search of the existing fNIRS system and how they arecombined with EEG measuremnt. She/he will next validate the efficacy of EEG+fNIRS with existing EEG headset andoff-the-shelf components. The candidate will recognize the key challenges in combining these two modalities and willalso be involved in developing algorithms to extract maximal information from this mutimodal system.

Chris van Hoof

ESAT/MICAS

Srinjoy Mitra✔

Literature search, PCB design/test and algorithm development

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A Sturdy Cascaded Sigma-delta ADC for CMOS Image Sensor readout circuit

Image Sensors, especially CMOS Image Sensors, have been experiencing an explosive growth recently due to highdemands of mobile imaging, digital still and video cameras, Internet-based cameras, surveillance, time-of-flightimaging, and biometrics. Incremental Sigma-delta ADCs have been recently applied as column ADCs in order toachieve low-noise Image Sensor readout circuits. For a fast conversion, the number of ADC sampling must be small,but at the cost of the lower noise suppression. Although a high-order Sigma-delta modulator can increase theconversion time without losing the noise-shaping benefit, its high un-stability potential limits the number of order andthe speed of the conversion accordingly. A common solution, a multiple-stage or cascaded sigma-delta (MASH)modulator, has been applied to achieve a short conversion time without sacrificing the stability property of the circuits.But they prone to the quantization noise leakage due to the mismatch between the analog modulator and the digitalfilter.In this work, a Sturdy Cascade Sigma-delta ADC will be employed at the column level of Image Sensors to achieveboth a low-noise and fast readout circuit. Not only does this kind of ADC utilize the high-speed andgood-noise-shaping MASH property discussed above, but also it suppresses the noise leakage inherited in theMASH structure. Through this work, the student will have a good chance to grasp knowledge in Image Sensor, tostudy the Incremental Sigma-delta ADC, and to design a recently-proposed ADC, which requires a large amount oflab works.

Professor Georges Gielen

ESAT, MICAS

Ha Le-Thai, email: [email protected]✔

Lab

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Novel host guest combinations for increasing the exciton diffusion length in bilayer organic photovoltaic devices (OPVs) using triplet excitons

The absorption of a photon in an organic semiconductor yields a tightly-bound exciton that must diffuse to a donor–acceptor interface to dissociate into free charge carriers. While efficient absorption an absorbing layer exceeding theexciton diffusion length (LD) of singlet excitons which is limited to a few nanometers due to their short (~1 ns)lifetimes. This pro¬blem was solved by the construction of bulk heterojunction OPVs, which reach the bestcom¬promise between interfacial surface area and light absorption. For organic compounds, it is, however, difficult tocontrol the phase separation between electron donor and acceptor molecules, in order to obtain, on one hand,phases with a length scale commensurate with LD and on the other hand, a bi-continuous network to facilitatecharge dissociation and collection at their respective electrodes. Therefore it remains tempting to try to increase theefficiency of exciton transport in a bilayer donor-acceptor OPV which we plan to do using triplet excitons. Thisstrategy is based on the hypothesis thatLD will be much longer for triplet excitons due to their longer lifetime (byseveral orders of magnitude). This should allow to harvest excitons generated farther away from a donor–acceptorinterface. The initial geminate electron hole pair formed by dissociation of this triplet exciton should also have adecreased rate of recom¬bination. The material to be developed consists of a host:guest system where a fluorescenthost material, used for light absorption as well as for charge and exciton transport is combined with a guest serving toconvert initially generated host singlet excitons into triplet excitons.While proof of principle experiments were done for host:guest layer based on OC1C10-PPV (poly(2-methoxy-5-decyloxyphenyleme)vinylene), this system has the drawback that its absorption spectrum poorlymatches the solar spectrum. As the present benchmark material for OPVs is P3HT (poly (3-hexyl)-thiophene)(available commercially or though collaborations), guests with a sufficient small singlet triplet band gap and singletenergy to match the position of the energy levels must be designed. Preliminary experiments suggested limitedefficiency for singlet quenching of P3HT by [dpbq]2Ir(acac), due to a marginal over¬lap between absorption of theguest and emission of P3HT or by insufficient miscibility of P3HT and the guest. Therefore novel iridium complexeswith lower singlet energy and/or better expected miscibility will be designed and synthesized by the team of prof.Dehaen (Chemistry Department). As alternative guests based on a tetrabenzoporphyrin will be explored as theirsinglet and triplet energy levels are expected to match those of P3HT.Initially the position of the singlet and triplet excited states and HOMO and LUMO of the guests will be determined bystationary spectroscopy and cyclic voltametry respectively. For several suitable host guest combinations, the singletquenching of P3HT, the formation and decay of guest triplet, the formation of host triplets, triplet migration in the hostwill be investigated using several types of ultrafast time resolved absorption and emission spectroscopy. Nanosecondtransient absorption will be used to study charge carrier (polaron) generation and recombination in a bilayer systemwith an electron accepting layer (PCBM and a perylene diimids). Finally the figures of merit (open circuit voltage,(VOC), short circuit current (ISC), fill factor (FF) and ext) of a bilayer OPV with and without guest in the P3HT layerwill be compared. As the generation of triplet electron hole pairs and the bilayer architecture will suppress geminateand nongeminate recombination respectively we also hope to replace PCBM by perylene imid acceptors which areexpected to yield a better VOC.

Mark Van der Auweraer

Sciences\Chemistry\Molecular Imaging and Photonics\Laboratory for Photochemistry andSpectroscopyYannick Baeten✔ ✔

experimental (spectroscopy, measurements of photocurrents)

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Increasing the exciton diffusion length in bilayer organicphotovoltaic devices (OPVs) via an energy collecting layer

The absorption of a photon in an organic semiconductor results in the creation of a tightly-bound exciton that mustdiffuse to a donor–acceptor interface to dissociate into free charge carriers. As the exciton diffusion length, LD, ofsinglet excitons is limited to a few nanometers constitutes a major bottleneck for achieving high external efficiencies,as bulk excitons do not reach the interfaces within their short (~1 ns) lifetimes. This problem was solved by theconstruction of bulk heterojunction OPVs, which are designed to reach the best compromise between interfacialsurface area and light absorption in layers thick enough (50–100 nm) to absorb a majority of the incident light. Fororganic compounds, it is, however, difficult to control the phase separation between electron donor and acceptormolecules, in order to obtain, on one hand, phases with a length scale commensurate with LD (on the order of 10 nmor less) and on the other hand, a bi-continuous network (to facilitate charge dissociation and collection at theirrespective electrodes). Therefore it remains tempting to try to increase the efficiency of exciton transport in a bilayerdonor-acceptor OPV. For this aim, following strategy will be explored: downhill singlet-singlet energy transfer to anintermediate energy acceptor layer. This strategy is based on the observation that Förster type energy transfer to alayer of chromophores has a smaller distance (d) dependence (proportional to d^-4), than to a single acceptor(proportional to d^-6). This should also lead to an increase of the distance for singlet transport to the donor acceptorinterface in bilayer OPV’s.We want to build and characterize an OPV with a vapour deposited energy and electron acceptor layer. On thebenchmark material,poly (3-hexyl)-thiophene coated on ITO:Pedot, we will vapor deposit a proper energy acceptinglayer, followed by an electron acceptor layer and a counter electrode for extracting the electrons. To combine efficientenergy transfer with the absence of charge carrier generation the energy acceptor must have a bandgap of 1.6-1.7eV and a LUMO below that of P3HT. On the other hand to avoid hole trapping the HOMO should close to or slightlybelow that of P3HT. As the alternating copolymer of PCPDTBT meets those requirements analogous oligomers willbe synthesized in collaboration with the Laboratory for Organic Synthesis (Wim Dehaen).The position of the energy levels of the oligomers will be determined using stationary spectroscopy and cyclicvoltammetry. The conditions for vapor deposition of a thin (< 10 nm) homogeneous layer of the oligomers will beoptimized and if necessary changes in the molecular structure will be proposed. Bilayers of P3HT and selectedoligomers will be prepared and the energy transfer to the acceptor layer will be investigated by stationary and timeresolved fluorescence combined with picosecond transient absorption. The influence of the thickness of the energyacceptor layer in the range 1 to 10 nm on the energy transfer efficiency will be checked. By comparing carriermobilities in P3HT with those in the bilayer it will also be investigated to what extent the energy acceptor layerinfluences the hole migration. The carrier mobilities will be determined by the Time Of Flight technique (TOF) ordetermination of space charge limited currents. In a next step the bilayer will be extended with a vapor depositedelectron acceptor layer (fullerene or perylene diimid) and the photo-induced charge generation (and recombination)will be investigated by time resolved fluorescence spectroscopy, picosecond and nanosecond transient absorption.For one or two most promising energy acceptor layers an OPV will be made and its figures of merit compared tothose of a corresponding OPV without energy acceptor layer. At different stages the results will be compared withthose of simulations performed in collaboration with the team of prof. Beljonne at the University of Mons.



experimental (spectroscopy, measurements of photocurrents)

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Spintronics in chiral organic materials: a new dimension in molecularconductive materials

In spintronics we try to obtain currents that are carried by electrons of holes with a preferential alfa or beta spin. Whilethis is already an established field in inorganic materials (computer memories, hard disks etc.) we try to extend thisphenomenon to molecular materials that are able to conduct electrons and holes using chiral molecules. Therelevance of chirality for advanced electric, optical and magnetic properties of molecular materials has beenrecognized as well from a theoretical as an experimental view point. Magnetoresistance experiments, showed that(limited) spin-polarized electron currents can be detected in some achiral organic materials up to room temperature.Continuing the original physical top-down approach for spin injection by magnetic electrodes in achiral organicconducting materials, we will explore in a stepwise manner whether the combination of a molecular chiral interphasebetween a magnetic electrode and an achiral organic material can function as a spin valve for spin controlled chargeinjection. Possible applications range from an improved efficiency of OLEDS to information processing.This work, which is focused on low molecular weight chiral pi-conjugated compounds as helicenes is complementaryto ongoing research on chiral conjugated polymers. As alternatives for helicenes we can explore chiralindolocarbazoles for hole injection. These materials are or will be available through collaboration with the team ofWim Dehaen (Laboratory of Organic Synthesis).In a first step we will compare the efficiency of a single enantiomer of a chiral molecule to a racemate thereof,deposited on a magnetic electrode to obtain spin polarized currents which will be detected using magnetoresistance.In this framework injection of opposite spins will be favored by two complementary enantiomers of a single chiralsubstance and hence a different magnetoresistance should be observed for the two enantiomers. We will alsocompare the charge carrier mobility of single enantiomers to those of racemates in the absence and presence of anapplied field by either time of flight experiments or the determination of space charge limited currents. As alternativefor the magnetoresistance we will also explore to what extent these thin layers allow detection of the spin polarizedinjection by the non-linear magnetic circular dichroism.In order to determine the factors relevant for spin-polarized injection we will vary in a next step the strength of theapplied electric field, the temperature the thickness of the chiral layer (transition from tunneling to hopping currents),the combination of the electrode material and the chiral organic material.In a second step we will study a two layer system consisting of a chiral layer with suitable redox potential and efficientspin polarized injection deposited on commercially available or synthesized low molecular weight achiral electron andhole transporting molecules . We will determine the transfer and further transport of the spin polarized chargecarriers using magnetoresistance and non-linear magnetic circular dichroism.For the study of the magnetic effect on currents and optical properties we will collaborate with the Laboratory forMolecular Electronics and Photonics (Thierry Verbiest).


Sciences\Chemistry\Molecular Imaging and Photonics\Laboratory for Photochemistry andSpectroscopyArvid Cloet✔ ✔

experimental (spectroscopy, measurements spectra or currents, sample preparation)

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Characterization and imaging of buried interfaces between thinlayers

In spite of their lower efficiency organic solar cells can, due to their expected lower cost, be a valuable alternative forsolar cells of crystalline silicon. The most promising configuration is for the moment the bulk heterojunction consistingof a bicontinuous percolating network of a conjugated polymer (hole transport) and a fullerene phase (electrontransport).The morphology of this system which depends strongly on the preparation conditions (solvent, parametersfor spin coating) is critical for the performance of the solar cell.. In order to elucidate the kinetics of charge separation,charge transport and recombination often bilayer systems are investigated. While these systems show a lowerexternal quantum yield due to lower light absorption close to the interface they are more suitable to observe andmodel the different elementary steps of the functioning of the solar cell. Furthermore their construction is lesssensitive to the experimental parameters (solvent, evaporation rate, annealing conditions) than the bulkheterojunctions which could also be favorable for eventual large scale production. However also in this type ofdevices the detailed structure of the interface between the electron donor and electron acceptor layer will beimportant for the kinetics of charge generation charge separation and charge recombination. It is the aim of thesiswork to explore the possibilities of SHG techniques for the characterization or bilayer type organic solar cells byimaging the buried interface between two organic layers. Second harmonic imaging microscopy (SHIM) will be usedto map the interface between an electron donor and electron acceptor in a typical bilayer solar cell using existingmaterials (e.g. poly(3-hexylthiophene (P3HT) and a fullerene derivative (PCMB) in the absence of an applied electricfield. Due to the lack of symmetry necessary for second harmonic generation (SHG) only PCMB and P3HT moietiesclose to the interface will contribute to the SHG signal. By choosing appropriate wavelengths of the incomingradiation it will be attempted to monitor both sides of the interface in a selective way. The dependence the interfacestructure, revealed by SHIM upon the conditions (solvent, concentration, annealing) for the deposition of the polymerby spin coating will be investigated. It will be attempted to correlate the resolved structure with the degree ofcrystallinity of the P3HT, determined by optical absorption. In collaboration with the team of A. Jonas (UCL) it will beattempted to correlate the results with those obtained by X-ray reflectivity. Although interfaces are intrinsically non-centro symmetric and, hence, should generate a second-order non-linear optical signal, the magnitude of theresponse is often too low for practical implications. Hence it will be explored whether an efficient probe can provideopportunities for better imaging of buried interfaces. For choice of the probes it is essential that they do not act ashole (when incorporated in the electron donor) or electron (when incorporated in the electron acceptor layer) traps.This requires a suitable redox potential compared to that of the electron donor or acceptor layer. Here poly(indolocarbazoles) or sterically hindered poly(dithienopyroles), will be combined with probes based on Bodipy for theelectron donor layer. For the electron acceptor layer PCMB will be combined with with sterically unhindered oligo-dithienopyroles.



experimental (spectroscopy, microscopy, sample preparation)

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Structure and electronic properties of conjugated columnar poly-electrolytes

Conjugated polymers with suitable (charged) side chains can self-organize to rodlike structures in aqueous medium.It is the aim of this project to study the photophysics (charge and energy transport) of such structures using fastspectroscopy. Using single molecule spectroscopy the emission spectrum and fluorescence decay of a singleisolated chain deposited on a substrate from an aqueous solution will be recorded. Complimentary to thephotophysical experiments deposited molecules will be investigated using scanning probe microscopy (Atomic forcemicroscopy, scanning tunneling microscopy). The polymers will be obtained from the "Max Planck Institut fürPolymerforschung" in Mainz and Gent University. To determine the structure of the assemblies formed in aqueoussolution it is possible to collaborate with the UCL. (Université Catholique de Louvain).


Sciences\Chemistry\Molecular Imaging and Photonics\Laboratory for Photochemistry andSpectroscopyArvid Cloet✔


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Characterization and spectroscopy of organic quantum dots

It can be expected that block copolymers of conjugated polymers consisting of sections with hydrophobic andsections with hydrophylic side chains form in aqueous medium a micelle with a core with hydrophobic side chainsand a shell with hydrophilic side chains. This prompts questions on possible aggregation of the chromophores, theoccurrence of energy hopping and the possibility to form a single quantum dot. In the latter case a safe (no cadmium)and flexibly adaptable alternative for inorganic quantum dots would exist for in vivo medic-diagnostic applications anfor use as a research tool in molecular biology. We will try to answer the questions mentioned above using stationaryand time-resolved fluorescence spectroscopy op bulk samples and single micelles. The polymers will be obtainedthrough the division of "Moleculair Design and Synthesis" of K.U.Leuven, or through collaboration with UHasselt,UGent or the "Max Planck Institut für Polymerforschung" in Mainz. For structural characterization of the micellescollaboration with the UCL is possible


Sciences\Chemistry\Molecular Imaging and Photonics\Laboratory for Photochemistry andSpectroscopyArvid Cloet✔


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Neurotropic electrodes for high resolution neural interfacing

The neurotropic electrode has proven to be one of the more stable, long lasting ways of establishing a connection between electronics and the brain. Such electrodes consist of a hollow glass cone in which a growth factor releasing substance is present, which lures neurons to grow processes into the cone. The neurons are then read out by gold contacts also present in the cone.

Up to now, such electrodes have been made by hand, making high resolution readout difficult. The challenge in this thesis would be to find out

(a) How a miniaturized, high resolution version of the neurotropic electrode can be made using MEMS technology, e.g. based on DRIE or SU-8 technology.(b) How to fill the microsized cones with a growth factor releasing substance(c) What the in vivo performance of the miniaturized version would be, in terms of the ability to record action potentials and local field potentials, and lifetime.

More information about the neurotropic electrode can be found online (a good starting point being http://en.wikipedia.org/wiki/Neurotrophic_electrode) or from the daily supervisor-to-be. ([email protected])

Robert Puers

ESAT-MICAS

Frederik Ceyssens

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fabrication process development and testing ; rather experimental

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Trapping and analyzing single molecules in nanopores

Conventional nanopore molecular analysis relies on the existence of a different characteristic blockade of the ionicflux through the nanopore depending on the molecule properties, specifically for DNA. Due to the low spatialresolution of the current nanopores, this was only demonstrated with a biological nanopore for the translocation ofindividual nucleotides. In addition, the high molecular translocation speed in a nanopore makes it difficult todistinguish the small difference in ionic current between the four bases. Other approaches employ single moleculelabels attached to longer DNA to analyze the DNA properties. Here, also the high and not well controlled speed of theDNA is an issue to characterize the translocation behavior.

The problem we want to tackle in this Master thesis, is slowing down the DNA translocation through the pore. Typicaltranslocation times per nucleotides in a DNA strand for solid-state-nanopores vary between nano- and microseconds,which is too quick to enable electric or optical analysis on the single base level. Several research groups alreadydemonstrated the slowing down of DNA translocation. In this project, we will exactly control the translocation speedby attaching the DNA to a polystyrene bead which can be trapped and manipulated with sub-nanometer spatialresolution by optical tweezers. Subsequently the DNA will be trapped in the nanopore by applying an electricalpotential across it. We will electrically characterize these translocation events of DNA with and without labels bymonitoring the ionic current and correlating it to fluorescence events.

The work is mainly experimental, but will be complemented with a limit amount of optical and ionic finite elementmodeling.

Pol Van Dorpe

Sciences/Dept. of Physics - research group at imec

Pieter Neutens✔

Experimental work: optics/device fabrication (70%) Simulations (30%)

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Hybrid cellulose-conducting polymer nanoparticles

Cellulosic nanomaterials have become the focus of intense research. Aside from their renewability andbiodegradability, they are also one of the sole sources of high aspect ratio nanoparticles which allow ready surfacemodification without lost of inherent properties.Cellulose nanowhisker are monocrystalline rigid rods with a rectangular cross-section extracted from native cellulose.They display 1o and 2o hydroxyl groups on the surface which can be selectively modified while retaining thecrystalline nature of the nanoparticles. In particular, we have been able to selectively modify the 1o hydroxyl groupswith azides which can then be used to perform click chemistry (e.g. Eyley and Thielemans, Chem. Commun., 47(14),4177-4179 (2011)).Because of their high aspect ratio, these nanowhiskers have also been investigated as a templating material forelectrically conducting polymers (e.g. Thielemans et al., J. Phys. Chem C, 114(41), 17926-17933 (2010); Weber etal., Mater. Chem. 2007, 17 (26), 2746−2753). The driving force for the templating generally depends on electrostaticinteractions.In this project, we will combine these two fields by chemically grafting electrically conducting polymers (ECPs) to thesurface of cellulose nanowhiskers. We will do this by utilising acetylene-modified ECPs and azide-modifiednanowhiskers in a Huisgen 1,4-cycloaddition (azide-alkyne cclick reaction).The advantages will be (1) stronger interactions between support and ECP leading to high cycling tability during use,(2) wider processing range, and (3) versatility to introduce additional functionality as desired (e.g. electrochromes orionic groups).The experimental part of this work will involve the extraction of cellulose nanowhiskers, their surface modification andcharacterisation, polymer synthesis and reaction with azidated nanowhiskers and study of the electronic behaviour ofthe obtained materials in terms of self-assembly, conductivity, capacitance and cycling stability.

Guy Koeckelberghs/Wim Thielemans

Polymer Chemistry and Materials/KULAK

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Tip-enhanced Raman spectroscopy of graphene/molecular systems

Context:Tip-enhanced Raman spectroscopy (TERS) is a technique which combines the nanometer scale resolution ofscanning probe microscopy with the chemical specificity of optical spectroscopy. Graphene, a popular material ofrecent times, is a single layer of graphite and a perfect two-dimensional crystalline material with very high electronmobility and other interesting properties. Graphene also offers the possibility of acting as a protective barrier toimmobilize thin molecular layers and even individual molecules so that they can be analyzed with differenttechniques.

Objective: TERS works using the greatly enhanced electric fields produced near to metallic nanostructures when theyare irradiated with laser light of the correct wavelength. In order to carry out effective TERS experiments sharp,contamination free metallic tips with dimension of a few tens of nanometers need to be used. A first objective will beto optimize the production of metal tips suitable for use in TERS experiments. A second objective is to produce arange of samples on different substrates (transparent / opaque and conductive/ non-conductive) which combinegraphene and different molecular systems. These molecular systems may include thin liquid layers of differentmolecules, individual DNA molecules or ordered self-assembled networks. The graphene layers will act either as abase for adsorption for these molecules or as a protective layer covering them. The third objective will be to useTERS to study the above systems and produce nanometer scale maps of the chemical nature of the samples.During these experiments the Raman spectra for both the molecules and the graphene layers will be collected. Thiswill allow us to study not only the molecules themselves but also how their presence affects the electronic propertiesof the graphene layers.

Work to be done: Firstly, you will optimize the production of metallic tips for TERS experiments. The production ofthese tips involves the electrochemical etching of wire to produce nanostructured tips. Scanning electron microscopy(SEM) will be used to directly study the structure of the end of the tips and relate this to their effectiveness as TERSprobes. Secondly, you will produce samples which combine graphene and different molecular systems to study withTERS. This will involve deposition of graphene onto different substrates and characterization using atomic forcemicro (AFM) and scanning tunneling microscopy (STM). Finally, you will combine tips and samples to perform TERSexperiments.

Steven De FeyerHiroshi Uji-iDivision of Molecular Imaging and Photonics

Maksym Rybachuk✔ ✔

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Nanostructuring 2D materials: a new approach towards sensors?

Context:Graphene, a popular material of recent times, is a single layer of graphite and a perfect two-dimensional crystallinematerial with very high electron mobility and other interesting properties. Graphene has become an ideal object forboth fundamental studies and electronic applications, including sensing. Also MoS2 is a promising material in thisrespect

Objective:A first objective is to carry out the molecular self-assembly of mono- and bicomponent mixtures at the interfacebetween a liquid and graphene or MoS2 and to visualize the molecular ordering - the result of self-assembly - bynon-optical microscopy techniques such as scanning tunneling microscopy or atomic force microscopy. A secondobjective is potentially the growth of multilayered materials via Atomic Layer Deposition on top of the self-assembledmonolayer which acts as a template. A third objective is the characterisation of molecule covered graphene orMoS2-based devices to probe the effect of molecule - substrate interactions on the electrical properties.

Work to be done: You will investigate the self-assembly of molecules on top of the graphene layers or MoS2 bystate-of-the-art microscopy tools such as scanning probe microscopy. You will probe how the adsorption of molecularnanopatterns on graphene or MoS2 affects the electronic properties of these materials (sensing). Based on theseinsights, you will explore the electrical characteristics of devices with integrated molecular nanopatterns.

Steven De FeyerHiroshi Uji-iStefan De GendtDivision of Molecular Imaging and PhotonicsMolecular Design and Synthesis / IMECKunal Mali✔ ✔

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Self-assembly of supramolecular protein structures on surfaces

Context:

Biomolecule-based synthetic nanostructures constructed by self-assembly are in high demand for development ofbiomaterials because of their biocompatibility, biodegradability, and defined morphology. In particlular, proteinassemblies have potential to be used in practical applications in fields such as tissue engineering, biomineralization,light harvesting , cascade reactions and drug delivery systems. Proteins may also prove to be attractive buildingblocks for artificial superstructures because their well-defined structures have high recognition ability and specificreactivity towards target molecules.

Objective:

The Aim of this project is to build chemical or biological nanostructures on surfaces to create new artificialbio-nanomaterials. In the first instance the candidate will self-assemble monolayers of a protein structure atop ofgraphite (graphene) or gold surfaces. Then, specific binding groups will be introduced genetically or by targetedchemical modifications within the protein structures. This will allow growing 3D self-assembled substrates, layer bylayer with well-defined structues.

Work to be done:

First, you will optimize the protocol for reconstituting biological nanostructures on gold or graphite or graphenesubstrates. You will investigate the self-assembly of molecules on top of the substrate by state-of-the-art microscopytools such as scanning probe microscopy, and in particular scanning force microscopy. Once 2D protein structure willbe characterized, you will introduce another layer of biological structures in order to form 3D films of protein structurewith controlled stoichiometry.

Steven De FeyerGiovanni MaggliaStefan De GendtDivision of Molecular Imaging and PhotonicsNanopore devicesWillem Vanderlinden✔ ✔

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Exploration of efficient electroporation protocols for intracellular recording of action potentials using configurations of microelectodes on chip

Multi-electrode arrays are an elegant and fast technique to sense electrical activity of in vitro electrogenic cells suchas neurons and cardiac cells. Despite the ability to record from many cells at the same time, the signal quality and theresolution of this technique are still not optimal. Recently, Imec developed a technique that makes it possible torecord intracellular action potentials using on-chip electroporation (Braeken et al., Lab Chip, 2012). Such intracellularsignals are 500 times larger in amplitude and preserve the original shape of the action potential, improving the qualityof the recording drastically.The project aims to further investigate the principle of electroporation using on-chip electrical stimulation. The studentwill make use of a novel experimental platform designed for testing different electrode configurations, topologies andmaterials, such as three-dimensional electrodes, carbon nanotubes, etc. Effects of electroporation protocols will beevaluated using fluorescent imaging techniques and recording of the spontaneous electrical activity of cardiac andneuronal cells using the multi-electrode array platform of imec.

Liesbet Lagae

IMEC/LST

Andim Stassen, Dries Braeken✔ ✔


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Characterization of optical waveguides for optogenetic stimulation of in vitro and in vivo neurons

Since the first reports in literature only a few years ago, optogenetics is one of the fastest growing and mostpromising fields in neuroscience. Optogenetic stimulation is based on optical activation or inhibition of neurons thathave been genetically modified to express light-sensitive opsins in their membranes. Today, optical stimulation in vivois mainly performed using bulky optical fibers with limited selectivity. Imec is investigating optical stimulation of cellsusing a novel type of devices that make use of waveguide technology to guide visible light into in vitro and in vivoprobes. By positioning multiple light entry and exit sites we want to ensure selective stimulation of single cells isfeasible.The student will be involved in characterizing on-chip waveguides to investigate optical losses in the substrate, theefficiency of coupling of light into and from the substrate, and the efficiency of optogenetic stimulation of single cellsin vitro and in vivo. Parameters of efficient stimulation and the effect on single cells will be studied using opticalimaging and electrical recording techniques.

Liesbet Lagae

IMEC/LST

Luis Hoffman, Dries Braeken✔ ✔


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High-density Carbon Nanotube Electrodes for Recording and Stimulating Electrogenic Cells

Electrogenic cell types, such as heart or brain cells, rely on electrical signals to communicate with one another. Inorder to gain insights in the fundamental processes of brain cell communication, unravel the cause of brain disorders,or validate the effect of certain drugs on heart cells, it is important to record these signals in a minimally invasive andlong-term manner. Our imec research group developed a state-of-the-art chip which is smaller than the size of afingernail, but yet contains tens of thousands of subcellular-sized electrodes, each individually addressable and ableto record and stimulate cells on top. Obviously, the quality of the signal depends highly on the properties of theelectrode material. Prerequisites are a good biocompatibility and a high recording and stimulation efficacy. Recently,carbon nanomaterials – such as carbon nanotubes – have attracted considerable interest due to their exceptionalelectronic, thermal and structural properties. Different and independent studies show that the interface createdbetween carbon nanomaterials and the cellular membrane can yield a high-quality electrical coupling. Using atechnique called ‘capillary forming’, complex three-dimensional structures such as overhanging wells, inward oroutward bending ‘flower petals’ and intricate microhelices can be fabricated, which can dramatically increase theintimate coupling between the cell and the electrode. The student will be involved fabricating and characterizingdifferent flavors of carbon structures using electrochemical, electrophysiological and optical techniques.

Liesbet Lagae

IMEC/LST

Jordi Cools, Dries Braeken✔ ✔


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Controlling light-matter interactions with plasmonic nanoantennas

Plasmonic nanoantennas are metallic nanoparticles that can be considered as classical oscillators at the nanoscale.They act as antennas, converting electromagnetic waves at optical frequencies into localized fields. As such, theyprovide an effective way to study light-matter interactions at the nanoscale by coupling photons in and out ofnanoscale volumes and manipulate them.Applications of surface plasmon resonances are widespread, nurtured by nanotechnology, and already approachinga level of maturity that gives them a prominent position to contribute to some of today’s most important challenges:energy harvesting, cancer treatment, disease diagnostics, DNA sequencing, and optical computing.In our group we explore plasmonic antennas for their potential use in innovative biomedical technologies. Forinstance, directional antennas are designed to route specific light colors emitted by luminescent molecules. Highquality factor antennas with very high near-field enhancements in combination with a gain medium can even act asplasmonic nanolasers, paving the way towards highly integrated on-chip biological experiments.In this master thesis, the interaction of plane light waves, as well as local quantum emitters, with new plasmonicantenna designs will be studied. The student will gain hands-on experience with sample preparation in the imeccleanroom, scanning electron microscopy (SEM), and optical experiments (in close collaboration with the KU LeuvenDepartment of Physics. The experimental results will be verified and complemented by full-field 3D electromagneticsimulations.

Pol Van Dorpe

IMEC/LST

Niels Verellen, Jiaqi LI✔ ✔

30% literature, 30% modeling, 40% experimental

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Gram staining using Raman spectroscopy

Gram staining is a widely used method to differentiate bacteria on the chemical and physical properties of their cellwalls into Gram-positive or Gram-negative. Gram positive bacteria stain violet due to the presence of a thick layer ofpeptidoglycan in their cell walls, which retains the crystal violet these cells are stained with. A standard proceduretypically takes three steps: staining with a water-soluble dye called crystal violet, decolorization, and counterstaining.The gram stain is one of the most frequently used stains in a clinical microbiology laboratory, but as this procedure istime-consuming, a simple spectroscopic method to replace this method would largely be beneficial. Raman scatteringis an optical spectroscopy method and allows to differentiate chemical biomolecules based on their vibrational orrotational modes. It has been shown to be allow for differentiation of cells and may allow as well to spectroscopicallydifferentiate bacteria.You will combine state-of-the-art confocal Raman spectroscopy with advanced signal processing using principalcomponent analysis to image and differentiate both gram-positive and –negative bacteria.

Pol Van Dorpe

IMEC/LST

Evelien Mathieu✔ ✔


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Gold nanostars for imaging and photothermal treatment of cancer

Cancer is still one of the most leading death causes in the world and the demand for more precise and sensitiveimaging and therapy techniques remains high. In the latest decennium, nanoparticles have been opted as a contrastagent to improve the detection limit for optical tumor imaging or even to treat cancer.During this thesis, gold nanoparticles will be examined as they can be both used for cell therapy upon irradiation andfor imaging based on surface enhanced Raman scattering (SERS). More specifically, gold nanostars will be coatedwith a SERS label and subsequently coupled with biological ligands to target specific receptor molecules on thetumor cells. Using multiple SERS labels, each with a specific spectrum, multiplexing is possible allowing to visualizedifferent cell types or molecules. Besides imaging, the treatment will occur by photothermal therapy since theparticles will absorb light at a specific wavelength and convert it into heat. This heat is deadly for tumor cells sincethey are more temperature sensitive compared to normal cells.The thesis student will be strongly involved in the different aspects of this topic, including the chemical synthesis ofnanoparticles, Raman spectrometry, in vitro studies and microscopy techniques.

Liesbet Lagae

IMEC/LST

Antoine D'Hollander, Hilde Jans✔ ✔


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Antibody stabilizers for lateral flow assays

Lateral flow immunoassays are especially designed for single use at a point of care/need. The best-known lateralflow system today is the pregnancy test. In all lateral flow systems, antibodies are immobilized on a solid support oron a transducer for selective detection of their analyte. However, when an antibody comes into contact with a solidsupport, the folding conformation can change to a partially unfolded or totally unfolded state. Unfolded antibodiesshow a reduced or even a total loss of their activity. Therefore, immobilized antibodies must be stored in anenvironment beneficial to stabilize their conformation. Furthermore, guaranteed stability of immobilized antibodies ona solid support is an important key to achieve reliability and stable interfaces for lateral flow immunoassaycommercialization.This thesis aims to characterize different commercial stabilizers and methods to preserve the 3D conformation of theantibody for application in lateral flow systems. Hereto different characterization methods will be used. This researchshould lead to robust and reliable biointerfaces for lateral flow detection schemes.

Liesbet Lagae

IMEC/LST

Karolien Jans✔ ✔


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Quantitative Protein Kinetics Analysis Using a Refractometric LSPR Sensor with an Improved Figure of Merit

Proteins are vital parts of living organisms, and it’s important to explore their structures and functions. Theinteractions between proteins, from transient, low-affinity to stable, high-affinity, define much of cellular behavior, andanalysis of their interaction networks will help to assign functions to uncharacterized proteins. Furthermore, during thedevelopment of therapeutics, such as antibodies, molecules are frequently selected based on their binding kineticsand selectivity for a target ligand, as this single parameter is often predictive of activity in in-vitro and in-vivo assays.The standard analysis method, surface plasmon resonance (SPR), suffers from the fact that its decay length is muchlarger than the protein size and thus might not provide an optimum sensing ability. However, its nanoscalecounterpart, localized surface plasmon resonance (LSPR) is very promising to solve this problem.LSPR is a resonantly excited coherent electron oscillation at a metal nanoparticle surface, and its wavelengthposition is highly sensitive to local refractive index changes within the electromagnetic near-field of the nanoparticles.This effect forms the basis of LSPR biosensors. The electromagnetic field decay length has the same length scale asproteins, making biomolecules an ideal analysis target. In addition, it provides the possibility of miniaturization andmultiplexing, as well as the compatibility with microfluidics for point-of-care personalized diagnostics.At imec, we have recently developed a LSPR sensing platform with the spectral linewidth as narrow as ~10nm,offering a supreme figure of merit to potentially reduce the limit of detection. The thesis student will compare itssensing ability to that of the conventional SPR platform, and take advantage of the sensing system to investigate theprotein-protein interactions and their binding/unbinding kinetics in real time.

Pol Van Dorpe

IMEC/LST

Jiaqi Li✔ ✔


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High quality-factor resonators in silicon nitride waveguides

Dielectric waveguides consisting of a high-index core surrounded by lower-index cladding layers allow low-lossguiding of light. For photonic integrated circuits, the focus still lies on silicon photonic waveguide structures for 1300and 1550 nm wavelengths. However for several applications in biology and chemistry, waveguides for shortwavelength operation are desirable. Silicon nitride is a promising material for optical waveguides due to its lownon-linearity and its transparency in the visible and infrared spectrum. Last year, a low-loss silicon nitride waveguideplatform was developed. By an extensive materials study in the 200 mm line of imec, the propagation losses werereduced below 0.5 dB/cm at a wavelength of 532 nm while maintaining a low autofluorescence. In the picture, thecoupling from a fiber to a 250 nm wide waveguide on chip is shown.For integrated biosensing applications, the development of compact, high-quality factor resonators at visiblewavelengths is of paramount importance. In this thesis project, the student will start from the developed silicon nitridewaveguide technology and design novel high quality-factor waveguide resonators. Initially, two types of resonatorswill be considered: linear 1D photonic crystal resonators and ring resonators. The main focus will be on the linearphotonic crystal resonators, for which both the Bragg gratings and the resonant cavity will have to be designed andoptimized on the working frequency of 532 nm. This will be done by performing FDTD or FEFD simulations, followedby experimental confirmation of the simulated properties on the fabricated samples by means of waveguidetransmission spectroscopy.The student will gain hands-on experience with optical experiments. Sample preparation will be handled by thestudent in the imec III-V cleanroom in cooperation with the daily advisor. The student will obtain experience in opticaland electron beam lithography and master various deposition and etching techniques. Further samplecharacterization will be done by optical microscopy, scanning electron microscopy and waveguide transmissionspectroscopy. The candidate should have a strong interest in photonics and nanofabrication.

Pol Van Dorpe

IMEC/LST

Pieter Neutens✔


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TNFα detection in cell-culture medium of activated cells

Cytokines (e.g. IL6, IL10, TNFα and many others) are an important class of secreted proteins that play a key role inthe immune response. They are secreted by many cell types like macrophages, monocytes, T-cells, B-cells, etc. Thissecretion is often in very small amounts with a peak of only a few hours after activation of the cells. In literature, thedetection of cytokines is mainly done by RT-PCR or ELISA, which are both sensitive techniques, but they do notallow real-time detection. Therefore, a need remains for real-time detection methods that allow rapid, quantitative,close-to-the-cell (to reduce dispersion effects) cytokine analysis. A type of biosensor that can meet theserequirements are silicon waveguide ring resonators.Silicon waveguide ring resonators are based on the total internal reflection properties of silicon. Silicon waveguidering resonators contain a bus waveguide, for the input of the light, a silicon ring shape close to the bus waveguideand an output waveguide to the detector. When the ring is close enough to the bus waveguide, the light can coupleinto the ring and positive interference of discrete wavelengths can occur. These wavelengths are dependent on thetotal length of the ring, but also the refractive index near the ring surface. This property results in a detectablewavelength shift when for example proteins bind to the ring, which makes it ideal for real-time, label-free sensing.As a proof-of-principle we will make use of the U-937 cell line which is known to secrete elevated levels of TNF-αwhen stimulated with for example phorbol myristate acetate (PMA). The cells will be trapped in cellular bioreactorsnear the sensor surface for real-time detection of the secreted TNF-α. These results will be compared to resultsobtained with the BIAcore tool and Enzyme-Linked Immunosorbent Assay (ELISA).This topic is a collaboration between IMEC and the MeBIOS group of Jeroen Lammertyn at KULeuven.

Liesbet Lagae and Jeroen Lammertyn

IMEC/LST

Jef Ryken✔


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Spin wave computing

CMOS technology and transistor scaling have been the main drivers of the huge productivity growth registered overthe past 50 years. However, transistor scaling is approaching its physical limits and new devices, circuits andarchitectures are being investigated. Even more stringent than the scaling of the transistor itself, the scaling of theinterconnect (the metallic wires connecting transistors) is seen as the main limiter for immediate size and powerscaling.To replace the silicon transistor, many devices have been proposed and are currently are varying levels of maturity—from concept to experimental demonstration. The physics behind these devices spans from charge transport insemiconductors, to Dirac electrons, to correlated electron effects, to spin transport and spin waves and to optics. Inthe case of the interconnect, the focus is on materials that show ballistic electron transport at room temperature suchas carbon nanotubes.Rather than looking at separate components for devices and for interconnect, we will investigate functional blockswhich perform basic logic functions. These blocks will be built with components using collective excitations such ascharge density waves, spin waves and plasmons in various materials. Collective excitations are expected toovercome many of the traditional limitations associated with CMOS because of their intrinsic properties: a) lowenergy of the excitations is translated in low energy of operation; b) the collective nature of the excitation allows theinformation thus stored or propagated to have higher immunity to external perturbations; c) the interconnect carryingthe information is an intrinsic part of the fabric of computation—hence there is no need to convert back and forthbetween state variables that can be modulated in the computation and state variables that can be transported in theinterconnect.The objective of this thesis is to study how such collective excitations can be used for computation. The focus will beplaced on spin waves and we will study different materials and devices for spin wave computation. You will beinvolved in choosing the right materials for this application and designing, building and characterizing devices andfunctional blocks. The work will involve simulation aspects but also experimental aspects at it is multidisciplinary bynature.

Marc Heyns, Iuliana Radu

Imec, Physics or MTM

Iuliana Radu✔

experimental simulation

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Reference Device for Nonlinear Microwave Measurements

All measurements are traceable to either S.I. units (e.g., kg, m, K) or to a physical phenomenon. For example,electrical measurements of linear microwave/millimeter wave components are traceable to distance (m). Amplitudemeasurements of non-linear microwave components are traceable to temperature (K). Vectorial (i.e., amplitude andphase) non-linear microwave measurements are recent and their traceability path is still under research. The presentapproach consists in relating non-linear measurements to electro-optical properties of some materials, but therequired measurement set-ups are very expensive, highly sensitive, and available only in a few metrology labsaround the world. The objective of this master thesis is to look into an alternative based on electrical quantities only.In particular, it will be investigated whether the inherent physical properties of diodes can be exploited for developinga reference device that will be portable, cheap, and therefore easily accessible by users of nonlinear microwavemeasurement systems around the world.

The master thesis starts with a literature study to understand the concept of measurement traceability, as well as thecurrent state-of-art on vectorial nonlinear measurement traceability. Next, a simulation based study is to beconducted to explore whether the physical properties of certain diode configurations can be exploited to develop aphysics based reference device. The theoretical study will be supported by dedicated experimental tests, as needed.Once the optimal configuration has been determined, the reference device will be designed, fabricated, andthoroughly tested.

This master thesis is in cooperation with Agilent Technologies, manufacturer of nonlinear microwave measurementinstrumentation, as well as with NPL, the National Metrology Lab of the UK.

Prof. D. Schreurs

Fac. Engineering/ div. ESAT-TELEMIC

D. Schreurs, D. Humphreys (NPL)✔ ✔

literature 10%, conceptual study (40%), design (30%), measurements (20%)

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Combined electron and single molecule fluorescence microscopy for in situ catalyst characterization

Over the last decade, nanotechnology has taken an important place in materials science. Not only have traditionalmaterials been miniaturized, the ability to structure materials at the nanoscale has also resulted in the development ofnew materials with remarkable and unique properties compared to their larger counterparts. As such it has becomevery important to characterize nanostructured materials at relevant length scales and under realistic conditions and todirectly correlate this to the local performance. One research field that heavily relies on the fabrication of new, moreefficient (nanostructured) materials with unique properties is heterogeneous catalysis. Here the performance ofcatalytic particles depends on several factors like the chemical composition, the structure at the smallest scales, theaccessibility of the active sites,… . Traditionally improvements resulted from a combination of kinetic studies withbulk, ex situ physicochemical characterization. In this approach it is not straightforward to relate the effects ofnanoscale features to the local performance. Detailed information on the catalytic processes has been retrieved fromin situ spectroscopy but these focus in general solely on the catalysts themself, overlooking information on thechemical transformation. Furthermore information is mostly averaged over one, large spot. Rationalization of catalystdesign would hence strongly benefit from a direct correlation of insights in the molecular dynamics to local propertiesof the catalyst.In this project you will help in the development of a novel microscopy tool that combines an atmospheric scanningelectron microscope (aSEM), capable of measuring samples at atmospheric pressure and even in liquid!, with anadvanced fluorescence microscope (FM) that can detect single catalytic turnovers. This will allow to directly correlatenano-scale structural properties (aSEM) with the catalytic activity (FM) at the same small length scales.This project is a close collaboration between the COK (Thomas Franklin, Maarten Roeffaers) and the MolecularImaging and Photonics group of Johan Hofkens.

Maarten Roeffaers

Bioscience engineering - Center for surface chemistry and catalysis

Thomas Franklin✔ ✔ ✔

microscope development, catalyst synthesis and testing

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Active encoding of zeolites with metallic nanostructures

Recently our lab succeeded in writing 3D fluorescent micropatterns inside individual silver containing zeolite crystalsof about 20 µm in size; focusing a laser inside the crystals creates these patterns. At the focal spot of the laser silverions are photochemically reduced into small clusters exhibiting a remarkably strong fluorescence. Furtheroptimization of this technique was possible by using a unique photoactivation approach based on 2-photon excitation.This resulted in a strongly improved spatial resolution of about 250 nm. Thus, microsized (bar)coding inside zeolitesis now possible. Preliminary results show that also highly energetic X-rays and even electron beams are ably tolocally generate metallic silver nanoclusters. The possibility to actively encode nanosized structures inside thesesilver-zeolites will be investigated with a novel setup that is currently being built in the lab. This setup uniquelycombines simultaneous fluorescence and electron microscopy.This project aims to apply electron beam activation to locally generate highly luminescent clusters. Furthermore suchmetal nanoparticles arranged in periodic patterns are expected to exhibit exceptional optical properties making theminteresting candidates for the generation of metamaterials and photonic crystals.This project allows you to learn and use advanced microscopy techniques, unique in the world, and combine thesewith materials synthesis and characterization. Active support is available from the COK (Thomas Franklin, MaartenRoeffaers) and the laboratory for photochemistry and spectroscopy (Eduardo Coutino, Johan Hofkens).

Maarten Roeffaers


Eduardo Coutino✔ ✔

materials synthesis, microscope development, nanofabrication

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Seeing is believing: development of advance optical microscopes for catalyst characterization

The importance of catalysts for industrial processes is commonly known. In order to reduce production costs and toreduce the pressure on the environment, researchers have been optimizing the chemical processes. Heterogeneouscatalysts uniquely enable a reduction of waste streams and lower the reactor corrosion and the catalysts can bereused.In order to further optimize catalyst performance insight into the different dynamic processes that interplay - diffusion,ad-/desorption and catalytic conversion at the molecular scale - should be further enhanced.The center for surface chemistry and catalysis in collaboration with the lab of prof. Hofkens at the department ofchemistry has developed a revolutionary approach based on fluorescence microscopy. By using powerful lasers andadvanced microscopes and detectors, it is now possible to follow indvidual molecules during the catalytic conversion.This unique approach enable nano-scale reactivity mapping however further improvements enabling 3D nanoscalemapping is still crucial. Furthermore we are currently exploring the use of non-linear optical microscopy which furtherbroadens the reactions scope.Within this project the student will get hands on experience with different types of catalysts such as zeolites,metal-organic frameworks and with the development of 3D super-resolution microscopy. This project is a closecollaboration between the COK (Alexey Kubarev, Maarten Roeffaers) and the department of chemistry (JohanHofkens).

Maarten Roeffaers


Alexey Kubarev✔ ✔ ✔

catalyst synthesis and characterization, microscope development

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Electrical characterization of nonlinear Resistive RAM cells

Resistive Random-Access-Memory (RRAM), based on resistance switching mechanisms, is emerging as a potentialnonvolatile memory candidate for below-20nm technology nodes, due to its better scalability, beyond the limitscurrently predicted for NAND Flash. RRAM cells as small as 10nm in size have been experimentally demonstratedand are shown to have low voltage operation, very fast switching time, in the order of ns and below, small energyconsumption per switching and good reliability.To take on the benefits of these excellent attributes to circuit level, additional self-rectifying functionality is requiredfor the resistive switching stack. This will enable suppression of the parasitic "sneak leakage" paths, paving the waytowards the implementation of high density memory arrays.

The main task of this internship/thesis is to characterize RRAM cells that show self-rectifying characteristics, in orderto understand the main relationships between the operating parameters, switching behavior, as well as reliabilitytrade-offs.

You will be using state-of-the-art instrumentation and you will apply statistical principles in data collection usingin-house developed characterization methodologies, so as to ensure a short response time in characterization. Youwill process data and assist in their interpretation. Feedback for process improvement is a key point.

You must have a good background in semiconductor physics and knowledge of CMOS technology. You must befluent in at least one programming/data analysis environment such as Matlab or similar and familiar with LabView andbasic instrumentation for electrical testing. You will work in an international R&D team; a good command of Englishlanguage is required.

The detailed content of the work will be defined in detail at the moment of starting this project

Prof. Guido GROESENEKEN

imec (ESAT/INSYS)

Dr. Bogdan GOVOREANU✔

electrical characterization (60%), data analysis (25%), literature (15%)

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Optical pressure sensor at a fiber tip for high-temperature applications

Fiber-optic sensors are attractive for pressure monitoring. Fabry-Pérot interferometry is used to detect the deflectionof a pressure sensitive diaphragm at the tip of an optical fiber (see Fig. a). Advantages are their small size(measurements in limited space), their good sensitivity, their harsh environment resilience (EMI, corrosive gases, …)and their high operational temperature. Operation has been demonstrated up to 600 °C for fused silica optical fibers.

The accurate probing of the strong three-dimensional flow fields in turbo-machinery (total and static pressure, flowangle and level of turbulence) is still a considerable engineering challenge. The aim of this thesis is to improve theperformance of currently available state-of-the-art fiber-optic sensors (see Fig. b). Starting from sensor concept anddesign, the novel sensor has to be micro-fabricated and characterized.

(a) Fabry-Pérot sensor principle; (b) FIB images of different configurations of Fabry-Pérot pressure sensors at the tipof an optical fiber

Workload:• 10% Concise literature study to get yourself acquainted with subject and previous work• 20% Design of optical pressure sensor• 50% Micro-fabrication and opto-mechanical characterization• 20% Text and defense

Prof. Robert Puers

ESAT-MICAS

Grim Keulemans✔ ✔

Experimental

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Manipulating Graphene Devices

Graphene, an atomically-thin sheet of carbon atoms arranged in a sp2 honeycomb lattice, has been successfullyisolated for the first time only in 2004 (this achievement was awarded the Nobel prize of Physics in 2010). Ever since,new exciting reports are appearing in literature about the peculiar electronic properties of graphene, which mainlyarise from the configuration of its energy band structure, combined with the intrinsically low occurrence of defects andthe stiffness of its lattice, allowing for the featuring of intriguing 2-D physical phenomena.

Graphene has been proposed as a candidate for many purposes, from electrodes to CMOS and post-CMOSelectronics. However, in order to make electronic applications of graphene realistic, one has to necessarily tune itselectronic properties, so that, for example, a bandgap can be introduced. Another important aspect of the currentgraphene research entails the finding of a synthetic alternative to micromechanical exfoliation for grapheneproduction, in order to achieve high quality, large scale graphene, addressable for CMOS-compatible devicefabrication

The objective is to explore new device architectures by manipulating the graphene properties with the goal to reachto the specs of future technology nodes. The student will learn how to handle graphene sheets, tune the bandgap,and will be trained to require skills to design, fabricate, and characterize graphene FETs. Some of the challengesinvolved:

1. the study of the interaction between graphene and the different active layers in the device; by investigation of theelectronic modifications of the graphene properties influenced by its environment;2. post-processing of graphene (e.g., transfer, device design and fabrication);3. electrical and structural characterization of (integrated) graphene devices;

The students will execute the research in imec’s NCAIS group – NAME (nano applications, materials andengineering) team.

S. De Gendt, M. Heyns

Imec’s NCAIS group – NAME (nano applications, materials and engineering) team

Inge Asselberghs / Steven Brems✔ ✔

Experimental

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nanomaterials and nanchemistry nanoelectronic design bionanotechnology nanodevices and nanophysics✔

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DEM simulations on the mechanical characterization of porous low-k

In microelectronic components, low-k dielectrics are materials with a small dielectric constant (“k”) that are used toinsulate electrically conductive parts from one another. In recent years, there is a rapidly increasing interest forporous materials because of their good insulating properties. The mechanical characterization of porous materialsremains a challenge, given their nano-scale dimensions, and their heterogeneous structure. An important tool tocomplement the experimental tests (e.g. nano indentation for elastic properties, four point bending to study adhesiveproperties), are numerical simulations. This study will focus on the modeling of mechanical properties of porouslow-k materials, by means of discrete elements. Instead of treating the porous material as homogenous, themicrostructure (i.e. matrix material and pores) will be included in the models. For this we use a discrete elementcode that is built up by spherical particles which present the matrix material, while the void spaces in betweenrepresent the pores .A first part is an explorative study, where the student familiarizes himself with the software, and validates hisapproach by comparing simple models (e.g. equivalent elastic properties as a function of the properties of matrixmaterial and porosity) to analytical results from literature.A second part consists of more advanced models where the deformation behavior of the porous material is studiedduring nano-indentation. Here, experimental data is available to validate the models, and in return the models cangive valuable insight in how different parameters (porosity, pore size (distribution), interconnectivity of pores,...)influence the indentation results. Moreover, we aim to validate and/or correct the experimentally extractedparameters by nano-indentation for future simulations on microelectronic components.Optionally, fracturing of the material can be examined in a later stage. More precisely, we are interested in cohesivestrength of the material as a function of the pore properties. Additionally, we are interested if nano fractures can occurlocally and alter the elastic properties without necessarily leading to an overall failure

prof. Ingrid De Wolf

MTM/Structural Composites & Alloys, Integrity and NDTIMEC/Reliability, Electrical test & modeling groupBjorn Debecker✔

Numerical Modelling

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61

62


Thesis title:

Description:

Promoter


Daily supervision


Type of work

Number of students

SEND


Multi-scale modeling of single-cell migration - Coupling a cell mechanical model with Rho GTPase signaling

Background:Cell migration is a complex mechanism that requires a well-tuned interplay between different regions and differentcomponents of the cell’s cytoskeleton. A validated three-dimensional multi-scale model for cell motility is needed toanswer important questions with respect to cell migration between other cells and matrix. Important examples of thiscan be found in cancer research: both the phenomena of metastasis and angiogenesis in tumors are closely relatedto the regulation of the mechanics of cell migration. Enzymes, such as Rho-GTPases (Cdc42, Rac and Rho) havebeen shown to play a central role for cell migration by mediating signal transduction to the actin cytoskeleton. Theyregulate cell motility by affecting nucleation, uncapping and de-polymerization of actin filaments and actin myosincontractility. Directed cell movement is enabled by spatial polarization and mutual exclusion between on the onehand Cdc42/Rac and on the other hand Rho.Models, consisting of ordinary differential equations (ODEs) or partial differential equations (PDEs) have beenformulated that describe cross-talk schemes between these proteins and the diffusion of their inactive forms.However, a complete description of their effect on cell migration requires modeling the structural components of thecytoskeleton that these proteins affect, and describing how the mechanical properties of these components aremechanically altered – both in space and in time.

Content:In this project, the student will develop a multi-scale formulation that on one hand describes the cross-talk betweenRho-family GTPases and their effect on cell migration and on the other hand represents the key components of thecytoskeleton that are essential for cell migration. For this a separation of scales is necessary: a small scale fordescribing the molecular interactions between the Rho-GTPases and a large scale that describes spatial organizationof a complete migrating cell. Because we are interested in both spatial and temporal changes in the cytoskeleton, amodeling technique is required that is able to cope with dynamic behavior and large deformations. For this, amesh-free particle-based simulation framework is chosen. This framework describes the mechanical components ofthe cytoskeleton as interacting particles – moving freely in space - with predefined mechanical potentials. Changes inthese interaction properties will be derived from the output of the lower-scale model (e.g. concentration of activatedRho GDPs). Cell polarization and spatial segregation results directly from these low-scale model properties.The model will be validated by comparing the movement of a cell under a microscope with the motility predicted bythe multi-scale migration model. Moreover, using specific fluorescent markers for the various Rho-Family GTPases,the in vitro spatio-temporal dynamics of these proteins can be compared with the dynamics predicted by the model.Finally, using traction force microscopy experiments, the forces that a moving cell exerts on the substrate can bemeasured. This as well can be compared to the simulated substrate forces exerted by the cells. The latterexperiments will be executed by other researchers, that the student will collaborate with.

Hans Van Oosterwyck

Engineering / Biomechanics section

Bart Smeets✔

computational

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62

63


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SEND


Model-based characterization of cell mechanics - Particle-based model combined with Atomic Force Microscopy measurements

Background:The mechanical properties of cells play a crucial role in governing the way cells will behave, grow and interact withtheir three-dimensional environment. For example, new evidence demonstrates that cell-generated forces(intracellular tension) can promote cell differentiation in the absence of, or even in spite of signals from soluble cues.The last years, research on the mechanical and structural aspects of cell biology has been growing sharply.However, characterizing mechanical phenomena is challenging: it is inherently coupled with the three-dimensionalspatial structure of the cell and therefore requires advanced measurement techniques, often combined withcomputational models that provide the link between ‘simple’ forces and complex cellular behavior.

Content:Model development – The students will develop an in silico representation of a cell which captures the cell’s keymechanical components. For this, they will start from an existing particle-based model that simulates the contactinteractions between a cell and its environment. The challenge in this task lies in formulating a simplified but sufficientdescription of the most important elements of the cell cytoskeleton: microtubuli, the actin cortex and the nucleus. Thismodel will be used to simulate the dynamics of cell spreading on a flat substrate.Model calibration - Essential model parameters such as the Young’s Modulus and adhesion energy will be measuredusing Atomic Force Microscopy (AFM). This instrument consists of a microscopic cantilever with a well-defined tipthat is being pressed against the surface of the cell. The deflection of the cantilever is then quantified by measuringthe deviation of a focused laser beam on an array of photodiodes. From this, a profile of the cell surface can bereconstructed and the local mechanical properties of the surface can be estimated with high accuracy after duecalibration of the cantilever. The parameters measured in this way for the specific cells of interest combined withknown cell behavior should suffice for predicting spreading curves using the model.Model validation – In addition to comparing the expected spreading curves to cell spreading experiments, the samemeasurement technique will be used to validate the developed particle-based model. For this, a simulation of aspread out cell that is indented by a microscopic cantilever is compared with the indentation of a spread out cellmeasured using AFM (Figure 2).Having available a validated in silico mechanical representation of the cell, the model can be used to help answer alarge number of relevant biological questions: How does the choice of substrate affect the tension in the intracellularcytoskeletal components? What is the effect of the three-dimensional nature of the environment? Can we controlmechanotransduction processes by changing the structural and mechanical properties of the cell’smicroenvironment?

Hans Van Oosterwyck

Engineering / Biomechanics section

Tim Odenthal✔

50% computational / 50% experimental

2

63

64


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SEND


Functionalizing nanoporous monolayers for advanced biosensing

Small devices for biosensing play a pivotal role in the analysis of biological pathogens and ligand-receptorinteractions or for the evaluation of genetic expression patterns or in vivo interaction networks. To this end, thesedevices typically employ the immobilization of so-called probe molecules on a solid support (the sensor substrate)and a solution containing the target molecules is brought in contact with the sensor substrate. Binding of the targetmolecules is qualitatively or quantitatively assessed via a macroscopic change of an electronic or optical parameter.

Despite the successes of biosensors in many different fields, the technology still suffers from low reproducibility whichrenders accurate quantification impossible or troublesome at best. Heterogeneous target-probe interactions at thesolid-liquid interface result from random orientations and surface densities of the immobilized probe molecules. Thisprocess of surface immobilization is hard to control. In the proposed work, you will attempt to improve significantly thereproducibility of biosensing devices via patterning of the probe molecules on gold or graphene surfaces with singlemolecule accuracy and controlled intermolecular separations.

To achieve this aim, we will take advantage of our extensive expertise in the creation of nanoporous monolayers,which can be created with atomic precision via supramolecular self-assembly of low-molecular weight organicmolecules. The size of these pores is variable, and depends on the molecular building block used to create themonolayer. However, they are in the range of a few nanometer, the size of a typical biomolecule. The goal of thisthesis is to create arrays of individual biomolecules trapped in the porous template layer in order to achieve highlyreproducible biosensors or microarrays. Local probe techniques, such as scanning force or scanning tunnelingmicroscopy will be used to characterize the sensor surfaces with (sub-) nanoscale accuracy, and surface plasmonresonance or electric response curves can be employed to assess the overall behavior of the sensor surfaces inaction.

Steven De FeyerHiroshi Uji-iDivision of Molecular Imaging and Photonics

Willem Vanderlinden✔ ✔ ✔

Experimental

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64

65


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SEND


Nanostructuring of diamond surfaces by anisotropic etching and its use for the growth of carbon nanotubes

Diamond is an allotrope of carbon with sp3 configuration. Due to its chemical inertness, etching of diamond is usuallyperformed almost exclusively with reactive ions with a resolution that is strongly limited to lithographical and costlyprocesses. Recently, a low cost, fast, and effective way of etching was reported yielding surface nanostructures suchas nanopores and nanochannels with dimensions down to about 15 nm [1]. This anisotropic etching of diamondsurface is based on a catalytic process that is comparable with the catalytic growth process of carbon nanotubes(CNTs). However, the nanostructuring technology of diamond materials is still in its infancy and the scientificunderstanding and technological control of nanopores and nanochannels in polycrystalline diamond thin films is verylimited.

This thesis aims at• investigating synthesis methods for the architecture of nanopores and nanochannels in single-crystal andpolycrystalline diamond.• using the nanostructured diamond for the growth of CNTs.

Main activities are:• Thin film deposition, high temperature annealing and catalytic etching.• Catalytic CVD growth of CNTs.• Characterization (e.g. SEM, AFM, micro-Raman).

Prof. Jin Won (Maria) Seo and Prof. Jean-Pierre Celis

Engineering/ Dept. Metallurgy and Materials Engineering

Dr. Ivan Buijnsters✔

experimental work

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65

66


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SEND


Study of nanostructured titanium oxide films synthesized by wet corrosion process

Nanostructured metal oxides have attracted much attention as advanced materials due to their unique properties,such as catalytic, electronic, photoconducting, and molecular sensing properties. Especially, nanostructrued titaniumoxide film (nTOFs) are of great interest because of their very broad potential application areas. However, one of theweak points of nTOFs has been the limitation towards large-scale and low-cost fabrication and their synthesisprocess that is not feasible for substrates of different shapes as well as for complex processing. Wet corrosionprocess (WCP) is a simple and convenient method that has been reported very recently to yield nTOFs. In thisresearch project, the WCP will be systematically studied for synthesizing nTOFs. The structural and physical (mainlyelectric and optical) properties will be investigated as a function of the diverse WCP conditions.The primary purpose of this project is to establish a novel process for synthesizing nTOFs and to explore theirpotential application in devices.Main activities:- Synthesis method of nTOFs films by wet corrosion process with various concentration of KOH aqueous solution.- Characterization: SEM, TEM, XRD, Raman, FTIR, UV-VIS, PL and electric measurements

Prof. Jin Won (Maria) Seo

Engineering Science / Dept. Metallurgy and Materials Engineering

Dr. So-Yoon Lee✔

experimental work

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66

67


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SEND


Correlative light and electron microscopy using cathodoluminescence for nanoscale tagging of genomic DNA with distinguishable colours

Correlative (i.e. combined) super-resolution (SR) fluorescence- and electron microscopy offers the possibility tocombine the molecular specificity of traditional fluorescence labeling of biomolecules with nanoscale imagingresolutions in ways never before possible. However, reliable co-registration of optical and electron images and opticalsignal degradation under electron beam irradiation are only a few of the challanges faced when exploring this newimaging method. Therefore, in the presented project, novel approaches to solve these problems will be explored.

By imaging the stable optical cathodoluminescence emitted by nanoparticles with controlled surface chemistry underelectron beam irradiation, multicolored images of biological samples will be recorded with unrivalled resolution andclarity. This will pave the way for the use of nanoparticle tags, providing the ability to achieve nanoscale mapping ofmolecular composition, indicated by cathodoluminescence colour, simultaneously acquired with structural electronimages in a single instrument. As a proof of principle, correlative SR Fluorescence- and electron microscopy imagingwill be applied to the structural mapping of genomic DNA.

In the past two decades, automated Sanger sequencing has dominated genomic analysis and was instrumental toone of the greatest achievements in biotechnology; the completion of the very first finished grade human genomesequence. Even though this robust technology has seen significant improvements over time, it still remainscomplicated process. Moreover, the human genome project only marked the beginning of an entirely new era, with anever increasing demand for high quality, high coverage sequences for applications in comparative genomics,forensics, epidemiology, but also applied medicine, diagnostics and therapeutics. Rising awareness on theimportance of minor sequence variations in health and disease triggered the realization that the cost and speed atwhich full genomic data could be obtained would have to be lowered, since sparking the development of 'nextgeneration' sequencing platforms. Despite significant progress, all of the current 'next-generation' sequencingtechnologies suffer from some major drawbacks.

Indeed, sequence information is produced as a set of short, abstract fragments, which need to be assembled into acomplete genome. This is an error-prone process, e.g. when trying to identify large-scale structural variations withinthe target genome which, although elusive, are particularly relevant for diagnostic and therapeutic use of genomicinformation in clinical settings.

SR 'genomic mapping' can address these shortcomings. Site-specific labeling of large- or even full-sized genomicfragments with high spatial density can aid to significantly enhance the information content of the map. Here, theability of (bio)-functionalized metal nanoparticles to interact specifically with DNA will be used in conjunction with theunique imaging capabilities offered by integrated scanning electron- and super-resolution fluorescence microscopy toenable rapid genomic mapping with significantly enhanced information content. This will unlock the full informationpotential of complex or repetitive genomic loci and enable DNA mapping at unprecedented speed and reduced cost.

Prof. dr. Johan Hofkens

Dept. Chemistry, Laboratory for Photochemistry and Spectroscopy (LPS)

Dr. Ir. Kris Janssen✔

Materials synthesis/Microscopy

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67

68


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SEND


Microchip based Impedance Sensors for in situ evaluation of Bacterial Biofilm Formation

Biofilms are complex, highly variable, surface-associated communities of microorganisms, embedded in aself-produced matrix. Within biofilms bacteria are up to 1000 times more tolerant to antibiotics, disinfectants and otherstresses. Several factors contribute to this increased tolerance, such as protection by the biofilm matrix, slow growthand low metabolic activity of bacteria within biofilms, biofilm heterogeneity and activation of stress response withinbiofilms. As a consequence biofilms cause very persistent contaminations and infections. The tolerance of a specificbiofilm is highly dependent on its specific structure and the type of antimicrobial used. E.g. early stage biofilms are ingeneral more sensitive than older biofilms; biofilms without cellulose in the matrix are more sensitive to sodiumhypochlorite; … . Rapid detection of biofilms and accurate monitoring of biofilm structure can thus not only notify thatantimicrobial treatment is required but could also give indications on the most effective type of antimicrobial treatmentand monitor the clearance process. These in situ characterization techniques would open the doors to ‘à la carte’treatment of biofilm contaminations –i.e. personalized medicine in the case of health care- and drastically reduce thecosts and problems related to biofilms. Yet, these are not available yet.

The aim of this project, which is a joint effort of CMPG (KU Leuven) and imec, is to deliver proof-of-concept for theapplication of electrochemical impedance sensors (microchip based) as an in situ tool to evaluate the gravity of abiofilm contamination.

Prof. Jozef Vanderleyden

Bioscience engineering

Dr. Hans Steenackers (CMPG-KU Leuven) and Dr. Dries Braeken (imec)✔ ✔

Experimental biology, microscopy, impedance measurement, interpretation based on physical models

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Calibration of stress sensors for 3D-IC applications

The 30-IC technology enables the high density integration of integrated circuits resulting in the smaller footprint of thechip and at the same time improving the signal integrity and to some extend the power consumption. It also enablesintegration of different CMOS technologies in one functional 30 module. However the 30-IC integration introduces anextra complexity into the micro-system thus affecting its reliability and thermo-mechanical stability. To quantify theseeffects the set of temperature and stress sensors has been developed. The response of these devices has also beenmeasured at different temperatures and at different levels and kinds of the mechanical stresses.The objective of this master thesis is to get more systematic experimental and theoretical information on thesensitivities of the sensors which are available on the different 30 test vehicles. In particular the work will be focusedon the calibration of stress sensors at vertical (out-of-plane) stresses and at the calibration of stress sensors atdifferent temperatures.

The work will include:

1. Literature study2. Developing the experimental techniques and the methodology to enable the calibration of different sensors3. Performing the experiments4. Analyzing the results and drawing the conclusions

Ingrid De Wolf

MTM

Vladimir Cherman and Wei Guo✔ ✔

Labwork and analysis

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Modeling of stress evolution during void formation in copper interconnect

This proposal is best situated in the domain of electromigration behavior in back end of line interconnects. Forproposing process changes to suppress electromigration on future technology nodes, understanding void formationkinetics and its link to the potential relaxation of stresses in copper interconnects is crucial.

lmec's paper at the IEEE International Reliability Symposium in 2011 clearly demonstrated a slow down of void driftvelocity during void formation. Simple one-dimensional models exist to model stress evolutions along a copperinterconnect.

This thesis subject deals with the complete understanding of void formation kinetics, where a link needs to be madebetween void size and tensile stress built-up and relieve.

The subject is mainly suited for a person with strong background in physics who likes to dig into mathematicalformula's and loves solving differential equations!

Ingrid De Wolf

MTM

Kristof Croes✔ ✔

Solving differential Equations

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Modeling of embedded planar and non-planar MIM capacitors into SiliconInterposer for 2.5D and 3D technologies

As the scaling down of MOS transistor starts achieving its physical limits, new solutions to continuously increase theperformance of future microprocessors are being investigated. Three dimensional integrated circuits (3D-IC) offers aunique way to increase the performance of current technologies by vertically or horizontally stacking chips withactive electronic components. Stacking different chips together (e. g. Memory and Logic) provides severalbenefits against classical planar ICs. 3D-ICs have a higher degree of functionality integration, less powerconsumption and offers an alternative to reduce or maintain the cost per chip. Reducing the interconnectionlength between chips reduce signal delay, increases transmission speed, and allows a higher operationspeed of the device. 3D technology also enables heterogeneous integration where different process technologiesare used to optimize circuit performance and combined lately together into a single 3D-IC.

Among the different 3D technologies, Silicon Interposer (SI) technology, also known as 2.5D or 2D, emerges asa highly versatile and flexible solution and the natural intermediate evolution step between single IC and full 3D-IC.In 2.5D interposers the chip dies are bonded to the SI and horizontally stacked together side-by- side. Differenttechnologies (CMOS, MEMS, photonics, 3D-IC, etc.) share the same silicon handle die. Inter-chip interconnectionsare done using the metal layers on the interposer and the connections to the laminate's package are done viaflip-chips or Cu-pillars at the back side of the SI. Through silicon via (TSV) in the SI get the signal from the front sideto the back side of the SI.

In order to enhance the functionality of Silicon Interposers, passive and simple active devices will be integratedinto the SI, replacing those existing in the stacked chips or outside the chip package. In that sense, MIM capacitorsare devices that can be easily integrated into the SI, replacing the decoupling capacitors at chip or packaginglevel. Embedded capacitors on Silicon Interposer can be used for a wide range of DC and RF applications as powerdecoupling, signal coupling, pump charging, DC/DC power conversion, etc. To have a wide range of capacitancevalues, while having a reasonable occupied surface on the SI, capacities densities of 1, 10, 100 nF/mm2 or higherare needed. Trenched MIM capacitors with nanometric layer thickness are ideal devices to obtain such high densitylevels. Targeted final capacitance values goes from 10 nF to 4.7uF.

The student is expected to simulate the performance of current planar embedded MIM capacitors into SI as well asof non-planar MIM capacitors to be integrated into future SI technologies. The work include the optimization ofthe different material parameters as well as evaluation of different trench shapes and dimensions. Simulations will bedone using commercial 3D and 2.5D EM simulation tools as HFSS or ADS Momentum up to 60GHz. The RLC equivalent model of the simulated capacitors will be extracted. Distributed models of capacitors forpower decoupling will be also investigated.

Patrick Reynaert

IMEC/TDE/SDA

Cesar Roda Neve & Mikael Detalle✔

Simulation

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Electromagnetic Analysis of Cryptographic Devices

Side channel attacks allow an attacker to extract secret cryptographic keys from embedded devices such as smartcards, FPGAs, or RFID tags. These attacks exploit information leaked by the devices trough the so-called sidechannels, the most common ones being the power consumption and the electromagnetic (EM) emanations. Thesepowerful techniques have been used in the last years to attack multiple commercial products (for instance Keeloq,Atmel CryptoMemory, NXP Desfire, or Xilinx bitstream encryption), and are a great concern for industry.

This thesis focuses on EM side channel attacks. One of the key factors to enable EM attacks consists in having ahigh quality experimental setup that allows, for instance, the scanning of the whole chip surface to obtain a map ofEM emanations. This process can be automated by placing the device under test on top of a XY table remotelycontrollable from a PC, which also collects and processes the measurements obtained by the oscilloscope via an EMprobe. Further setup improvements include the addition of postprocessing analog circuitry, e.g. to filter or amplify thecollected EM measurements.

The first part of this thesis consists analyzing the existing EM measurement setup. Depending on the backgroundand/or interests of the student, the focus of this part can be to improve the software components, the design of EMprobes, antenna coils, or postprocessing analog circuitry. In the second part of the thesis the student will employ theexperimental setup to perform practical EM attacks on cryptographic devices. Background in cryptography is notrequired.

Prof. Ingrid Verbauwhede

Departement Elektrotechniek - ESAT / COSIC

Benedikt Gierlichs <[email protected]>Josep Balasch <[email protected]>✔

15% literature, 15% theoretical work, 70% practical work

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Security-aware circuit design

Cryptography has become a key part of our everyday life. Just think of the bank cards, smart phones, RFID tags andwireless networks. Since small portable devices are used to handle our private data they are required to usecryptography. However, these devices are vulnerable to a special class of attacks that exploit power consumption orthe electromagnetic radiation of the device to discover secrets from the user. These are called side-channel attacks(SCA) and they are very powerful tools used to break the security of otherwise unbreakable devices.

Security risks need to be taken into account when designing circuits for secure embedded devices. A substantialamount of design tricks to improve security is available in literature. The goal of this thesis is to develop circuit-levelcountermeasures against SCA. The student can select one or more of the offered options (register file, SRAM,integer multiplier...) and develop a circuit resistant against side-channel attacks. The work includes circuit design,layout design and security analysis.

Prof. Ingrid Verbauwhede and Prof. Wim Dehaene

Departement Elektrotechniek - ESAT / COSIC

Vladimir Rozic <[email protected]>✔

30% literature, 20% theoretical work, 50% Circuit Design

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Electrical investigations on advanced rear-side passivation in next generationsilicon solar cells

ContextCrystalline silicon solar cells have a market share of more that 85% in roof top installations. While the standardthickness in production nowadays is at ~180 μm (156x156 mm2), the solar cell roadmap is directing towards thinnerand thinner cells by further increasing the efficiency in order to further reduce the cost/Wp. In this frameworkdielectric passivation of the rear surface of the solar cell provides a major input to improve the conversion efficiency.

Imec backgroundWithin the IMEC PhotoVoltaic department new fabrication processes are developed to provide thinner cells,requested for future production. In the framework of reducing the thickness of the silicon substrates the influence ofthe rear-side surface recombination becomes important. Already at silicon solar cell thicknesses of 150um therear-side surface recombination current participates in the loss current and leads to degradation of the cellperformance. Novel back-side passivation materials like e.g. AlOx are investigated on surface passivation. Novelpassivation materials are benchmarked against existing passivation schemes like thermal SiOx.

Internship descriptionIn this framework, it is proposed to interns (between 3rd and 5th year of Master or equivalent) to participate to theshort loop testing of the dielectric material AlOx. The extraction of the interface trap density (Dit) and the charges (Q)in the dielectric layer is performed by C-V measurements. Minority carrier lifetime measurements are performed tocalculate the surface recombination velocity, which is a measure for the passivation quality of the dielectric layer.Detailed task description:

- Determine lifetime and C-V data from dedicated test devices- Analysis and interpretation of the measured data- Comparison of the results with literature and simulations

Jef Poortmans

IMEC PV department

Joachim John ([email protected])✔ ✔

Experimental (70%), Theory (20%), Literature (10%)

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Solid electrolyte thin films for lithium ion microbatteries

Lithium-ion batteries (LIBs), first commercialized by Sony Energy Tech., are now the dominant rechargeable systemsin the market. LIBs have attracted a great deal of interest due to their high energy and power densities. They areused in portable electronics (e.g., cellular phones, digital cameras, and laptop computers) and are considered as theperfect candidates for electric transportation (e.g., electric vehicles (EVs) and hybrid electric vehicles (HEVs)).However, in addition to safety concerns, those LIBs based on liquid organic electrolytes suffer capacity and powerfade during both cycling and storage.

In this respect, fabrication of all-solid-state power sources is a critical issue for advanced lithium batteries and the keycomponent for success lies in the development of an alternative solid electrolyte. Next to solving the issues withsafety (flammable liquid electrolyte), the transition to a solid-state electrolyte would mean significantimprovements in the battery performance as well: higher energy density, longer battery life time and widertemperature range of operation. High priority criteria of solid electrolyte to achieve higher energy density andlong-term stability are high Li+ ionconductivity, low electronic conductivity, stability against chemical reaction with electrodes and wide stability window(high decomposition voltage).

Among various solid-state batteries, the thin film battery (TFB) is a fast growing category. Thesemicrobatteries make use of a thin solid electrolyte layer between cathode and anode sequentially deposited on to asubstrate by various deposition processes. A thin layer of solid electrolyte provides considerable savings in terms ofvolume and mass of the battery compared to liquid or polymer electrolyte. Therefore, allowing direct integration withmicrosystems such as sensors or implants.

In this project, we will explore the possibility of preparing thin film electrolytes by electrodeposition of variouscompounds such as phosphates, borates, and oxides. Deposition of borates, for example, will give Li-B-O thin films.Literature shows that nitrogen-doping of such films would result in Li-B-O-N thin films which offers improved ionicconductivity and enhanced chemical stability. Chemical and physical analytical techniques will be used to determinethe composition and morphology of the deposit. Also, the electrochemical and electrical properties of the depositedmaterials will be characterized.

Philippe Vereecken

FBIW / IMEC

Philippe Vereecken, Abdel-Aziz El Mel, Mohammad Kassem✔

experimental

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Deposition and characterization of a-Si layers to passivate epitaxial emitterson thin silicon foils on glass

Solar energy is the most promising renewable energy source that will replace traditional carbon-based energy.However, the price is still hampering the breakthrough for commercial use.To reduce the cost, a reduction of the thickness of the silicon substrate up to a 40-um thin foil is proposed. This foil isepitaxially grown on a mechanically weak layer and detached from its parent substrate after bonding to a glasscarrier. In this way, cheap but high quality substrates are created.However, this new type of ‘bonded’ substrates cann’t be processed as a standard silicon wafer. All processes need tobe compatible with the material that is used for bonding: existing processes need to be adapted or new techniquesneed to be used.

To obtain high efficiency solar cells from this type of substrates, passivation of the front and rear surface are veryimportant. Front-side processing is done before bonding of the epitaxial foil and therefore existing processes can beused.The focus of this project is situated in the passivation of the rear-side of the epitaxial foil, where the emitter is located.The growth of amorphous silicon (a-Si) of a few nanometers will be used to passivate the p-type epitaxial emitter.First, an existing process for standard wafers will be adapted and optimized for the epitaxial emitter on the bondedfoil. Secondly, this process will be integrated in the full solar cell process flow to create the first epi-foil solar cells.

Jef Poortmans

Kris Van Nieuwenhuysen✔ ✔

Experimental (60%), theory (20%), literature (20%)

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Study of oxygen precipitation in n-type wafers

In the solar cell community there is a trend to shift from p-doped wafers to n-doped wafers for high quality solar cells.N-type wafers typical have a larger minority carrier lifetime with respect to p-type wafers. The lower the minoritycarrier lifetime, the higher the losses due to recombination and the lower the efficiency of the final solar cell. At imec,the solar cells with highest efficiencies are interdigitated back contact cells, cells where all the contact are located onthe rear of the cell. Also these cells are made on n-type wafers which have a sufficiently high minority carrier lifetime.

From experiments we know that that n-type wafers which start with a high minority carrier lifetime at the beginning atthe start of the solar cell processing, can end up with a low lifetime at the end. The reason for this is believed to bethe formation of oxygen precipitation in the wafer during the high temperature steps involved in the solar cell processflow.

The goal of this thesis is a detailed study on this oxygen precipitation. For this, dedicated wafers with a range in initialoxygen concentration will be subject to a range of high temperature processes. Minority carrier lifetime will bemonitored by photoluminescence imaging and radio frequency photoconductance measurements. Oxygenprecipitation will studied by FTIR. Aim is to confirm the link between low lifetimes, high temperature processing andoxygen precipitation and to give on onset on how to limit the oxygen precipitation by adapting the high temperaturesteps.

Jef Poortmans

Maarten Debucquoy ([email protected])✔ ✔

experimental

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Characterization and modeling of oxide border traps in Ge/III-V MOSFETs

Recent developments on CMOS-driven III-V and Ge MOS (Metal-oxide-semiconductor) technologies provide newopportunities in advancing the performance envelope of logic devices as well as lowering the operating power. Thequest of high speed/low power post-Si CMOS with heterogeneous integration calls for in-depth studies on variousaspects including device modeling and characterization, performance benchmarking, reliability/passivation/contactstudies and ultimately, scaling beyond 10nm node. Recently, the impact of oxide traps (border traps) on deviceperformance has been demonstrated [1] on III-V and Ge MOSFETs.

The proposed research activities for the internship include (but not limited to):1. Electrical characterization of III-V/Ge planar MOS- and FIN- FETs for gate stack performance, and oxide andinterface evaluation (Admittance analysis, AC-transconductance, charge pumping... ), paired to devicebenchmarking.2. Modeling and simulation: relating the border traps and electrical results measured on devices with differentchannel materials, gate stacks and layer structures.

[1] D. Lin, et al, p. 645 IEDM 2012

Guido Groeseneken

IMEC CMOST, ESAT

Dennis Lin and Koen Martens✔

experimental / simulations

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Investigation of Self-Assembled Monolayers for Advanced InterconnectsSchemes

As the total transistors and interconnects sizes come down to few tens of nanometers a shift in paradigm for themanufacture and integration of microelectronics components becomes apparent. Organic molecules - owing to theirsize, mechanical flexibility and chemical tunability - fit well in this slot and, thus, are expected to play a key role in ICdownscaling. In this respect, self-assembled monolayers (SAMs) seem the best candidates. SAMs are a prototypicalform of nanotechnology: the SAM precursor molecules carry the “instructions” required to generate an ordered,nanostructured material without external intervention. SAMs demonstrate that molecular-scale design, synthesis, andorganization can generate macroscopic materials properties and functions. Although the details of thethermodynamics, kinetics, and mechanisms of assembly will differ significantly, these monomolecular films establisha model for developing general strategies to fabricate nanostructured materials from individual nanometer-scalecomponents. Because SAMs can assemble onto surfaces of any geometry or size, they provide a general and highlyflexible method to tailor the interfaces between nanometer-scale structures and their environment with molecular (i.e.,subnanometer scale) precision. SAMs can control the wettability and electrostatic nature of the interfaces ofindividual nanostructures and thus their ability to organize into large assemblies adding chemical functionality,thermodynamic stability (e.g., improving the adhesion at the dielectric/metal interface).

In particular, metallization of SAMs, i.e. the formation of metallic overlayers or clusters on top of monomolecularorganic films, is of great importance for many areas of fundamental and applied research. Albeit this problem wasactively addressed in the last years, reliable methods to the deposition of metal on top of the SAM are continuing tobe a topic of intense research. This task is challenging since most of the studies show an undesirable metalpenetration through the SAM. It is generally believed that this is caused by structural defects in the monolayer. Cu isthe interconnect material of choice in the metallization step for advanced semiconductor device manufacturing. Thecurrent approaches to Cu metallization include chemical vapor deposition (CVD), physical vapor deposition (PVD),selective electroless deposition (ELD) and electroplating. As device sizes decrease, accommodated by scaling andmaterials changes, electrochemical deposition is considered the most promising method due to its many advantagessuch as good uniformity and gap filling ability, selectivity and low processing temperatures. Nevertheless, due to theneed for applied power and non-uniform current distribution of Cu electroplating, Cu ELD is especially emphasizedfor future interconnect technologies. In addition, ELD Cu is a promising alternative to PVD Cu for both high aspectratios through silicon vias in 3D architectures and narrow damascene lines, where the limitations of the PVDtechnique are reached. In the ELD method deposition occurs via the chemically-promoted reduction of metal ionswithout an externally applied potential. It is therefore a soft deposition technique expected having the potential toeliminate or greatly reduce the metal penetration through the SAMs observed for medium-to-low-reactivity metals,such as copper. The purpose of this work is to develop and characterize an ELD process on the thin SAM organicfilm. The effects of the SAMs chemistry (functional groups, vapor vs. liquid phase deposition, deposition solventsetc...) and ELD experimental conditions (pH, temperature, time, concentrations, post-deposition thermal treatment)on the deposition mechanism and efficiency of the electroless Cu bath (e.g. in terms of Cu thickness and roughnesscontrol, adhesion at the interfaces dielectric/SAMs/Cu, ...) will be investigated.

In parallel, the choice of the SAMs precursor molecules and deposition conditions will be optimized in order toimprove and control the SAMs’ Cu diffusion barrier and pore sealing performance on ultra-porous low dielectricconstant materials currently integrated in the advanced damascene architectures. Introducing pores into a dielectricposes several challenges for successful integration into microelectronic circuits. Insulating films with low dielectricconstant (low-k) are critically required for semiconductor manufacturing [1]. Low dielectric constant films are usuallycreated by introducing pores containing air or other gases, with dielectric constant close to 1, into a matrix materialwith dielectric constant in the range 2-3. The desired dielectric constant of the resultant film is typically 2.2 or less.The low dielectric constant matrix material frequently includes carbon, typically in the form of methyl groups (-CH3)bound to silicon. Unfortunately, subsequent processing steps such as etching often cause the methyl groups to belost and replaced with hydroxyl groups (-OH). This leads to an intrinsic increase in dielectric constant. Even moreseriously, Si-OH groups tend to bind water molecules which lead to a further increase in dielectric constant andleakage current as water enters the pores of the low-k dielectric, and even the bulk of the matrix itself. In addition, themechanical strength of the dielectric is reduced by porosity, potentially leading to failure during chemical mechanicalplanarization or during wire-bonding to the finished chip. Thus it is expected that porous low-k material in amicrocircuit will need to be hermetically sealed from ambient moisture. Copper also diffuses readily through porouslow-k materials, so an effective barrier is needed to confine the copper within the copper wires. The SAMs barrier towater and copper must be very thin ~less than 2 nm so that it does not occupy volume needed for thecurrent-carrying copper wires. If the barrier thickness is smaller than the largest pores, it becomes difficult to bridgethe pores on the surface of the dielectric with a thin continuous barrier. Nevertheless, in this case, using smallhydrophobic SAMs precursor molecules may be effective for recovering the low dielectric constant after damage.Sealing of porous dielectrics and/or damage recovering by SAMs will be explored.

[1] International Technology Roadmap for Semiconductors, 2009 edition, Interconnect chapter:http://www.itrs.net/Links/2009ITRS/2009Chapters_2009Tables/2009_Interconnect.pdf

Stefan De Gendt

Herbert Struyf/Silvia Armini✔

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Effect of dummy structure fill on planarity in chemical mechanical polishing

Chemical mechanical polishing (CMP) is a widely used technology in silicon device manufacturing in order to attainhigh levels of planarization. imec is developing CMP process steps on insulating films like silicon oxide or nitride, aswell as conductive metal layers such as copper, aluminum, or tungsten. As the CMP process in general in verydependent on pattern density, device structures are being surrounded by dummy structures to achieve betterperformance. These dummy structures are designed together with the devices and can vary in fill size, density andshape.

The aim of this study is to learn which dummy structures result in the best CMP planarity. A dedicated test mask isavailable and will be used for characterization for ILD0 oxide and metal gate CMP. Both CMP steps in crucial inadvanced RMG (replacement metal gate) processing.

The student will get trained on the CMP processing tool (300 mm wafer size silicon processing) and will thencharacterize the performance by means of several metrology options like thickness and stepheight measurements(for ILD0 oxide CMP) and electrical line measurements (for metal gate CMP). An extensive part of this work will be indata management and data analysis. The outcome of this study will be implemented in future designs within imec.

The student will work independently, but daily follow-up by the process step responsible from imec’s CMPdevelopment group will be provided. Frequent reports will be requested to guarantee timely input and/or feedback.

Stefan De Gendt

Katia Devriendt/Patrick Ong/Herbert Struyf✔

Test material definition/creation, CMP, Data collection, management and analysis

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Advanced barrier CMP slurry development

In order to build even smaller devices, very narrow structures have to be filled with copper to achieve advancedinterconnects. The aspect ratio of these lines makes them hard to fill without defects and voids. One of theapproaches that helps the deposition of copper into narrow structures is to vary the underlying barrier-seed layer. Thechoice of this layer improves copper electroplating and can make ELD Cu deposition possible. In the subsequent processing steps, the copper as well as the underlying barrier-seed layer needs to be removed inthe field area, leaving conducting material only within the interconnect structures. This is achieved through a CuChemical Mechanical Polishing (CMP) step followed by a barrier CMP step (which removes the barrier-seed layer).When polishing these barrier layers using CMP, there are several process issues that can occur. First of all, thebarrier metal needs to be removed quickly and evenly, which can be hard due to native oxides on the surface.Second, it is necessary to keep corrosion issues under control during the CMP process.

The goal of this project is to optimize barrier-seed layer removal rates on blanket wafers while limiting (galvanic)corrosion using model slurries which are optimized for barrier CMP. In order to achieve a good removal rate, differentoxidizers and complexing agents are added to model slurries while surfactants/inhibitors are added to protect thesurface against corrosion and improve planarity. Static etch rates for these slurries need to be determined to estimateextent of static corrosion. Other CMP parameters (e.g. pressures, flow rates) can be adjusted to further improve theprocess. Basic electrochemical measurements can be done as well to determine the effect on the corrosion currentsin the Cu-barrier CMP system for different slurry additives.For the best performing slurries, it needs to be ascertained that the defectivity and planarity of the polished surface isgood. Performance with respect to other device materials needs to be checked. Time permitting, these slurries maybe tested on patterned wafers as well as on other advanced barrier materials.Applied techniques include CMP on our experimental polisher, sheet resistance measurements, defectivity analysis,electrochemical tests, etc.

A basic knowledge of chemistry is necessary, some experience in electrochemistry is a plus.

Stefan De Gendt

Lieve Teugels✔

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Development of porous AAO test structure to study carbon nanotube growthin vias with extreme dimensions

Due to their remarkable electrical, thermal and mechanical properties, carbon nanotubes (CNT) have beenconsidered for various applications in different fields of research. One particular application, situated in the world ofintegrated circuits, are CNT based interconnects.At the contact level of DRAM interconnects, very narrow (sub-11 nm) via holes with a high aspect ratio (A/R > 50)need to be filled with a conducting material. This is no longer possible with the conventional metallization techniquesas fill issues arise at these extreme dimensions. CNTs, however, offer an elegant solution to this because of its truebottom-up growth process. Moreover, one MWCNT in a sub-11 nm contact hole satisfies the requirements for the viaresistance set by the ITRS.To study the growth and the electrical properties of CNTs in these small holes, a test structure is needed. For this, ananodized aluminum oxide (AAO) template on top of TiN is considered. When anodizing aluminum, aligned pores startto propagate vertically from the top to the bottom of the Al layer. The pore size and morphology can be changed anddepends on the anodizing conditions. Once the pores reach the underlying TiN, the anodization process is stopped.An additional step is needed to clean the bottom of the pores to guarantee an excellent electrical contact with theTiN. After this, nanoparticles (Ni or Co) have to be deposited at the bottom that will catalyze the growth of CNTs. Thefinal step is to introduce this template in a CVD chamber where CNTs can be grown.The focus of this master thesis is on the development of a AAO template and on the study of the growth of CNTtherein. After successful CNT growth is demonstrated, different integration approaches can be used to electricallyevaluate the electrical properties of the CNTs in the AAO template. The experimental work will both take place in theelectrochemical lab as well as in the cleanroom.

Prof. Philippe Vereecken

Nano Applications Materials Engineering (NAME, imec)

Johannes Vanpaemel, Marleen van der Veen✔ ✔

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Bottom-up fill of deep holes with nanowires for future contact schemes

Nanowires are expected to play a key role in the transistor and interconnect down scaling as the paradigm forintegration of microelectronics components is entering the sub-22nm scale. Conventional metals will no longer simplymeet the requirements needed for the performance and conventional depositions methods are no longer a fillingsolution at sub-14nm dimensions.

The aim of this project is to realize CMOS compatible nanowire deposition in extreme small dimensions at thenanoscale. The focus is to deposit the metals like Cu and W, or alloys, using a void-free and preferably frombottom-up growth process. Techniques that can be considered for the metallic nanowire growth are chemical vapordeposition, atomic layer deposition, or selective electroless or electrochemical deposition. The bottom-up growth willbe studied on metallic contacts or barrier layers. Several test vehicles for the bottom-up growth will be available forthe growth tests.

The characterization of the vertical nanowires grown on a conductive substrate will focus on the relation between thestructural properties and the electrical properties. The ultimate goal is to identify metallic nanowires that can showballistic transport on a sub-10nm scale. For this, it’s needed to study and understand how the electrical conductionthrough the nanowires is influenced by the dimensions (diameter and length), and whether optimization of the growthcan improve the nanowires performance. The experimental work will both take place in the electrochemical lab aswell as in the cleanroom. Successful grown nanowires could be tested further in full integration schemes using theadvanced imec pilot line on 300mm full wafer level.

The work will start from earlier findings within the cross-functional metallization teams bridging the group of H. Struyfand the InterConnect Integration program of Ds. Zs. Tökei.

Prof. Philippe Vereecken

imec (ECAT: Electrodeposition, CMP And Thinning)

Dr. Marleen van der Veen✔ ✔

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Energy spectrum of a cylindrical superlattice nanowire

In this thesis the energy spectrum for a cylindrical nanowire consisting either out of heterostructure superlattice orperiodic gate configurations or periodic width fluctuations will be calculated. In first instance the student will considera simple periodic potential profile along the axis of the nanowire to understand the formation of the minibandspectrum as a function of periodicity and potential energy heights. Once this problem is solved we will considerperiodic all-around gates and study the energy spectrum as a function of the applied gate voltages, wire radius,spacing between the gates. Finally, the case of a periodic superlattice heterostructure and an infinite array ofperiodically spaced width fluctuations will also be considered.

The research is situated in the broader quest for devices that can be fabricated in future sub-10 nm nodes. Amongstother challenges, one problem to overcome is to suppress unwanted currents that remain present when transistorsare in sub-threshold mode (‘off’). One approach to this problem is the use of minibands to filter out the electrons thatcontribute to this unwanted current. Hence a good understanding of the influence of wire geometry, superlatticeparameters, etc. on the formation of minibands is necessary. Since the usual semi-classical approximations forsemiconductors are no longer useful on this length-scale, calculations will start from solving the Schrödinger equationitself, a paradigm called wavefunction engineering that is becoming increasingly more important as devices continueshrinking.

The student will perform the aforementioned calculations by making acceptable approximations which will render theproblem tractable. If necessary the student can also rely on available software to numerically solve the problem. Thestudent will make an analysis of the energy spectrum and draw preliminary conclusions with respect to the transportproperties of the charge carriers in the nanowire.

The candidate should have a strong background/interest in solid-state physics, quantum mechanics andcomputational physics.

Marc Heyns

MTM

Bart Sorée✔ ✔

Theoretical / computational

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Unraveling the quantum mechanical properties of nanoparticles with scanningtunneling microscopy

Nanoparticles, providing the bridge between the atomic and the bulk level, attract a lot of attention in solid statephysics. Their properties do not simply scale with their size and cannot be readily predicted. A profound knowledge oftheir behavior is of crucial importance for fundamental physics, but also, e.g., for the operation of futurenanoelectronic circuits and data storage media. Controlled preparation of nanoparticles on a substrate allows probingtheir physical properties with high spatial and energy resolution by means of scanning tunneling microscopy (STM)and spectroscopy (STS).For this thesis project, you will create nanoparticles (clusters) in the gas phase by means of condensation ofevaporated atoms, and deposit them on atomically flat substrates. The central goal of this research project is asystematic investigation of the size dependence of the electronic properties of these deposited clusters by STS.More precisely, you will study the properties of individual nanoclusters for which the interaction with the substrate isminimized. This can be achieved by depositing the nanoclusters on metallic substrates that are covered with a thinNaCl layer that acts as a tunnel barrier and basically eliminates the interaction with the underlying substrate. You willinvestigate electron quantum-mechanical confinement phenomena and Coulomb charging effects that are expectedbecause of the finite size of the nanoclusters.

Dr. Koen Schouteden, Prof. Ewald Janssens, Prof. Peter Lievens, Prof. Chris VanHaesendonckFaculty of Science, Lab. of Solid State Physics and Magnetism

Dr. Koen Schouteden, Zhe Li✔

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Oxides with a high dielectric constant on high mobility semi-conductors Ge and InGaAs

Dielectric oxides are critical elements in many electronic devices for logic applications such asmetal-oxide-semiconductor field-effect-transistors (MOSFET) as well as in several memory devices (FLASH andDRAM). The requirements (band gap and dielectric constant) for the different applications (F=Flash, L=Logic,D=Dram) are illustrated in the adjacent Figure.

From a fundamental viewpoint, one of the key design challenges in this field, is to create dielectrics heterostructureswith a high dielectric constant while maintaining a very low leakage current. The appropriate materials currently donot exist! Artificial structures with novel electric dipole configurations – including interfacial monolayers will bedesigned, developed and tested during this project1.

From an experimental point of view, these oxides will be integrated with semiconductors such as Ge and InGaA incapacitor and transistor structures2. One of the major issues that prevents the use of Ge and InGaAs MOSFETstoday, is the large amount of electrically active defects at the interface. By controlling the interface structure andchemistry as well as the interatomic stacking sequence using molecular beam epitaxy, novel surface passivationstrategies will be developed on top of which a high K oxide will be grown (ε > 60).

This project can be executed both from a fundamental viewpoint or from a more experimental viewpoint. Theactivities will take place in the framework of a European collaboration with industrial partners such as IBM.

1EM Vogel, Nature Nanotechnology, 2, 25 (2007); W. Andreoni et al, Appl. Phys. Lett., 96, 062901 (2010).2YN Sun et al., IEEE Elec. Dev. Lett., 28, 473-475 (2007); C. Marchiori et al., J. Appl. Phys., 106, 114112 (2009).

Prof JP Locquet, Prof JW Seo

Faculty of Science / Faculty of Engineering

Dr Mariela Menghini, Drs Chen-Yi Su, Drs Tomas Smets✔

Experimental / Simulations

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Design of a new magnetic deflection system for atomic clusters

Stern and Gerlach developed in 1922 an experiment to deflect particles to illustrate basic principles of quantummechanics. They were able to demonstrate that electrons and atoms have intrinsically quantum properties. TheStern-Gerlach experiment involves sending a beam of particles through an inhomogeneous magnetic field andobserving their deflection (Fig. 1) [1]. In 2012, a Rabi-type magnet was designed, built and installed at the Clustersand Laser Spectroscopy research group for the deflection of atomic clusters(http://fys.kuleuven.be/vsm/class/research/magdef.php). The system will be operational one of the next months.

In this thesis proposal, alternative designs for the Rabi-type Stern-Gerlach magnet will be considered. The designsuffers from the contradictory requirement to provide both a high magnetic field and a high magnetic field gradient.The conception of alternative design will be carried out by making extensive use of 2D and 3D magnetic fieldsimulation tools as available and developed in the Wave Propagation and Signal Processing research group at theKU Leuven – Kulak.

Remark: The thesis work can be carried out everywhere and can be supervised accordingly. However, a regularpresence (e.g. one day per week) in Kortrijk (www.kulak.be) is recommended. Travelling (train) and additional lodgingcosts (student home) will be refunded.

Ewald Janssens, Herbert De Gersem

Laboratory of Solid-State Physics and Magnetism

Ewald Janssens, Herbert De Gersem✔

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Optimization of a high-field magnet for pulsed operation

In the Pulsed Fields Group at the Department of Physics and Astronomy, pulsed magnetic fields of about 70 T aregenerated in the bore of a cylindrical magnet submersed in liquid nitrogen and excited by a capacitor bank. Duringspring 2012, the existing capacitor bank of in total 0.5 MJ has been replaced by a 2 MJ capacitor bank. In theory, thiswould enable to operate the magnets at a substantially higher field. However, severe thermal and mechanicalrestrictions hamper such straightforward up scaling.The present magnets have been designed and optimized for several decades until now [1,2,3]. To that purpose,calculation routines on the basis of (semi-)analytical formulae have been developed. Over the years, expertise hasbeen gained on the magnet layout, winding techniques, reinforcement fibers (carbon, glass fiber) and impregnationtechnology. Until today, magnets are constructed, tested and used in the laboratory.The simulation of the magnet system requires the calculation of coupled electromagnetic, structural dynamic(strength) and thermal fields in time domain. Despite of the remarkably high accuracy of the existing semi-analyticaltechniques, it is expected that finite-element simulation offer higher design flexibility, thereby possibly opening theway towards higher fields and longer life times. A coupled finite element simulation has already been reported in [4].This thesis proposal aims at the application of a 2D transient, electromagnetic, structural dynamic, thermal finiteelement field simulation to an axisymmetric model of the magnet (although mechanical deformation disturbs thecylindrical symmetry). An intermediate goal consists of achieving a sufficiently reliable simulation tool, e.g.comparable to the existing semi-analytical models. Finally, the model will be applied for parameter studies, i.e., forchanging the existing design according to the new capacitor bank and the new design of the cryogenic equipment.

[1] L. Li, F. Herlach, Deformation analysis of pulsed magnets with internal and external reinforcement, IEE ScienceMeas. Technol. 6, 1995, 1035–1042.[2] F. Herlach, T. Peng, J. Vanacken, Experimental and theoretical analysis of the heat distribution in pulsedmagnets, IEEE Trans. Appl. Supercond. 16(2), 2006, 1689-1691.[3] F. Herlach, N. Miura (eds), High Magnetic Fields: Science and Technology, World Scientific Publishing, ed. 1, vol.1, Magnet technology and experimental techniques, 2008.[4] H. Witte, A. Gaganov, N. Kozlova, J. Freudenberger, H. Jones, Pulsed magnets - advances in coil design usingfinite element analysis, IEEE Trans. Appl. Supercond. 16(2), 2006, 1680-1683.

Remark: The thesis work can be carried out everywhere and can be supervised accordingly. However, a regularpresence (e.g. one day per week) in Kortrijk (www.kulak.be) is recommended. Travelling (train) and additional lodgingcosts (student home) will be refunded.

Herbert De Gersem, Johan Vanacken

Laboratory of Solid-State Physics and Magnetism

Herbert De Gersem, Johan Vanacken✔

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First-principles modeling of high-mobility semiconductor/insulator interfaces

A next step in boosting progress and performance of semiconductor devices implies, in replacement of the current Si,incorporation of semiconductors of higher intrinsic carrier mobility. When introduced at the nano scale, this willrequire new analysis and physics insight. Understanding the fundamental properties of such gate stacks is importantin order to understand their behavior in devices. The work to be performed encompasses computation and modeling the structural and electronic properties ofinterfaces of high-mobility semiconductors (e.g., Ge, GaAs) with high-quality metal oxide insulators, based on densityfunctional theory. A second point of interest includes 2 dimensional materials (graphene, silicene, MoS2, …) and Silayers with main focus, besides practical stability, on band structure and transport properties. As a propelling tool, the results will be correlated, when possible, to experimental results obtained through structuraland electrical observations. This work will be performed in collaboration with IMEC.

Prof. M. Houssa

Faculty of Science /Semiconductor Physics Section

E. Scalise, A. Belmonte, M. Mees, B. van den Broek, Prof. M. Houssa✔

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Internal electron photo-emission in semiconductor nano-layers and nanostructures

The energy spectrum of electron states in nanometer-thin insulating layers and at their interfaces with, e.g.,semiconductors (Si, Ge, AIIIBV, etc.) can be characterized into great detail using observations of optically-inducedelectron transitions across the interface (the internal photo-emission effect, as compared to the better known classicalsolid/vacuum photoelectric effect ingeniously described way back by A. Einstein). This method allows the moststraightforward and unique determination of the fundamental energy parameters of a two-solids nanostructure, likeband gap, height of energy barriers and band offsets at the interfaces The spectroscopy of internal photoemission will be applied to the study of insulating materials currently tested foruse in new novel micro-and nanoelectronic devices, this within a framework of international collaboration, includingIMEC. Part of the experimental work will imply electrically contacting a basic heterostructure and measure photoemissioncurrents through a computerized monitoring system. Among the targeted results, the student should acquire the skill of inferring interfacial band offsets at a newlyconceived semiconductor/insulator heterostructure based on the understanding of the physical processes occurringduring carrier photo-emission.

Prof. V. V. Afanas’ev; Prof. A. Stesmans


Mr. F. Cerbu; Prof. V. V. Afanas’ev✔

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Probing structural quality of semiconductor interfaces using electron spin resonance

When dimensionally down scaling solid structures from the macro over the microscopic down to the nano (quantum)size, the relative importance of surfaces and interfaces gradually increases, even towards taking an all dominant role:One atomic-size imperfection my imply life or dead for the envisioned functional (physical) property. The technique ofmagnetic resonance, applied to electrons (ESR), is the unique tool enabling, besides characterization, identificationon true atomic scale of imperfections in fully non-destructive way through sensing the magnetic moment of unpairedelectrons. Part of the work to be performed implies assisting in taking ESR spectra at low (cryogenic) temperatures andsimulation of observed spectra to infer the relevant parameters. The ESR data will be complemented with a parallelstudy of the electrical properties of the centers, thus aiming to back up electrical understanding with atomic insight. Actual challenges imply the interfaces in Ge/GeO2/SiO2, Ge/Si/HfO2, and GaAs/oxide entities, where identificationof crucial interface traps is envisioned. One more item of interest concerns centers in near-interfacial insulatinglayers.

Prof. A. Stesmans


Ms. S. Iocova; Mr. Sang Nguyen; Dr. M. Jivanescu; Prof. A. Stesmans✔

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Embedded semiconductor nanoparticles characterized by electron spin resonance

Part of the enhanced attention paid to solid state nanoparticles derives from the interest in the study of changingfundamental properties of solids when size is reduced down to the nanoscale. A separate class concernssemiconductor nanoparticles embedded in dielectrics, particularly studied for interesting properties, such asremarkable photoluminescence, and potential for (memory) electronic devices.

In these phenomena, occurring point defects commonly play a crucial role, of fundamental impact, making theircharacterization, and much hoped for, ultimate identification, main targets. In the current work, electron spinresonance (ESR) is applied as a prime non-destructive technique to attain identification on atomic scale,simultaneously enabling probing of the immediate atomic and structural environment. Part of the work to be carried out implies assisting in taking ESR data at low temperatures and simulation of relevantparameters to infer relevant parameters. Interpretation on the basis of underlying theories will reveal specific particleproperties. Of current interest are Si and Ge particles embedded in various dielectric matrices as well as Si nanowiresembedded in SiO2, the research being carried within continuous international collaboration. This is done inconjunction with application of electrical studies to infer properties such as charge trapping and alteringsemiconductor band structure properties.

Prof. A. Stesmans


Mr. Sang Nguyen; Dr. M. Jivanescu; Prof. A. Stesmans✔

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Metallic nanoclusters for the spatially-controlled attachment of proteins and cells

Immobilization of biomolecules on substrates is required in many different academic as well as industrial areas (e.g.biosensing, catalysis, bioseparation or bioelectronics). Since biomolecules are usually attached to surfaces differentfrom their native environment, maintaining their biological activity remains challenging. As it is well known that themicro- and nano-environment of immobilized molecules and cells plays an important role for the function and specificproperties of the biomolecules [1], different approaches have been proposed and used to selectively immobilizebiomolecules onto various substrates. Recently, bare metallic nanoclusters deposited on a solid substrate have beenused as specific binding site for protein adsorption [2].The aim of this project is to analyze the influence of the size and the density of the deposited clusters on theimmobilization of proteins. Vacuum-deposited platinum nanoclusters [3] will be produced with a size range of 1nm –5nm (matching the size of a single protein molecule) and with different densities. These clusters, deposited on abiocompatible, protein-repellent substrate [4], function as specific binding sites for biomolecules. Proteins will beattached to the clusters, either directly or via a linker molecule[5].You will use atomic force microscopy (AFM) techniques to investigate the cluster sizes and densities after thedeposition as well as after their bio-functionalization. With atomic force spectroscopy you will probe the interactionbetween the immobilized molecule and its complementary molecule (e.g. using receptor-ligand system). Quantitativeas well as structural information about the immobilized molecules will be obtained by quartz crystal microbalanceexperiments. Using these complementary analysis techniques, you are aiming to determine to what extend thespacing and size of the clusters can be changed in order to control qualitatively and quantitatively the immobilizationof biomolecules at the nanoscale.

References[1] Lee, Y.-S. & Mrksich, M. (2002), Trends in Biotechnology, 20 (12), S14-S18.[2] Palmer, R. E. & Leung, C. (2007), Trends in Biotechnology, 25 (2), 48-55.[3] Vandamme, N., et al. (2003), Journal of Physics: Condensed Matter, 15, 2983-2999.[4] Alcantar, N. A., et al. (2000). Journal of Biomedical Materials Research, 51, 343–351.[5] Rusmini, F., et al. (2007), Biomacromolecules, 8, 1775-1789.

C. Bartic, M. J. Van Bael

T. Peissker✔ ✔

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Bio-templated metal nanowires from protein fibers

In Nature, materials exhibit a high degree of refinement, including a variety of molecular functionalities andinteractions, specific physical properties, together with exquisite structures which can be observed at different lengthscales. Such diversity and specificity can be used to address some of the current issues and challenges ofnanosciences. One particular challenge in this field is the high throughput production of conductive nanowires able tointerconnect nanometer-sized building blocks which will be used in future electronic and bioelectronic applications.Many biological molecules and organisms are able to self-assemble into fibrilar structures. DNA, rod-like viruses,microtubules and protein fibers have for example been tested as potential templates for the synthesis of conductivenanowires.1 Owing to their good resistance to heat, flexibility and dimensions, β-sheet-rich amyloid protein fibers areespecially suited for nanofabrication.In this project, Hen Egg White Lysozyme (HEWL) will be used to produce amyloid fibers.2 Gold nanoparticles withspecific affinity for aminoacids present on the protein surface will then be grafted in order to reach variable metalcoverage along the fibers. Finally, lysozyme fibers will also be chemically modified to enhance nanoparticle bindingwithout affecting the fibers integrity. The properties of hybrid fibers will be monitored by means of Atomic ForceMicroscopy, together with surface and solution spectroscopies (UV-Vis, fluorescence).

[1]T. Scheibel, R. Parthasarathy, G. Sawicki, X.-M. Lin, H. Jaeger, S. L. Lindquist (2003) PNAS, 100, 8, 4527.[2]L. N. Arnaudov, R. de Vries (2005) Biophys. J., 88, 1, 515.

C. Bartic

O. Deschaume✔ ✔

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Investigation of mechanical properties of cellular membranes upon interactionwith amyloid beta peptides: a study relevant for Alzheimer's Disease (AD)pathology

The AD mechanisms are not yet understood. Recent theories are based on the interaction of a small peptide -Amyloidβ (Aβ) - with the neuronal membranes [1]. This peptide are produced in different aloforms (variable number ofamino acids) among which the most abundant are Aβ40 and Aβ42 [2]. The mixture of this aloforms with a specificratio (Aβ42:40=3:7) has been proven to have a toxic effect on neurons both in vitro and in vivo studies [3].The aim of this thesis work is to study how the peptides are distributed on the cellular membrane and how theirpresence is influencing the membrane elasticity. More specifically, you will investigate the formation of amyloidion-channels and/or pore-like structures in membranes by means of atomic force microscopy (AFM) - topographicalimaging and force spectroscopy - combined with fluorescence microscopy (Figure 1).Fluoresce microscopy allows to visualize if the amyloid peptides have a preferential arrangement on the cellmembrane. Combining it with the Quantitative Imagin (QI) AFM one can map the morphological and mechanical localchanges of the membrane exposed to the Amyoid β peptides by comparison with the control cells.

References:[1] The Amyloid Hypothesis of Alzheimer's Disease: Progress and Problems on the Road to Therapeutics, J. Hardy,D. J. Selkoe, Science, Vol. 297 no. 5580, 2002, 353-356[2] The toxic Aβ oligomers and Alzeimer`s disease: an emperor in need of clothes, I. Benilova et al., Natureneuroscience, Vol. 15, No. 3, 349-357 (2012)[3] Neurotoxicity of Alzheimer`s disease Ab peptide is induced by small changes in the Ab42 to Ab40 ratio, I.Kuperstein et al., The EMBO Journal, 3408-3420 (2010)

C. Bartic, C. Van Haesendonck

Andreea-Alexandra Ungureanu✔ ✔

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Quantum dots interaction with enzymes

Quantum dots (QDs) are semiconductor nanocrystals with sizes between 2 and 10 nm. In a QD, the free chargecarriers are confined in all three dimensions. This quantum confinement gives rise to size-dependent properties. Anexample is the decreasing bandgap as the dot gets smaller. As a consequence, QDs can be engineered to emit lightover the entire visible range by varying their size. Another aspect of quantum dots is their large surface-to-volumeratio, which makes them very sensitive to the environment. For quantum dots suspended in solutions, a small pHvariation pH can cause huge changes in the light emission intensity.Coupling QDs with biological molecules opens new possibilities in biosensing and bioimaging[1,2]. One interestingclass of biomolecules are enzymes, proteins that catalyze biochemical reactions. A quantum dot may sense thesereactions, because they generate reactions products that locally alter the environment (e.g. local pH changes). In thecase of redox-active enzymes, also direct transfer of electrons from the reaction site to a nanoparticle has beenillustrated[3].The goal of this project will be to study the interaction between QDs and enzymes. Fluorescence microscopy,photoluminescence spectroscopy and conducting AFM will be used to assess the mechanisms through which theenzymatic reaction influences the optical properties of QDs.

[1] Willner et al. The FEBS Journal 2007, 274, 302-309.[2] Alexson et al. J. Phys.: Condens. Matter 2005, 17, 637-656.[3] Lioubashevski et al. JACS. 2004, 126, 7133-7143.

C. Bartic, M. J. Van Bael

D. Debruyne, O. Deschaume✔ ✔

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Local visualization of vortex dynamics

Low temperature scanning probe microscopy (SPM) techniques are very powerful tools to investigate a variety ofinteresting superconducting systems. The spatial resolution of these systems allows researchers to map thevariations in the superconducting condensate or variations in the magnetic field profile at the nanometer scale. Thenanoscale magnetism and superconductivity (NSM) group of the KU Leuven is a key player to develop and use thesetechniques to investigate the static and dynamic properties of vortex matter in a superconductor [1].

The aim of this thesis is create a nano-size vortex container using high resolution electron beam lithography andstudy rectification effects [2,3] of these confined vortices using state of the art scanning probe techniques. Duringtheir thesis students will be immersed in the fascinating world of nanoscience by developing nanoscale systems andperforming top notch experiments to explore their behavior under extreme conditions (low temperature and highmagnetic fields).

For more information contact Dr. J. Guttierez: [email protected]

[1] R. B. G. Kramer R. B. G. Kramer, A. V. Silhanek, J. Van de Vondel, B. Raes and V. V. Moshchalkov, Phys. Rev.Lett. 103, 067007 (2009)[2] C. C. de Souza Silva, J. Van de Vondel, M. Morelle and V. V. Moshchalkov, Nature 440, 651 (2006)[3] R. P. Feynman et al., The Feynman Lectures on Physics (Addison-Wesley, Reading, MA, 1963).

Prof. J. Van de Vondel and Prof. V. V. Moshchalkov

Faculty of Science/Nanoscale Superconductivity and Magnetism

J. Van de Vondel and J. Guttierez✔

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Investigation of spin dynamics using non-local spinvalves

The two fundamental properties of an electron are its charge and spin. In conventional electronics information isrepresented, manipulated and transported in the form of the electron charge, while the spin degree of freedom isignored. Nevertheless, in a wide variety of structures the combined interaction of the electron properties with itsenvironment leads to very interesting new phenomena. A well known example is the Giant Magneto Resistance(GMR) effect in multilayered ferromagnet/metal structures, which quickly led to the miniaturization of the recordingheads of hard-disk drives, and earned Fert and Grünberg the 2007 Nobel Prize in Physics. These experiments pavedthe way to a new type of electronics based on the active manipulation of the electron spin, i.e. spintronics.

Ten years ago the investigation of spin dynamics took a very fast and productive flight. This was mainly due todevelopments in electron beam lithography, which allowed for nanostructured non-local spin devices, opening a newand vast world of possibilities [1, 2]. Within this thesis we will start exploring spin dynamics using non-local spindevices. The student will combine high resolution electron beam lithography and shadow evaporation techniques toachieve these devices. The obtained structures will be investigated using high resolution, low temperature, transportmeasurements.

For more information contact J. Van de Vondel: [email protected]

[1] F. J. Jedema, A. T. Filip and B.J. van Wees, Nature 410, 345 (2001)[2] I. Neumann, J. Van de Vondel, G. Bridoux, M. V. Costache, F. Alzina, C. M. Sotomayor Torres, S. O. Valenzuela,SMALL 9, 156 (2013)

Prof. J. Van de Vondel


J. Van de Vondel✔

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Dynamical interplay of light and superconductivity at nanoscale

Superconductivity is a macroscopic quantum effect with a variety of fascinating properties. As reflected in its name,one of those is the dissipation less flow of electrical current – a feature very much appreciated for desired energysavings. Nevertheless, the superconducting state is highly sensitive to a variety of external factors, such astemperature, the magnetic field, or exposure to light – i.e. bombardment of relatively high energetic photons, to namea few. Although the latter effect is useful to construct superconductor-based single photon detectors, the underlyingphysics is not fully understood.

The aim of this thesis is to expand our knowledge about the nontrivial interplay of superconductivity and light. Theincentive for these new hybrid structures is given by recent breakthroughs achieved in the field of plasmonics, inwhich the interplay of light with nanostructured metallic materials is investigated [1].

Within this thesis we will create a completely new type of hybrid systems combining a thin superconducting film withsuch a nanostructured metallic film. These structures will be investigated using, low temperature, transportmeasurements.

For more information contact J. Van de Vondel: [email protected]

[1] N. Verellen, Y. Sonnefraud, H. Sobhani, F. Hao, V. V.Moshchalkov,P. Van Dorpe, P. Nordlander, and S. A. Maier,Nano Letters 9 (4), 1663-1667 (2009).

Prof. J. Van de Vondel


J. Van de Vondel✔

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The nature of pnictide high temperature superconductors

In 2008 the iron pnictide compounds where discovered to be superconducting with a relative high criticaltemperature. Previously most high-temperature superconductors were copper based and consisting out of layers ofCuO2 sandwiched between other substances. The new pnictide superconductors are based instead on conductinglayers of iron and a pnictide and seems to show promise as the next generation of high temperaturesuperconductors.We will characterize “micro-devices” and “whiskers” from these pnictide superconductors and construct theTemperature (T) –Magnetic field (H) - Current density (J) phase T-H-J diagram using high pulsed magnetic fields. Inthis way we will determine the potential for applications of these new superconducting micro-structures.

J. Vanacken / Jun Li

INPAC

J. Vanacken✔ ✔

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Nanoscale optical confinement in plasmonic resonators for enhanced light-matter interactions

Plasmonic nanoantennas are metallic nanoparticles that can be considered as classical oscillators at the nanoscale.They act as antennas, converting electromagnetic waves at optical frequencies into localized fields. As such, theyprovide an effective way to study and manipulate light-matter interactions at the nanoscale by coupling photons inand out of nanoscale volumes. Applications are widespread and rapidly evolving: energy harvesting, cancertreatment, disease diagnostics, DNA sequencing, optical computing, etc.

Recently, we demonstrated multi-mode plasmonic resonators which support multiple plasmonic modes, includingsuperradiant, subradiant, and Fano resonances. Each mode can have a tailored mode volume, electromagnetic fieldenhancement, and quality factor. The tunability of these parameters allows to achieve much stronger interactions withquantum emittors (Purcell effect), bio-molecules (biosensing), and nonlinear optical processes (e.g second harmonicgeneration) – as illustrated in the figure.

In this thesis, novel multi-mode nanoresonators for specific experimental applications will be investigated. Thestudent will take part in all aspects of the research: design, development, and experimental characterization.

Dr. N. Verellen and Prof. V.V. Moshchalkov

Faculty of Science / INPAC

Dr. N. Verellen✔

Experimental & simulations

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Near field optical microscopy of plasmonic nanosystems

The optical excitation of surface plasmons on metallic nanostructures provides numerous ways to control andmanipulate light at nanoscale dimensions. This has stimulated the development of novel optical materials, innovativenew devices, and applications with significant technological and societal impact. Plasmonic excitations allow theguiding of light and localization of optical fields beyond the diffraction limit. Any progress in nanoplasmonictechnology depends on a detailed knowledge of the plasmonic properties with nanoscale optical resolution, i.e., oneneeds the ability to look into the optical near field, beyond the diffraction limit. A technique allowing circumventing thislimitation from classical optics is Scanning Near Field Optical Microscopy (SNOM) (see figure).

In this thesis, plasmonic nanoantennas will be investigated using the SNOM technique. The aim is to obtain a deeperunderstanding of the electromagnetic near field distributions in individual and coupled resonators, as well as adetailed comparison between their near and far field spectral response. Finite difference time domain (FDTD)simulations will be used to back-up the experimental results.

Dr. N. Verellen and Prof. V.V. Moshchalkov

Faculty of Science, INPAC

Dr. N. Verellen and D. Denkova✔

Experimental & Simulations

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Metal germanide formation on Ge1-xSnx

To boost the performance of semiconductor devices, efforts are being made to enhance the charge carrier mobility inthe active areas of a transistor. To this end, alternative materials (compared to Si) are studied, such as Ge and –more recently – Ge1-xSnx. Adding Sn induces biaxial strain in the channel of the transistor and improves the mobilityof both holes and electrons. However, to implement GeSn, it is crucial to find a suitable material for electricalcontacts. Such contact electrodes are typically formed by thermal reaction of a thin metallic film with thesemiconductor material, resulting in the sequential formation of a number of crystalline phases. For metallic contactson Si (and to a lesser extent Ge), this reaction is largely understood. However, adding Sn significantly complicatesthe reaction process, in particular since Sn is expected to redistribute during the solid phase reaction.In this project you will investigate the influence of Sn on the solid phase reaction mechanism of a series of near-nobleelements. The germanide phase formation sequence will be studied using in situ X-ray diffraction (XRD), in whichXRD spectra are acquired continuously during the thermal treatment, enabling to investigate the phase formation inreal time (see Fig. 1). For these measurements, we will make considerable use of the in situ XRD setup of GhentUniversity. The elemental redistribution (depth profile) of all composing elements and in particular of Sn, will beprobed using Rutherford backscattering spectrometry (RBS). RBS is a nuclear scattering technique, available at theInstituut voor Kern- en Stralingsfysica, yielding quantitative compositional depth information by recording the energyof the backscattered He ions that are impinging on the sample.

prof. André Vantomme, prof. Kristiaan Temst and prof. W. Vandervorst

Faculty of Science, Nuclear Solid State Physics

Koen van Stiphout and Nuno Santos✔ ✔

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Phonons in nanostructured materials

In reduced dimensionality systems such as nanostructures, the vibrational properties, described by the phonondensity of states (PDOS), are expected to be affected by geometrical confinement, leading to strong deviations fromthe bulk behavior. A good understanding of the size and elastic strain effects on the material vibrational properties isnot only of great interest from a fundamental aspect but it will also be extremely valuable for a wide range ofapplications, such as for heat transfer control in nanoscale electronics devices.The measurement of the vibrational properties of nanoscale materials has remained until recently a great challenge,since conventional techniques allowing to access the full PDOS, such as inelastic neutron or inelastic x-rayscattering, could not be used to probe such small sample volumes. The recent availability of high brilliance thirdgeneration synchrotron sources has enabled significant advances in x-ray scattering techniques, such as nuclearinelastic scattering (NIS). The NIS technique relies on a resonant phonon-assisted nuclear excitation with detection ofthe incoherent decay products, using specific “Mössbauer active” isotopes such as 57Fe, 119Sn, 151Eu, amongwhich 57Fe is by far the easiest and most widely used.

This experiment is intended to investigate the vibrational properties of a model 2D confined system made of ironnanowires embedded in an alumina matrix. 2D confined systems have two confined directions, leaving the thirddirection, in the present case the direction parallel to the nanowires axis, unconfined. By performing this experiment,we expect to obtain insight into size and strain effects that may affect the phonon density of states of iron nanowires.In particular we aim at providing answers to the following questions. Do we observe any size effect, and if so can it berelated to the nanowires diameter? How are the vibrational properties of iron nanowires modified as the temperatureand thus the axial strain is increased? Are the related thermodynamic properties, such as thermal conductivity,significantly modified?

prof. André Vantomme and prof. Kristiaan Temst


Claire Petermann✔ ✔

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Artificial multiferroics: Magnetoelectric coupling at the interface between ferromagnetic and ferroelectric materials

Multiferroic materials have been a hot topic of research in recent years. One of the potential applications could be inthe creation of high-powered computer memories and other data storage devices with a much higher storagecapacity as compared to the present memory devices. These are rare materials in which two or more ferroic orderparameters are simultaneously present. Our interest lies in the coupling between ferroelectric and ferromagneticorder parameters, which is called magneto-electric (ME) coupling. Magneto-electric coupling offers the interestingperspective to influence the magnetic state by applying an electric field. The ME coupling is rather weak in singlephase multiferroic materials. Therefore our aim is to couple the ferroic orders of a ferroelectric (lithium niobate) and aferromagnetic (Fe3Pt) material via an interface in a multilayer structure.

The ferromagnetic layers will be grown on the ferroelectric substrates using molecular beam epitaxy (MBE). Thefocus of this master project is to elucidate the microscopic magnetic structure of the ferromagnetic layer close to theinterface with the ferroelectric substrate. For that purpose the Fe3Pt layer will be grown using the 57Fe isotope,allowing to apply hyperfine techniques like Mössbauer spectroscopy and synchrotron-based nuclear resonantscattering to locally quantify the chemical and magnetic state. Furthermore we will apply an electric field across thethickness of the sample, enabling to observe the change in magnetic properties as a function of electric field, i.e. adirect probing of the magneto-electric coupling.

prof. André Vantomme, prof. Kristiaan Temst and prof. Margriet Van Bael


Manisha Bisht and dr. Vera Lazenka✔ ✔

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Local magneto-structure of dilute magnetic semiconductors

Spintronics is a growing branch of physics and technology, exploiting the electron spin for information storage,processing and transmission. A critical step towards the full development of spintronics lies in the realization ofsemiconducting materials which display electrically tunable ferromagnetism, which is typically achieved bymagnetically doping ordinary (non-magnetic) semiconductors. These materials are known as dilute magneticsemiconductors (DMS).Among many generations of DMS materials, III-V semiconductors such as GaAs doped with Mn (i.e., Ga1-xMnxAs)have become model DMS systems. The carrier-mediated ferromagnetism established in these materials leads tounique spintronic phenomena which are much weaker or not present in metals and non-magnetic semiconductors,e.g. tunnelling anisotropic magnetoresistance. However, despite such intense research and major developments,DMS materials are still far from understood. For example, the degree of hole localization and the origin of the uniaxialmagnetic anisotropy are yet to be established. Some of these open questions are even at the very basis of the DMSmagnetism, e.g. the position (site) of the magnetic impurities in the host lattice. Answering such questions will requireexperimental techniques which are element specific and provide magnetic and structural information at the atomiclevel.This project consists of investigating the local structure and magnetism of Mn-dopedIII-V semiconductors (GaAs, InAs…). Particular emphasis will be given to determining the lattice sites occupied bythe Mn atoms in the III-V host lattice, using a unique combination of β- emission channeling (at ISOLDE-CERN,Geneva) and X-ray absorption fine structure (at ESRF, Grenoble). Polarized neutron reflectivity (at ILL, Grenoble,and HZB, Berlin) will be used to investigate the magnetization reversal mechanisms and their relation to the magneticanisotropy. Within this topic, we offer the possibility of Erasmus exchange with Instituto Superior Técnico (Lisbon).

prof. André Vantomme and prof. Kristiaan Temst


dr. Lino Pereira✔ ✔

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Electronic properties of doped ZnO nanowires

Oxide based semiconductors and in particular ZnO based materials with wide band gap offer unique possibilities forapplications in electronic devices due to their remarkable electronic, optical and optoelectronic characteristics. Theapplication potential is further increased by considering ZnO nanowires, where the strongly reduced dimensions giverise to pronounced quantum confinement effects that allow a further tailoring of the functional properties.

For your master thesis you will probe the electrical properties of individual ZnO nanowires with a typical diameter of50 nm and a length around 1 μm. For that purpose you will first use electron beam lithography to attach electricalcontacts to individual ZnO nanowires that are deposited on an insulating substrate from a liquid suspension. You willthen measure down to liquid helium temperatures the magnetoresistance of the wires as a function of the appliedmagnetic field strength and orientation. This will allow you to investigate the influence of various types of electronand hole doping. You can further investigate with nanometer resolution the homogeneity of the doping by using acombination of electrostatic force microscopy (EFM) and scanning gate microscopy (SGM). With EFM you will beable to measure the electrical potential distribution in a current-carrying nanowire. On the other hand, with theconductive EFM tip acting as a gate electrode, it is also possible to induce a controllable local potential perturbationand to obtain a SGM image of the nanowire. Finally, you will replace the standard gold contacts with ferromagneticcobalt electrodes to induce a spin-polarized current, which is of direct interest for applying the ZnO wires in spintronicrelated applications.

Prof. Chris Van Haesendonck

Faculty of Science / Solid State Physics and Magnetism Section

Dr. Yujia Zeng, Dr. Alexander Volodin✔ ✔

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Tuning the electronic properties of graphene by absorbates

During the last few years it has become possible to isolate individual atomic layers of carbon from a graphite crystal.These so-called graphene layers have unique two-dimensional electrical transport properties that are very sensitiveto the attachment of atoms or molecules to the layers. This offers interesting possibilities for the use of graphene asgas sensor or as biosensor.

You will prepare the appropriate graphene samples by mechanical exfoliation of few-layer graphene that is obtainedby thermal decomposition of a carbon containing gas on a metallic substrate. The exfoliation will be achieved bymanipulation with the tip of a scanning tunneling microscope (STM). You will then deposit various atoms andmolecules to tune the electronic properties of the graphene by the adsorbed atoms or molecules. The electronicproperties, including in particular the influence of the adsorbates, can be investigated with atomic resolution usingtunneling spectroscopy measurements with the STM. All experiments will be done in ultra-high vacuum (UHV) inorder to avoid the influence of unwanted contamination on the experimental results.

For the interpretation of the experiments you will rely on density functional theory (DFT) based simulations(collaboration with the theory group of Prof. François Peeters at the University of Antwerp).



Dr. Koen Schouteden, Dr. Alexander Volodin✔ ✔

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Novel catalysts based on deposited size-selected mono and bimetallicgas-phase clusters for fuel cells applications

Hydrogen produced by reforming of natural gas from biomass is a major source of clean and renewable energy thatcan be efficiently converted in electricity in polymer fuel cells (PEMFC). However it generally contains a significantamount of CO that is quickly poisoning the PEMFC Pt alloy anode. Preferential oxidation of CO (CO-PROX)catalyzed by noble metal (platinum) nanoparticles is one of the most efficient methods to reduce CO concentrationsin the H2-rich gas stream. However Pt catalysts lack selectivity in the presence of water and their high cost and lowavailability limit their future industrial applications. An alternative is the use of 3d transition metal catalysts such asmonometallic Cu or bimetallic Cu-Au on CeO2 support that has recently demonstrated promising performances.However their activity needs to be significantly improved and optimised before they can be applied at an industriallevel.The aim of our project is to gain new understanding on the role played by the metal cluster size, composition andsupport on the catalytic performance of these novel CO-PROX catalysts.To achieve this goal we will use a novel approach based on deposited size-selected gas-phase clusters produced bylaser ablation. This will replace the wet-chemical preparation method that is currently used to prepare them and thatdoes not offer the required flexibility to tailor the size and the composition of the nanoparticles.■ Cu-based mono and bimetallic (Cu-Au) ultra small gas-phase size-selected clusters will be deposited onto largesurface area SiO2 and CeO2 supports with a full control over their size (few atoms to 4 nm) and composition (CuAu3,CuAu).■ The structure and morphology of the deposited clusters will be extensively characterized with surface Atomic ForceMicroscope (AFM) and TEM for the most promising systems.■ The catalyst activity of powdered catalysts will be tested in microreactors fitted with ultra-sensitive detectiontechniques. In a second stage the structure of the most promising systems will be investigated in situ under realisticcatalytic conditions at the ESRF synchrotron using X-ray Absorption Spectroscopy.The fundamental insight of the role of the size, composition and support gained in this investigation is expected tolead to a significant improvement in the design process of novel CO-PROX high performance catalysts.

Dr. Didier Grandjean, Prof. Peter Lievens

Faculty of Science, Lab. of Solid State Physics and Magnetism

Dr. Didier Grandjean, Saleh Aghakhani✔ ✔

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The structure and hydrogen storage capacity of transition metal dopedaluminum clusters

Safe and efficient hydrogen storage remains one of the main challenges on the way of implementation of hydrogenfuel cells on an industrial scale. With the aim to find alternative solutions for gaseous hydrogen technology, lightsolid-state materials with high hydrogen storage capacity are considered. In this context small aluminum clusters areprospective. However, pure aluminum particles show relatively high activation barriers (0.7−1 eV) to dissociativechemisorption of hydrogen molecules, whereas low hydrogen adsorption/desorption energy barriers are needed forhydrogen regeneration at room temperature. Theory predicts that adding low concentrations of Ti, V, or Cr mightlower the hydrogen adsorption/desorption energy barriers.In this thesis work you will produce beams of transition metal doped aluminum clusters, AlnTM (n = 2-30, TM = Ti, V,Cr) using a laser vaporization cluster source. The ability of the clusters to absorb hydrogen will be investigated in thegas phase (i.e. unsupported) mass spectrometry. The saturation regime for hydrogen adsorption of bare and dopedaluminum clusters will be examined.In addition the structure of size selected bare and doped hydrogenated aluminum clusters will be determined bycombining multiphoton infrared spectroscopy with density functional theory calculations. With infrared spectroscopyone can identify vibrational transitions that are characteristic for the cluster geometry. These measurements requirean intense infrared laser source and will be carried out at the free electron laser FELIX (Free Electron Laser forInfrared eXperiments) at the Radboud University in Nijmegen, the Netherlands. The density functional theorycalculations are no part of the thesis work and are available via collaborations with theory groups.

Prof. Ewald Janssens, Prof. Peter Lievens


Dr. Vladimir Kaydashev✔ ✔

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Magnetic coupling in chromium oxide clusters

Clusters are small particles composed of a countable amount of atoms. Small metal clusters exhibit magneticproperties that are very different from the corresponding bulk materials. In addition, the magnetic properties candramatically change by addition of oxygen atoms. It is theoretically predicted that the exchange coupling between thelocal magnetic moments in small CrnOm clusters depends strongly on the oxygen content. Specifically theantiferromagnetic chromium dimer, Cr2, may be turned into a ferromagnetic, or non-magnetic system by successiveoxygen addition.In this thesis project you will measure the total magnetic moment of CrnOm clusters (n = 2-4, m = 0-6) as function ofthe number of chromium atoms and the oxidation state using a magnetic deflection experiment. Hereto, a home-builthigh vacuum cluster beam setup will be used and the deflection of a particle ensemble in a strong inhomogeneousmagnetic field (Stern-Gerlach magnet) will be recorded by a position sensitive detector. The unusual magneticproperties of unsupported clusters will be determined as function of the temperature of the clusters.

Prof. Ewald Janssens, Prof. Peter Lievens


Yejun Li, Nguyen Thanh Tung✔ ✔

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Electric Field induced Metal - Insulator - Transition for NVM applications

For non-volatile memory (NVM) applications, the goal is to change from flash technology towards more compact andscalable designs using alternative mechanisms. Phase change (PCM) and resistive switching memories (RRAM) aretwo popular approaches. While many “switching” mechanisms are proposed, we focus here on purely electronicphase transition between an insulating and a metallic state. The adjacent Figure shows the resistivity changes versustemperature for the Pr(Ca,Sr)MnO3 compound.

From a fundamental viewpoint, one of the key challenges is that the metal insulator transition (MIT) in correlatedelectron systems is still not fully understood (Mott vs Peierls transition). In addition, novel materials and/orheterostructures must be designed1 and tested whereby the gap opens far above room temperature, and far from“disturbing” structural phase transitions.

From an experimental point of view, MIT oxide thin films will be deposited using sol-gel and molecular beam epitaxymethods. The metal-insulator transition will be determined as function of applied electric fields and temperature.Finally they will be integrated into functional devices such as memory elements and varistors2.

This project can be performed both from a fundamental and from an experimental viewpoint. The activities take placein the framework of a collaboration with industrial partners.

1J Cao et al., Nature Nanotechnology 4, 732, (2009); M Tomczak et al., EuroPhysics Letters, 86, 37004 (2009).2MJ Lee, Advanced Materials, 19, 3919 (2007); BJ Kim et al., IEEE Electron Device Letters 31, 14 (2010).

Prof JW Seo, Prof JP Locquet


Dr Mariela Menghini, Drs Leander Dillemans✔ ✔


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Magneto-electric heterostructures and composites for novel devices

In many applications of magnetic materials – as in hard disk storage – a large magnetic field is needed to reverse themagnetization. However the application of a large magnetic field required the integration of bulky electro-magnets,which is not easy to achieve. A remedy is offered by magneto-electric materials, where there is an intimate couplingbetween the magnetic spins and the electric dipoles. Hence the application of an electric field leads to amagnetization reversal. And vice versa, the application of a magnetic field leads to a ferroelectric dipole moment.

From a fundamental viewpoint, one of the key design challenges is that this magneto-electric coupling is rather weakleading to unpractically small effects. A strong magneto-electric material operating above room temperature does notexist today! Artificial structures with a strong coupling between the magnetic spins and electric must be designed,developed and tested1. This can be done in (0-3) composites (shown here) or in (2-2) heterostructures.

From an experimental point of view, magneto-electric composites and heterostructures will be deposited using sol-geland molecular beam epitaxy methods. The magneto-electric coefficients will be determined as function of appliedmagnetic and electric fields, both as a function of frequency and temperature. Finally they will be integrated intofunctional devices such as tunnel junctions as well as electric field and magnetic field tunable microwave filters2.This project can be performed both from a fundamental or an experimental viewpoint. The activities will take place inthe framework of a collaboration with IBM.

1RJ Zeches et al., Science 326, 5955, 977 (2009); AJ Hatt et al., Physical Review B81, 054109 (2010).2P Maksymovych et al., Science, 324, 5933, 1421 (2009); AS Tatarenko et al., J. Electroceramics 24, 5 (2010).



Dr M Menghini, Dr M. Thakur, Drs. L Dillemans✔ ✔


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Nanoparticles for Electron Emission Cancer Tumor Treatment

Many different chemical and physical routes are currently followed of the treatment of tumor cells. One such methodis based on the natural emission of Auger electrons from radionuclides such as 123I, whereby one decay releasesabout 15 electrons with an average energy of 7.5 keV. This methods has several disadvantages and an alternativemethod is to use photo-excited electrons from K and L shells under moderate x-ray radiation (keV range) asillustrated in the adjacent Figure. These electrons will be emitted from a nanoparticle (NP). This allows for a muchlower energy and targeted approach than the standard MeV radiation therapy.

From a fundamental viewpoint, one of the key challenges is to determine the optimal size, shape and materialcomposition of the NP that will lead to the maximum amount of double DNA strand breaks for the lowest irradiationdose. For this, novel alloy core-shell nanoparticles will be designed1 -- as illustrated in the above Figure -- and theirelectron emission spectrum will be simulated numerically.

From an experimental point of view, alloy NP will be synthesized in a core-shell structure using different methods2. Inthe next step, the NP will be functionalized using antibodies that first bind to cancer cells and then penetrate towardsthe DNA parts. Finally, the functionalized NP will be dispersed in cancer cell cultures, their uptake will be determinedand the therapeutic effect of the x-ray irradiation on the tumour growth rate will be determined.

This project can be performed both from a fundamental as well as from a practical viewpoint. The activities will takeplace in the framework of a strong collaboration with the University Hospital.

1F Van den Heuvel et al., Phys Med Biol, 55, 4509-4520 (2010)2S Pal et al., J. Nanoscience and Nanotechnology 10, 775 (2010).

Prof JP Locquet, Prof F Van den Heuvel, Prof JW Seo


Dr. Amin Wirth-Tijani, Drs Bert De Roo✔ ✔


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Oxide semiconductors with high mobility and low band-gap for photovoltaic applications

Semiconductor technology including solar cells combines two very different and incompatible materials, namelysimple semiconductors and oxides. The former (Si, Ge, InGaAs) are essential for efficient carrier transport while thelatter enable various functionalities (such as dielectric, ferroelectric, piezoelectric, ...). These material incompatibilitiesalways lead to sub-optimal properties and devices. There exists however a large class of oxide semiconductors witha carrier mobility around 100 cm2/Vs much larger than amorphous Si. Some of these are currently used astransparent conducting oxides (TCO).

From a fundamental viewpoint, there are two key challenges, namely to design1 materials and heterostructureswherein first a higher carrier mobility is possible and second whereby the band-gap can be reduced to the range 0.7 -2 eV. Oxide compounds that fulfill these goals currently do not exist! In particular the options related to suboxideshave not been explored much.

From an experimental point of view, oxide semiconductors will be grown using sol-gel and molecular beam epitaxy.After growth they will be annealed at high temperature under different conditions. The electrical properties (resistivity,carrier mobility, band-gap) will be determined as a function of temperature. Finally an n and p-type oxide will becombined with oxide transparent conductors (TCO) into photovoltaic devices and structures2.

This project can be performed both from a fundamental and from an experimental viewpoint. The activities will takeplace in the framework of a collaboration with industrial partners.

1B. Falabretti et al., J Applied Physics 102, 123703 (2007); J Robertson, J Non-Crystalline Solids 354, 2791 (2008).2H. Ohta et al., Advanced Functional Materials, 13, 139 (2003); K. Nomura et al., Science, 300 1269 (2003).

Prof JP Locquet, Prof. JW Seo


Dr Savitha Thayumanasundaram, Drs Vijay Shankar, Drs Chen-Yi Su✔ ✔


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Fabrication of Lithium coin cells using Ionic liquids and Olivine

Lithium-ion batteries are the systems of choice, offering high energy density, flexibility and longer lifespan than mostother types of battery. The life time of a battery depends on the nature of the interfaces between the electrodes andelectrolyte, whereas safety is a function of the stability of the electrode materials. Cathode materials based on lithiummetal phosphates (LiMPO4, M= Co, Ni, Fe, Mn) (operation voltage ≥5 V) can offer safety, power and energy tosatisfy the fast growing large platform applications.

The strongest assets of ionic liquids (ILs) such as stability at high anodic potentials, wide liquid range and highconductivity make them attractive as lithium battery electrolytes.

From a fundamental viewpoint, there are two challenges, i) creating materials (fluorophosphates see adjacent figure)that allow a better strain accommodation upon charging/discharging and low interfacial resistance ii) selection ofsuitable ILs to overcome its electrochemical stability problem at the cathode and to prevent cathodic decompositioninto electrolytes.

From an experimental point of view, Li2MPO4F (M = Co, Ni) will be synthesized either by solid state reaction orsol-gel method and its thermal and structural properties will be investigated. Finally complete Lithium coin cells will befabricated using optimized cathode and ILs.

1S. Nishimura et al., Nature Materials, 7, 707 (2008)2H. Ohno et al., Journal of Power Sources 1174, 342 (2007)



Dr Savitha Tayumanasundaram, Drs Vijay Shankar Rangasamy✔ ✔


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Theoretical study of strongly correlated electron systems

The theoretical description of interacting many-particle systems remains one of the grand challenges incondensed-matter physics. Solving the full many-particle Schrodinger equation is impossible, as the computationaleffort increases exponentially with system size. One solution is to treat the electron-electron interactions at amean-field level, reducing the many-electron problem to a single-electron problem. Models based on thisapproximation, e.g. density functional theory (DFT), are very successful at explaining the properties of weaklycorrelated systems, but generally fail at describing properties due to strongly correlated electrons such asmetal-insulator transitions, magnetoelectricity, high Tc superconductivity, colossal magnetoresistance, …Anotherapproach is to simplify the full Hamiltonian to a model Hamiltonian. This simplified model can’t explain the detailedfeatures of real materials, but still can give a good quantitative description. However, even for the simplest model, inwhich only the on-site Coulomb interaction is considered, the exact solution is only knows for the one dimensionalmodel. Therefore, various approximations were developed to gain insights into the model. The dynamical mean-fieldtheory (DMFT), is such an approximation which maps the lattice onto a quantum impurity model subject to aself-consistent condition.

The real breakthrough in describing strongly correlated electron systems came recently, with the combination of DFTand DMFT (DFT+DMFT). The strategy here is based on the observation that although DFT often leads to qualitativelywrong results for the strongly correlated materials, it can usually provide quite reliable parameters for these systems.These parameters can be in turn used to construct a many-body Hamiltonian which is specific for the particularmaterial under study.

The main goal of this project is to study strongly correlated electron systems like those showing a metal-insulatortransition (V2O3, VO2) or multiferroic behavior (BiFeO3, BiMnO3) in connection with the experimental workperformed in the group. The activities of the student will include the further implementation of the impurity solver aswell as the application to real materials. Extensive programming experience is a plus.

This project is performed in close collaboration with ETH Zurich and the student will be able to exchange results andinteract with them on a regular basis including visits.



Drs Bart Ydens, Drs Petar Bakalov, Drs Peter Staar (ETH Zurich)✔ ✔

theoretical, simulations

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Optical and electrical properties of amorphous and crystalline group IV materials

Silicon, germanium and tin belong to group IV of the periodic table. When these elements are ordered in a crystal,they become semiconducting and exhibit unique optical and electrical properties. The degree of structural orderingdetermines these properties. Silicon is the most widely used semiconductor material, especially in electronics andphoto voltaics (PV). Alloying Si with Ge lowers the band gap and increases the carrier mobility. Even higher carriermobilities and lower band gaps can be obtained by alloying Ge with Sn. Higher carrier mobilities are useful toincrease the switching speed of electronic devices. Low band gap energies are useful to better match the solarspectrum in PV applications or for infrared photodetectors.

In this project SixGeySn1-x-y layers will be characterized. The optical and electrical properties in function ofcomposition will be determined. The influence of order (amorphous, poly crystalline and single crystalline) on theoptical and electrical properties will be investigated. The ordering and crystal quality will be measured by X-raydiffraction (XRD). Atomic force microscopy will be applied to get information on the surface morphology androughness. Absorption spectroscopy will be used to determine the extinction coefficient and deduce the optical bandgap energy. The carrier mobility and concentration will be investigated with Hall effect and capacitance-voltagemeasurements, respectively. SiGeSn layers, deposited by molecular beam epitaxy or plasma enhanced chemicalvapor deposition, will be provided to the student.

The main goal of this thesis is to determine the optical and electrical properties of amorphous and crystallinesemiconducting layers of group IV. Al2O3 substrates will be used as transparent substrate for absorptionspectroscopy measurements. Si and Ge substrates will be used to obtain crystalline layers of high structural quality.

The activities of this master thesis include absorption spectroscopy, X-ray diffraction, atomic force microscopy, Halleffect and capacitance-voltage measurements to investigate the optical band gap, crystal quality, surfacemorphology, carrier mobility and carrier concentration, respectively.

Prof JW Seo, Prof JP Locquet


Dr Ruben Lieten, Drs Tomas Smets✔ ✔

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Probing the magneto-electrical properties of thin-film manganites

For your master thesis you will investigate thin films of a specific type of complex oxides (manganites) that reveal atthe same time ferroelectric and ferromagnetic order. The coupling between both order parameters in these so-calledmagneto-electrical materials results in a multifunctional material, where the ferromagnetism can be affected byapplying an electrical field and the ferroelectricity can be affected by applying a magnetic field.

The samples that you will investigate are thin films of multifunctional metal oxide materials that are obtained bymagnetron sputtering in a reactive oxygen atmosphere from targets prepared by solid-state synthesis. You willdetermine the coupling between ferromagnetism and ferroelectricity using magnetic force microscopy (MFM) andpiezoelectric force microscopy (PFM) that can image with nanometer resolution the ferromagnetic domain structureand the ferroelectric domain structure, respectively. The available MFM and PFM measuring set-ups provide theunique possibility to do measurements down to liquid helium temperature while applying an electric and/or amagnetic field. In contrast to standard measurements on a macroscopic scale, the scanning probe microscopybased measurements you will perform offer the great advantage that they do not suffer from variations of the localelectrical conductivity which often occur in oxide films.



Dr. Alexander Volodin✔ ✔

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Electrical properties of metalized nanotubes of self-assembling peptides

Biological proteins and peptides have the intrinsic ability to self-assemble into elongated solid nanofibrils, which maygive rise to amyloid diseases or inspire applications ranging from tissue engineering to nanoelectronics. Apart fromthe fibrils, which are extensively studied, another intriguing state of self-assembly is that of nanotubes. Thenanotubes are hollow cylinders with a typical outer diameter of 100 nm. The nanotubes are less frequently observedand their self-assembly is not yet that well understood. However, these tubes have attracted a lot of interest aspossible key components for nanotechnology.

The purpose of this thesis work is to control the growth of nanotubes having a length of several micrometer and aninner diameter of a few tens of nanometer. The hollow nanotubes will then be metalized either at the inner wall or atthe outer wall by reduction of metal ions (Ag, Cu, …) and deposited onto a properly functionalized substrate. Afterstructural characterization with nanometer resolution using scanning force microscopy and transmission electronmicroscopy (in collaboration with the University of Antwerp), the electrical uniformity of the metallic nanotubes will beprobed with frequency-dependent measurements of the electrical conductance as well as with electrostatic forcemicroscopy. For these measurements it is necessary to attach metallic gold contacts to the metalized nanotubesusing electron beam lithography.

Prof. Chris Van Haesendonck, Prof. Carmen Bartic, Dr. Johan Snauwaert


Katrien Herdewyn✔ ✔

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Self-Assembled Monolayers as passivation solution for III-V semiconductors

The passivation of III-V semiconductor surfaces and, in particular, GaAs has been the subject of intensive studies inrecent years. The interest in developing durable passivation is mainly derived from the need to remove the highdensity of problematic oxide-related surface states that originate from the tendency of the semiconductors to oxidizein ambient conditions. Since the defect states detrimentally affect the electronic and optical properties of the materialsthe role of efficient passivation is critical in enhancing the performance of III-V based devices. Although numerouspassivation methods have been proposed, ranging from plasma hydrogenation to inorganic sulfidization, using wetand dry chemical treatments, poor reproducibility, contamination, and rapid degradation under atmosphericconditions have limited the widespread use of these techniques in the processing and fabrication of devices. One ofthe more promising approaches to GaAs passivation involves the deposition of organic self-assembled monolayers(SAMs) on the surface of the semiconductor. The inherent ability of absorbed monolayers to modify the physical andchemical properties of solid surfaces makes them attractive for the effective control of II-V semiconductors. Inparticular, SAMs have proven to be successful in passivating the electrical activity of unfavorable GaAs danglingbonds through the formation of a ordered array of molecules chemically bound to the surface. Consequently, thisnovel passivation mechanism has demonstrated its relevance as a prospective means of preventing further chemicalmodification while at the same time maintaining the desired electronic properties of the underlying surface, especiallyin the case of nanoscale device structures for which there is a large surface-to-volume ratio.In this study, different SAMs precursors will be explored with the final goal achieving a reliable III-V semiconductorspassivation scheme. Several thin films and surface characterization techniques, such as X-ray reflectivity (XRR),Ellypsometry (EP), water contact angle (CA), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectronspectroscopy (XPS) will be used to characterize the deposited films.

Annelies Delabie

Chemistry department

Christoph Adelmann/Silvia Armini✔ ✔

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A/D converters for image sensors

CMOS Image sensors have seen a huge demand increase over the past years due mass implementation of camerasin several consumer applications such as mobile phones, mp3 players, tablets, digital still cameras, etc.Analog-to-digital converters (ADC) have a great impact on the performance of the imagers. High frame rate imagesensors, needed in more and more applications, require high speed, low power ADCs. In this thesis work the studentwill initially perform a comparative analysis of existing ADC architectures and then come up with a new architecture tobe designed in a 0.18um technology.

Prof. Georges Gielen

ESAT MICAS

Adi Xhakoni✔

20% literature study, 40% transistor level simulation, 20% layout, 20% thesis writing

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Modeling of tunable band gap bilayer structures and devices

It is possible to tune the band gap in bilayer graphene and transition-metal dichalcogenides by external electric fieldsapplied perpendicular to the layers. The band gap of bilayer graphene increases while the band gap of MoS2,MoSe2, MoTe2, and WS2 bilayer structures continuously decreases with increasing applied electric field. This fieldeffect suggests potential directions for the fabrication of novel electronic and photonic devices.

The focus of this master thesis will be on the modeling of the bilayer graphene tunneling field effect transistor either inthe P-N or P-I-N configuration. The possibility of tuning the band gap (electric field) by sweeping the gate voltageoffers a new path towards switching transistor devices on or off. Preliminary simulations have already shown thatsub-60 subthreshold slope current-voltage characteristics with reasonable Ion/Ioff ratios can be achieved.

The student will make use of an existing simulation program based on the Non-Equilibrium Green’s Function (NEGF)formalism. The purpose is to model, understand and investigate the device characteristics as a function of gatevoltage, insulator thickness and multiple gate configurations.

The candidate should have a strong background/interest in solid-state physics, quantum mechanics andcomputational physics.

Guido Groeseneken

Electrical Engineering

Bart Sorée✔

theoretical / computational

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Topological insulators for spin-torque devices

A topological insulator is a revolutionary material which has a bulk band gap while the edge or surface has a gaplessstate protected by time reversal symmetry. Due to the time reversal symmetry protection, the 1D edge state or 2Dsurface state is expected to be robust against time reversal invariant external perturbations. This research fieldemerged in 2005 with the discovery and theoretical prediction of 2D topological insulators with protected 1D edgestates. Since then, also 3D topological insulators with 2D protected surface states have been theoretically predictedand experimentally observed. At this moment the research field of topological insulators is one of the hottest topicsboth in theoretical and experimental physics as the search for new topological insulator materials, physical propertiesand possible applications is accelerating.

One of the most promising 3D topological insulator material known today is Bi2Se3 which exhibits a single helicalDirac cone as the energy dispersion relation for the 2D surface state while the bulk has a large band gap. The energydispersion relation of the 2D surface state looks very similar to that of graphene with the exception that the chargecarriers exhibit spin-lock, that is spin and momentum are perpendicular to each other and directed in the plane of the2D topological surface state, with the spin being the real intrinsic electron spin. In graphene there is also a fixedhelicity but in this case it is the pseudo spin associated with the A and B sublattice and the momentum that arealigned either parallel or anti-parallel. One of the interesting consequences of the 2D helical state of a 3D topologicalinsulator is that spin polarized currents can be induced by applying a voltage across the surface. Besides Bi2Se3,there are other materials being classified as topological insulators and the quest for new topological insulatormaterials is still ongoing.

The charge carriers on the surface of a topological insulator thus exhibit spin-lock, i.e. spin and momentum areperpendicular to each other, both momentum and spin being parallel to the surface of the topological insulator. As aresult when a net current flows a spin-polarized current will be induced where the spin polarization is perpendicular tothe current direction. This removes the requirement of a hard magnetic ferromagnetic material to spin-polarize theincoming electrons in a standard spin-torque memory device.

The goal of this thesis is to look into the possible applications of topological insulators. In first instance this can bedone by doing a literature study, but the student is expected to gain sufficient insight into the physical properties ofthese materials and make a first analysis of using them for spin-torque memory devices.

Marc Heyns

Electrical Engineering

Bart Sorée✔

theoretical / computational

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Superconductivity in nanostructured tin

α and β tin (Sn) are two stable phases of tin: α-Sn is a semiconductor with quasi zero bandgap, β-Sn is a lowtemperature superconductor with a bulk transition temperature of 3.7K. Several studies have reported that Sndeposited on a Si(111) surface undergoes a phase transition from the α to the β phase for increasing layer thickness.β-Sn belongs to the group of weakly-coupled superconductors. Strong phonon confinement effects are believed to bethe main cause for the increase of the critical transition temperature that is observed in very thin Sn layers and Snnanostructures.In this master-thesis project, you will use cluster deposition and molecular beam deposition in UHV to producenanostructured Sn. You will study the structural properties and possible phase transition by x-ray scattering andscanning probe microscopy. A unique opportunity for this year’s master thesis will be the first use of Mössbauerspectroscopy on the 119Sn isotope as a local nuclear probe for a detailed characterization of the structure andchemical environment. The superconducting properties will be measured by cryogenic electrical transport andSQUID-based magnetization experiments.Depending on beamtime allocation, also synchrotron-based nuclear methods to measure the phonon density ofstates in the nanostructured Sn samples can be part of this master thesis.

Prof. Margriet Van Bael, Prof. André Vantomme, Prof. Kristiaan Temst

Faculty of Science/ Lab. of Solid State Physics and Magnetism and Institute for Nuclear andRadiation Physics (nuclear solid state physics group)Kelly Houben, Dr. Thomas Picot

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Manipulating superconductivity by embedding Fe nanoparticles

Superconductivity and ferromagnetism are well known to be two antagonistic phenomena, meaning that they excludeeach other. When an interface between a superconductor and a ferromagnet is created, a “proximity effect” appearswhich leads to a modification of the superconducting properties. This effect can be used to manipulate thesuperconducting properties by modifying the magnetic state of the ferromagnet. It is expected, however, that theferromagnet is also influenced by the superconductor. So far, very little is known on how the ferromagnet behaveswhen the superconductor becomes superconducting since the strong diamagnetic response of the superconductorprevents the study of the ferromagnet using conventional methods. In this project, isotope selective local-probenuclear methods will be used to gain this unique insight into the ferromagnet. The system to be studied is asuperconductor/ferromagnet hybrid created by ion implantation of 57Fe ions into a Pb thin film, or by codeposition ofFe and Pb clusters to create a cluster-assembled Pb matrix with embedded Fe clusters. This is a new class ofhybrids which offers new possibilities in terms of superconductivity tuning. Your work will include the optimization ofthe preparation parameters to create the hybrid, structural characterization and advanced measurements of themagnetic and superconducting properties using laboratory-based (magnetization and magnetotransport experiments,Mössbauer spectroscopy) and synchrotron based* methods (nuclear resonant scattering).*depending on beam-time allocation

Prof. Margriet Van Bael, Prof. André Vantomme, Prof. Kristiaan Temst

Faculty of Science/ Lab. of Solid State Physics and Magnetism

Kelly Houben, Dr. Lino da Costa Pereira, Dr. Thomas Picot✔

experimental

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Magnetic properties of small atomic clusters

Atomic clusters constituted of a few atoms display uncommon properties very different from single atoms and bulkmaterials resulting from the large fraction of surface atoms and the discrete nature of the energy level spectrum. Inparticular, magnetic properties of small clusters are expected to display strong oscillations of their magnetic momentand magnetic anisotropy as a function of their size, geometry, and composition. Investigation of such small clusters isof high fundamental interest and is moreover very relevant for future applications as it could lead to the ultimatememory bit of information in magnetic storage devices.In this thesis, you will produce small magnetic clusters using a plasma magnetron sputtering cluster source allowingto control their mass to atomic precision using a high resolution RF quadrupole mass filter. Clusters of different sizeswill be deposited on a substrate using different deposition parameters. The resulting cluster shape and sizedistribution will be studied in detail by scanning probe microscopy. The atomic structure of individual clusters will beinvestigated using scanning tunneling microscopy measurements while the magnetic properties of ensembles ofclusters will be characterized using measurements of the magneto-optical Kerr effect (MOKE).

Prof. Ewald Janssens, Prof. Peter Lievens, Prof. Margriet Van Bael

Faculty of Sciences, Lab. of Solid State Physics and Magnetism

Dr. Arnaud Hillion, Dr. Thomas Picot, Dr. Koen Schouteden✔

experimental

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master nanoscience and nanotechnology - ku leuven · 2013. 5. 7. · master nanoscience and...

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