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Projects for Physics Students 2019/20

1. 2D SAM – Saturable Absorber Mirrors based on 2D Nanomaterials

Supervisor: Werner Blau

Location: TCD

Laser sources producing sub-picosecond optical pulses are essential for most photonic

technologies. For many medical, industrial and scientific uses, solid-state lasers

constitute the short-pulse source of choice. The primary advantage is that materials can

be processed with precision down to the nanometre scale without heating or damaging

adjacent material due to the fact that extremely high peak powers are incident on the

sample for only about 100 femtoseconds.

Regardless of wavelength, the majority of ultrashort laser systems employ a mode-

locking technique, whereby a non-linear optical element – called saturable absorber -

turns the laser continuous wave output into a train of ultrashort optical pulses. Some

selected 2D nanomaterials are a novel and promising approach to realize saturable

absorber devices with a performance that the existing semiconductor based devices

cannot provide. The objective of this project is to demonstrate a new saturable absorber

device for ultrafast lasers in the lab, that is easily processed, cheaper, more reliable and

versatile, based on available nanostructures.

2. Green Photonics: Ultrafast and Nonlinear Optical Properties and Photonic

Applications of Microbiologically Synthesised Nanocomposites

Supervisor: Werner Blau

Location: TCD

Photonics technology plays an important part in many areas of our daily life. Most active

photonic devices rely on inorganic semiconductors. In addition to raw material cost and

supply concerns, environmental, toxicity and recycling issues, the increasing use of

nanostructures has created a concomitant increase in complexity and cost of fabrication

equipment. In this project, a novel approach to deal with all the above problems by

microbiological fabrication of photonic nanostructures is taken, with the additional benefit

of addressing lifecycle issues and thus contributing to the preservation of our

environment through reuse of heavy metal waste. Originating from a special respiratory

reduction mechanism in some bacteria, microbiologically synthesised inorganic

nanomaterials present uniquely well-defined physical structures with outstanding optical

properties. As such nanostructures can easily be incorporated into similarly

microbiologically fabricated transparent polymer host matrices, practical engineering

materials can be made relatively simply. Specific project goals are their demonstration

in a selected nonlinear optical device, most likely an optical limiter, based on a

microbiologically synthesised nanomaterial.

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3. Plasmon-enhanced upconverting nanoparticles

Supervisor: Professor Louise Bradley

Location: TCD

Upconverting nanocrystals (UCNPs) can be excited using near-infrared excitation and

emit light at wavelengths ranging from 350 nm to 800 nm depending on the nanocrystal

composition. They have been a topic of considerable interest for optical imaging,

microscopy and sensing of biological samples as they provide approximately a factor of

10 improvement in sensitivity compared with traditional UV pumped fluorescent labels.

They are also a promising means for extending the absorption range of solar cells into

the NIR. However, a significant issue with these materials is their low quantum yield. The

objective of this proposal is to enhance the emission/absorption properties and

conversion efficiency UCNPs through interaction with the increased local

electromagnetic field in the vicinity of multi-resonance plasmonic nanostructures. The

project will involve the synthesis and optical characterization of the plasmon-enhanced

upconverting nanoparticles. It may also involve simulation of the structures using a finite

difference time domain method, to design the optimum structure geometries and to

elucidate on the experimental observations. Based on the interests of the student the

project can be more biased toward experimental or computational research.

4.

Electrically tuned plasmonic metasurfaces

Supervisor: Professor Louise Bradley

Location: TCD

Post-fabrication tuning of plasmonic structures and metamaterials across the visible and

near-infrared spectral ranges continues to pose significant challenges. This project will

explore dynamic tuning based on vanadium dioxide (VO2), a phase change material that

can be switched from an insulating to metallic phase both thermally and electrically. The

project will involve the growth of VO2 by plasma laser deposition, the fabrication of

plasmonic structures by e-beam lithography, and characterisation of the phase change

properties of the VO2 and tuning of the plasmonic metasurface properties via the

electrically actuated phase change of the VO2 material. Complementary simulations to

design structures and interpret experimental observations will be performed using finite

difference time domain software. Based on the interests of the student the project can

be more biased toward experimental or computational research.

5.

Predicting molecular self-assembly in two-dimensions

Supervisor: Dr Nuala Caffrey

Location: TCD

Surface-confined self-assembly of functional molecules is a promising method to

fabricate two-dimensional supramolecular structures with predefined morphologies and

functionalities. The 2D morphology, and hence the surface functionality, depends on the

individual molecular shape, the nature and position of its interacting sites, the molecular

electronic properties and the overall topology of the material. Coarse-grained simulation

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models can determine the factors which determine the surface morphology. Here the

molecule is represented by a model building block with a particular shape and

predefined interaction centers.

This project will use lattice Monte Carlo to mimic the self-organisation of molecules into

naturally emerging 2D patterns. Stable structural phases will be found and the conditions

required to induce particular phases determined. The results of the lattice Monte Carlo

simulations will then be validated using density functional theory calculations and the

electronic properties of the resulting networks ascertained. The student will write their

own canonical ensemble Monte Carlo code to achieve this, as well as learn how to use a

density functional theory code to calculate the electronic structure of the molecular

networks.

The aim will be to reproduce correctly the formation of various adsorbed phases which

have been observed experimentally in ultra-high vacuum or at the liquid/solid interface

including exotic fractal metal–organic aggregates (see Figure from Chem. Commun., 51,

14164 (2015)), and to go beyond this to predict molecules which will produce other novel

surface morphologies and functionalities.

6.

Equilibration and the thermodynamics of non-Markovian Environments

Supervisor: Dr Steve Campbell

Location: TCD

Put a smaller system in contact with a larger environment and, thanks to

thermodynamics, the two will equilibrate. If we introduce a second bath at a different

temperature, we enter the rich world of non-equilibrium systems. When all of the players

in this game are classical systems, the various energy exchanges are fairly well

understood. However, for quantum systems and quantum baths things are trickier. In

this project we will explore how properties of the baths affect the equilibration of a

quantum system to its non-equilibrium steady state. In particular, by exploiting a so

called collision-model framework to model the quantum environments, we will examine

how Markovian (memoryless) vs. non-Markovian baths affect the rate of equilibration

and the ensuing non-equilibrium steady state properties. This is a theoretical project that

will involve both analytical and numerical calculations performed with the aid of

Mathematica.

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7.

Quantum Darwinism

Supervisor: Dr Steve Campbell

Location: TCD

The world around us, to the best of our knowledge, is described by quantum mechanics.

Somewhat perversely the defining features of the theory, quantum superpositions, are

not seen on a macroscopic scale. Therefore a fundamental issue facing physics today is

to understand how the familiar classical world around us emerges despite its underlying

description being quantum mechanical. The theory of decoherence goes someway to

elucidating this dichotomy, however it only partially addresses the issue. Quantum

Darwinism has been proposed as a means to explain how, using only the basic tenants

of quantum mechanics, a "classically objective" state can emerge from a fully quantum

description. This is achieved by invoking the notion of "only the fittest information will

survive". In this project we will test the validity of this description starting from a simple

spin-star model that readily exhibits quantum Darwinism and examine under what

conditions classical objectivity is lost. This is a theoretical project that will involve both

analytical and numerical calculations performed with the aid of Mathematica.

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Onsager Entanglement for High Efficiency Mobile Power

Supervisor Dave Carroll

Location: Wake Forest University

This project seeks to further develop power scavenging technologies for ambient sources. Power scavenging at relatively low temperatures is inefficient according to Carnot. However, by coupling multiple scavenging modalities together, these inefficiencies can be circumvented, at least in part. Recent work by our group has shown that by coupling piezo-electric materials and thermoelectric materials into a meta-structure (with specific symmetries), the combined

power scavenging can exceed the expected linear combination of the modalities individuality. The phenomena is well described by Onsager’s nonequilibrium approaches and has led to the development of wearable power sources capable of charging phones, ipads, sensors and more. The team is now trying to apply these materials in larger arrays for space suites in a project sponsored by NASA and aimed at Mars exploration

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9.

AC driven Per-LED

Supervisor Dave Carroll

Location: Wake Forest University

The WFU group has pioneered the use

of AC-drive for the creation of high

brightness, very high efficiency lighting

systems. Such systems, from home

interior illumination to laptop displays,

represent more than 25% of all the

electricity generated in the U.S. and

very nearly this amount in Europe.

Unfortunately, lighting developed so far,

while bright and efficient (exceeding 300 LPW at 30,000 Cd/m2) has had a single

important drawback, and that is lifetime. A modern commercial LED can last 100,000

hours without failure, and so any replacement technology must do the same. At the

moment, no other lighting system has come close. That is all about to change. We have

recently developed a new inorganic perovskite material that has shown high brightness

and efficiency, but also tremendous robustness. Indeed, we have shown that devices

made from it can even function under water for thousands of hours! These amazing

devices, can be made in any color, and are completely flexible. Moreover, they are quite

simple to process. The next steps in this remarkable development is to increase its

overall efficiency, pushing the boundaries of light generation through the control of spin

statistics in the structure using nano-scale antennae imbedded in the emitter

10.

Topological Quantum Memory Elements

Supervisor Dave Carroll

Location: Wake Forest University

The development of universal quantum computing systems requires the development of stable quantum memory elements. Over the past few years this has taken a number of divergent pathways, most involving cryogenic arrays of spin systems. In this program we are examining an orthogonal approach through the use of topologically complex, symmetry protect states associated with 2D dichalcogenide systems. Such systems are known for their CP – protected edge states,

and modification of these edge states so that the accumulation of geometric Berry’s phases can be constructed may provide a unique mechanism for the fabrication of quantum memory. We have already developed the curious topological systems (as shown) and are now beginning detailed investigation into electronic properties

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11.

Spin optoelectronics in magnetic materials

Supervisor: Jean Besbas, K. Rode, J. M. D. Coey

Location: TCD

The Spin Hall Effect (SHE) is the spin-dependent deflection of a current in conductive materials with high spin-orbit coupling. This effect, which allows generating a spin current, i.e. a flow of angular momentum in a thin film, is currently under scrutiny for its potential applications in magnetic recording. Recent developments have shown that the photon spin, or helicity, of an externally applied laser light can sometimes be a source of SHE.1 More recently the change of conductance induced by light helicity has been proved sensitive to the SHE in low band gap semiconductor BiSbTeSe and unexpectedly in metallic platinum (Fig. 1).2 The interest of these discoveries is twofold. First, they establish a new way to universally measure and characterize the SHE with optical excitation and an electrical detection. Second, it could possibly lead to optoelectronic devices making use of the spin of the electron. For long, it was believed that metals could not be affected by the helicity of the light in the way that semiconductors are.3 However, this paradigm has been revisited with the discovery of helicity-dependent magnetic switching in ferrimagnets.4,5 Therefore, we plan to take a new step ahead and characterize the interplay between SHE and the helicity-dependent photoconductance of ferrimagnetic metals. In this project, the student will be involved in the development of an experiment allowing the measurement of the SHE by using the dependence of the conductivity on the helicity of a laser beam. The work will be centered in the state-of-the-art CRANN photonics laboratory. The setup will consist of a far-field microscope and will utilize continuous and femtosecond pulse of laser light to affect the photoconductance. The student will take an important part in mounting and aligning the microscope, electrically interfacing and measuring the samples. We are planning to investigate various thin film magnetic materials such as SrRuO3, LaMnO3 and the newly developed Mn2RuxGa (MRG) from the Magnetism and Spin Electronics Group. Further experiments could be performed on heavy metals with a high SHE such as Pt and Ta.

Figure 1: Helicity dependent photovoltage as a function of position on a Pt stripe for I= 6 mA. The SHE yields a signal at the edges of the Pt microstructure.2 1 K. F. Mak, K. L. McGill, J. Park, and P. L. McEuen, Science 344, 1489 (2014). 2 Y. Liu, J. Besbas, Y. Wang, P. He, M. Chen, D. Zhu, Y. Wu, J. M. Lee, L. Wang, J. Moon, N.

Koirala, S. Oh and H. Yang, Nat. Commun. 9, 2492 (2018). 3 F. Dalla Longa, J. T. Kohlhepp, W. J. M. De Jonge, and B. Koopmans, Phys. Rev. B 75,

224431 (2007). 4 C. D. Stanciu, F. Hansteen, A. V. Kimel, A. Kirilyuk, A. Tsukamoto, A. Itoh, and Th. Rasing,

Phys. Rev. Lett. 99, 047601 (2007). 5 S Mangin, M. Gottwald, C-H. Lambert, D. Steil, V. Uhlíř, L. Pang, M. Hehn, S.

Alebrand, M. Cinchetti, G. Malinowski, Y. Fainman, M. Aeschlimann, and E. E.

Fullerton, Nat. Mater. 13, 286 (2014).

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Spin Liquids Supervisor: M. Venkatesan Z. Gercsi, and J. M. D. Coey

Location: TCD

The spin liquid is an unusual quantum state of matter which is thought to exhibit a quantum phase transition at T = 0 to an unusual disordered collective magnetic state. By

far the simplest example from a chemical point of view is Mn [1,2]. This is the stable phase above 725 C, but it can be stabilized by arc melting. The structure is cubic, with two different sites 8c and 12d as illustrated in the figure below. It is believed that the Mn on 8c sites in nonmagnetic, whereas that on 12d sites carries a moment but the topology of these sites, which form linked triangles, is such that the antiferromagnetic nearest-neighbour interactions are completely frustrated. Recently, we made a surprising discovery; When we prepared a Mn3Al2 alloy, expecting the Al to occupy 8c positions, we found that the alloy was strongly ferromagnetic, with a moment of 1.3 µB per formula, and a Curie temperature of about 600 K. We want to understand how adding Al, which is nonmagnetic, can have such a big effect on the Mn spin liquid. Also, we need to know if the Mn3Al2 alloy is really ferromagnetic, or ferrimagnetic. In this project, the student will prepare a series of Mn5-xAlx alloys, and trace out the magnetic phase diagram as a function of x. In this way be can begin to understand how breaking the frustration breaks up the spin liquid. The work will involve preparing the alloys by are melting, and characterizing them by X-ray diffraction and magnetometry. A neutron diffraction experiment in the Netherlands to determine the magnetic order is possible.

The cubic crystal structure of Mn. A triangle of 12d Mn atoms is highlighted.

References: [1] J. A. M. Paddison et al Phys. Rev. Letters 110 267207 (2013) [2] H. Nakamura et al, J Phys. Cond. Mat., 9 4601 (1997)

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3D printing of permanent magnets Supervisor: Z. Gercsi, M. Venkatesan and J. M. D. Coey

Location: TCD

3D printing of magnetic materials offers novel and creative ways to design magnets with new shapes and functionalities that are not possible with current manufacturing technologies. In this project, we explore the properties of 3D-printed magnetic circuits based on high performance Sm-Fe-N permanent magnets, which were discovered in TCD [1], and are now produced commercially in Japan [2]. The Sm2Fe17N3 powder, prepared by a low-temperature gas-phase interstitial modification [3], will be used for the printing. The powder has superior corrosion resistance and thermal stability compared to Nd2Fe14B powder. It exhibits a room-temperature coercivity of 690 kAm-1, with an isotropic remanence of 700 kAm-1. The maximum energy product for the powder, assuming full density, is 162 kJm-3. A magnetic circuit comprises a magnet and an airgap, and optionally soft iron to guide

the flux. The design of magnetic circuits is an art, facilitated by computer simulation. The

permanent magnet behaves like a battery that is the source of the magnetomotive force

(mmf) (the magnetic analogue of emf), as it is the segment of the circuit where the

magnetic potential rises. Rare earth permanent magnets are particularly suited for use in

ironless circuits, where flux is confined to the magnets themselves and to the airgap.

Flux concentration is achievable in special designs where the flux density in the airgap

exceeds the remanent induction of the magnet, Bg/Br > 1.

The project involves designing and printing magnets of different shapes from using melt-

spun Sm-Fe-N powders, manufactured in Japan. The 3D printer is based in the new

Additive Manufacturing Laboratory in CRANN/AMBER. They will be characterized in

detail by high resolution microscopy and SQUID magnetometry. We are particularly

interested in printing magnet shapes that cannot be manufactured by traditional methods

of injection moulding, and an initial goal after measuring the density and magnetization

achievable with simple shapes and Fe/Sm-Fe-N composites, will be to realize a design

that cannot be produced in any other way together with a magnetizing method. The

developed magnets circuits may then be used for various experiments in our magnetism

research group, such as the new Kerr microscope.

References: [1] J. M. D. Coey and Sun Hong, J Magn Magn Mater 87 L251-254 (1990) [2] T. Iriyama et al, IEEE Trans. Magn., 28 2326 (1992) [3] R. Skomski, Ch 4 in Rare-Earth Iron Permanent Magnets (J. M. D. Coey, editor) Clarendon

Press, Oxford 1996, p178

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14.

Understanding the factors limiting charging time and power delivery in

supercapacitors.

Supervisor: Professor Jonathan Coleman

Location: TCD

Note: This is not a lab-based project but involves finding, extracting and analysing

published data.

Supercapacitors are energy storage devices midway between capacitors and batteries

which store energy via the storage of electrons and ions at a conductor/electrolyte

interface. Supercapacitors don’t store huge amounts of energy, however, they can be

charged very quickly and deliver their energy rapidly which makes them suitable for high

power applications. However, there is currently no quantitative understanding of the

factors limiting their power delivery/charging time. Recently Prof Coleman’s group have

developed a simple model for understanding the equivalent problem in batteries. It is

straightforward to convert this model to represent supercapacitors. This project will

involve searching the literature for supercapacitor capacity versus charging rate data

(thousands of papers are available). The data will then be fit to the model to output the

charging time constant. Another equation will be used to fit the time constant data to

various physical parameters such as electrode thickness, conductivity, porosity etc. This

will allow us to understand the relationship between charging time (and hence power)

limitations and physical materials properties.

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Do lithium ion batteries based on 2D materials have overly-long charging times?

Supervisor: Professor Jonathan Coleman

Location: TCD

With the growing popularity of mobile electronics, bigger, better batteries are urgently

required. One approach is to identify new electrode materials which can store more

lithium than is currently possible. Recently, 2-dimensional materials such as graphene,

MoS2 and phosphorene have been shown to store large quantities of lithium. However,

there are indications that such electrodes are very slow to charge. This may be a

consequence of the fact that the nanosheets making up the electrode tend to lie parallel

to the electrode surface, forcing ions to travel round them and so increasing the length of

the path ions need to take during charging (or discharging). This project will perform

careful measurements of the charging time of electrodes made from various 2D

materials of various sizes. The aim is to determine if charging times are slower than

other materials and investigate the causes

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Reinforcing nanosheet networks with insulating nanotubes

Supervisor: Jonathan Coleman

Location: TCD

Networks of 2D materials such as graphene can be easily formed into networks which

are useful in a range of applications such as printed electronic devices and battery

electrodes. However, such networks are very brittle. This has been resolved for battery

electrodes by adding carbon nanotubes. The nanotubes reinforce the networks and

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have the added advantage of increasing the conductivity. However, if the network is to

be used in an electronic device (such as channel material in a transistor), conductivity

enhancements must be avoided. One solution would be to use Boron Nitride nanotubes

(BNNTs) which are strong yet insulating. This project will fabricate networks of 2D

nanosheets such as MoS2 reinforced with BNNTs. It will involve measuring both

mechanical properties and conductivity as a function of BNNT content to ascertain the

level of reinforcement and ensure the conductivity is unaffected.

17.

Adhesion thermomechanics of roll-to-roll nanoimprint lamination for tissue

scaffolds

Supervisor: Professor Graham Cross

Location: TCD

While nano/microfabrication is the cornerstone of advances in information and

communications technology, other industries that could greatly benefit from

miniaturization cannot easily incorporate the highly specialized methods and materials of

semiconductor manufacturing. Roll-to-roll nanoimprint lamination (R2RNIL) allows

efficient, deterministic nanostructuring throughout a 3D volume, a problem remaining

largely unsolved to date. A prime motivation is realizing scaffolds suitable for use as

internal bandages in regenerative medicine: These require multiscale structuring that

goes beyond existing additive manufacturing capabilities like 3D-printing which is limited

to micrometre resolution, or stochastic techniques like electrospinning which produce

large volumes of nanoporous materials but generally at one length scale. With R2RNIL,

in-plane (xy) control of all micrometre to nanometre dimensioning is realized, while more

limited z direction modulation is possible by evolving lamination period. In this project the

role of temperature and speed will be studied for successful lamination of

nanostructured surfaces with dimensions critical to controlling stem cell replication and

devolution into specific phenotypes (muscle, bone, tendon, etc.)

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18.

Optimized heat conduction by channelling in a microscopic inelastic contact

Supervisor: Professor Graham Cross

Location: TCD

The problem of heat conduction across contacting solids is important in both

fundamental statistical mechanics and applied physics. It has also become a obstacle to

progress in the performance of solid-state electronics, and is a major factor contributing

to the breakdown of Moore’s Law we are now experiencing. The Solid State Thermal

Interface Materials (SSTIM) is a novel solution to the solid-solid interface thermal

bottleneck. It consists of a compliant array of rigid, high thermal conductivity micro-

bridges that use local plasticity to overcome contact resistance. The SSTIM concept

attempts to address the 5 order-of-magnitude gap between ideal thermal contact

resistances achieved in highly specialized laboratory experiments and what is realized in

practice for the consumer electronic devices we use every day. In this applied physics

computer simulation project, we will model the thermal transport at a microscopic solid

state contact under the conditions of plastic deformation. Using multi-physics finite

element simulation techniques, we will investigate the role of diamond indenter shape

and low thermal conductivity surface layers on SSTIM heat bridge performance, and

attempt to find ideal geometries that maximize heat conduction for minimum mechanical

force.

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Atomic force microscopy studies of graphene self-assembly

Supervisor: Professor Graham Cross

Location: TCD

The Cross Group recently discovered1 that 2D materials like graphene can

spontaneously slide, peel and tear via intrinsic thermodynamic forces. This self-

assembly behaviour is reminiscent of capillary dewetting of a liquid droplet from a

hydrophobic surface, and operates in air at scales ranging from nanometres to the

nearly visible. Pleat structures formed by the process consist of a folded-back ribbon

adhered by van der Waals forces to its host sheet below. Nucleation of an embryonic

pleat spontaneously sets in motion growth (moving to the lower right in the figure) by

peeling from the substrate and tearing the sheet. Two conditions enable this self-

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assembly: First is large area superlubricious incommensurate contact of the ribbon

crystal lattice to its host sheet that allows it to slide almost free of friction over long

distance, and second is the presence of an interfacial force arising from interface

thermodynamics that spontaneously propels the ribbon forward. These structures may

eventually form the basis for THz scale nanoelectromechanical systems. In this project,

we will employ atomic force microscopy (AFM) with diamond probes to characterize

pleat nucleation and growth.

Graphene self-assembly imaged by atomic force microscopy.

[1] Annett J., Cross, G. L. W., Self-assembly of graphene ribbons by spontaneous self-tearing

and peeling from a substrate, Nature 535, 271-275, (2016).

20.

Au films for applications in plasmonic applications

Supervisor: Prof. John Donegan

Location: TCD

Gold (Au) is the key material for plasmonic applications owning to its strong optical

response and its resistance to chemical processes. Studies have shown that Au think

films. Our studies have shown that monolayer adhesion of metals such as Ti, Ta and W

are all very effective at reducing the tendency for de-wetting of the films.

In this project, we will look at a set of samples with large Au grains, and compare with

normal films having small grains, to determine how movement of the adhesion metals

along the grain boundaries affects the de-wetting behavior. We will determine the

activation energy for the de-wetting behavior and using TEM and other surface analysis

techniques, we will look for methods that further enhance the long-term stability of Au-

films in high-power plasmonic applications.

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21.

Printing and characterization of Fresnel Zone Plate lenses in optical waveguides

Supervisor: Prof. John Donegan

Location: TCD

The Nanoscribe 3D printing tool can produce optical waveguides with thickness less than

1 micron. This allows for a very fast fabrication of waveguide devices. The Fresnel zone

plate is a structure that focusses light within a waveguide, increasing the optical intensity

by upto a factor of 20. This in turn allows us to observe strong nonlinear optical effects.

In this project, the student will become familiar with making waveguide structures and then

fabricating the zone plate structures. This will be followed by optical and structural

characterization of the waveguide structures including the generation of nonlinear effects.

The project is mostly experimental but will deal with aspects of modelling optical

waveguides.

22.

Athermal operation of semiconductor lasers at 1.3 m with high order gratings

Supervisor: Prof. John Donegan

Location: TCD

The Photonics group in TCD has developed a new method to develop single mode lasers.

This involves using a grating with high order which then allows for a simple fabrication

process. To date, these lasers have been demonstrated at 1.5 m but recently the group

has now developed lasers which will operate at 1.3 m.

In this project, we will study the performance of these lasers and how they vary with the

parameters of the high order grating, including depth and width of the slots that form the

grating. Studies will be carried out of both single mode lasers and laser arrays to see how

their performance changes will the design of the grating and the slots that form the laser

device. The work is mostly experimental but will also involve modelling of semiconductor

laser devices.

23.

Understanding the Production of Biofuel by Thermal Degradation of Biomass

using TGA-MS

Prof. Stephen Dooley

Location: TCD

Biofuel produced from biomass is a promising and sustainable solution to the multiple

energetic challenges the planet is facing such as; global warming, fossil fuel depletion and

increase in energy consumption per capita. [1] Thermal decomposition or pyrolysis of

biomass to produce liquid fuel has attracted a lot of interest due to the potential to use

existing infrastructure.[2] Even though the technology is well established, the scientific

understanding of the physical phenomena is lacking.

This project aims to improve our understanding of the physical-chemistry phenomena

behind biofuel formation during the thermal decomposition of biomass in order to predict

and tailor their properties. The idea behind this project is to determine the role of the

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polymerisation of the various constituents of the biomass typically, cellulose,

hemicellulose and lignin.

This project is experimentally based and will involve TGA-MS measurements, detailed

kinetic modelling and various characterization techniques (TEM and SEM) can be

included.

[1] M.I. Jahirul, M.G. Rasul, A.A. Chowdhury and Nanjappa Ashwath, Energies, 2012, 5.

[2] S. Chakraborty, V. Aggarwal, D. Mukherjee and K. Andras, Asia-Pac. J. Chem. Eng. 2012, 7.

24.

Moleular Physics and Machine Learning Modelling of Isomer Populations of

Lignocellulosic Derived Carbohydrates in Alcohol Solutions

Prof. Stephen Dooley

Location: TCD

The depletion of oil reserves and global environmental concerns necessitates the

development of alternative processes for producing fuels from renewable sources. Of key

interest is the production of ‘green’ biofuels components from the reaction of

lignocellulosic biomass in alcohols. For example, potential biofuel components 5-

ethoxymethylfurfural and ethyl levulinate can be readily produced through the reaction of

biomass derived carbohydrates, D-glucose and D-fructose, with ethanol and a Brønsted

acid. However, comprehension of even basic reaction kinetic and mechanistic details of

such systems is currently lacking, and thus represents one of the barriers to designing a

viable process for fuel synthesis. It is well known in aqueous solutions that carbohydrates

such as D-glucose and D-fructose can exist as 5 different isomers. The distribution of

these isomers can have a significant effect on the reaction mechanism and kinetics for

form biofuel components. Such key information has yet to be determined for D-fructose or

D-glucose in alcohol solutions.

During this project, the student will further advance molecular thermodynamic, machine

learning and data science techniques to model the molecular physics details of how these

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carbohydrates dynamically reaction alcohol solutions. The student will work with a team

of three post doctors and two graduate students in the Sustainable Energy Laboratory of

Prof Stephen Dooley at Trinity College Dublin. The key aim of this project will be to

determine the effect of temperature and hydrogen cation concentration on the isomeric

distribution of lignocellulosic derived D-fructose and D-glucose in alcohol solutions.

Experience with sophisticated spectroscopic techniques such as liquid phase 1H and

13C Nuclear Magnetic Resonance (NMR) spectroscopy and/or mass spectrometry will

also be gained. Interest in the numerical modelling of basic molecular physics processes

will be needed.

25.

Raman characterisation of group-10 transition metal dichalcogenides

Supervisor: Professor Georg Düsberg

Location: Universität der Bundeswehr, München, Germany

Recent research in two-dimensional (2D) atomically thin materials focusses on suitable

materials for application in FETs and sensor devices. Next to the first produced 2D-

Material Graphene, the semiconductors of the Group-6 transition metal dichalcogenides

(TMDs) such as MoS2 and WSe2 were intensely studied. These materials have direct

bandgaps in the visible light regime (1 eV)1 when present as monolayers.

However, these TMDs have shown to be prone to degrade at environmental conditions.

Recent research puts emphasis also on group-10 TMDs such as PtSe2 which have

proven to be stable in air for over a year2. These group-10 TMDs provide strong

tunability of the electrical and optical properties2 making them suitable for FETs and

sensor devices3.

The incorporation of PtSe2 based FETs in state of the art device fabrication present in

the semiconductor industry required scalable processes with reliable reproducibility. This

can only be achieved by controlling a well understood wafer-scale growth process of

these materials. Getting insight in the critical fabrication parameters and analysing the

resulting material characteristics is thereby the main task.

This project covers the task of performing Raman measurements providing a fast and

nondestructive method suitable to gain knowledge about material distribution, quality

and film thickness. Reliable thickness data will be obtained by AFM measurements to

characterize a layer number depended behaviour of the specific Raman modes.

REFERENCES

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1. Yim, Chanyoung; Lee, Kangho; McEvoy, Niall; O’Brien, Maria; Riazimehr, Sarah; Berner,

Nina C. et al. (2016): High-Performance Hybrid Electronic Devices from Layered PtSe 2 Films

Grown at Low Temperature. In ACS Nano 10 (10), pp. 9550–9558. DOI:

10.1021/acsnano.6b04898.

2. Yu, Zhihao; Pan, Yiming; Shen, Yuting; Wang, Zilu; Ong, Zhun-Yong; Xu, Tao et al. (2014):

Towards Intrinsic Charge Transport in Monolayer Molybdenum Disulfide by Defect and

Interface Engineering. In Nat Commun 5 (1), p. 3042. DOI: 10.1038/ncomms6290.

3. Zhao, Yuda; Qiao, Jingsi; Yu, Zhihao; Yu, Peng; Xu, Kang; Lau, Shu Ping et al. (2017): High-Electron-Mobility and Air-Stable 2D Layered PtSe2 FETs. In Advanced materials (Deerfield Beach, Fla.) 29 (5). DOI: 10.1002/adma.201604230.

26.

Transition Metal Dichalcogenide Doping

Supervisor: Professor Georg Düsberg

Location: Universität der Bundeswehr, München, Germany

Transition metal dichalcogenides (TMDs), such as e.g. MoS2, WSe2 represent a large

family of layered 2D materials, which cover a broad variety of electronic, optical and

mechanical properties and therefore can serve as the functional part in various

microelectronic devices. Due to the materials monolayer nature the properties of 2D

materials strongly depend on the environment, which makes control and modification of

the surface chemistry a powerful tool to obtain changes in the materials behaviour.

Functionalization of the monolayer surface can lead to doping via charge transfer,

resulting in improved electrical properties, which is then exploited in chemiresistor or

ChemFETs for chemical sensing. The suggested project focuses on the diverse

possibilities of doping TMDs by decorating the surface with organic molecules or

inorganic nanoparticles. Results on the hybrid inorganic-organic structures will be

monitored by techniques, like Raman spectroscopy, XPS, and scanning probe

techniques.

REFERENCES

Berner, N. C. et al. Understanding and optimising the packing density of perylene bisimide layers

on CVD-grown graphene. Nanoscale 7, 16337–42 (2015).

Kim, H. et al. Optimized single-layer MoS2 field-effect transistors by non-covalent

functionalisation. Nanoscale 10, 17557–17566 (2018).

27.

Modelling polaritons in dielectric nanostructures (theoretical/computational)

Supervisor: Professor Paul Eastham

Location: TCD

Polaritons are quasiparticles that occur in semiconductors, and are part photon and part

exciton. Because of this they may be useful as part of the energy conversion process

between light and electricity in photovoltaics. However, this requires trapping of the

polariton in a region of space, an effect usually achieved using an optical cavity. In this

project you will explore whether polaritons can, in fact, be trapped without the use of

optical cavities, in structures such as two-dimensional semiconductor sheets or

nanoscale crystallites. This project is theoretical and computational, and will involve

using existing computational packages to develop and analyse simulations of light

propagation in nanostructured dielectrics.

17

28.

Optimal networks for robust synchronization (theoretical/computational)

Supervisor: Professor Paul Eastham

Location: TCD

It was noted by Huygens that two clocks, placed on opposite sides of a wall, begin to tick

together. This phenomenon of synchronization is a general one, which occurs for many

other oscillating systems, and as such it plays an important role in physics, engineering,

and biosciences. An important example is the synchronization required for electrical

power grids to operate. In this project you will explore a simplified model of a system of

many oscillators connected together (the Kuramoto model). You will develop a

computational method that can determine how these oscillators can be connected up in

such a way that they will all synchronize.

29.

Geometry of disordered networks: from 2D to 3D

Supervisor: Mauro Ferreira

Location: TCD

This project attempts to study the geometry of networks created by 2D sheets randomly

deposited on an insulating substrate forming a 3D pile. If the sheets are conducting and

the network is sufficiently dense, we may transform an otherwise insulating material into

a conducting one. The conductivity of such a material is crucially dependent on the type

of contacts that exists between neighbouring sheets and the statistics of such contacts is

essential to understand the physical properties of these materials. The project consists

of carrying out a thorough study of the statistics and the geometry of such networks. The

project involves a good balance of analytical and numerical work and is a good

opportunity to put in practice a number of concepts learned throughout your degree.

30.

Physical properties of nanowire networks

Supervisor: Mauro Ferreira

Location: TCD

Abstract: Thin films composed of networks made of an array of nanowires have been

attracting a lot of attention due to their promising physical properties. The goal of the

present project is to develop simple theoretical models capable of describing the

physical properties of such networks. Transport, optical, thermal and magnetic are some

of the possible physical properties to be investigated. In order to achieve this, we must

separate the project in two complementary parts: one involving the development of a

macroscopic model and another which consists of the microscopic details of the

network. The student will be in charge of developing such models and will involve good

analytical and numerical skills.

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31.

Stretching/compressing 2D materials to mimic human eye adaptation:

Supervisor: Prof Andres Castellanos-Gomez

Location: Consejo Superior de Investigaciones Científicas (CSIC), Instituto de

Ciencia de Materiales de Madrid (ICMM)

Two-dimensional (2D) materials have triggered the interest of the scientific community

focusing on optoelectronics because of their very high performance in photodetection

applications. Apart from the high performance in photodetectors, 2D materials present a

special feature that distinguishes them from 3D semiconducting materials: mechanical

deformations have a strong impact on their optical properties. This feature can be

exploited to mimic the remarkable adaptation ability of the human eye to very different

illumination conditions. In this project we will fabricate optical modulators and

photodetectors whose spectral response could be adjusted by means of an external

deformation to achieve devices that can effectively operate under high illumination as

well as under dark conditions.

32.

Testing Information scrambling on a quantum computer Supervisor: John Goold

Location: TCD

Eggs do not unscramble. Local information gets spread over global degrees of freedom

and complexity emerges which renders recovery of local information from local

operations on your physical system impossible. The same is true in quantum mechanics.

Information scrambling is now currently a hot topic in quantum systems and basic ideas

can be studied in what is known as random unitary circuits. The task of this project is to

first write code to generate dynamics on a random unitary circuit where 2-qubit gates are

sampled from the Clifford group. The behaviour of the total correlations of the quantum

state as a function of time and to try to measure it on a simulated version of the IBM

quantum computer. To undertake the project the student should be good at

programming and have excellent mathematical skills and a good understanding of

quantum mechanics.

33.

Energy fluctuations in quantum refrigerators Supervisor: John Goold Location: TCD

Quantum thermal machines are quantum dynamical systems that convert random heat

into a useful output. Refrigerators are a very important class of such machines, since

cooling is an essential prerequisite for many nascent quantum technologies such as

quantum computation. In this theoretical project we will investigate a simple model of a

quantum refrigerator, in order to understand how different kinds of energy resources

affect cooling performance. In particular, we will explore how driving the refrigerator with

a coherent field (e.g. laser light) differs from thermal driving (e.g. light from an

incandescent bulb), specifically in regard to fluctuations of energy. The student will have

the opportunity to learn about open quantum systems and how to predict their dynamics.

Since this is a project in theoretical physics. The student should have excellent

mathematical skills.

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34.

Steady state heat transport in Fibonacci quasi crystals. Supervisor: John Goold Location: TCD The aim of this project is to study the heat transport in the simplest realisation of a quasi-

crystal which is the Fibonacci chain where the diagonal energies are modulated

according to the Fibonacci series. The set up will employ tools from scattering theory

and open systems in order to evaluate the current as a function of both the strength of

the potential energy and system size. This will enable us to extract current scaling from

finite size scaling and explore the conjecture of the existence anomalous diffusion with a

continuously varying exponent. Potential applications are in the direction of heat current

engineering in nanostructure which do not have Bloch theorem. This is a project in

theoretical physics. The student is required to have excellent mathematical and

numerical skills.

35.

Nanomechanics of click-chemistry anchored single dsDNA molecules interacting with small organic molecules Supervisor: Professor Martin Hegner Location: TCD

The nanomechanics of individual natural polymers such as the dsDNA can be

investigated by scanning probe microscopy and optical tweezers force spectroscopy.

Normally the individual nucleic-acid based molecules are anchored to micron scaled

spheres that are acting as molecular handles to be trapped in highly focused laser

beams. The anchoring to the interface is usually provided using biomolecular

recognition, we will explore the possibility to enhance the binding using click chemistry

modified tailor made ends and compare to existing protocols. The molecules will be

visualised using scanning probe microscopy and the mechanics investigated by pulling

the individual molecules with optical tweezers. The individual dsDNA mechanics shows

a characteristic signature in its natural environment. While interacting with biological

molecules or small organic molecules the mechanics can be significantly altered and

indicate adverse or biological relevant effects. In particular the students will:

1. Learn how to prepare and purify tailor made dsDNA molecules that enable click

chemistry anchoring to modified polystyrene microspheres.

2. Design a coupling protocol for click chemistry modified molecules and compare to

3. current protocols applying biomolecular recognition

4. Operate a scanning force microscope to visualise the generated molecules

5. Measure nanomechanics of the generated dsDNA while they interact with buffers

6. and small organic molecules using optical tweezers technology

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36.

Experimental studies of foam-fibre interactions

Supervisor: Professor Stefan Hutzler

Location: TCD

This experimental project concerns structure and properties of foam-fibre dispersions

and the resulting solidified samples. The so-called foam forming process can be used for

paper making but also for the production of novel fibrous materials made from natural

fibres, such as found in peat.

The work will be carried out in close collaboration with a PhD student.

References:

Haffner B, Dunne FF, Burke SR, Hutzler S (2017), Ageing of fibre-laden aqueous foams,

Cellulose 24 231-239.

Burke SR, Möbius ME, Hjelt T, Hutzler S (2019), Properties of lightweight fibrous structures

made by a novel foam forming technique, Cellulose 26, 2529-2539.

37.

Experimental studies of foam-film interactions

Supervisor: Professor Stefan Hutzler

Location: TCD

Soap films can be used as model systems for the study of failure statistics. The project

will involve data gathering and analysis for a range of different experimental set-ups,

such as films formed in rings or bubble arrays in cylinders.

The work will be carried out in close collaboration with a PhD student.

38.

Development of an Electron Counting Circuit with Nanosecond-scale Sensitivity

Supervisor: Professor Lewys Jones

Location: TCD

The internship will be based in the Advanced Microscopy Laboratory

(www.tcd.ie/crann/aml).

A sole-use desk and PC will be provided to the student. Lab-bench space will be

provided in TTEC Unit 7.

In many fields of imaging and microscopy analogue sensors and detection are being

replaced with all digital approaches. Electron microscopy is now beginning this exciting

modernisation, bringing all digital imaging to atomic-resolution microscopy.

In 2018, a previous student working in the group achieved the first successful hardware

implementation of a new digital pulse read-out system. Live waveforms were captured

using a PC streaming oscilloscope, and the signal gradient was subsequently used to

identify individual electron impact events (see figure). This impressive achievement lead

21

to a UK&IRL patent filing, three international conference

presentations, and a research paper being written.

The current implementation is still limited though;

because of the limited clockspeed of the streaming

oscilloscope (32MHz) electron impacts are recorded with

a relatively poor timing precision which can lead to event

pile-up. Further, the PC-streaming data handling

approach is bandwidth limited by the USB connection,

and buffering limited by the available RAM (16Gb).

Instead a new alternative strategy is proposed, to take

advantage of flexible logic design to perform genuine

edge detection pulse counting in hardware. New

education focussed development boards (see figure) now

allow students

to access the capabilities of field programmable gate

arrays (FPGAs) at a sub €400 price point. Such hardware

should allow counting speed to be increased by ~15x (to

450MHz), while also reducing the subsequent data

transmission bandwidth needed by ~2,000x. This would

enable higher signal-noise images to be recorded as well

as enabling movie acquisition for the first time (rather

than just single frames) without the need to purchase

additional RAM.

The role of the student will be to replicate the previous

software-streaming + numerical-analysis approach but in genuine hardware logic. The

will gain experience in the use of benchtop waveform generators, digital oscilloscopes,

as well as visual block-level programming. The student will benefit from the assistance

of the on-site professional support staff in the AML, as well as being fully embedded in

the research group.

Ideal Candidate: The ideal candidate will have an interest in electronics and/or

programming. Previous experience is not necessary as all training will be provided.

Expected Outcomes: The configured FPGA

will be used to record data to contribute to a new

research manuscript in the group. The student

will also be expected to produce poster and/or

deliver a seminar as part of the ‘AML

Nanotechnology Seminar’ series.

Budget / Resource Plan: The project will utilise

a Digilent Artix-7 FPGA Development Board

(€330), exact model TBD. Approx. €100 is

allocated for BNV termination connectors,

cables and other minor electronics incidentals.

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39.

Prediction and Measurement of Electron Lenses Aberrations

Supervisor: Professor Lewys Jones

Location: TCD

The internship will be based in the Advanced Microscopy Laboratory

(www.tcd.ie/crann/aml ). A sole-use desk and PC will be provided to the student.

Abstract:

Transmission electron microscopy (TEM) is an invaluable tool in modern materials

science. The performance of these instruments depends on many factors, including

importantly the quality of the construction and alignment of the electron lenses.

This project will attempt to understand

the performance of current generation

TEM lenses using both computer

simulation and practical experimental

measurements. Computer simulations

using COMSOL will be performed to

understand the effects of magnetic field

saturation as well as the focal properties

of electromagnetic lenses [1]. The

student will first build the model

geometry in the simulation environment

and then investigate the influence of various properties including lens-power, polepiece

shape and gap-separation. The influence on focal-length will be identified and if possible

optimised.

In addition to these simulations, and subject to progress, the student will have the

opportunity to undertake their own experimental contrast transfer function (CTF)

measurements using a JEOL-2010 TEM in the Advanced Microscopy Laboratory (AML).

These measurements will involve recording carefully calibrated images of few-

nanometre thick amorphous carbon

films to determine the CTF as a

function of defocus [2]. From these

measurements the coefficient of

spherical aberration (a key measure

of quality) will be calculated for the

lens system.

Ideal Candidate: The ideal candidate will have an interest in electron microscopy and/or

programming. Previous experience is not necessary as all training will be provided.

Good general computer skills will be essential. Experience with MatLab, ImageJ or

Python would be advantageous.

Expected Outcomes: The successful outcome of this project will see the student

develop tools to predict and experimentally verify the spherical aberration of one of the

TEM instruments in the Advanced Microscopy Laboratory (JEOL-2010).

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40.

Evaluation of 3D Printed polymers for Electron Microscope Sample

Holders/Supports

Supervisor Professor Lewys Jones

Location: TCD

The internship will be based in the Advanced Microscopy Laboratory (www.tcd.ie/crann/aml ). A sole-use desk and PC will be provided to the student. Lab-bench space will be

provided in TTEC Unit 7.

Abstract:

X-ray microanalysis is a powerful tool in the transmission electron microscope (TEM) for the identification of chemical species. However, the sample holders and support grids used often comprise of metals (especially copper and steel) and can cause either unwanted signal absorption/shadowing [1] or unwanted system peaks (data artefacts). Typical copper grid geometries are shown below, having a diameter of 3.05 mm:

The aim of this project is to determine the suitability of using new generation high-resolution two-photon polymer printers such as the NanoScribe GT2 in the AMBER Additive Research Lab (ARL) for the printing of TEM grids. Lower resolution higher temperature printers such as the 3Gence F340 will be evaluated for larger sample cartridge component printing, including the use of the polymer PEEK [2]. The student will be required to first reproduce the 3D geometry of existing grids (like those shown above) using 3D design software (Solidworks), before converting the files for 3D printing. Following the 3D printing, the student will assess the mechanical suitability of the printed part including evaluating any expansion or shrinkage of the material. Ideal Candidate: The ideal candidate will have an interest in nanoscience or electron microscopy. Good computer skills will be necessary and experience in 3D graphics/design would be a bonus. Specific previous experience is not necessary as all training will be provided. Expected Outcomes: On successful completion of this project we will have 3D printed a polymer TEM grid and assessed it’s suitability for imaging use. Any shrinkage/expansion resulting from the printing will be evaluated and corrected, and the vacuum compatibility of the polymer will be assessed. Electrical conductivity will be verified both of as-printed grids, and of gold-coated grids. Budget Plan: The project will require printing the prototype grids in the Additive Research Lab (approx. €300), and subsequent characterisation of their performance using a JEOL2100 TEM in the Advanced Microscopy Lab (approx. €200). Smaller costs, such as gold coating etc., will be absorbed by the Ultramicroscopy group.

24

References: [1] J. Kraxner, M. Schäfer, O. Röschel, G. Kothleitner, G. Haberfehlner, M. Paller, and W. Grogger, Ultramicroscopy 172, 30 (2017). [2] S. Koshiya and K. Kimoto, Micron 93, 52 (2017).

41.

Analysing 3D Printed Metal Parts using X-rays and Electrons

Supervisor: Professor Lewys Jones

Location: TCD

The internship will be based in the Advanced Microscopy Laboratory (www.tcd.ie/crann/aml ). A sole-use desk and PC will be provided to the student. Lab-bench space will be provided in TTEC Unit 7.

3D printing, or additive manufacturing, is a rapidly evolving area of industry. However, it as a new technology it poses many challenges in materials characterisation and certification. Many existing metrics of materials properties, structure, and strength now need to be re-evaluated. This project aims to determine some micro-scale properties of 3Dprinted metal parts; including the surface-finish/porosity, crystal structure, or traces of chemical impurity. Small metal test ‘coupons’ will be designed and manufactured in the AMBER Additive Research Lab (ARL) under supervision before being evaluated using scanning electron microscopy (SEM) for both surface finish and composition. Electron backscattered diffraction (EBSD) will be used to determine variation is surface crystal structure where possible. X-ray micro-CT will be used to study the presence (if any) of internal voids or of sputter into nearby unfused powder. The implications for component integrity and also powder recycling will be evaluated. Ideal Candidate: An interest in electron microscopy or 3D drawing (CAD) or 3D printing would be beneficial. Specific previous experience is not necessary as all training will be provided. Expected Outcomes: The student will contribute to an ongoing study of the suitability of 3D printing techniques in high-performance failure-critical industries. Budget Plan: This project will require 3D printing in titanium (approx. €250) followed by characterisation using SEM and micro-CT (approx. €200). Incidental additional SEM consumables costs will be absorbed by the Ultramicroscopy group.

25

42.

Development of an electroless deposition process for 3D printed RF components

Supervisor: Professor David McCloskey

Location: TCD

Ideally candidate will have interest/ working knowledge of chemical processing.

This project will develop an electroless deposition process to work with polymer and

ceramic 3D printed RF components. In our group we are using additive manufacturing to

produce custom 3D parts for next generation wireless communications systems (5G

networks). These networks will use a denser cell networks and higher frequencies to

service more users with high bandwidth applications such as Virtual Reality, Augmented

Reality, Mobile video on demand. These new frequencies under investigation require non-

standard components which are either extremely expensive, or impossible to find. The

resolution of modern stereolithographic 3D printers has improved to such a level that

custom parts can be directly printed. One issue is that these parts require a metal interface

in order to perform properly [1]. Electroless deposition is a process where non conducting

materials can be coated with a thin layer of conducting metal [2]. This allows a cheap and

scalable process for development of prototype devices [3].

The student will develop this process, and apply to test waveguide and resonator

structures. The performance of the devices will be characterised, and the process

optimised to produce smooth continuous, conformal coatings. If successful this process

will then be applied to technologically relevant designs produced in collaboration with

Nokia Bell Labs.

References:

[1] Otter, William & Lucyszyn, Stepan. (2016). 3-D printing of microwave components for 21st

century applications. 1-3. 10.1109/IMWS-AMP.2016.7588327.

[2] J. Shen, M. Aiken, C. Ladd, M. D. Dickey and D. S. Ricketts, "A simple electroless plating

solution for 3D printed microwave components," 2016 Asia-Pacific Microwave Conference

(APMC), New Delhi, 2016,pp.1-4. doi: 10.1109/APMC.2016.7931434

[3] Mandke, Yashodhan & Henry, Rabinder. (2017). Review of Additive Manufacturing 3D Printed

Microwave Components for Rapid Prototyping.

[4] Ghazali, Ifwat & Chahal, Premjeet & Park, Kyoung Youl. (2018). 3D Printed Metallized Plastic

Waveguide for Microwave Components. Advancing Microelectronics. 45. 12-16. 10.4071/2380-

7016-45.2.1.

[5] A review of electroless nickel plating, Loto, C.A. Silicon (2016) 8: 177.

https://doi.org/10.1007/s12633-015-9367-7

Fig.1

(a) 3D printed

(b)Example of complexity of a 3D printed part. This

is a monopulse antenna array which usually consists

of multiple components, now printed as a single

compact part.

26

43.

Integrated polymer refractive index sensors based on whispering gallery mode

optical detection.

Supervisor: Professor David McCloskey

Location: TCD

Light can be efficiently trapped in micron scale dimensions using devices known as

whispering gallery mode resonators. These are spherical or cylindrical shaped devices

which act like tiny interferometers, and exhibit sharp dips in transmission when coupled to

via fibres or waveguides. The positon and full width half maximum of these dips are

strongly dependant on the refractive index of the surrounding environment. This allows

the use of these devices as extremely sensitive refractive index sensors [1]. By correctly

functionalising these devices trace amounts of chemicals or biological particles can be

detected. This project will develop the UV lithography process necessary to produce

whispering gallery mode resonators in SU8 using the facilities available in CRANN. The

ultimate goal of the project is to combine this technique with integrated turbulent

microfluidics a chemical or biosensor with sensitivity in the ppb range.

References:

[1] Optical microcavities, Kerry Vahala.

[2] C. Delezoide et al., "Vertically Coupled Polymer Microracetrack Resonators for Label-Free

Biochemical Sensors," in IEEE Photonics Technology Letters, vol. 24, no. 4, pp. 270-272,

Feb.15, 2012. doi: 10.1109/LPT.2011.2177518

44.

Characterisation of thin film thermoelectrics

Supervisor: Professor David McCloskey

Location: TCD

Thermoelectric materials allow the direct conversion of heat flux into electrical current

and vice versa. As such they can be used to generate electrical power using waste heat.

Another important application of thermoelectrics is as solid state coolers. When a current

is passed through a thermoelectric material heat will be extracted from one contact and

deposited at the other. As such we can use this effect as a heat pump. Since it is a solid

state device it have no moving parts and no vibration which has resulted in its adaptation

for niche markets such as CCD array cooling, space applications and temperature

control of laser diodes.

Standard Thermoelectric Modules utilise bulk semiconductor alloys such as Bi2Te3 and

BiSbTe. They consist on an array of alternating n and p type semiconductor legs which

27

are connected electrically in series and thermally in parallel. Typical leg lengths are of

the order of 2-3mm. A new class of thermoelectric cooler is emerging utilising thin films

with thickness in the range of 10μm. These devices can be embedded in the lithographic

design of electronic and optoelectronic devices allowing a much smaller footprint and

higher energy efficiency. Under high heat flux conditions seen in integrated circuits thin

film thermoelectrics clearly out-perform their bulk counterparts. Commercial thin film

TECs are currently available as standalone external modules, but as of yet a fully

integrated TEC with optoelectronic device has remained elusive.

Figure 1 (a) Commercial thin film thermoelectric modules (b) Thin film modules

compared to conventional bulk modules for same cooling power. (c) Cooling

performance chart for comparison of bulk vs thin film. Even measuring the

performance of these devices becomes challenging as small temperature differences

must be accurately measured over distances as short as 10μm. In our research

group we have developed optical and electronic techniques to measure thermal

conductivity, volumetric heat capacity, electrical conductivity, Seebeck and Peltier

Coefficients, electrical and thermal interface conductances. These are all the

parameters required to measure the device performance. This project will apply

these techniques to investigate the thermoelectric performance of thin film polymer

thermoelectric coolers. Particular attention will be paid to minimising the electrical

interface conductance which limits the performance of thin film TECs.

References: [1] http://www.mouser.com/pdfDocs/Laird_ThinFilmThermoelectricHandbook.pdf [2] Coatings 2018, 8(7), 244; https://doi.org/10.3390/coatings8070244

[3] Handbook of thermoelectrics, D.M. Rowe, Chapter 58

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45.

Field Effect Phase Modulation in 2D Nanomaterials

Supervisor: Professor David McCloskey

Location: TCD

Surface normal optical modulators are attractive devices for a wide range of applications

such as free-space photonic links for mobile platforms [1], chip-to-chip optical

interconnects [2], high-speed transceivers [3], optical correlators [4], and optical vector-

matrix multipliers [5]. These devices use a large array of lithographically defined pixels

which can modulate the amplitude of the reflected light to encode and transmit information

in a massively parallelised fashion (See Fig.1).

Figure 2 (a) Schematic of single pixel multiple quantum well structure for 1550nm. (b) Micrograph of typical pixel designs from above, and typical SMA connected package. (c) Image of a 2x128 modulator array. [6]

Surface-normal modulators (SNMs) are conventionally based on multi-quantum well

structures and can achieve modulation frequencies above hundreds of kilohertz, with

demonstrations in InP up to 40 GHz [6]. Achieving this performance requires expensive

fabrication techniques with slow and costly regrowth steps, and back-etching. Due to the

weak interaction of light with individual QWs a large stack must be made up to 5 μm which

limits the bandwidth to MHz range.

Recently it has been demonstrated that the reflectivity of 2D semiconducting materials can

be effectively controlled through electrical gating [7]. The tunability results from the effects

of injected charge carriers which broaden the spectral width of excitonic interband

transitions by the creation of trions [8], resulting in a large change of complex refractive

index.

This project will develop an interferometry setup to measure the phase shift on reflection

from test devices produced through the AMBER centre. We will investigate theoretically

and experimentally the limits in switching frequencies for these devices.

References

[1] “Large aperture multiple quantum well modulating retroreflector for free space optical data

transfer on unmanned aerial vehicles,” Opt. Eng., vol. 40, pp. 1348–1356

29

[2] “High-speed, dual-function vertical cavity multiple quantum well modulators and

photodetectors for optical interconnects,” Opt. Eng., vol. 40, pp. 1186–1191

[3]“High-speed integrated optoelectronic modulation circuit,” IEEE Photon. Technol. Lett., vol. 13,

no. 2, pp. 626–628.

[4] “Design and evaluation of a multiple quantum well SLM based optical correlator,” in Optical

Pattern Recognition XI, Proc. SPIE, vol. 4043, pp. 66–71.

[5] Development of a large high-performance 2-D array of GaAs-AlGaAs multiple quantum-well

modulators,” IEEE Photon. Technol. Lett., vol.15, no. 10, pp. 1531–1533, (2003).

[6] Surface-Normal Ge/SiGe Asymmetric Fabry–Perot Optical Modulators Fabricated on Silicon

Substrates," in Journal of Lightwave Technology, 31, 3995 (2013).

[7] Giant Gate tunability of Optical Refractive index in Transition Metal Dihalcogenide

Monolayers, Nano Lett. ,17, 3613 (2017)

[8]Control of strong light-matter interaction in Monolayer WS2 through electric field gating, Nano

Lett.DOI:10.1021/acs.nanolett.8b02932 (2018)

46.

A study of growth and magnetic properties of Au-capped Fe atomic-width

nanowire arrays self-assembled on a vicinal platinum single crystal surface

Supervisor: Cormac McGuinness

Location: TCD

The magnetic properties of bare Fe atomic-width and height nanowires grown by self-

assembly at the step edges of platinum vicinal single crystal stepped surfaces such as

Pt(997) have been investigated in the past [1]. Capping such self-assembled nanowire

arrays by a few monolayers of gold is expected to change greatly the magnetic behaviour

of these systems as has been observed to occur for cobalt nanowires [2]. The self-

assembled growth of Fe nanowires on Pt(997) will be attempted and these nanowires will

be capped with an ultra-thin Au layer. Preparation of the Pt(997) surface and the growth

of these nanowires will occur in ultra-high vacuum (UHV) chambers. In UHV the growth

will be characterised by low energy electron diffraction (LEED) and Auger electron

spectroscopy (AES) and also by in-situ reflection anisotropy spectroscopy (RAS) in the

visible and near-visible regions. Upon successful growth then the capping layer prevents

oxidation upon removal from the chamber and ex-situ magnetic measurements such as

magneto-optic Kerr effect (or RAS-MOKE) measurements will measure the magnetic

hysteresis of the Au-capped Fe nanowire arrays at room temperature and at a range of

temperatures below room temperature. In addition, further ex-situ measurements by x-ray

photoemission spectroscopy (XPS) can serve to confirm the electronic structure and

metallicity of the capped Fe nanowires. It is the intention that these samples will then be

studied at synchrotron radiation sources by x-ray magnetic circular dichroism (XMCD)

techniques. The student will become skilled in many aspects of surface science, vacuum

technology, magnetic surface optical linear spectroscopy and analytical techniques.

[1] R. Cheng, K.Y. Guslienko, F.Y. Fradin, J.E. Pearson, H.F. Ding, D. Li, and S.D. Bader, Phys. Rev. B 72, 014409 (2005). [2] M.J. Duignan, J.P. Cunniffe, P.-A. Glans, E. Arenholz, C. McGuinness, and J.F. McGilp, Phys. Status Solidi B, 253, 241 (2016).

30

47.

The measurement of the reflectance anisotropy spectrum (RAS) arising from penta-silicene nanoribbons formed on Ag(110) Supervisor: Cormac McGuinness Location: TCD This project is to measure for the first time the optical anisotropy due to penta-silicene

nanoribbons that can be formed on Ag(110) surfaces. It has recently been shown by

Cerda et al. that a monolayer of silicon evaporated onto Ag(110) surfaces can form a

variety of penta-silicene nanoribbons [1]. These nanoribbons form parallel to the Ag

[110] rows displacing one of the surface rows i.e. of the missing row reconstruction,

where the silicon forms a chain of distorted pentagons within the missing row troughs

(a,b). Each pentagon consists of four co-planar silicon atoms in the trough with the fifth

silicon adatom buckling the planarity of the pentagon (e). These one-dimensional silicon

surface nanostructures have been controversial. Evidence from Cerda et al [1] for both

single and double silicene penta-nanoribbon formation now gives confidence that the

above is an accurate picture.

This experimentally challenging project involves the preparation of ultra-clean Ag(110)

surfaces in ultra-high vacuum, verification of this via low energy electron diffraction

(LEED) and by Auger electron spectroscopy (AES), the calibration and evaporation of

<1ML of Si onto these surfaces (to be verified via AES). The goal being the

measurement of the anisotropic optical properties of the penta-silicene nanoribbons as

measured in situ during the penta-silicene nanoribbon formation via reflection anisotropy

spectroscopy (RAS) and subsequent structural measurement by LEED. Earlier surface

differential reflectance spectroscopy (SDRS) measurements by Borensztein et al [2]

were obtained for what should be the same system described by Cerda et al. but as of

yet no direct RAS measurement has been acquired from this penta-silicene system. The

objective is to complete such measurements. The student will become skilled in many

aspects of surface science, vacuum technology, surface optical linear spectroscopy and

analytical techniques.

[1] J. I. Cerda et al, Nature Communications, 7, 13076, 2016 10.1038/ncomms13076 [2] Y. Borensztein et al., Phys. Rev. B, 89, 245410 (2014) 10.1103/PhysRevB.89.245410

31

48.

Self-consistent data analysis of x-ray magnetic circular dichroism x-ray absorption spectra of sub-monolayer cobalt nanowire arrays. (Computational/Data analysis) Supervisor: Cormac McGuiness

Location: TCD X-ray magnetic circular dichroism (XMCD) is a synchrotron radiation based x-ray

spectroscopy used to measure the magnetic moments and probe magnetic behaviour of

materials on an elementally selective basis due to the distinct binding energies of the

orbitals probed to connect with the magnetically polarised unoccupied states. XMCD

uses circularly polarised x-rays where differential x-ray absorption of a material in a

magnetic field is measured in four differing modes: +B+, -B+ , +B-, and +B-

corresponding to the two differing circular polarizations available (+, -) and the differing

applied fields parallel (B+) or anti-parallel (B-) to the direction of propagation of the x-

rays. The XMCD spectrum is computed from the difference of any pair of the x-ray

absorption spectra. For bulk materials where the underlying x-ray absorption signal is

strong, the XMCD is not susceptible to transient problems related to the measurement.

However in the case of very small x-ray absorption signals due to small amounts of

material, e.g. sub-monolayer coverages of the material being probed, transient problems

(noise as well as differing spectral backgrounds due to variable flux from the x-ray

monochromator or machine issues) from each separate measurement have an untoward

effect on the ability to compute XMCD. This project envisages the development of a

robust self-consistent data analysis method whereby a quartet of spectra (or octet of

spectra), known to be probing the same amount of material, are treated to obtain reliable

XMCD spectra. XMCD data previously obtained at synchrotrons in Sweden (MAX-lab)

and the US (ALS) are available for this project. This data arises from gold-capped cobalt

nanowire arrays self-assembled on vicinal regularly stepped platinum substrates such as

Au(4-7ML)/Co(0.39-0.78ML)/Pt(997) investigated by us in the recent past [1,2].

[1] J. P. Cunniffe, D. E. McNally, M. Liberati, E. Arenholz, C. McGuinness, and J. F. McGilp, Phys. Status Solidi B, 247, 2108 (2010) [2] M.J. Duignan, J.P. Cunniffe, P.-A. Glans, E. Arenholz, C. McGuinness, and J.F. McGilp, Phys. Status Solidi B, 253, 241 (2016).

49. Project removed from list.

50.

The packing structure of disordered platelet suspensions

Supervisor: Professor Matthias Möbius

Location: TCD

Microscopic platelet particles naturally occur in clays, for example. More recently 2D

nanoparticles such as graphene and many others can be produced. Suspensions of

these nano-sheets are often used to make films for battery electrodes or can be used as

fillers to enhance the mechanical properties in nanocomposites. One important quantity

is the volume fraction at which these particles form a stress bearing network and its

dependence on particle aspect ratio. You will investigate this experimentally by studying

a system of sheets suspended in a fluid and compare your results with theoretical

predictions. Furthermore you will study the disordered structure using a CT scanner.

32

51.

Droplet splashing of 2D nanosuspensions

Supervisor: Professor Matthias Möbius

Location: TCD

Beyond a critical impact velocity liquid droplets splash on a solid surfaces. This

phenomenon is important in the context of printed electronics, where nanoparticle inks

are used to print circuits on substrates. As splashing limits the resolution of feature

sizes, it is important to understand it for nanoparticle suspensions which exhibit a

different flow behaviour than ordinary liquids. In this project you will measure the onset

of splashing for a 2D nano-suspension, such as aqueous graphene oxide, and the

influence of particle concentration, which is unknown. This experimental project involves

using a high speed camera to probe the dynamics of the splashing process.

52.

Integrated Optical-Electrical Modelling and Characterisation for Light Trapping

Effect in Thin Film Organic Photovoltaic Cells

Supervisor: Dr. Chenguang Wang and Professor Deirdre O’Carroll

Location: TCD

Solar cells absorb solar light energy and convert it to electricity directly by the

optoelectronic reaction known as photovoltaic effect. Organic photovoltaic (OPV) cells has

been studied for decades as potential candidates to replace the silicon solar cells because

of the advantages such as light weight, thin film, flexible shape, simple fabrication, etc.

Recent new materials have developed the power conversion efficiency to 14% in

experimental condition, which close to the commercial silicon products’. This project will

use electromagnetic and electrical modelling methods to study the working mechanism of

OPV cells, from photon absorption, exciton excitation, exciton diffusion, carrier transport

and collection. Also, current-voltage measurement of the OPV cells will be taken to verify

the modelling results.

53.

Light Extraction and Beam Steering Effect in Organic Light Emitting Diode with

Nano Patterned Encapsulation Thin Film.

Supervisor: Dr. Chenguang Wang and Professor Deirdre O’Carroll

Location: TCD

Plastic organic light emitting diodes (P-OLEDs) are being used widely because of their

thinness, shape flexibility, and low pixilation. P-OLEDs typically exhibit homogeneous

luminance density so that no preferred angular emission direction. Also, because of the

instability of organic polymer materials, an encapsulation thin film is normally placed on

the device to isolate the ambient environment. Here, electromagnetic simulations are used

to design nanostructures on the encapsulation layer of the OLED and to quantify the extent

to which the light illuminance directions and intensities will be changed, followed by the

fabrication process by using photo lithography and plasma etching. Light emission angular

characterisation is probably involved in this project as well by doing the quantum yield

measurement.

33

54.

Quantum Efficiency Enhancement in Organic Light Emitting Diode with Plasmonic

Metasurfaces for Different Coloured Light Emission

Supervisor: Dr. Chenguang Wang and Professor Deirdre O’Carroll

Location: TCD

Plastic organic LEDs (P-OLEDs) are being used widely because of their thinness, shape

flexibility, and low pixilation. However, the phosphorescent P-OLED emitters are unstable

due to long emission lifetimes, excited-state quenching, and large band gap. These

drawbacks will lead to the energy waste and heat generation of the OLED by non-radiative

recombination. This project theoretically and experimentally investigates the use of silver

plasmonic metasurface structures to increase the light extraction efficiency, radiative

decay rate and stability of inverted P-OLED devices. Electromagnetic simulations are

used to design silver metasurfaces and to quantify the extent to which they increase

radiative decay rate of OLED emissive layers. Nano imprint lithography technique is used

to fabricate the silver metasurface and experimental measurement works will be included

to test the performance of OLEDs with designed metasurface structures.

55.

Quantum-mechanical simulation of magneto-optical spectroscopy

Supervisor: Professor David O’Regan

Location: TCD

Certain materials exhibit the phenomenon of rotating linearly-polarised light passing

through them, an effect known as optical activity or magneto-optical response. The

related spectroscopic techniques, in particular, electronic circular dichroism (ECD) and

optical rotatory dispersion (ORD) directly probe the chirality of the material in question.

These techniques are particularly important for characterising similar molecules or

nanostructures with different chirality, whose absorption spectra may be identical but

whose magneto-optical may differ enormously. ECD also plays a role in the study of

magnetic materials with a strong orbital component to magnetism. Experimental ECD

signals are often very clear, but can be difficult to understand without some prior

knowledge of the crystal structure. This is why a theoretical description, necessarily

quantum-mechanical, is an essential, but hitherto almost entirely absent, companion to

experimental magneto-optical spectroscopy. Up to now, relatively very few first-

principles quantum calculations of magneto-optical spectra have been carried out, and

code for carrying them out is not very widely available. The proposed project first entails

a study of the rather interesting and under-developed quantum-mechanical theory of

angular momentum and related magneto-optical response, and how they can be

computed using the output of computer simulations using the widely used atomistic

simulation method known as density-functional theory (DFT), and its linear-scaling

generalisation. This project aims to bring to completion research carried out by summer

interns, involving abstract theory and its software implementation in parallelised code for

high-performance computing architectures.

See https://arxiv.org/abs/1703.05056

34

56.

Developing empirical rules for correcting density-functional theory: how best to

simulate entangled electronic states using pure ones?

Supervisor: Professor David O’Regan

Location: TCD

The computer simulation of molecules and materials using density-functional theory is

beset by a number of well understood, but difficult to correct, systematic errors. As a

result, it yields very inaccurate predictions in a wide range of systems. An established

route to addressing one of the main problems is by adding a correction involving a

parameter known as the Hubbard U. Adding a parameter to the theory is undesirable,

and a number of recipes have been developed for calculating an optimal value for U,

whereby the theory again becomes parameter-free. We will investigate a new such

recipe, testing it systematically on series of small molecules comprising transition metals

across the periodic table. With this, we may also be able to establish empirical rules for

how the U parameter should vary with atomic number, charge, spin, and bond-length.

We will also look at trends in the Hund’s J parameter, which can help to correct strong

’static correlation’ errors that occur in density-functional theory calculations when strong

multi-reference or entanglement effects arise, since these calculations need to work with

a pure state one. This will be particularly helpful to the simulation of systems where

bonds break (e.g., in catalysis for water splitting or CO2 reduction), and in multiple-

valence degenerate systems (transition metal oxides used to store lithium ions in high-

performance batteries).

See and https://arxiv.org/abs/1704.08076 and Phys. Rev. B 94, 220104(R) (2016).

57.

Methodology for efficient computational screening for photovoltaic active layer

materials

Supervisor: Professor David O’Regan

Location: TCD

Photovoltaic solar cells are leading candidates for the energy needs of remote,

personally wearable, and autonomous (Internet-of-Things type) off-grid devices. For the

large-scale roll out of small format cells, requirements include low economic and

environmental cost, flexibility, durability, and ease of manufacture. Organic and polymer

cells are clear candidates, but they suffer from poor efficiencies in simpler, single-layer

cell geometries, limiting their market share. Dramatic improvements to the efficiently of

these materials can be yielded when multi-exciton generation effects are harnessed,

particularly rapid fission of singlets into multiple excitations, via dark and charge-transfer

(CT) states, reactions which can even be endothermic if entropy driven. Theory and

simulation are beginning to offer valuable insights into these optically dark but important

processes, including work in the School demonstrating a new ‘constrained DFT’ code for

large, disordered systems. In this project, we will explore a new, inexpensive technique

for simulating singlet, triplet, and CT excitations with minimal prior physical assumptions,

including their polarons, migration barriers, exciton binding, spin-flip conversion

constants, and oscillator strengths. In particular, we will concentrate on the singlet-

fission effect in pentacene, classifying its low-lying excitations with this new

methodology.

See Phys. Rev. B 93, 165102 (2016) and https://arxiv.org/abs/1802.01669 . For wider context,

see Nature Physics 13, 114–115 (2017); 13, 176–181 (2017); 13, 182–188 (2017).

35

58.

Many-body theory of exciplexes for OLED devices

Supervisor: C. H. Patterson

Location: TCD

Some optical excitations in matter result in transfer of an electron between two distinct

parts of a molecule or from one molecule to a neighbouring molecule. These are known

as charge transfer (CT) excitations. When a CT excitation occurs between two

molecules there is a coulombic attraction between the negatively charged acceptor

molecule and the positively charged donor molecule. The donor and acceptor molecules

are unbound in the ground state but become bound in the excited state. This is known

as an exciplex. Exciplexes are finding applications as light emitters for organic LEDs

(OLEDs) because of this delocalised nature of the excited state. Optical excitations exist

as spin-parallel or anti-parallel excited states called triplets and singlets. When excited

states are formed by optical pumping (or by injecting electrons and holes as in an OLED)

there are three triplet excited states formed for every singlet. However, only the singlet

states fluoresce readily (photon emission). Exciplexes are important for OLED emitters

as the delocalised nature of the CT excited state means that singlet and triplet excited

states have similar energies. This allows thermal interconversion of triplets to singlets

and an increase in the theoretical efficiency from 25% to 100%. This project will use

many-body quantum methods to calculate properties of exciplexes.

[1] Exciplex: an intermolecular charge-transfer approach for TADF, M. Sarma and K.-T. Wong,

ACS Appl. Mater. Interfaces 10, 19279 (2018).

59.

Reflectance anisotropy of the SrTiO3(110) surface

Supervisor: C.H. Patterson

Location: TCD

Two dimensional electron gases form at oxide heterostructures such as LaAlO3/SrTiO3.

These 2DEG systems have interesting properties including superconductivity. The (110)

surface of SrTiO3 has been shown to have an anisotropic 2DEG [1] using angle

resolved photoemission experiments. The surface has also been studied in TCD using

reflectance anisotropy [2]. The aim of this project is to model the effects of oxygen

vacancies at this surface on the optical anisotropy spectrum using density functional

theory. TCD experimentalists found that annealing this surface in vacuum at high

temperature resulted in a new feature in the optical anisotropy of SrTiO3(110) around

1 eV photon energy, well below the oxide bulk band gap of 3.7 eV. They attributed the

low energy feature to oxygen vacancies at the surface. In this project you will model

oxygen vacancies at this surface and calculate the optical anisotropy using methods

described in Ref. [3].

[1] Anisotropic two-dimensional electron gas at SrTiO3(110), Z. Wang et al, PNAS 111, 3933

(2014)

[2] Optical anisotropy of SrTiO3(110) for different surface terminations, K. Fleischer et al. Phys.

Stat. Sol. B 255, 1700459 (2018)

[3] Reflectance anisotropy of the anatase TiO2(001)-(4x1) surface, P. Kumar and

C. H. Patterson, J. Phys. Condens. Matter 26, 445006 (2014)

36

60.

Reflectance Anisotropy of the Ag(110) surface

Supervisor: C. H. Patterson

Location: TCD

Reflectance anisotropy spectroscopy (RAS) offers a method for probing electronic

optical transitions for electrons confined to the outer atomic layers of materials. It

requires the surface atomic layers to have reduced lateral symmetry (a surface

anisotropy) and the underlying bulk material to have isotropy. This is the case for the

(110) faces of close packed metals such as the Ag(110) surface. This project will be to

calculate the RAS spectrum for Ag(110), to identify which electronic transitions are

responsible for the RAS signal and to compare to available experimental data [1].

Through the project you will learn about electronic structure of surfaces, density

functional theory and high performance computing. To learn more about RAS and its

applications to surface states [2].

[1] Martin et al. Phys. Rev. B 76, 115403 (2007).

[2] Jorgji et al. Phys. Rev. B 87, 195304 (2013).

61.

Electron scattering from bilayer islands in graphene

Supervisor: Dr Stephen Power

Location: TCD

Figure 3: Bilayer islands surrounding by single layer graphene during CVD growth

(from Luo et al, J. Mat. Chem C. 4, 7464 (2016))

Graphene has an unusual electronic properties that are well-described using the

relativistic Dirac equation in place of the more standard Schrodinger equation. The

electronic properties of graphene are strongly dependent on the number of atomic

layers, with electrons in a system of two layers (bilayer graphene) behaving very

different to the single layer case.

This project will simulate how electrons in single layer graphene scatter from bilayer

regions, which commonly form during some growth processes (see Figure 1). The aim is

to determine whether this scattering can be controlled by applying an electric field. The

project will also determine if such a setup has potential valleytronic applications. The

student will:

• Learn the tight-binding and Dirac spinor representations of electrons in single

layer and bilayer graphene

37

• Examine how barrier and spherically-symmetric scattering geometries can be

solved using the Dirac approach for simple potential terms

• Solve the full scattering problem for a range of realistic parameters, and calculate

the valley-splitting efficiencies of these systems.

62.

Machine-learning prediction of edge-state magnetism in graphene

Supervisor: Dr Stephen Power

Location: TCD

Figure 4: Section of a graphene ribbon with mixed edges grown using chemical "bottom-up" techniques (from Ruffieux et al, Nature 531, 489 (2016))

Graphene is a two-dimensional hexagonal lattice of carbon atoms whose ground-

breaking physical and electronic properties have been investigated in great detail over

the last decade. Recent experimental techniques allow graphene to be produced both at

very large scales for industrial purposes, and at the nanometre scale required for

investigating fundamental physics.

The latter approach allows for a high-degree of control over the edge geometries of finite

flakes or narrow ribbons of graphene. This is particularly exciting because, although

carbon is generally considered nonmagnetic, local magnetism can arise near edges with

particular geometries. Magnetic edge features have received much attention from

theorists, and recent experiments show convincing signatures of their presence.

Although the expected magnetic behaviour of small scale or periodic systems can be

easily predicted, the computational power required increases rapidly when larger or

disorder systems (with a mix of different edge types) are considered. This project aims to

solve some of these problems by training a machine-learning algorithm to predict the

magnetic properties of arbitrary graphene systems using only their geometry and a

knowledge of the properties of similar structures.

The student(s) will

• Learn tight-binding methods required describe non-magnetic graphene samples

• Implement a self-consistent procedure to calculate magnetic profiles

• Generate a training set and develop a suitable descriptor to capture its important

features

• Train machine-learning algorithms to predict the magnetic profiles of unseen

samples using its knowledge of the training set.

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63.

Machine-learning force fields for phase diagram predictions

Supervisor: S. Sanvito

Location: TCD

Machine learning is rapidly becoming a powerful tool to discover patterns in apparently uncorrelated data [1]. It comprises a range of computational methods, which underpin the most diverse applications, going from image recognition to natural language processing, to complex optimisation and classification problems. The use of machine learning in materials science instead is in its infancy [2], mostly because of the relatively poor availability of data. This issue is, however, mitigated by the access to large databases of computed properties [3], so that machine learning algorithms can serve the purpose of replacing numerically costly computational methods. One particular use of machine learning in materials science is related to the construction of highly accurate atomic potentials [4]. These can describe the interaction between atoms at a level of accuracy comparable to that of the much more demanding first principles methods at a fraction of their computational cost. In this project we will explore how such machine-learning force fields can predict the phase diagram of binary compounds. In particular we will study of the force fields can describe compounds presenting different stoichiometry and different structure. The student will:

1. Learn the basics of machine learning 2. Construct a machine-learning force field for a binary phase diagram 3. Extract elementary properties with the machine learning force field

References [1] T. Hastie, R. Tibshirani and J. Friedman, The elements of statistical learning, Springer. [2] R. Ramprasad, R. Batra, G. Pilania, A. Mannodi-Kanakkithodi and C. Kim, Machine learning in materials informatics: recent applications and prospects, npj Comp. Mat. 3, 54 (2017). [3] S. Curtarolo, G.L.W. Hart, M.B. Nardelli, N. Mingo, S. Sanvito and O. Levy, The high- throughput highway to computational materials design, Nature Materials 12, 191-201 (2013). [4] V. Botu , R. Batra, J. Chapman and R. Ramprasad, Machine Learning Force Fields: Construction, Validation, and Outlook, . Phys. Chem. C 121, 511 (2017).

64.

Use of Generative Adversarial Networks in physics

Supervisor: S. Sanvito

Location: TCD

Generative Adversarial Networks (GANs) belong to a class of machine learning algorithms, where two neural networks compete with each other [1]. These have widespread applications in several fields, with the most celebrated success being in image processing/recognition. A classical example of how GANs work is that of picture generation. In this case a first neural network (call it “Alice") generates pictures (for example, human faces), which are included in a database of images of real people. Then a second neural network (call it “Bob") sort the real images of people from the computer-generated ones. Bob and Alice then play against each other, namely Alice generates more and more realistic pictures and Bob refines its discrimination ability. The game ends when Bob is no longer able to distinguish the real images from the computer-generated ones. At this point Alice’s ability is to generate pictures of people indistinguishable from those of real people. An example of this scheme at work can be found at https://thispersondoesnotexist.com/. Similar methods have been used to generate characters of Anime cartoons [2] or to age people in photographs [3] In this project we will attempt to use GANs for solving physics problems that require sampling a vast distribution of configurations [4]. This, for instance, is the case when calculating phase transitions of quantum models (e.g. the Ising model), or in general for extracting temperature-dependent properties. In this project the student will:

39

1. Learn the basics of machine learning 2. Construct a simple GAN model 3. Extract finite-temperature properties of a simple quantum model

References [1] I. Goodfellow, J. Pouget-Abadie, M. Mirza, B. Xu, D. Warde-Farley, S. Ozair, A. Courville, Y. Bengio, Generative Adversarial Networks, arXiv:1406.2661 (2014). [2] Y. Jin, J. Zhang, M. Li, Y. Tian, H. Zhu and Z. Fang, Towards the Automatic Anime Characters Creation with Generative Adversarial Networks, arXiv:1708.05509 (2017). [3] G. Antipov, M. Baccouche and J.-L. Dugelay, Face Aging With Conditional Generative Adversarial Networks, arXiv:1702.01983 (2017). [4] Z. Liu, S.P. Rodrigues and W. Cai, Simulating the Ising Model with a Deep Convolutional Generative Adversarial Network, arXiv:1710.04987 (2017).

65.

Electronic structure simulations of spin-phonon coupling in molecular materials

Supervisor: S. Sanvito

Location: TCD

Magnetic materials represent the conventional way to store information in hard drives. This is done by orienting the magnetization of a material along one spatial direction with either positive (the bit has value 0) or negative (the bit has value 1) polarization. Molecular magnetic materials represent the smallest units that can be used to store information but they usually have a very low working temperature [1]. This limitation mainly comes from the interaction between the molecular spin, that generates the magnetic moment, and molecular phonons [2]. In order to optimize the production of these materials a deep understanding of the physical principles governing the spin- phonon interaction is needed. In this context, electronic structure theory can be used to simulate magnetic proprieties of materials and get access to the correlation between the chemical nature of molecules and their magnetic properties. In this project we will exploit electronic structure methods to explore the effect of different chemical environments on molecular magnetic anisotropy and its coupling with molecular vibrations. The student will:

1. Learn the basics of electronic structure theory 2. Learn how to calculate magnetic anisotropy in molecular compounds 3. Extract elementary correlations between magnetism and structural parameters

References [1] Bogani L. and Wernsdorfer W., Molecular spintronics using single-molecule magnets, Nat. Mater. 7, 179-186 (2008). [2] Lunghi A., Totti F., Sessoli R. and Sanvito S., The role of anharmonic phonons in under-barrier spin relaxation in single molecule magnets, Nat. Commun. 8, 14620 (2017).

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66. Quasi-classical spin dynamics in compensated ferrimagnetic systems – a 1D/2D approach to understanding pinning and nucleation of domain walls and skyrmions (theory/computation) Supervisor: Dr. Plamen Stamenov Location: TCD

The project will involve the theoretical and computational modelling of spin dynamics in a relatively new class of magnetic materials – the Zero-Moment Half-Metals (ZMHM). ZMHMs are posing a challenge to understand and exploit a rather unique for spin electronics combination of high bulk spin polarisation, stray field immunity and intrinsically high resonance and switching frequencies, effectively limited by the exchange energy in the system. Nano-scale ultrafast and non-volatile MRAM elements and terahertz oscillators are only two examples of applications, which could benefit hugely from the utilisation of ZMHMs. The complete theoretical (ab initio) modelling of these materials is rather challenging, for the incomplete knowledge of their intrinsic and extrinsic disorder and the fine details of the effective interactions in the system, including higher order exchange and spin-orbit torques. Here a divide and conquer approach will be used to theoretically and computationally model within an effective spin Hamiltonian approach the dynamics of domain walls and other topological objects, such as skyrmions, which become possible with the inclusion of Dzyaloshinskii-Moriya interactions. The influence of magnetic field, electric current and local pinning on the mobility and dissipation within these objects will be clarified. The work will start with an existing 1D code for quasi-classical spin simulation and transition it into a 2D version towards the end of the project, looking for phenomena that cannot be mapped-down successfully in 1D. Sz1e-2Sz0.5e-2Sz0.0e-22e-22Sz4e-2Sz5e-2Sz6e-222

Figure 1. Time-evolution of a 1D skyrmion in a two-lattice compensated ferrimagnet, at different

values of the applied magnetic field, for a chain of 100 spins, with DM interactions included.

Sz

1e-2

Sz

0.5e-2

Sz

0.0e-2 2e-2

Sz

3e-2

Sz

Sz

4e-2

Sz

5e-2

Sz

6e-2

Sz

7e-2

Sz

8e-2

41

67.

High-Power Broadband Ferromagnetic Resonance in Thin Magnetic Films and Microstructures Using Δmz – SQUID-based Detection at Low Temperatures (experiment) Supervisor: Dr. Plamen Stamenov Location: TCD

FerroMagnetic Resonance (FMR) has been instrumental in characterising the

magnetisation and the effective anisotropy fields in a large number of bulk materials and

some repetitive microstructures. Conventional FMR relies on narrow band inductive

excitation and detection of the precessional motion of the local magnetisation averaged

over some volume – typically of the order of mm3. The superb sensitivity of modern

SQUID-based magnetometers allows for a different approach towards the FMR

measurement problem – direct measurement of the precession cone angle as a function

of frequency, applied magnetic field and temperature, by detecting the mz component of

the magnetisation and the small decrease in its value upon microwave excitation Δmz.

This can, in principle, allow for the continuous broadband tracking of the FMR modes in

a broad range of the applied magnetic field and thus permit direct comparisons with

theory and micromagnetic modelling.

The project will involve the preparation of magnetic thin films of novel magnetic materials

(Co/Pt multilayers, CoFeB), their lateral patterning and comparative FMR study by both

SQUID-based and conventional inductive techniques. Within this study, an in-house-

developed probe will be utilized and a new high-power broadband amplifier will be

developed, pushing the envelope of precession cone angles that can be investigated. A

success in this will inform the design of high power microwave circulators and filters for

the 5G networks of the near future.

Figure 1. The principle of resonance detection via SQUID magnetometry in one diagram, the

high-power SFMR measurement assembly (rod), which fits into the bore of a commercial

Quantum Design MPMS 5 magnetometer, and data on the magneto-static resonance modes of

an YIG sphere, with their corresponding indexes.

42

68.

Anisotropy of the Conductivity and Hall Effect in Zero-Moment Half-Metallic Systems Supervisor: Dr. Plamen Stamenov (experiment) Location: TCD

The project will involve the experimental investigation of a relatively new class of

magnetic materials – the Zero-Moment Half-Metals (ZMHM), using their prototype Mn2-

xRuxGa, in a thin film form. ZMHMs have the potential to offer the rather unique for spin

electronics combination of high bulk spin polarisation, stray field immunity and

intrinsically high resonance and switching frequencies. Nano-scale memory elements

and terahertz oscillators are only two examples of possible applications.

Highly oriented and/or epitaxial films prepared by sputtering at different conditions

(temperature, Ru-target current, etc.) will be used to determine the anisotropy of the

conductivity and Hall effect tensor in these, typically tetragonally-distorted ZMHMs. The

measurements will be executed at both low-temperature and room-temperature, in

magnetic fields of up to 14 T, in order to discern the influence of the two ferrimagnetic

sub-lattices. Fitting models and visualization software will be prepared, taking into

account the magnetic space-group and general symmetries of the crystalline films, which

will allow for the quantitative interpretation of the anisotropy and correspondingly the

strength of the various spin-orbit and exchange interactions in the system. The

information gained will be critical for the development of prototype magnetic devices

working in the high-GHz and low-THz regions.

Figure 1. Top-left to bottom right: spontaneous hall effect loops and their corresponding torque

fits for field applied perpendicular to the film plane (MRG), in-plane rotational scan showing the 4-

th order anisotropy, in-plane and out-of plane field scans and their fits, using a combination of a

torque model and an analytical hysteronic distribution.

0 15 30 45 60 75 90

-1.0

-0.5

0.0

0.5

1.0

0 60 120 180 240 300 360-1.0

-0.5

0.0

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1.0

0 60 120 180 240 300 360

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

-15 -10 -5 0 5 10 15-1.0

-0.5

0.0

0.5

1.0

0 60 120 180 240 300 360-1.0

-0.5

0.0

0.5

1.0

xy/

N xy

()

Data 1 T

Data 2 T

Data 14 T

Fit 1 T

Fit 2 T

Fit 14 Txy/

N xy

()

Data 1 T

Data 2 T

Data 14 T

()

()

xy/

N xy

Data

Fit

Data

Data

Fit

Fit

xy/

N xy

()

xy/

N xy

Data

Data

Fit

Fit

43

69.

Tailoring the nonlinear optical performances of sulphur-based transition metal

dichalcogenide by defect engineering

Supervisor: Jun Wang

Location: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of

Sciences, Shanghai 201800, China

This project focuses on investigation of the nonlinear optical performances of sulphur-

based transition metal dichalcogenides (TMDs) by defect engineering. We need to

characterize the morphology, structure, and optical properties of the sulphur-based

TMDs before and after defect engineering and investigate the influence of defects on the

nonlinear optical performance of the TMDs using the Z-scan technique with femtosecond

pulses ranging from visible to infrared. The optical nonlinear parameters such as

absorption coefficients, third-order susceptibility and damage threshold need to be

obtained. The defect dependence of the nonlinear optical behaviour should be studied

systematically. The intrinsic mechanisms of the optical nonlinearity are to be clarified.

(See our previous work: Tailoring the nonlinear optical performance of two-dimensional

MoS2 nanofilms via defect engineering. Nanoscale 10, 17924-17932 (2018))

70.

Investigation of the nonlinear refractive index dispersion in layered transition

metal dichalcogenides

Supervisor: Jun Wang

Location: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of

Sciences, Shanghai 201800, China

Third-order optical nonlinearity, concerning both nonlinear absorption (NLA) and

nonlinear refraction (NLR), is becoming an important parameter to evaluate the potential

applications of materials in a number of fields, such as integrated optics, optical

switching devices, and optical signal processing. Therefore, the exploitation of materials

with higher nonlinear refractive index and nonlinear absorption coefficient has great

practical application values. Transition metal dichalcogenides (TMDs) have attracted

tremendous attention owing to their superior nonlinear responses. Our previous work

revealed a dispersion of nonlinear refractive index in the WS2 films that translated from

44

positive in the monolayer to negative in bulk material. However, the values are not

identical with the calculation results via the Kramers-kronig (KK) relation. This project will

focus on the study of NLA and NLR properties in TMD films. We need to characterize

the morphology, structure and optical properties of TMDs. Investigate the layer number

and excitation wavelength dependence of the NLA and NLR performances of mono- and

few-layer TMDs (like WS2 and MoS2, etc.) using the Z-scan technique with femtosecond

pulses ranging from visible to infrared. The intrinsic mechanisms of NLR dispersion are

to be clarified.

(See our previous work: Dispersion of nonlinear refractive index in layered WS2 and

WSe2 semiconductor films induced by two-photon absorption. Opt. Lett. 41(17), 3937

(2016))

71.

Stimulated Brillouin scattering in bulk polymer composites and polymer fibers

containing 2D nanoparticles

Supervisor: Jun Wang

Location: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of

Sciences, Shanghai 201800, China

The goal is to perform a Stimulated Brillouin scattering (SBS) intensity control in optical

fibres with the help of dispersed nonlinear absorbing 2D nanoparticles. The particles

deemed perspective to study are graphene, tellurium, -antimonene, hexagonal boron

nitride and others, one of them can be chosen for one project. The project comprises

polymer composite preparation, its characterization with absorption and Raman spectra

and measurements of SBS with 1064 nm nanosecond laser. The project strategy will be,

at first, to disperse nanoparticles in a polymer composition cautious to fit immersion

composition to minimize the light scattering in it. At second, to obtain SBS and energy

measurements in pure polymer composition and in the 2D-doped composite to

determine the Brillouin gain factor change. The third step will be to introduce the polymer

composite into a capillary to simulate optical fibre and obtain SBS in it, making the same

comparative energy measurements.

The goal will be achieved when SBS control will be demonstrated in the fibre geometry

and its intensity characteristic will be measured depending on the nanoparticle

concentration. The project is the development of work published in

https://doi.org/10.1364/OE.26.034346 and https://doi.org/10.1364/OE.27.011029.

45

72.

Saturable absorption of 2D nanoparticles in 1D photonic crystal

Supervisor: Jun Wang

Location: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of

Sciences, Shanghai 201800, China

The goal is to construct a saturable absorber based on periodic structure of polymer

layers (blue and red in the figure) containing dispersion of 2D nanoparticles with strong

saturable absorption (SA) behaviour. The absorber is a dielectric mirror with the minimal

transmission at selected wavelengths (photonic crystal bandgaps) enhancing light

electric field at these wavelengths and the SA of the 2D structure.

Perspective 2D material which are graphene, tellurium, -antimonene, black phosphorus

can be chosen to perform the project. The project comprises nanoparticle dispersion

preparation, its characterization with absorption and Raman spectra, preparation of the

multilayer structure and its characterization with absorption spectra and femtosecond Z-

scan at different wavelengths. The project strategy: 1) dissolve polymers having different

refractive indices (PVA and PVK as an example), 2) suspend 2D nanoparticle in one of

the polymer solutions, 3) spin-coat alternating layers on the substrate, 4) characterize

the structure with absorption spectra and AFM profiles, 5) perform Z-scan measurement

of the samples at wavelengths inside the photonic crystal bandgaps. The goal will be

achieved when an enhancement of SA properties of nanostructure will be demonstrated

as compared to the bulk polymer composite film. The project is the development of work

archived in https://arxiv.org/abs/1808.07668

73.

Helium-ion beam for nanofabrication

Supervisor: Hongzhou Zhang

Location: TCD

The precise creation of surface structure is crucial to the future of the nanotechnology.

High resolution Ion beam machining is one of the key enabling methodologies allowing

for the creation of 10nm fine structures [1]. However as the demands for finer structures

begin to approach the maximum capabilities of current machinery alternatives must be

investigated. The Helium-ion Microscope with its sub nm spot size and milling

capabilities shows excellent promise in this area. The milling rate of the HIM is a factor

of a hundred times slower than the commonly used Focused-ion beam system. This low

removal rate allows for more controlled amounts of material to be removed resulting in

finer etching, while beam damage and contamination must be evaluated. In this project,

we will mainly use SRIM (software packages for simulating the transport of ions in matter

[2]) to study the interaction of the ion beam with a range of specimens with an objective

of understanding its capability and limitation in nanoscale fabrication.

References:

Fox, D., et.al. Nanopatterning and Electrical Tuning of MoS2 Layers with a Subnanometer

Helium Ion Beam. Nano Lett 15 (8), 5307 (2015).

46

SRIM: http://www.srim.org/

74.

Understanding the origins of luminescence tuning in ZnO nanostructures via ion

irradiation

Supervisor: Hongzhou Zhang

Location: TCD

ZnO nanostructure is one of the most-intensively-investigated materials in recent years

because of its extraordinary properties and remarkable potential applications. The

ultimate goal of this project is to tune the photoemission of ZnO nanowires via site-

specific defect and strain engineering utilising focused-ion beam irradiation. The He+

beam induced surface sputtering, lattice damage and strain field will adjust the

dimensions, surface roughness, and refractive index of the ZnO sample. Our preliminary

experimental results show that the position of the wavelengths of the Whispering Gallery

Mode (WGM) in a ZnO microrod [1] exhibit a ion-dose-dependent shift, while the

success of effective tuning relies on the knowledge of localised defect generation and

the origin of the light emission. To gain such knowledge, this summer project will focus

on understanding the shift of the WGMs. The student will develop a COMSOL model [1]

and simulate the light emission of ZnO microrod to identify the defects that are

responsible for the luminescence tuning and hence optimise the strategy of ion

irradiation. This project also involves cutting-edge charged-particle microscopy, e.g. Cs-

correct scanning transmission electron microscopy (STEM), nanobeam diffraction,

electron energy loss spectroscopy (EELS), cathodoluminescence (CL), and helium ion

microscopy (HIM). The student will have the opportunity to gain knowledge and skills in

advanced materials characterisation.

References:

Czekalla, C., et al., Whispering gallery modes in zinc oxide micro- and nanowires. Physica Status

Solidi B-Basic Solid State Physics, 2010. 247(6): p. 1282-1293.

COMSOL: https://www.comsol.com/

75.

Photoelectron spectroscopy elucidates energy-level alignment at functional

organic-inorganic interfaces

Supervisor: Steffen Duhm

Location: Functional Nano & Soft Materials Laboratory (FUNSOM) at Soochow

University, China

More details can be obtained once a student expresses an interest.

Supervisor Website: http://funsom.suda.edu.cn/funsomen/c4/0c/c3002a50188/page.htm

76.

Fabrication of perovskite micro/nano crystals for the high-performance

optoelectronic devices

Supervisor: Jiansheng Jie

Location: Functional Nano & Soft Materials Laboratory (FUNSOM) at Soochow

University, China

More details can be obtained once a student expresses an interest.

Supervisor Website: http://www.jjs-group.com/

47

77.

Nanoelectronic characterization of layered dielectrics using conductive atomic

force microscopy.

Supervisor: Mario Lanza

Location: Functional Nano & Soft Materials Laboratory (FUNSOM) at Soochow

University, China

More details can be obtained once a student expresses an interest.

Supervisor Website: http://lanzalab.com

78

Design and Synthesis of Emerging Perovskite Nanocrystals for Photovoltaic

Application

Supervisor: Wanli Ma

Location: Functional Nano & Soft Materials Laboratory (FUNSOM) at Soochow

University, China

More details can be obtained once a student expresses an interest.

Supervisor Website: http://funsom.suda.edu.cn/funsomen/c3/fc/c3002a50172/page.htm

79

Self-powered sensing system based on triboelectric nanogenerator

Supervisor: Xuhui Sun

Location: Functional Nano & Soft Materials Laboratory (FUNSOM) at Soochow

University, China

More details can be obtained once a student expresses an interest.

Supervisor Website: http://funsom.suda.edu.cn/funsomen/c4/a0/c3002a50336/page.htm

80

Synergistic Device Architecture for Highly-Efficient Flexible Perovskite Light-

Emitting Diodes

Supervisor: Jianxin Tang

Location: Functional Nano & Soft Materials Laboratory (FUNSOM) at Soochow

University, China

More details can be obtained once a student expresses an interest.

Supervisor Website http://funsom.suda.edu.cn/funsomen/c3/f7/c3002a50167/page.htm