Quantum Wells, Nanowires,

Nanodots, and Nanoparticles

Y. Tzeng

ECE

Auburn University

Auburn, Alabama

July 2003

Quantum confinementTrap particles and restrict their motionQuantum confinement produces new

material behavior/phenomena “Engineer confinement”- control for

specific applicationsStructures

(Scientific American)

Quantum dots (0-D) only confined states, and no freely moving onesNanowires (1-D) particles travel only along the wireQuantum wells (2-D) confines particles within a thin layerhttp://www.me.berkeley.edu/nti/englander1.ppt

http://www.unipress.waw.pl/CE/Network/network.pdf

Energy-band profile of a structure containing three quantum wells, showing the confined states in each well. The structure consists of GaAs wells of thickness 11, 8, and 5 nm in Al0.4  Ga0.6  As barrier layers. The gaps in the lines indicating the confined state energies show the locations of nodes of the corresponding wavefunctions.

Quantum well heterostructures are key components of many optoelectronic devices, because they can increase the strength of electro-optical interactions by confining the carriers to small regions. They are also used to confine electrons in 2-D conduction sheets where electron scattering by impurities is minimized to achieve high electron mobility and therefore high speed electronic operation.

http://www.utdallas.edu/~frensley/technical/hetphys/node11.html#SECTION00050000000000000000

http://www.utdallas.edu/~frensley/technical/hetphys/hetphys.html

http://www.physik.uni-wuerzburg.de/TEP/Website/events/ESS_2001/Reithmaier/EU_summer_2001_talk2.pdf

Confinement Effects

http://www.chem.utoronto.ca/staff/GAO/flashed/courses_files/chm238y_4_B.pdf

All TiNano 40 Series products are in the 30-50 nm primary particle size range. Surface treated products exhibit very littlecrystal growth or change of phase when held in an oxidizing atmosphere at 800º C for over 100 hours. Altium™ TiNano 40 Series slurry products are dispersed to primary crystallites in aqueous media and exhibit specific surface areas (BET) of 40-60 m²/g. The slurry product offers the advantage of requiring no dispersion, and also eliminates the handling of fine powders. A spray-dried product is also available that consists of readily dispersable agglomerates of primary particles.

http://adserv.internetfuel.com/cgi-bin/omnidirect.cgi?SID=23&PID=2&LID=10&OSDELAY=10

Commercial TiO2 Nanoparticles

Nanoparticles have been used in our daily life.

Carbon black ( a nanoscale carbon) is used for writing and painting and

is added to rubber to make tires more wear resistance.

Nano phosphors in CRTs display colors.

Polishing compounds for smoothing silicon wafers include nanoscale alumina and silica, etc.

Hard disks in our computers contain nanoscale iron oxide magnetic particles.

Nanoscale zinc oxide and titania block UV light for sunscreens.

Nanoscale platinum particles are critical to the operation of catalytic converters.

Metallic nanoparticles make stained glass and Greek vase colorful.

Nanoscale thin films have also been the heart of our silicon chips for our computers, digital cameras, and photonic devices for quite a while.

The Altair Manufacturing Plant: http://adserv.internetfuel.com/cgi-bin/omnidirect.cgi?SID=23&PID=2&LID=10&OSDELAY=10

The Altair Crystal Phase Growth Process http://adserv.internetfuel.com/cgi-bin/omnidirect.cgi?SID=23&PID=2&LID=10&OSDELAY=10

Application Development Activities

Altair has on-going collaboration projects that specifically address commercial applications using our proprietary nanoparticle technology including:

•Battery Materials

•Thermal Spray

•Solid Oxide Fuel Cell and High Temperature Conductive Oxides

•Photo-catalytic Activity

•Catalysts and Catalyst Support / Surface Modification

•Photovoltaics

•Pigment Process

•Sunscreen Applications

•Arsenic Removal from Drinking Water

•Air Purification in HVAC Systems

http://adserv.internetfuel.com/cgi-bin/omnidirect.cgi?SID=23&PID=2&LID=10&OSDELAY=10

Nanotechnology may help overcome current limitations of gene therapy

Hybrid "nanodevice" composed of a "scaffolding" of titanium oxide nanocrystals attached with snippets of DNA may one day be used to target defective genes that play a role in cancer, neurological disease and other conditions.

Nanocomposites not only retain the individual physical and biological activity of titanium oxide and of DNA, but, importantly, also possess the unique property of separating when exposed to light or x-rays.

Researchers would attach to the titanium oxide scaffolding a strand of DNA that matches a defective gene within a cell and introduce the nanoparticle into the nucleus of the cell, where the DNA would bind with its "evil twin" DNA strand to form a double-helix molecule.

The scientists would then expose the nanoparticle to light or x-rays, which would snip off the defective gene.

http://www.atomworks.org/NUArgonne4.18.03

http://people.bu.edu/theochem/rabani.pdf

http://people.bu.edu/theochem/rabani.pdf

http://www.unipress.waw.pl/CE/Network/network.pdf

http://www.chem.utoronto.ca/staff/GAO/flashed/courses_files/chm238y_4_B.pdf

http://www.eps12.kfki.hu/files/WoggonEPSp.pdf

http://www.evidenttech.com/pdf/wp_biothreat.pdf

http://www.evidenttech.com/why_nano/why_nano.php

February 2003The Industrial Physicist Magazine

Quantum Dots for Sale                      Nearly 20 years after their discovery, semiconductor quantum dots are emerging as a bona fide industry with a few start-up companies poised to introduce products this year. Initially targeted at biotechnology applications, such as biological reagents and cellular imaging, quantum dots are being eyed by producers for eventual use in light-emitting diodes (LEDs), lasers, and telecommunication devices such as optical amplifiers and waveguides. The strong commercial interest has renewed fundamental research and directed it to achieving better control of quantum dot self-assembly in hopes of one day using these unique materials for quantum computing. Semiconductor quantum dots combine many of the properties of atoms, such as discrete energy spectra, with the capability of being easily embedded in solid-state systems. "Everywhere you see semiconductors used today, you could use semiconducting quantum dots," says Clint Ballinger, chief executive officer of Evident Technologies, a small start-up company based in Troy, New York... http://www.evidenttech.com/news/news.php

Quantum Dots for SaleThe Industrial Physicist reports that quantum dots are emerging as a bona fide industry.

http://www.evidenttech.com/index.php

Evident NanocrystalsEvident's nanocrystals can be separated from the solvent to form self-assembled thin films or combined with polymers and cast into films for use in solid-state device applications. Evident's semiconductor nanocrystals can be coupled to secondary molecules including proteins or nucleic

acids for biological assays or other applications.

Emission Peak[nm] 535±10 560±10 585±10 610±10 640±10

Typical FWHM [nm] <30 <30 <30 <30 <40

1st Exciton Peak[nm - nominal]

522 547 572 597 627

Crystal Diameter[nm - nominal]

2.8 3.4 4.0 4.7 5.6

Part Number (4ml)SG-CdSe-Na-TOL

05-535-04 05-560-04 05-585-04 05-610-04 05-640-04

Part Number (8ml)SG-CdSe-Na-TOL

05-535-08 05-560-08 05-585-08 05-610-08 05-640-08

http://www.evidenttech.com/why_nano/docs.php

EviArrayCapitalizing on the distinctive properties of EviDots™, we have devised a unique and patented microarray assembly. The EviArray™ is fabricated with nanocrystal tagged oligonucleotideprobes that are also attached to a fixed substrate in such a way that the nanocrystals can only fluoresce when the DNA probe couples with the corresponding target genetic sequence.

http://www.evidenttech.com/why_nano/docs.php

http://www.evidenttech.com/pdf/wp_biothreat.pdfhttp://www.evidenttech.com/why_nano/docs.php

EviDots - Semiconductor nanocrystalsEviFluors- Biologically functionalized EviDotsEviProbes- Oligonucleotides with EviDotsEviArrays- EviProbe-based assay system

Optical Transistor- All optical 1 picosecond performanceTelecommunications- Optical Switching based on EviDotsEnergy and Lighting- Tunable bandgap semiconductor

http://www.evidenttech.com/why_nano/docs.php

http://www.chem.utoronto.ca/staff/GAO/flashed/courses_files/chm238y_4_B.pdf

http://www.chem.utoronto.ca/staff/GAO/flashed/courses_files/chm238y_4_B.pdf

http://nano.ece.uci.edu/Lectures/SiNanocrystals.pdf

http://www.intec.rug.ac.be/horizon/pdf/network/pres_ecoc2002/SINERGIA_ECOC2002.pdf

Comparison of Particle Size and Resulting Photoluminescence

particle size

resulting photoluminescen

ce band peaks

1.0 nm blue (400 nm)

1.67 nmgreen (540

nm)

2.15 nmyellow (570

nm)

2.9 nm red (620 nm)

High quantum efficiency: 50% to 60%.

Ultrabright: several times greater than that of fluorescein or other biological markers.

Long-lasting: Silicon nanoparticles fluoresce up to 100 times longer than other materials used in biological applications.

Selectable photoluminescence: The wavelength varies according to the size of the particles

Easy to use: Differently sized silicon nanoparticles can be excited with a single laser to obtain various colors.

Easy to manufacture: Large quantities of uniformly sized silicon nanoparticles can be produced by making small modifications to the fabrication process.

http://www.otm.uiuc.edu/technology/Silicon-nanoparticles.htm#benefits

Properties and Advantages of Silicon Nanoparticles

Biological Applications

Biosensors,

Imaging,

Targeted drug delivery,

Destruction of pathogens

This technology is an ideal alternative to

common dyes, which can be

toxic,

burn out quickly, and are

difficult to use when labeling

multiple biological materials.

Silicon nanoparticles are

incredibly bright, are

highly photostable, and

can be sized to emit varying photoluminescence in response to a single light source.

Their emission brightness exceeds that of fluorescein in the blue wavelength (400 nm).

http://www.otm.uiuc.edu/technology/Silicon-nanoparticles.htm#benefits

Silicon Nanoparticles for Optical Applications

Lasers, Frequency doublers/mixers, Light amplifiers, Optical interconnects

Bulk silicon and porous silicon are indirect bandgap materials and poor emitters of light.

Silicon nanoparticles produce stimulated emissions significantly greater than Group III-V sources.

Furthermore, they allow luminescent superlattices and microelectronic architectures to be integrated, combining optical and electronic circuits within silicon.

http://www.otm.uiuc.edu/technology/Silicon-nanoparticles.htm#benefits

The process for making the silicon nanoparticles uses highly catalyzed electrochemical etching in hydrofluoric acid (HF) and hydrogen peroxide (H2O2) to disperse crystalline silicon into ultrasmall nanoparticles. The wafer is laterally anodized while being advanced slowly into the etchant, producing a large meniscus-like area. Because HF is highly reactive with silicon oxide, H2O2 catalyzes the etching, producing smaller particles. Moreover, the oxidative nature of the peroxides produces high-quality chemical and electronic samples.

UIUC’s Electrochemical Process for Producing Silicon Nanoparticles

http://www.otm.uiuc.edu/technology/Silicon-nanoparticles.htm#benefits

The pulverized wafer is then transferred to an

ultrasound bath for a brief treatment, under which

the film crumbles into colloidal suspension of ultrasmall blue particles.

Larger particles are less amenable to dispersion due to stronger interconnections.

A post-HF treatment weakens those particles, and then

an ultrasound treatment disperses the particles.

The mix is centrifuged, and the resulting residue contains the largest red particles, while

the suspension contains the green/yellow particles.

The residue is redissolved and sonicated.

The red-emitting particles stay in suspension, while

the green particles may be separated by additional sonication and/or the addition of a drop of HF.

Commercial gel permeation chromatography may be used to separate the particles further, if necessary, or to obtain additional accuracy in separation of the other particles.

The particles are separated into several vials, each containing particles of uniform size, with near 90% to 100% efficiency.

http://www.otm.uiuc.edu/technology/Silicon-nanoparticles.htm#benefits

•Quantum dots are nano-sized deposits of one semiconductor embedded in another semiconductor that has a larger energy bandgap than that of the core.

•Since the dot material has an energy bandgap that is smaller than that of the surrounding material, it can trap charge carriers.

•When a photon arrives at the first dot of two electrically connected quantum dots made of gallium arsenide and aluminum gallium arsenide, it excites an electron into the conduction band of the dot.

•A strong bias voltage between these two quantum dots transfers this electron to the second quantum dot.

•This dot acts as a single-electron transistor, which is switched by the electron to register the photon.

•This one-way transfer of single electrons is crucial because it prevents an excited electron returning to its ground state in the

first quantum dot before it can be registered.

Quantum dots for detection of low energy single photon

http://physicsweb.org/article/news/6/6/1

Put peptide molecules that have very specific protein sequences into semiconductor quantum dots, which then very specifically bind to particular locations on cell surfaces.

By using the molecular-recognition capabilities of peptide molecules, scientists have made selective electrical contacts to neurons. The cadmium sulfide contacts act as photodetectors, allowing researchers to communicate with the cells using precise wavelengths of light.

In the past, a variety of objects have been attached to cells using biorecognition, such as fluorescent dyes, enzymes and radioactive labels.

Relatively large electrode grids have also been implanted into patients to encourage neuron growth over the grid arrays.

There was still about a 1-micron gap between the neurons and the electrodes.

The quantum dot (Schmidt's) method slims that down to 3

nanometers.

Activate neurons with quantum dots

http://www.eetimes.com/story/OEG20011204S0068

Nanoparticles Well Studied in Nanoparticles Well Studied in Isolation…Isolation…Why Nanoparticle Arrays?Why Nanoparticle Arrays?

A: Device Integration

A: New Functionality in Ordered Ensembles

Ar inlet

silicon source rod

Turbopump

graphite crucibleand silicon melt

water cooledCu electrodes

Si nanocrystal synthesis and Si nanocrystal synthesis and classification by size classification by size

nanocrystal aerosol

excess aerosol

•Silicon evaporated in an atmosphere of ultra pure Ar, creating an aerosol

•Nanocrystals synthesized in a clean environment to avoid oxidation

electric field linesparticle trajectories

sample flow, Qs

excess flow, Qe

VDMAsheath flow, Qsh

•Size classification done with a radial differential mobility analyzer (RDMA)

•Before entering RDMA particles are charged

•After classification, particles are deposited on a Si substrate or SiO2 film S.-H. Zhang et al. Aerosol Science and Technology, 23:357-372(1995)

aerosol flow,

Qa

Details of size Details of size classificationclassification

Dp2

E

0 2 4 6 8 10 12 14

x 3x 4x 7 2.8 nm(0.6 nm)

5.2 nm(1.4 nm)

8.0 nm(1.6 nm)

10.8 nm(1.8 nm)

111 V54.1 V24.5 V10.0 V

Nanocrystal Diameter, Dp (nm)

0.0

2.0

4.0

6.0

8.0

Dp1

ve1ve2 ve2 < ve1 Dp2 > Dp1

N/

Dp (

1010

nm

-1 c

m-2)

(charge q)

R.P. Camata et. al. Appl. Phys. Lett. 68 (22), 27 May 1996

Sheath flow

Aerosol particles

Caltech Nanoparticle Memory Caltech Nanoparticle Memory ProjectProject

Previous work:

1 transistor/cell nonvolatile memory with Si nanoparticle floating gate:

•thin tunnel oxide•fast•greater reliability

Materials:AFM Charging of Si Nanoparticles, and Nanoscale Charge Imaging via Electrostatic Force Microscopy

Devices:

D h

(Tiwari et al Appl. Phys. Lett. 68 (10), 4 March 1996)

DhDh

Improved PerformanceNonvolatile Memory

Tip charging of Single Si Tip charging of Single Si nanocrystalsnanocrystals•Scanning tip first

brought to rest above

particle

•Tip lowered toward

sample (change set

point)

•Voltage pulse of

-10- -25V applied

•Tip set point returned

to precharging value

and height changes

monitored

0 10 20 30 40

0.0

0.5

1.0

1.5

2.0

Time after charging (minutes)

Re

lativ

e H

eig

ht

(nm

) -V

Single Particle DischargeSingle Particle Discharge

4 minutes 15 minutes 21 minutes

29 minutes 38 minutes

•Charging trapping state not known in detail•Transport mechanism not well characterized

Where is the charge Where is the charge stored?stored?

defects in oxide?

nanocrystals?

nanoparticle/oxide interface states?

surface states?

Si/SiO2 interface states?

Efm

Ec

Ev

Ef

Flatband Lineup of Si Nanocrystals in SiOFlatband Lineup of Si Nanocrystals in SiO22

Si AFM tip

Si SubstrateSiO2

Ene

rgy

Position

Performance of LPerformance of Leffeff = 0.2 = 0.2 m Nanoparticle Memorym Nanoparticle Memory

Industry News about Industry News about Nanoparticle MemoryNanoparticle Memory

Industry estimates forecast that flash memory revenue will hit $13 billion this year, up from $7.7 billion in 2002, according to Jim Handy, a memory services executive with Semico Research. By 2007, flash memory is expected to be a $43 billion industry.

Chip giant Intel is experimenting with Ovonics Unified Memory, which uses the same material as DVD discs. Motorola,

meanwhile, is looking at silicon nanocrystals, which replace a solid layer inside the transistor with a lattice of silicon atoms. Nanocrystal chips could hit the market by 2006.

Other alternatives being developed include: magnetic RAM (MRAM), which isn't really magnetic; ferroelectric RAM (FeRAM), which involves shifting atoms in a crystal; and polymer memory, which is made from the stuff used in liquid-crystal display screens.

http://news.com.com/2009-1040-994240.htmlBy Michael KanellosStaff Writer, CNET News.com

March 27, 2003, 4:00AM PT

Nanocrystal Shape Control Boosts Efficiency of New Solar Cells

Hybrid nanocrystal-polymer solar cell is made by blending CdSe nanocrystals with P3HT, a conducting polymer, to form a 200 nm thick film sandwiched between an aluminum top contact (orange) and a transparent bottom contact (blue). Nanocrystal shape affects the cell efficiency.

Monochromatic quantum efficiencies of over 50% are achieved by using rod-like nanocrystals that are partially aligned with the path of current flow in the device.

http://www.lbl.gov/~msd/PIs/Alivisatos/02/02-01_Nanosolar.ppt

http://www.qdots.com/new/news/events/mbrucheznihposter.pdf

http://www.qdots.com/new/news/events/mbrucheznihposter.pdf

http://www.qdots.com/new/news/events/mbrucheznihposter.pdf

http://www.qdots.com/new/news/events/mbrucheznihposter.pdf

http://corninfo.chem.wisc.edu/writings/dendrimers.pdf

http://www.physics.purdue.edu/nanophys/laetitia/laetitia-report.pdf

Why nanowires?

“They represent the smallest dimension for efficient transport of electrons and excitons, and thus will be used as interconnects and critical devices in nanoelectronics and nano-optoelectronics.” (CM Lieber, Harvard)

General attributes & desired properties Diameter – 10s of nanometers Single crystal formation -- common crystallographic orientation

along the nanowire axis Minimal defects within wire

Minimal irregularities within nanowire arrays

http://www.me.berkeley.edu/nti/englander1.ppt

http://www.physics.purdue.edu/nanophys/laetitia/laetitia-report.pdf

http://www.physics.purdue.edu/nanophys/laetitia/laetitia-report.pdf

Nanowire fabrication

Challenging! Template assistance Electrochemical deposition

Ensures fabrication of electrically continuous wires since only takes place on conductive surfaces

Applicable to a wide range of materials High pressure injection

Limited to elements and heterogeneously-melting compounds with low melting points

Does not ensure continuous wiresDoes not work well for diameters < 30-40 nm

CVD Laser assisted techniques

http://www.me.berkeley.edu/nti/englander1.ppt

Magnetic nanowires

Important for storage device applications

Cobalt, gold, copper and cobalt-copper nanowire arrays have been fabricated

Electrochemical deposition is prevalent fabrication technique

<20 nm diameter nanowire arrays have been fabricated

Cobalt nanowires on Si substrate(UMass Amherst, 2000)

http://www.me.berkeley.edu/nti/englander1.ppt

Silicon nanowire CVD growth techniques

With Fe/SiO2 gel template (Liu et al, 2001)Mixture of 10 sccm SiH4 & 100

sccm helium, 5000C, 360 Torr and deposition time of 2h

Straight wires w/ diameter ~ 20nm and length ~ 1m

With Au-Pd islands (Liu et al, 2001)Mixture of 10 sccm SiH4 & 100

sccm helium, 8000C, 150 Torr and deposition time of 1h

Amorphous Si nanowiresDecreasing catalyst size seems to

improve nanowire alignmentBifurcation is common30-40 nm diameter and length ~

2m http://www.me.berkeley.edu/nti/englander1.ppt

Template assisted nanowire growth

Create a template for nanowires to grow within

Based on aluminum’s unique property of self organized pore arrays as a result of anodization to form alumina (Al2O3)

Very high aspect ratios may be achievedPore diameter and pore packing densities

are a function of acid strength and voltage in anodization step

Pore filling – nanowire formation via various physical and chemical deposition methodshttp://www.me.berkeley.edu/nti/englander1.ppt

Anodization of aluminum Start with uniform layer of ~1m Al Al serves as the anode, Pt may serve as the

cathode, and 0.3M oxalic acid is the electrolytic solution

Low temperature process (2-50C) 40V is applied Anodization time is a function of sample size and

distance between anode and cathode Key Attributes of the process (per M. Sander)

Pore ordering increases with template thickness – pores are more ordered on bottom of template

Process always results in nearly uniform diameter pore, but not always ordered pore arrangement

Aspect ratios are reduced when process is performed when in contact with substrate (template is ~0.3-3 m thick)

Al2O3 template preparation

http://www.me.berkeley.edu/nti/englander1.ppt

(T. Sands/ HEMI group http://www.mse.berkeley.edu/groups/Sands/HEMI/nanoTE.html)

The alumina (Al2O3) template

100nmSi substrate

alumina template

(M. Sander)http://www.me.berkeley.edu/nti/englander1.ppt

Works well with thermoelectric materials and metals

Process allows to remove/dissolve oxide barrier layer so that pores are in contact with substrate

Filling rates of up to 90% have been achieved

(T. Sands/ HEMI group http://www.mse.berkeley.edu/groups/Sands/HEMI/nanoTE.html)

Bi2Te3 nanowireunfilled pore

alumina template

Electrochemical deposition

http://www.me.berkeley.edu/nti/englander1.ppt

Template-assisted, Au nucleated Si nanowires

Gold evaporated (Au nanodots) into thin ~200nm alumina template on silicon substrate

Ideally reaction with silane will yield desired results

Need to identify equipment that will support this process – contamination, temp and press issues

Additional concerns include Au thickness, Au on alumina surface, template intact vs removed

100nm1µm

Au dots

template (top)

Au

(M. Sander)http://www.me.berkeley.edu/nti/englander1.ppt

Nanometer gap between metallic electrodes

Electromigration caused by electrical current flowing through a gold nanowire yields two stable metallic electrodes separated by about 1nm with high efficiency. The gold nanowire was fabricated by electron-beam lithography and shadow evaporation.

Before breaking

After breaking

http://www.lassp.cornell.edu/lassp_data/mceuen/homepage/Publications/EMPaper.pdf

SET with a 5nm CdSe nanocrystal

Nanoscale size exhibits the following properties different from those found in the bulk:

quantized conductance in point contacts and narrow channels whose characteristics (transverse) dimensions approach the electronic wave length

Localization phenomena in low dimensional systems

Mechanical properties characterized by a reduced propensity for creation and propagation of dislocations in small metallic samples.

Conductance of nanowires depend on

the length,

lateral dimensions,

state and degree of disorder and

elongation mechanism of the wire.

Quantum and localization of nanowire conductance

http://dochost.rz.hu-berlin.de/conferences/conf1/PDF/Pascual.pdf

Conductance during elongation of short wires exhibits periodic quantization steps with characteristic dips, correlating with the order-disorder states of layers of atoms in the wire.

The resistance of “long” wires, as long as 100-400 A exhibits localization characterization with ln R(L) ~ L2

Short nanowire “Long” nanowire

http://dochost.rz.hu-berlin.de/conferences/conf1/PDF/Pascual.pdf

Electron localization

At low temperatures, the resistivity of a metal is dominated by the elastic scattering of electrons by impurities in the system. If we treat the electrons as classical particles, we would expect their trajectories to resemble random walks after many collisions, i.e., their motion is diffusive when observed over length scales much greater than the mean free path. This diffusion becomes slower with increasing disorder, and can be measured directly as a decrease in the electrical conductance.

When the scattering is so frequent that the distance travelled by the electron between collisions is comparable to its wavelength, quantum interference becomes important. Quantum interference between different scattering paths has a drastic effect on electronic motion: the electron wavefunctions are localized inside the sample so that the system becomes an insulator. This mechanism (Anderson localization) is quite different from that of a band insulator for which the absence of conduction is due to the lack of any electronic states at the Fermi level.

http://www.cmth.ph.ic.ac.uk/derek/research/loc.html

Molecular nanowire with negative differential resistance at room temperature

http://research.chem.psu.edu/mallouk/articles/b203047k.pdf

ErSi2 nanowires on a clean surface of Si(001). Resistance of nanowire vs its length.

ErSi2 nanowire self-assembled along a <110> axis of the Si(001) substrate, having sizes of 1-5nm, 1-2nm and <1000nm, in width, height, and length, respectively. The resistance per unit length is 1.2M/nm

along the ErSi2 nanowire. The resistivity is around 1cm, which is 4 orders of magnitude larger than that for known resistivity of bulk ErSi2, i.e., 35 cm. One of the reasons may be due to an elastically-elongated lattice spacing along the ErSi2 nanowire as a result of lattice mismatch between the ErSi2 and Si(001) substrate.

http://www.riken.go.jp/lab-www/surf-inter/tanaka/gyouseki/ICSTM01.pdf

Resistivity of ErSi2 Nanowires on Silicon

Last stages of the contact breakage during the formation of nanocontacts.

Electronic conductance through nanometer-sized systems is quantized when its

constriction varies, being the quantum of conductance, Go=2 e2/h, where e is the electron charge and h is the Planck constant, due to the change of the number of electronic levels in the constriction.

The contact of two gold wire can form a small contact resulting in a relative low number of eigenstates through which the electronic ballistic transport takes place.

Conductance current during the breakage of a nanocontact. Voltage difference between electrodes is 90.4 mV

http://physics.arizona.edu/~stafford/costa-kraemer.pdf

Setup for conductance quantization studies in liquid metals. A micrometric screw is used to control the tip displacement.

Evolution of the current and conductance at the first stages of the formation of a liquid metal contact. The contact forms between a copper wire and (a) mercury (at RT) and (b) liquid tin (at 300C). The applied bias voltage between tip and the metallic liquid reservoir is 90.4 mV.http://physics.arizona.edu/~stafford/costa-kraemer.pdf

Conductance transitions due to mechanical instabilities for gold nanocontacts in UHV at RT: Transition from nine to five and to seven quantum channels.

Conductance transitions due to mechanical instabilities for gold nanocontacts in UHV at RT: (a) between 0 and 1 quantum channel. (b) between 0 and 2 quantum channels.

http://physics.arizona.edu/~stafford/costa-kraemer.pdf

http://www.physics.purdue.edu/nanophys/laetitia/laetitia-report.pdf

http://www.physics.purdue.edu/nanophys/laetitia/laetitia-report.pdf

http://www.physics.purdue.edu/nanophys/laetitia/laetitia-report.pdf

http://www.physics.purdue.edu/nanophys/laetitia/laetitia-report.pdf

http://www.physics.purdue.edu/nanophys/laetitia/laetitia-report.pdf

http://www.physics.purdue.edu/nanophys/laetitia/laetitia-report.pdf

http://www.physics.purdue.edu/nanophys/laetitia/laetitia-report.pdf

http://www.physics.purdue.edu/nanophys/laetitia/laetitia-report.pdf

http://www.physics.purdue.edu/nanophys/laetitia/laetitia-report.pdf

http://www.physics.purdue.edu/nanophys/laetitia/laetitia-report.pdf