Nano Education (1)

7/30/2019 Nano Education (1)

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Alexander A. BalandinNano-Device Laboratory

Department of Electrical Engineering

Materials Science and Engineering Program

University of California Riverside

Advanced Nanomaterials


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Alexander A. Balandin

UCR Bell Tower

City of Riverside

UCR Botanic Gardens

Joshua Tree Park, Californ ia

UCR Engineering Building


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Nano-Device Laboratory (NDL)Department of Electrical EngineeringUniversity of California Riverside

Profile: experimental and theoretical research in nano materials and devices

Research at NDL has been

funded by NSF, ONR, SRC,

DARPA, NASA, ARO, AFOSR,

CRDF, as well as industry,

including IBM, Raytheon and

TRW

Research &Appl ications

Raman, Fluorescence

and PL Spectroscopy

Electronic

Devices and

Circuits

Optoelectronics

Direct Energy

Conversion

Bio-

Nanotech

Thermal and Electrical

Characterization

Device Design and

Characterization

Nanoscale Characterization

Theory and

Modeling

Prof. A.A. Balandin

about the lecturer


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Outline of the Lecture

Introduction new materials and nanotechnology

Biological Objects as Nanotemplates growth and characterization hybrid bio-inorganic structures

Quantum Dots properties applications in solar cells and thermoelectrics

Carbon Materials diamond; graphite; amorphous carbon; etc.

Carbon Nanotubes properties and applications

Graphene nanometrology of graphene graphene applications

Conclusions


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Materials and Nanotechnology

Part I


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Why New Materials are Important?

Electronics: Silicon (Si) and SiO2 Optoelectronics: GaAs and other direct

band-gap semiconductors

Thermoelectrics: bismuth telluride (Bi2Te3)

Photovoltaic solar cells: poly-Si Coating: diamond-like carbon (DLC)


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How small is a nanometer?1 nanometer = 10-9 meter

10,000X smaller than the diameter of human hair.

Nanotechnology = development offunctional devices at

the length scale of approximately 1 - 100 nm range (100s atoms)Latest generation computer logic devices (Intel, AMD) are < 50 nm

and therefore they are in the realm of nanotechnology.

Breaking down of traditional and artificial barriers between

scientific disciplines.Use knowledge of Biology, Chemistry, Physics, Engineering

to develop useful technologies.

Top downand bottom upapproaches

Nanotechnology and New Materials


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Examples of Major Innovations atMaterials Level

Information from Intelweb-site

http://download.intel.com/technology/silicon/HighK-MetalGate-PressFoils-final.pdf


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Examples of Innovations at theMaterials Level: Solar Cells

Quantum dot

superlattice as

an intrinsic

layer

Front contact

n type

p type

Light coating

Back contactShockley limit: ~33% conversion efficiencyfor bulk materials due to the loss of excess

kinetic energy of the hot photo-generatedcarriers and energy loss of photons whichare less than materials band gap.

Thermodynamic limit for conversion: ~93%

Q. Shao, A.A. Balandin, A.I. Fedoseyev and M. Turowski,

"Intermediate-band solar cells based on quantum dot supra-crystals,"Appl ied Physics Letters, 91: 163503 (2007)


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Biological Objects asTemplates for Nanofabrication

Part II


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Hybrid Virus-Inorganic Nanostructures

Plant Viruses as Nano-Templates

Nanofabrication Benefits:suitable dimensionssmall size dispersionselective attachment

SEM of a pure TMV and TMV end-to-endassembly (left); nanowire interconnectmade of metal coated TMV assembly (right).

W.L. Liu, A.A. Balandin, et al.,Appl. Phys. Lett.,86, 253108 (2005).


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Nanofabrication Using Virus Nano-Templates

X-Ray Characterization

Pl

TEM micrograph of the pure TMV and metal coated TMV. Scalebar is 50 nm. Nano-Device Laboratory (NDL), UCR, 2005.

Nanostructure Growth:

University of California Riverside (UCR), 2005


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Analysis of Optical Phonons in Hybrid Bio-Inorganic Nanostructures

800 1000 1200 1400 1600 1800

0

10000

TMV-Au

TMV-Pt

Pheres(1005cm-1)

C-Hdef(1

332cm-1)

C-Hdef(1

454.5cm-1)

I

ntensitty(a.u.)

Raman Shift (cm-1)

AmideI(1655cm-1)

TMVRaman spectra of TMV, Pt coated TMV and Au

coated TMV: the Amide I line at 1655cm-1

, C-Hdeformation lines at 1454.5cm-1 and 1332cm-1,and the phenylalanine residue line at 1005cm-1.The Amide I lines of TMV-Pt and TMV Au are at1664cm-1 and 1672cm-1respectively.

Amide I line is related to TMV coat protein capsid, the line shi ft

indicates the change of vibrational modes due to the binding ofmetal with certain functional group in the shell protein .

Note: water is strong infrared (IR) absorbingmedium, and generally Raman is better thanFourier transform infrared (FTIR) methods.

Measured spectra under 488 nm excitation;room temperature; backscattering configuration.


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Mobility Increase Via Electron PhononScattering Suppression

Log-log plot of the electron-phonon scattering rates (T = 1K) for TMV/silicon and empty silicon nanotubes as a functionof the electron energy above the band gap.

*

e

m=

V.A. Fonoberov and A.A. Balandin,Nano Letters, 5, 1920 (2005).

Log-log plot of the low-field acoustic-phonon limited electronmobility for TMV/silicon and empty silicon nanotubes.

Phonon Transport Regimes

Low Energy


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Quantum Dots: Properties andApplications

Part III


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30 nm

Cross-sectional TEM of MBEgrown Ge/Si QDS. Sample:Prof. J ianlin Liu (UCR)

Quantum Dot Superlattices:Terminology and Assumptions

In-plane ordering of quantum dot isnot implied by the term QDS.Periodicity of the layers along thegrowth direction is normally implied.

Si layer

GexSi1-xquantumdots

Substrate

Schematic of Ge/Si QDS.

Electrons: Variation of the energy band gap and/or band offset

Phonons: Variation of the elastic constants and/or mass density

Ordered quantum dot array grown byelectrochemistry. After A.A. Balandin, etal.,Appl. Phys. Lett., 76, 137 (2000).

AFM of image of InAs QDs grown on Si (100) substrate.

After K.L. Wang and A.A. Balandin, Quantum Dots:Physics and Applications (Wiley, 2001).


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Conventional Quantum Well Superlattices:Mini-Band Formation

From P. Yuh and K.L. Wang, Phys.

Rev. B, 38, 13307 (1988)

MultipleQuantum WellStructure

Quantum Well Superlattice

Wave functionoverlapmini-band formation

superlattice implies periodicity and strong W.F. overlap

AlGaAs

AlGaAsGaAs

Z AxisW

Quantum well

Z Axis

EE202 Fundamentals of

Semiconductors andNanostructures


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Motivations for the Quantum DotResearch: Applications Driven

Al ternative inexpensivefabrication of QDs:

electrochemical self-assembly

Infrared (IR) and Near IR

Photodetectors; QD Lasers;

LEDs; QD Quantum

Cascade Lasers

Photovoltaic Applications of QDS

Electronic and Spintronic Application of QDs

Encoding informationwith charge and spinstates localized in QD:low power; ultra fast;ultra-high density; logicand memory; single-electron transistor

Appl ications of QDs in

Nonlinear Optics

III-V QDs integratedon Si substrates

TEM ofcolloidalZnO QD

Strong optical non-linearity: frequencyup-conversion; THz radiation; ultra-

fast all optical-switching

Increasedefficiency andradiation hardness

QDS Thermoelectric Applications


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Solar Cell Applications of QDS

Quantum dot

superlattice as

an intrinsic

layer

Front contact

n type

p type

Light coating

Back contact

Shockley limit: ~33% conversionefficiency for bulk materials dueto the loss of excess kineticenergy of the hot photo-generated carriers; energy loss

of photons which are less thanmaterials band gap; andradiative recombination

Thermodynamic limit forconversion: ~93%

43% conversion efficiency oftwo-gap tandem solar cells hasbeen reported.

QDS-based PV cell: 24.6%efficiency as reported by S.Suraprapapich et al., SolarEnergy Materials (2006)


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Suggested Mechanisms for the PVEfficiency Improvement in QDS Solar Cells

4 6 8 10 12 14 16 18 20

0.4

0.6

0.8

1.0

1.2

1.4

InAs Bulk

GaAs Bulk

Band-gapEnergy(eV)

InAs Quantum Dot Size (nm)

)11

(8 **2

2

heQD

gmmd

hE +=

Tunable effective band-gap and multicolor / tandemdesigns for increased efficiency

A. Mart et al, Novel semiconductor solar cell structures: Thequantum dot intermediate band solar cell, Thin Solid Films,511-512 (2006) 638-644

Intermediate band assisted absorption / three-

level concept

Improved radiation hardness

R. Leon et al., Changes in luminescence emission inducedby proton irradiation: InGaAs/GaAs quantum wells and

superlattices,App. Phys. Lett., 76, 2075 (2000).

Light trapping and absorption of normallyincident light / quasi-direct band gap

M.A. Green, Prospects for photovoltaic efficiency enhancementusing low-dimensional structures,nanotechnology, 11, 401 (2000).

three-levelconcept


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Charge Carrier Mobility in Ge/Si QuantumDot Superlattices: Transport Regime

Hall Mobility Measurements Results

band-type rather than hopping type electron conduction:

~T-3/2 not G~Goexp{-(To/T)x}

30 nm

dot density 3.5-30.0 x 108 cm-2; dot base: 40 nm 120nm; aspect ratio: ~10

H=|RH|, where RH=(p-nb2)/[e(p+nb)2], and b=e/h rat io of dr if tmobilities; RH>0 p-type conduction; B=0.37 T

Y. Bao, A.A. Balandin, J .L. Liu and Y.H. Xie,

Applied Physics Letters, 84: 3355 (2004).


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Efficiency Calculation for IB Solar Cells

A. Luque, and A. Marti, Phys. Rev. Lett. 78, 5014 (1997).

Q. Shao, A.A. Balandin, A.I. Fedoseyev and M.Turowski, "Intermediate-band solar cells based onquantum dot supra-crystals," Applied Physics Letters, 91:163503 (2007).I intermediate band position

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

20

30

40

50

60

70 Three band

Single gap

Ts=6000K

Tc=300K

2.52.3(GaP)2.01.81.6

1.3(InP)1.4(GaAs)

1.1(Si)

Efficiency(%)

Energy I(eV)


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Optimization of Intermediate Band in QDS

Minibands formed in InAs0.9N0.1/GaAs0.98Sb0.02quantum dot supra-crystal along [(100)] quasi-crystallographic direction. Optimized parameters:

L=4.5nm, H=2nm.

0.0 0.1 0.2 0.3 0.40.60

0.62

0.64

1.1

1.2

1.3

1.4

1.5

VB

111

112

211

0.2eV

0.03eV

Electron

Energy(eV)

q100

(nm-1)

1.48eV

1.29eV

1=0.03eV

E23=0.58e

V

0.19eV

2=0.20eV

E12=0.80e

V

GaAs0.98Sb0.02 GaAs0.98Sb0.02InAs0.9N0.

1

E13=1.41eV

111

211&112


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Fine-Tuning QDS for Solar Cell Applications

3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6

44

45

46

47

48

49

50

51

Efficiency(%)

Dot Size (nm)

H=1.5nm

H=2.0nmH=2.5nm

0.62 0.64 0.66 0.68 0.700.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Den

sityofStates(1020cm

-3eV-1)

Electron Energy (eV)

111

Electron DOS in the mini-band 111 serving asan intermediate band in the QDS solar cell.

Upper Bound Detailed-BalanceEfficiency

Q. Shao, A.A. Balandin, A.I. Fedoseyev and M. Turowski,

"Intermediate-band solar cells based on quantum dot supra-crystals," Applied Physics Letters, 91: 163503 (2007).


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Can QDS Help with ThermoelectricApplications?

ZT increase: carrier confinement

Change in carrier DOS near EF Semimetal semiconductor transitions

Scattering rates

2D is better than bulk 1D is better than 2D Is quais-0D better than 1D??? you needmini-band transport regime

ZT increase: thermal conductivity

Increased phonon interface scattering:thickness W phonon MFP

Decreased phonon group velocity duephonon confinement: ~ W


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Strong ZT Increase is Possible inOptimized Quantum Dot Superlattice

2

e ph

TZT

=

+

Thermoelectric Figure of

Merit Z:

- Seebeck coefficient

electrical conductivity

thermal conductivity

T absolute temperature

10-3

10-2

10-1

1

10

102

-0.1-0.2 0 0.1 0.2-0.3

QDS with bulklattice thermalconductivity of156 W m-1K-1

QDS with reduced lattice thermalconductivity of 15 W m-1K-1

Fermi Energy (eV)

ZTQDC/ZTB

mini-bandtransportregime

Enhancement of the thermoelectric figure of merit throughthe electron and phonon dispersion engineering in QDS

A.A. Balandin and O.L. Lazarenkova,Applied Physics Letters, 82: 415 (2003).


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Thermal Conduction inNanostructured Materials

Cr/Au heater-

thermometer

sensors

patterned on top

of the samples by

photolithography.

Home-Buil t 3- ThermalConductivity Setup Transient Plane Source (TPS) Technique

0 1 2 3 4 50.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

Measurement Time: 5 s

Dissipated PowerSample: 0.05 WSi Wafer: 0.5 W

TEMPERATURERISE(oC)

TIME (s)

SILICON REFERENCESAMPLE

Thermal

conductivityand heat

capacity

extraction

from the T(t)

dependence.


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Thermal Conduction in QDS asPhonon Hopping Transport

0 100 200 300 4000

4

8

12

Ther

malConductiv

ity(W/mK)

Temperature (K)

Sample A (Ge 1.8 nm)

Sample B (Ge 1.5 nm)

Sample C (Ge 1.2 nm)

t=0.232

t=0.178

t=0.151

0.0 0.2 0.4 0.6 0.8 1.0

10-3

10-2

10-1

100

K/K

bulk

Hopping Parameter t

100K-mod. 200K-mod.

300K-mod. 400K-mod.

100K-exp. 200K-exp.

300K-exp. 400K-exp.

d=100nm

d=10m

Measured and Calculated Thermal ConductivityTransition to the Bulk Limit

Bulk limit: t very large or d very large

M. Shamsa, W.L. Liu, A.A. Balandin and J.L. Liu

Applied Physics Letters, 87: 202105 (2005).


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Overview of Carbon Materials

Part IV


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Carbon: Basic Properties

Carbon is a chemical element with the symbol C and atomic number 6. It is a group 14, nonmetallic,

tetravalent element, that presents several allotropic forms of which the best known are graphite (thethermodynamically stable form under normal conditions), diamond, and amorphous carbon. There arethree naturally occurring isotopes: 12C and 13C are stable, and 14C is radioactive, decaying with a half-life of about 5700 years.

Atomic number: 6

Atomic weight: 12.011

Oxidation states: 2, 4, -4

Electron configuration: [He]2s22p2

PSiAlNCB

Carbon is present as carbon dioxide in the atmosphere and dissolved inall natural waters. It is a component of rocks as carbonates of calcium(limestone), magnesium, and iron. Coal, petroleum, and natural gas arechiefly hydrocarbons. Carbon is unique among the elements in the vastnumber of variety of compounds it can form. Organic chemistry is thestudy of carbon and its compounds.

http://www.webelements.com/webelements/elements/text/C/key.html


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Allotropes of Carbon

Eight allotropes of carbon: a) Diamond, b)

Graphite, c) Lonsdaleite, d) C60

(Buckminsterfullerene or buckyball), e) C540, f)

C70, g) Amorphous carbon, and h) single-walled

carbon nanotube (CNT)

http://www.dendritics.com/scales/c-allotropes.asp

http://cst-www.nrl.navy.mil/lattice/struk/carbon.htmlhttp://en.wikipedia.org/wiki/Allotropes_of_carbon


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Electronic Applications of Diamond

relevant diamond properties:

EB=107 V/cm

V.A. Fonoberov and A.A.Balandin, "Giant enhancement ofthe carrier mobility in siliconnanowires with diamond coating,"Nano Letters, 6: 2442 (2006)

Enhancement of electron

mobility in silicon nanowires

coated with diamond


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200 40010

-3

10-2

10-1

100

101

102

Hopping Model (22nm, t=0.32)

Hopping Model (26nm, t=0.2)

Minimum K for Carbon

Hopping Model (2m, t=0.9)

Bulk Diamond: Callaway Model

The

rmalConductivity(W/cmK)

Temperature (K)

PolyNCD_25NCD_0

SEM of nanocrystallinediamond film on siliconsubstrate.

Microcrystalline Diamond Films

W.L. Liu, M. Shamsa, V. Ralchenko, A.Popovich, A. Saveliev, I. Calizo, and A.A.Balandin,Appl. Phys. Lett. 89, 171915 (2006).

SEM of 30-m thickpolycrystalline

diamond (top) onsilicon substrate(bottom).


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Diamond-like Carbon: Propertiesand Applications

Main application:coating

Diamond-like carbon (DLC) isan amorphous carbon with asignificant fraction of C-C sp3bonds

DLCs with the highestsp3content are called tetrahedralamorphous carbons (ta-C)

J . Robertson, Semicond. Sci. Technol. 18, S12 (2003)

graphitic C

Diamond-like C

sp2

sp3

H

a-C:H

no films

polymers

ta-C:Hta-C

sputtered a-C


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Properties and Applications ofCarbon Nanotubes

Part V


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Carbon nanotubes are molecular-scale tubes of graphitic carbon with outstanding properties.

They are among the stiffest and strongest fibers known, and have remarkable electronicproperties and many other unique characteristics. For these reasons they have attracted hugeacademic and industrial interest. Commercial applications have been rather slow to develop,however, primarily because of the high production costs of the best quality nanotubes.

Basics of Carbon Nanotubes

1985: discovery of

buckminsterfullerene C60and other fullerenes

1990: discovery of carbonnanotubes using arc-evaporation apparatus

TEM of multi-wall carbon nanotubes (MW-CNTs)

Diameter of MW-CNTs: 3 30 nm

Diameter of SW-CNT: 1-2 nm

Bonding: sp2 with each atomjoined to three neighbors as ingraphite

http://www.dendritics.com/scales/c-allotropes.asp

http://cst-www.nrl.navy.mil/lattice/struk/carbon.html


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Different Types of Nanotubes

SWNTs have a diameter of close to 1 nm with a tube length thatcan be many thousands of times longer.

The structure of a SWNT can be conceptualized by wrapping aone-atom-thick layer of graphite called graphene into a seamlesscylinder.

The way the graphene sheet is wrapped is represented by a pairof indices (n,m) called the chiral vector. The integers n and m

denote the number of unit vectors along two directions in thehoneycomb crystal lattice of graphene. If m=0, the nanotubes arecalled "zigzag". If n=m, the nanotubes are called "armchair".Otherwise, they are called "chiral".


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CNTs are the strongest andstiffest materials on earth, interms of tensile strength andelastic modulus respectively.CNT can be metallic orsemiconducting, depending on

chirality.CNTs have extremely highthermal conductivity

Properties of Carbon Nanotubes

Material Young's Modulus (TPa) Tensile Strength (GPa)

SWNT ~1 (from 1 to 5) 13-53Armchair SWNT 0.94 126.2

MWNT 0.8-0.9 150

Stainless Steel ~0.2 ~0.65-1

Possible applications: electronic; mechanical;thermal management


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Synthesis of Carbon Nanotubes

Arc Discharge

Nanotubes were observed in 1991 in the carbon soot of graphiteelectrodes during an arc discharge by using a current of 100amps. During this process, the carbon contained in the negativeelectrode sublimates because of the high temperatures causedby the discharge. Because nanotubes were initially discoveredusing this technique, it has been the most widely used method of

nanotube synthesis. The yield for this method is up to 30 percentby weight and it produces both single- and multi-wallednanotubes with lengths of up to 50 microns.

Laser Ablation

In this method the pulsed laser vaporizes a graphite target in a high temperature reactor while an

inert gas is bled into the chamber. The nanotubes develop on the cooler surfaces of the reactoras the vaporized carbon condenses. It was invented by Richard Smalley and co-workers at RiceUniversity. This method has a yield of around 70% and produces primarily single-walled carbonnanotubes with a controllable diameter determined by the reaction temperature. However, it ismore expensive than either arc discharge or CVD.


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Chemical Vapor Deposition

Chemical Vapor Deposi tion: CVD

During CVD growth a substrate is prepared with a layer of metalcatalyst particles, usually nickel, cobalt, iron, or a combination.

The diameters of the nanotubes that are to be grown are relatedto the size of the metal particles. This can be controlled bypatterned or masked deposition of the metal, annealing, or by

plasma etching of a metal layer. The substrate is heated toapproximately 700C. To initiate the growth of carbonnanotubes, two gases are bled into the reactor: a process gas(such as ammonia, nitrogen, hydrogen, etc.) and a carbon-containing gas (such as acetylene, ethanol, methane, etc.).Nanotubes grow at the sites of the metal catalyst; the carbon-containing gas is broken apart at the surface of the catalyst

particle, and the carbon is transported to the edges of theparticle, where it forms the nanotubes. CVD is the mostpromising method for industrial scale deposition in terms of itsprice and flexibility. Unlike other methods CVD is capable ofgrowing nanotubes directly on a desired substrate.

thermal evaporator


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Tip Growth Base Growth

CxHy CxHy

MCy

- H2

CxHy CxHyMCy

- H2

- H2

Typically occurs when there are

very weak metal-surface interactions

Occurs when the metal-surface

interactions are strong

M = Fe, Ni, Co, Pt,Rh, Pd and others

Adsorption and decomposition of feedstock on the surface of the catalyst particle

Diffusion of carbon atoms into the particle from the supersaturated surface

Carbon precipitates into a crystalline tubular form

CVD Growth Mechanisms forCarbon Nanotubes


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Alexander A. Balandinwww.intel.com/research/silicon/90nm_press_briefing-technical.htm

1970 1980 1990 2000 2010 2020

0.1

10

1

0.01

Length(m)

Year

Unexpected Acceleration of Moores Law

silicide

1.2nmSiO2

Strained Si

GateLength

State of Art MOSFET

Source Drain

Motivations for the ElectronicApplications of Carbon Nanotubes


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silicon metal interconnects interlevel dielectrics

gate dielectric

Min thickness?

Poly SiGate

Source Drain

1.2 nm GateOxideSiO2

switching energy, a transient

time,

thermal conductance, dopantfluctuations

Materials Limits of ConventionalCMOS Technology

www.intel.com/research/silicon/90nm_press_briefing-technical.htm


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CNT quantum wire interconnects

Diodes and transistors forcomputing

Data Storage

Field emitters for instrumentation

Flat panel displays

THz oscil lators

Challenges Control of diameter, chirality Doping, contacts Novel architectures (not CMOS based!)

Development of inexpensive manufacturing processes

V0 VDD

Carbon nanotube

Vin

Applications: Electronics


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High strength composites

Cables, tethers, beams

Functionalize and use as polymer back bone

Heat exchangers, radiators, thermal barriers

Radiation shielding

Filter membranes, supports

Body armor, space suits

Challenges- Control of properties, characterization

- Dispersion of CNT homogeneously in host materials

- Large scale production

- Application development

Applications: Structural andMechanical


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Carbon Nanotubes for ThermalManagement Applications

New techniques for thermal management with nanocomposite polymers use lowpercentages of dispersed carbon nanotubes. Materials are prepared usingconventional polymer processing techniques.

Thermal Grease Appl ications:

CPUs for desktop and notebook computers and servers

Chipsets and power components

Thermally Conductive Gap Fillers

Applications:

Notebook and desktop computersHandheld microprocessor devices

Telecommunications hardware

Memory modules

Power conversion equipment

Flat panel displays

Audio and video components


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Carbon Nanotube Composites

0.320.320.27Thermal conductivity

K (W/mK)

0.05

(above)

0.5

(above)

0.004

(below)

Percolation

p (wt %)

MWCNT

composite

SWCNTcomposite

SWCNTcomposite

Sample

Characteristic

Carbon nanotube suspensions and composites

Preliminary results of the hot-disk measurements

Experimental Observations:

Significant discrepancy in the reported values

Aligned vs disordered CNT networks

Different effect of MWCNT and SWCNT

Theoretical

considerations:

Effectivemediumapproximation [C.-W. Nan et al., CPL,375, 666 (2003)]:fails to explainexperimental data

Percolationtheory description

[M. Foygel et al.,PRB, 71, 104201(2005)]: improvedphysics


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CNT based microscopy: AFM, STM

Sensors: force, pressure, chemical

Biosensors

Molecular gears, motors, actuators

Batteries, Fuel Cells: H2, Li storage

Nanoscale reactors, ion channels

Biomedical- Lab on a chip- Drug delivery- DNA sequencing- Artificial muscles, bone replacement,

bionic eye, ear...

Challenges Controlled growth

Functionalization with

probe molecules

Robustness

Integrat ion

Signal processing Fabrication techniques

Applications: Sensors, NEMS, Bio


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Carbon nanotubes viewed as the ult imate nanofibers ever made Carbon fibers have been already used as reinforcement in high strength, light

weight, high performace composites:

- Expensive tennis rackets, air-craft body parts

Nanotubes are expected to be even better reinforcement

- C-C covalent bonds are one of the strongest in nature

- Youngs modulus ~ 1 TPa the in-plane value for defect-free graphite Problems- Creating good interface between CNTs and polymer matrix necessary

for effective load transfer

CNTs are atomically smooth; h/d ~ same as for polymer chains CNTs are largely in aggregates behave differently from individuals

Solutions

- Breakup aggregates, disperse or cross-link to avoid slippage

- Chemical modification of the surface to obtain strong interface with

surrounding polymer chains

WHY?

Application: PolymerNanocomposites


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High aspect ratio allows percolation at lower compositions than spherical fillers(less than 1% by weight)

Neat polymer properties such as elongation to failure and optical transparency

are not decreased.

ESD Materials: Surface resistivity should be 1012

- 105 /sq

- Carpeting, floor mats, wrist straps, electronics packaging

EMI Applications: Resistivity should be < 105 /sq- Cellular phone parts

- Frequency shielding coatings for electronics

High Conducting Materials: Weight saving replacement for metals

- Automotive industry: body panels, bumpers (ease of painting without a

conducting primer)

- Interconnects in various systems where weight saving is critical

Conducting Polymers Basedon Carbon Nanotubes


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Carbon nanotubes can be embedded in high performance

composites as reinforcing agents and strain sensors allowing for

nondestructive monitoring and distributed sensing of large

structures

SWNT fibers with 60% wt SWNT tensile strength similar to spider silk- These fibers can be woven into textiles to create garments

with sensing and EMI shielding capabilities.

Thermally conductive coatings (with nanotubes incorporated into

polymers)

- Deicing aircrafts in cold weather by applying current to the

coatings

Smart Materials and SpecialCoatings


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Graphene: The UnrolledCarbon Nanotube

Part VI


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Graphene: the Unrolled CarbonNanotube

Individual atomic layers of sp2-

hybridized carbon bound in two-

dimensions. Crystalline graphite, the

most thermodynamically stable from

of carbon, is composed of graphene

layers.

Graphene Revolution brought

about by K.S. Novoselov and A.K.

Geim with the help of bulk graphite

and Scotch tape.

Novoselov, et al., Science(2004)


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The Unexpected Discovery

R.E. Peierls (1934) and L.D. Landau (1937): Strictly 2D crystals cannot exist: thermal fluctuations should destroy the

order resulting in melting 2D lattice at any finite temperature

N.D. Mermin and H. Wagner (1966): Magnetic long-range order does not exist in 2D

Experimental observations were in agreement: Below a certain thickness (~10 atomic layers), the films become

thermodynamically unstable and segregate into islands or decompose

The way around the theory predictions: Theory prohibits perfect 2D crystals but does not prohibit nearly perfect 2D

crystals in 3D space Bending and microscopic roughening can stabilize 2D crystals


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Counting Graphene Layers

Optical visualization on magicsubstrates

Single LayerGraphene

Bi-LayerGraphene

AFM inspection does notsolve the problem

Alternatives: low-temperature transportstudy or cross-sectional TEM


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Raman Spectroscopy of Graphene

1200 1400 1600 1800 2000 2200 2400 2600 2800 30000

5000

10000

15000

20000

25000

30000

35000

40000

2708 cm-1

2691 cm-1

1580 cm-1

Intensity(a

rb.units)

Raman Shift (cm-1)

1582 cm

-1

G peak 2D peak

single layer

bi-layer

A.C. Ferrari et al., Phys. Rev. Lett. 97, 187401 (2006).

I. Calizo et al., Nano Letter7, 2645 (2007)

Backscattering Configuration

Excitation: 488 nm


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2D-band features of graphene are highly reproducible

and, together with the G-peak position, can be used to

count the number of graphene layers.

Raman Spectroscopy asNanometrology Tool

2300 2400 2500 2600 2700 2800 2900 30000

4000

8000

12000

16000

20000

24000

Intensity(arb.units)

Raman Shift (cm-1)

Graphene @ 300Kexc

= 488 nm

1 layer

2 layers

3 layers

4 layers

5 layers

2600 2650 2700 2750 28000

2500

5000

7500

10000

12500

15000


Raman Shift (cm-1)

Experimental ResultFitted ResultLorentzian Peaks

exc

=488 nm

5 layers

4 layers

3 layers

2 layers

1 layer

Nanometrology is the science of

measurement at nanometer scale


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Substrate Effect on Graphene

1000 1500 2000 2500 30003000

4000

5000

6000

7000

8000

Intensity(arb.u

nits)

Raman Shift (cm-1)

graphene layers on n+

GaAs substrateexcitaion: 488 nm

G peak: 1580 cm-1

2D band: ~ 2736 cm-1

2D-band features: indicate five-layer graphene

Spectra does not change much for GaAs substrate

Note: it is not obvious that the Raman features remain the

same when you place graphene on arbitrary substrate graphene - substrate coupling


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Counting the Number of AtomicPlanes in Graphene Layers

2640 2660 2680 2700 2720 2740 2760

4000

6000

8000

10000

12000

2720 cm-1

2698 cm-1

2688 cm-1

2667 cm-1

2D-band region

488 nm excitation

bi-layer grapheneon Si/SiO

2

bi-layer grapheneon glass

INTENSITY(ARB

UNITS)

RAMAN SHIFT (cm-1)

2D = 26911 layer

2D1B = 2661, 2D1A = 2688, 2D2A =

2706, 2D2B = 2719

2 layers

D2A = 2697, D2B = 27193 layers

D2A = 2702, D2B = 27324 layers

D2A = 2728, D2B = 27625 layers

2D Peak Features (cm -1)

2600 2650 2700 2750 2800

1000

2000

3000

4000

5000

6000

SL G


Raman Sh i f t ( cm-1

)

Experimental Result

Simulated Result

Lorentz ian Peaks

ex c = 488 nm

B L G


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Quality Monitoring with RamanSpectroscopy

1250 1300 1350 1400 1450 1500 1550 1600 1650 1700 17500

2000

4000

6000

8000

10000

Excitation: 488 nm

G Peak

D Band

1359 cm-1

1582 cm-1

INTENSITY(ARBITRARYUNITS)

RAMAN SHIFT (cm-1)

Single Layer GrapheneInitial Bulk Graphite

1581 cm-1

Defect or disorder induced D

mode in graphene and graphiteD mode is excitationdependent: 40-50 cm-1/eV

Graphene quality and edgestate monitoring

F. Parvizi, D. Teweldebrhan, S. Ghosh, I. Calizo, A.A.Balandin, H. Zhu and R. Abbaschian, Micro & Nano Letters,3: 29 (2008)


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Properties and Applications ofGraphene

Part VII


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Suspended Graphene

Trench

(b)

(a)

(c)

TrenchSLG

FLG

substrate

FLG

5 m

(b)

(a)

1 600 2000 240 0 280 00

400

800

1200 exc i tat ion : 488 n m

S U S P E N D E D G R A P H E N E

INTENSITY

(ARB.UNITS)

R A M A N S H IF T ( c m-1

)

1 5 8 3 c m-1

2700 cm-1


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Electrical Resistance of GrapheneInterconnects

0.0 0.1 0.2 0.3 0.4 0.50

1

2

3

4

5

6

Ids(A

)

Vds

(V)

300K350K375K400K425K

450K475K500K525K

Single Layer Graphene Resistor

1 m1 m

300 350 400 450 5000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

NormalizedR

esistance

Temperature (K)

single layer graphene resistor

bilayer graphene resistor

theoretical prediction for SLGafter Vasko and Ryzhii [20]

5 m5 m

Unlike in metals the resistance of graphene reduces with increasing temperature

Q. Shao, G. Liu, D. Teweldebrhan, A.A. Balandin,Resistance Quenching in Graphene Interconnects

http://arxiv.org/abs/0805.0334


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Back-Gated Graphene Devices

FIB fabricated platinum wires were used aselectrodes and the oxide was deposited as dielectriclayer. The thickness of oxide is 30 nm.

-3 -2 -1 0 1 2 3

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

Ids(

A)

Vds (volt)

Graphene benefic as compared to

carbon nanotubes: better

integration with CMOS

Balandin Group data: http://ndl.ee.ucr.edu/index.html


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65

High-Heat Flux Thermal Management

Table : Room-temperature thermal conductivity in best heat conductorsSample K (W/mK) Method Comments Referencediamond ~ 1000 2200 3-omega; other bulk Berman et al.MW-CNT > 3000 electrical individual Kim et al.SW-CNT ~ 3500 electrical individual Pop et al.SW-CNT 1750 5800 thermocouples bundles Hone et al.

Issues:

The value of thermal conductivi ty

Compatibili ty with Si CMOS technology

Electrical insulator vs conductor

Bulk vs nanostructure

Anisotropy of the thermal conduct ivi ty Coefficient of thermal expansion

Temperature stabili ty

Theoretical Predictions:

Graphene should havevery high thermal

conductivity

Experimental Difficulties:

Conventional methodsdo not work for graphene

Lateral Heat Spreaders or

Thermal Interface Materials

Transistors or Interconnects


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66

High Pressure High TemperatureSynthesis of Graphene

F. Parvizi, D. Teweldebrhan, S. Ghosh, I. Calizo, A.A.Balandin, H. Zhu and R. Abbaschian, Properties of grapheneproduced by the high pressure high temperature growthprocess, Micro & Nano Letters, 3, 29 (2008)

(a)

(b)

(c)

Graphene was produced by the high pressure hightemperature growth process from the natural

graphitic source material by utilizing the molten Fe-Ni catalysts for dissolution of carbon.


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New Approach for MeasuringGraphene Thermal Properties

A.A. Balandin, S. Ghosh, W. Bao, I. Calizo, D. Teweldebrhan,F. Miao and C.N. Lau, "Superior thermal conductivity of single-

layer graphene," Nano Letters, 8: 902 (2008).


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Temperature Coefficients ofGraphene Peaks

2650 2700 2750

700

800

900

1000

1100

1200

1300

1400

1500

Intensity(arb.u

nits)

Raman Shift (cm-1)

373 K113 K

single layer graphene

2DBand

exc

= 488 nm

2650 2700 2750

700

800

900

1000

1100

1200

1300

1400


Raman Shift (cm-1)

373 K113 K

bi-layer graphene

2D Band

exc

= 488 nm

100 150 200 250 300 350 400

1576

1578

1580

1582

1584

1586

1550 1575 1600 1625625

750

875

1000

G, BLG

= -0.015 cm-1/K

G, HOPG

= -0.011 cm-1/K

Intens

ity(arb.units)

Temperature (K)

exc

= 488 nm

HOPG

BLG

373 K123 K


Raman Shift (cm-1)

1578 cm

-11582 cm

-1SL G

Temperature dependence of the G peak position for BLG and HOPG. Theinset shows the shape of the G peak and its shift for SLG. Reality check:excellent agreement for HOPG data.

I. Calizo, A.A. Balandin, W. Bao, F. Miao and C.N. Lau, Nano Letters, 91,

071913 (2007).


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Temperature Coefficients ofGraphene Peaks

0 T = +o is the frequency ofG mode whentemperature T is extrapolated to 0 K

First-order temperature coefficient:

( )T VV T

V T P

d d

T T VdT dV

d d dV T T

dT dV dT

+ = +

= +

Two fundamental contributions to the temperature coefficient:

explicit(self-energyor pure temperature) due tochanges in vibration amplitude (change in the occupation ofthe phonon state)

implicit(volumetric) due to changes in the inter-atomicdistances with temperature (related to Gruneisen constant)

Non-fundamental contribution: thermalexpansion expansion mismatch strain

83-3731584-0.011Ghighly ordered graphite

113-3731582-0.015Gbi-layer graphene83-3731584-0.016Gsingle-layer graphene

T range (K)peak at 0K (cm -1)(cm -1/K)peakmaterial


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70

Measurements of the ThermalConductivity of Suspended Graphene

Trench

(b)

(a)

(c)

TrenchSLG

FLG

substrate

FLG


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71

Extraction of the ThermalConductivity Data

( / 2 )[ / ] .G H G G G H H DP a a P =

/G H O P GI I =

Excitation laser acts as a heater: PG

Raman spectrometer acts as a thermometer: TG=/G

Thermal conductivity: K=(L/2aGW)(PG/TG)

1( / 2 ) ( / ) .G G G

K L a W P =

0 1 2 3 4

-6

-4

-2

0

2

4

SLOPE: -1.292 cm-1/mW

SUSPENDED GRAPHENE

GPEAKPOSITIONSHIFT(cm-1)

POWER CHANGE (mW)

EXPERIMENTAL POINTSLINEAR FITTING

0 1 2 3 4 5

103

104

105

106

INTEGRATEDIN

TENSITY(ARB.

UNITS

)

EXCITATION POWER ON SAMPLE (mW)

REFERENCE HOPGSUSPENDED GRAPHENE


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Giant Thermal Conductivity ofGraphene: Thermal Management

Table I: Room-temperature thermal conductivi ty in graphene and CNTs

Hone et al.bundlesthermocouples1750 5800SW-CNT

Pop et al.individual;

suspended

electrical~ 3500SW-CNT

Kim et al.individual;

suspended

electrical> 3000MW-CNT

Balandin et alindividual;

suspended

optical~ 3500 5300SLG

ReferenceCommentsMethodK (W/mK)

Sample Type


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Lecture Summary

Introduction new materials and nanotechnology

Biological Objects as Nanotemplates growth and characterization hybrid bio-inorganic structures

Quantum Dots properties applications in solar cells and thermoelectrics

Carbon Materials diamond; graphite; amorphous carbon; etc.

Carbon Nanotubes properties and applications

Graphene nanometrology of graphene graphene applications

Conclusions


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Acknowledgements

Photo: Nano-Device Laboratory (NDL) group members atUniversity of California Riverside, November 2006.

Documents

Nano Education (1)