Nano Education (1)
Transcript of 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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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
Intensity(arb.units)
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
Intensity(arb.units)
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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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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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
Intensity(arb.units)
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
Intensity(arb.units)
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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Measurements of the ThermalConductivity of Suspended Graphene
Trench
(b)
(a)
(c)
TrenchSLG
FLG
substrate
FLG
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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.