graphene: thermal properties and possible applications · alexander a. balandin, university of...
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Alexander A. BalandinNano-Device Laboratory
Department of Electrical Engineering and
Materials Science and Engineering Program
University of California – Riverside
Graphene: Thermal Properties
and Possible Applications
IEEE Talk, November 2010
Alexander A. Balandin, University of California - Riverside
2
UCR Bell Tower
City of Riverside
UCR Botanic Gardens
Joshua Tree Park, California
UCR Engineering Building
Alexander A. Balandin, University of California - Riverside
Nano-Device Laboratory (NDL) Department of Electrical EngineeringUniversity of California – Riverside
Profile: experimental and theoretical research in phonon engineering and nanodevices
Research at NDL was funded
by NSF, ONR, SRC, DARPA,
NASA, ARO, AFOSR, CRDF, as
well as industry, including
IBM, Raytheon, TRW, etc.
Research &
Applications
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
PI: Alexander A. Balandin
Alexander A. Balandin, University of California - Riverside
Outline
Introduction and Motivations
Raman Nanometrology of Graphene
Counting the layers
Temperature effects
Heat Conduction in Graphene
Measurements
2D phonon transport
Graphene Transistors and Communication Applications
Low-noise graphene FETs
Triple-mode graphene amplifier
“Graphene-like” Exfoliation of other Quasi-2D Crystals
Conclusions
4
Alexander A. Balandin, University of California - Riverside
5
Graphene: The True 2D System
A. Geim and K. Novoselov:
Nobel Prize in Physics, 2010
“Graphene revolution” brought
about by K.S. Novoselov and A.K.
Geim with the help of bulk
graphite and “Scotch” tape.
The first paper was published
by the Manchester, U.K. –
Chernogolovka, Russia group:
Novoselov, et al., Science (2004).
Individual atomic layers of sp2-
hybridized carbon bound in two-
dimensions. Crystalline graphite
is composed of graphene layers.
“Unrolled Carbon Nanotube”
Alexander A. Balandin, University of California - Riverside
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The “Unexpected” Discovery
R.E. Peierls (1934) and L.D. Landau (1937):
Strictly 2D crystals cannot exist in the harmonic approximation;
thermal fluctuations should destroy long-range 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
“Lost in Translation”:
Theory prohibits perfect 2D crystals but does not prohibit “nearly
perfect” 2D crystals in 3D space
Going beyond harmonic approximation: bending, stretching and
corrugations and microscopic roughening can stabilize 2D crystals
Alexander A. Balandin, University of California - Riverside
7
Why Should Engineers Care about Graphene?
Exotic physical properties
Electrons as massless relativistic Dirac fermions
Anomalous quantization of Hall conductance
Possible electronic and optoelectronic applications
High electronic mobility
High-speed devices, sensitive detectors, interconnects, etc.
High thermal conductivity
Benefit for electronics, thermal management
Optical transparency
Transparent electrodes for touch-screens and PV cells
Extremely strong and stiff
MEMS/NEMS material, extremely thin resonator
Alexander A. Balandin, University of California - Riverside
8
How Real are Real-Life Graphene Applications?
Flexible graphene sheet with silver electrodes printed on it can
be used as a touch screen when connected to control software.
Credit: Byung Hee Hong, SKKU.
http://www.technologyreview.com/computing/25633/page1/
Alexander A. Balandin, University of California - Riverside
9
Part I: Raman Nanometrology of Graphene
Alexander A. Balandin, University of California - Riverside
10
Raman Spectroscopy of Graphene
Alternatives:
low-temperature transport study
cross-sectional TEM
few other costly methods
Visualization on Si/SiO2 substrates D band: A1g (~1350 cm-1); G peak: E2g; 2D band
A.C. Ferrari et al., Phys. Rev. Lett. 97, 187401 (2006).
I. Calizo, et al., Nano Lett., 7, 2645 (2007).
Graphene is a single atomic layer of carbon atoms by definition!
Alexander A. Balandin, University of California - Riverside
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2D-band features of graphene are reproducible
and can be used to count the number of
graphene layers.
Raman Nanometrology of Graphene:
Counting the Number of Atomic Planes
2300 2400 2500 2600 2700 2800 2900 30000
4000
8000
12000
16000
20000
24000
Inte
nsity (
arb
. u
nits)
Raman Shift (cm-1)
Graphene @ 300K
exc = 488 nm
1 layer
2 layers
3 layers
4 layers
5 layers
Deconvolution of 2D (G’) Band
I. Calizo, et al., Appl. Phys. Lett., 91, 201904 (2007).
I. Calizo, et al., Appl. Phys. Lett., 91, 071913 (2007).
Alexander A. Balandin, University of California - Riverside
12
Quality Monitoring with Raman Spectroscopy
1250 1300 1350 1400 1450 1500 1550 1600 1650 1700 1750
0
2000
4000
6000
8000
10000
Excitation: 488 nm
G Peak
D Band
1359 cm-1
1582 cm-1
INT
EN
SIT
Y (
AR
BIT
RA
RY
UN
ITS
)
RAMAN SHIFT (cm-1)
Single Layer Graphene
Initial Bulk Graphite
1581 cm-1
Defect or disorder induced D
mode in graphene
D mode is excitation
dependent: 40-50 cm-1/eV
F. Parvizi, et al., Micro & Nano
Letters, 3, 29 (2008).
Alexander A. Balandin, University of California - Riverside
13
Temperature Coefficients of Graphene
Raman Peaks
-150 -75 0 75
1576
1578
1580
1582
1584
1530 1575 1620
2500
5000
7500
10000
12500
G P
ea
k P
osi
tion
(cm
-1)
Temperature (C)
G Peak Position
Linear Fit of Data
Bi-Layer Graphene
slope = -0.015 cm-1/C
Raman Shift (cm-1
)
Inte
nsi
ty (
arb
. u
nits
)
Bi-layer
Graphene
exc = 488 nm
G Peak
1580 cm-1
Phonon frequency downshift with T is unusual when the bond-bond distances shorten with T since normally
lattice contraction leads to the upward shift of the frequencies.
Note: the sign is negative
Temperature is controlled externally; very low excitation power on the sample surface is used (< 0.5 – 1 mW).
Alexander A. Balandin, University of California - Riverside
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Explanation of the Anomalous Sign and
FWHM Behavior of Graphene G Mode
Ab-initio calculations of N. Bonini et al.,
Phys. Rev. Lett., 99, 176802 (2007).
Alexander A. Balandin, University of California - Riverside
15
Part II: Thermal Conductivity of Graphene
IEEE Spectrum illustration of
the first measurements of
thermal conductivity of graphene
(Spectrum, October, 2009)
The UCR Experiment
Alexander A. Balandin, University of California - Riverside
Basics of Heat Conduction
16
Fourier’s law:
Definitions and Basic Theory
Phonon vs. electron conduction:
jq
iiNQ,
, ,)(q
qqq
Heat current carried by phonons :
Te
kK Be
22
3
RT thermal conductivity of important materials:
Silicon (Si): 145 W/mK
SiO2: 1-13 W/mK
Copper: 400 W/mK
RT thermal conductivity for carbon materials:
Diamond: 1000 – 2200 W/mK
Graphite: 200 – 2000 W/mK (orientation)
DLC: 0.1 – 10 W/mK
CNTs: 3000 – 3500 W/mK
Very wide range of K for carbon materials
depending on their lattice and dimensionality
TKS
Q
Alexander A. Balandin, University of California - Riverside
The switch to multi-core
designs alleviates the growth in
the thermal design power (TDP)
increase but does not solve the
hot-spot problem
Non-uniform power densities
leading to hot-spots (>500 W/cm2)
Data is after R. Mahajan et al., Proceed. IEEE (2006)
Why Engineers Need to Worry about
Heat Conduction
IEEE Spectrum illustration of the
thermal issues in the feature
article Chill Out: New Materials
and Designs Can Keep Chips
Cool by A.A. Balandin.
No BIG fan
solutions!
Alexander A. Balandin, University of California - Riverside
Thermal Transport at Nanoscale: Crystalline Semiconductors and Insulators
300 400 500 600 700 800 0
20
40
60
80
100
120
140
160
TEMPERATURE (K)
TH
ER
MA
L C
ON
DU
CT
IVIT
Y (
W/m
-K) Si Bulk Diffuse Scattering (p=0)
Si Nanowire: A
Si Nanowire: B
Thermal conductivity usually decreases as one goes from bulk
material to nanostructure or thin film
J. Zou and A.A. Balandin, J. Appl. Phys., 89,
2932 (2001).
Phonon - boundary scattering:
Lp
p
B
1
11
Thermal conductivity of bulk Si at room
temperature: K= 148 W/m-K
Thermal conductivity of Si nanowire with
cross section of 20 nm x 20 nm: K=13 W/mK
Phonon spectrum modification
Phonon group velocity changes
Phonon density of states change
18
Thermal transport in crystalline nanoscale
carbon materials will mostly affected by the
phonon - boundary scattering
Alexander A. Balandin, University of California - Riverside
Measurement of Thermal Conductivity:
Available Experimental Techniques
3-Thermal Conductivity Setup
Transient Plane Source Technique
Laser – Flash Technique
T2 T1
T2>T1
TKS
Q
S
Measurement Principles
Alexander A. Balandin, University of California - Riverside
Thermal Conductivity Measurements with
Micro-Raman Spectrometer
Importance of the Suspended Portion of Graphene
Formation of the specific in-plane heat front
propagating toward the heat sinks
Reduction in the graphene – substrate coupling
Determining the fraction of the power dissipated in
graphene through callibration procedure
G mode D mode
Idea of the Experiment:
Induce locale hot spot in the middle of the suspended
graphene flake and monitor temperature rise in the middle
with increasing excitation laser intensity.
Graphene Specifics:
Atomic thickness: good for this method
Heat transport: diffusive or partially diffusive thermal transport
In-plane phonon modes: less effect from the substrate and possibility of graphite calibration
Alexander A. Balandin, University of California - Riverside
2121
Measurement of the Thermal Conductivity
Laser acts as a heater (confirmed by Stoke –
Anti-Stoke intensity ratio): DPG
Raman “thermometer”: DTG=D/cG
Thermal conductivity: K=(L/2aGW)(DPG/DTG)
1( / 2 ) ( / ) .G G GK L a W Pc D D
0 1 2 3 4
-6
-4
-2
0
2
4
SLOPE: -1.292 cm-1/mW
SUSPENDED GRAPHENE
G P
EA
K P
OS
ITIO
N S
HIF
T (
cm-1
)
POWER CHANGE (mW)
EXPERIMENTAL POINTS
LINEAR FITTING
A.A. Balandin, S. Ghosh, W. Bao, I. Calizo, D. Teweldebrhan,
F. Miao and C.N. Lau, Nano Letters, 8: 902 (2008).
Thermal conductivity of rectangular flake (L is
the half-length):
Connect DPD DPG through calibration
Alexander A. Balandin, University of California - Riverside
22
Thermal Conductivity of Single Layer Graphene:
Comparison with Carbon Nanotubes
Table I: Experimental RT Thermal Conductivity of Graphene and CNTs
Sample K (W/mK) Method Comments Reference
SLG ~ 3000 – 5000 optical individual Balandin et al., Nano Lett. (2008)
MW-CNT ~ 3000 electrical individual Kim et al., Phys. Rev. Lett. (2001)
SW-CNT ~ 3500 electrical individual Pop et al., Nano Lett. (2006)
SW-CNT 1750 – 5800 thermocouples bundles Hone et al., Phys. Rev. B (1999)
SW-CNT 3000 - 7000 thermocouples individual Yu et al., Nano Lett. (2005)
CNTs ~1500 - 2900 electrical individual Fujii et al., Phys. Rev. Lett. (2005)
Sample K (W/mK) Method Comments Reference
CNTs ~6600 MD predicted higher K for graphene Berber et al. PRL (2000)
CNTs ~2980 MD strong defect dependence Che et al., Nanotech. (2000)
graphite ~2000 C-K basal plane (a-plane) Klemens et al., Carbon (1994)
Table II: Theoretical RT Thermal Conductivity of Graphene and CNTs
Alexander A. Balandin, University of California - Riverside
23
Fundamental Property: Divergence of the Lattice Thermal Conductivity in 2-D Crystals
K ~ log(N) in 2D
K ~ Nα in 1D, α≠1
N – system size[1] K. Saito, et al., Phys. Rev. Lett. 104, 040601 (2010).
[2] A. Dhar. Advances in Physics 57, 457 (2008).
[3] G. Basile et al. Eur. Phys. J. 151, 85 – 93 (2007).
[4] L. Yang et al. Phys. Rev. E 74, 062101 (2006).
[5] L. Delfini et al. Phys, Rev. E 73, 060201R (2006).
[6] S. Lepri et al. Chaos 15, 015118 (2005).
[7] J. Wang, B. Li. Phys. Rev. Lett. 92, 074302 (2004).
[8] S. Lepri et al. Phys. Rep. 377, 1 (2003).
[9] R. Livi and S. Lepri. Nature 421, 327 (2003).
[10] O. Narayan et al., Phys. Rev. Lett., 89, 20601 (2002).
[11] A. Dhar. Phys. Rev. Lett. 86, 5882 (2001).
[12] A. Lepri and R. Livi, J. Stat. Phys. 100, 1147 (2000).
[13] T. Pozen et al., Phys. Rev. Lett., 84, 2857 (2000).
[14] S. Lepri et. al. Europhys. Lett. 43, 271 (1998).
Thermal conductivity in 2D lattice
vs. Nx. Data is after S. Lepri et al.
(Ref. [8]).
Consensus: The intrinsic thermal conductivity of
2-D or 1-D anharmonic crystals is anomalous.
Alexander A. Balandin, University of California - Riverside
24
Klemens Theory of the Phonon
Thermal Conductivity of Bulk Graphite
max
min
2
,2 2,
( ) [ ( ) / ]1{( ( ) ) }
4 [ [ ( ) / ] 1]
q
s ss U s
s TA LA qB s
d q exp q kTK q q dq
k T h dq exp q kT
2,max
, 2 2
1 ssU s
s B
M
k T
N. Mounet et al, Phys. Rev. B 71, 205214 (2005). P.G. Klemens, J. Wide Bandgap
Materials, 7, 332 (2000).
Intrinsic Umklapp-Limited Thermal Conductivity:
Umklapp life-time, which defines MFP:
In bulk graphite there is natural low-bound
cut-off at ~4 THz. The heat transport is two-
dimensional only above this frequency.
Klemen’s value for graphite: K=1900 W/mK
2-D: C() ~ K ~T-1-1
3-D: C() ~ 2
jq
iiNQ,
, ,)(q
qqq
Alexander A. Balandin, University of California - Riverside
25
Theory of the Phonon Heat Conduction
in Graphene
max
min
2
,2 2,
( ) [ ( ) / ]1{( ( ) ) }
4 [ [ ( ) / ] 1]
q
s ss U s
s TA LA qB s
d q exp q kTK q q dq
k T h dq exp q kT
2,max
, 2 2
1 ssU s
s B
M
k T
P.G. Klemens, J. Wide Bandgap Materials, 7, 332 (2000).
Thermal conductivity in graphene:
,max
,min
ss ss
s B
M
k T L
Graphene:MFP = L – physical size of the system
Limitation on MFL: L= vs
Limiting low-bound frequency:
Alexander A. Balandin, University of California - Riverside
26
Uniqueness of Heat Conduction in Graphene
“Intrinsic” Thermal Conductivity Value is Defined by the Flake Size
The phonon transport in graphene is 2D all the way down to zero frequency
D.L. Nika, S. Ghosh, E.P. Pokatilov, A.A. Balandin,
Appl. Phys. Lett., 94, 203103 (2009).
,max
,min
ss ss
s B
M
k T L
Low-bound cut-off frequency is defined by the
condition that the phonon MFP can not exceed
the physical size of the graphene flake:
Alexander A. Balandin, University of California - Riverside
27
Phonon Transport in Graphene and FLG:
Accurate Theory vs Experiment
Enhancement of
Umklapp scatterings in
bilayer in comparison with
monolayer due to the two-
fold degeneracy of phonon
energy spectra in bilayer
S. Ghosh, W. Bao, D.L. Nika, S.
Subrina, E.P. Pokatilov, C.N. Lau
and A.A. Balandin, "Dimensional
crossover of thermal transport in
few-layer graphene," Nature
Materials, 9, 555 (2010).
Alexander A. Balandin, University of California - Riverside
Thermal Management Applications:
Graphene Laterals Heat Spreaders
S. Subrina, D. Kotchetkov and A.A. Balandin, Graphene heat
spreaders, IEEE Electron Device Lett., 30, 1281 (2009).
Significant
reduction of the
hot-spot
temperature due to
incorporation of
graphene layers
US Patent Pending, 2008
Alexander A. Balandin, University of California - Riverside
Graphene Interconnects and Heat Spreaders
Q. Shao, G. Liu, D. Teweldebrhan and A.A. Balandin,
Applied Physics Letters, 92: 202108 (2008).
Alexander A. Balandin, University of California - Riverside
Thermal Interface Materials with Graphene
TIMs are materials with the relatively high thermal conductivity introduced to the joint to fill the air gaps.
http://www.ecnmag.com/tags/products/Materials/
Current TIM based on polymer, grease filled with silver, alumina require 50-70% loading to achieve 1-5 W/mk. F. Sarvar et al. Elect. Sys. Technology Conference (2006)
Alexander A. Balandin, University of California - Riverside
31
Part III: Graphene Transistors for
Communication Applications
Alexander A. Balandin, University of California - Riverside
Types of Intrinsic
Electronic Noise:
Thermal noise:
SI=4kBT/R
Shot noise:
SI=2e<I>
Flicker 1/f noise:
SI ~ I2/f
G-R noise:
SI ~ 1/(1+f2t2)
See A.A. Balandin (Ed.), Noise and Fluctuations Control in Electronic Devices (ASP, 2002).
log f
1/f
WHITE
HF
G-R
100 kHz
Electronic Device Noise
No
ise
Sp
ectr
al D
en
sity S
V(V
2/H
z)
Up-conversion
Types of Electronic Noise and their
Practical Importance
Alexander A. Balandin, University of California - Riverside
Bottom-Gate and Top-Gate Graphene
Field-Effect Transistors
-1.0 -0.5 0.0 0.5 1.012.0u
14.0u
16.0u
18.0u
20.0u
22.0u
I DS
(A
)
VTG (V)
Top Gate Function of Single
Layer Graphene Device
VDS
=0.1V
-60 -40 -20 0 20 40 60
0.0
2.0x10-5
4.0x10-5
Vg
D
Vds
=20 mV
Vds
=40 mV60 mV
80 mVV
ds=100 mV
So
urc
e -
Dra
in C
urr
en
t (A
)
Gate Bias Vg (V)
The fabrication of pads and contact bars was performed using electron beam
lithography Cr/Au metal deposition by electron beam evaporator.
Top gate dielectric of ~20 nm HfO2 is grown by the atomic layer deposition (ALD).
The low-temperature ALD allows for fabrication of the dielectric with low leakage.
Alexander A. Balandin, University of California - Riverside
Noise Spectrum of Bilayer Graphene
Field-Effect Transistor
1 10 100 1000 1000010
-24
10-23
10-22
10-21
10-20
10-19
10-18
10-17
10-16
Bilayer Graphene Device
13 V
0 V
20 V
-20 V
45 V
1/f
No
ise
Sp
ectr
al D
en
sity S
I (A
2/H
z)
Frequency (Hz)
Vds
=20 mV
Q. Shao, G. Liu, D. Teweldebrhan, A. A. Balandin, S. Rumyantsev, M. Shur and D. Yan, "Flicker noise in
bilayer graphene transistors," IEEE Electron Device Letters, 30, 288 (2009).
Alexander A. Balandin, University of California - Riverside
S. Vijayaraghavan, et al., J. Appl. Phys. 100, 024315 (2006).
P.G. Collins, et al., App. Phys. Lett. 2000, 76, 894.
A.A. Balandin, Noise in Electronic Devices (ASP, 2002).
fNI
SIH 2
Upper bound: number of carriers equal
to the number of atoms in M-SWNTs.
Different role of contacts
Different exposure to environment
1/f Noise: Graphene vs Carbon Nanotubes
Hooge parameter:
G. Liu, W. Stillman, S. Rumyantsev, Q. Shao, M. Shur and A.A.
Balandin, "Low-frequency electronic noise in the double-gate single-
layer graphene transistors," Appl. Phys. Lett., 95, 033103 (2009).
Alexander A. Balandin, University of California - Riverside
Where Does The Noise Comes From?
-60 -40 -20 0 20 40 601E-10
1E-9
1E-8
1E-7
f=10Hz
SI/I2
(1/H
z)
Vg (V)
-60 -40 -20 0 20 40 601E-9
1E-8
1E-7
1E-6
f=10Hz
SI/I
2×
W×
Lg (m
2/H
z)
Vg (V)
Noise spectral density SI/Id2 normalized to
channel area results in a much narrower
dispersion: noise originates in graphene layer
Studied devices with a wide range of channel
areas: from 1.5 to 80 mm2
S. Rumyantsev, G. Liu, W. Stillman, M. Shur and A.A.
Balandin, "Electrical and noise characteristics of graphene
field-effect transistors: Ambient effects and noise sources,"
J. Physics: Condensed Matter, 22, 395302 (2010).
Alexander A. Balandin, University of California - Riverside
The ambipolar electronic
transport in graphene
transistors leads to increased
amplifier functionality
Mode 1
Mode 3
Mode 2
Mode 1: common-drain mode (amplifier is
biased at left branch of the ambipolar curve)
Mode 2: common-source mode (amplifier is
biased at right branch of the ambipolar curve)
Mode 3: frequency multiplication mode
(amplifier is biased at the Dirac point)
Triple-Mode Graphene Amplifier:
The Next “Killer” Application?
X. Yang, G. Liu, A.A. Balandin and K. Mohanram, “Triple-mode graphene amplifier,” ACS Nano (2010).
Collaboration with Rice University
Alexander A. Balandin, University of California - Riverside
38
Enhanced Functionality of
Graphene Amplifier
a) The schematic for triple-
mode graphene amplifier. (b)
The I-V characteristics of the
graphene transistor. (c), (d), (e)
are the output of the amplifier at
different biasing points
Binary phase shift keying (BPSK)
modulation with graphene
amplifiers: (a) biasing points and
(b) experimental results.
The graphene circuit can realize the
modulation necessary for phase shift
keying and frequency shift keying, which
are widely used in wireless applications
such as Bluetooth, RFID, and ZigBee.
Alexander A. Balandin, University of California - Riverside
39
Part IV: “Graphene-Like” 2D Crystals
Alexander A. Balandin, University of California - Riverside
40
A.A. Balandin and K.L. Wang, Phys. Rev. B (1998).
A.A. Balandin and K.L. Wang, J. Appl. Phys. (1998).
The thermoelectric figure of merit: ZT=S2T/(Ke+Kp)
S is the Seebeck coefficient, is the electrical conductivity and K is the thermal conductivity.
Electron Quantum Confinement Acoustic Phonon Confinement
M.S. Dresselhaus, et al. Phys. Solid State (1999).
L.D. Hicks and M.S. Dresselhaus, Phys. Rev. B (1993).
Low potential barrier in Bi2Te3/Bi2Se3; Bi2Te3/Sb2Te3
Thermoelectric Motivation for “Graphene-Like” Exfoliation of Bi2Te3
Alexander A. Balandin, University of California - Riverside
Topological Insulators: Benefits of Few-Quintuple Exfoliated Films
41
Improved gating for tuning the
Fermi level position
Reduce the volume component
of transport
Band-gap modulation
Better quality of materials with
less unintentional doping
FQL can be better than SGL
For review see
M.Z. Hasan and C.L. Kane, arXiv: 1002.3895
X.-L. Qi and S.-C. Zhang, arXiv: 1008.2026.
J. Moore, Nature Physics, 5, 378 (2009).
Alexander A. Balandin, University of California - Riverside
“Graphene-Like” Exfoliation of Different Type
of Dirac Materials: Topological Insulators
D. Teweldebrhan, V. Goyal and
A.A. Balandin, "Exfoliation and
characterization of bismuth
telluride atomic quintuples and
quasi-two-dimensional crystals,"
Nano Letters, 10, 1209 (2010).
Alexander A. Balandin, University of California - Riverside
Raman Spectroscopy of the Atomically Thin Films of Bi-Te Topological Insulators
43
K.M.F. Shahil, M.Z. Hossain, D. Teweldebrhan and A.A.
Balandin, "Crystal symmetry breaking in few-quintuple
Bi2Te3 films: Applications in nanometrology of topological
insulators," Appl. Phys. Lett., 96, 153103 (2010).
Alexander A. Balandin, University of California - Riverside
Room-Temperature Electrical Characterization Bi-Te Atomic Films
44
Weak gating at RT
Resistivity is ~10-4 Wm
D. Teweldebrhan, V. Goyal, M. Rahman and
A.A. Balandin, "Atomically-thin crystalline films
and ribbons of bismuth telluride," Appl. Phys.
Lett., 96, 053107 (2010). - Issue's Cover
Alexander A. Balandin, University of California - Riverside
Thermoelectric Topological Insulators
V. Goyal, D. Teweldebrhan
and A.A. Balandin,
“Mechanically exfoliated
stacks of thin films of Bi2Te3
topological insulator films”,
Appl. Phys. Lett. (2010).
ZT increase by ~140 – 250% at room
temperature
The enhancement is expected to be
larger at low T
Alexander A. Balandin, University of California - Riverside
46
Outlook: “The Carbon World”
IEEE Spectrum artistic rendering of the hybrid silicon – carbon 3D chip with
graphene heat spreaders, graphene interconnects and graphene transistors.
Graphene Applications
Transparent electrodes
Touch screens
Heat spreaders
Sensors
Interconnects
High-Frequency
Analog, RF, Mixed Signal
Alexander A. Balandin, University of California - Riverside
47
Acknowledgements
Nano-Device Laboratory (NDL) research group, UCR 2010.