Content uploaded by Rameez Samnakay
Author content
All content in this area was uploaded by Rameez Samnakay on Mar 16, 2015
Content may be subject to copyright.
Selective chemical vapor sensing with few-layer MoS2 thin-film transistors:
Comparison with graphene devices
R. Samnakay, C. Jiang, S. L. Rumyantsev, M. S. Shur, and A. A. Balandin
Citation: Applied Physics Letters 106, 023115 (2015); doi: 10.1063/1.4905694
View online: http://dx.doi.org/10.1063/1.4905694
View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/106/2?ver=pdfcov
Published by the AIP Publishing
Articles you may be interested in
Direct fabrication of thin layer MoS2 field-effect nanoscale transistors by oxidation scanning probe lithography
Appl. Phys. Lett. 106, 103503 (2015); 10.1063/1.4914349
Top-gated chemical vapor deposited MoS2 field-effect transistors on Si3N4 substrates
Appl. Phys. Lett. 106, 062101 (2015); 10.1063/1.4907885
Growth-substrate induced performance degradation in chemically synthesized monolayer MoS2 field effect
transistors
Appl. Phys. Lett. 104, 203506 (2014); 10.1063/1.4873680
Low-frequency 1/f noise in MoS2 transistors: Relative contributions of the channel and contacts
Appl. Phys. Lett. 104, 153104 (2014); 10.1063/1.4871374
Electrical performance of monolayer MoS2 field-effect transistors prepared by chemical vapor deposition
Appl. Phys. Lett. 102, 193107 (2013); 10.1063/1.4804546
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
169.235.187.11 On: Mon, 16 Mar 2015 17:19:32
Selective chemical vapor sensing with few-layer MoS
2
thin-film transistors:
Comparison with graphene devices
R. Samnakay,
1,2
C. Jiang,
2
S. L. Rumyantsev,
3,4
M. S. Shur,
3
and A. A. Balandin
1,2,a)
1
Phonon Optimized Engineered Materials (POEM) Center, Materials Science and Engineering Program,
University of California–Riverside, Riverside, California 92521, USA
2
Nano-Device Laboratory, Department of Electrical Engineering, Bourns College of Engineering,
University of California–Riverside, Riverside, California 92521, USA
3
Department of Electrical, Computer, and Systems Engineering, Center for Integrated Electronics,
Rensselaer Polytechnic Institute, Troy, New York 12180, USA
4
Ioffe Physical-Technical Institute, St. Petersburg 194021, Russia
(Received 19 November 2014; accepted 28 December 2014; published online 13 January 2015)
We demonstrated selective gas sensing with MoS
2
thin-film transistors using the change in the chan-
nel conductance, characteristic transient time, and low-frequency current fluctuations as the sensing
parameters. The back-gated MoS
2
thin-film field-effect transistors were fabricated on Si/SiO
2
sub-
strates and intentionally aged for a month to verify reliability and achieve better current stability.
The same devices with the channel covered by 10 nm of Al
2
O
3
were used as reference samples. The
exposure to ethanol, acetonitrile, toluene, chloroform, and methanol vapors results in drastic
changes in the source-drain current. The current can increase or decrease by more than two-orders
of magnitude depending on the polarity of the analyte. The reference devices with coated channel
did not show any response. It was established that transient time of the current change and the nor-
malized spectral density of the low-frequency current fluctuations can be used as additional sensing
parameters for selective gas detection with thin-film MoS
2
transistors. V
C2015 AIP Publishing LLC.
[http://dx.doi.org/10.1063/1.4905694]
Two-dimensional (2D) layered materials have attracted
significant attention owing to their unusual electronic and op-
tical properties.
1–4
Among these material systems, semicon-
ducting MoS
2
is one of the most promising.
5,6
Each layer of
MoS
2
consists of one sub-layer of molybdenum sandwiched
between two other sub-layers of sulfur in a trigonal prismatic
arrangement.
7
A direct band gap of a single-layer MoS
2
is
1.9 eV.
8,9
Single-layer and few-layer MoS
2
devices have
been proposed for electronic, optoelectronic, and energy
applications.
1–4,10
Recently, MoS
2
film-based field-effect tran-
sistors (FETs) were tested for sensing NO and NO
2
, other
gases, and water vapor.
11–16
The sensing signal utilized in
these experiments was the relative change in the resistance,
DR/R. The devices with 2D channels are natural candidates
for sensor applications due to the ultimately high surface-to-
volume ratio and widely tunable Fermi-level position.
In this letter, we report on selective detection of ethanol,
acetonitrile, toluene, chloroform, and methanol vapors with
the MoS
2
thin-film FETs (TF-FETs). The tests were con-
ducted with the as fabricated devices and intentionally aged
devices. The focus of the study was on the aged MoS
2
TF-
FETs. Practical applications require that sensors remain sta-
ble and operational for at least a month period of time. No
prior study of the operation of the aged MoS
2
TF-FETs has
been reported. As it will be clear from the further discussion,
there are additional reasons why operation of aged TF-FETs
is of interest. In addition to the relative change in the source-
drain current, DI
D
/I
D
, we used the normalized spectral den-
sity of the low-frequency current fluctuations, S
I
/I
D
2
, and the
characteristic transient time of the current as the sensing pa-
rameters (here, I
D
is the source-drain current). Our results
show that the aged MoS
2
devices perform better as the sen-
sors in terms of their current stability, sensitivity to the ana-
lyte, and reduced contributions of metal contacts to the noise
level. Comparison with the graphene FETs reveals signifi-
cant differences in the effects of exposure to chemical vapors
on DR/R and S
I
/I
D
2
, suggesting differences in the physical
mechanisms of low-frequency current fluctuations.
17–19
Thin films of MoS
2
were mechanically exfoliated from
bulk crystals and transferred onto Si/SiO
2
substrates follow-
ing the standard approach.
1
The thickness H of the films
ranged from bi-layer to a few layers. Micro-Raman spectros-
copy (Renishaw InVia) confirmed the crystallinity and thick-
ness of the MoS
2
flakes after exfoliation. The spectroscopy
was performed in the backscattering configuration under
k¼488-nm laser excitation using an optical microscope
(Leica) with a 50objective. The excitation laser power was
limited to less than 0.5 mW to avoid local heating. Figure 1
shows the schematic of MoS
2
TF-FET (a), optical micros-
copy image of a representative device (b), and Raman spec-
trum of the channel material (c). The observed Raman
features at 382.9 cm
1
(E
1
2g
) and 406.0 cm
1
(A
1g
) are
consistent with literature reports.
20
Analysis of the Raman
spectrum indicates that this sample is 2–3 layer MoS
2
film.
The thickness identification is based on the frequency differ-
ence, Dx, between the E
1
2g
and the A
1g
peaks. The increase
in the number of layers in MoS
2
films is accompanied by the
red shift of the E
1
2g
and blue shift of the A
1g
peaks.
20
Devices with MoS
2
thin-film channels were fabricated
using the electron beam lithography (LEO SUPRA 55) for
patterning of the source and drain electrodes and the
a)
Author to whom correspondence should be addressed. Electronic mail:
balandin@ee.ucr.edu
0003-6951/2015/106(2)/023115/5/$30.00 V
C2015 AIP Publishing LLC106, 023115-1
APPLIED PHYSICS LETTERS 106, 023115 (2015)
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
169.235.187.11 On: Mon, 16 Mar 2015 17:19:32
electron-beam evaporation (Temescal BJD-1800) for metal
deposition. The Si/SiO
2
(300-nm) substrates were spin-
coated (Headway SCE) and baked consecutively with two
positive resists: first, methyl methacrylate (MMA) and then,
polymethyl methacrylate (PMMA). The resulting TF-FETs
consisted of MoS
2
thin-film channels with Ti/Au (10-nm/
100-nm) contacts. The heavily doped Si/SiO
2
wafer served
as a back gate. The majority of the bi-layer and tri-layer
thickness MoS
2
devices had a channel length, L, in the range
from 1.3 lm to 3.5 lm, and the channel width, W, in the
range from 1 lmto6lm. Some of the devices were covered
with 10-nm Al
2
O
3
layer to serve as the reference samples in
control experiments.
It is known that defective and doped graphene has the
greater sensitivity for CO, NO, NO
2
, and other gases.
21
The
same can possibly be true for thin film MoS
2
devices. In par-
ticular, it has been shown that the high density of edge states
enhances the sensitivity.
16
Therefore, aged, i.e., more defec-
tive devices can be more attractive for gas sensing applica-
tions. In the present work, we found that aged MoS
2
TF-FETs
were more stable and had negligible contact contribution to
the drain-to-source resistance. The aged MoS
2
devices were
characterized by the on-to-off ratio of 10
4
, electron mobility
l0.5 cm
2
/V s and negligible contact resistance. The new, as
fabricated, devices had mobility values in the range from 1 to
8cm
2
/V s, which is typical for the back-gated MoS
2
TF-
FETs.
10,22,23
An estimate for the contact resistances was
obtained by plotting the drain-to-source resistance, R
DS
,vs.
1/(V
G
-V
TH
), and extrapolating this dependence to zero. Figure
2shows a representative transfer current-voltage (I-V) charac-
teristic for the aged MoS
2
TF-FET used in this study. For
comparison, typical I-Vs for a graphene device are also
shown. Analyzing I-Vs for MoS
2
thin films and graphene, one
can see possible implications for sensor operation: graphene
device has much higher currents owing to graphene superb
mobility, while MoS
2
devices have better gating and on-off
ration owing to MoS
2
band gap.
For testing the sensor operation, the vapors were produced
by bubbling dry air through the respective solvents and diluting
the gas flow with the dry air. The resulting concentrations were
0.5 P/P
o
, where P is the vapor pressure and P
o
is the saturated
vapor pressure. When the sample is exposed to the vapor, the
vapor molecules, which attach the channel surface, create nega-
tive or positive charges at the MoS
2
surface (see Fig. 1(a)). The
latter depletes or enhances the electron concentration in the
channel depending on the vapor species. For testing MoS
2
TF-
FETs, we selected three polar solvents: acetonitrile (CH
3
CN—
polar aprotic), ethanol (C
2
H
5
OH—polar protic), and methanol
(CH
3
OH—polar protic); as well as two non-polar solvents: tol-
uene (C
6
H
5
-CH
3
) and chloroform (CHCl
3
).
Figure 3shows the drain current as a function of time in
MoS
2
TF-FET exposed to ethanol, methanol, and acetonitrile,
FIG. 1. Schematic of the MoS
2
thin-film sensor with the deposited mole-
cules that create additional charge (upper panel). Optical microscopy image
of a representative MoS
2
TF-FET (middle panel). Raman spectrum of the
MoS
2
thin-film channel showing the E
1
2g
and the A
1g
peaks. The increase in
the number of layers in MoS
2
films is accompanied by the red shift of the
E
1
2g
and blue shift of the A
1g
peaks. The energy difference, Dx, between
the E
1
2g
and the A
1g
peaks, indicates that the given sample is a tri-layer
MoS
2
film.
FIG. 2. Current-voltage characteristics of the aged MoS
2
TF-FET used in
the study. A typical graphene FET transfer characteristic is also shown for
comparison in the same scale. Graphene reveals much higher current owing
to superior electron mobility. MoS
2
TF-FET is characterized by better on-
off ratio owing to its energy band gap. Different curves correspond to differ-
ent samples.
023115-2 Samnakay et al. Appl. Phys. Lett. 106, 023115 (2015)
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
169.235.187.11 On: Mon, 16 Mar 2015 17:19:32
respectively (from top to bottom). For all chemical vapors, the
measurements were conducted at the small drain-source volt-
age V
D
¼0.1 V. The high gate bias of V
G
¼60 V is explained
by the presence of 300-nm thick SiO
2
layer in the back gate.
One can see from Fig. 3that in all cases of polar solvents, the
drain current increased upon exposure to the vapor and
decreased after the vapor exposure was turned off. The results
were reproducible for several switching on and off over in a
month old MoS
2
TF-FETs tested over a period of few days.
The time constants, s,forI
D
increase and decrease were dif-
ferent for each examined analyte. Note that the current of the
reference sample—the same device with the channel coated
by Al
2
O
3
—did not reveal any changes.
Figure 4presents drain current as a function of time in
MoS
2
TF-FET exposed to chloroform and toluene, respec-
tively (from top to bottom). To better illustrate a large range
of the current change, Fig. 4also shows the data for chloro-
form in a semi-logarithmic scale. The exposure to the vapors
of non-polar solvents has an opposite effect on I
D
. The drain
current reduces by more than two-orders of magnitude,
almost completely switching the device off. We found also
that the response of the MoS
2
transistors to some vapors
demonstrates a memory effect: current remains small or
even continue to decrease after the vapor flow is switched
off. The current (resistance) is completely restored after gate
and voltage biases are set to zero. The svalues were different
for each analyte. Although not shown, no changes in current
were observed for the reference samples. It is important to
note that the data presented in Figs. 3and 4were for devices
intentionally aged by a month. Initially, the aging study was performed to verify that MoS
2
TF-FETs maintain their char-
acteristic. Any practical sensor applications require that the
FETs are operational for at least a month. Interestingly, we
observed that the characteristics of the aged devices even
improved in terms of their current stability and sensitivity.
The as fabricated MoS
2
TF-FETs responded in the same way
to the polar and non-polar analytes as the aged devices.
We have recently demonstrated the use of the low-
frequency current fluctuations of I
D
in graphene devices as
an additional sensing parameter.
24,25
Some gases induce
bulges at characteristic frequencies in the spectral density of
the low-frequency current fluctuations S
I
/I
D
2
of graphene
FETs or change its average value. In order to test the same
approach for MoS
2
TF-FETs, we measured the low-
frequency noise spectral density in MoS
2
TF-FETs exposed
to open air and chemical vapors. The details of our low-
frequency measurements have been reported by us else-
where.
26
Figure 5shows S
I
/I
D
2
of MoS
2
TF-FET for differ-
ent vapors. Red lines show the noise spectra measured in
open air with intervals of a few days. The change of the noise
spectra was found only as a result of the exposure to the ace-
tonitrile vapor (indicated by green lines). The inset in Fig. 5
magnifies the low-frequency part of spectra indicating good
noise spectra measurements reproducibility. One can see that
S
I
/I
D
2
/1/f (here, f is the frequency) without traces of
bulges for all spectra including those measured under aceto-
nitrile vapor. This is in a drastic contrast to graphene devi-
ces. In this sense, S
I
/I
D
2
is a better sensing parameter for
graphene rather than for few-layer MoS
2
films. However, the
properly calibrated average level of S
I
/I
D
2
can still be used
for MoS
2
TF-FETs in combination with sand DI
D
/I
D
.
FIG. 3. Drain-source current versus time in MoS
2
TF-FET exposed to the
vapors of polar solvents: ethanol (upper panel), methanol (middle panel),
and acetonitrile (lower panel). The data were taken at the same gate voltage
V
G
¼60 V and drain voltage V
D
¼0.1 V for each case. The reference sam-
ple—the same device with the Al
2
O
3
coated channel—has not revealed any
variations in current as shown in the upper panel.
FIG. 4. Drain-source current versus time MoS
2
TF-FET exposed to the
vapors of non-polar solvents: chloroform (upper and middle panels) and tol-
uene (lower panel). The data were taken at the same gate voltage V
G
¼60 V
and drain voltage V
D
¼0.1 V for each case.
023115-3 Samnakay et al. Appl. Phys. Lett. 106, 023115 (2015)
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
169.235.187.11 On: Mon, 16 Mar 2015 17:19:32
Table Isummarizes the data for examined chemical vapors
including their type, dielectric constant e, and two sensing
parameters. In addition to the relative current change,
DI
D
/I
D
, we also show the ratio of the drain current under gas
exposure to the initial current before exposure, I
0
. The I
D
/I
0
metric is illustrative for the situation when the drain current
decreases. For comparison, the DI
D
/I
D
data for graphene
FETs is also shown. As seen, the presence of the band gap in
MoS
2
, allows one to achieve a larger change in the current
(orders of magnitude in some cases) than in graphene devi-
ces. For some vapors, it is possible to completely switch off
MoS
2
by the gas. The latter makes MoS
2
very attractive for
the gas sensing applications.
Although the exact mechanism of vapor molecule inter-
actions goes beyond the scope of this work and requires at-
omistic simulations, one can observe certain trends from
data in Table Iand Figs. 3and 4. The characteristic time con-
stants for current change under the exposure to polar mole-
cules are much shorter than those for non-polar molecules.
The vapors of non-polar solvents, characterized by small e,
induce current quenching in the thin MoS
2
channel. The
vapors of polar solvents with much larger e, on contrary
increase the electrical current in MoS
2
channel likely via
inducing additional charges. Indeed, considering that efor a
few-layer MoS
2
is around 4,
27
the polar molecules would
create a much larger dielectric mismatch with MoS
2
. There
are other possible mechanisms of MoS
2
TF-FET selectivity.
It can be related to different binding energies of the gas
molecules attached to the defect sites on MoS
2
film surface.
Such a mechanism was proposed to explain selectivity of
reduced graphene oxide devices.
28
It was proposed that
MoS
2
layers tend to interact strongly with the donor-like
analytes and their selectivity can be affected by the underly-
ing substrate.
14
Alternatively, there was a suggestion that the
exposed edge states in few-layer MoS
2
play the dominant
role in selective gas detection.
16
This mechanism assumes
that the basal plane, without defects, terminated by S atoms,
which lacks dangling bonds, is not active in molecule detec-
tion. The edge sites terminated by Mo or S atoms missing
coordination bonds are more active in attaching gas mole-
cules.
16
In this scenario, few-layer MoS
2
films with more
edge step sites can be preferential at the TF-FET channel.
The absence of bulges in MoS
2
TF-FETs, which is in
contract to graphene FETs, can be related to different mecha-
nisms of low-frequency noise in these two material systems.
We have previously shown that low-frequency noise in
MoS
2
thin films is similar to that in conventional semicon-
ductors and can be described well by McWhorter model,
which assumes that the dominant noise contribution comes
from the number of careers fluctuations.
26
Graphene, similar
to metals, reveals noise response, which does not comply
with the McWhorter model.
17–19,29,30
Although the low fre-
quency noise mechanism in graphene is still under debates,
19
it is clear now that it is different from that in MoS
2
. The lat-
ter makes the response of noise to the gas exposure to be
also different in these two materials.
In conclusion, we demonstrated selective gas sensing
with MoS
2
TF-FETs using the change in the channel current,
characteristic transient time, and low-frequency noise spec-
tral density as the sensing parameters. The exposure to etha-
nol, acetonitrile, toluene, chloroform, and methanol vapors
results in drastic changes in the source-drain current. The
current can increase or decrease by more than two-orders of
magnitude depending on the analyte type (polar vs. non po-
lar). The MoS
2
TF-FETs intentionally aged for a month were
robust and demonstrated even better stability and sensitivity.
The reference devices with coated channel did not show any
response. Unlike graphene devices and thin-film MoS
2
tran-
sistors do not show characteristic bulges in the low-
frequency current fluctuation spectra. The differences in the
low-frequency noise response are likely related to differen-
ces in the noise mechanisms and require further study. The
tested MoS
2
TF-FETs revealed orders of magnitude change
in current (resistance) upon gas exposure, which is in con-
trast to graphene devices. The obtained results are important
for practical applications of MoS
2
thin films and other van
der Waals materials.
FIG. 5. The normalized spectral density of the low-frequency source-drain
current fluctuations measured for MoS
2
TF-FET in open air and under expo-
sure to the vapors. The data were taken at the same gate voltage V
G
¼60 V
and drain voltage V
D
¼0.1 V for each case. The spectral density of MoS
2
TF-FET under vapor exposure reveals 1/f dependence without any traces of
bulges unlike graphene FETs. The inset magnifies the low-frequency part of
the spectra.
TABLE I. Chemical vapors and sensing parameters of MoS
2
TF-FET.
Vapor Type es(s) I
D
/I
0
MoS
2
FET DI
D
/I
D
(%) MoS
2
FET DI
D
/I
D
(%) graphene FET
Ethanol Polar protic 24.6 35 3.778 þ300 50
a
Methanol Polar protic 33.0 20 3.714 þ280 40
a
Acetonitrile Polar aprotic 37.5 130 1.625 þ60 35
a
Chloroform Non-polar 4.81 550 0.231 75 25
a
Toluene Non-polar 2.38 900 0.012 98 þ15
a
a
The data for graphene is taken from Ref. 24.
023115-4 Samnakay et al. Appl. Phys. Lett. 106, 023115 (2015)
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
169.235.187.11 On: Mon, 16 Mar 2015 17:19:32
The work at UC Riverside was supported by the
Semiconductor Research Corporation (SRC) and Defense
Advanced Research Project Agency (DARPA) through
STARnet Center for Function Accelerated nanoMaterial
Engineering (FAME). S.L.R. acknowledges partial support
from the Russian Fund for Basic Research (RFBR). The
work at RPI was supported by the National Science
Foundation under the auspices of the EAGER program.
Authors thank Dr. V. Tokranov for the help with sample
fabrication and Dr. Potyrailo for discussions on gas
sensing.
1
A. K. Geim and I. V. Grigorieva, Nature 499, 419 (2013).
2
D. Teweldebrhan, V. Goyal, and A. A. Balandin, Nano Lett. 10, 1209 (2010).
3
M. Chhowalla, H. S. Shin, G. Eda, L.-J. Li, K. P. Loh, and H. Zhang, Nat.
Chem. 5, 263 (2013).
4
Z. Yan, C. Jiang, T. R. Pope, C. F. Tsang, J. L. Stickney, P. Goli, J. Renteria,
T. T. Salguero, and A. A. Balandin, J. Appl. Phys. 114, 204301 (2013).
5
J. Heising and M. G. Kanatzidis, J. Am. Chem. Soc. 121, 11720 (1999).
6
Y. Kim, J.-L. Huang, and C. M. Lieber, Appl. Phys. Lett. 59, 3404 (1991).
7
J. L. Verble and T. J. Wieting, Phys. Rev. Lett. 25, 362 (1970).
8
S. W. Han, H. Kwon, S. K. Kim, S. Ryu, W. S. Yun, D. H. Kim, J. H.
Hwang, J.-S. Kang, J. Baik, H. J. Shin, and S. C. Hong, Phys. Rev. B 84,
045409 (2011).
9
K. F. Mak, C. Lee, J. Hone, J. Shan, and T. F. Heinz, Phys. Rev. Lett. 105,
136805 (2010).
10
G. Eda, H. Yamaguchi, D. Voiry, T. Fujita, M. Chen, and M. Chhowalla,
Nano Lett. 11, 5111 (2011).
11
H. Li, Z. Yin, Q. He, H. Li, X. Huang, G. Lu, D. W. H. Fam, A. I. Y. Tok,
Q. Zhang, and H. Zhang, Small 8, 63 (2012).
12
D. J. Late, B. Liu, H. S. S. R. Matte, V. P. Dravid, and C. N. R. Rao, ACS
Nano 6, 5635 (2012).
13
Q. He, Z. Zeng, Z. Yin, H. Li, S. Wu, X. Huang, and H. Zhang, Small 8,
2994 (2012).
14
F. K. Perkins, A. L. Friedman, E. Cobas, P. M. Campbell, G. G. Jernigan,
and B. T. Jonker, Nano Lett. 13, 668 (2013).
15
M. Shur, S. Rumyantsev, C. Jiang, R. Samnakay, J. Renteria, and A. A.
Balandin, “Selective gas sensing with MoS
2
thin film transistors,” in IEEE
Sensors 2014, Valencia, Spain, 2–5 November 2014.
16
S. L. Zhang, H. H. Choi, H. Y. Yue, and W. C. Yang, Curr. Appl. Phys.
14, 264 (2014).
17
M. Z. Hossain, S. Rumyantsev, M. S. Shur, and A. A. Balandin, Appl.
Phys. Lett. 102, 153512 (2013).
18
S. L. Rumyantsev, D. Coquillat, R. Ribeiro, M. Goiran, W. Knap, M. S.
Shur, A. A. Balandin, and M. E. Levinshtein, Appl. Phys. Lett. 103,
173114 (2013).
19
A. A. Balandin, Nat. Nanotechnol. 8, 549 (2013).
20
C. Lee, H. Yan, L. E. Brus, T. F. Heinz, J. Hone, and S. Ryu, ACS Nano
4(5), 2695 (2010).
21
K. R. Ratinac, W. Yang, S. P. Ringer, and F. Braet, Environ. Sci. Technol.
44, 1167 (2010).
22
H. Wang, L. Yu, Y.-H. Lee, Y. Shi, A. Hsu, M. Chin, L.-J. Li, M. Dubey,
J. Kong, and T. Palacios, Nano Lett. 12, 4674 (2012).
23
M. Xu, T. Liang, M. Shi, and H. Chen, Chem. Rev. 113, 3766 (2013).
24
S. Rumyantsev, G. Liu, M. S. Shur, R. A. Potyrailo, and A. A. Balandin,
Nano Lett. 12, 2294 (2012).
25
S. Rumyantsev, G. Liu, R. A. Potyrailo, A. A. Balandin, and M. S. Shur,
IEEE Sens. J. 13, 2818 (2013).
26
J. Renteria, R. Samnakay, S. L. Rumyantsev, C. Jiang, P. Goli, M. S. Shur,
and A. A. Balandin, Appl. Phys. Lett. 104, 153104 (2014).
27
E. J. G. Santos and E. Kaxiras, ACS Nano 7(12), 10741 (2013).
28
J. T. Robinson, F. K. Perkins, E. S. Snow, Z. Q. Wei, and P. E. Sheehan,
Nano Lett. 8, 3137 (2008).
29
S. Rumyantsev, G. Liu, W. Stillman, M. Shur, and A. A. Balandin,
J. Phys.: Condens. Matter 22, 395302 (2010).
30
G. Liu, S. Rumyantsev, M. S. Shur, and A. A. Balandin, Appl. Phys. Lett.
102, 093111 (2013).
023115-5 Samnakay et al. Appl. Phys. Lett. 106, 023115 (2015)
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
169.235.187.11 On: Mon, 16 Mar 2015 17:19:32
