Plasmonic Hot Electron Induced Photocurrent Response at Metal Junctions MoS

Plasmonic Hot Electron Induced Photocurrent Response at Metal Junctions MoS
ARTICLE
Plasmonic Hot Electron Induced
Photocurrent Response at
MoS2Metal Junctions
Tu Hong,† Bhim Chamlagain,‡ Shuren Hu,§ Sharon M. Weiss,†,§ Zhixian Zhou,‡ and Ya-Qiong Xu*,†,§
†
Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37212, United States, ‡Department of Physics and
Astronomy, Wayne State University, Detroit, Michigan 48201, United States, and §Department of Physics and Astronomy, Vanderbilt University, Nashville,
Tennessee 37212, United States
ABSTRACT We investigate the wavelength- and polarization-dependence of
photocurrent signals generated at few-layer MoS2metal junctions through
spatially resolved photocurrent measurements. When incident photon energy is
above the direct bandgap of few-layer MoS2, the maximum photocurrent response
occurs for the light polarization direction parallel to the metal electrode edge,
which can be attributed to photovoltaic effects. In contrast, if incident photon
energy is below the direct bandgap of MoS2, the photocurrent response is
maximized when the incident light is polarized in the direction perpendicular to
the electrode edge, indicating different photocurrent generation mechanisms. Further studies show that this polarized photocurrent response can be
interpreted in terms of the polarized absorption of light by the plasmonic metal electrode, its conversion into hot electronhole pairs, and subsequent
injection into MoS2. These fundamental studies shed light on the knowledge of photocurrent generation mechanisms in metalsemiconductor junctions,
opening the door for engineering future two-dimensional materials based optoelectronics through surface plasmon resonances.
KEYWORDS: plasmonics . scanning photocurrent microscopy . MoS2 . photovoltaic effect . photothermoelectric effect . polarization
T
he development of two-dimensional
(2D) materials, such as graphene
and transition metal dichalcogenides
(TMDCs), has opened up new horizons in
the realm of physics and engineering that
could lead to the revolution of future nanoelectronics, optoelectronics, and energy
harvesting.15 One of the most promising
applications of 2D materials is for photodetectors.611 Various hybrid structures
have been developed to enhance the
photoresponse in 2D materials.614 Among
them the simplest configuration is the
metal2D materialmetal device, in
which the photocurrent can be generated
at metal2D material junctions. Metal
molybdenum disulfide (MoS2)metal devices have attracted much interest for
photodetector applications due to their potential for achieving ultrahigh sensitivity.6
Intensive research efforts have focused on
elucidating the physical mechanisms that
give rise to photoconductivity in metal
MoS2-metal devices.6,1518 Two major mechanisms have been proposed to explain
HONG ET AL.
the photocurrent response at MoS2metal
junctions: photovoltaic effect (PVE) and
photothermoelectric effect (PTE).6,15,16
Recently, plasmon excitations in metallic
nanostructures have been demonstrated to
modulate the structural and optical properties of MoS2 and other 2D materials. For
example, hot carrier injection can change
the doping of graphene19 and induce structural phase transitions in MoS2.20,21 The
efficiency of the hydrogen evolution reaction can also be enhanced by depositing
Au-coated Ag nanorattles on MoS2 to induce its localized phase transition under
plasmon resonance excitation.22 Moreover,
the photoluminescence of MoS2 can be
influenced by surface plasmons of Au nanoantennas, where the photoluminescence
intensity is significantly enhanced and
strongly dependent on the incident polarization when the wavelength is close to
resonance with the surface plasmons of
nanoantennas.23 The surface plasmon resonances induced by metals may also affect
the photocurrent response at MoS2metal
VOL. 9
’
NO. 5
’
* Address correspondence to
yaqiong.xu@vanderbilt.edu.
Received for review February 14, 2015
and accepted April 14, 2015.
Published online April 14, 2015
10.1021/acsnano.5b01065
C 2015 American Chemical Society
5357–5363
’
2015
5357
www.acsnano.org
ARTICLE
Figure 1. Electrical transport characterization of a 9 nm thick MoS2 FET. (a) Output characteristics of the device measured at
various gate voltages between 0 and 60 V. Inset: AFM image of the device. The scale bar is 2 μm. (b) Four-terminal conductivity
of the device measured with the back-gate voltage sweeping from 20 to 60 V at different temperatures. Inset: Field-effect
mobility as a function of temperature estimated from the four-terminal conductivity in the gate voltage ranging from 40 to 60 V.
junctions. It is, therefore, desirable to study the relative
contributions of PVE, PTE, and surface plasmons to the
overall photoresponse at MoS2metal junctions. Understanding the photonelectron conversion mechanisms at MoS2metals will offer a new approach for
engineering future 2D material based optoelectronics.
Here, we investigate the polarization- and wavelength-dependence of photocurrent signals generated
at few-layer MoS2metal junctions through spatially
resolved photocurrent measurements. When incident
photon energy is above the direct bandgap of fewlayer MoS2, the maximum photocurrent response occurs for the light polarization direction parallel to the
metal electrode edge. This anisotropic photocurrent
response may result from the light-generated anisotropic distribution of carriers in momentum space,
which has been demonstrated in the photoresponse
at graphenemetal junctions.24 Interestingly, we find
that if incident photon energy is below the direct
bandgap of MoS2, the photocurrent intensity is reduced by 2 orders of magnitude and mainly attributed
to the polarized absorption of the plasmonic Au electrodes. When the wavelength is close to resonance
with the surface plasmons of the Au electrodes, the
photocurrent intensity is strongly dependent on the
incident polarization with about 8 times larger for laser
polarization perpendicular to the metal electrode than
for parallel polarization. Plasmonically engineered
photocurrent response in metalsemiconductor junctions may provide a new way to design future 2D
photodetectors, in particular, in the near-infrared and
infrared regimes.
RESULTS AND DISCUSSION
Few-layer MoS2 crystals (6 nm 10 nm) were produced by repeated splitting of bulk crystals using a
mechanical cleavage method, and subsequently
HONG ET AL.
transferred to a degenerately doped Si substrate
with 290 nm SiO2. To minimize charged impurities
and charge traps on the substrate surface, the Si/SiO2
substrates were covered with crystalline self-assembled monolayers (SAMs) of octadecyltrimethoxysilane (OTMS) prior to the transfer of mechanically
exfoliated MoS2 flakes.25,26 Optical microscopy was
used to identify thin MoS2 crystals, which were further
characterized by Park-Systems XE-70 noncontact
atomic force microscopy (AFM). MoS2 field effect transistors (FETs) were subsequently fabricated using standard electron beam lithography and electron beam
deposition of 5 nm Ti and 40 nm Au, where the Si
substrate is used as the back gate. An AFM image of a
typical MoS2 device is shown in the inset of Figure 1a,
where the length of metal electrodes is 10 μm and the
widths of the wide and narrow electrodes are 2 μm and
200 nm, respectively. Electrical properties of the devices were measured by a Keithley 4200 semiconductor parameter analyzer in a Lakeshore cryogenic probe
station under high vacuum (1 106 Torr). Figure 1
shows the electrical characteristics of a 9 nm thick
MoS2 FET (as determined by AFM). The IdsVds curves
exhibit ohmic characteristic for gate voltages steping
from 0 to 60 V, indicating a negligible Schottky barrier
between the Au electrodes and MoS2 (Figure 1a), in
agreement with a previous report (∼50 meV).27 The
device displays a predominately n-type behavior, with
the estimated room-temperature field-effect mobility
μ ∼ 50 cm2 V1 s1 as extracted from the gate dependence of four-terminal conductivity σ (Figure 1b).28 As
the temperature decreases, the mobility increases
following a μ ∼ T2.0 dependence, consistent with
the recent results on high quality MoS2 encapsulated
by boron nitride (Figure 1b inset).29
To investigate the local photoresponse at MoS2metal
junctions, we performed spatially resolved scanning
VOL. 9
’
NO. 5
’
5357–5363
’
5358
2015
www.acsnano.org
ARTICLE
Figure 2. (a) Schematic illustration of the MoS2 device and
the optical setup. (b) Scanning photocurrent image and
(c) reflection image of the MoS2 device illuminated by 785 nm
laser. Incident light polarization directions are defined as
marked, where 0 denotes polarization direction along the
metal electrode edge and 90 denotes polarization direction
perpendicular to the metal electrode edge. The scale bars are
2 μm. (d) Photocurrent response of the MoS2 FET as a
function of gate voltage with illumination of 532 nm (green
curve), 785 nm (red curve), and 1550 nm (blue curve) laser,
respectively. The source-drain bias is 10 mV. The lasers were
defocused to form a spot large enough to cover the entire
MoS2 flake. (e) Band structure of few-layer MoS2, an indirect
bandgap semiconductor with a direct bandgap at K (K)
points. The valence band splitting is not shown.
photocurrent measurements in an Olympus microscope setup (Figure 2a). A linearly polarized continuous
wave laser source was expanded and altered by a
nanometer-resolution scan mirror. The laser beam
was then focused by a 40 objective (N.A. = 0.6) into
a diffraction-limited spot (∼1 μm) on the samples. The
polarization direction of the laser beam was changed
by a half-wave plate followed by a polarizer. All experiments were performed in high vacuum (1 106 Torr).
Figure 2b shows a scanning photocurrent image of a
MoS2 device at zero bias, whose corresponding reflection image was recorded simultaneously (Figure 2c).
The outer two electrodes of the MoS2 FET were used as
source and drain while the middle two electrodes were
floating during the measurement. Figure 2d shows the
photocurrent signals ΔIpc = Ids,illumination Ids,dark under
laser illumination of three different wavelengths (532,
785, and 1550 nm), where the source-drain bias is
10 mV. With 532 nm (2.33 eV) illumination, a significant
photocurrent response is mainly attributed to the
increment of electrons that are efficiently excited
through a direct bandgap close to 1.9 eV at K(-K) points
HONG ET AL.
Figure 3. Scanning photocurrent images of MoS2 illuminated by (a) 532 nm, (b) 785 nm, and (c) 1550 nm laser,
respectively. The black dashed lines outline the metal
electrodes, whereas the blue dashed lines mark the MoS2
edges. The intensities of the photocurrent response are
normalized. (d) Line profiles of the photocurrent response
along the dashed green lines in (ac). The photocurrent
intensities are displaced for clarity. The solid curves are
Gaussian fits of the line profiles at the MoS2-metal junction.
The black arrows denote the photocurrent “tails” on the
electrodes. The orange background indicates electrode
positions. (e) Schematic illustration of PVE and (f) PTE
mechanisms. Eg represents the bandgap of MoS2.
(Figure 2e).30,31 As a result, the direct bandgap transition and PTE will be responsible for the photocurrent
response. The photocurrent signals induced by 785 nm
(1.58 eV) excitation may be related to the indirect
bandgap optical transition between Brillouin zone Γ
point and K point in few-layer MoS2 (1.2 eV). This
process requires a phonon to change the momentum,
resulting in a relatively low quantum efficiency and
leading to a significant reduction of PVE-induced photocurrent response. Moreover, there is a non-negligible
photocurrent response upon 1550 nm (0.8 eV) illumination, whose photon energy is not enough to excite
electrons from the valence band of MoS2. Here, the PVE
induced by the indirect bandgap transition does not
contribute to the photocurrent response. Therefore,
PTE or other new mechanisms are required to explain
the photocurrent generation when the photon energy
is below the direct bandgap of MoS2.
To clarify the photocurrent generation mechanisms
in MoS2metal junctions, we look into the spatially
resolved scanning photocurrent images of the MoS2
FET illuminated by 532, 785, and 1550 nm laser,
respectively (Figure 3ac). The black dashed lines are
VOL. 9
’
NO. 5
’
5357–5363
’
5359
2015
www.acsnano.org
VPTE ¼ (SMoS2 SMetal )ΔT
16,32
From the Mott relation,
coefficient as
(1)
we can obtain the Seebeck
π2 kb2 T 1 dG
S ¼ 3e G dE (2)
E ¼ EF
where kb is the Boltzmann constant, e is the electron
charge, G is conductance, and EF is Fermi energy. We
estimated the Seebeck coefficient of our MoS2 device
at different Fermi levels from eq 2 and obtained
S ∼ 40 μV/K at Vg = 0 V. This value increases to its
maximum (∼2 103 μV/K) when Vg approaches
toward 40 V, which is comparable to the reported
bulk value of MoS233 and about one to 2 orders of
magnitude smaller than that observed in monolayer
MoS2.17
To further explore the relative contributions of different photocurrent generation mechanisms to the overall photocurrent response, we performed polarizationdependent photocurrent measurements, where 0
denotes the polarization direction along the metalMoS2 contact edge (Figure 2c). The photocurrent
response at a MoS2-metal junction was systematically
investigated when the junction was illuminated by
lasers from 500 nm (2.48 eV) to 1050 nm (1.18 eV) in
50 nm steps. As shown in Figure 4, the maximum
photocurrent response occurs at 90 light polarization
HONG ET AL.
for lasers with photon energies below the direct bandgap of MoS2 (with wavelength of 750 nm or longer),
whereas the maximum photocurrent is generated by
photons polarized at around 0 when the excitation
photon energy is above the direct bandgap of MoS2
(with laser wavelength of 650 nm or shorter). Since PTE
should be isotropic and independent of the incoming
light polarization, the generation of thermally induced
charge carriers could not explain our observation. If
the photon energy is high enough to excite carriers
through the direct bandgap at K (K) points in MoS2
Brillouin zone, the built-in electric field at MoS2metal
junctions can separate the photoexcited charge carriers to generate photocurrent (PVE). The polarization
dependence measurements suggest that the interband transition at K (-K) points is maximized when
photons are polarized parallel to the electrode edges.
This result indicates that the valence electrons in MoS2
prefer to absorb photons with the polarization direction perpendicular to the momentum of electrons. A
similar phenomenon has been demonstrated in the
photoresponse at graphene-metal junctions, in which
it was shown that when the polarization angle of the
incident light is perpendicular to the momentum of
electrons, the absorption of light for valence electrons
in graphene is maximum, leading to anisotropic photocurrent signals.24
When the excitation laser energy is below the direct
bandgap (1.9 eV) of MoS2 (especially below the indirect
bandgap of 1.2 eV), a new mechanism is needed to
explain the photocurrent generation due to the absence of optical transitions through the bandgap. It is
well-known that photoexcited hot electrons in metal
electrodes can cross over the Schottky barrier and be
injected into the conduction band of semiconductors
(Figure 5a). The Schottky barrier between Au electrodes and few-layer MoS2 is very small as demonstrated
in our electrical transport measurements (Figure 1a)
and previous studies (∼50 meV),27 which is well below
the excitation photon energies in our experiments. The
injection yield of hot electrons Y follows the Fowler
equation
Y∼
1 (pω φB )2
8EF
pω
ARTICLE
the edges of the metal electrodes, and the blue dashed
lines show the edges of the MoS2. A line profile of
photocurrent intensities in each image is extracted
along the dashed green line in the vertical direction
and presented in Figure 3d. The photocurrent intensities were normalized and displaced for clarity, and
the solid curves are Gaussian fittings of the photocurrent values. The strongest photocurrent responses are
observed at the MoS2metal junction for illumination
with different photon energies. As shown in Figure 3e,
potential barriers are formed at MoS2metal junctions
due to Fermi level alignment, leading to a built-in
electric field that separates the photoexcited charge
carriers when photon energies are greater than the
bandgap of MoS2 (PVE). However, when the photon
energy is below the bandgap, the PVE induced photocurrent response is significantly reduced, owing to the
absence of interband transitions. Moreover, by comparing the photocurrent profiles and the Gaussian
fittings, we notice strong photocurrent “tails” in the
metal region for all laser wavelengths as pointed by the
black arrows in Figure 3d, indicating that PTE (Figure 3f)
also contributes to the photocurrent generation at
MoS2metal junctions. A temperature difference (ΔT)
arises upon laser absorption due to the difference in
Seebeck coefficients (S) between MoS2 and metal
electrodes. This temperature gradient leads to a photothermal voltage (VPTE) across the junction,
(3)
where p is the reduced plank constant, ω is the incident
light frequency, φB is the Schottky barrier, and EF is
Fermi energy. The injection yield depends on the
wavelength of the excitation light instead of its polarization, which cannot explain the polarization dependence of photocurrent signals. In fact, the photocurrent response depends on not only the injection
yield of hot electrons but also the metal absorption. As
shown in Figure 5b, when the illumination wavelength
is close to 850 nm, the anisotropic ratio of the photo0
current response (I90
pc /Ipc) achieves its maximum (∼8),
which is significantly reduced when the width of the
VOL. 9
’
NO. 5
’
5357–5363
’
5360
2015
www.acsnano.org
ARTICLE
Figure 4. Normalized photocurrent intensities at a MoS2-metal junction (200 nm-wide metal electrode) as a function of
incident light polarization with illumination wavelength from 500 to 1050 nm. Gate voltage and source-drain bias were 0 V
during the measurements.
which is related to its respective electric field through
the time-averaged Poynting vector S:
Ipc ∼ Iab ∼ ÆSætime ∼ jEj2
(4)
2
Figure 5. (a) Schematic illustration of hot electron injection
from a metal electrode to MoS2. Eg represents the bandgap
of MoS2. (b) The wavelength dependence of measured
0
photocurrent response (I90
pc /Ipc) at MoS2-metal junctions.
(c) The calculated |E90|2/|E0|2 of metal electrodes by using
FDTD as a function of wavelength. (d) Photocurrent power
dependence with 650 nm (1.91 eV, black triangles) and
850 nm (1.46 eV, green squares) laser polarized in 0 (solid)
and 90 (hollow).
metal electrode increase from 200 nm to 2 μm. The
metal absorption Iab is proportional to the energy flux,
HONG ET AL.
The |E| ratio between two polarizations is calculated
using finite difference time domain (FDTD) simulations
(Figure 5c). The geometries are chosen according to
device dimensions measured by AFM. The calculated
|E90|2/|E0|2 shows a resonance peak at 850 nm, in good
agreement with the resonance peak observed in
photocurrent measurements. Moreover, the resonance
intensity of |E90|2/|E0|2 is reduced by increasing the
width of electrode from 200 nm to 2 μm. The relatively
low anisotropic ratio of photocurrent in our devices
may result from shape imperfections and the strong
absorption of the Ti adhesion layer in the near-infrared
regions, which can lead to a strong damping of the
surface plasmon resonance.34,35 The consistence of the
resonance between the calculated |E90|2/|E0|2 of metal
0
electrodes and photocurrent measurements (I90
pc /Ipc)
confirms that the polarized photocurrent response
can be primarily attributed to the surface plasmon
resonance in metal electrodes. We also performed
power dependence measurements of the photocurrent
VOL. 9
’
NO. 5
’
5357–5363
’
5361
2015
www.acsnano.org
METHODS
REFERENCES AND NOTES
CONCLUSIONS
Device Fabrication and Electrical Characterization. Degenerately
p-doped silicon substrate with 290 nm of thermally grown
SiO2 was first treated by oxygen plasma for 10 min to enhance
hydrophilicity. Subsequently, a 3 mM octadecyltrimethoxysilane (OTMS) (from Sigma Aldrich) solution in trichloroethylene
was drop-casted on the substrate and allowed to assemble for
10 s. The substrate was then spun at 3000 rpm for 10 s to
uniformly cover the entire surface followed by immersion in
ammonia (NH3) vapor at room temperature overnight. Finally,
the substrate was rinsed with deionized (DI) water and bath
sonicated in toluene for about 5 min. Multilayer MoS2 flakes
were produced by mechanical exfoliation of MoS2 crystals (from
SPI) and subsequently transferred to the OTMS-SAM-modified
SiO2 substrates. Optical microscopy and Park-Systems XE-70
noncontact mode atomic microscopy (AFM) were used to
identify and characterize thin MoS2 flakes. Four-probe MoS2
FET devices were fabricated using standard electron beam
lithography and subsequent electron beam deposition of
5 nm of Ti covered by 40 nm of Au. Electrical properties of the
devices were measured by a Keithley 4200 semiconductor
parameter analyzer in a lakeshore Cryogenic probe station
under high vacuum (1 106 Torr).
Scanning Photocurrent Measurements. Spatially resolved scanning photocurrent measurements were performed in an Olympus microscope setup. A linearly polarized continuous wave
laser source was expanded and its position was changed by a
nanometer-resolution scan mirror. A 40 objective (N.A. = 0.6)
was used to focus the laser beam into a diffraction-limited
spot (∼1 μm) on the samples. The polarization direction of the
laser beam was changed by a half-wave plate followed by
a polarizer. All experiments were performed in high vacuum
(1 106 Torr).
FDTD Simulations. The |E|2 ratio was calculated using threedimensional finite-difference time-domain simulations
(Lumerical FDTD Solutions) with the following specifications.
The geometries were chosen to match the device dimensions.
The light source was defined as a plane wave. The mesh size was
a uniform 4 nm and the entire simulation space was surrounded
by a perfectly matched layer (PML) that absorbed any fields
reaching the boundaries. Frequency domain field and power
monitors were used to record the optical field at the interface
between electrodes and the underlying SiO2. The width of
the optical field monitors was set to be 2 μm wider than the
electrodes such that the optical field within 1 μm from the
edges of electrodes would be collected.
Conflict of Interest: The authors declare no competing
financial interest.
Acknowledgment. This work was supported by the National
Science Foundation (ECCS-1055852 and CBET-1264982 to
Y.X.; ECCS-1128297 and DMR-1308436 to Z.Z.; ECCS-1407777
to S.W.).
HONG ET AL.
ARTICLE
In conclusion, we investigate the relative contributions of PVE, PTE, and surface plasmons to the
overall photoresponse at MoS2-metal junctions
through polarization- and wavelength-dependent
scanning photocurrent measurements. We demonstrate that when incident photon energy is above the
direct bandgap of few-layer MoS2, the photocurrent
response is primarily attributed to PVE and maximized
for the light polarization direction parallel to the metal
electrode edge. When the incident photon energy is
below the direct bandgap of MoS2, the photocurrent
signals mainly result from surface plasmons of Au
electrodes, which are 2 orders of magnitude smaller
than those induced by PVE. These fundamental studies
may offer a new design rule for future 2D material
based photodetectors, in particular, in the near-infrared
and infrared regimes.
response at a MoS2-metal junction. Both PVE (650 nm)
and surface plasmon (850 nm) induced photocurrent
signals have a linear dependence with incident power
(Figure 5d), while the PVE induced photocurrent response is 2 orders of magnitude greater than photocurrent signals generated through surface plasmons in
metal electrodes.
1. Bonaccorso, F.; Sun, Z.; Hasan, T.; Ferrari, A. C. Graphene
Photonics and Optoelectronics. Nat. Photonics 2010, 4,
611–622.
2. Wang, Q. H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.;
Strano, M. S. Electronics and Optoelectronics of
Two-Dimensional Transition Metal Dichalcogenides. Nat.
Nanotechnol. 2012, 7, 699–712.
3. Xu, M. S.; Liang, T.; Shi, M. M.; Chen, H. Z. Graphene-Like
Two-Dimensional Materials. Chem. Rev. 2013, 113, 3766–
3798.
4. Novoselov, K. S.; Fal'ko, V. I.; Colombo, L.; Gellert, P. R.;
Schwab, M. G.; Kim, K. A Roadmap for Graphene. Nature
2012, 490, 192–200.
5. Jariwala, D.; Sangwan, V. K.; Lauhon, L. J.; Marks, T. J.;
Hersam, M. C. Emerging Device Applications for Semiconducting Two-Dimensional Transition Metal Dichalcogenides. ACS Nano 2014, 8, 1102–1120.
6. Lopez-Sanchez, O.; Lembke, D.; Kayci, M.; Radenovic, A.;
Kis, A. Ultrasensitive Photodetectors Based on Monolayer
MoS2. Nat. Nanotechnol. 2013, 8, 497–501.
7. Britnell, L.; Ribeiro, R. M.; Eckmann, A.; Jalil, R.; Belle, B. D.;
Mishchenko, A.; Kim, Y. J.; Gorbachev, R. V.; Georgiou, T.;
Morozov, S. V.; et al. Strong Light-Matter Interactions in
Heterostructures of Atomically Thin Films. Science 2013,
340, 1311–1314.
8. Yu, W. J.; Liu, Y.; Zhou, H. L.; Yin, A. X.; Li, Z.; Huang, Y.; Duan,
X. F. Highly Efficient Gate-Tunable Photocurrent Generation in Vertical Heterostructures of Layered Materials. Nat.
Nanotechnol. 2013, 8, 952–958.
9. Koppens, F. H. L.; Mueller, T.; Avouris, P.; Ferrari, A. C.;
Vitiello, M. S.; Polini, M. Photodetectors Based on
Graphene, Other Two-Dimensional Materials and Hybrid
Systems. Nat. Nanotechnol. 2014, 9, 780–793.
10. Pospischil, A.; Furchi, M. M.; Mueller, T. Solar-Energy
Conversion and Light Emission in an Atomic Monolayer
p-n Diode. Nat. Nanotechnol. 2014, 9, 257–261.
11. Baugher, B. W. H.; Churchill, H. O. H.; Yang, Y. F.;
Jarillo-Herrero, P. Optoelectronic Devices Based on Electrically Tunable p-n Diodes in a Monolayer Dichalcogenide. Nat. Nanotechnol. 2014, 9, 262–267.
12. Mueller, T.; Xia, F. N. A.; Avouris, P. Graphene Photodetectors for High-Speed Optical Communications. Nat. Photonics 2010, 4, 297–301.
13. Hong, T.; Chamlagain, B.; Lin, W.; Chuang, H.-J.; Pan, M.;
Zhou, Z.; Xu, Y.-Q. Polarized Photocurrent Response in
Black Phosphorus Field-Effect Transistors. Nanoscale
2014, 6, 8978–8983.
14. Geim, A. K.; Grigorieva, I. V. Van der Waals Heterostructures. Nature 2013, 499, 419–425.
15. Wu, C.-C.; Jariwala, D.; Sangwan, V. K.; Marks, T. J.; Hersam,
M. C.; Lauhon, L. J. Elucidating the Photoresponse of
Ultrathin MoS2 Field-Effect Transistors by Scanning
VOL. 9
’
NO. 5
’
5357–5363
’
5362
2015
www.acsnano.org
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
ARTICLE
16.
Photocurrent Microscopy. J. Phys. Chem. Lett. 2013, 4,
2508–2513.
Buscema, M.; Barkelid, M.; Zwiller, V.; van der Zant, H. S. J.;
Steele, G. A.; Castellanos-Gomez, A. Large and Tunable
Photothermoelectric Effect in Single-Layer MoS2. Nano
Lett. 2013, 13, 358–363.
Kwak, J. Y.; Hwang, J.; Calderon, B.; Alsalman, H.; Munoz, N.;
Schutter, B.; Spencer, M. G. Electrical Characteristics of
Multilayer MoS2 FET's with MoS2/Graphene Heterojunction Contacts. Nano Lett. 2014, 14, 4511–4516.
Furchi, M. M.; Polyushkin, D. K.; Pospischil, A.; Mueller, T.
Mechanisms of Photoconductivity in Atomically Thin
MoS2. Nano Lett. 2014, 14, 6165–6170.
Fang, Z. Y.; Wang, Y. M.; Liu, Z.; Schlather, A.; Ajayan, P. M.;
Koppens, F. H. L.; Nordlander, P.; Halas, N. J. Plasmon-Induced
Doping of Graphene. ACS Nano 2012, 6, 10222–10228.
Kang, Y. M.; Najmaei, S.; Liu, Z.; Bao, Y. J.; Wang, Y. M.; Zhu,
X.; Halas, N. J.; Nordlander, P.; Ajayan, P. M.; Lou, J.; et al.
Plasmonic Hot Electron Induced Structural Phase
Transition in a MoS2 Monolayer. Adv. Mater. 2014, 26,
6467–6471.
Brongersma, M. L.; Halas, N. J.; Nordlander, P. PlasmonInduced Hot Carrier Science and Technology. Nat. Nanotechnol. 2015, 10, 25–34.
Kang, Y.; Gong, Y.; Hu, Z.; Li, Z.; Qiu, Z.; Zhu, X.; Ajayan, P. M.;
Fang, Z. Plasmonic Hot Electron Enhanced MoS2
Photocatalysis in Hydrogen Evolution. Nanoscale 2015,
7, 4482–4488.
Najmaei, S.; Mlayah, A.; Arbouet, A.; Girard, C.; Leotin, J.;
Lou, J. Plasmonic Pumping of Excitonic Photoluminescence in Hybrid MoS2-Au Nanostructures. ACS Nano
2014, 8, 12682–12689.
Kim, M.; Yoon, H. A.; Woo, S.; Yoon, D.; Lee, S. W.; Cheong, H.
Polarization Dependence of Photocurrent in a MetalGraphene-Metal device. Appl. Phys. Lett. 2012, 101,
073103.
Ito, Y.; Virkar, A. A.; Mannsfeld, S.; Oh, J. H.; Toney, M.;
Locklin, J.; Bao, Z. Crystalline Ultrasmooth Self-Assembled
Monolayers of Alkylsilanes for Organic Field-Effect Transistors. J. Am. Chem. Soc. 2009, 131, 9396–9404.
Wang, X.; Xu, J.-B.; Wang, C.; Du, J.; Xie, W. HighPerformance Graphene Devices on SiO2/Si Substrate
Modified by Highly Ordered Self-Assembled Monolayers.
Adv. Mater. 2011, 23, 2464–2468.
Das, S.; Chen, H. Y.; Penumatcha, A. V.; Appenzeller, J. High
Performance Multilayer MoS2 Transistors with Scandium
Contacts. Nano Lett. 2013, 13, 100–105.
Chamlagain, B.; Li, Q.; Ghimire, N. J.; Chuang, H.-J.; Perera,
M. M.; Tu, H.; Xu, Y.; Pan, M.; Xaio, D.; Yan, J.; et al. Mobility
Improvement and Temperature Dependence in MoSe2
Field-Effect Transistors on Parylene-C Substrate. ACS Nano
2014, 8, 5079–5088.
Cui, X.; Lee, G.-H.; Kim, Y. D.; Arefe, G.; Huang, P. Y.; Lee,
C.-H.; Chenet, D. A.; Zhang, X.; Wang, L.; Ye, F.; et al.
Multi-Terminal Electrical Transport Measurements of
Molybdenum Disulphide Using van der Waals Heterostructure Device Platform. 2014, arXiv:1412.5977.
Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F. Atomically
Thin MoS2: A New Direct-Gap Semiconductor. Phys. Rev.
Lett. 2010, 105, 136805.
Splendiani, A.; Sun, L.; Zhang, Y. B.; Li, T. S.; Kim, J.; Chim,
C. Y.; Galli, G.; Wang, F. Emerging Photoluminescence in
Monolayer MoS2. Nano Lett. 2010, 10, 1271–1275.
Xu, X. D.; Gabor, N. M.; Alden, J. S.; van der Zande, A. M.;
McEuen, P. L. Photo-Thermoelectric Effect at a Graphene
Interface Junction. Nano Lett. 2010, 10, 562–566.
Mansfield, R.; Salam, S. A. Electrical Properties of Molybdenite. Proc. Phys. Soc., Sect. B 1953, 66, 377.
Jeppesen, C.; Mortensen, N. A.; Kristensen, A. The Effect of
Ti and ITO Adhesion Layers on Gold Split-Ring Resonators.
Appl. Phys. Lett. 2010, 97, 263103.
Habteyes, T. G.; Dhuey, S.; Wood, E.; Gargas, D.; Cabrini, S.;
Schuck, P. J.; Alivisatos, A. P.; Leone, S. R. Metallic Adhesion
Layer Induced Plasmon Damping and Molecular Linker as
a Nondamping Alternative. ACS Nano 2012, 6, 5702–5709.
HONG ET AL.
VOL. 9
’
NO. 5
’
5357–5363
’
5363
2015
www.acsnano.org
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising