3 research outputs found
Influence of Gas Adsorption and Gold Nanoparticles on the Electrical Properties of CVD-Grown MoS<sub>2</sub> Thin Films
Molybdenum
disulfide (MoS<sub>2</sub>) has increasingly attracted attention from
researchers and is now one of the most intensively explored atomic-layered
two-dimensional semiconductors. Control of the carrier concentration
and doping type of MoS<sub>2</sub> is crucial for its application
in electronic and optoelectronic devices. Because the MoS<sub>2</sub> layers are atomically thin, their transport characteristics may
be very sensitive to ambient gas adsorption and the resulting charge
transfer. We investigated the influence of the ambient gas (N<sub>2</sub>, H<sub>2</sub>/N<sub>2</sub>, and O<sub>2</sub>) choice on
the resistance (<i>R</i>) and surface work function (WF)
of trilayer MoS<sub>2</sub> thin films grown via chemical vapor deposition.
We also studied the electrical properties of gold (Au)-nanoparticle
(NP)-coated MoS<sub>2</sub> thin films; their <i>R</i> value
was found to be 2 orders of magnitude smaller than that for bare samples.
While the WF largely varied for each gas, <i>R</i> was almost
invariant for both the bare and Au-NP-coated samples regardless of
which gas was used. Temperature-dependent transport suggests that
variable range hopping is the dominant mechanism for electrical conduction
for bare and Au-NP-coated MoS<sub>2</sub> thin films. The charges
transferred from the gas adsorbates might be insufficient to induce
measurable <i>R</i> change and/or be trapped in the defect
states. The smaller WF and larger localization length of the Au-NP-coated
sample, compared with the bare sample, suggest that more carriers
and less defects enhanced conduction in MoS<sub>2</sub>
Band Alignment at Au/MoS<sub>2</sub> Contacts: Thickness Dependence of Exfoliated Flakes
We investigated the
surface potential (<i>V</i><sub>surf</sub>) of exfoliated
MoS<sub>2</sub> flakes on bare and Au-coated SiO<sub>2</sub>/Si substrates
using Kelvin probe force microscopy. The <i>V</i><sub>surf</sub> of MoS<sub>2</sub> single layers was larger
on the Au-coated substrates than on the bare substrates; our theoretical
calculations indicate that this may be caused by the formation of
a larger electric dipole at the MoS<sub>2</sub>/Au interface leading
to a modified band alignment. <i>V</i><sub>surf</sub> decreased
as the thickness of the flakes increased until reaching the bulk value
at a thickness of ∼20 nm (∼30 layers) on the bare and
∼80 nm (∼120 layers) on the Au-coated substrates, respectively.
This thickness dependence of <i>V</i><sub>surf</sub> was
attributed to electrostatic screening in the MoS<sub>2</sub> layers.
Thus, a difference in the thickness at which the bulk <i>V</i><sub>surf</sub> appeared suggests that the underlying substrate has
an effect on the electric-field screening length of the MoS<sub>2</sub> flakes. This work provides important insights to help understand
and control the electrical properties of metal/MoS<sub>2</sub> contacts
Asymmetrically Coupled Plasmonic Core and Nanotriplet Satellites
Here,
we report asymmetrical multiple electromagnetic coupling
of plasmonic core and nanotriplet satellites. Within the plasmonic
core and nanotriplet satellites, an enhanced local field is generated
which expands across the core due to multiple electromagnetic coupling
between a core and nanotriplets. Based on 3D simulations of our plasmonic
nanosystem, the overall local field enhancement reaches to over 10<sup>4</sup> times, compared with that of a single nanoparticle array.
A strong local field distribution across the core to nanotriplets
as well as the critical role of the plasmonic core is demonstrated
through the 3D simulations. It is proposed that a self-assembled nanotriplet
array is completed through two stages of dewetting of a gold thin
film on an anodic aluminum oxide (AAO) template. Formation of the
core–nanotriplet satellites is significantly influenced by
geometrical parameters (i.e., the pore diameter and depth) of the
AAO template. Our experimental results show that the local field of
our plasmonic nanostructures is amplified up to ∼110 times
by adopting a core into the nanotriplet satellites, compared with
that of the nanotriplets array without a core. This approach offers
a promising strategy for creating an advanced nanoplasmonic platform
with strong local field distribution and high-throughput production