Enhanced Light Absorption and Efficient Carrier Collection in MoS2 Monolayers on Au Nanopillars

Abstract

We fabricated hybrid nanostructures consisting of MoS2 monolayers and Au nanopillar (Au-NP) arrays. The surface morphology and Raman spectra showed that the MoS2 flakes transferred onto the Au-NPs were very flat and nonstrained. The Raman and photoluminescence intensities of MoS2/Au-NP were 3- and 20-fold larger than those of MoS2 flakes on a flat Au thin film, respectively. The finite-difference time-domain calculations showed that the Au-NPs significantly concentrated the incident light near their surfaces, leading to broadband absorption enhancement in the MoS2 flakes. Compared with a flat Au thin film, the Au-NPs enabled a 6-fold increase in the absorption in the MoS2 monolayer at a wavelength of 615 nm. The contact potential difference mapping showed that the electric potential at the MoS2/Au contact region was higher than that of the suspended MoS2 region by 85 mV. Such potential modulation enabled the Au-NPs to efficiently collect photogenerated electrons from the MoS2 flakes, as revealed by the uniform positive surface photovoltage signals throughout the MoS2 surface.

Photocurrent of Graphene/Au-Nanopillar: Near-Unity Degree of Linear Polarization

“…Thus, the use of SiO 2 -nanopattern templates instead of etching the noble metals with high chemical stability provides a simple approach to obtain plasmonic nanostructures. 25 Gr monolayers, grown by chemical vapor deposition, were dry transferred on the Au-coated substrates (Figure S1, Supporting Information). 26−28 The area of the patterned array was 500 × 500 μm 2 , and hence a flat Au region (AuF) and the Au nanopillar region (AuNP), could be obtained on an identical substrate, as illustrated in Figure 1a.…”

“…The SEM images of AuNP reveal that the Au thin film has a rough surface due to migration and agglomeration during the evaporation (Figure S2, Supporting Information). 25 Figures 1c and 1d are optical microscope images of the Au-coated patterned substrates before and after the Gr transfer, respectively. The central dark regions in Figures 1c and 1d correspond to the AuNP and Gr/AuNP regions, respectively.…”

“…The nanofabrication processes of SiO 2 are well-established and are widely used. Thus, the use of SiO 2 -nanopattern templates instead of etching the noble metals with high chemical stability provides a simple approach to obtain plasmonic nanostructures …”

“…Figure a shows a schematic diagram of a Gr monolayer transferred to a Au-coated nanopatterned substrate. Periodic SiO 2 nanopillar (NP) arrays (period: 500 nm, height: 50 nm, top diameter: 250 nm, and bottom diameter: 300 nm) were fabricated on SiO 2 /Si substrates using electron-beam lithography and subsequent dry-etching processes. , On such patterned SiO 2 /Si substrates, Au (100 nm) and Ti (10 nm) thin films were deposited using electron-beam evaporation. The amount of Au deposited at the NP sidewalls is constrained by highly directed evaporation because the deposition was carried out at low pressures of around 1 × 10 –6 Torr.…”