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

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