Anomalous Light-Induced Charging in MoS₂ Monolayers with Cracks

Abstract

Monolayer MoS 2 devices with Au electrodes were fabricated on SiO 2 / Si substrates with 50 nm high SiO 2 nanopillar (NP) array patterns. In the NP patterns, many cracks were found in the MoS 2 flakes, which were generated by the NP-induced mechanical strain during the wet transfer process. The cracks broke a few tens of micrometer MoS 2 flakes, producing micrometer-sized flakes. Some of the small MoS 2 flakes were suspended over the NPs, and others were not. The suspended flakes were highly strained, but the nonsuspended flakes were unstrained. Lightinduced charging behaviors at the MoS 2 flakes on the NPs were distinct from those on flat SiO 2 . More interestingly, positive and negative charging of an identical flake could be observed during repeated light on-and-off cycles. The strain-induced potential gradient in the MoS 2 flakes on the NPs could cause exciton dissociation and charge migration under illumination, giving rise to light-induced charging. The polarity and amount of charges could be determined by the strain states and initial net charges of a specific flake and its neighboring flakes.

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

“…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.…”