Anomalous Light-Induced Charging in MoS2 Monolayers with Cracks

( )Monolayer MoS2 devices with Au electrodes were fabricated on SiO2/Si substrates with 50 nm high SiO2 nanopillar (NP) array patterns. In the NP patterns, many cracks were found in the MoS2 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 MoS2 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 MoS2 flakes on the NPs were distinct from those on flat SiO2 . 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 MoS2 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.