Charge Pumping by Contact Electrification Using Electrostatic Force Microscopy in Bi- and Trilayered MoS2 Nanosheets

摘要

Pumping charges into nanostructures by contact electrification is important for controlling and manipulating a device functionality in tribotronics. This study demonstrates a controlled charge transfer by contact electrification on a few-layered MoS2 nanosheet obtained by a chemical vapor deposition process. Nucleation sites present in the MoS2 nanosheets with sharp-tip features are used to transfer the charge between conducting tip and MoS2 nanosheets during contact electrification. The biased tip touching nucleation site pumps charges on the nanosheets, resulting in sharp change in contrast during dynamic electrostatic force microscope (EFM) scanning. A systematic analysis of charge transfer is performed by studying the phase and amplitude changes in EFM mode and surface potential change in Kelvin probe force microscope (KPFM) mode. Charge pumping is achieved by controlling tip bias, tip lift height, and scan rate. The charge density on the nanosheets is increased by raising the tip bias. On the contrary, the charge density decreases as the tip lift height is increased. The tip proximity to the nucleation site is used to control the transfer of charges pumped into the MoS2 nanosheet. The sustenance of pumped charges in the nanosheet is important for potential applications of 2D materials. Charge diffusion between MoS2 nanosheets and the Si/SiO2 substrate after charge pumping is studied by monitoring the time-dependent phase shift in EFM and surface potential in KPFM modes, and charge decay times of 6.9 and 7.5 h, respectively, are estimated. Controlled charge pumping through contact electrification in MoS2 can provide ample opportunity to build a new class of two-dimensional (2D) MoS2-based tribotronic devices.