In Situ Probing the Localized Optoelectronic Properties of Defective Monolayer WS2

Probing the nanoscale localized optoelectronic properties induced by defects in two-dimensional (2D) transition-metal dichalcogenides challenges the spatial resolution and functionalities of many analytic tools. Herein, tip-enhanced photoluminescence (TEPL) combined with in situ photosensitive Kelvin probe force microscopy was used to fulfill such demand by exemplifying highly defective monolayer WS2 (1L-WS2) prepared by chemical vapor deposition. The contact potential difference (CPD) results indicate weak variation of work function without light but strong fluctuation of surface photovoltage (SPV) depending on the excitation laser wavelength and power. TEPL measurements reveal that the PL intensities of neutral exciton (A0) and trion (A–) vary quickly in the scale of a few hundreds of nanometers, which can be closely correlated to the distribution of SPVs. The CPD and TEPL results indicate the important role of defects in mediating the optoelectronic behaviors of 1L-WS2 in the nanoscale. The obtained results would further improve the understanding of the localized optoelectronic properties of intrinsic defects in 2D materials.