Investigating the Laser Irradiation of Monolayer MoS 2 Using Tip-Enhanced Photoluminescence at the Nanoscale

Laser ablation and irradiation have long been established as efficient methods to prepare atomic-scale thickness two-dimensional (2D) electronic devices based on transition metal dichalcogenides (TMDs). However, comprehending the spatially nonuniform material transition of TMD thin layers intrinsically induced by the nonuniform heating of a tightly focused laser beam requires an analytical tool with nanoscale spatial resolution. Herein, tip-enhanced photoluminescence (TEPL), achieving a remarkable spatial resolution of 19 nm, was utilized to image the laser-irradiated monolayer (1L) MoS 2 to meet these requirements. TEPL imaging reveals that with an optimized laser power density of 2.51 × 10 9 mW/cm 2 and a short dwell time of 17 s, p-doping and enhanced A exciton photoluminescence (PL) intensity emerge at the laser focus center. Conversely, prolonged dwell time exceeding 20 s induces irreversible A exciton PL intensity reduction owing to the oxidation at the focal center and simultaneously causes PL enhancement at the peripheral region surrounding it. These TEPL results indicate that the far-field laser irradiation-induced temporal PL spectral variation of MoS 2 arises from the local competition between the p-type doping-induced PL enhancement and the oxidation-induced PL quenching. By optimizing the laser power and dwell time, a large area and high quality p–n junction can be fabricated on 1L MoS 2 flake via pixel-by-pixel scan. By integrating the TEPL results with the far-field temporal PL spectral variation, our findings give new insights into interpreting the laser irradiation process of MoS 2 at the nanoscale and would be helpful for developing novel TMD-based optoelectronic devices.