Nitrogenation of microscopic MoS2 surfaces by oxidation scanning probe lithography

MoS2 has found many applications in optoelectronics, energy harvesting, and catalysis due to its unique properties and functionalities. It has been shown that its properties can be tuned by thermal oxidation and plasma treatment. Herein, we examined the capability of oxidation scanning probe lithography (o-SPL) for direct nitrogenation of the MoS2 crystals under ambient conditions. By utilizing Kelvin probe force microscopy together with Auger electron spectroscopy, we found out that the o-SPL method was able to simultaneously oxidize and nitrogenize MoS2 flakes when a relatively high input voltage was exerted. Under such harsh conditions, oxygen and nitrogen atoms were incorporated and replaced the sulfur atoms within MoS2. At the same time, large surface topographical changes were observed mostly due to sample delamination. On the contrary, low input voltage was able to produce large topographical changes associated only with desulfurization but without any oxidation/nitrogenation. Finally, high voltage o-SPL treatment of MoS2 samples pre-oxidized in air also produced their nitrogenation coupled with oxidation.