Highly Air-Stable\nN‑Doped Two-Dimensional Violet\nPhosphorus with Atomically Flat Surfaces

Few-layer violet\nphosphorus (VP) shows excellent potential in optoelectronic\napplications due to its unique in-plane anisotropy and high mobility.\nHowever, the poor air stability of VP severely limits its practical\napplications. This article reports highly air-stable VP obtained by\na two-step nitrogen plasma treatment where the nitrogen volume flow\nrate is controlled to coordinate physical etching and chemical doping.\nSpecially, this plasma process can remove partial oxidations formed\non the VP surface with barely etching to the intrinsic VP surface\nbut efficiently incorporates nitrogen into VP, resulting in surface\nnitrogen-doped VP (N-VP) nanosheets with atomically smooth surfaces\nthat exhibit excellent air stability. Atomic force microscopy images\nshow that the N-VP nanosheet, nearing a monolayer thickness, maintained\nits surface morphology and flatness unchanged in ambient air for over\n60 days. The improved stability of N-VP can be partly due to its atomically\nsmooth surface, which reduces the number of active or oxidation sites.\nFurther elucidation was made by density functional theory calculations,\nshowing that this ultrastability may intrinsically be attributed to\nrepairing P vacancies by N dopants. This research provides a feasible\nstrategy for significantly enhancing the durability of VP.