Phase-Controllable Synthesis of Ultrathin Molybdenum Nitride Crystals Via Atomic Substitution of MoS₂

MXenes are emerging members in the two-dimensional (2D) material family and are highlighted by their high electrical conductivity. Among different MXenes, molybdenum-based MXenes, especially molybdenum nitrides (MoNx), are rarely accessible through the common synthetic approach of selective etching due to the absence of stable MAX phase precursors. In this work, we apply the atomic substitution approach to synthesize two phases of ultrathin nonlayered molybdenum nitrides (i.e., Mo5N6 and δ-MoN) from 1.6 to 42.9 nm thickness by converting layered MoS2 under different temperatures. The morphology and 2D nature of MoS2 are well remained in both phases. These newly created 2D materials are further characterized using Raman spectroscopy, high-resolution transmission electron microscopy, and electrical measurements, suggesting that both phases are highly crystalline and highly conductive down to the thickness of a few nanometers. Moreover, Ohmic contacts are formed between the ultrathin nitrides and Cr/Au electrodes, suggesting the great potential of the obtained nitrides for nanoelectronic device applications. The stability test shows that the Ohmic contact is well maintained after 4 weeks under ambient conditions with a slight degradation in conductivity. This study extends the 2D family by providing highly conductive members, offering desired building blocks for solid-state nanoelectronic devices.