Environmental stability of bismuthene: oxidation mechanism and structural stability of 2D pnictogens

Recently a new group of two-dimensional (2D) materials, originating from the group V elements (pnictogens), has gained global attention owing to their outstanding properties. Due to a high surface-volume ratio and extraordinary chemical activity, 2D pnictogens such as phosphorene and antimonene are highly sensitive to exposure to the environment. Hence, upon exposure to oxygen and water molecules, they may easily oxidize, which leads to the degradation of their structure. In this work, we perform a first-principles investigation on the effects of environmental oxygen and water molecules on the structural stability of newly emerging group V 2D material bismuthene. It is proposed that the oxidation process of bismuthene and other 2D pnictogens under ambient conditions can involve three general steps: adsorption of oxygen molecules, dissociation of oxygen molecules, and interaction of water molecules with the oxygen species anchored at the surface to form acids. Importantly, recent experiments reported on high stability of bismuthene even at high temperatures. Here we show that the underlying reason for such structural stability of bismuthene may have similar roots to the stability of antimonene which originates from an acceptor role of water molecules on that material, while for materials with lower stability, like phosphorene and InSe, water molecules act as donors. The present work uncovers the oxidation mechanisms and suggests the ways for maintaining the stability of bismuthene and its 2D pnictogen counterparts, which may be important for their fabrication, storage, and applications.