Charge Redistribution Mechanisms in SnSe2 Surfaces Exposed to Oxidative and Humid Environments and Their Related Influence on Chemical Sensing

Tin diselenide (SnSe 2 ) is a van der Waals semiconductor, which spontaneously forms a subnanometric SnO 2 skin once exposed to air. Here, by means of surface-science spectroscopies and density functional theory, we have investigated the charge redistribution at the SnO 2 -SnSe 2 heterojunction in both oxidative and humid environments. Explicitly, we find that the work function of the pristine SnSe 2 surface increases by 0.23 and 0.40 eV upon exposure to O 2 and air, respectively, with a charge transfer reaching 0.56 e - /SnO 2 between the underlying SnSe 2 and the SnO 2 skin. Remarkably, both pristine SnSe 2 and defective SnSe 2 display chemical inertness toward water, in contrast to other metal chalcogenides. Conversely, the SnO 2 -SnSe 2 interface formed upon surface oxidation is highly reactive toward water, with subsequent implications for SnSe 2 -based devices working in ambient humidity, including chemical sensors. Our findings also imply that recent reports on humidity sensing with SnSe 2 should be reinterpreted, considering the pivotal role of the oxide skin in the interaction with water molecules.