Hydrogen-driven transition from a 2D-metal monochalchogenide to a surface alloy

Hydrogen-driven transformations are an interesting approach in the modification of surfaces and low dimensional materials, and their control at the atomic scale is crucial in the final outcome. SnSe is a semiconducting material that stands out for its exceptional thermoelectric and optoelectronic properties along with its promising applications in photovoltaics. However, little less is known about its 2D form, β-SnSe, a metal monochalcogenide with a buckled honeycomb structure. In this work, we report the room temperature transition of β-SnSe into Au 2 Sn, a surface alloy behaving as a strong correlated material with potential spintronic applications, through a hydrogen-induced atomic modification. We find two main stages upon the hydrogenation process: the breaking of the Sn-Se bond followed by the formation of H 2 Se, which will be rapidly desorbed from the surface; and the generation of a Au 2 Sn surface alloy with the unbound Sn and the subsurface Au atoms. We track the transformation from the metal monochalcogenide to the surface alloy in detail using a multi-technique approach that correlates the structural and chemical properties at each step of the process along with ab-initio calculations that point towards the possible underlying mechanisms of the transformation.