Novel Au- and Ge-based two-dimensional materials formed through topotactic transitions of AlB2-like structures

Abstract

The topotactic reaction of a layered compound, for example CaGe₂, with HCl solution is a common and facile method to produce two-dimensional (2D) materials. In this work we demonstrate with first-principles calculations that this technique can potentially lead to a whole new family of 2D materials starting from three-dimensional crystals with AlB₂-like structures. As representative cases, we show here that the de-intercalation of Sc and Ca atoms from ScAuGe and Ca₂AuGe₃ crystals is strongly exothermic and produces the stable 2D monolayers AuGeH and AuGe₃H₃, respectively. Remarkably, both metals (AuGeH) and semiconductors (AuGe₃H₃) can be prepared by this method. Based on the broad availability of AlB₂-like structures with varying stoichiometries, there are several possibilities to prepare novel functional 2D materials with suitable topotactic transitions.