Synthesis of Ti₄Au₃C₃ and its derivative trilayer goldene through chemical exfoliation

Achieving large two-dimensional (2D) sheets of any metal is challenging due to their tendency to coalescence or cluster into 3D shapes. Recently, single-atom-thick gold sheets, termed goldene, was reported. Here, we ask if goldene can be extended to include multiple layers. The answer is yes, and trilayer goldene is the magic number, for reasons of electronegativity. Experiments are made to synthesize the atomically laminated phase Ti₄Au₃C₃ through substitutional intercalation of Si layers in Ti₄SiC₃ for Au. Density functional theory calculations suggest that it is energetically favorable to insert three layers of Au into Ti₄SiC₃, compared to inserting a monolayer, a bilayer, or more than three layers. Isolated trilayer goldene sheets, ~100 nanometers wide and 6.7 angstroms thick, were obtained by chemically etching the Ti₄C₃ layers from Ti₄Au₃C₃ templates. Furthermore, trilayer goldene is found in both hcp and fcc forms, where the hcp is ~50 milli-electron volts per atom more stable at room temperature from ab initio molecular dynamic simulations.