Epitaxial Growth of Molecular Graphene on Metal Surface Alloy

Abstract

Molecular graphene provides an attractive man-made artificial system to realize designer Dirac fermions with exotic properties and significant implications in electronics/spintronics, but its large-scale fabrication remains a challenge as the available approach involves molecule-by-molecule manipulation of CO on a metal surface using a scanning tunneling microscopy tip. Here, we propose the epitaxial growth of molecular graphene on metal surface alloy, where CO molecules could be naturally self-assembled into a hexagonal lattice. Via high-throughput first-principles calculations, the adsorption behaviors of CO on 30 surface alloys Cu₂M (M represents the alloyed element) with a ($\sqrt{3}\times \sqrt{3}$)-R30° superstructure on Cu(111) is explored. By systematically analyzing the structures, energetic and electronic properties of the adsorbed systems with different CO coverages, three surface alloys, Cu₂Zn, Cu₂Ga, and Cu₂Ge, on which molecular graphene can be spontaneously formed, are successfully screened out. Remarkably, the self-assembled molecular graphene is featured by an effective four-band model involving the molecular (${\pi }_{2p_x}^{\ast }$, ${\pi }_{2p_y}^{*}$) orbitals of CO on a hexagonal lattice, leading to quantum spin Hall effect. This work paves an avenue for the large-scale growth of artificial graphene, which should stimulate immediate interest among experimentalists in the synthesis, characterization, and implementation of topological states for dissipationless transport and quantum computing.