Atomic structure and electronic properties of the two-dimensional (Au,Al)/Si(111)2×2 compound

A combination of scanning tunneling microscopy, angle-resolved photoelectron spectroscopy, ab initio random structure searching, and density functional theory electronic structure calculations was applied to elucidate the atomic arrangement and electron band structure of the (Au,Al)/Si(111)2×2 two-dimensional compound formed upon Al deposition onto the mixed 5×2/3×3 Au/Si(111) surface. It was found that the most stable 2×2-(Au, Al) compound incorporates four Au atoms, three Al atoms, and two Si atoms per 2×2 unit cell. Its atomic arrangement can be visualized as an array of meandering Au atomic chains with two-thirds of the Al atoms incorporated into the chains and one-third of the Al atoms interconnecting the chains. The compound is metallic and its electronic properties can be controlled by appropriate Al dosing since energetic location of the bands varies by ∼0.5eV during increasing of Al contents. The 2×2-(Au, Al) structure appears to be lacking the C3v symmetry typical for the hexagonal lattices. The consequence of the peculiar atomic structure of the two-dimensional alloy is spin splitting of the metallic states, which should lead to anisotropy of the current-induced in-plane spin polarization.