We propose new pristine Si(111) surfaces with nearly flat and metallic property, based on first-principles calculations. The surfaces are composed of connected armchair ribbons, in which the constituent Si atoms are threefold  (DB) or fourfold (DH) coordinated (Left panel). The calculated electronic structures show that the surfaces are metallic, as in topological insulators, in which the insulating bulk is surrounded by metallic surfaces (Right panel). Their unique structural and electronic properties are worthy of note to investigate and are expected to open a new realm of semiconductor materials if they are realized experimentally.

Keywords: Silicon surface, Metallic surface, Si, DFT