Structural stability and electronic properties of Sr induced (5×4) reconstruction on Si(111) surface

Abstract

Honeycomb-chain-channel (HCC) and π-bond Seiwatz chain (SC) are the well-known reconstructions induced by alkaline earth metal on Si(111) surface. Here we identify by ab initio calculations a stable intermediate phase of Sr/Si(111)-(5×4) HCC+SC. This new reconstruction satisfies the electron counting rule with the Sr coverage of 3/10 monolayer. In each (5×4) surface unit cell, six Sr atoms are distributed as evenly as possible in the two channels. One of the channels contains two Sr atoms on the top site T4 and one Sr atom on the hollow site H3, while another channel contains two Sr atoms on site H3 and one on site T4. Electronic band structures and band-decomposed charge density distributions show that there are seven occupied surface states (S1–S5, Σ1 and Σ2) and two unoccupied surface states (S6 and S7) near the Fermi level. Moreover, we find that this new (5×4) surface structure is a semiconductor with a surface band gap of 0.62 eV, determined by the S2 and S6 surface states in honeycomb Si chains.