La induced Si3 trimer monolayer on Si(111) surface: an ab initio study

Abstract The π -bond Seiwatz chain (SC) is one of the well-known reconstruction induced by alkaline or rare earth metals on Si(111) surface. Here we identify by ab initio calculations a new reconstruction of La induced quasi-two-dimensional Si 3 trimer monolayer on Si(111)- ( 3 × 3 ) R 30 ° surface. Its surface unit cell has one La atom and one Si 3 trimer with the same La coverage (1/3 monolayer) as SC structure and the Si 3 trimer satisfies the electron counting rule with a transfer of valence electrons from La atom, formally as L a 3 + [ S i − ] 3 , in correspondence to the milkstool model for Bi trimers on Si(111) surface. Band structure calculations show a semiconducting character with an indirect surface band gap of 0.76 eV. Moreover, a two-stage conversion process between the Si 3 trimer and SC structure is verified by the climbing-image nudged elastic band method. These findings pave the way for further exploration of the new surface structure and its outstanding properties.