Calculation of Surface‐Induced Core‐Level Shifts for Covalent Semiconductors C, Si, Ge, and α‐Sn I. (111) 2 × 1 Surfaces

Abstract

AbstractA theory is developed for the surface induced core‐level shift. Since the many body relaxation mechanism can be neglected only the initial‐state potential effect is considered. Starting from tight‐binding assumptions the shift is related to ion charges accompanying the reconstruction, the hybridization state, the polarity of chemical bonds, and the atomic configuration. The atomic configurations are taken from total energy minimizations, dynamical LEED or ion scattering studies. The other input parameters are calculated self‐consistently. The developed theory is applied to the (111) 2 × 1 surface of group IV materials. Various fundamental reconstruction models — buckling, π‐bonded chains, and π‐bonded molecules — are studied. The shifts resulting for eight atoms per surface elementray cell and the associated core electron line shapes seem to favour the chain model in the (111) 2 × 1 case. The molecule model cannot be completely ruled out only from core‐level shift calculations because of its homopolar bond character.