Influences of Si dopant on geometry and energetic stability of terminated diamond (111)-1 × 1 surfaces

Abstract

Based on the density functional theory calculations, more reasonable model and calculation method were proposed for evaluating the local adsorption energy of certain terminating species on Si-doped diamond surfaces. Influences of substitutional Si dopant in the 1st or 2nd C layer on local adsorption energy of the H, O, OH or F terminating species were studied for the first time. The combined influences of the terminating species and Si dopant on various parameters, such as bond length, total electron density, bond population, atomic charge, Fukui function and density-of-states (DOS), were further discussed. The Si dopant, either within the 1st or the 2nd layer, showed clear, but local, effects for all the species. It was found that onto the clean surface (without any adsorbate in the initial state), the Si1 dopant contributed to the increase of local adsorption energy values for the O, OH and F adsorbates binding to it, as well as the decrease of that for H, because it had smaller electronegativity than C and positive atomic charge. The adsorption energy for one OH attracted by the adjacent C1 binding to the Si2 was smaller than that by other C1, owing to the negative atomic charge. However, those for O and F atoms were larger instead, owing to the 3d unoccupied orbital around Si2 that was probably occupied by the lone electron pairs around O and F. The primary structural change induced by Si incorporation was the elongation of the SiC and SiA (adsorbates) bonds, accompanied by the decrease of electron density, compared with corresponding CC and CA bonds, attributed to the larger radius of the Si. Among the four terminating species, the O atom performed the highest reactivity to the electrophilic or nucleophilic attack. This is the first time the adsorption on the Si-doped diamond films is calculated, and above results can help to understand related chemical processes on the Si-doped diamond films.