Origin of the Surface Facet Dependence in the Oxidative Etching of the Diamond (111) and (100) Surfaces from First-Principles Calculations

This work elucidates the surface facet dependence on the oxygen adsorption and oxidized surface morphology of the diamond (111) and (100) surfaces to give insights that will improve the polishing, etching, and fabrication of diamond devices. We used spin-polarized density functional theory to systematically simulate the O adsorption and CO and CO₂ desorption reactions from pristine and etched diamond (111) and (100) surfaces. The results show that the surface facet dependence is caused by two factors: (1) the difference in the reactivity of the O₂ and (2) the difference in the carbonyl orientation of the O-terminated surfaces. The O₂ adsorption and activation energies on the C(111)-(2 × 1) surface are weaker and higher, respectively, compared to those on the C(100)-(2 × 1) surface. Moreover, the O₂ adsorption energy on the C(111)-(2 × 1) weakens with O₂ coverage. At monolayer O coverage, the carbonyl groups on the C(111)-(1 × 1):O surface have an inclined orientation which causes high steric repulsion between adjacent O atoms. The repulsion decreases with less neighboring molecules, leading to staggered etching, formation of islands, and loss of well-defined crystallographic orientation of the surface atoms. For the C(100)-(1 × 1):O surface, the carbonyl groups have an upright orientation and have low steric repulsion. The CO desorption activation energy is lower near an existing vacancy, leading to rowwise etching, which preserves the crystallographic orientation of the surface atoms.