Theoretical Studies of the Erosion of (100) and (111) Diamond Surfaces by Hyperthermal O(~3P)

摘要

Direct dynamics simulations, based on density functional-based tight-binding theory with self-consistent charges and also on density functional theory, were used to investigate hyperthermal O(~3P) atom collisions with (111) and (100) diamond surfaces. Surface functionalizations produced initially, shortly after the start of oxygen-atom exposure, and during steady-state conditions were investigated. Hydrogen atoms are removed from both surfaces by the incoming oxygen atoms, leading to hydroxyl radicals and water molecules. Both surfaces can be damaged by the incoming oxygen during the initial stages of exposure, resulting in the removal of carbon as CO2 molecules, and functionization of the surfaces with oxygen. The (111) surface is dominated by oxy radicals during steady-state exposure and also has a significant number of carbon atoms with dangling bonds. The (100) surface becomes nearly completely covered by ketone and ether functional groups. Its (2 x 1) reconstruction is opened in the process. Once covered, the (100) surface resists further erosion, presumably because the ether and ketone groups make the surface carbon atoms unattractive to incoming O atoms which act as electrophiles. Two mechanisms exist for the removal of carbon atoms from the (111) surface. The surface can become graphitized by incoming O atom impacts, and graphite is quickly eroded by hyperthermal O atoms. It can also be directly converted to CO2 as a β-scission-like process makes carbon atoms adjacent to oxy radicals susceptible to electrophilic attack.