Nitrogen, oxygen, and hydrogen bonding and thermal stability of ambient exposed nitrogen-terminated H-diamond (111) surfaces studied by XPS and HREELS

We report on the chemical composition, bonding, and in-vacuum thermal stability (up to 1000 °C) of nitrogen plasma terminated H-Diamond(111) (H-Di(111)) surfaces followed by ambient exposure. The nitrogen-plasma exposures include radio frequency (RF) (at pressure: 3 × 10⁻² (damaging) and 7 × 10⁻² Torr (non-damaging)) and microwave (MW) nitrogen plasmas and studied by X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS). The largest nitrogen intake was observed upon exposure to RF(N₂) damaging plasma, followed by MW(N₂) and non-damaging RF(N₂) plasmas. A similar trend follows the adsorption of adventitious oxygen. The XPS analysis shows that most of the adventitious oxygen is adsorbed in a CO_x configuration upon nitride surfaces exposure to ambient conditions. However, upon high temperature annealing of the damaging RF(N₂) plasma exposed surface, some NO_x (species) were detected by XPS. From the HREELS analysis, the hydrogen adsorbed on the H-Di(111) is not fully removed by exposure to the different nitrogen plasmas. These measurements show that NH(ads) species are formed on the surface and are desorbed upon vacuum annealing in the 500–700 °C range. This study may be of importance in all ex-situ applications influenced by the near-surface physicochemical and electronic properties of nitrogen-terminated H-Di(111) surfaces.