Thermal oxidation of the hydrogenated diamond (1 0 0) surface

Hydrogenated single-crystal diamond (1 0 0) surfaces were exposed to dry O2 under UHV conditions at temperatures ranging from room temperature to 1000 °C. The surfaces were largely inert to O2 at 850<Tsub<950 °C, but they reacted rapidly with O2 at higher temperatures. Thermal oxidation with unactivated molecular O2 occurred only after the surface hydrogen had desorbed, usually at about 950 °C but depended partially on the condition of the surface. Oxidation at Tsub>950 °C generated an overlayer of graphitic sp2 carbon on the diamond surface, as confirmed by low energy electron diffraction, Auger electron spectroscopy and C-KLL lineshape analysis, electron loss spectroscopy and high resolution electron energy loss spectroscopy. Relatively little surface oxygen (or hydrogen) remained after oxidation, probably due to thermal desorption. By comparison, the surfaces of unheated diamonds exposed to oxygen activated by a hot metal filament (O2∗) were terminated with a full monolayer of oxygen in the form of ether or carbonyl groups, and had only a small amount of sp2 carbon. Deuterium- and hydrogen-terminated surfaces behaved identically towards oxygen addition.