Chemistry of hydrogen and oxygen on the diamond (100) surface

Abstract

The first investigation of the adsorption of water on diamond (100) by infrared multiple-internal-reflection spectroscopy using a natural type IIa diamond internal reflection element is reported. Following exposure to water at elevated temperatures, infrared absorption features are observed at 1250 and 1200 cm$\sp{-1}$; 1125 and 1080 cm$\sp{-1}$; and 720 cm$\sp{-1}$, and assigned to ether (C-O-C), hydroxyl (C-OH), and carbonyl ($>$C=O) modes, respectively. It is thought that water adsorbs dissociatively and at higher temperatures the adsorbed hydroxyl species further decompose to ether, carbonyl, and hydride surface species. The substantial observed reactivity of diamond with modest exposures to water indicates a potentially important role for surface hydroxyl and oxide species in the surface chemistry of diamond films grown by chemical vapor deposition. Direct evidence for the diamond surface hydride structures, obtained by deuterium substitution, is also presented. Infrared evidence is seen for both monodeuteride and dideuteride surface structures, with one or two deuterium atoms per surface carbon atom ($\delta\sb{\rm CD}$ mode at 901 cm$\sp{-1}$ and $\delta\sb{\rm CD\sb2}$ mode at 1125 cm$\sp{-1}$, respectively). The thermal stability of oxides on diamond (100) was investigated by annealing experiments. Infrared modes assigned to hydroxyl and carbonyl species disappear, presumably via desorption, upon heating the oxidized diamond surface above 1000$\sp\circ$C. Finally, surface reactions induced by exposure to a hot acid solution used to etch graphite from diamond were also investigated by infrared spectroscopy. The primary absorption band at 1020-1120 cm$\sp{-1}$ is assigned to hydroxyl groups and infrared absorptions near 1250 cm$\sp{-1}$ are assigned to ether groups. We conclude that the acid solution oxidizes the diamond surface.