Higher coverage of carboxylic acid groups on oxidized single crystal diamond (001)

The effects of crystal orientation to the surface chemistry of single crystal diamond (001) and (111) were investigated after wet chemical oxidation. Direct carboxylation has been successfully achieved via wet chemical oxidation on native diamond (001) and (111) surface with distinguished portions of carboxylic acid groups (-COOH). High resolution X-ray photoelectron spectroscopy (XPS) analysis revealed that various kinds of chemical groups including both single and double oxygen-related components were covalently functionalized onto the single crystal diamond. The percentages of -COOH are approximately 9.2% and 4.7% on (001) and (111) surface respectively, showing evidently that the density of -COOH groups on (001) surface is surprisingly higher than that of (111) surface. Comprehensive comparison revealed that oxygen-related groups is higher on (001) compared with that of (111) surface. The conversion mechanism was supposed to explain the evolution from hydrogenated to oxygenated functionalizations on diamond with differently oriented crystal facets, and the crystal orientation was the significant factor in controlling the surface reactivity and hence the oxidization process.