Effects of molecular contamination and sp2^2 carbon on oxidation of (100) single-crystal diamond surfaces

The efficacy of oxygen (O) surface terminations of specific moieties and densities on diamond depends on factors such as crystallinity, roughness, and crystal orientation. Given the wide breadth of diamond-like materials and O-termination techniques, it can be difficult to discern which method would yield the highest and most consistent O coverage on a particular subset of diamond. We first review the relevant physical parameters for O-terminating single-crystalline diamond (SCD) surfaces and summarize prior oxidation work on (100) SCD. We then report on our experimental study on X-ray Photoelectron Spectroscopy (XPS) characterization of (100) diamond surfaces treated with oxidation methods that include wet chemical oxidation, photochemical oxidation with UV illumination, and steam oxidation using atomic layer deposition. We describe a rigorous XPS peak-fitting procedure for measuring the functionalization of O-terminated samples and recommend that the reporting of peak energy positions, line shapes, and full-width-half-maximum values of the individual components, along with the residuals, are important for evaluating the quality of the peak fit. Two chemical parameters on the surface, sp$^2$ C and molecular contaminants, are also crucial towards interpreting the O coverage on the diamond surface and may account for the inconsistency in prior reported values in literature