The effect of UV and thermally induced oxidation on the surface and structural properties of CVD diamond layers with different grain sizes

This work is a continuation of previously reported research regarding the effects of hydrogen treatment on the structural properties of polycrystalline CVD diamond layers with different grain sizes [1]. Here, we report studies of the hydrogenated diamond layers which were oxidized in two steps, first by UV irradiation in air and then by annealing at 300 degrees C in air. After each process step, the structural and surface properties of diamond layers were monitored by Raman spectroscopy, SEM, XPS, and CA (contact angle) measurements. The reported study investigates the impact of the UV ozone oxidation and the low-temperature thermal oxidation on the chemical composition, morphology of diamond surface, and structural properties of the diamond layer. This work shows that microcrystalline and nanocrystalline diamond layers behave differently upon oxidation. In general, the microcrystalline samples were more readily oxidized during UV treatment. This might be attributed to both, the diamond grain sizes, and the less ordered form of the amorphous carbon phase present in those samples. Also, the structural studies revealed that a slight ordering of amorphous carbon phase in the microcrystalline sample with the biggest diamond grains occurred for both oxidation processes, implicating the graphitization of the sp2/sp3 phase.