Polishing mechanism and surface damage analysis of type IIa single crystal diamond processed by mechanical and chemical polishing methods

The polishing mechanisms and surface damages of mechanically and chemically polished diamond crystals were investigated. A metal bonded diamond wheel was used for mechanical polishing, while an SiO2 wheel was used for chemical polishing. After polishing, samples underwent surface treatment with hydrogen plasma to exhibit negative electron affinity. SEM observation revealed that the scratches consisted of dark cracks with cleavage facets. Dark contrast was observed around the cracks on the hydrogen terminated diamond surface, indicating that carriers excited by primary electrons were eliminated by crystal defects around the cracks. The polishing rate increased nonlinearly with the rotating speed of the SiO2 wheel. The difference of polishing rate of the (100) surface between the < 110 > direction and the < 100 > direction became smaller when using the SiO2 wheel than when using the metal bonded diamond grinding wheel. The polishing rates became more isotropic, suggesting that the wear reactions of the diamond and the SiO2 wheel were mainly chemical. Although abrasion traces were also observed by optical microscopy on the sample polished by an SiO2 wheel, dark contrast due to lattice distortion or crystal defects was not observed by SEM. This result shows that the sample surface and subsurface chemically polished by the SiO2 wheel had very little damages. (C) 2015 Elsevier B.V. All rights reserved.