Diamond polishing mechanisms: An investigation by scanning tunnelling microscopy

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Abstract
The morphology of the polished surfaces of semiconducting diamonds has been examined by scanning tunnelling microscopy. The faces polished along a direction of difficult abrasion show a rough structure which indicates that material was removed by fracture and chipping on a nanometre scale. The faces polished along a direction of easy abrasion are characterized by a superposition of many smooth grooves which are 20–100 nm wide and 2–12 nm deep. Cracks suggesting a stick-slip process were found. The smallest structures were 1 nm in size. The morphology of these surfaces indicates a process dominated by mechanical interactions of diamond on diamond. A mechanism is proposed which is based on adhesion, followed by plucking of fragments of the order of size of nanometres or smaller from the surfaces. Optical microscopy of the polishing scaife shows the presence of broad grooves, and Raman spectroscopy indicates only the presence of diamond. Analyses of the black powder formed during polishing revealed iron in the form of carbides and oxides, diamond particles and probably amorphous carbon.