Carbon atom exchange between the diamond surface and lubricant during polishing

Diamond surfaces prepared in the usual way, by polishing with diamond grit mixed with olive oil, are known to be atomically bulk-like (unreconstructed), although the polishing mechanism is still debated. Broken bonds at the surface are normally saturated by hydrogen atoms or H-containing groups. The hydrogen is usually assumed to be donated by the oil, but the latter's molecules include double bonds, i.e. are unsaturated with respect to hydrogen. Using carbon-13 labelled oil and nuclear resonance profiling, we find evidence that the oil molecules and the surface achieve mutual saturation by bonding to one another. As such, the outermost carbon atoms of a polished diamond surface thus come from the oil, and not from the diamond. Some implications are discussed.