Mechanism of surface smoothing of diamond by a hydrogen plasma

As-polished diamond (100)- and (111)-oriented single crystals and natural diamond powders of 0.12-25 mu m diameter were treated in atomic hydrogen generated by a microwave plasma or by a hot tungsten filament. Post-treatment atomic force microscopy (AFM) showed smoothing and step bunching on (100) and (111) surfaces. Natural diamond powders, which were quite irregular and rough prior to treatment, remained the same size but became markedly smoother and well-faceted, as observed by scanning electron microscopy (SEM). The degree of faceting was sensitive to plasma power level or filament temperature and substrate temperature but was independent of H-2 flow rate. The size and degree of faceting appeared to be the same after plasma treatment for isolated and closely packed particles. We argue that surface diffusion is the dominant smoothing mechanism, but clear evidence of etching was observed at substrate temperatures of 975 degrees C and above. (C) 1997 Elsevier Science S.A.