EXPERIMENTAL-EVIDENCE OF DIFFERENT CRYSTALLINE FORMS IN CHEMICAL-VAPOR-DEPOSITED DIAMOND FILMS

Diamond films have been obtained on Ta polycrystalline substrates from mixtures of methane and hydrogen by the hot-filament chemical vapor d eposition technique. The structural characteristics of the polycrystal line deposits have been investigated by reflection high energy electro n diffraction (RHEED), while the surface morphologies have been observ ed by scanning electron microscopy or carbon replica transmission elec tron microscopy. For one of the films, the formation of thermal spikes during the deposition process yielded a structure giving a RHEED patt ern with d spacings and intensities not corresponding to the already i dentified carbon and diamond phases. On the base of the RHEED pattern the observed phase has been identified as a face-centered-cubic lattic e, belonging to the space group F (4) over bar 3m and ascribed to a so -called X-diamond polytype.