CHARACTERIZATION OF CRYSTAL FACES OF POLYCRYSTALLINE HFCVD DIAMOND FILMS BY STM STS/

Among the numerous techniques available for the characterization of di amond films scanning tunnelling microscopy (STM) in combination with s pectroscopy (STS) provides information about the morphology and electr onic surface properties down to the atomic scale. Here results of STM/ STS obtained on diamond films are reported. 0.5 to 1.25 mu m thick fil ms have been grown on silicon substrates by hot filament chemical vapo ur deposition (HFCVD) by variable CH4/H-2 mixtures in the range of 0.5 % to 3% CH4. Morphological features of diamond crystallites were studi ed in detail by STM. A distinct increase of the surface roughness of ( 111) crystal faces with increasing CH4 concentration (from 0.5% to 3%) was found. For a CH4 concentration of 3% (100) faces were smoother th an (111) faces. STS revealed significant differences in the tunneling current/voltage (I/V)-characteristics between (111) and (100) crystal surfaces. For (111) surfaces distinct changes in the I/V-characteristi cs depending on the CH4 concentration were observed: The I/V-character istics change and the conductivity increases raising the CH4 concentra tion from 0.5% to 3%. This effect is explained with increasing formati on of non-diamond carbon (NDC) on (111) surfaces for higher CH4 concen trations. Thus NDC is also responsible for the enhanced surface roughn ess observed on (111) surfaces with increasing CH4 concentrations.