TEM OBSERVATIONS OF DIAMOND FILMS PREPARED BY MICROWAVE PLASMA CVD

Diamond films synthesized by microwave plasma chemical vapor deposition were studied using a high-resolution transmission electron microscope. The concentration of the reactant gas, CH4, was varied from 0.5 to 10% and lattice images of diamond crystals were obtained for all specimens. It was found that an increase of CH4 concentration raised both the density of twin-boundaries and stacking faults, but reduced the grain size. In CH4 concentrations higher than 5%, the grain size was 10-30 nm and other phases such as graphite or amorphous carbon were not detected in the grain. The grain boundaries were 0.5-1 nm in width which correspond to a few carbon atoms. These carbon atoms on grain-boundaries seemed to take a non-crystalline structure because they did not show lattice image. From results of Raman spectra, X-ray diffraction, and transmission electron microscopy observations of these films, it was concluded that the films synthesized at high CH4 concentration consisted of fine-grained diamonds and that the broad peaks of Raman spectra are mainly due to carbon atoms on grain boundaries. © 1992.