DIRECT CORRELATION OF MICROTWIN DISTRIBUTION WITH GROWTH FACE MORPHOLOGY OF CVD DIAMOND FILMS BY A NOVEL TEM TECHNIQUE

A thick as-grown diamond film was examined directly by conventional tr ansmission electron microscopy (TEM) without thinning, and the importa nt microstructures near the growth surface were characterized. Specime n preparation for TEM involved simply fracturing the film; some of the diamond grains located on the specimen edge were thin enough to be di rectly examined by TEM. The 3-D topography of the diamond grains locat ed at the intersection of the growth and the fracture surfaces was obt ained using secondary electron images, so that the 2-D projected grain geometry could be derived easily to help interpret the TEM images. A diamond film grown with a [001] texture and having grains 2-3 mum diam eter with {001} facets parallel to the substrate and four inclined {11 1} facets was examined. Grains with fracture surfaces that intersected the top (001) facet, grains with fractures that intersected only {111 } facets, and unfractured grains were studied. It was found that the c ore volume bounded by the (001) top facet and its projected column def ined by orthogonal internal {110} were free from microtwins, but conta ined a few dislocations. The remaining volume around this core, bounde d by {111} facets (of grain boundaries) and the internal {110}, was fi lled with microtwins. The microtwins were not merely at the {111} surf aces. Our results reveal a growth mechanism in which microtwins are fo rmed as material is added to {111} but not {001}. ne formation of micr otwins in CVD diamond is thus clearly associated with growth on {111} surface facets.