Direct correlation of microtwin distribution with growth face morphology of CVD diamond films by a novel TEM technique

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Abstract
A thick as-grown diamond film was examined directly by conventional transmission electron microscopy (TEM) without thinning, and the important microstructures near the growth surface were characterized. Specimen preparation for TEM involved simply fracturing the film; some of the diamond grains located on the specimen edge were thin enough to be directly examined by TEM. The 3-D topography of the diamond grains located at the intersection of the growth and the fracture surfaces was obtained 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 μm diameter with {001} facets parallel to the substrate and four inclined {111} 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 core volume bounded by the (001) top facet and its projected column defined by orthogonal internal {110} were free from microtwins, but contained a few dislocations. The remaining volume around this core, bounded by {111} facets (or grain boundaries) and the internal {110}, was filled with microtwins. The microtwins were not merely at the {111} surfaces. Our results reveal a growth mechanism in which microtwins are formed as material is added to {111} but not {001}. The formation of microtwins in CVD diamond is thus clearly associated with growth on {111} surface facets.