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I. INTRODUCTION AND BACKGROUND Diamond has potential for use in both electronic and wear resistant coating applications due to its high hardness, strength, thermal conductivity, electron saturated drift velocity, hole and electron mobilities, chemical and thermal stability, radiation hardness, and optical transmission.2"4 Researchers throughout the world are currently attempting to grow single crystal films of diamond using low pressure (i.e., less than one atmosphere) gases to make the fabrication of electronic devices which utilize these outstanding properties feasible. Such research has been encouraged by recent results which indicate that epitaxial diamond films can be grown on diamond substrates.5"8 Despite this, microcracking and poor surface morphologies after several microns of growth are still major concerns in this homoepitaxy. Furthermore, for thin film devices of diamond to be economically viable, heteroepitaxial growth is believed to be necessary. Previous investigations9"13 have yielded only highly defective, polycrystalline films when non-diamond substrates are utilized. The research presented in this paper is part of a continuing effort to understand defect structures and particle morphologies in such polycrystalline CVD diamond. This understanding will yield information on the nucleation and growth of these films which will, in turn, aid researchers in attempts to achieve heteroepitaxial growth of high quality diamond. The surface morphologies and defect structures in CVD diamond have been reported previously.11415 In general, highly faceted polycrystalline films (average J. Mater. Res., Vol. 5, No. 4, Apr 1990

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grain size ~1 fiva) have been observed; however, deviations from this faceting were also present depending on location on the substrate and the methane concentration in the feedgas. Well-faceted diamond crystals were observed near the center of the sample whereas a less faceted, cauliflower texture was observed near the edge of the sample, presumably due to variations in temperature across the surface of the sample. Regarding methane concentration effects, threefold {111} faceted diamond crystals were predominant in a film grown with 0.3% CH4 in H 2 while fourfold {100} facets were observed in films grown with 1.0% and 2.0% CH4 in H2. Cyclic growth patterns of these facets due to secondary nucleation have also been reported.16 Transmission electron microscopy of the diamond films1 has shown that the majority of diamond crystals have a very high defect density comprised of {111} twins, {111} stacking faults, and dislocations. The presence of these crystallographic defects (twins, stacking faults, and dislocations) in CVD diamond is not surprising since natural and high pressure synthesized diamond have also been observed to have high concentrations of these defects.1718 In the present research, high resolution TEM (HREM) has been used to examine these defects on an atomic scale. The interpretation of HREM micrographs is not trivial and i