Growth defects in diamond films
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J. L. Hutchison University of Oxford, Oxford, United Kingdom
L. H. Robins, E. N. Farabaugh, and A. Feldman National Institute of Standards and Technology^ Gaithersburg, Maryland 20899 (Received 3 August 1992; accepted 4 November 1992)
Growth defects in diamond films grown by plasma-assisted chemical vapor deposition (CVD) were studied by high resolution electron microscopy. Several features of the microstructure were resolved and their importance to the growth of the diamond film was evaluated. The observations included various twin boundaries of the type 2 = 3, as well as 2 = 9, 2 = 27, and X = 81, which form by an interaction of lower order twins. These higher order boundaries are loci of intersection points of growing planes on two adjacent twins and can serve as an indicator for the local crystal growth direction. The central nucleation site for the growing planes in many cases can be traced back to a quintuplet twin point. A twin quintuplet has five re-entrant angles and thus serves as a preferred nucleation site for new planes as the crystal grows.
I. INTRODUCTION
II. EXPERIMENTAL
Planar lattice defects, namely stacking faults and twins, are abundant in chemical vapor deposited (CVD) diamond structure, while diamonds that grow under thermodynamically stable conditions, such as natural diamonds, have a very low density of these defects. These differences are important to understanding the nucleation and growth of diamond films and may provide clues toward better control of microstructure and properties of CVD films. The fine features of these growth defects can be clearly observed and studied by high resolution electron microscopy (HREM) which provides, in addition to detailed atomic resolution images, crystallographic information on the defects and their boundaries. Several reported studies on CVD diamond films1"7 used HREM and obtained a view of the nature of stacking faults, twins, and twinning configurations, as well as the interface between the substrate and the diamond film. It is the purpose of our study to investigate closely the crystallography of these defects, and, more importantly, to determine their role in the nucleation and growth of CVD diamond films.
A. Specimen preparation
a)
Guest scientist at the Johns Hopkins University and at the National Institute of Standards and Technology. b) Ceramics Division, Materials Science and Engineering Laboratory, Technology Administration, United States Department of Commerce. J. Mater. Res., Vol. 8, No. 3, Mar 1993 http://journals.cambridge.org
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The fabrication of the free-standing CVD diamond films used in this study has been discussed in a previous article.8 The deposition was made by microwave plasmaassisted CVD on a commercial silicon wafer. In order to promote diamond nucleation, defects were introduced onto the polished surface of the substrate by rubbing with 1 /Am diamond powder. The deposition conditions are given in Table I. The diamond grain size was about 0.1 /im and optical reflectance measurements suggest that
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