Twinning and faceting in early stages of diamond growth by chemical vapor deposition
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Scott R. Sahaida Electronic Materials Center, Kobe Steel USA Inc., 79TW Alexander Drive, Research Triangle Park, North Carolina 27709
Jeffrey T. Glass Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7919 (Received 18 May 1992; accepted 23 July 1992)
Flat, hexagonally shaped diamond platelets were observed during the initial stage of microwave plasma assisted deposition of diamond. The platelets are approximately 2.5 /mm in linear dimension and are oriented with their large six-sided faces parallel to the silicon substrate. A re-entrant groove, running parallel to the large six-sided face, is present in the small side faces of the platelets. Larger diamond crystals, with a fully developed three-dimensional morphology, all have re-entrant grooves in other directions. The observations support the hypothesis that the growth rate of {111} faceted diamond crystals is greatly enhanced by the presence of microtwins (multiple stacking errors), which give rise to re-entrant corners where they intersect the crystal surface. Fully developed {111} faceting and a strong influence of re-entrant corners is expected when the average lifetime of a carbon atom bonded once to the surface is much less than the average time between addition of adatoms at adjacent surface sites. I. INTRODUCTION Stacking errors of the {111} planes are commonly found in {111} faceted diamond grown by chemical vapor deposition. A single stacking error is a rotation of adjacent layers by 60° from their correct positions in the diamond-cubic crystal. The energy difference between correct and incorrect stacking is small because the two cases differ only in next nearest neighbor positions. If every layer has the "incorrect" stacking the resulting crystal is lonsdaleite or "hexagonal" diamond. Multiple stacking errors along {111} planes have important geometric consequences that can mediate further crystal growth and which can give rise to various types of crystal morphologies and defects. In this paper we consider the important special case of parallel pairs of stacking errors. A pair of stacking errors in parallel (111) planes is classified by the number, n, of layers of correct stacking in between the errors. A pair of adjacent stacking errors (n = 0) is called an intrinsic stacking fault; a pair with a single layer of correct stacking (n = 1) is called an extrinsic stacking fault. Pairs of stacking errors with n > 1 are called microtwins or, for very large n, a twin band. These errors are illustrated in Fig. 1. For simplicity, in this paper we will often refer to any pair of parallel stacking faults as a twin, regardless of the value of n. J. Mater. Res., Vol. 7, No. 11, Nov 1992 http://journals.cambridge.org
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The intersection of a pair of parallel {111} stacking errors with the surface of a diamond-cubic crystal gives rise to a re-entrant corner. See Figs. l(c) and l(d). The re-entrant corner provides a self-regenerating site for the nucleation of new layers and leads
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