Morphological variations in flame-deposited diamond
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A. Tamhane Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210
J. H. D. Rebello Department of Mechanical Engineering, The Ohio State University, Columbus, Ohio 43210
S. A. Dregia Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210
V. V. Subramaniam Department of Mechanical Engineering, The Ohio State University, Columbus, Ohio 43210 (Received 11 March 1993; accepted 1 November 1993)
An oxy-acetylene flame, impinging vertically upward on an Si(OOl) substrate, is systematically examined for morphological variations in the resulting diamond deposits. The flame is operated under near neutral (O 2 /C 2 H 2 ratio near 1.0) conditions in the unconfined, open atmosphere. Singly twinned crystal morphologies in addition to the usual (001) faceted structures are observed and reported for the first time. Similar morphological variations are observed along the radial as well as the axial (vertical) coordinate directions in the flame. Large changes in morphology are observed for changes in vertical position as small as 50
I. INTRODUCTION Ever since Hirose's discovery that diamond can be synthesized from an oxy-acetylene flame,1 several studies have been conducted on this system.2"6 One interesting characteristic of flame deposition is its fast growth rate. Other than the plasma-arcjet technique, flame deposition is the only technique producing growth rates in excess of 50 /xm/h. The deposits usually contain large faceted grains that exhibit various morphologies. Several researchers have observed diamond grains with square facets [i.e., (001)] in the central portion of the diamond deposits, under certain flame conditions.7"10 This is in stark contrast to the (111) facets usually observed on films deposited from the dilute hydrocarbonhydrogen gas mixtures by Hot-Filament Chemical Vapor Deposition (HFCVD) and Microwave Plasma CVD.11 13 Ravi concluded that high substrate temperatures in flame deposition were responsible for the predominance of (001) facets.7 Radial variations in the morphology of flame deposits have also been noted.8'9 Aside from the aforementioned works, there has been no systematic evaluation of the variation of film morphology with position in the flame. In this paper, diamond growth in different regions of the flame is shown to lead to different morphologies, directly influenced by gas phase composition. A description of the experimental apparatus is given in the next section, followed by a discussion of the experimental observations, and results are given in Sec. IV. Finally, J. Mater. Res., Vol. 9, No. 3, Mar 1994
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a summary, along with the most significant conclusions, is given in Sec. V. II. EXPERIMENTAL APPARATUS The deposition apparatus consisted of a Victor 100CKV-W66538 welding torch with a no. 1 brazing tip (AIRCO Gas & Gear). An aluminum ramp with a 28° incline was used to position the flame directly upward with respect to gravity, and perpendicular to t
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