The influences of reactant composition and substrate material on the combustion synthesis of diamond
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The influences of reactant composition and substrate material on the combustion synthesis of diamond Colin A. Woldena) Department of Chemical Engineering, Colorado School of Mines, Golden, Colorado 80401-1887
Charles E. Draper and Z. Sitar Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7919
J. T. Prater Army Research Office, Research Triangle Park, North Carolina 27709-2211 (Received 15 September 1997; accepted 27 March 1998)
It has been observed that diamond deposition by flat flame chemical vapor deposition is achieved over a very narrow range of reactant composition. We demonstrate that this diamond deposition window is strongly determined by the nature of the substrate material. Furthermore, once a continuous diamond film is formed, the window appears to be independent of the original material. Substrates examined include silicon, glass, titanium, tungsten, nickel, and molybdenum. The dependence of growth rate, morphology, and quality on reactant composition has been quantified using scanning electron microscopy, Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). It was found that the highest quality diamond was grown at conditions where diamond does not nucleate on ultrasonically scratched silicon. Thus, the production of high quality diamond on silicon by combustion synthesis requires different conditions for nucleation and growth.
I. INTRODUCTION
The ability to uniformly deposit high quality diamond over significant areas has been demonstrated by a number of groups using flat-flame burners operated at both atmospheric1,2 and reduced3,4 pressure. The two most critical variables in combustion CVD of diamond are reactant composition and substrate temperature. We previously reported on the latter, demonstrating that textured growth could be achieved by controlling substrate temperature at a fixed composition in a combustion system operated at 47 Torr.5 In describing the reactant mixture of combustion chemical vapor deposition (CVD) experiments, it is common to use the ratio of oxygen to acetylene, R O2 : C2 H2 . In experiments using conventional welding torches at atmospheric pressure, it was found that diamond could be deposited over a fairly broad range, 0.70 , R , 1.00.6 This large range was attributed to the two-dimensional structure of the welding torch, which creates substantial radial and axial concentration gradients. In contrast, the composition domain for flat flame systems is considerably restricted. Kim and Cappelli4 deposited diamond on molybdenum over a range of 1.03 , R , 1.10. However, most researchers using flat flames have reported only a single composition for successful diamond growth.1–3,5,7
In our previous studies5,8 we found that diamond deposition occurred on silicon over a very narrow range (0.995 , R , 1.005). At lower values of R amorphous carbon was deposited and at higher values no growth was observed. During a subsequent study of diamond deposition on gl
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