An experimental study of the temperature and stoichiometry dependence of diamond growth in low pressure flat flames
- PDF / 2,101,936 Bytes
- 9 Pages / 576 x 792 pts Page_size
- 4 Downloads / 158 Views
A study of the temperature and stoichiometry dependence of diamond synthesis in low pressure premixed acetylene-oxygen flames is presented. A specially designed low pressure flat flame operating at 40 Torr is employed to deposit diamond films uniformly over areas of at least 2 cm 2 . Under optimized conditions of substrate temperatures and flame equivalence ratios, high quality translucent diamond that is well faceted is synthesized exhibiting first-order Raman fullwidths (half maximum) of about 2.5 cm" 1 . Diamond growth rates under these optimum conditions are approximately 4 yu,m/h. The film growth rate is found to drop off substantially at high substrate temperatures, with little or no carbon deposited beyond a temperature of 1070 °C. The growth behavior in response to changes in flame equivalence ratio and substrate temperature is discussed in terms of the possible role that oxygen-containing species may have on surface chemistry. The results described here are also used to project a base cost for manufacturing diamond under these process conditions.
I. INTRODUCTION Diamond synthesis from products of gaseous combustion reactions in mixtures of acetylene and oxygen at atmospheric pressure was first reported by Hirose and Mitsuizumi.1 Although elegant and simple, such a deposition strategy suffers from limited and nonuniform deposition areas (some millimeters in diameter) and extremely high heat fluxes (a few kW/cm 2 ) to the substrate.2 In order to overcome nonuniformities in film deposits, Murayama and Uchida3 designed an atmospheric "flat flame" that operates in a substrate-stabilized regime (the flame is detached from the burner) and achieved growth rates as high as 40 ^ m / h over 15 mm in diameter. An extension of Murayama and Uchida's burner was employed by McCarty etal.,4 which made further use of optimized nozzle designs to maximize reagent-use efficiencies and minimize edge effects. The use of low pressure flat flames to circumvent some of the problems associated with limited deposit area and high heat fluxes was first suggested by Cooper and Yarbrough.5 Their approach involved the use of a commercially available, porous sintered stainless steel burner to distribute a premixed supply of oxygen and acetylene and support a flame in a low pressure vacuum chamber, maintaining a pressure over a range of 25-50 Torr. In a stagnation-flow configuration, such low pressure flames have the advantage of being scalable to large areas, provided that you can maintain a uniform flow of reactants at a fixed distance from the substrate surface. Recently, Glumac and Goodwin6 designed a
a) Author
to whom all correspondence should be sent. J. Mater. Res., Vol. 10, No. 1, Jan 1995
low pressure burner consisting of an array of holes through which the premixed fuel and oxidizer exited from a mixing plenum. They demonstrated good quality diamond growth on a molybdenum substrate for a single set of deposition conditions and reported growth rates of about 0.6 /Ltm/h.6 More importantly, they verified the scalability of these
Data Loading...
