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A thermodynamic criterion for selection of gas compositions for diamond deposition

Jacob, KT and Gundiah, N and Menon, AG (1996) A thermodynamic criterion for selection of gas compositions for diamond deposition. In: High Temperature Materials and Processes, 15 (4). 223-235 .

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Abstract

Isoactivity lines for carbon with respect to diamond as the standard state have been calculated in the ternary system C-H-O at 1223 K to identify the diamond deposition domain. The gas composition is calculated by suppressing the formation of all condensed forms of carbon using the SOLGASMIX free-energy minimization program. Thirty six gas species were included in the calculation. From the gas composition, isoactivity lines are computed using recent data on the Gibbs energy of diamond. Except for activities less than 0.1, the isoactivity lines are almost linear on the C-H-O ternary diagram. Gas compositions which generate activity of diamond ranging from 1 to 100 at 1223 K fall inside a narrow wedge originating from the point representing CO. This wedge is very similar to the revised lens-shaped diamond growth domain identified by Bachman et al., using inputs from experiment. The small difference between the calculated and observed domains may be attributed to variation in the supersaturation required for diamond deposition with gas composition. The diamond solubility in the gas phase along the isoactivity line for a(di)=100 and P=6.7 kPa exhibits a minimum at 1280 K, which is close to the optimum temperature found experimentally. At higher supersaturations, non-diamond forms of carbon, including amorphous varieties, are expected. The results suggest that thermodynamic calculations can be useful for locating diamond growth domains in more complex CVD systems containing halogens, for which very little experimental data is available.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Freund publishing house.
Keywords: Theoretical study;Crystal growth from vapors;CVD;Diamonds; Synthetic mineral;Gas mixture;Mixing ratio;Temperature effects;Pressure effects;Thermodynamic properties;Chemical composition;Substrates;Nonmetals;
Department/Centre: Division of Chemical Sciences > Materials Research Centre
Division of Physical & Mathematical Sciences > Instrumentation and Applied Physics (Formally ISU)
Date Deposited: 21 Apr 2011 06:36
Last Modified: 21 Apr 2011 06:36
URI: http://eprints.iisc.ernet.in/id/eprint/37043

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