Cylindrically symmetric diamond parts by hot-filament CVD

In the absence of forced substrate cooling, the substrate temperature in hot-filament CVD diamond deposition is controlled by the heat coming from the filaments in the form of radiation, gas conduction and atomic hydrogen generation and recombination. Atomic hydrogen heat transport is the dominant process of substrate heating. In many industrial applications, forced substrate cooling cannot be used because of the geometry of the CVD diamond part or the impracticality of cooling connections. Overheating of an uncooled substrate can only be avoided by using as few filaments as possible because of the high heat flux emanating from each filament. In general, utilization of only a few filaments will lead to nonuniform and irregular diamond deposits. However, if the ratio of the substrate diameter to the filament-substrate spacing is kept within certain limits determined by theory and confirmed by experiments, cylindrically symmetric diamond parts can be successfully deposited on a stationary uncooled substrate with only one or two filaments. (C) 1997 Elsevier Science S.A.