ABSTRACT
Hot tungsten filaments were first used to generate atomic hydrogen for removal of non-diamond carbon from diamond by S. P. Chauhan et al. The design of hot-filament reactors involves an artful choice of dimensions, materials and operating conditions that permit the generation and transport of sufficient quantities of atomic hydrogen and hydrocarbon free radicals to the growth surface. The conditions leading to carbon deposition on the filaments can be estimated by calculating the equilibrium gas phase composition adjacent to the filament. Considerations in choosing filament material include mechanical stability, chemical stability, and incorporation of metal into the diamond. The filaments can change structurally, for example, by cracking, bending or creeping, due to carburization and hydrogen embrittlement. Hot-filament reactors operate in a fluid mechanical regime that permits in situ measurement of growth rates using a microbalance. Tungsten impurities have been detected by secondary ion mass spectroscopy in diamond films grown using hot-filaments.
