H atom production in a hot filament chemical vapour deposition reactor

Abstract

Multiphoton ionisation spectroscopy of atomic hydrogen, resonance enhanced at the two photon energy by the 2s1;2S 1/2 state, and subsequent analysis of the resulting Doppler broadened lineshapes, has been used to provide direct, spatially resolved relative H atom number densities and gas temperature profiles in the vicinity of a coiled Ta hot filament (HF ) in a reactor used for diamond chemical vapour deposition. The eVects of filament temperature and H 2 pressure on the relative H atom number densities and the gas temperature profiles have been investigated, as have the eVects of small amounts of added CH 4 . The eVective activation energy for H atom production so obtained (E a =237±22 kJ mol’1) suggests that the HF provides a particularly eYcient means of heating (and thus promoting the dissociation of ) H 2 molecules that adsorb onto its surface. © 1999 Elsevier Science S.A. All rights reserved.