Resonance enhanced multiphoton ionisation probing of H atoms in a hot filament chemical vapour deposition reactor

Abstract

We demonstrate some of the merits and limitations of using multiphoton ionisation (MPI) spectroscopy, resonance enhanced at the two photon energy by the state, to detect H atoms within a hot Ðlament 2s1 ;2S 1@2 reactor used for diamond chemical vapour deposition (CVD). Subsequent analysis of the Doppler broadened lineshapes obtained in this way allows determination of spatially resolved, relative H atom number densities and gas temperatures. The e †ects of pressure and Ñow rate, Ðlament temperature and radial distance from H 2 the Ðlament on the relative H atom number densities and the gas temperature proÐles have each been investigated for the case of pure and, in some cases, in the presence of added The present Ðndings H 2 CH 4 . complement and extend previous measurements obtained using alternative in situ detection methods, and are generally consistent with current models of the gas phase chemistry prevailing in low power diamond CVD reactors. They also serve to reÐne the role of the hot Ðlament in the H atom production process, and to illustrate continuing ambiguities regarding the way in which the local relative H atom number densities vary with Ðlament temperature, with the presence of trace quantities of added hydrocarbon, and the interpretation of these dependencies.

Hydrogen dissociation on high-temperature tungsten

“…(If the chamber were coated with amorphous silicon from other studies, SiH 4 would be etched from surfaces by H, perhaps producing such an anomalous p dependence.) Similar values of E diss have also been observed for H 2 dissociation on other metals [17]. The striking fact that 2E diss ffi E H 2 , the vapor-phase H 2 dissociation energy, for all metals studied has long been recognized.…”

What [plasma used for growing] diamond can shine like flame?

“…34 The most common filament materials are W, Ta, or Re because of their high melting points. Laser and mass spectroscopic measurements of key species (including H atoms, [35][36][37][38][39][40] and CH3 radicals 37,41,42 ) in HF-activated CH4/H2 gas mixtures, coupled with thermodynamic and gas-kinetic modelling, 27,43 have yielded a fairly complete picture of the prevailing gas-phase chemistry.…”

Catalytic Decomposition of H2O(D2O) on a Heated Ir Filament to Produce O and OH(OD) Radicals

“…In this technique, radical species are produced from material gases on heated metal surfaces without co-producing ionic or metastable excited species. In order to make clear the decomposition and ejection mechanisms, many studies have been carried out to identify the radical species produced [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Although it has been rather difficult to produce oxidizing radicals, we have recently shown that atomic oxygen can be produced efficiently by the catalytic decomposition of O 2 , NO, N 2 O, and NO 2 on a heated Ir filament [7,8].…”