Mechanism of diamond film growth by hot-filament CVD: Carbon-13 studies

Abstract

Mixed carbon-12/carbon-13 diamond films were synthesized by hot-filament chemical vapor deposition, using mixtures of ¹³CH₄ and ¹²CH₄ or ¹²C₂H₂ in H₂. The first-order Raman peak at 1332 cm⁻¹ for ¹²C-diamond was found to shift by 50 cm⁻¹ to 1282 cm⁻¹ for pure ¹³C-diamond. For mixed-isotope films, the Raman peak frequency shifts linearly between these values as a function of the ¹³C mole fraction. The mechanism of diamond film growth by hot-filament CVD has been investigated by growth from mixtures of ¹³CH₄ and ¹²C₂H₂, using the shifted Raman frequency to determine the relative incorporation rates of ¹³C and ¹²C into the film. The ¹³C mole fraction in the film agrees closely with the ¹³C mole fraction inferred for the methyl radical but differs substantially from that of acetylene, indicating that the methyl radical is the dominant growth precursor under the conditions studied.