The activation energies of diamond with different grain sizes

Full text: The effect of substrate temperature on the growth rate and properties of diamond with different grains sizes are investigated. Experimental conditions used gaseous mixture of 1 to 20 vol.% methane balanced with hydrogen using a argon-free and argon-rich in a Hot Filament Chemical Vapor Deposition reactor - HFCVD. Scanning electron microscopy, x-ray diffraction and Raman spectroscopy evaluated the morphology, thickness growth rate, crystallite size, renucleation rate, diamond quality and amorphous carbon content. For each gas mixtures the deposited films presented different morphologies (microcrystalline – MCD and nanocrystalline – NCD). An Arrhenius plot of growth and renucleation rate as a function of substrate temperature yields a values for the activation energy. The activation energy calculated by the thickness growth rate show a common trend value (around 7 kcal/mol) independently of film morphologies. Nevertheless the activation energy calculated by mass growth rate show different values for MCD (10 kcal/mol) and NCD (6 kcal/mol) growth. An extensive comparison with the values calculated here and most determinations in the literature propose that these differences exist and that is independently of the CVD method used. Additionally, the calculated renucleation rate (or the defect formation rate) and its dependence on substrate temperature propose that the renucleation process can be thermally activated, with different activation energy values for MCD (around 24 kcal/mol) and NCD (around 12 kcal/mol) growth. The correlation of the values found with the gas mixture suggests that the activation energies values are mainly governed by methane and hydrogen in the gas mixture, independent of argon in the reactor feeding. The crystallite size, sp2 content, renucleation and growth rates also present very similar tendencies with substrate temperature despite the huge gas mixture variation. These observations may help bridging MCD and NCD into a single understanding of diamond growth. (author)