Methyl radicals dynamics on (100)--(2x1):H diamond surfaces based on refined variational transition state calculations of gas-surface reaction rate coefficients

Overview & Synopsis

Theoretical modelling of diamond growth should ideally provide estimates of the growth rate depending on experimental conditions. To that end, a description of all possible reactions related to the competing adsorption, desorption and migration mechanisms is required. Here, we provide precise calculations of the reaction rate coefficient of methyl-related reactions on hydrogen-terminated (100) diamond surface, as $\mathrm{CH_3}$ is known to be the main growth precursor in chemical vapor deposition (CVD) growth of diamond. To achieve this goal, we successfully combined Density Functional Theory (DFT) and variational transition state theory (VTST), allowing to extend our analysis to barrierless reaction. Our rigorous treatment of the quasi-free rotation of $\mathrm{CH_3}$ adsorbates on the surface allows us to overcome numerical errors for the finite difference calculations of the vibrational spectra for evaluating the partition functions of the system. Our results suggest that the mechanism that deplete the $\mathrm{CH_3}$ concentration the most is the absorption on a surface radical site. We also evidence the anisotropy of $\mathrm{CH_3}$ migration along the dimer of the (100)-(2x1):H surface. In a more general perspective, the calculated reaction rates coefficient for methyl reactions and migration presented in this work, together with the data for hydrogen reaction and other main gas surface reactions, bridge the gap between the atomic-scale description and the large-scale modelling of diamond growth.