The H-terminated diamond (111) and (100) − 2 × 1 slab is composed by 4- and 6-layers carbon atoms, respectively.
The pink, gray and white balls are boron, carbon and hydrogen atoms, respectively. The calculating model shown in Figure 1 indicates a substituted boron doped diamond slab. As the aim of this study is to explore whether the CH 3 radicals can still be adsorbed on the dopants, the center carbon atom in the first C layer is substituted by boron, nitrogen or silicon atoms. Although it is reported that the substitutional B and N dopants within the second C layer will have the largest influence on the diamond growth rate especially on the rate-determining H-abstraction step. Thus, diamond (111) and (100) models are both used to study the adsorption energy in this study. The final morphology of diamond films is determined by the growth rate of diamond (111) and (100) facets. The number of k points (2 × 2 × 1) was generated using the Monkhorst-Pack scheme, and the cutoff energy was set to 280 eV. The PW91 functional and spin-polarized general gradient approximation are selected under the periodic boundary conditions. Thus, the boron doping may hinder the formation of the (100) facet during the CVD diamond deposition under a certain condition.Īll theory calculations are carried out using Cambridge Sequential Total Energy Package (CASTEP) code, which is based on density functional theory. However, the BH 2 pre-adsorbed on diamond (100) − 2 × 1 surface may interact with surface radical carbon site and result in a large reduction of CH 3 adsorption energy. The adsorption energy can be slightly enhanced when BH 2 radical is pre-adsorbed on diamond (111) surface. In the case of radical doping, the adsorption energy of CH 3 will be reduced due to the steric hindrance between NH 2 or SiH 3 with CH 3.
The substituted silicon doping has little influence on the CH 3 adsorption, as Si atom has the same outer valence electron structure with C atom. However, the empty p orbitals of boron atom will help the chemical adsorbing of CH 3 radicals. Boron substituted doping will disfavor the adsorption of CH 3 due to the lacking of valence electron. The calculation results indicate that the CH 3 radicals are hardly adsorbed on nitrogen atoms and thus may cause vacancy in the diamond lattice easily. The substituted doping and radical doping of diamond (111) and (100) − 2 × 1 surface are both considered. To better understand the influence mechanism of boron, nitrogen and silicon dopants on the growth of chemical vapor deposition (CVD) diamond film, density functional calculations have been performed to reveal the different impact of the impurities on the CH 3 adsorption on diamond surface.
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