Quantum-chemical Simulation of Divacancy Defects on C(100)-(2×1) Diamond Surface

The paper presents the results of the quantum-chemical simulation of the divacancy defect V₂ and the "split" divacancy V-C-V in the surface layers of C(100)-(2×1) diamond. Calculations were performed using the semi-empirical PM3 method realized in a MOPAC software package and ab initio methods implemented in Firefly (known as PC GAMESS). Six configurations of the divacancy defect V₂ are considered. It is shown that the position of the divacancy in the first layer of the surface is the most energetically favorable. The calculations of geometric and electronic characteristics of the divacancy in the ground state are performed. The energy characteristics of atomic hydrogen adsorption on the surface containing divacancies are estimated. It is shown that the divacancy defect V₂ on the diamond surface has an increased chemical activity as compared with an ordered surface. Potential adsorption sites are atoms in the divacancy V₂ region with double bonds. The formation of the “split” V-C-V divacancy is more energetically favorable than the formation of the divacancy V₂ in 3-4 layers of the surface. It is explained by the formation of graphene-like surface structures (Нexagons) from atoms of the first two surface layers caused by the existence of vacancies in the third layer of the cluster under dimer row. The formation of such a defect is accompanied by a change in the bond orders, hybridization of atomic orbitals and adsorption activation energy for hydrogen atoms compared with the ordered surface. Thus, the divacancy defects in the C(100)-2×1 diamond surface layers cause significant changes in the geometry and electronic state of the surface. Depending on the location of the defect, the active or passive chemisorption centers may be formed affecting the mechanism and energy of the process.