Optimization of structures and properties of vacancy-defected graphene modified by Si atoms

Intrinsic graphene has so many advantages that it is regarded as an alternative material for silicon in the semiconductor industry; however, it is difficult to be directly applied into electronic devices because of its uncontrollable electrical conductivity. Therefore, it is urgent to modify the electrical properties of graphene to promote its application in practical production. Scientists have been looking for modified methods to make graphene controllable in order to effectively adjust its conductive ability. As one of the effective means to modify the properties of many materials, the bombardment with high-energy particles can regulate the electrical properties of graphene easily by doping the heterogeneous particles in graphene, and therefore attracts extensive attention of researchers. Si is the suitable choice as doped atoms in graphene because Si and C are congeners of chemical elements with some similar properties. Herein the processes of bombarding graphene with Si-6 clusters were simulated by the molecular dynamics method for investigating the structural evolution during bombardment. The microstructures of the system were observed by visualization software, and the detailed structural changes of graphene were recorded in the meantime. The results indicate that Si6 is not able to cause damage to C-C bonds in graphene at the low energy range [0.875, 55.9] eV but destroys the structures of graphene easily and introduces vacancy defects with the regular edge at the high energy range (above 503.9 eV). The bombarded graphene tends to form a variety of complex structures when the energy of Si-6 is in the range of (55.9, 503.9] eV. The effects of different bombardment energy on graphene were investigated, which gives us a reference value (0.146 eV) for the initial energy that each Si atom used to repair the graphene needs. Then, the repairing processes of vacancy-defected graphene obtained by bombardment were performed with different numbers of Si atoms by the molecular dynamics methods. The first-principles methods are used to optimize the repaired geometric configurations left by molecular dynamics simulations to obtain the stable structures needed in the subsequent calculations of the electronic structures. The optimized configurations show that the carbon dangling bonds caused by vacancy defects can be saturated by the introduction of Si atoms. Moreover, the results calculated by first-principles methods differ from those by molecular dynamics methods and there is a strong interaction between Si atoms, which forms three-dimensional structures at the vacancy defects. The electronic structures of the three optimized configurations show that the band gaps of graphene are opened and the conductivity of graphene with four vacancies is reduced by the introduction of Si atoms. This study provides a new idea for the modification of graphene and will hopefully be valuable for designing modern gas sensing and electronic devices.