The Distributions Of Si Atoms And Structures Of Sialographies G-SiC₇:a First-principles Study

To discover two-dimensional materials with better properties and more promising applications is an important goal of current physics research.Graphene and silicene forming from the group IV elements C and Si have excellent properties.They have broad application prospects in energy storage and conversion,information processing and catalysis,and hence are promising candidate materials for electronic device of next generation.Siligraphene,obtained by graphene doped with Si atoms,has recently received wide attention,since it has many excellent properties that graphene and silicene do not have.Graphene has a planar structure and silicene a buckled one.The structure of siligraphene that is derived from them is still undetermined.The properties of siligraphene are closely related to the distribution of Si atoms and its morphological structure,but current researches are based on the assumption that siligraphene has a planar structure and a highly symmetrical Si atom distribution,which has not yet been verified by experiments nor by theory.In order to go beyond these assumptions,we studied all possible Si distributions and their planar and non-planar structures of siligraphene g-Si C₇ based on density functional theory.Firstly,out of the 35960 Si distributions of g-Si C₇,365 inequivalent ones are selected,and then for each inequivalent one,the stability of the planar and non-planar structures is compared.As far as the Si distribution is concerned,Si atoms tend to gather together to reduce the energy,while the more dispersed Si distribution usually has higher energy;as far as the planarity of the structure is concerned,studies have found that there are many non-planar structures with energy appreciably lower than the planar ones.Among all possible Si distributions,only 8 planar structures are found to be stable with respect to out-of-plane perturbations.We further studied the dynamical,thermodynamical and mechanical stability of the three structures with the lowest energy,and found that they are all stable.It is found that these three structures have the two Dirac energy valleys in the first Brillouin zone preserved in spite of the considerable structural deformations.There is a considerable band gap is opened at the Dirac point.The calculated Berry curvature is opposite at the inequivalent Dirac valleys,showing that they have energy valley freedom.Our studies have shown that siligraphene tends to have a more concentrated Si distribution and non-planar structure,and the most stable structures have good electronic properties.