The Calculation Of Fine Structure Of Electron Energy Loss Spectra Of BC ₂ N Materials

In recent years, ternary compounds of boron, carbon and nitrogen have received special attention in international academic community. BC2N possesses extremely hardness and the properties of thermal and chemical stability. The hexagonal BC2N with layered structure is used as the starting material to synthesize the superhard material of BC2N. Theoretical investigation has predicted that the band gaps of monolayer hexagonal BC2N vary with atomic arrangement. As a result, the layered BC2N has potential application in optoelectronic devices. BC2N polymorphs have been predicted theoretically and the BC2N materials have been synthesized experimentally with various methods, however, a conclusive determination of the synthesized BC2N structure is still a challenging task.First-principle calculation has been widely used in material property research. Theoretical simulation of electron energy loss spectroscopy can give a reliable prediction of experiment spectra and determine the connection between crystal structure and spectra features.In this work, electron energy-loss near-edge fine structures (ELNES) were calculated using a pseudopotential plane wave method from density functional theory (DFT). The core-hole effect was treated by employing the supercell approximation and "excited" pseudopotential for the excited atom. With a proper choice of the supercell, cutoff energy, and sampling k point, the calculation on cubic and hexagonal polymorphs of C and BN are carried out and compared with experiment. In the second part, geometry optimization and ELNES calculation of sp2-and sp3-bonded BC2N polytypes were carried out. We also calculated ELNES of graphene and doped graphene to elucidate the relation between chemical environments and ELNES fine structures in layered B-C-N materials. The transition to the final states with px,y and pz symmetries are present for the highly anisotropic layered materials. The spectral features are closely related to the atomic species and arrangement. The theoretical spectrum can be used as fingerprints to characterize the structure of BC2N polymorphs.