First-Principles Study Of Surfaces Property From The β-Sic (111) Derived Structure And Its Water Molecule Adsorption

This paper mainly studies theβ-SiC (111), as well as theβ-SiC (111)-derived structures'surface atoms, chemical bonding and electronic properties. And further studies the interaction between water molecules andβ-SiC (111) or its derivative structures.In this paper, the CASTEP module of materials simulation software (materials studio) with the density function theory (DFT) was applied forβ-SiC (111)-derived structures'chemical bonding, feature, band structure and electronic properties.The study found, with the increase of the removal silicon atoms, the surface atoms and chemical bonds have significant changes, showing uneven shape. The first layer atoms have a tendency to subsidence. The charge number of the carbon atoms bonding with the removal Si atom reduced, because of the hanging bonding electrons shift to the new bonding or inner layers. The charge on the bonding between C, Si atoms increased, leading to the more stronger covalent property. According to the band structure and density of states, for the not complete removal Si surface, as the number of removal Si atoms increase, the surface band gap get smaller, the conductivity became stronger. The effect of the carbon atoms changed from the almost no contribution to the eventual decision for the surface property. And the band structure energy moved gradually to high-energy, showing greater activity. Water molecules on theβ-SiC (111) and its derived structures surface decomposed. With the reduction of the silicon atoms, hydrogen, oxygen atoms and the atoms on the surface formed more and more chemical bonding. The charge of silicon atoms of the surface shifted to the carbon atoms gradually. From the band structure analysis, after the H2O adsorption, the band number ofβ-SiC (111) and its derived structure (a) reduced, and conductivity decreased. The band gap of derived structure (b), (c), (d) get larger, especially the (d), from the metallic nature to the semiconductor. That shows, when the H2O adsorbed on the derived structure (a), (b), (c), the decomposed water molecule formed chemical bonding with C or Si atoms, decreasing the hanging bonding electrons. By the analysis of density of states, the join of H2O molecule lead to some small peak. With the removal of silicon atoms, the density of states near the femi energy is mainly from Si atom electrons to C atom electrons, which is the same with the trends before adsorption. The peak value of the density of states near the femi energy reduced, causing the reduction of conductivity. And the oxygen has some contributions to the deep energy states. The fluctuations ofβ-SiC (111) and its derived structure energy bands (a), (b), (c), (d) slows, showing the locality of band electrons increased, and the effective mass is relatively large. The fluctuations of derived structure (c), (d) energy bands is larger than the clean surfaces, showing the electronic localization weakened, and a smaller effective mass. The density of states shifted to the high energy.