Effect of sulfur passivation on 6H-SiC surface stability
Based on first-principles calculation, the surface stability of S-passivated 6H-SiC in different terminals are researched through investigating surface energy, charge distribution and density of states with the change of sulfur coverage from1/4 monolayer (ML) to 1 monolayer (ML). Our calculations show that S-passivated Si-terminal surface performs better than Si-terminal surface. Surface-state of 6H-SiC is reduced by about 1-4 electrons/eV due to S passivation. Meanwhile as the sulfur coverage increasing, surface energy is decreased from about -5.2eV/nm2 to about -40 eV/nm2 which leads to a more stable structure. According to theoretical calculation and mechanism analysis, the most stable structure is 3/4 ML sulfur atoms absorb in bridge site on Si-terminal surface.
Photoemission study of Si-rich 4H-SiC surfaces and initial SiO2 SiC interface formation
Photoemission studies of Si-rich polar and nonpolar 4H-SiC surfaces before and after oxygen exposures are reported. For the clean Si-rich (0001) -3×3 surface, three prominent surface-shifted compon ...
Model of vitreous SiO2 generated by an ab initio molecular-dynamics quench from the melt.
We studied liquid and vitreous SiO2 by performing first-principles molecular-dynamics simulations. Diffusion in the liquid is shown to occur through correlated jump events, which disrupt the network only for short time periods. The persistence of the network even at high temperatures is confirmed by the average structural properties of the liquid. By quenching from the melt, we obtained a model for the glass, which forms a perfectly chemically ordered network. Structural and electronic properties of our model glass present a remarkable agreement with vitreous SiO2: the calculated total structure factor closely agrees with data from neutron diffraction experiments and features in the x-ray photoemission spectrum are well reproduced by the electronic density of states. This agreement strongly supports other structural properties which are yet unavailable from experiment such as partial pair correlation functions and bond-angle distributions. A comparative study of the electronic density of states in liquid, vitreous, and crystalline SiO2 shows that enhancement of disorder gives rise to a reduction of the gap.