C-terminated Surfaces Research Articles

Adsorption of a monolayer of iron on beta -SiC(100) surfaces.

The linear-muffin-tin-orbital method is used to study the adsorption of a monolayer of Fe atoms on the \ensuremath{\beta}-SiC(100) surface. Adsorption energies of Fe on both Si- and C-terminated (100) surfaces are calculated. It is found that Fe can adsorb on both the Si- and C-terminated (100) surfaces. In the case of a clean Si-terminated surface, the 2${\mathit{p}}_{3/2}$ core level of the surface Si atoms shifts downward, since the surface Si atom loses more of its electrons than does the bulk Si atom. When a monolayer of Fe atoms adsorbs on this surface, the 2${\mathit{p}}_{3/2}$ core level shifts upward; this is due to the fact that charge transfers from Fe to the surface Si atom. In addition, the layer projected density of states is also studied.

Reconstructions at Si- and C-Terminated Surfaces of 2H-SiC: an ab Initio Molecular Dynamics Study

AbstractThe reconstruction patterns of Si- and C-terminated surfaces of wurtzite SiC are studied by ab initio molecular dynamics. The (1×1) relaxed, (1×2) buckled, and (2×1) л-bonded chain geometries are considered. In the (l×1) geometry, inward relaxation of the C-terminated surface is much stronger than that of the Si-terminated surface. The C-terminated surface is stable with respect to (2×1) buckled reconstruction, but the Si-terminated surface is not. At both surfaces, the (2×1) л-bonded chain geometry is energetically the most favorable. The Si-C л-bonded chains are buckled and slightly dimerized. In both cases, the outermost atoms are carbons, due to the bond length constraints of the л-bonded chain reconstruction.

Adsorption of aluminum on beta -SiC(100) surfaces.

Adsorption properties of Al on \ensuremath{\beta}-SiC(100) surfaces are studied by using the extended H\uckel theory. The Al/\ensuremath{\beta}-SiC(100) interface is sharp and the Al-SiC interaction is limited to a narrow region at the interface. The adsorption of Al on the Si-terminated (100) surface hardly affects the Si-C bond, whereas the adsorption of Al on the C-terminated (100) surface weakens the Si-C bond. Moreover, the Al-Si interaction is weaker than the Al-C interaction. Our results agree qualitatively with experimental observation.

Geometric and electronic study of the beta -SiC(100) surface

The Keating model is employed to determine the geometric structure of the (2*1) reconstructed beta -SiC(100) surface. The symmetric dimerization for both the Si- and C-terminated (100) surfaces is obtained by minimizing the elastic energy. The extended Huckel band calculation is performed for the electronic structures of both the ideal and the (2*1) reconstructed beta -SiC(100) surfaces. The results show that the ideal surfaces are metallic, whereas the (2*1) reconstructed surfaces are semiconducting. Moreover, the band structures calculated agree quite well with the experimental results. The density of states is also calculated and discussed.

Adhesion and bonding of polar and non-polar SiC surfaces to Ti(0001)

The atom superposition and electron delocalization molecular orbital calculations have been performed for studying the interfacial bonding and adhesion of some polar and nonpolar surfaces of α- and β-SiC with the close-packed Ti(0001) surface, using large cluster models and idealized structures. Polar SiC surfaces studied in this work are the Si- and C-terminated (111) and (100) planes and the nonpolar surfaces with equal concentration of Si and C, i.e., β-SiC(110), α-SiC(101̄0) and α-SiC(112̄0). For the unrelaxed polar SiC surfaces, the average Si/Ti and C/Ti interfacial bond strengths are maximum for the β-SiC(110)/Ti(0001) interface due to two dangling surface state orbitals on each surface atom in place of one on the (111) SiC surfaces. The Si- and C-terminated (100) surfaces undergo dimerization. Adhesion energies for the (111) and (100) surfaces to Ti(0001) are comparable when surface relaxation and reconstruction effects are considered. Nonpolar α- and β-SiC surfaces bind comparatively weakly to titanium, and their adhesion energies to Ti(0001) are all approximately equal. In each case of interfacial bonding the sp hybridized dangling orbitals on Si and C surface atoms are stabilized by bond formation with Ti 3d band orbitals.

Comparative electron spectroscopic studies of surface segregation on SiC(0001) and SiC(0001̄)

Electron spectroscopic comparison of the C-rich SiC(0001̄) and Si-rich SiC(0001) surfaces after cleaning and disordering by Ar+ ion sputtering and subsequent annealing is reported. The chemical behavior of the two disordered surfaces differs significantly. Three distinct temperature regions with different carbon surface segregation kinetics are discernible on SiC(0001̄). On SiC(0001) only one temperature region for C-segregation is observed. Below 900 K, no spectroscopic differences between the two crystal surfaces are observed. Between 900 and 1300 K, both faces are terminated by a surface graphite layer and the C-rich face shows an additional carbon surface segregation process. Above 1300 K, the C-terminated surface graphitizes at a higher rate than the Si-terminated surface. Massive graphitization on both surfaces above 1300 K is attributed to Si(g) sublimation from the SiC surfaces. The results demonstrate that extensive surface disordering of polar SiC faces does not destroy the memory for the polarity of the original crystal insofar as high-temperature surface chemistry is concerned.

Electron-stimulated desorption of positive ions from hexagonal α-SiC

Electron-stimulated desorption (ESD) of positive ions (H +, O +, +OH, F + and Cl +) from the Si- and C-terminated surfaces of hexagonal α-SiC has been observed for electron energies in the 5–105 eV range. Comparison of these results with those for the ESD of the same ions from the surfaces of Si and condensed hydrocarbons leads to a model for the H +, +OH, F + and Cl + threshold desorption process based on transitions from deep valence Si and C “s-like” levels to states in the conduction band, followed by Auger decay to form a localized multiple valence-hole configuration. O + desorption, on the other hand, is initiated by O 2s ionization. Evidence is found for a strong dependence of the F + threshold on the local chemical bonding. The results indicate that the thresholds for ESD of these ions from SiC are determined more by the electronic excitation of the substrate than by direct excitation of the adsorbate bond.