Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5426382 | Surface Science | 2006 | 6 Pages |
A surprising metallization of the SiC(0Â 0Â 1)-(3Â ÃÂ 2) surface induced by hydrogen adsorption was discovered in recent experiments. The effect was ascribed to dangling bonds created on the third layer of the surface system by H adsorption and stabilized by steric hindrance. We have investigated the surface metallization by density functional calculations. Our total-energy minimizations show that dangling bonds on the third layer are very unstable. Instead, H adatoms form angular Si-H-Si bonds on the third layer after the asymmetric dimers on the top layer have been saturated by H forming monohydrides. The novel Si-H-Si bonds on the third layer give rise to a metallic surface, indeed. But the mechanism for metallization is very different from the one suggested originally. Likewise, H atoms can also occupy bridge positions in angular Si-H-Si bonds on the second layer and induce metallization, as well. In addition to monohydrides on the top-layer dimers, we have also investigated dihydride surfaces with additional H on the second and/or third layer. The dihydride surface structure with H adsorbed on both the second and third layers is energetically most favorable and is also metallic. In all three cases the new Si-H-Si bonds are the origin of the surface metallization while its nature is somewhat more intricate, as will be discussed.