Hydrogen-induced metallization of the 3C–SiC(0 0 1)-(3 × 2) surface

A surprising metallization of the SiC(0 0 1)-(3 × 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.