Theoretical study of Ti adsorption on Si(001) surfaces

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Abstract
Ti adsorption on a Si(001) surfaces has been investigated by first-principles pseudopotential calculations. The calculations have been performed on two adsorption structures, a Ti atom adsorbed at the pedestal site and at the dimer vacancy (DV) site, that have been recently observed by scanning tunneling microscopy (STM). For both structures, the local density of states is qualitatively in good agreement with the STM image profiles. We have found that the adsorption energies for the pedestal-site and DV-site adsorptions are 4.7 and 5.3 eV/adatom, respectively, and that the DV-site adsorption is energetically more favorable. The nature of Ti-Si and Si-Si bonds is also discussed in terms of charge-density distribution. For the DV-site adsorption, we have found considerable redistribution of the charge density in the substrate, that is, the breakage of the bulk Si bonds. This gives an insight into a precursor state of silicidation.