A molecule of H2S on the Si(001)c(2x4) surface:: a first principles calculation

We have investigated the energetics and atomic geometries of a H2S molecule on the Si(001)c(2 x 4) surface using first principles total energy calculations. In our study we have considered partial and fully dissociative geometries. In the first case, the H2S molecule is broken up in to HS and H subunits. Although the most stable configuration corresponds to the adsorption of the HS and the H in the same Si dimer, we have found other meta-stable configurations. The second case corresponds to the dissociation of the molecule in to S and two Hs. Now, the most stable configuration corresponds to the adsorption of the S and the H atoms on two different Si dimers. Again, several metastable structures are found. Our calculations indicated that a complete dissociation of the molecule is energetically more favorable than partial dissociation. This result is in agreement with ultraviolet photoelectron spectroscopy and scanning tunneling microscopy experiments that found that at low temperatures the dissociation is partial, but at higher temperatures the H2S molecule is adsorbed as a S and two Hs. (C) 2002 Elsevier Science B.V. All rights reserved.