Ranjit Patia, N. Sahooa,b, B. N. Devc, G. Schatzd and T. P. Dasa *
a Department of Physics, State University of New
York at Albany, Albany, New York, 12222, USA
b Department of Radiation Oncology, Albany Medical College, Albany, New York, 12208, USA
c Institute of Physics, Bhubaneswar, 751005, Orissa, India
d Fakultät für Physik, Universität Konstanz, 78457 Konstanz, Germany
* Corresponding Author: FAX 1-(518)-442-5260
We have subjected the Dimer Adatom Stacking fault (DAS) model  for the 7x7 reconstruction of the Si(111) surface to a rigorous test through electronic structure investigations associated with adsorbed In atoms. Our results explain the important features of the observed nuclear quadrupole interaction  of the 111Cd* nucleus resulting from K-capture in 111In. The first features is the experimental observation  of two sets of Nuclear Quadrupole Interaction (NQI) tensors at the 111Cd* sites on the reconstructed surface, one associated with the corner site and the other with the edge site. The NQI tensor involving the larger asymmetry parameter h is found from our work to be associated with the corner site, while that with the somewhat smaller h is associated with the edge site. These assignments agree with those suggested earlier  from the experimentally observed strengths of 111Cd* PAC signals and the results from STM investigations  regarding the relative populations of the corner and edge sites. The results of the present investigations thus strongly support the DAS model. Our investigation also leads to 111Cd* quadrupole coupling constants (e2qQ) for the two sites, in reasonable agreement with experiment, the only difference being the near equality of the e2qQ for the two sites from theory while experiment indicates that the e2qQ for the edge site is a little smaller than for the corner site. We shall discuss possible sources that could improve this aspect of the agreement between theory and experiment.
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