Influence of Reconstruction on Electron Distribution at Silicon <111> Surface: Effect on Nuclear Quadrupole Interactions Associated with Indium Adatoms

Ranjit Pati1, N. Sahoo1,2, B. N. Dev3, G. Schatz4, T. P. Das1

1 Department of Physics, State University of New York at Albany, Albany, New York, 12222, USA
2 Department of Radiation Oncology, Albany Medical College, Albany, New York, 12208, USA
3 Institute of Physics, Bhubaneswar, 751005, Orissa, India
4 Fakultät für Physik, Universität Konstanz, D-7750 Konstanz, Germany

The Dimer Adatom Stacking fault (DAS) model for the 7x7 reconstruction of the Si(111) surface has been subjected to a rigorous test through electronic structure investigations associated with adsorbed In atoms. The results of our investigations explain the important features of the observed nuclear quadrupole interaction [1] of the 111Cd* nucleus resulting from K-capture in 111In. Among these features is the experimental observation [2] of two sets of Nuclear Quadrupole Interaction (NQI) tensors at the 111Cd* site, one associated with the corner site and the other with the edge site on the reconstructed surface. The NQI tensor involving the larger asymmetry parameter h is found to be associated with the corner site, while that with the somewhat smaller h is associated with the edge site. These assignments are in agreement with those suggested earlier [2] from the experimental measurement of the strengths of 111Cd* PAC signals and the results from STM investigations [3] regarding the relative populations of the corner and edge sites. Thus the results of the present investigations provide strong support for the DAS model. The calculated 111Cd* quadrupole coupling constants (e2qQ) for the two sites are also in reasonable quantitative agreement with experiment, the only difference with experiment being the near equality of the e2qQ for the two sites from theory while the experimental results indicate that the e2qQ for the corner site is a little larger than for the edge site. Possible sources that could improve the agreement in this respect between theory and experiment will be discussed.

[1] K. Takayanagi et al., J. Vac. Sci. Technol. A3, 1502 (1985)
[2] G. Krausch et al., Phys. Rev. Lett. 68, 377 (1992)
[3] J. Nogami et al., J. Vac. Sci. Technol. B6, 1479 (1988)

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