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Z. Hu, A. Biedermann, E. Knoesel, T.F. Heinz:
"Quantitative study of adsorbate-adsorbate interactions of hydrogen on the Si(100) surface";
Physical Review B, 68 (2003), 155418-1 - 155418-10.

The equilibrium spatial distribution of hydrogen atoms adsorbed on the
clean Si(100)-2x1 surface under
ultrahigh vacuum conditions has been investigated by means of scanning
tunneling microscopy (STM). Singly
occupied dimers, doubly occupied dimers, and clusters of adjacent doubly
occupied dimers along a dimer row
are observed. Through the evaluation of large-area STM images, a
quantitative assessment of the prevalence of
the different adsorbate configurations has been obtained for a range of
hydrogen coverages from 0.03 to 0.59
monolayers. At moderate coverages, most of the hydrogen adatoms are found
in doubly occupied dimers, while
a relatively small number are present as singly occupied dimers or as part
of clusters of doubly occupied
dimers. The interaction between doubly occupied dimers was examined by
determining the experimental size
distribution of clusters and the spatial correlation function for the
doubly occupied dimers. A nearest-neighbor
interaction model is compared with experiment within analytic
approximations and through full Monte Carlo
simulations. The model is found to agree well with the experimental
results. An effective pairing energy of
epsilon=0.31+/-0.04 eV and an effective clustering energy of
omega=0.04+/-0.01 eV are inferred. These results are
independent of any hypothesis concerning the adsorption/desorption
pathways, but have implication for possible
pathways and their kinetics.

http://aleph.ub.tuwien.ac.at/F?base=tuw01&func=find-c&ccl_term=AC04405963