The Ho/Si(111)-1 x 1 and H-Ho/Si(111)-1 x 1 surfaces have been investigated
by low energy electron diffraction I-V curve analysis. Several structural
models have been tried and the optimum structure has been obtained using a
combination of search methods. In the case of the Ho/Si(111) surface, Ho at
oms sit on T4 sites of the Si(111) near bulk-like layer and are located und
erneath a Si bilayer which is rotated 180 degrees with respect to the subst
rate Si layers. This is the same structure as proposed by medium-energy ion
scattering. In the case of the H-Ho/Si(111)-1 x 1 surface, Si atoms in the
surface bilayer have normal stacking and are located above the same latera
l position as the topmost bulk layer. (C) 2001 Elsevier Science B.V. All ri
ghts reserved.