The surface atomic and electronic structure of ErSi1.7 layers epitaxia
lly grown on Si(111) is studied by angle-resolved ultraviolet photoemi
ssion spectroscopy. The experimental results are compared to electroni
c band-structure calculations for various reasonable surface atomic co
nfigurations. Satisfactory agreement is obtained for two geometries co
nsisting of reconstructed ErSi1.7 (0001) surfaces. Both reconstruction
s involve a buckled Si top layer similar to (111) double layers in bul
k Si but differ in their registries with respect to the bulk silicide
layer underneath, leading to a silicide surface termination with ErSi1
.7 stoichiometry. In contrast, the calculations clearly show that a su
rface termination with ErSi1.7 stoichiometry involving an ordered arra
y of vacancies in the buckled Si top layer would result in a quite dif
ferent surface electronic structure incompatible with the experimental
one. This allows us to rule out this model often invoked in previous
work. Finally, models exposing a bulklike flat Si graphitelike top lay
er, with or without vacancies, can also safely be ruled out on the bas
is of the present data.