Optical transitions between surface state bands have been detected on
the Si(111)-Pb(root 3 x root 3) mosaic phase by means of surface diffe
rential reflectivity (SDR) in the energy range between 1.3 and 3.8 eV.
The SDR spectrum, obtained between the clean and the hydrogenated sur
face, presents a broad structure in this energy range with a maximum a
t 3.0 eV. The spectrum has been deconvolved into three Gaussian single
ts at energies 1.8, 2.5 and 3.05 eV. These transitions have been, tent
atively, assigned to different points in the surface Brillouin zone. N
o contribution from the hydrogenated surface is expected. as observed
by angle resolved photoemission. (C) 1997 Elsevier Science B.V.