Image states on Pd(111) with various coverages of Ag were investigated
by two-photon photoemission spectroscopy for temperatures between 90
and 1300 K. The formation of three-dimensional islands, smooth layers,
and surface alloys is identified. The transition from one-dimensional
localization in front of the surface to, three-dimensional localizati
on on top of Ag islands with diameters between 10 and 100 Angstrom is
observed. The high-resolution spectroscopy of image states provides a
new tool to study the growth mode, morphology, and island size distrib
ution of ultrathin metal films.