GROWTH MODE AND ELECTRONIC STRUCTURE OF SILVER ON ${\rm ZnO}(10\overline{1}0)$

The growth mode and electronic structure of the vapor-deposited Ag overlayer on the ${\rm ZnO}(10\overline{1}0)$ surface is investigated by angle-resolved photoemission spectroscopy utilizing synchrotron radiation. The coverage dependent measurements of the two-dimensional band structure by the Ag 4d states reveal that the bands with a dispersing feature are developed from the low coverage region, suggesting that the Ag adatoms aggregate to form clusters with a laterally ordered structure. The Ag clusters grow in size with increasing the Ag coverage whereas the ordered atomic structure of the Ag cluster is preserved. From the analysis of the Ag 5sp band, the Ag clusters have a nonmetallic electronic structure at low coverages, and the metallic nature is developed as the size of the clusters becomes enlarged.