Growth of nanosize Ag dots with uniform height on a Si(111)-7x7-C2H5OH surface, and their electronic properties

C2H5OH adsorbs by dissociating on Si-adatom/Si-rest atom pair sites on Si(111)-7x7 surfaces. A half of six Si adatoms and three Si rest atoms are changed to Si-OC2H5 and Si-H in every half unit cell at the saturation. When an Ag atom was deposited on this surface, it was stabilized on an intact Si adatom remained in the half unit cell and it did not migrate by hopping. With the increasing number of deposited atoms, uniform height with ca. 5-nm size Ag dots were grown in wide area. A similar growth mode was observed by depositing Ga and Zn on this surface. We deduced that the uniform height growth of 5-nm dots may be given by a layer-by-layer growth of dots in the natural templates composed of six half unit cells. Scanning tunneling spectroscopy indicated that one-monolayer Ag dots had nonmetallic energy gap of ca. 2.2 V at the Fermi level, but the energy gap became narrower with the increasing number of layers and became metallic at eight or nine layers.