Surface states in the epitaxial growth of titanium on copper (111)

The growth of Ti on a Cu(111) surface appears from the Auger electron yield to be layer by layer, although there is no evidence of an ordered film until low-energy electron diffraction beams characteristic of the basal plane of Ti appear at about six monolayers. Appearance-potential-spectroscopy studies of the unfilled 3d band of Ti reveal the presence of a band of surface states at the Fermi level even for coverages less than one monolayer. Heating the Ti film to 4000C results in the formation of an alloy film with the probable composition TiCu. At 5500C the amount of Cu in the surface region increases, leading to an alloy film with probable composition near TiCu3. In both alloys the Cu atoms donate electrons to the Ti, with the result that d-band holes appear on the Cu sites. The Ti surface states are extinguished in the alloys, indicating that the nature of the Ti: Cu bond for adsorbed Ti atoms is distinctly different from bonding in the alloys