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

Abstract

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 400 \ifmmode^\circ\else\textdegree\fi{}C results in the formation of an alloy film with the probable composition TiCu. At 550 \ifmmode^\circ\else\textdegree\fi{}C the amount of Cu in the surface region increases, leading to an alloy film with probable composition near ${\mathrm{TiCu}}_{3}$. 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.