Observation of ultrathin metastable fcc Ti films on Al(110) surfaces.

Abstract

High-energy ion-scattering spectroscopy, x-ray-photoemission spectroscopy, and low-energy electron diffraction (LEED) were used to study the growth of very thin Ti films on Al(110) surfaces at room temperature. The Al surface peak areas in the backscattering spectra of 0.96-MeV ${\mathrm{He}}^{+}$ ions, incident along the [1\ifmmode\bar\else\textasciimacron\fi{} 1\ifmmode\bar\else\textasciimacron\fi{}0] direction of Al(110), decreased sharply during the deposition of the first five monolayers of Ti. This suggests a growth model in which a pseudomorphic Ti film with a fcc structure forms, shadowing the Al surface atoms. This model is supported by LEED measurements where sharp diffraction spots persisted with the rectangular symmetry of the substrate lattice structure. Throughout this coverage regime, the attenuation of the Al photopeak intensities as a function of Ti coverage agrees with the attenuation rate calculated using a laminar growth mode. With additional Ti deposition the Al surface peak intensities increase while the Al photopeak intensities remain unchanged. A discussion of possible growth models for the high-coverage regime is presented.