GROWTH AND THE STRUCTURE OF EPITAXIAL VO2 AT THE TIO2(110) SURFACE

Epitaxial VO2 layers have been grown on the TiO2(110) rutile surface u p to thicknesses of 5 ML. These ultrathin films have been characterize d by means of x-ray photoelectron spectroscopy (XPS), x-ray photoelect ron diffraction (XPD), low-energy electron diffraction (LEED), and ult raviolet photoelectron spectroscopy (UPS) measurements. LEED and XPD s tructural data demonstrate that the layer is both short- and long-rang e ordered, and that it has a rutile structure. The success in preparat ion of a single-crystalline epitaxial VO2 layer opens possibilities fo r studying the properties and the surface chemistry of this interestin g oxide, so far complicated by the difficulties in growing macroscopic crystals. From the He I spectra it turns out that the shape, position , and width of the 3d band closely resemble the UPS data of the bulk m onoclinic semiconductive phase. The reported results could add new clu es to a better understanding of the metal-to-semiconductor phase-trans ition phenomenon in VO2.