Epitaxial VO 2 layers have been grown on the TiO 2 ͑110͒ rutile surface up to thicknesses of 5 ML. These ultrathin films have been characterized by means of x-ray photoelectron spectroscopy ͑XPS͒, x-ray photoelectron diffraction ͑XPD͒, low-energy electron diffraction ͑LEED͒, and ultraviolet photoelectron spectroscopy ͑UPS͒ measurements. LEED and XPD structural data demonstrate that the layer is both short-and long-range ordered, and that it has a rutile structure. The success in preparation of a single-crystalline epitaxial VO 2 layer opens possibilities for studying the properties and the surface chemistry of this interesting 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 monoclinic semiconductive phase. The reported results could add new clues to a better understanding of the metal-to-semiconductor phase-transition phenomenon in VO 2 .

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Angle-scanned photoelectron diffraction measurements have been performed prior to and after CO exposure onto a Ni monolayer deposited on Pt(111). Ni is known to grow epitaxially on Pt(111), but there is evidence for an adsorbate-induced restructuring such that the initial atomically flat Ni layer gives place to at least two-layer-high Ni islands. As far as the driving force for the restructuring is concerned, some hypotheses can be put forward considering the Ni–Ni nearest neighbor distances in the Ni monolayer and in the restructured layer, along with some thermodynamical arguments.