The growth of epitaxial VN(111) nanolayer surfaces

Ultrathin films of vanadium nitride (1-20 monolayers = nanolayers) with (I 11) orientation have been grown on a Pt(111) surface by reactive evaporation of vanadium in NH3 atmosphere. The VN(111) surfaces have been investigated by X-ray and UV photoelectron spectroscopy, LEED, work function measurements, and ab initio DFT calculations. Nearly stoichiometric, well-ordered VN0.9 overlayers with their (1 x 1) unit cells rotationally aligned to the high symmetry directions of the Pt substrate have been obtained after annealing the films deposited at 300-500 degrees C in vacuum. The experimental valence band spectra have been compared to the theoretical density of states for differently terminated VN(111) surfaces, i.e. V and N terminated surfaces, bare and with chemisorbed hydrogen. The comparison suggests that the VN(111) nanolayers are terminated by a hexagonal layer of vanadium atoms, possibly covered with some chemisorbed hydrogen (which may originate from the preparation procedure). The VN nanolayer growth on Pt(111) follows a S trans ki-Krastanov layer-plus-island growth mode. (c) 2007 Elsevier B.V. All rights reserved.