Berlin 2008 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 12: Thin Film Characterisation: Structure Analyse and Composition (XRD, TEM, XPS, SIMS, RBS, ...)
DS 12.5: Vortrag
Dienstag, 26. Februar 2008, 12:45–13:00, H 2013
Growth of ultrathin Ni-Al alloyed layers on Ni(111): evidence for NiAl formation over a critical thickness of Ni3Al — •Séverine Le Moal1, Didier Schmaus2, and Camille Cohen2 — 1Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstr. 12, 53115 Bonn, Germany — 2Institut des NanoSciences de Paris, 140 rue de Lourmel, 75015 Paris, France
Ni-Al alloys are of great technological interest because of their mechanical and thermal properties (high hardness, high melting point). They also are resistant to corrosion, this latter property being due to the formation at their surface of a passive film of aluminium oxide that acts as a diffusion barrier. Ultrathin epitaxial oxides are also used as convenient supports for model catalysts. We have studied in detail the alloying process of thin Al layers deposited on Ni(111), under ultrahigh vacuum conditions, as a function of the deposited Al amount, the deposition and annealing temperatures and the annealing time. The use of many complementary techniques, either in situ in the UHV chamber connected to a Van de Graaff accelerator (Rutherford Backscattering Spectrometry, Ion Channelling, Nuclear Resonance Profiling,Low Energy Electron Diffraction, Auger Electron Spectroscopy), or ex situ (X-Ray Diffraction, Atomic Force Microscopy) enabled us to have detailed information on the morphology, the composition and the crystallographic structure of both the surface and the bulk of the alloyed layer. A transition in the alloying process has been evidenced: the formation of Ni3Al (fcc-L12) for Al deposits thinner than 5 ML is followed by the formation of NiAl (cc-B2) over this critical thickness.