AVS 53rd International Symposium
    Surface Science Thursday Sessions
       Session SS1-ThA

Paper SS1-ThA5
Oxidation of NiAl(111)

Thursday, November 16, 2006, 3:20 pm, Room 2002

Session: Reactivity of Oxide Surfaces II
Presenter: E. Loginova, Rutgers University
Authors: E. Loginova, Rutgers University
F. Cosandey, Rutgers University
T.E. Madey, Rutgers University
Correspondent: Click to Email
Our research is focused on faceting of Al@sub 2@O@sub 3@/NiAl(111) and is motivated by the possibility that alumina thin-film-covered NiAl facets might be used as oxide templates for transition metals in heterogeneous catalysis. We have performed a series of experiments aimed at understanding the adsorption of oxygen and oxygen-induced faceting of NiAl(111) using LEED, AES, SEM, AFM and high-resolution soft XPS (HRSXPS, by means of synchrotron radiation at NSLS). The atomically rough NiAl(111) surface remains planar at room temperature when exposed to oxygen. However, the oxygen-covered surface changes its morphology and becomes faceted upon annealing at 1100K and higher; nucleation and growth of nanoscale {110} facets are observed. The adsorption and reaction of oxygen are characterized by HRSXPS measurements of Al 2p and Ni 3p core levels for the faceted and planar surfaces. Moreover, after prolonged exposure to oxygen at elevated temperatures unusual three dimensional features exhibiting three-fold symmetry erupt from the surface and are oriented along low index <010> directions; their dimensions are several micrometers in length, and 250 to 400nm high. A SEM X-ray EDS mapping study indicates that these are spinel (NiAl@sub 2@O@sub 4@) structures. A proposed qualitative model of spinel formation is as follows: when the oxygen-covered surface is annealed to elevated temperatures, oxygen diffuses below the surface and aluminum oxide nanoclusters may nucleate together with neighboring Ni-rich regions. Upon further annealing, a subsurface nucleation of NiAl@sub 2@O@sub 4@ spinel takes place at the Al@sub 2@O@sub 3@/Ni interface. Lattice strain is relieved by eruption of the spinel structures above the surface.