AVS 49th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeP

Paper SS-WeP21
Surface Structural Studies of Epitaxial Ag/Ni/Pt(111) and Ni/Ag/Pt(111) Ultrathin Films

Wednesday, November 6, 2002, 11:00 am, Room Exhibit Hall B2

Session: Surface Science Poster Session
Presenter: C.W. Su, National Taiwan Normal University
Authors: C.W. Su, National Taiwan Normal University
Y.W. Chu, National Taiwan Normal University
H.Y. Ho, National Taiwan Normal University
C.S. Shern, National Taiwan Normal University
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The introduction of Ag films on the epitaxial x ML Ni/Pt(111) metal surface, x=1-5, as the capping layer Ag/Ni/Pt(111) or the buffer sandwich Ni/Ag/Pt(111) was investigated by means of Auger electron spectroscopy (AES) and ultraviolet photoelectron spectroscopy (UPS) in UHV. The evidences from monitoring the initial annealing temperature of the Ag/Ni/Pt(111) corresponded to the signals began to decrease in AES show that 1 ML overlayer of Ag retards the bulk diffusion of the Ni atoms toward the Pt substrate. Compared with our previous study,@footnote 1@ the initial temperatures of the system capped with Ag are higher than those capped without it. As for the behavior of atomic exchange, from Ni/Ag to Ag/Ni, has been observed on the annealed Ni/Ag/Pt(111) surface. Ag atoms migrate to the top at about 400 K and then reach an exchanging equilibrium at a high temperature. The thicker the Ni films, the higher the equilibrium temperature. The variations of electronic valence band by UPS though the annealing processes also attracted ours attention. In additional to the variations of the Fermi edge intensities and of the Ag-Ni hybrid d-band peaks during annealing, an extra peak in UPS appears gradually with the binding energy at about 11 eV on either the spectra of the Ag/Ni/Pt(111) or the Ni/Ag/Pt(111) even the temperature up to 825 K. The heating brought about the changes was contributed to additional chemical adsorption emerged from the surface. The most interesting case was the density of state (DOS) unexpectedly affected by an extra positive or negative bias on the sample. The shift of the UP spectra and the variation of the DOS were also remarkable. Finally, the possible explanations of the phenomena are to be discussed. @FootnoteText@ @footnote 1@C. W. Su, H. Y. Ho, C. S. Shern, and R. H. Chen, Surface Science 499, 103 (2002).