AVS 51st International Symposium
    Surface Science Wednesday Sessions
       Session SS2-WeA

Paper SS2-WeA2
Adsorption Induced Phase Separation followed in Real Time by High-pressure Scanning Tunneling Microscopy

Wednesday, November 17, 2004, 2:20 pm, Room 210C

Session: Surface Collision Dynamics
Presenter: J. Knudsen, University of Aarhus, Denmark
Authors: J. Knudsen, University of Aarhus, Denmark
R.T. Vang, University of Aarhus, Denmark
E.K. Vestergaard, University of Aarhus, Denmark
F. Besenbacher, University of Aarhus, Denmark
Correspondent: Click to Email
The validity of surface science experiments as an efficient tool in catalysis research is often questioned due to the enormous difference in pressure conditions. For single metal systems the issue is most often concerned with the equivalence between adsorption phases obtained under low pressure and low temperature versus high pressure and high temperature phases. But for the case of more complex model systems such as bimetallic alloys the stability of the model catalyst becomes an additional important factor. We have developed a high-pressure fast-scanning STM which serves as an ideal tool for studies of high pressure induced morphological and structural changes in real time by the acquisition of STM movies. In this way we have been able to describe in great detail a CO induced phase separation of a Au/Ni(111) surface alloy. The STM movies reveal how a removal of nickel atoms from the topmost layer of the alloy surface is nucleated at the step edges of the surface. The gold atoms are left behind on the surface, and small gold clusters are formed in the wake of the moving step edge. Based on these experimental findings we propose a model, in which nickel atoms are removed by the formations of nickel carbonyls; a reaction that is well known from studies of clean nickel surfaces. Finally, we present recent studies of the stability of a Cu/Pt(111) surface alloy under high CO pressures. Exposure of the Cu/Pt(111) surface alloy to CO leads to the formation of clusters on the surface. The atomic details of this adsorbate-induced structural change of the Cu/Pt(111) alloy are currently being investigated.