AVS 47th International Symposium
    Surface Science Monday Sessions
       Session SS2+EL-MoA

Paper SS2+EL-MoA4
Thickness Dependence of the Unoccupied Electronic States in the Pd/Ru(0001) System

Monday, October 2, 2000, 3:00 pm, Room 209

Session: Electronic Structure and Excitations
Presenter: W.-K. Siu, Rutgers University
Authors: W.-K. Siu, Rutgers University
T. Mensing, Rutgers University
R.A. Bartynski, Rutgers University
Correspondent: Click to Email
The unoccupied electronic structure of the Pd/Ru(0001) system has been examined using inverse photoemission spectroscopy for Pd thicknesses in the 1 - 15 monolayers range. Previous studies indicate that in the sub-monolayer coverage range, the desorption temperature of CO on Pd/Ru(0001) is less than that of CO/Pd(111) or CO/Ru(0001). Similarly, we have previously shown that the desorption temperature for CO from the Cu/fccCo/Cu(100) metallic quantum well (MQW) system is a non-monotonic function of film thickness and is correlated with MQW states crossing the Fermi level. This suggests that quantum size effects can influence the strength of the chemisorption bond. As Pd interacts more strongly with CO, our objective is to investigate the occurrence of MQW states in the Pd/Ru(0001) system and determine their influence in CO chemisorption. Metallic quantum well (MQW) states are observed at the @Gamma@ point of the Pd thin film. The energies of these states change as a function of the film thickness. A simple phase accumulation model provides a semiquantitative understanding of this behavior. There is also an unoccupied surface state at @Gamma@, which shifts to higher energy with increasing film thickness, approaching that of the single crystal Pd(111) surface state. We have also determined the energy dispersion with parallel momentum of the unoccupied Pd states along the @Gamma@K and @Gamma@M directions. Finally, the influence of MQW states on the adsorption of CO on the Pd/Ru(0001) system will be discussed.@footnote 1@ @FootnoteText@ @footnote 1@ Supported by NSF-DMR #98-01681 and ACS-PRF #33750-AC6,5.