AVS 50th International Symposium
    Surface Science Friday Sessions
       Session SS1-FrM

Paper SS1-FrM9
Different Changes in Work Function of Low- and High-index Cu Surfaces with Lattice Displacement in Surface Acoustic Wave Propagation

Friday, November 7, 2003, 11:00 am, Room 327

Session: Catalysis IV: Reactivity of Complex Systems
Presenter: H. Nishiyama, Nagaoka University of Technology, Japan
Authors: H. Nishiyama, Nagaoka University of Technology, Japan
N. Saito, Nagaoka University of Technology, Japan
Y. Inoue, Nagaoka University of Technology, Japan
Correspondent: Click to Email
Surface acoustic wave (SAW) generated on a poled ferroelectric crystal by applying rf electric power has been demonstrated to markedly enhance the catalytic activity of thin polycrystalline metal (Ag, Pd, Ni, Cu) films for different kinds of the metal-catalyzed reactions such as ethanol decomposition, ethanol and CO oxidation. The enhancement of the catalytic activity and the changes in the selectivity with SAW suggest that the SAW could affect the work function of the catalyst metal surfaces. To confirm the view, in the present study, photoelectron emission spectroscopy (PEEM) was employed, since photoemission characteristics are directly related to the work function of the metal surfaces. Thin Cu metal films treated by either annealing or sputtering have been used, and their atomic scale surface structures were inferred by the characteristic CO stretch frequency obtained in infrared reflection absorption spectroscopy (IRAS). It was shown that annealing gave rise to a Cu(111)-like low index plane mainly, whereas sputtering produced a large density of step sites and high index planes such as (311) and (211). The different SAW effects on the low- and high-index Cu surfaces were observed: the SAW propagation decreased the PEEM intensity for the low-index plane such as Cu(111), whereas it increased the PEEM intensity for the high index planes and step sites. The results indicated that the SAW enhanced the work function of a densely packed Cu surface and reduced that of a less packed Cu surface with coordinatively-unsaturated metal atoms. Dynamic and vertical lattice displacement by SAW was proved to have prominent structure-sensitive effects enough to change the electronic structures of the metal surface.