Strained thin copper films as model catalysts in the materials gap

Thin copper films on silicon constitute model systems to investigate the influence of lattice strain on activity in heterogeneous catalysis. Thin copper films on silicon were investigated by ultraviolet photoelectron spectroscopy (UPS) to reveal the effect of strain in the copper films on the electronic structure of the surface. For cleaned and adsorbate-free surfaces, no effect of strain on the electronic structure was detected by UPS. Conversely, an oxygen-containing film exhibited a distinct effect of strain induced by cyclic heating and cooling on the electronic structure. Comparison with studies on a Cu single crystal under methanol oxidation reaction conditions revealed a characteristic hysteresis behavior in both the adsorbate structure and the catalytic properties of the metal surface. Hence, copper model systems that are suitable to unravel the correlation between strain and catalytic activity need to take the disordered microstructure of ‘‘real’’ copper catalysts into account. The present experiments reveal the correlation between surface restructuring and catalysis on the one side and the influence of lattice strain on either restructuring or the electronic structure of the surface on the other side.