Pd on Cu(1 1 1) studied by photoelectron diffraction

The PdCu alloy system, which has important catalytic properties, has been the subject of many experimental and theoretical studies using a large number of different techniques. Theoretical and experimental structural studies converge in predicting ordered alloys for the Pd/Cu(1 1 0) and Pd/Cu(1 0 0) surfaces. No such agreement exists for the Pd/Cu(1 1 1) surface, however; indeed, few structural studies have been performed for this surface. Here, we report the first application of X-ray photoelectron diffraction (XPD) (using synchrotron radiation) in combination with LEED to determine the structure of ultra-thin epitaxial Pd films (∼1 ML) evaporated on Cu(1 1 1) single crystal surfaces. The analysis of the data was performed with the multiple scattering diffraction program of Chen and Van Hove. For the preparation condition used, a random surface alloy seems to form in the first three layers. The first interlayer distance expands whereas the second seems to contract.