PdxCu1-x alloys are used for hydrogen purification membranes. Segregation to the surface is likely to affect their properties. Surface segregation has been studied in a Pd70Cu30 alloy using both x-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS). The results show that the topmost atomic layer is rich in Cu. On the other hand, the near-surface region consisting of the immediate subsurface layers is rich in Pd. Furthermore, the adsorption of sulfur on the surface causes the complete elimination of Cu from the topmost layer.
A high throughput method for study of surface segregation has been developed that is based on the deposition of thin Composition Spread Alloy Films (CASFs) that contain all possible bulk compositions of the PdxCu1-x alloy. Spatially resolved surface analysis of the surface of the PdxCu1-x CASF has been achieved using XPS. The results show that the near-surface region of the alloy is Pd rich over a wide range of bulk Pd concentrations.