Surface of PdCuAu ternary alloys: a combined LEIS and XPS study

Abstract

PdCuAu ternary alloy sampleswith different compositionwere synthesized on top of ZrO2-modified porous stainless steel disks by the sequential electroless deposition technique. The structure, morphology and bulk composition of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy and energy dispersive X-ray spectroscopy (EDX). Complete alloy formation with a pure fcc phase for the Pd71Cu26Au3, Pd70Cu25Au5 and Pd67Cu24Au9 samples and a bcc structure for the Pd62Cu36Au2 and Pd60Cu37Au3 samples were obtained upon annealing at 500 °C for 120 h as revealed by XRD. A combination of low-energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS) was used to investigate the surface properties of the PdCuAu alloys.<br />XPS results confirmed alloy formation under the annealing conditions. XPS analysis also revealed that the near-surface regions of the alloys became enriched in Pd with respect to the bulk composition determined by EDX. In contrast, LEIS and angle-resolved XPS analyses showed that the top-most surface layers in all samples were copper-rich compared with the bulk composition. This high Cu surface concentration could impart resistance to bulk sulfide formation to the PdCuAu alloy membranes.