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

Abstract

PdCuAu ternary alloy samples with different composition were synthesized on top of ZrO 2 -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 Pd 71 Cu 26 Au 3 , Pd 70 Cu 25 Au 5 and Pd 67 Cu 24 Au 9 samples and a bcc structure for the Pd 62 Cu 36 Au 2 and Pd 60 Cu 37 Au 3 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. 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.

Surface Segregation Across Ternary Alloy Composition Space: CuxAuyPd1–x–y

“…In purple, Beikler 69 and Taglauer 69,70 (purple, ◀) measurements on CuAu. In red, Miller 10 (red, ▼) measurements on CuAuPd. of ternary alloy segregation is far more comprehensive than any prior study of the Cu x Au y Pd 1−x−y system and, to the best of our knowledge, any other ternary alloy.…”

“…In purple, Beikler and Taglauer , (purple, ◀) measurements on CuAu. In red, Miller (red, ▼) measurements on CuAuPd.…”

“…1 2 , 4 4 − 5 4 S e g r e g a t i o n i n PdAu, 1,22,52,55−60 PdCu, 7,25,27,28,61 and CuAu 62,63 binary alloys has been described frequently in the literature, and CuAuPd segregation has also been reported at a few discrete compositions. 10,12 It is known that under vacuum conditions, Au and Cu in Pd alloys are the surface-enriched elements. Their segregation minimizes system energy by reducing the strain energy of the bulk lattice and by covering the surface with low-surface energy alloy components.…”

“…To understand completely the key factors governing segregation, comprehensive study across the alloy composition space is needed; however, such studies are rare and most focus on a single alloy composition. The complicated interactions within a ternary system make it important for studies to span the entire composition space, rather than just using a few discrete compositions. − Although thermodynamic models − and computational methods − for binary alloy segregation have been developed based on numerous experimental studies under vacuum and in the presence of adsorbates, ,,− they cannot be easily extended and validated to describe segregation in ternary alloys because of a lack of experimental data …”

Surface Segregation of Ternary Alloys: Effect of the Interaction between Solute Elements

“…For example, surface segregation of Pd‐Cu‐Ag was investigated by X‐ray photoelectron spectroscopy (XPS) 19,20. Low energy ion scattering spectroscopy (LEISS) was adopted to investigate the surface segregation of Pd‐Cu‐Au 21. However, the surface segregation of a ternary alloy in both vacuum and a gas atmosphere has never been systematically investigated and discussed.…”