High-Throughput Characterization of Surface Segregation in CuxPd1–x Alloys

Abstract

A high throughput methodology for the study of surface segregation in alloys has been developed and applied to the Cu x Pd 1―x system. A novel offset-filament deposition tool was used to prepare Cu x Pd 1―x composition spread alloy films (CSAFs), high throughput sample libraries with continuous lateral composition variation spanning the range x = 0.05―0.95. Spatially resolved low energy ion scattering spectroscopy (LEISS) and X-ray photoelectron spectroscopy (XPS) were used to characterize the films' top-surface and near-surface compositions, respectively, as functions of alloy composition, x, and temperature. Electron backscatter diffraction (EBSD) was used to identify the bulk phases in the CSAF as a function of alloy composition, x. Films equilibrated by annealing at temperatures ≥ 700 K displayed preferential segregation of Cu to their top-surfaces at all bulk compositions; segregation patterns did not, however, depend on local structure. The Langmuir―McLean thermodynamic model was applied to segregation measurements made in the temperature range 700―900 K in order to estimate the enthalpy (ΔH seg ) and entropy (ΔS seg ) of segregation as a function of bulk Cu x Pd 1―x composition. Segregation measurements at x = 0.30 on the CSAF compare well with results previously reported for a bulk, polycrystalline Cu 0.30 Pd 0.70 alloy, demonstrating the utility of the CSAF as a high throughput library for study of segregation.