Local density of unoccupied states in ion-beam-mixed Pd-Ag alloys.

Abstract

X-ray absorption spectroscopy (XAS) measurements have been used to probe the electronic structure of ion-beam-mixed (IBM) Pd-Ag thin films with bulk alloys being studied for comparison. Pd ${\mathit{L}}_{3}$ and Ag ${\mathit{L}}_{3}$ absorption edges for pure Pd, Ag, and ${\mathrm{Pd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ag}}_{\mathit{x}}$ alloys are discussed. Structural information from both x-ray diffraction and the XAS fine structure oscillations are discussed. The observed decrease of the white-line feature strength, at the Pd ${\mathit{L}}_{3}$ edge, indicates that the local density of unoccupied Pd 4d states declines upon alloying with Ag in a manner similar to that observed in previous bulk studies. However, while the Pd d-hole count decreases monotonically for bulk alloys, in the IBM alloys it saturates at higher levels in the Ag-rich materials. This disparity is interpreted on the basis of a modified charge transfer due to structural differences in the IBM alloys. The Ag ${\mathit{L}}_{3}$ near-edge region is largely unchanged in these alloys, indicating that the charge transferred away from the Ag site is dominantly of non-d type. Our experimental results are discussed in the context of recent electronic structure calculations and of previous work on this alloy system. \textcopyright{} 1996 The American Physical Society.