Surface-induced phase separation in Pd–Ag alloy: the case opposite to surface alloying

Abstract

Since Pd–Ag alloys constitute a well known prototype binary alloy system, phase separation at the surface was not expected. However, we have shown direct evidence of surface-induced phase separation in Pd–Ag alloys using photoemission spectroscopy. This phenomenon is just the opposite of surface alloying between two miscible elements. The miscibility gap in this alloy near the surface is clearly observed in our core level spectra. The characteristics of this surface-induced phase separation have been probed over various composition ranges using x-ray photoelectron spectroscopy.

Coordination-Resolved Electron Spectrometrics

“…Another example is the catalytic nature of alloys. Ag and Cu often form alloys with Pd because their interactions typically result in improved heterogeneous catalysts ,, that behave quite differently in reactionsreduction or oxidation. , CuPd is more active for the CO and alkene oxidation, CO, NO, benzene, toluene, and 1,3-butadiene hydrogenation, and ethanol decomposition . AgPd is a good candidate for hydrogenation and permeation. , …”

Microscopic, spectroscopic and electrochemical characterization of the surface of Pd–Ag alloys

“…The Ag-Pd phase diagram is characterized by complete miscibility in the liquid and solid states, which means that Pd and Ag form homogeneous solid solutions in the whole concentration range without a miscibility gap [15][16][17]. The lattice constant of the alloy increases almost linearly from 3.884 Å for pure Pd to 4.086 Å for pure Ag [18][19][20].…”

Electronic states of ultrathin Co layers on Cu

“…However, magnetic overlayer systems like Cr/Fe(100) [3] and Fe/Cu(100) [4] have been reported to form a surface alloy or a mixing using scanning tunneling microscope (STM), though they are almost immiscible in bulk phase. Also the surface induced phase separation in bulk miscible system has been reported in AgPd alloy [5]. Stimulated by the several reports on the STM results of the Co/Cu(001) [6] and Co/Cu(111) [7], we have used the photoemission spectroscopy to study the status of the initial stage of the Co growth on Cu surface with two different orientations.…”