Nanoscale Structuring in Au–Ni Films Grown by Electrochemical Underpotential Co‐deposition

• Published in: ChemElectroChem Vol. 1; no. 4; pp. 787 - 792
• Main Authors: Liang, Defu, Rajput, Parasmani, Zegenhagen, Jorg, Zangari, Giovanni
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag 15.04.2014; John Wiley & Sons, Inc
• Subjects: alloys; electrodeposition; Formations; Grain boundaries; nanoscale phase separation; Nanostructure; Nickel; Phase separation; Self assembly; Thermodynamics; underpotential; Underpotential deposition
• ISSN: 2196-0216; 2196-0216
• DOI: 10.1002/celc.201300214

Nanoscale phase separation is a simple but powerful method for the self‐assembly of nanostructures, which enables properties to be tuned by tailoring the phase composition, size, and topology of the structures. We demonstrate, contrary to thermodynamic predictions, the spontaneous nanoscale phase separation of Au–Ni alloy films, grown by electrochemical underpotential deposition of Ni onto a surface constantly renewed by the ongoing reduction of Au at overpotential. Strain‐energy relaxation during film growth, in combination with the net attractive interaction between Au and Ni atoms, results in the dynamic formation of a nanoscale alloy structure, consisting of Au‐rich grains of about 5 nm in size surrounded by relatively thick (2–3 nm) Ni‐rich grain boundaries. The estimated cohesive energy of such alloy configurations is stronger than that of the phase‐separated mixture, suggesting the formation of an unexpected local equilibrium configuration for the Au–Ni binary system, stabilized by the grain nanosize and the high density of grain boundaries. Alloy Alloy: Au–Ni alloys are electrochemically deposited at underpotential conditions for Ni, in contrast with bulk alloy thermodynamics. Underpotential deposition is made possible by the attractive interactions between Au and Ni atoms. Phase separation at the nanometer scale results from a balance between attractive Au–Ni interactions and strain energy that originates from atomic volume mismatch.