Electrodeposition of AuxAg1-X Alloys from Thiosulfate Solutions

Abstract

Silver (Ag) and gold (Au) are noble metals of particular interest for future plasmonic, and (bio)sensing applications due to their unique coupling with light in the visible range.[1,2] Recent studies suggest that AuxAg1-x alloy nanostructures of different geometry, composition and size can exhibit interesting new optical phenomena.[3,4,5] Therefore developing new environmentally-friendly (cyanide-free) electrodeposition route to fabricate AuxAg1-x alloys is desirable.[6] Thiosulphate-based solutions are less toxic, and this solution was previously studied for pure Au,[7] pure Ag [8] and recently for AuxAg1-x alloys.[6]In this work, we will present a systematic study of electrodeposition of AuxAg1-x alloys from thiosulphate solutions on Au and indium-tin-oxide (ITO) substrates. Thin-film alloys (20 nm-100 nm thickness on Au on ITO) of different compositions were electrodeposited by variation of Ag+: Au+ ion concentrations in the solution. The structure of the deposited alloys was explored as a function of the electrodeposition potential and film thicknesses by Atomic Force Microscopy (AFM), and Scanning Electron Microscopy (SEM). Chemical composition of the electrodeposited alloys was determined using X-Ray Photoemission Spectroscopy (XPS).The electrodeposition on the two substrates showed higher Ag content in the films than expected from the solution composition ratios. Comparison of the linear sweep voltammetry for deposition of alloys on Au and ITO show that the potential at which alloys start depositing for ITO is more negative than on Au. Stoichiometry of films varied between Au20Ag80 to Au50Ag50. Diffusion-limited deposition of alloys at lower overpotentials produced smooth, homogenous films on Au substrates; at potentials higher than 1 V vs MSE, hydrogen-evolution reaction assisted non-uniform growth and formation of instabilities at the surface in both substrates. The electrodeposited alloys were characterised by surface composition and structure sensitive UPD processes such as Pb UPD and Cu UPD. The results showed a correlation between the UPD peaks potential shifts and the UPD charge with alloy compositions.