The morphology of the Au island films evaporated on solid substrates is usually preserved in ambient conditions for years. However, modulation of surface tension by immersion of the films in reactive solutions or applying electrochemical control drastically increases kinetics of restructuring.
We found that immersion of Au island films evaporated on different substrates (ITO, FTO, mica, polystyrene) into aqueous ammonia-hydrogen peroxide solution (1.4M NH3, 1.4M H2O2) results in fast coalescence and ripening of the islands. “Solvent annealing” produces films with morphology similar to that obtained after high temperature annealing. Kinetics of transformation varies from hours at 4 oC to seconds at 60 oC. Fast surface diffusion of Au adatoms is most probably induced by the interaction with OH radicals generated by catalytic decomposition of H2O2. Island movement on substrate surface is enhanced in the presence of ammonia in the solution; mechanism of this process is currently under study.
In the electrochemical conditions modulation of surface tension of Au island films on ITO and FTO by deposition of Pb monolayer (underpotential deposition, UPD) results in compete change of the film morphology. In unannealed films island movement and coalescence results in the formation of wormlike structures. Large Au islands obtained after “solvent annealing” are also mobile forming dimers and chain structures after a few cycles UPD. Surface mobility of Au islands is pH-dependent, and island movement is substantially suppressed at high pH of the solution.