Processing of nanoporous Ag layers by potential-controlled displacement (PCD) of Cu

A cementation-like process taking place under potential control and introduced in this work as a "potential-controlled displacement" (PCD) is developed as a new method for processing of nanoporous Ag structures with controlled roughness (porosity) length scales. Most of the development work is done in a deoxygenated electrolyte containing 1 x 10(-3) M AgClO(4 )+ 5 x 10(-2) M CuSO(4) + 1 x 10(-1) M HClO(4) using a copper rotating disk electrode at 50 rpm. At this electrolyte concentration, the Ag deposition is under diffusion limitations whereas the Cu dissolution displays a typical Butler-Volmer anodic behavior. Thus, a careful choice of the operational current density enables strict control of the ratio between the dissolving and depositing metals as ascertained independently by atomic absorption spectrometry (AAS). The roughness length scale of the resulting surfaces is controlled by a careful selection of the current density applied. The highest surface area and finest morphology is obtained when the atomic ratio of Ag deposition and Cu dissolution becomes 1:1. Preseeding of uniform Ag clusters on the Cu surface made by pulse plating of Ag along with complementary plating and stripping of Pb monolayer is found to yield finer length scale resulting in up to a 67% higher surface area. An electrochemical technique using as a reference value the charge of an underpotentially deposited Pb layer on a flat Ag surface is used for measuring the real surface area. Scanning electron microscopy (SEM) studies are conducted to examine and characterize the deposit morphology of Ag grown by PCD on Cu substrates.