Electrochemical synthesis of Ag/Co multilayered nanowires in porous polycarbonate membranes

Abstract

The electrodeposition of Ag/Co multilayers into 20 μm thick ion track etched polycarbonate membranes with pore diameter of 120 nm were studied using a single bath containing cobalt sulphate, silver cyanide and potassium pyrophosphate. Cyclic voltammetry and transmission electron microscopy (TEM) was used to determine deposition conditions for pure Ag and 97 wt.% Co layers. The Co rich metallic nanowires were deposited at −1100 mV and the Ag nanowires were deposited at −600 mV vs. Ag/AgCl. By using Faraday's law and linear relation between the charges passed during the time interval for each metal layers and bilayer thickness, a current efficiency of 58% was determined for pulsed deposition of Co. This implies that hydrogen or initial layer re-dissolution of Co during Ag deposition consumes 31% of the charge passed during Co deposition. Multilayered nanowires with 8 and 15 nm thick Ag and Co rich layers, respectively, exhibit well-defined layers in TEM. X-ray diffraction investigations of 20 μm long, Ag, Co and Ag/Co multilayered nanowires show that the Ag deposits exhibited a f.c.c. 〈111〉 texturing while the Co deposit exhibited basal plane diffraction of h.c.p. (002) and f.c.c. (111). Magnetic measurements on Ag/Co multilayered nanowires have been made with the external field parallel and perpendicular to the film plane on two series of multilayers: thickness of Co (50 and 15 nm)/Ag (8 nm). In the case of longer cylinder (t Co=50 nm) the axis along the wire starts to become the easy axis (lower saturation field) as expected in the limit where t Ag=0 (case of single Co nanowires), due to the shape anisotropy.