Electrodeposition of Ag/Co and Au/Co compositionally modulated thin films and nanowire arrays

Sammanfattning: In the past decade, electrochemical synthesis of metallic nanowires within the pores of porous membranes have attracted considerable attention because of their special optical, electronic, and magnetic properties as well as potential for nanotechnological applications. The concept of using membranes as a template for fabrication of metallic nanowires by electrodeposition is considered as an alternative solution to overcome the difficulty of fabricating fibrils with very small diameters by lithographic methods. In this thesis, electrodeposition processes based on a single electrolyte were developed in order to produce compositionally modulated Ag/Co and Au/Co systems for one-dimensional nanowires and 2-dimensional thin films. The methods developed are based on pulse-plating in which two metals are deposited from a single solution bath using either potentiostatic or galvanostatic control and a pulsed deposition technique. Here, the nobler element is kept at much lower concentration than the less noble element so that the rate of reduction of the nobler element becomes diffusion limited. The chemical response of multilayered nanowire is evaluated by cyclic voltammetry and interpreted in comparison with electrochemical behaviour of recessed disk microelectrode. The electrochemical deposition of 8 nm Ag/15 nm Co as well as 4 nm Au/12 nm Co multilayers based on the new technique called nanomaterial membrane-based synthesis have been performed. As a working electrode, ion track etched polycarbonate membranes were employed. The morphology of the deposited films as well as deposited so called "Nanodes" have been investigated by transmission electron microscopy, x-ray diffraction, scanning electron microscopy, atomic force microscopy and energy-dispersive x-ray spectroscopy. Magnetic measurements with the external field parallel and perpendicular to the film plane on Ag/Co and Au/Co multilayered nanowire arrays have been investigated. In case of Co nanowires, difference of saturation fields between the parallel and perpendicular orientation fields corresponds well to the expected demagnetisation field value due to the shape anisotropy in case of an infinite thin Co cylinder. The evidence of magnetic anisotropy was observed on Au/Co multilayered nanowires.