Electrochemical deposition of Co nanowire arrays; quantitative consideration of concentration profiles

Electrodeposition of Co into ion track etched polycarbonate membranes by a chronoamperometric method has been studied. The concentration variation and diffusion limiting current during nanoprocessing for growth of Co in nanoelectrode applications are described for two regimes; in the vicinity of the electrode and at the mouth of pores. The behaviour of the as-deposited nanoelectrodes can be modelled as a recessed microelectrode. A diffusion controlled limiting current of the nanodes is studied by the Cottrell equation at short times, i.e. current alphat(-1/2), At longer times, a steady-state current is obtained due to gradually increasing radii, r, of the spherical diffusion zones from each recessed nanode, i.e. current alpha (1/(r + L)), where L is the membrane thickness. The experimental value of diffusion coefficient D for Co ions was found: D = 2.5 x 10(-5) cm(2) s(-1). XRD and TEM measurements on 250 nm diameter and 20 mum long Co nanowires showed a hexagonal closed packed phase with a < 100 > texturing. The nanowires exhibited an enhanced magnetic coercivity in comparison to bulk Co. The difference of saturation fields between the parallel and perpendicular orientation fields corresponds well to the expected demagnetisation field of 2 piM = 8796 Oe value due to the shape anisotropy in case of an infinite thin Co cylinder. (C) 2001 Elsevier Science Ltd. All rights reserved.