Preparation and Properties of Co-Doped ZnO Nanowires

Spintronics aims at developing a new generation of electronic materials for consumer products based on electron spin rather than on electron charge. Its main objective is the fabrication of new devices based on semiconductor materials with magnetic behavior (so called diluted magnetic semiconductors). These devices combine the manipulation of electrons as classically known in semiconductor devices with an additional degree of freedom namely the manipulation of spins. Doped zinc oxide is considered a major candidate for spintronics due to its ferromagnetic character and Curie-Weiss temperature above ambient [1-3]. Among all kind of nanostructures, nanowires are being used as building blocks in ultra miniaturized electronic and sensing devices [4]. Here, we describe the synthesis of Co doped ZnO nanowires by electrochemical deposition in nanoporous templates. For the electrodeposition of pure ZnO, we employed a 0.1 M Zn(NO3)2 electrolyte. Cobalt nitrate was added for electrodeposition of Co-doped ZnO nanowires. In both cases, addition of PVP (polyvinylpyrrolidone) to the electrolyte increased the template wettability and resulted thus in a larger pore filling efficiency in the case of polycarbonate membranes. Figure 1a displays the polarization curves for the electrodeposition of undoped ZnO (dotted line) and Co-doped ZnO (solid line). The cathodic current for deposition of the Co-doped ZnO nanowire array starts increasing at a lower potential than its undoped ZnO counterpart. The chronoamperometric curves in Fig. 1b also evidence differences between the deposition of pure ZnO and Co-doped ZnO nanowires at U = -800 mV at room temperature. In particular, it can be observed that the current employed for deposition of Co-doped ZnO nanowires is higher than the correspondent current for the growth of undoped ZnO nanowires at all stages of the deposition process. The higher nitrate concentration alone can not explain this increase in current, rather attributed by the authors to a catalytic effect of Co ions for the process of reduction of nitrate ions.