Electrodeposition of metals and alloys into the anodic aluminum oxide (AAO) membrane is one of the most promising and widely used methods for obtaining nanowires with a high aspect ratio. In most cases, after growing of nanowires, the AAO membrane is dissolved in NaOH to yield freestanding nanostructures. Those nanostructures have versatile applications (e.g., as catalytic, magnetic, or semiconductors). In literature many authors usually pay attention to investigations of free-standing nanowires, but do not take into account the uniformity of the obtained nanostructures. Meanwhile, the uniform growth of nanowires is an important factor if one considers obtaining of devices based on nanostructures. The Co-W alloys have been chosen for deposition into the AAO membrane due to the complex of their mechanical, magnetic and tribological properties, which have already been proved on flat surfaces by the authors of the present report. Thus, the aim of this study is to investigate electrodeposition of Co-W alloys nanostructures into the AAO membrane and to secure a good control over a uniform filling and alloying elements.figureFig. 1. SEM cross-section images of nanowiries into AAO at cathodic potential of 0.9 V vs Ag/AgCl: a – pH 5, 20°C and b - pH 6.7 60°C. a b Electrodeposition of Co-W nanowires was carried out from the citrate-borate electrolyte at pH 5, 6.7 and 8. Deposition was carried out in the industrial AAO membrane (Whatman) with a thickness of 60 μm (with ~2 μm filter layer) and an average pore diameter of 240 nm, at temperature of 20 60 ˚C. Prior to the electrodeposition the gold sputtering had been carried out in order to form have a conductive substrate. After the electrodepostion of Co-W nanowires, samples were broken and the cross-section was studied using SEM and EDX. Co–W alloys were produced by: a) galvanostatic electrodeposition at cathodic current density: 6 ÷ 12 mA/cm2; b) potentiostatic electrodeposition at cathodic potential range of 0.8 - 1.1 V; c) pulse electrodeposition at pulse duration (ton): 4 ÷ 2000 ms, pulse cathodic current density (ion ) 7.5 ÷ 60 mA/cm2, duty cycle=20 %. It was demonstrated that the tungsten content depends on the electrodeposition conditions (pH, temperature, current density (potential). It was shown that at pH 6.7 a uniform growth of nanowires cannot be achieved because of a high hydrogen evolution, thus further investigations have been focused on lower pH. At pH 5, potentiostatic, galvanostatic and pulse electrodeposition methods were investigated in more detail. The best uniform filling is achieved during pulse depositions at ton = 200 ms and ion=15 mA/cm2, at temperature 20˚C. Nevertheless, the galvanostatic and potentiostatic regimes also give good results in the view of uniform filling (fig. 1).