The influence of the alumina barrier-layer thickness on the subsequent AC growth of copper nanowires

In order to reveal the role of the alumina barrier-layer thickness, δb, on the copper nanowires electrochemical growth within the alumina pores, the experiments varying porous alumina template parameters and subsequent AC electrolysis conditions were performed. A linear dependence of δb on the final anodizing voltage, Ua,fin, was verified from 40 to 5 V by the electrochemical impedance spectroscopy technique. The further decrease in Ua,fin was not followed by the concomitant decrease in δb presumably due to uneven formation of the native aluminum oxide in a reaction between the aluminum and ambient oxygen. The spectrometric analysis of deposited copper content has shown that the range of AC voltages used for copper nanowires growth within the alumina pores sharply increases with decrease in the Ua,fin and so, in the δb. The most favourable Ua,fin range for the uniform growth of copper nanowires is 15-7.0 V. This is because: (i) the decrease in Ua,fin below 7 V results in the alumina framework peeling off from the Al surface, during subsequent AC electrolysis; (ii) the AC filling of template with δb>20nm (Ua,fin>20 V) leads to the breakdown of alumina.