Influence of magnesium and aluminium ions on the copper a.c. deposition into aluminium anodic oxide film nanotubes

The influence of Mg²⁺ and Al³⁺ ions on a.c. deposition of copper nanowires into aluminium anodic oxide film (AOF) nanotubes has been studied using cyclic voltammetry and d.c. plasma emission spectrometry. From the analysis of copper quantities deposited into the Al AOF nanotubes (m_Cu), 0.02 M MgSO₄ concentration was found to be optimal for Cu(II) solutions. Moreover, it was shown that Mg²⁺ and Al³⁺ ions not only prevent the breakdown of the barrier layer of AOF, but change the rate of copper deposition and modify the shape of the m_Cu against pH plots depending on the a.c. voltage applied. From the analysis of the quantities of magnesium (m_Mg) incorporated into the Al AOF nanotubes, presumably in the form of Mg(OH)₂, the m_Mg against pH dependences were determined in MgSO₄ and MgSO₄ + CuSO₄ solutions. An increase in m_Mg from 30 g dm^–2 to 1 mg dm^–2 at pH 1.5 and from 6 g dm^–2 to 16 g dm^–2 at pH 7.0 was found under the same a.c. treatment conditions from MgSO₄ solutions without and with Cu²⁺ ions, respectively, indicating the incorporation of Mg(OH)₂ into the Al AOF nanotubes to be lower up to about one hundred times in the case of Cu deposition. Based on the experimental results, it was suggested that incorporation of the Mg(OH)₂ particles into the Al AOF nanotubes occurred simultaneously with growing copper nanowires under a.c. bias is insignificant, if the pH of the CuSO₄ + MgSO₄ solution is 2.5.