Formation of hemispherical pom-pom-like clusters of nanowires during potentiostatic oxidation of copper in NH₄HCO₃ is reported. High-purity copper was oxidized in a three-electrode setup at constant electrode potential ranging from 200 mV to 1000 mV vs. Ag|AgCl|sat. KCl for 14 h. The obtained clusters of nanwires were examined using FE-SEM, XRD and XPS techniques. The diameter of nanowires, composed mainly of CuO, Cu₂O, Cu(OH)₂, and Cu₄O₃, was ca. 50–70 nm. The diameter of the clusters strongly depends both on the applied potential and the time of electrooxidation, and was found to be in the range of 1–3 μm. The mechanism for the formation of such nanowires clusters is proposed.

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Anodic aluminum oxide was formed by employing mild and hard anodizing in sulfuric acid followed by mild anodizing in oxalic acid without oxide removal in-between at 40 and 45 V. Such multi-step anodizing, combining hard anodizing in sulfuric acid with mild anodizing in oxalic acid allowed to form a highly-ordered nanoporous template with a barrier layer at the pore bottoms thin enough for further processing. Four different conditions of electrochemical barrier layer thinning, with varied voltage steps and their time durations, were investigated. Optimized conditions allowed to provide conductivity at the pore bottoms and made the nanoporous oxide templates suitable for electrodeposition. It was found that the most effective barrier layer thinning approach employs voltage steps Un + 1 = 0.75·Un with each step (n) being 10 s long. To check applicability of the formed templates, copper electrodeposition from sulfate-borate bath was done. Copper nanowires with average length of about 14–16 μm and diameter of about 35–40 nm were obtained by using through-hole AAO templates.@en

Copper foil was anodized in 1 M KOH at potentials ranging from −400 to −100 mV vs. Ag|AgCl electrode. Cyclic voltammetry showed a distinct peak with a maximum at around −150 mV. For anodizing at −100 and −200 mV, nanowires with diameters of ca. 19 and 24 nm respectively were found to be grown. Moreover, photoluminescence and X-ray diffraction show that the dominant phase is the CuO phase. At lower potentials, cuboidal micron sized crystals were formed and Cu₂O was found to be the major phase.

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