Ni growth inside ordered arrays of alumina nanopores: Enhancing the deposition rate

High aspect ratio Ni nanowires (NWs) were electrodeposited inside ordered arrays of self-assembled pores (∼50 nm in diameter) in anodic alumina templates by a potentiostatic method. A systematic comparative study is here reported on Ni deposition at different applied potentials between −0.5 and −4.0 V (vs. Ag/AgCl). A detailed analysis of the structural, morphological and magnetic properties of the Ni NWs was performed using scanning electron microscopy, X-ray diffraction and vibrating sample magnetometer. Smooth, well-defined and highly-oriented (2 2 0) face-centered cubic Ni NWs were obtained for the whole range of applied potentials (E). The Ni deposition rate (η) was observed to strongly depend on E [η (μm min−1) = 4.5 × |E| − 3.5], reaching ∼12 μm min−1 for E ∼ −3.5 V. However, at high cathodic potentials (E ≤ −2.5 V) we found that H2 gas bubbles are more likely to nucleate inside the nanopores stopping further Ni deposition. Magnetic measurements revealed the high shape anisotropy of the fabricated nanostructures, and allowed us to estimate the native oxide layer thickness (∼1.5 nm) formed around the Ni NWs, inside the alumina template.