Growth mechanism for controlled synthesis of metal nanotube and nanowire arrays using anodic aluminum oxide templates

We report the controlled fabrication of Ni nanotube and nanowire arrays by electrodeposition using anodic aluminum oxide (AAO) as a template. Ni nanotube arrays or nanowire arrays were obtained by changing the concentration of the electrolyte and the overpotential of the electrodeposition. The introduction of chelating species is crucial for nanotube formation because they can regulate the effective concentration of the electrolyte. A possible mechanism for the formation of the nanotubes/nanowires is proposed by considering the different contributing factors for the growth rate of the wall (V_w) and that of the bottom (V_b). Ni nanotube arrays can be obtained when V_w>V_b either at a high electrolyte concentrations (C_Ni2+) and at a more negative electrodeposition potential (U_ed) or at a lower C_Ni2+ with a less negative U_ed. Ni nanowire arrays can also be obtained when V_w≈V_b either at a high C_Ni2+ with a less negative U_ed or at a lower C_Ni2+ with a more negative U_ed. This mechanism may be used as a general strategy for the controlled synthesis of nanotube or nanowire arrays containing many kinds of metals such as Cu, Co, and Au etc.