Highly ordered and nanometer-scaled nickel wire arrays were successfully prepared by supercritical electrodeposition method using anodized aluminum oxide (AAO) template. The results show that the well-ordered and free-standing nickel nanowire arrays can be constructed uniformly on a titanium-coated silicon wafer after removing the AAO template. The diameter and length of the nickel nanowire in the arrays can be obtained, about 100？nm and 10？um, respectively. Based on Box-Behnken design and Response Surface Methodology (RSM), a regression model was built by fitting the experimental results with a polynomial equation. The current density, pressure, and temperature are critical important factors of the growth mechanism of deposited nanowires. The optimal length of nanowires, 10.03？μm, can be achieved at the following conditions: current density 0.23？A/cm2, pressure 107？bar, and temperature 53°C. 1. Introduction One of the most important challenges in materials science and technology today is the preparation of ordered nanostructure arrays with controlled properties and dimensions for industrial application [1]. It is of great interest in the trend toward miniaturization and densification of electronic parts and components which tend to become smaller in size with a larger number of individual devices [2]. Thus, porous alumina films and nanocomposites based on AAO membranes could be used as perfect model objects for a deeper understanding of processes on nanoscaled in spatially ordered systems [3]. Several reports have been published on nanowire arrays-filled porous AAO films, for materials including single-metal nanowires [4], ferromagnetic alloy nanowires [5], and multilayered nanowires [6]. Electrodeposition of metal or alloy in AAO pores needs to stabilize an electric current distribution during operation owing to the high aspect ratio of AAO pores [7]. A common problem exists during electroplating, which is the electric current also causing the dissociation of water in addition to the electrolysis of metal ions due to the handicap of solution transport in nanometer space. The dissociation of water may create several defects on the growth mechanism of deposited metal alloy [8]. Due to the low viscosity, high diffusivity, and zero surface tension nature of supercritical carbon dioxide (Sc-CO2), plating technology with Sc-CO2 has attracted special attention because Sc-CO2, in particular, can transport the solute into fine nanometer space of the materials without shrinking or causing other harm due to the interface tension that exists between liquids and
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