Preparation of an Ultrahigh Aspect Ratio Anodic Aluminum Oxide Template for the Fabrication of Ni Nanowire Arrays

Abstract

This work reports a two-step constant-current anodization approach for the fabrication of an anodic aluminum oxide (AAO) template having an aspect ratio>1000. The effects of oxidation current densities and oxidation time on the morphologies, pore size, and thickness of AAO templates were studied. The results indicated that the morphology and thickness were significantly affected by both the oxidation time and the oxidation current density. High-quality AAO templates with 150-200 nm pore sizes, 200 μm thicknesses, and 1000-1300 aspect ratios could be prepared under a constant-current density of 8 mA∙cm-2 and an oxidation time of 18 h. Using the AAO template, Ni nanowire arrays were fabricated by electrochemical deposition and were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) techniques. The Ni nanowire arrays were parallel to each other, with diameters of 150 nm, lengths of 180-200 μm, and aspect ratios of 1200-1300. These parameters compared favorably [Article] doi: 10.3866/PKU.WHXB201203026 www.whxb.pku.edu.cn 物理化学学报(Wuli Huaxue Xuebao) Acta Phys. -Chim. Sin. 2012, 28 (6), 1545-1550 June Received: December 16, 2011; Revised: February 24, 2012; Published on Web: March 2, 2012. ∗Corresponding author. Email: wuping@njnu.edu.cn; Tel: +86-25-85891780. The project was supported by the National Natural Science Foundation of China (20905036, 21175067), Research Fund for the Doctoral Program of Higher Education of China (20103207110004), Natural Science Foundation of Jiangsu Province, China (BK2011779), Foundation of the Jiangsu Education Committee, China (09KJA150001, 09KJB150006, 10KJB150009), Program for Outstanding Innovation Research Team of Universities in Jiangsu Province, China, and Priority Academic Program Development of Jiangsu Higher Education Institutions, China. 国家自然科学基金(20905036, 21175067),高等学校博士学科点专项科研基金(20103207110004),江苏省自然科学基金(BK2011779),江苏省高 校自然科学研究项目(09KJA150001, 09KJB150006, 10KJB150009),江苏高校优秀科研创新团队和江苏省高校优势学科建设工程项目资助 C Editorial office of Acta Physico-Chimica Sinica 1545 Acta Phys. -Chim. Sin. 2012 Vol.28 with those of the AAO template, thus indicating that it can be used for preparation of one-dimensional nanowire arrays with an ultrahigh aspect ratio. The effects of the aspect ratios on the magnetic characteristics of the Ni nanowire arrays were examined by comparing their coercivities and remanence ratios in parallel and perpendicular directions, respectively. The results indicated that Ni nanowire arrays with an aspect ratio>1000 clearly displayed a magnetic anisotropy, while the arrays with an aspect ratio of 200 did not. Thus an AAO template with an ultrahigh aspect ratio can be fabricated using a two-step constant-current anodization method, and that the AAO template may find applications in the fabrication of one-dimensional, high-aspect ratio nanowire arrays with special optical and magnetic properties.