Growth behavior of nanoporous anodic aluminum oxide and its application

Abstract

Anodic aluminum oxide (AAO) containing high-aspect ratio pore channels is widely used as a template for fabricating nanowires or other one-dimensional nanostructures Conventional anodic aluminum oxide (AAO) templates were performed using two-step direct current anodization (DCA) at low temperature (0-5°C) A higher electrolyte temperature results in dissolution effects therefore damages the pore structure This problem is resolved by means of a hybrid pulse anodization (HPA) technique in which a period of small negative potential is applied to suppress the Joule heating effect during the AAO preparation process In this dissertation improvement of AAO quality in single-step anodization was developed by hybrid pulse technique Moreover the growth of nanoporous AAO in Al films deposited by various sputtering conditions has been further studied In the anodization of bulk Al the single-step HPA and DCA anodization in oxalic acid and the various environment temperature was investigated The pore distribution uniformity and circularity of AAO by HPA is much better than DCA HPA which can sustain higher environment temperature is helpful to increase the growth rate and enlarge the pore size of AAO films On the other hand the growth behavior of porous alumina on a hemisphere curved surface has been examined and discussed by an HPA process on low-purity bulk Al at room temperature In the anodization of Al film the various Al target power and substrate bias were performed to form different surface morphology of the sputtered Al thin films which were further investigated for the AAO synthesis quality The Al films with smaller mean grain size and smoother morphology deposited at relatively low target power with bias were beneficial for more uniform pores size distribution Accordingly the various Al target powers of 50 to 185 W were performed to form different two-dimensional (2D) and three-dimensional (3D) surface morphologies The 3D porous structure which is different from general 2D planar AAO has been successfully demonstrated using HPA on the film with greatly rough hillock-surface formed at the highest power of 185 W In addition the role and effect of residual stress on pore generation of AAO have been investigated into anodizing the various-residual-stresses aluminium films The tensile residual stress lessened the compressive oxide growth stress to reduce AAO plastic deformation leading to smaller pore distance and higher pore density Finally the enhancement of photocatalytic performance and improvement of adhesion of P25 TiO2 by AAO with over-etched 3D nanoporous structure was demonstrated

Date of Award	2014 Aug 9
Original language	English
Supervisor	Chen-Kuei Chung (Supervisor)