Characterization of anodic porous alumina by AFM

The topography of supported and unsupported anodic aluminum oxide (AAO) films was measured by AFM under different testing modes. The supported film, attached onto an aluminum substrate, is mechanically stable and the contact mode shows good resolution for imaging the intrinsic features of the surface. Additionally, the non-contact mode can detect the presence of adsorbed species on the surface, which are not detected by the contact mode. On the contrary, for the unsupported alumina film, the non-contact mode shows better resolution, even for surface pore detection. These results are discussed in view of the different mechanical properties of both types of alumina films, and the magnitude of the sample-tip interaction for each operation mode. In relation with the pore arrangement, a single-step anodization process results in a dense but non-regular pore pattern. Regular pore arrays was obtained with a two-step anodization method using both oxalic and sulfuric acid as oxidation agents. AFM characterization allows the evaluation of the order of the pore array, the pore density and the external shape of AAO films obtained under different experimental approaches. A reliable determination of the internal diameter and shape of the pores is not well accomplished under the present experimental conditions. (C) 2001 Elsevier Science B.V. All rights reserved.