Characterization of anodic porous alumina by AFM

The topography of supported and unsupported anodic aluminum oxide (AAO) fil ms was measured by AFM under different testing modes. The supported film, a ttached onto an aluminum substrate, is mechanically stable and the contact mode shows good resolution for imaging the intrinsic features of the surfac e. Additionally, the non-contact mode can detect the presence of adsorbed s pecies on the surface, which are not detected by the contact mode. On the c ontrary, for the unsupported alumina film, the non-contact mode shows bette r resolution, even for surface pore detection. These results are discussed in view of the different mechanical properties of both types of alumina fil ms, 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 ob tained with a two-step anodization method using both oxalic and sulfuric ac id as oxidation agents. AFM characterization allows the evaluation of the o rder of the pore array, the pore density and the external shape of AAO film s obtained under different experimental approaches. A reliable determinatio n of the internal diameter and shape of the pores is not well accomplished under the present experimental conditions. (C) 2001 Elsevier Science B.V. A ll rights reserved.