Influence of surface morphology on oxide growth in porous alumina
M. Lelonek, O. Kopp, M. Knoll
University of Muenster, DE
Keywords: porous alumina, pore bifurcation, pore termination
Abstract:The growth of nanoporous alumina on concave or convex aluminium surfaces has been investigated. The number of pores during anodic oxidation increases or decreases almost linearly with the thickness of the oxide which is due to bifurcation or termination of single pores during alumina growth. The anodic oxidation has been constantly conducted in oxalic acid at 40 V. Therefore the average interpore distance has not changed during alumina growth. In earlier papers it has been shown that a bifurcation of pores is the result of the change of voltage and the electrolyte. We have demonstrated that a termination or a bifurcation of pores is also possible by structuring the aluminium to a curved surface with concave or convex properties before oxidation. Those results do not depend on the substrate characteristics or on the alumina preparation techniques. Also it has been evaluated that different oxide thicknesses for the same oxidation time with the same reaction parameters and thus different growth rates within the oxides in planar, convex and concave areas are caused by different radii in the curvature. The stronger the curvatures of the surface, the more the growth rates differ from the planar spots. The influence of the electrical field strength on those differences is discussed in a simple model.