title: Self-ordered anodic aluminum oxide formed by H2SO4 hard anodization.
abstract: The self-ordering of nanoporous anodic aluminum oxide (AAO) in the course of the hard anodization (HA) of aluminum in sulfuric acid (H2SO4) solutions at anodization voltages ranging from 27 to 80 V was investigated. Direct H2SO4-HA yielded AAOs with hexagonal pore arrays having interpore distances D(int) ranging from 72 to 145 nm. However, the AAOs were mechanically unstable and cracks formed along the cell boundaries. Therefore, we modified the anodization procedure previously employed for oxalic acid HA (H2C2O4-HA) to suppress the development of cracks and to fabricate mechanically robust AAO films with D(int) values ranging from 78 to 114 nm. Image analyses based on scanning electron micrographs revealed that at a given anodization voltage the self-ordering of nanopores as well as D(int) depend on the current density (i.e., the electric field strength at the bottoms of the pores). Moreover, periodic oscillations of the pore diameter formed at anodization voltages in the range from 27 to 32 V, which are reminiscent of structures originating from the spontaneous growth of periodic fluctuations, such as topologies resulting from Rayleigh instabilities.
authors.affiliation: Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle, Germany.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Schwirn
authors.forename: Woo
authors.initials: W
authors.lastname: Lee
authors.forename: Reinald
authors.initials: R
authors.lastname: Hillebrand
authors.forename: Martin
authors.initials: M
authors.lastname: Steinhart
authors.forename: Kornelius
authors.initials: K
authors.lastname: Nielsch
authors.forename: Ulrich
authors.initials: U
authors.lastname: Gösele
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D003460:Crystallization / Q000379:methods*; D004566:Electrodes; D004595:Electroplating / Q000379:methods*; D006244:Hardness; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D013464:Sulfuric Acids / Q000737:chemistry*; D013499:Surface Properties; D013718:Tensile Strength
chemical_list: D046911:Macromolecular Substances; D013464:Sulfuric Acids; D000537:Aluminum Oxide; C033158:sulfuric acid