title: Unveiling the Hard Anodization Regime of Aluminum: Insight into Nanopores Self-Organization and Growth Mechanism.
abstract: Pores growth mechanism and their self-ordering conditions are investigated for nanoporous alumina membranes synthesized by hard anodization (HA) of Al in a broad range of anodic conditions, covering oxalic acid electrolytes with concentrations from 0.300 M down to 0.075 M and potentiostatic anodization voltages between 120 and 225 V. The use of linear sweep voltammetry (LSV) and scanning and transmission electron microscopy, together with image analysis techniques allow one to characterize the intrinsic nature of the HA regime. HA of aluminum is explained on the basis of a phenomenological model taking into account the role of oxalate ions and their limited diffusion through alumina nanochannels from a bulk electrolyte. The depletion of oxalate ions at the bottom of the pores causes an increased growth of the alumina barrier layer at the oxide/electrolyte interface. Furthermore, an innovative method has been developed for the determination of the HA conditions leading to self-ordered pore growth in any given electrolyte, thus allowing one to extend the available range of interpore distances of the highly ordered hexagonal pore arrangement in a wide range of 240-507 nm, while keeping small pore diameters of 50-60 nm.
authors.affiliation: Departamento de Física, Universidad de Oviedo , Calvo Sotelo s/n, 33007-Oviedo, Asturias Spain.|Laboratorio de Membranas Nanoporosas, Universidad de Oviedo , Edif. Severo Ochoa, Campus del Cristo s/n. 33006-Oviedo, Asturias Spain.
authors.forename: Víctor
authors.initials: V
authors.lastname: Vega
authors.affiliation: Institut für Angewandte Physik, Universität Hamburg , Jungiusstraße 11, 20355-Hamburg, Germany.
authors.forename: Javier
authors.initials: J
authors.lastname: García
authors.affiliation: Institut für Angewandte Physik, Universität Hamburg , Jungiusstraße 11, 20355-Hamburg, Germany.
authors.forename: Josep M
authors.initials: JM
authors.lastname: Montero-Moreno
authors.affiliation: Departamento de Física, Universidad de Oviedo , Calvo Sotelo s/n, 33007-Oviedo, Asturias Spain.
authors.forename: Blanca
authors.initials: B
authors.lastname: Hernando
authors.affiliation: Department of Chemistry and Pharmacy, Friedrich-Alexander-University, Erlangen-Nürnberg , Egerlandstraße 1, 91058-Erlangen, Germany.
authors.forename: Julien
authors.initials: J
authors.lastname: Bachmann
authors.affiliation: Departamento de Física, Universidad de Oviedo , Calvo Sotelo s/n, 33007-Oviedo, Asturias Spain.
authors.forename: Víctor M
authors.initials: VM
authors.lastname: Prida
authors.affiliation: Institut für Angewandte Physik, Universität Hamburg , Jungiusstraße 11, 20355-Hamburg, Germany.
authors.forename: Kornelius
authors.initials: K
authors.lastname: Nielsch
keywords: anodic aluminum oxide; diffusion limited reaction; hard anodization; nanoporous alumina; self-organization