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An asymmetric two‐step anodization process is used to fabricate hierarchical nanoporous anodic alumina templates (HNAATs) with different geometric characteristics. This nanostructure consists of an outer hexagonal lattice of concavities in the interior of which pores grow. The anodization conditions (anodization voltage, and type and concentration of the acid electrolyte) between the first and the second step are considerably varied to obtain different types of templates. Two growth regimes (mild and hard), three types of acid electrolytes (phosphoric, oxalic and sulphuric) and three acid electrolyte concentrations (0.3, 0.2 and 0.1 M) are combined. In addition, the voltage ratio between the second and the first step of the anodization process is ranged from 0.11 to 0.71. By modifying these parameters, it is possible to control the fabrication process and obtain HNAATs with a wide range of morphologies.

The deposition of specific materials into ordered pores arranged in a regular lattice allows the fabrication of ordered fiber arrays. Porous silicon is an attractive candidate for use as a template because the porosity and pore size can be tuned. Polymer microfibers using macroporous silicon with various pore depths as template system is reported here. The method entails vacuum infiltration of a polymer solution into the pores of the template. Two different types of polymer were selected in order to obtain ordered arrays of fibers made from Polymethyl methacrylate or Polydimethylsiloxane. Microtubes were obtained when we used a silicon membrane as a template, whereas microfibers were obtained when we used a silicon template with pores opened only at one end. © 2008 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim

Macroporous silicon membranes, prepared by photo-electrochemical etching, were subjected to pore widening performed by multiple oxidation/oxide-stripping cycles. We study the dependence of pore cross section and diameter on the oxidation parameters. The anisotropy of the oxidation process allows us to correct the faceted pore shape after the etching and to obtain pores with circular cross section. The shown post-treatment of macroporous silicon extends the possibilities of the electrochemical etching process to produce structures with a desired geometry. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper presents a technique for fabricating high-aspect-ratio silicon dioxide pillars by electrochemical etching of n-type silicon in hydrofluoric acid (HF) solutions. Basic process flow and etching conditions are described, which make it possible to obtain high-aspect-ratio pillar arrays with good uniformity. Pillar arrays of different dimensions (i.e. diameter and separation) and of different arrangements can be produced in a single etch step on the same wafer. The large surface area makes these pillar arrays possible candidates for applications in biological sensing. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In their article on pp. 668–674, A. Santos, J. Ferré‐Borrull, J. Pallarès and L. F. Marsal report an asymmetric two‐step anodization process which is used to fabricate hierarchical nanoporous anodic alumina templates. The cover picture illustrates an atomic force microscopy (AFM) 3D image of a nanostructure consisting of an outer hexagonal lattice of concavities in the interior of which nanopores grow. The modification of the different anodization parameters makes it possible to control the fabrication process and obtain hierarchical nanoporous anodic alumina templates with a wide range of morphologies and applications.

The cover picture shows SEM images of the porous silicon membranes with controlled pore geometry which are subject to this issue's Editor's Choice article [1]. The authors demonstrate how the rounded-square shape of pores in a silicon membrane prepared by photo-electrochemical etching can be turned into a circular cross section using multiple oxidation/oxide-stripping cycles.The image on the left is a side view onto a cleaved sample after eleven oxidation steps. The enlarged inset shows pore walls as thin as about 250 nm, including one set of the slightly thicker marks produced by reducing the current in order to obtain feedback on the etching rate. One oxidation step further, the membrane releases individual silicon pillars with a very large aspect ratio, as is illustrated by the top view on the right.The first author holds a post-doctoral position at the Electronics Department of the Technical University of Catalonia, where his research focuses on the fabrication of 2D and 3D photonic crystals based on macroporous silicon.Also featured on the cover is a Review Article by Chivukula et al., surveying the various types of acoustic-wave devices utilizing surface-acoustic, acousto-optic and photo-acoustic effects for applications in biology and medicine [2]. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)