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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)

The charge transfer state (CTS) band of the Eu3+:La2O3nanocrystals were studied in detail in order to understand the shift of the maximum of this band. Eu3+:La2O3nanoparticles present a broad CTS band. However, the maximum is peaking below 300 nm, far below the limit of the solar spectrum arriving to the surface of the Earth and it makes difficult the application of this material as down-shifting in solar cells. In order to shift the CTS band towards blue wavelengths, different synthesis methods such as hydrothermal and sol-gel modified Pechini methods were used to prepare these nanoparticles, and adding additional CTS bands with co-doping ions such as Bi3+was explored as well. The crystalline structure of Eu3+:La(OH)3, Eu3+:La2O3, Bi3+:Eu3+:La(OH)3and Bi3+:Eu3+:La2O3and the cell parameters of Eu3+:La2O3and Bi3+:Eu3+:La2O3were analyzed by X-ray powder diffraction technique and their morphology was observed by transmission electron microscopy. Once we obtained the cell parameters refining the XRD patterns by Full-prof software, we were able to calculate the Eu3+-O distance by ATOMS software through the structure previously represented following the Pauling model. The results found suggest that we need to take into account another parameter apart from the Eu3+-O distance to explain the CTS band small shift.

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)

The characteristics of Au/ P3HT (poly [3-hexylthiophene])/n-type crystalline silicon (n-c-Si)/Al heterojuntion diodes for solar cells applications are presented. A P3HT layer, 80 nm thick was spincoated on silicon substrate followed by thermal annealing and metal deposition. The capacitance-voltage measurements showed that the junction is abrupt. The mechanisms of conduction over temperature range from 300K to 360K is ohmic for voltages below 0.1 V and multi-step tunneling for medium voltage values from 0.1 V to 0.6V. Afterwards, the current-voltage characteristic is affected by a relatively high series resistance. The solar cell characteristics reported Voc=0.3 V and Isc=1.5 mA/cm2. The conversion efficiency of the structure was 0.65 %, which can ideally reach 3.25 % depending on the absorption in the top conductive layer.