Editorial: Engineered Nanoporous Materials for Chemical Sensors and Biosensors

Abstract not availableAbel Santos, Lluis F. Marsal and Tushar Kumeri

Generation of Tamm Plasmon Resonances for Light Confinement Applications in Narrowband Gradient-Index Filters Based on Nanoporous Anodic Alumina

Gold-coated gradient-index filters based on nanoporous anodic alumina (Au-coated NAA−GIFs) were used as model platforms to elucidate how Tamm plasmons can be tailored by engineering the geometric features of the plasmonic and photonic components of these hybrid structures. NAA−GIFs with well-resolved, intense photonic stopbands at two positions of the visible spectrum were fabricated through sinusoidal pulse anodization. These model photonic crystals were used to assess how the quality of Tamm plasmon resonances can be enhanced by tuning the features of the dielectric mirror and the thickness of the porous gold coating layer. It is found that the highest value of the quality factor of Tamm resonance (QTamm = 237) is obtained for 11 nm of gold on a dielectric mirror with low porosity corresponding to the resonant spectral position of λTamm of ∼698 nm. Our analysis indicates that Tamm resonances in asproduced Au-coated NAA−GIFs are weak due to the constrained range of wavelengths (narrow bands) at which these photonic crystal structures reflect light. However, after broadening of their photonic stopband upon pore widening, Tamm resonances become better resolved, with higher intensity. It is also observed that the quality of light confinement worsens progressively with the thickness of the porous gold coating layer after a critical value. In contrast to conventional surface plasmon resonance systems, this hybrid Tamm porous system does not require complex coupling systems and provides a nanoporous structure that can be readily tailored for a range of photonic technologies such as sensing and lasing.Alejandro Rojas Gómez, Laura K. Acosta, Josep Ferré-Borrull, Abel Santos, and Lluis F. Marsa

Stacked nanoporous anodic alumina gradient-index filters with tunable multispectral photonic stopbands as sensing platforms

This study presents the development and optical engineering of stacked nanoporous anodic alumina gradient-index (NAA-GIFs) filters with tunable multispectral photonic stopbands for sensing applications. The structure of these photonic crystals (PC) is formed by stacked layers of NAA produced with sinusoidally modified effective medium. The progressive modification of the sinusoidal period during the anodization process enables the generation and precise tuning of the characteristic photonic stopbands (PSB) (i.e., one per sinusoidal period in the anodization profile) of these PC structures. Four types of NAA-GIFs featuring three distinctive PSBs positioned within the visible spectral region are developed. The sensitivity of the effective medium of these NAA-GIFs is systematically assessed by measuring spectral shifts in the characteristic PSBs upon infiltration of their nanoporous structure with analytical solutions of d-glucose with several concentrations (0.025–1 M). This study provides new insights into the intrinsic relationship between the nanoporous architecture of these PCs and their optical properties, generating opportunities to fabricate advanced optical sensing systems for high-throughput and multiplexed detection of analytes in a single sensing platform.Laura K. Acosta, Francesc Bertó-Roselló, Elisabet Xifre-Perez, Abel Santos, Josep Ferré-Borrull, and Lluis F. Marsa

Microcrystalline silicon thin film transistors obtained by Hot-Wire CVD

Polysilicon thin film transistors (TFT) are of great interest in the field of large area microelectronics, especially because of their application as active elements in flat panel displays. Different deposition techniques are in tough competition with the objective to obtain device-quality polysilicon thin films at low temperature. In this paper we present the preliminary results obtained with the fabrication of TFT deposited by hot-wire chemical vapor deposition (HWCVD). Some results concerned with the structural characterization of the material and electrical performance of the device are presented

Thin Film Transistors obtained by Hot-Wire CVD

Hydrogenated microcrystalline silicon films obtained at low temperature (150-280°C) by hot wire chemical vapour deposition at two different process pressures were measured by Raman spectroscopy, X-ray diffraction (XRD) spectroscopy and photothermal deflection spectroscopy (PDS). A crystalline fraction >90% with a subgap optical absortion 10 cm -1 at 0.8 eV were obtained in films deposited at growth rates >0.8 nm/s. These films were incorporated in n-channel thin film transistors and their electrical properties were measured. The saturation mobility was 0.72 ± 0.05 cm 2/ V s and the threshold voltage around 0.2 eV. The dependence of their conductance activation energies on gate voltages were related to the properties of the material

Surface ablation of RbTiOPO4 by femtosecond laser

We report here the results obtained in surface ablation of RbTiOPO4 single crystals by femtosecond laser. We fabricated and characterized one-dimensional (1D) diffraction gratings with different lattice spacings of 15 and 20 μm, and with a sub-modulation of the period introduced in the later. The optical and electronic microscopy characterization and filling factor analysis of these diffraction gratings are reported. We also show that the roughness generated on the grooves by the ablation process can be improved by chemical etching.This work was partially funded by the European Commission under the Seventh Framework Program under Project Cleanspace FP7-SPACE-2010-1-GA-263044, supported by the Spanish Government under Projects PI09/90527, TEC2009-09551, AECID A/024560/09, FIS2009-09522, HOPE CSD2007-00007 and SAUUL CSD2007-00013 (Consolider-Ingenio 2010), by Catalan Government under Projects 2009SGR235 and 2009SGR549, by Junta de Castilla y León under Project GR27, and by the Research Center on Engineering of Materials and Systems (EMaS) of the URV. J.J.C. is supported by the Education and Science Ministry of Spain and European Social Fund under the Ramón y Cajal program, RYC2006-858. We also acknowledge support from the Centro de Laseres Pulsados, CLPU, Salamanca, Spain

Photoluminescence and cathodoluminescence of Eu:La2O3 nanoparticles synthesized by several methods

Abstract : Europium-doped La2O3 nanocrystalline powders with sizes ranging from 4 nm to 300 nm have been obtained by the modified Pechini, hydrothermal with conventional furnace, hydrothermal with microwave furnace, and precipitation with ultrasonic bath methods. X-ray diffraction techniques were used to study the evolution of the prepared gels towards the desired crystalline phase. We determined the size and the morphology of the nanoparticles by electronic microscopy. Finally, we studied and analyzed the luminescence properties of the trivalent europium in the hexagonal La2O3 nanocrystals by photoluminescence and cathodoluminescence

Light absorption modeling of ordered bulk heterojunction organic solar cells

10.1016/j.cap.2013.07.016Ordered bulk heterojunction organic solar cells are devices that combine the advantages of the planar bilayer and the bulk heterojunction architectures. They offer uninterrupted pathways to electrodes for effective charge collection and an extended Donor-Acceptor interface for efficient exciton dissociation. Additionally, this interface can also be a potential approach to increase photon absorption by light trapping. Light absorption and charge carrier generation of organic nanostructures are studied by means of ?nite-element modeling for a wide range of structuring widths, periods and heights for poly(3-hexylthiophene):1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (P3HT:PCBM) structures. Results show an increase in light absorption at certain wavelengths in the P3HT region with respect to an equivalent planar bilayer model. This increase can be attributed to two phenomena: for the smallest periods the structures behaves like an effective medium, while for periods of the order of magnitude of the incident light wavelength there is light trapping. The maximum increase in absorption was achieved for a 250 nm-width and 500 nm periodicity structure with a height of 40 nm. Exciton diffusion has also been studied to evaluate the effective amount of absorbed light contributing to photocurrent. In this case, best results correspond to the smallest sizes (1.25-12.5 nm-width) for all the considered heights, achieving an increment in the photocurrent up to more than a factor 6 if compared with that of the reference planar bilayer device. This study can be used to optimize our devices, which are achieved via nanoporous anodic alumina templates

Two-dimensional finite-element modeling of periodical interdigitated full organic solar cells

10.1063/1.4788819By means of ?nite-element numerical modeling, we analyze the in?uence of the nanostructured dissociation interface geometry on the behavior of interdigitated heterojunction full organic solar cells. A systematic analysis of light absorption, exciton diffusion, and carrier transport, all in the same numerical framework, is carried out to obtain their dependence on the interface geometrical parameters: pillar diameter and height, and nanostructure period. Cells are constituted of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61. Results show that light absorption is maximum for pillar heights of 80 nm and 230 nm. However, due to the short exciton diffusion length of organic materials, the analysis of the exciton diffusion process reveals that the 80 nm thickness gives rise to a higher photocurrent, except for the smaller pillar diameters. In terms of ef?ciency, it has been observed that the charge carrier transport is weakly dependent on the geometric parameters of the nanostructured interface if compared with the exciton diffusion process. The optimal cell is a device with a pillar height of 80 nm, a structure period of 25 nm, and a ratio of the nanopillar diameter to the period of 0.75, with an ef?ciency 3.6 times higher than the best planar bilayer reference device. This structure is such that it reaches a compromise between having a high proportion of P3HT to increase light absorption but preserving a small pillar diameter and interpillar distance to ensure an extended exciton dissociation interface