Hybrid Nanostructured Porous Silicon-Silver Layers for Wideband Optical Absorption

As subwavelength nanostructures are receiving increasing attention for photonic and plasmonic applications, we grew nanostructured porous silicon (n-PS) and hybrid n-PS/Ag layers onto silicon substrates and measured their reflection and absorption characteristics as functions of the wavelength, angle of incidence, and polarization state of incident light. The experimental results show that the absorption characteristics of the hybrid n-PS/Ag layer can be controlled by selecting the appropriate combination of its thickness and porosity, together with the density of infiltrant silver nanoparticles. The observed wideband optical absorption characteristics of the hybrid n-PS/Ag layers might be useful in light-harvesting devices and photodetectors, since the overall efficiency will be increased as a result of increased field-of-view for both s- and p-polarization states of incident lightR.J.M.-P. thanks Ministerio de Educación, Cultura y Deporte (Spain) for funding under grant reference number PRX17/00095. P.D.M. and A.L. thank the Charles Godfrey Binder Endowment at Penn State for continued support of their research activities. R.R. thanks the Egyptian Ministry of Higher Education, Missions section, for funding under Joint Supervision grant, call 2015–201

Quantum tunneling in low-dimensional semiconductors mediated by virtual photons

Quantum tunneling, a phenomenon that has no counterpart in classical physics, is the quantum-mechanical process by which a microscopic particle can transition through a potential barrier even when the energy of the incident particle is lower than the height of the potential barrier. In this work, a mechanism based on electron/hole annihilation and creation with the participation of virtual photons is proposed as an alternative to explain quantum tunneling processes in semiconductors. Finally, tunneling times are discussed within the proposed frameworkThis work was part of ATTRACT that has received funding from the European Union’s Horizon 2020 Research and Innovation Programm

Assessment of the SBAC atmospheric correction technique applied to Landsat 8-TIRS from ground LST measurements in the Barrax test site

La peculiar estructura y propiedades físico-químicas del silicio poroso nanoestructurado ha estimulado el uso de este material en una amplia variedad de aplicaciones. En el campo de la optoelectrónica, la posibilidad de producir estructuras multicapa en las que cada una de las capas tiene propiedades ópticas particulares, permite la fabricación de filtros ópticos interferenciales con un comportamiento predefinido. En este trabajo se han utilizado estructuras multicapa de silicio poroso para filtrar la luz incidente sobre un sustrato fotosensible de silicio con la intención de modular su respuesta espectral. El comportamiento óptico del filtro de silicio poroso fue simulado antes de su fabricación, y las medidas ópticas demostraron un buen acuerdo entre el comportamiento del filtro obtenido y las predicciones teóricas. Mediciones de fotocorriente han demostrado que los filtros de silicio poroso han reducido el rango espectral de fotosensibilidad del silicio, de los >750 nm originales a unos 150 nm. Filtros con distintos diseños han permitido no sólo estrechar la banda espectral de sensibilidad del detector pancromático de Si, sino también sintonizarla a lo lago de todo el rango visible. El silicio poroso nanoestructurado es compatible con las técnicas convencionales de fabricación microelectrónica, lo que hace posible incorporar estos filtros interferenciales sobre una amplia variedad de sensores y fotodiodos pancromáticos VIS, NIR o SWIR convencionales. Los resultados presentados en este trabajo demuestran que los filtros interferenciales de silicio poroso reestructurado resultan muy prometedores para el desarrollo de sensores multi- e hiperespectrales de bajo costeThe particular structure and physico-chemical properties of nanostructured porous silicon has stimulated the use of this material in many different applications. In the field of optoelectronics, the possibility of fabricating multilayer stacks where each individual layer has different optical properties allows the formation of optical interference filters with a predesigned behavior. In the present work, nanostructured porous silicon interference multilayer structures have been used to filter incident light reaching a Si photosensitive wafer in order to tailor its spectral response. The optical behavior of the porous silicon filters was simulated prior to their fabrication, and optical measurements showed good agreement between the simulated and experimental spectra. Photocurrent measurements have shown that the porous silicon filters narrowed the spectral responsitivity of silicon, from the original value of >750 nm down to around 150 nm. Different filter designs allowed to not only narrowen, but also tune the Si panchromatic sensitivity along the whole visible range. Porous silicon is compatible with standard microelectronic fabrication processes, making it possible to incorporate these interference filters onto a wide variety of conventional panchromatic VIS, NIR or SWIR broad band sensors. These results show that nanostructured silicon interference filters are a promising tool for developing cost-effective multi- and hyperspectral narrowband sensor

Special section guest editorial: Nanostructured thin films: Fabrication, characterization, and application

Martín-Palma, Raúl José, Jen, Yijun, "Special section guest editorial: Nanostructured thin films: Fabrication, characterization, and application", Journal of Nanophotonics, Elsevier B.V., 5 (1), 51599, (2011). Copyright 2013 Society of Photo Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibite

The impact of nanostructured silicon and hybrid materials on the thermoelectric performance of thermoelectric devices: review

Nanostructured materials remarkably improve the overall properties of thermoelectric devices, mainly due to the increase in the surface-to-volume ratio. This behavior is attributed to an increased number of scattered phonons at the interfaces and boundaries of the nanostructures. Among many other materials, nanostructured Si was used to expand the power generation compared to bulk crystalline Si, which leads to a reduction in thermal conductivity. However, the use of nanostructured Si leads to a reduction in the electrical conductivity due to the formation of low dimensional features in the heavily doped Si regions. Accordingly, the fabrication of hybrid nanostructures based on nanostructured Si and other different nanostructured materials constitutes another strategy to combine a reduction in the thermal conductivity while keeping the good electrical conduction properties. This review deals with the properties of Si-based thermoelectric devices modified by different nanostructures and hybrid nanostructured material

Electrical characterization of mis schottky barrier diodes based on nanostructured porous silicon and silver nanoparticles with applications in solar cells

The accurate determination of the electrical properties of photovoltaic devices is of utmost importance to predict and optimize their overall optoelectronic performance. For example, the minority carrier lifetime and the carrier diffusion length have a strong relationship with the carrier recombination rate. Additionally, parasitic resistances have an important effect on the fill factor of a solar cell. Within this context, the alternating current (AC) and direct current (DC) electrical characteristics of Si-based metal–insulator–semiconductor (MIS) Schottky barrier diodes with the basic structure Al/Si/TiO2/NiCr were studied, aiming at using them as photovoltaic devices. The basic diode structure was modified by adding nanostructured porous silicon (nanoPS) layers and by infiltrating silver nanoparticles (AgNPs) into the nanoPS layers, leading to Al/Si+nanoPS/TiO2/NiCr and Al/Si+nanoPS+AgNPs/TiO2/NiCr structures, respectively. The AC electrical properties were studied using a combination of electrochemical impedance spectroscopy and Mott–Schottky analysis, while the DC electrical properties were determined from current–voltage measurements. From the experimental results, an AC equivalent circuit model was proposed for the three different MIS Schottky barrier diodes under study. Additionally, the most significant electrical parameters were calculated. The results show a remarkable improvement in the performance of the MIS Schottky barrier diodes upon the addition of hybrid nanoPS layers with embedded Ag nanoparticles, opening the way to their use as photovoltaic device

Nanoporous silicon-based surface patterns fabricated by UV laser interference techniques for biological applications

The fabrication of selectively functionalized micropatterns based on nanostructured porous silicon (nanoPS) by phase mask ultraviolet laser interference is presented here. This single-step process constitutes a flexible method for the fabrication of surface patterns with tailored properties. These surface patterns consist of alternate regions of almost untransformed nanoPS and areas where nanoPS is transformed into Si nanoparticles (Si NPs) as a result of the laser irradiation process. The size of the transformed areas as well as the diameter of the Si NPs can be straightforwardly tailored by controlling the main fabrications parameters including the porosity of the nanoPS layers, the laser interference period areas, and laser fluence. The surface patterns have been found to be appropriate candidates for the development of selectively-functionalized surfaces for biological applications mainly due to the biocompatibility of the untransformed nanoPS regions.Postprint (author's final draft

The Link between Culture and Economy. The Case of Spring Fiestas in Seville

Las Fiestas de Primavera de Sevilla (FPS) constituyen el principal evento cultural de la ciudad con importantes implicaciones sociales, turísticas y económicas. Nuestro trabajo analiza esta dimensión de la cultura de la ciudad en un doble plano. Por un lado, se lleva a cabo una caracterización de las FPS, prototipo de patrimonio cultural material e inmaterial. Por otro lado, se lleva a cabo un estudio de Impacto Económico, calculado a partir de la suma de tres efectos. En primer lugar, los efectos directos derivados del gasto necesario realizado por instituciones públicas y privadas para la celebración del evento. En segundo lugar, los efectos indirectos, producto del gasto efectuado por los participantes en los eventos. Por último, se estiman los efectos inducidos para la economía en su conjunto, mediante los multiplicadores calculados a partir de una tabla Input-Output. La principal contribución del artículo es abordar un estudio de impacto económico de un bien cultural complejo y de naturaleza compuesta, como ejemplo de valoriza-ción económica a través de la cultura. Los resultados muestran un impacto económico estimado para el año 2009 de 915,8 millones de euros, que representan un 4,66% del PIB de la ciudad de Sevilla.Spring Fiestas in Seville (SFS) constitute the main cultural event that takes place in the city, with strong social, economic and touristic implications. Our paper analyzes this cultural dimension of the city from two perspectives. First, we analyze the SFS as a model of cultural heritage, both material and immaterial. Secondly, we make an economic impact study estimated as an addition of three effects: Direct effect that derivate from private and public institution’s expenditures which are necessary in order to celebrate SFS; Indirect effect produced by expenditures of participants in the events and Induced effect estimated using multipliers derived from input-output tables. The main contribution of the paper is to analyze the economic impact of a complex cultural good of a mix nature, as an exam-ple of economic valuation through the culture. Results show an estimated economic impact for 2009 of 915.8 million of euros that means 4.66% of city of Seville GDP

On the study of the single-stage hole-flanging process by SPIF

Recent studies show the capability of single-point incremental forming to perform successfully hole-flanging operations using multi-stage strategies. The aim of this work is to investigate the ability of the SPIF process to perform hole-flanges in a single stage, contributing to a better understanding of the formability of the sheet in this demanding situation. To this end, a series of experimental tests in AA7075-O metal sheets are performed in order to evaluate the limiting forming ratio. The physical mechanisms controlling sheet failure during the process are analyzed and discussed. In the test conditions studied this failure is postponed necking followed by ductile fracture in the wall of the flange.Ministerio de Economía y Competitividad DPI2012-3291

Preliminary investigation on homogenization of the thickness distribution in hole-flanging by SPIF

A drawback of the hole-flanging process by single-stage SPIF is the non-uniform thickness obtained along the flange. Multi-stage strategies have been used to improve it, however they increase notably the manufacturing time. This work presents a preliminary study of the tool paths for a hole-flanging process by SPIF in two stages. An intermediate geometry of the piece is proposed from the analysis of the thickness distribution observed in previous single-stage process. A simple optimization procedure is used to automate the intermediate part design, the NC code generation for the tool path and the validation of the optimal forming strategy by means of FEA