110 research outputs found
Highly efficient photodegradation of methylene blue by a composite photocatalyst of bismuth nanoparticles on silicon nanowires
No full textWhen synthetic dyes are used to embellish the world, the wastewater holding these hazardous materials is wantonly released into the biosphere. Appropriate treatment for such effluents is thereby indispensable. In this context, the present study was conducted to fabricate an eco-friendly, cost-effective and new bismuth modified silicon nanowires (Bi@SiNWs)-based photocatalysts toward superior photocatalytic degradation of methylene blue (MB) dye under both UV and solar irradiations. SiNWs were synthesized by silver-assisted chemical etching while Bi nanoparticles were anchored onto the NWs via thermal evaporation. By assessing the morphology, elemental composition, structure and crystallinity characteristics, these Bi@SiNWs nanocomposites are systematically identified. Extensive investigations of blank SiNWs and Bi@SiNWs optical properties — reflectance, transmittance, absorption coefficient, absorbance and optical band-gap — are presented. Near-perfect absorbance above 97%, over the visible wavelength region, has been achieved owing to the synergistic effect of Bi decoration on SiNWs. Accordingly, Bi@SiNWs showed remarkable photocatalytic ability for the degradation of MB up to 44% and 89% under UV and solar irradiation, respectively, only within 120 min. Repeated cycle runs revealed that the Bi@SiNWs composite photocatalyst exhibits strong reusability and photo-stability. Lastly, we will thoroughly provide the plausible mechanism for the photocatalytic degradation of MB over Bi@SiNWs. Our outcomes validate the potent role of Bi@SiNWs photocatalysts for effective environmental remediation.M. Naffeti and P.A. Postigo acknowledge the service from the X-SEM Laboratory at IMN and funding from CSIC under i-COOP
2020 program (COOPA20431), Spain
Heat dynamics in optical ring resonators
No full textWe present an analytical model for the dynamical self-heating effect in air-cladded optical microring resonators (ORRs). The spatially and time resolved temperature field is calculated by integrating the corresponding boundary value problem of the heat equation. It turns out that the self-heating amplitude is approximately proportional to the total absorbed power and anti-proportional to the thermal conductivity of the cladding material. Further, two-photon absorption plays a major role in the heating process, even for moderate input powers, due to the strong light confinement. Heating times are determined to be in the microsecond range and may limit the response time of ORR devices. The explicit formulas for the temperature fields allow a much faster determination of heating properties compared to elaborate finite element simulations. Thus, our model is predestinated for scanning large parameter spaces.This work is funded through the project 17FUN05 “PhotOQuant” within the Programme EMPIR. The EMPIR initiative is
co-founded by the European Union’s Horizon 2020 research and innovation program and the EMPIR Participating
Countries.Peer reviewe
Solar-cell efficiency enhancements using 2D photonic crystals
No full textIncreased performance can also be achieved for photon-sensing devices
such as photodetectors and thermo-photovoltaic devices.
The performance of solar cells (SCs) can be enhanced significantly
by employing 2D photonic crystals (2D-PCs). They can
either be used as omnidirectional, broadband antireflection coatings
(ARCs) or applied to thin-film SCs (where PC effects are
much more significant than in generic SCs). Although multilayer
ARCs are commonly used, problems related to material
selection, thermal mismatch, sensitivity to thickness variations,
and instability of the thin-film stacks persist. Tapered, submicrometer
patterned structures may offer a more practicalmethod
for ultrabroadband, omnidirectional, antireflection operation.1
We have developed an optimized PC ARC that combines good
optical properties (low reflectivity over a wide range of wavelengths)
with high mechanical stability based on application of
a thin dielectric layer perforated with the PC pattern. (A slight
patterning of the PC inside the indium phosphide—InP—
layer is required for optimum performance.) Thus, mixed, thin
dielectric-layer/bulk patterning can be used for best optical
and mechanical results compared to alternatives such as motheye-
like fabrication, nanorods, and nanostructures employing
oblique-angle deposition methods, which may be damaged seriously
even by smooth contact with other surfaces.The author acknowledges project grants Consolider GENESIS
CSD2006-0004 (Spanish Ministry of Education and Culture) and
NANOGEFFES ENE2009-14481-C02-02.Peer reviewe
Highly Efficient Silicon Nanowire Surface Passivation by Bismuth Nano-Coating for Multifunctional Bi@SiNWs Heterostructures
No full text© 2020 by the authors.A key requirement for the development of highly efficient silicon nanowires (SiNWs) for use in various kinds of cutting-edge applications is the outstanding passivation of their surfaces. In this vein, we report on a superior passivation of a SiNWs surface by bismuth nano-coating (BiNC) for the first time. A metal-assisted chemical etching technique was used to produce the SiNW arrays, while the BiNCs were anchored on the NWs through thermal evaporation. The systematic studies by Scanning Electron Microscopy (SEM), energy dispersive X-ray spectra (EDX), and Fourier Transform Infra-Red (FTIR) spectroscopies highlight the successful decoration of SiNWs by BiNC. The photoluminescence (PL) emission properties of the samples were studied in the visible and near-infrared (NIR) spectral range. Interestingly, nine-fold visible PL enhancement and NIR broadband emission were recorded for the Bi-modified SiNWs. To our best knowledge, this is the first observation of NIR luminescence from Bi-coated SiNWs (Bi@SiNWs), and thus sheds light on a new family of Bi-doped materials operating in the NIR and covering the important telecommunication wavelengths. Excellent anti-reflectance abilities of ~10% and 8% are observed for pure SiNWs and Bi@SiNWs, respectively, as compared to the Si wafer (50–90%). A large decrease in the recombination activities is also obtained from Bi@SiNWs heterostructures. The reasons behind the superior improvement of the Bi@SiNWs performance are discussed in detail. The findings demonstrate the effectiveness of Bi as a novel surface passivation coating, where Bi@SiNWs heterostructures are very promising and multifunctional for photovoltaics, optoelectronics, and telecommunications.M. Naffeti acknowledge the Tunisian Ministry of Higher Education and Scientific Research as well as University of Tunis. M. Naffeti and P.A. Postigo acknowledge the service from the X-SEM Laboratory at IMN and thank Benito Alén for providing the necessary facilities to carry out the PL measurementsPeer reviewe
Theoretical and experimental study of the Suzuki-phase photonic crystal lattice by angle-resolved photoluminescence spectroscopy
No full textA complete theoretical and experimental analysis of the photonic band structure for the Suzuki-phase lattice is presented. The band diagrams were calculated by two-dimensional plane wave expansion and three-dimensional guided-mode expansion methods. Angle resolved photoluminescence spectroscopy has been used to measure the emission of the photonic crystal structure realized in active InAsP/InP slabs. Photonic bands with a very low group velocity along an entire direction of the reciprocal lattice have been measured, which may have important applications on future photonic devices. The experimentally determined dispersion is in very good agreement with the calculated photonic bands. The presence of defect modes produced by microcavities in the Suzuki-phase lattice has also been established
Uso de un material para la fabricación de un cubreobjetos, un portamuestras o un recipiente de cultivo cecular
No full textLa presente invención se refiere al uso de un material que comprende un recubrimiento capaz de reflejar luz de una longitud de onda entre 350nm y 850 nm, correspondientes a las regiones del espectro electromagnético del VIS, IR y UV, y un sustrato transparente a la luz VIS, para la fabricación de un cubreobjetos, un portamuestras o un recipiente de cultivo celular, particularmente un cubreobjetos, un portamuestras o un recipiente de cultivo celular que se utilizan en microscopía ópticaThe invention relates to the use of a material comprising a coating that can reflect light with a wavelength between 350 nm and 850 nm, corresponding to the VIS, IR and UV regions of the electromagnetic spectrum, and a substrate that is transparent to VIS light, for the production of a cover slip, a sample holder or a cell culture container, in particular a cover slip, a sample holder or a cell culture container used in light microscopy. [EN]Peer reviewedConsejo Superior de Investigaciones Científicas (España), Centro Nacional de Investigaciones OncológicasA1 Solicitud de patente con informe sobre el estado de la técnic
Use of a material for the production of a cover slip, a sample holder or a cell culture containter
No full textLa presente invención se refiere al uso de un material que comprende un recubrimiento capaz de reflejar luz
de una longitud de onda de entre 350 nm y 850 nm, correspondientes a las regiones del espectro electromagnético del VIS, IR y UV, y un sustrato transparente a la luz VIS, para la fabricación de un cubreobjetos, un portamuestras o un recipiente de cultivo celular, particularmente un cubreobjetos, un
portamuestras o un recipiente de cultivo celular que se utilizan en microscopía óptica.Peer reviewedConsejo Superior de Investigaciones Científicas (España), Centro Nacional de Investigaciones Oncológicas (CNIO)B1 Patente sin examen previ
Design, fabrication and characterization of photonic crystals on III-V compounds: from classical to quantum light sources
No full textTesis doctoral inédita. Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de Materiales. Fecha de lectura: 11-12-200
Defect reduction in heteroepitaxial InP on Si by epitaxial lateral overgrowth
No full textJunesand, Carl et al.Epitaxial lateral overgrowth of InP has been grown by hydride vapor phase epitaxy on Si substrates with a thin seed layer of InP masked with SiO2. Openings in the form of multiple parallel lines as well as mesh patterns from which growth occurred were etched in the SiO2 mask and the effect of different growth conditions in terms of V/III ratio and growth temperature on defects such as threading dislocations and stacking faults in the grown layers was investigated. The samples were characterized by cathodoluminescence and by transmission electron microscopy. The results show that the cause for threading dislocations present in the overgrown layers is the formation of new dislocations, attributed to coalescence of merging growth fronts, possibly accompanied by the propagation of pre-existing dislocations through the mask openings. Stacking faults were also pre-existing in the seed layer and propagated to some extent, but the most important reason for stacking faults in the overgrown layers was concluded to be formation of new faults early during growth. The formation mechanism could not be unambiguously determined, but of several mechanisms considered, incorrect deposition due to distorted bonds along overgrowth island edges was found to be in best agreement with observations. © 2014 by American Scientific Publishers All rights reserved.The authors would like to acknowledge the financial support of the Swedish Foundation for Strategic Research (SSF), the Swedish Research Council (VR), Swedish Governmental Agency for Innovation Systems (Vinnova) and the Taiwan National Research Council.Peer Reviewe
Fabricación y caracterización de materiales nanoestructurados en áreas extensas para aplicaciones en dispositivos fotónicos
No full textEn esta Tesis se han desarrollado diversos procesos para la fabricación de materiales nanoestructurados. En todos ellos se ha partido del uso de litografía blanda o coloidal para obtener áreas extensas y disminuir el coste del proceso.En primer lugar se desarrolló y optimizó un proceso para crear nanoestructuras en silicio mediante litografía blanda y ataque reactivo de iones (RIE). Con este proceso se obtuvieron nanocintas de silicio en área extensa y con una relación de aspecto > 1. Se observó que las propiedades hidrófobas o hidrófilas del silicio pueden ser adaptables según la necesidad, variando un único parámetro en el proceso de fabricación (la potencia) y también se obtuvo en las medidas de reflectividad un pico en la longitud de onda 280 nm en el cual absorben ciertos péptidos y aminoácidos. Este pico, que ya aparece en el silicio, es espectralmente más estrecho en el silicio nanoestructurado lo que le confiere unas propiedades más favorables para la detección óptica.En segundo lugar, se estudió la influencia de la forma, ordenamiento y tamaño de nanoestructuras sobre las propiedades ópticas del vidrio. Se llevó a cabo un análisis exhaustivo de la variación en la transmisión y en la dispersión de la luz. También se simuló como afectarían a la eficiencia de una célula solar el uso de estos vidrios nanoestructurados junto con el estudio de sus propiedades hidrófobas e hidrófilas. Mediante este procesado se consiguió un aumento de la hidrofobicidad para ciertos tipos de nanoestructuras mejorando de esta formas las propiedades de autolimpiado del vidrio y para otros tipos de nanoestructuras se aumentó la hidrofilicidad y por lo tanto su capacidad para evitar la formación de vaho, propiedades clave en paneles solares, sin perder la eficiencia de la transmisión de la luz, como demostraron las medidas sobre células solares realizadas en el simulador solar.Finalmente se utilizó la nanoestructuración de área extensa y de bajo coste para fabricar un sensor óptico de resonancia plasmónica superficial. El sensor consta de una red formada por nanohilos de Au con anchuras menores de 400 nm y 20 nm de espesor sobre vidrio. La caracterización del sensor demostró un límite de detección dentro del estado del arte y un tiempo de detección rápido (1 s) en comparación con otros dispositivos similares. El área extensa y la elevada homogeneidad del sensor permiten que pueda ser usado mediante un sistema óptico simple y portátil.<br /
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