Preparation of low cost SERS-substrates for virus characterization

Raman spectroscopy is a technique that allows the characterization and detection of a wide range of molecules. The characterization of biomolecules and viruses has been a novel application in the last decades. A relevant problem for applying this technique is the low intensity of the Raman signal and the low concentration of the analyte, which makes the identification of molecules and viruses quite difficult. An alternative to overcome this problem is the use of surface- enhanced Raman spectroscopy (SERS). This involves the use of SERS-substrates that generally are very expensive and can only be used once. In this work, we report the preliminary results of virus detection by SERS using low-cost homemade substrates and commercially available substrates. Characteristic Raman peaks associated with the influenza virus were detected. The results obtained with the homemade SERS-substrates are comparable to the obtained by using the comercial ones.Preparación de sustratos SERS de bajo coste para caracterización de virus La espectroscopia Raman es una técnica que permite la caracterización y detección de una amplia gama de moléculas. La caracterización de biomoléculas y virus ha sido una aplicación novedosa en las últimas décadas. Un problema relevante para aplicar esta técnica es la baja intensidad de la señal de Raman y la baja concentración de analito, lo que dificulta bastante la identificación de moléculas y virus. Una alternativa para superar este problema es el uso de SERS (surface-enhanced Raman spectroscopy). Esto implica el uso de sustratos SERS que generalmente cuestan una cantidad considerable de dinero y solo se pueden usar una vez. En este trabajo, reportamos resultados preliminares de la detección de virus por SERS utilizando sustratos caseros de bajo costo y sustratos disponibles comercialmente. Se detectaron picos característicos Raman asociados a virus de la influenza. Los resultados obtenidos con los sustratos SERS caseros son comparables a los obtenidos utilizando los comerciales

White light emitting diode prototypes based on cadmium sulfide and graphene carbon quantum dots

During the last years, semiconductor quantum dots (QDs) have attracted great attention due to the outstanding properties for solid-state lighting, display technology, biosensors, among others. White light emitting diodes (WLEDs) using down conversion approach is one of the new attractive alternatives in solid-state lighting. However, these devices present several shortcomings as near-UV light escape andQD-polymer incompatibility. In this work, we propose alternativePrototipos de diodos emisores de luz blanca basados en puntos cuánticos de sulfuro de cadmio y de grafeno  Durante los últimos años, puntos cuánticos (QDs) semiconductores han tenido gran atención debido a sus propiedades excepcionales para aplicaciones en iluminación de estado sólido, tecnologías de monitores, bio-sensores, entre otras. Los diodos emisores de luz blanca (WLED) que utilizan el enfoque de conversión descendente, son una de las nuevas alternativas para iluminación de estado sólido. Sin embargo, estos dispositivos presentan varias deficiencias como la fuga de luz cercana al UV y la incompatibilidad entre el QD y el polímero. En este trabajo proponemos prototipos alternativo

Exciton kinetics and luminescence in disordered InxGa 1-xP/GaAs quantum wells

Trabajo presentado en el 7th International Workshop on Nonlinear Optics and Excitation Kinetics in Semiconductors, NOEKS 2003, celebrado en Karlsruhe (Alemania), del 23 al 28 de febrero de 2003Continuous wave and time-resolved photoluminescence studies as a function of temperature have been performed on disordered InxGa 1-xP/GaAs quantum wells. Simulations of stationary and transient spectra, by using a two-exciton kinetic model, allow the observation of a red shift of the effective mobility edge when temperature increases. From the temperature dependence of the radiative lifetime it can be also deduced that independent localization of electrons and holes seems to be the most likely mechanism for exciton localization in our samples. On the other hand, values ranging from 0.8 to 5.6 ps have been obtained for the radiative lifetime at k∥ = 0.This work has been partially supported by the spanish CICYT under project TIC99-1035.Peer reviewe

Temperature dependence of the effective mobility edge and recombination dynamics of free and localized excitons in InGaP/GaAs quantum wells

3 páginas, 1 figura.-- Comunicación presentada al Proceedings of the International Conference on Superlattices, Nano-structures and Nano-devices ICSNN 2002 o-structures and Nano-devices ICSNN 2002.The temperature dependence of the effective mobility edge in semiconductor quantum wells containing disorder is reported for the first time. It is deduced by reproducing the experimental continuous wave and time resolved luminescence spectra by means of a two-class exciton kinetic model, which considers the co-existence of free and localized excitons and introduces a mobility edge defined by a Fermi function. The mobility edge varies faster than the PL peak energy when the temperature increases, passing from the high energy side of the PL band at low temperatures (recombination of localized excitons dominates) to the low energy side above 125 K (recombination of quasi-free excitons dominates).This work has been supportedby the Spanish CICYT under the project no. TIC99-1035.Peer reviewe

Consequences of the spatial localization on the exciton recombination dynamics in InGaP/GaAs heterostructures

5 páginas, 4 figuras.GaAs/InxGa1−xP quantum wells, with x=0.541 and 0.427, have been investigated by continuous wave and time resolved photoluminescence. Spatial localization of excitons due to alloy compositional defects seem to be responsible of the observed phenomenology: non-exponential decay behavior at long times and slow decrease of the effective recombination time by increasing temperature. A two-class exciton kinetic model, based on a mobility edge varying with the temperature explain the experimental results.This work has been supported by the Spanish Ministerio de Ciencia y Tecnolog ıa under project number TIC99-1035-C02. The main author (C.R.) also thanks the spanish Ministerio de Asuntos Exteriores (MUTIS program).Peer reviewe

Vertical stacks of small InAs/GaAs self-assembled dots: resonant and non-resonant excitation

4 páginas, 2 figuras.-- PACS: 78.67.Hc; 73.21.La; 78.55.Cr.-- Proceedings of the International Conference on Superlattices, Nano-structures and Nano-devices ICSNN 2002.We have performed photoluminescence experiments in samples containing self-assembled quantum dots with different spacer layer thicknesses. A strong filtering effect produced by the GaAs spacer layer on the dots size being stacked is observed for spacers thinner than 10 nm. This effect produces a blue shift of the emission band from stacked dots and a simultaneous line width narrowing. At the same time, given the existence of a broad dot size distribution in the first layer, bigger dots can evolve towards InAs cylinder-like structures, whose emission occurs at appreciably lower energies as compared to the emission band associated to dot stacks (with some GaAs separation).This workhas been supported by the Spanish CICYT under the Project No. TIC99-1035-C02 and European Commission GROWTH Program NANOMAT Project, Contract No. G5RD-CT-2001-00545.Peer reviewe

Influence of the InAs coverage on the phonon-assisted recombination in InAs/GaAs quantum dots

6 páginas, 3 figuras.In this work, a study of the relaxation mechanisms in InAs self-assembled quantum dots have been performed by means of photoluminescence (PL), resonant PL (RPL) and PL excitation. The observed phenomenology is different for samples with different InAs coverage. At low InAs coverages, two resonant Raman scattering lines are observed when the excitation energy is chosen inside the emission band. These lines are related to the TO and LO GaAs phonons. Multi-phonon relaxation of carriers (GaAs phonons) is clearly observed in RPL and excitation PL in the lowest InAs coverage sample. Neither such mechanism nor resonant Raman scattering is present in samples with larger InAs coverages, for which the average quantum dot size and areal density remain essentially constant.This work has been partially supported by the spanish Ministerio de Ciencia y Tecnolog ıa under project number TIC99-1035-C02, Ministerio de Asuntos Exteriores (MUTIS program) and the Generalitat Valenciana.Peer reviewe