Showing papers by "Oscar E. Martínez published in 2018"
TL;DR: These isolated, small glacier-fed streams typical of the Patagonian landscape appear highly vulnerable to global warming, and endemic elements could disappear at upper segments being replaced by other species common at rhithral environments.
16 citations
TL;DR: In this article, the effects of ex situ annealing in N ambient and in situ in As ambient on GaNSbAs/GaAs structures grown by molecular beam epitaxy were investigated by low temperature cross-sectional cathodoluminescence (CL).
Abstract: The effects of ex situ annealing in N ambient and in situ annealing in As ambient on GaNSbAs/GaAs structures grown by molecular beam epitaxy were investigated by low temperature cross-sectional cathodoluminescence (CL). The amount and distribution of Sb was measured by energy dispersive spectroscopy (EDS). The cross-sectional CL analysis of all samples reveals a shift of the near band edge (NBE) emission along the growth axis, presumably associated with a non-uniform incorporation of Sb during the growth process, in agreement with the Sb distribution measured by EDS in the as-grown sample. The NBE emission in the annealed samples presents a redshift with respect to the as-grown sample. This effect might be explained by a redistribution/activation of N in the GaNSbAs lattice since the Sb distribution measured by EDS does not reveal significant changes, within the error margin, with respect to the as-grown sample. The in situ annealed in the As overpressure sample shows the best properties for solar cells applications, i.e., a NBE peak position close to 1.0 eV and the lowest full width at half maximum of this emission.
4 citations
TL;DR: Agarwal et al. as discussed by the authors present el desarrollo de un novedoso sistema that permite el mapeo con alta resolucion espacial de the difusividad termica in funcion de la temperatura.
Abstract: RESUMEN Se presenta el desarrollo de un novedoso sistema que permite el mapeo con alta resolucion espacial de la difusividad termica en funcion de la temperatura hasta 1800K. El sistema se basa en una tecnica fototermica recientemente desarrollada por el grupo, consistente en la medicion con un laser de prueba de la curvatura inducida por el calentamiento con un laser modulado. La utilizacion de tecnologia de fibras opticas provee una alta robustez al equipo. Un horno para microscopio permite realizar rampas a velocidad controlada para el estudio de transiciones de fase y la medicion de la difusividad termica en funcion de la temperatura. Se pueden establecer mesetas para hacer barridos espaciales con resolucion microscopica para el estudio de la evolucion de las fases o hacer tratamientos termicos in situ para estudiar luego la distribucion espacial de las fases presentes. En este trabajo se presenta un ejemplo, donde la senal es colectada para un punto fijo y para una dada frecuencia de modulacion, en funcion de la temperatura de la muestra. Se disena para ello un sistema de correccion de enfoque que compensa la deriva termica generada por la expansion termica del sistema. El desplazamiento lateral es corregido utilizando un algoritmo de correlacion y la imagen de la camara. Este dispositivo fue utilizado para determinar la transicion de fase de una muestra testigo. Estas capacidades se muestran a partir de la determinacion de la energia de activacion de la transformacion de fase amorfo-cristal de una aleacion de Fe-B-Si.
2 citations
Posted Content•
TL;DR: A new algorithm for data deconvolution that allows the retrieval of the target function with super-resolution with a simple approach that after a measurement of the instrument response function (IRF), the measured data are fit by a superposition of point sources (SUPPOSe) of equal intensity.
Abstract: In this work we present a new algorithm for data deconvolution that allows the retrieval of the target function with super-resolution with a simple approach that after a precis e measurement of the instrument response function (IRF), the measured data are fit by a superposition of point sources (SUPPOSe) of equal intensity. In this manner only the positions of the sources need to be determined by an algorithm that minimizes the norm of the difference between the measured data and the convolution of the superposed point sources with the IRF. An upper bound for the uncertainty in the position of the sources was derived and two very different experimental situations were used for the test (an optical spectrum and fluorescent microscopy images) showing excellent reconstructions and agreement with the predicted uncertainties, achieving {\lambda}/10 resolution for the microscope and a fivefold improvement in the spectral resolution for the spectrometer. The method also provides a way to determine the optimum number of sources to be used for the fit.
18 Jan 2018
TL;DR: In this article, the cathodoluminescence (CL) depth profiling of the optical emissions from (0001) GaN/GaNbuffer/Al2O3 heterostructures has been performed at 77
Abstract: The cathodoluminescence (CL) depth profiling of the optical emissions from (0001) GaN/GaNbuffer/Al2O3 heterostructures has been performed at 77