Examinando por Autor "Kanyinda-Malu, Clement"

Mostrando 1 - 6 de 6

Design of GaAs nanowires array based photovoltaic solar cells: simulations of optical reflectance
(Elsevier, 2021-06-26) de la Cruz, Rosa maría; Kanyinda-Malu, Clement; Muñoz santiuste, Juan Enrique
We report the optical response of a periodic square array of GaAs nanowires embedded in epoxy as a candidate for photovoltaic solar cells. The simulated system is a multilayer array constituted by alternating layers of epoxy and an effective medium constituted by GaAs nanowires arrays embedded in epoxy. To discuss the optical response, we investigate the reflectance dependence on the number of bilayers considered in the array and the angle of incident light. The GaAs nanowire dielectric function is described in terms of Webb formalism to take into account the confinement energy of the excitons. The effective dielectric function of GaAs nanowires embedded in epoxy is evaluated within the Maxwell–Garnett theory. We evaluate the reflectance for s- and p-polarized light through the transfer matrix formalism for bilayers. For both s- and p-polarization, we observe an oscillating behavior of the reflectance, similar to that reported in the literature. We have also obtained a feature peaked around 850 nm. While the oscillations can be ascribed to multiple interference from periodic bilayers, the peak at 850 nm can be understood in term of the gap energy in the nanowire dielectric function. Attending to the reflectance dependence on the light incidence angle, we have found that for s-polarized light, the reflectance is higher with increasing angles, in comparison to p-polarized light cases.
Dielectric response of II-VI semiconductor core-shell ensembles: Study of the lossless optical condition
(ELSEVIER, 2014) De la Cruz, Rosa María; Kanyinda-Malu, Clement; Muñoz Santiuste, Juan Enrique
We theoretically investigate optical properties of II-VI core-shell distribution mixtures made of two type-I sized-nanoshells as a plausible negative dielectric function material. The nonlocal optical response of the semiconductor QD is described by using a resonant excitonic dielectric function, while the shell response is modeled with Demangeot formula. Achieving the zero-loss at an optical frequency ω, i.e., εeff = ε'eff + iε''eff with ε 'eff < 0 and ε''eff = 0, is of fundamental importance in nanophotonics. Resonant states in semiconductors provide a source for negative dielectric function provided that the dipole strength and the oscillator density are adequate to offset the background. Furthermore, the semiconductor offers the prospect of pumping, either optically or electrically, to achieve a gain mechanism that can offset the loss. We analyse optimal conditions that must be satisfied to achieve semiconductor-based negative index materials. By comparing with II-VI semiconductor quantum dots (QDs) previously reported in the literature, the inclusion of phonon and shell contributions in the εeff along with the finite barrier Effective Mass Approximation (EMA) approach, we found similar qualitative behaviours for the εeff.
Dielectric Tensor of a rectangular arrangement of Ag-nanoparticles in anisotropic LiNbO_3 : Analysis of the negative epsilon conditions
(ELSEVIER, 2020-03-15) de la Cruz, Rosa María; Kanyinda-Malu, Clement; Muñoz-Santiuste, Juan Enrique
En este artículo hemos analizado la respuesta óptica de un sistema ordenado de nanopartículas de plata (Ag NPs) embebidas en una matriz de un cristal uniaxial de LiNbO_3 como modelo de soporte para futuras dispositivos solares. El objetivo ha consistido en estudiar el efecto de la anisotropía del cristal envolvente sobre el tensor dieléctrico efectivo del conjunto Ag+LiNbO_3 teniendo en cuenta las interacciones entre las nanopartículas de Ag. Por ello, se han definido las funciones dieléctricas de Ag según el modelo de Drude mientras que las constantes dieléctricas de LiNbO_3 vienen definidas a través de sus expresiones experimentales de Sellmeier. Una vez determinadas las funciones dieléctricas, el conjunto de agregados de Ag y LiNbO_3 es tratado como un medio continuo a través del modelo extendido de Maxwell-Garnet. En el sistema simulado, las nanopartículas de Ag se sitúan en el plano ordinario del cristal de LiNbO_3 dando lugar a respuestas diferentes en las orientaciones X, Y, Z del campo eléctrico aplicado. Con el diseño descrito anteriormente, se analizan las respuestas dieléctricas del conjunto de agregados de Ag + LiNBO_3 en función de los parámetros estructurales como son la fracción de volumen, el tamaño de nanopartículas y la distancia o espaciado entre nanopartículas, incluyendo en el modelo la interacción las nanopartículas a través de las partes reales e imaginarias de las funciones dieléctricas del sistema bajo investigación. Este trabajo ha demostrado que una adecuada selección de parámetros estructurales puede dar lugar a sistemas llamados “Negative epsilon metamaterials o Near-Zero epsilon materials” cuyas constantes dieléctricas o índices de refracción pueden alcanzar valores negativos más codiciados en los dispositivos optoelectrónicos en la actualidad. Utilizado como multicapas, el sistema estudiado abre camino a los diseños de muchos sistemas que pueden usarse en futuras aplicaciones como células fotovoltaicas. El trabajo concluye con una determinación de una franja de condiciones de tamaños, fracciones de volumen o de disposición óptimas para conseguir respuestas dieléctricas que respondan a materiales con constantes dieléctricas negativas a nivel de laboratorio
Geometry-related optical properties in vertically aligned GaAs nanowires: A study of sizes and embedding medium
(Elsevier, 2023-10) De la Cruz, Rosa María; Kanyinda-Malu, Clement; Muñoz Santiuste, Juan Enrique
We report the effects of radius-, length- and pitch-sizes on the optical reflectance of a periodic square array of GaAs nanowires embedded in epoxy. The simulated system is a multilayer array constituted by alternating layers of epoxy and an effective medium of GaAs nanowires embedded in epoxy. For both s- and p-polarizations, we observe an oscillating behavior in the reflectance spectra, as a consequence of interferences in periodical systems. We found that the radius- and pitch-sizes significantly affect the reflectance of GaAs nanowires array, while the length-sizes do not present evidence of changes in the optical reflectance. For higher radius, the number of oscillations increases and consequently, the peak-to-peak distance decreases. Besides, there is a red-shift of the reflectance for increasing radius. For higher pitch, the number of oscillations also increases, and a red-shift is observed. We obtain dependence laws for the peak-to-peak distance and red-shift versus radius and versus pitch. These dependences obey approximate quadratic relations. Attending to the reflectance dependence on the light incidence angle, we have found that for s-polarized light, the reflectance is higher with increasing angles, in comparison to p-polarized light cases, independently of the radius and pitch values. For both polarizations, we found that the reflectance is increasing for greater radii and smaller pitches, independently of the incident angle.
Negative-epsilon conditions in the dispersive LiNbO3-Ag nanoparticles composites
(2017-02) de la Cruz, Rosa María; Kanyinda-Malu, Clement; Muñoz Santiuste, Juan Enrique
The silver (Ag)-embedded lithium niobate (LiNbO3) composites are theoretically analyzed under the effective medium Maxwell-Garnett approximation to account on the optimal conditions through which such composites present negative epsilon conditions. The dielectric function of Ag nanoparticles (NPs) is described by Drude theory with an additional Lorentz oscillator term to take into account the interband electronic transitions which typically occur in noble metals. The LiNbO3 dielectric function is evaluated through the Sellmeier equations. Once the effective dielectric function (epsilon(eff)) is evaluated, we investigate the negative epsilon condition (epsilon'(eff) < 0) as a function of the frequency. The results showed that, for given volumen fraction values, the negative epsilon (NE) condition is satisfied for critical sizes of Ag NPs. This condition defines an interval of energies, called NE range. That NE range enlarges for increasing radius and becames narrower for decreasing volume fractions. Furthermore, the calculated Frohlich frequency is nearly close to the lower-energy limit of NE range. In addition, the calculated extinction spectra of the composite are analyzed in terms of the radius of Ag NPs.
Simulations of optical reflectance in Vertically aligned GaAs nanowires array: the effect of the geometrical structural parameters
(ELSEVIER, 2022-04-26) De la Cruz, Rosa María; Kanyinda-Malu, Clement; Muñoz santiuste, Juan Enrique
We report the effects of radius-, length-and pitch-sizes on the optical reflectance of a periodic square array of GaAs nanowires embedded in epoxy. The simulated system is a multilayer array constituted by alternating layers of epoxy and an effective medium of GaAs nanowires embedded in epoxy. For both s-and p-polarizations, we observe an oscillating behavior in the reflectance spectra, as a consequence of interferences in periodical systems. We found that the radius-and pitch-sizes significantly affect the reflectance of GaAs nanowires array, while the length-sizes do not present evidence of changes in the optical reflectance. For higher radius, the number of oscillations increases and consequently, the peak-to-peak distance decreases. Besides, there is a red-shift of the reflectance for increasing radius. For higher pitch, the number of oscillations also increases, and a red-shift is observed. We obtain dependence laws for the peak-to-peak distance and red-shift versus radius and versus pitch. These dependences obey approximate quadratic relations. Attending to the reflectance dependence on the light incidence angle, we have found that for s-polarized light, the reflectance is higher with increasing angles, in comparison to p-polarized light cases, independently of the radius and pitch values. For both polarizations, we found that the reflectance is increasing for greater radii and smaller pitches, independently of the incident angle.