Light emitting devices based on nanostructured semiconductors

Light emitting devices based on high-efficiency photoluminescence (PL) fluorescent nanocrystals have been investigated in terms of the generation of light from the structure using a variety of deposition methods. An automated modified layer-by-layer (LbL) self-assembly technique has been employed to produce multilayers of thiol-capped red fluorescing CdTe nanocrystals. Indium- tin-oxide (ITO) and aluminium electrodes were used as the electrodes. Morphological characterization was carried out through Schottky field effect (SFEG) SEM and atomic force microscopy (AFM). The structures built presented clear red electroluminescence (EL) to the naked eye. Turn on voltages were found to be in the range of 3-6 volts while the onset current was in the order of tens of microamperes. The role of structure homogeneity, the presence of pinholes and lifetime extension were features addressed during this investigation. Samples with a lifetime of continuous operation in air longer than 60 minutes and highly stable EL spectra were achieved; EL was visible to the unaided eye, although the brightness was still below the commercial standards and has not yet been qualified

Insights into the relationship between inherent materials properties of PZT and photochemistry for the development of nanostructured silver.

Recently there has been great interest in using patterned ferroelectric materials for the photochemical growth of metal nanostructures. Variations in surface and sub-surface structure influence the photochemical processes. Here we show that crystallography, and hence remnant polarization, of the ferroelectric affects photo-deposition. The ratio of metal growth on c– and c+ domains varies from 1 : 2 for [100] to 1 : 100 for [111]. This is shown to be dependent on the variations in the band structu

Computer programs and digital materials usage for learning evaluation purposes: professors and students' perceptions

Este artículo presenta los resultados de un estudio de caso que se realizó con el objetivo de comprender cómo se está vinculando el uso de tecnología computacional y el uso de materiales digitales en los procesos de evaluación del aprendizaje en un escenario de educación superior, específicamente en la materia de contabilidad administrativa. Se realizaron observaciones sobre procesos de evaluación sumativa. También se entrevistó a docentes y estudiantes para comprender su percepción sobre las implicaciones formativas que emanan de la decisión de hacer uso de las TICs en procesos de verificación del aprendizaje. Los hallazgos permitieron la comprensión de diferentes factores que convergen en la decisión de utilizar o no TICs en el proceso de evaluación tales como: la concepción que tiene el docente sobre el propósito y diseño de un examen, la vinculación entre evaluación y aprendizaje, así como la inseguridad y desconfianza que genera la apertura a posibilidades de plagio, de fallas tecnológicas, además de caer en el riesgo de propiciar un ambiente de inequidad ante el desafío que implica manejar con pericia dichas herramientas; todos éstos, factores que provocan desaceleración en la inserción de las herramientas tecnológicas en procesos de verificación del aprendizaje.Este artigo apresenta os resultados de um estudo de caso que se realizou com o objetivo de compreender como se está vinculando o uso de tecnologia computacional e o uso de materiais digitais nos processos de avaliação da aprendizagem num contexto de educação superior, especificamente na matéria de contabilidade administrativa. Realizaram-se observações sobre processos de avaliação somática. Também se entrevistou docentes e estudantes para compreender sua percepção sobre os envolvimentos formativos que emanam da decisão de fazer uso das Cacoetes em processos de verificação da aprendizagem. Os achados permitiram o entendimento de diferentes fatores que convergem na decisão de utilizar ou não Cacoetes no processo de avaliação tais como: a concepção que tem o docente sobre o propósito e planejamento de um exame, a vinculação entre avaliação e aprendizagem, bem como a insegurança e desconfiança que gera a abertura à possibilidades de plágio, de falhas tecnológicas, além de cair no risco de propiciar um ambiente de iniqüidade ante o desafio que implica manipular com perícia ditas ferramentas; todos estes fatores provocam desaceleração na inserção das ferramentas tecnológicas em processos de verificação da aprendizagem.This article contains the results of a case study in a higher education institution context. The objective was getting to comprehend in a deeply way how are computing programs and digital materials being used for summative assessment purposes in management accounting lectures. Observations during computing exam applications as well as some interviews were held with both, professors and students to get their perceptions about consequences of deciding to use or not computing programs and support digital material. Findings revealed a conjunction of factors that permit deep comprehension about some attitudes towards the usage of computing tools. Indeed, insecurity and mistrust are reasons that involve decisions such as not using computing technology during examinations. Risks related to plagiarism possibilities and unfair conditions to solve exams are some of the reasons why computing technology is not becoming a familiar part of examinations tools in higher education

Screening of heterogeneous surfaces: charge renormalization of Janus particles

Nonlinear ionic screening theory for heterogeneously charged spheres is developed in terms of a mode-decomposition of the surface charge. A far-field analysis of the resulting electrostatic potential leads to a natural generalization of charge renormalization from purely monopolar to dipolar, quadropolar, etc., including mode-couplings. Our novel scheme is generally applicable to large classes of surface heterogeneities, and is explicitly applied here to Janus spheres with differently charged upper and lower hemispheres, revealing strong renormalization effects for all multipoles.Comment: 2 figure

Cathodic and Anodic Material Diffusion in Polymer/Semiconductor-Nanocrystal Composite Devices

In the present day, the information technologies and telecommunications sector continually increase their demand for low cost, low power consumption, high performance electroluminescent devices for display applications. Furthermore, general lighting applications, such as white light and large array colour displays, would also benefit from an increase in the overall efficiency. Several technologies are being investigated to fulfill these needs, such as organic light emitting diodes (OLED), polymeric light emitting diodes (PLED) and field effect emission devices. A new and promising technology is light emitting devices (LEDs) based on nanostructured materials. With organic LEDs (OLEDs) already making an impact on the market in an increasingly large number of applications, hybrid technologies based on organic/inorganic nano-composites are a potential the next step. The incorporation of highefficiency fluorescent semiconductor nanoparticles has been shown to have a beneficial effect on device performance, [1] modify the colour output from the device 2 and provide a simplified route to generation of LED type devices. [3

Fabrication and characterization of red-emitting electroluminescent devices based on thiol-stabilized semiconductor nanocrystals

Thiol-capped CdTe nanocrystals were used to fabricate light-emitting diodes, consisting of an emissive nanocrystal multilayer deposited via layer-by-layer, sandwiched between indium-tin-oxide and aluminum electrodes. The emissive and electrical properties of devices with different numbers of nanocrystal layers were studied. The improved structural homogeneity of the nanocrystal multilayer allowed for stable and repeatable current- and electroluminescence-voltage characteristics. These indicate that both current and electroluminescence are electric-field dependent. Devices were operated under ambient conditions and a clear red-light was detected. The best-performing device shows a peak external efficiency of 0.51% and was measured at 0.35mA/cm2 and 3.3V

Validación de una secuencia didáctica sobre conducción de calor en estudiantes de secundaria mexicanos

El diseño y aplicación de las secuencias didácticas ha tenido un auge en los últimos años en el campo de Didáctica de las Ciencias. Gracias a la dualidad que éstas presentan, es posible manejarlas como objeto de investigación. Es por ello que en esta contribución presentamos los resultados de la aplicación de la secuencia didáctica con el objeto de validarla, al compararla con los modelos iniciales y los modelos alcanzados por los estudiantes (post-intervención) con un modelo teórico propuesto. En el estudio participaron estudiantes mexicanos de segundo año de secundaria (13-15 años). Los resultados indican que después de la intervención el 63% de la muestra se acercó al modelo teórico postulado (27% modelo casi completo y 36% modelo completo). Sin embargo, algunas ideas previas persisten

Radiative capture reaction for 17^{17}Ne formation within a full three-body model

Background: The breakout from the hot Carbon-Nitrogen-Oxigen (CNO) cycles can trigger the rp-process in type I x-ray bursts. In this environment, a competition between $^{15}\text{O}(\alpha,\gamma){^{19}\text{Ne}}$ and the two-proton capture reaction $^{15}\text{O}(2p,\gamma){^{17}\text{Ne}}$ is expected. Purpose: Determine the three-body radiative capture reaction rate for ${^{17}\text{Ne}}$ formation including sequential and direct, resonant and non-resonant contributions on an equal footing. Method: Two different discretization methods have been applied to generate $^{17}$Ne states in a full three-body model: the analytical transformed harmonic oscillator method and the hyperspherical adiabatic expansion method. The binary $p$--$^{15}$O interaction has been adjusted to reproduce the known spectrum of the unbound $^{16}$F nucleus. The dominant $E1$ contributions to the $^{15}\text{O}(2p,\gamma){^{17}\text{Ne}}$ reaction rate have been calculated from the inverse photodissociation process. Results: Three-body calculations provide a reliable description of $^{17}$Ne states. The agreement with the available experimental data on $^{17}$Ne is discussed. It is shown that the $^{15}\text{O}(2p,\gamma){^{17}\text{Ne}}$ reaction rates computed within the two methods agree in a broad range of temperatures. The present calculations are compared with a previous theoretical estimation of the reaction rate. Conclusions: It is found that the full three-body model provides a reaction rate several orders of magnitude larger than the only previous estimation. The implications for the rp-process in type I x-ray bursts should be investigated.Comment: 10 pages, 10 figures. Corrected versio