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

Orlicz spaces for which the Hardy-Littlewood maximal operator is bounded

Let M be the Hardy-Littlewood maximal operator defined by [fórmula matemàtica inclosa a l'article] where the supremum is taken over all cubes Q containing x and IQI is the Lebesgue measure of Q. In this paper we characterize the Orlicz spaces L*ø, associated to N--functions ø, such that Mis bounded in L*ø. We prove that this boundedness is equivalent to the complementary N-function ψ of ø satisfying the Δ2-condition in [0,∞), that is, sups>o ψ (2s) / ψ (s) <∞

Ergodic results for certain contractions on orlicz spaces with fixed points

Let (X, M,ų) be a σ-finite measure space, Lø - Lø (X, M, ų) an Orlicz space associated to an N-function ø and let T : Lø→Lø be a linear operator with a fixed point h ≠ 0 a.e ., such that [fórmula matemàtica inclosa a l'article] and it is either a II 1 -contraction in Lø ∩ L1 or a II II∞ .-contraction in Lø ∩ L∞ The main result of this paper is that for a wide class of N functions ø 0, the ergodic maximal operator associated to T is bounded in L ø. Moreover, for every f € L ø we have the almost everywhere convergence and the norm convergente of certain weighted averages which include the Césàro averages

Two alternative estimation procedures for the negative binomial cure rate model with a latent activation scheme

In this paper two alternative estimation procedures based on the EM algorithm are proposed forthe flexible negative binomial cure rate model with a latent activation scheme. The Weibull modelas well as the log-normal and gamma distributions are also considered for the time-to-event datafor the non-destroyed cells. Simulation studies show the satisfactory performance of the proposedmethodology. The impact of misspecifying the survival function on both components of the model(cured and susceptible) is also evaluated. The use of the new methodology is illustrated with areal data set related to a clinical trial on Phase III cutaneous melanoma patients

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

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

Bartlett and Bartlett-type corrections for censored data from a Weibull distribution

In this paper, we obtain the Bartlett factor for the likelihood ratio statistic and the Bartlett-type correction factor for the score and gradient test in censored data from a Weibull distribution. The expressions derived are simple, we only have to define a few matrices. We conduct an extensive Monte Carlo study to evaluate the performance of the corrected tests in small sample sizes and we show how they improve the original versions. Finally, we apply the results to a real data set with a small sample size illustrating that conclusions about the regressors could be different if corrections were not applied to the three mentioned classical statistics for the hypothesis test

Generalized modified slash Birnbaum–Saunders distribution

In this paper, a generalization of the modified slash Birnbaum-Saunders (BS) distribution is introduced. The model is defined by using the stochastic representation of the BS distribution, where the standard normal distribution is replaced by a symmetric distribution proposed by Reyes et al. It is proved that this new distribution is able to model more kurtosis than other extensions of BS previously proposed in the literature. Closed expressions are given for the pdf (probability density functio), along with their moments, skewness and kurtosis coefficients. Inference carried out is based on modified moments method and maximum likelihood (ML). To obtain ML estimates, two approaches are considered: Newton-Raphson and EM-algorithm. Applications reveal that it has potential for doing well in real problems

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