The effect of rapid thermal annealing on the photoluminescence of InAsN/InGaAs dot-in-a-well structures

The effect of post-growth rapid thermal annealing on the optical characteristics of InAsN/InGaAs dot-in-a-well DWELL structures grown by molecular beam epitaxy on GaAs(1 0 0) has been studied. InAs/InGaAs DWELL structures have been used as a reference. Photoluminescence measurements of these samples show similar optical effects, such as a blueshift of the peak wavelength and a reduction of the full width of at half maximum PL emission, in both types of structures up to an annealing temperature of 750 °C. Nevertheless, at 850 °C, these effects are much more pronounced in the structures with N. These results suggest that an additional As–N interdiffusion process inside the InAsN quantum dots plays a dominant role in these effects at high annealing temperatures (850 °C) on InAsN/InGaAs structures

The influence of Ga composition of GaInAsN QDs on N incorporation.

Currently, dilute nitride III-N-As semiconductors, such as InGaAsN/GaAs quantum well material system, allow to develop very competitive lasers at long wavelength emission (1.3 µm). However, longer wavelengths, such as 1.55 µm, are very difficult to achieve without making worse the performance of the device. Alternatively, as it is well known, great efforts are being devoted to the study of dilute nitride III-N-As quantum dots (QDs) semiconductor [1]. Mainly, this is due to the attractive advantages that they show over other materials and structures: the strong reduction in the bandgap of the III-As semiconductor by adding even a few percent of nitrogen into them, and the interesting physical properties that the QDs offer to laser characteristics (e.g. low threshold current, etc

Optimization of InGaAsN(Sb)/GaAs quantum dots for optical emission at 1.55 µm with low optical degradation

Low optical degradation in GaInAsN(Sb)/GaAs quantum dots (QDs) p–i–n structures emitting up to 1.55 μm is presented in this paper. We obtain emission at different energies by means of varying N content from 1 to 4%. The samples show a low photoluminescence (PL) intensity degradation of only 1 order of magnitude when they are compared with pure InGaAs QD structures, even for an emission wavelength as large as 1.55 μm. The optimization studies of these structures for emission at 1.55 μm are reported in this work. High surface density and homogeneity in the QD layers are achieved for 50% In content by rapid decrease in the growth temperature after the formation of the nanostructures. Besides, the effect of N and Sb incorporation in the redshift and PL intensity of the samples is studied by post-growth rapid thermal annealing treatments. As a general conclusion, we observe that the addition of Sb to QD with low N mole fraction is more efficient to reach 1.55 μm and high PL intensity than using high N incorporation in the QD. Also, the growth temperature is determined to be an important parameter to obtain good emission characteristics. Finally, we report room temperature PL emission of InGaAsN(Sb)/GaAs at 1.4 μm

Evaluation of the In desorption during the capped process in diluted nitride In(Ga)As quantum dots

Diluted nitride self-assembled In(Ga)AsN quantum dots (QDs) grown on GaAs substrates are potential candidates to emit in the windows of maximum transmittance for optical fibres (1.3-1.55 μm). In this paper, we analyse the effect of nitrogen addition on the indium desorption occurring during the capping process of InxGa1−xAs QDs (x = l and 0.7). The samples have been grown by molecular beam epitaxy and studied through transmission electron microscopy (TEM) and photoluminescence techniques. The composition distribution inside the dots was determined by statistical moiré analysis and measured by energy dispersive X-ray spectroscopy. First, the addition of nitrogen in In(Ga)As QDs gave rise to a strong redshift in the emission peak, together with a large loss of intensity and monochromaticity. Moreover, these samples showed changes in the QDs morphology as well as an increase in the density of defects. The statistical compositional analysis displayed a normal distribution in InAs QDs with an average In content of 0.7. Nevertheless, the addition of Ga and/or N leads to a bimodal distribution of the Indium content with two separated QD populations. We suggest that the nitrogen incorporation enhances the indium fixation inside the QDs where the indium/gallium ratio plays an important role in this process. The strong redshift observed in the PL should be explained not only by the N incorporation but also by the higher In content inside the QD

Emphysema model in rats exposed to tobacco smoke. Morphometric and functional analysis

Several models of chronic obstructive pulmonary disease (COPD) in mice have been developed; the most similar to the habit of smoking is the inhalation of the smoke in mice. The objective was to develop and implement an experimental model of COPD in mice through the passive inhalation of smoke and demonstrate the physiological changes on ventilatory function and its correlation with 3 emphysema quantification methods. Materials and methods: Twenty Wistar mice were included in an experimental and control group. The experimental group was exposed to tobacco smoke, and we performed several pulmonary functional tests and imaging techniques. Results: Pulmonary function tests showed the volume expiration in the first second (VEF1) differs significantly between groups (p < 0.001). Pulmonary compliance was reduced in the experimental group by 50% in comparison to the control group (male vs control p < 0.001). Morphometric analysis: 17% reduction in lung volume with a destructive index (DI) of 45%. The intersection test had a DI of 43%. The free point test showed a DI of 44%. Conclusions: The implementation of our model generated the presence of emphysema and alterations in the lung physiology in the experimental group. We demonstrated evidence of 90% with emphysem

Frecuencia de aislamientos de Klebsiella pneumoniae multirresistente en pacientes ingresados en los diferentes servicios del Hospital Nacional Rosales.

La resistencia a los antimicrobianos representa un problema de salud pública emergente a nivel mundial declarado así por la Organización Mundial de la Salud. Los pacientes con infecciones causadas por bacterias farmacorresistentes corren mayor riesgo de muerte, además consumen más recursos sanitarios que los infectados por cepas no resistentes de las mismas bacterias u otras de diferente género. La resistencia de Klebsiella pneumoniae, una enterobacteria parte de la microbiota normal, que puede causar infecciones potencialmente mortales supera el tratamiento utilizado como último recurso (los antibióticos carbapenémicos) en casos de infecciones nosocomiales. Además de dar a conocer la naturaleza química de los antibióticos utilizados y cómo interactúan para estimular la producción de plásmidos de resistencia bacteriana. Pretendemos abordar de una manera muy extensa los principales hallazgos y estudios realizados en diferentes partes del mundo así también explicaremos el proceso de aislamiento que está estandarizado por el Ministerio de Salud Pública y Asistencia Social, equipos y procedimientos de diagnóstico implementados en el área de Bacteriología del Hospital Nacional Rosales. Todo con el fin de contar con un estudio integral y con datos actualizados, confiables y reales que permitan conocer la situación actual de la problemática

Resonant Raman-active localized vibrational modes in AlyGa{1-y}NxAs{1-x} alloys: Experiment and firstprinciples calculations

The localized vibrational modes associated with substitutional aluminium and nitrogen atoms in AlyGa1−yNxAs1−x have been studied within first-principles density functional theory using a supercell approach. Localized vibrational modes related to N-AlmGa4−m (1≤m≥4) complexes have been identified, which reveal the formation of N-Al4 units well above random abundance, in qualitative agreement with a large calculated value (391 meV) of the Al-N bond formation energy. We determine the resonant Raman-active modes from the selection rule obtained by calculating the electron-phonon coupling strength and optical transition matrix elements and compare them with resonant Raman spectroscopy measurements. The localized modes from Raman scattering measurements with frequencies around 325, 385, 400, 450, 500, and 540 cm−1 are found to be in good agreement with the calculated modes (326, 364, 384, 410, 456, 507, and 556 cm−1). The modes are classified as follows: the two modes at 326 and 556 cm−1 belong to the N-AlGa3 configuration; there are three modes which belong to N-Al2Ga2 with frequencies at 326, 364, and 507 cm−1; the N-Al3Ga configuration gives rise to modes whose frequencies are 384 and 456 cm−1; and the mode at a frequency of 410 cm−1 belongs to the N-Al4 complex. The comparison of line intensities from samples before and after rapid thermal annealing allows us to experimentally distinguish vibrational modes associated with different clusters, in agreement with the theoretical assignments

VAMOS: a Pathfinder for the HAWC Gamma-Ray Observatory

VAMOS was a prototype detector built in 2011 at an altitude of 4100m a.s.l. in the state of Puebla, Mexico. The aim of VAMOS was to finalize the design, construction techniques and data acquisition system of the HAWC observatory. HAWC is an air-shower array currently under construction at the same site of VAMOS with the purpose to study the TeV sky. The VAMOS setup included six water Cherenkov detectors and two different data acquisition systems. It was in operation between October 2011 and May 2012 with an average live time of 30%. Besides the scientific verification purposes, the eight months of data were used to obtain the results presented in this paper: the detector response to the Forbush decrease of March 2012, and the analysis of possible emission, at energies above 30 GeV, for long gamma-ray bursts GRB111016B and GRB120328B.Comment: Accepted for pubblication in Astroparticle Physics Journal (20 pages, 10 figures). Corresponding authors: A.Marinelli and D.Zaboro