Photoluminescence study of excitons in homoepitaxial GaN

High-resolution photoluminescence spectra have been measured in high-quality homoepitaxial GaN grown on a free-standing GaN substrate with lower residual strain than in previous work. Unusually strong and well-resolved excitonic lines were observed. Based on free- and bound exciton transitions some important GaN parameters are derived. The Arrhenius plot of the free A exciton recombination yields a binding energy of 24.7 meV. Based on this datum, an accurate value for the band-gap energy, EG(4.3 K) = 3.506 eV, can be given. From the donor bound excitons and their “two-electron” satellites, the exciton localization energy and donor ionization energy are deduced. Finally, estimates of the electron and hole masses have been obtained within the effective mass [email protected] ; [email protected]

Spatially resolved X-ray excited optical luminescence

Spatially resolved luminescence distributions in semiconductor heterostructures were investigated by core level excitation using hard X-ray (sub-) microbeams. Compact and mobile XEOL instruments have been developed and well adapted on the hard X-ray beamline ID22 of the European Synchrotron Radiation Facility for different wavelength collection ranges: UV-VIS and NIR. Linked by multimode optical fibers, their special designs provide precise scanning microscopy and allow easy access for multiple detection modes. Based on the hard X-ray microprobe station of ID22, details of the equipments, spectral data and representative examples are briefly described. Data collections from InAs and InGaN quantum heterostructures support the excellent performance of the optical devices. © 2011 Elsevier B.V. All rights reserved.This work was partially supported by the NANOWIRING Marie Curie ITN (EU project No. PITN-GA-2010-265073).Peer Reviewe

Errors of prescription, transcription and administration according to pharmacological group at hospital

Fundamentos: La mayoría de los estudios sobre errores de medicación se centran sólo en hallar prevalencias globales por pacientes, por fases del proceso o según un determinado grupo de fármacos, por lo que se da una visión parcial. El objetivo de este trabajo fue analizar y comparar la prevalencia de errores en prescripción, trascripción y administración y sus repercusiones clínicas en los principales grupos farmacológicos en un hospital de tercer nivel. Métodos: Estudio de inclusión prospectiva con observación directa disfrazada de la administración de medicamentos y comparación con prescripciones médicas y trascripciones presentes en la historia clínica. Los errores de medicación y sus efectos fueron clasificados por consenso de expertos. Se calcularon las diferentes tasas de errores y sus repercusiones con sus intervalos de confianza al 95% y se compararon utilizando la prueba de Chi cuadrado. Resultados: Se estudiaron 5578 fármacos prescritos, aunque se observó sólo la administración de 1879 dosis. Se encontraron un total de 117 grupos farmacológicos, donde el 50,1% (2795) de las prescripciones pertenecían sólo a 9 tipos. La prevalencia de errores de prescripción global fue de 4,79%, de trascripción de 14,61% y de administración 9,32%. Por grupos, las Heparinas tuvieron una menor prevalencia de errores en la fase de prescripción y en la de trascripción. Se obtuvo mayor número de errores en trascripción de los Analgésicos como el Paracetamol y el Metamizol y de los Laxantes, y una prevalencia de errores en administración superior al resto en Analgésicos como el Paracetamol y en los Inhibidores de la Bomba de Protones. Las repercusiones clínicas de los errores de medicación en la fase de prescripción fueron parecidas entre grupos farmacológicos. En trascripción Heparinas y Corticoides presentaron errores más graves, mientras que en la administración fueron los IECAS y las Estatinas (p<0,05). Conclusiones: Los fármacos considerados clásicamente como de alto riesgo presentaron menos errores (Heparinas, Corticoides), pero más graves. Los fármacos con mayor prevalencia de errores fueron los Analgésicos (Paracetamol) y los Inhibidores de la Bomba de Protones, pero tuvieron una menor repercusión clínica.Background: Most studies of medication errors are focused only on finding global prevalence by patients, by phases or according to a certain group of medication. It’s just a partial view of the problem. To analyze and compare the prevalence of errors in prescription, transcription and administration, and their clinical repercussions in different pharmacological groups in a third-level hospital. Methods: Prospective inclusion study with direct observation disguised as medication administration and comparison with prescriptions and transcriptions at history clinical. The ME and its clinical effects were classified by expert consensus. We calculated the different error rates and their repercussions with their confidence intervals at 95%. Then we compared using Chi-square tests. Results: We studied 5,578 prescribed drugs and we observed the administration of 1,879 doses. A total of 117 different pharmacological groups were found, although 50.1% of the prescriptions belonged to only 9 types. We found heparins had a lower prevalence of errors in prescription and transcription and aspirin also had a lower prevalence of prescription errors. On the opposite side, a greater number of errors were obtained in transcription of Paracetamol, Metamizole and Laxatives and a prevalence of errors in the administration phase superior to rest in Paracetamol and in Proton Pump Inhibitors. The impact of medication error increased as medication process progressed, being similar between groups in prescription. In transcription, Heparins and Corticosteroids presented more serious errors. In administration, medication error are more serious for Diuretics and Statins (p <0.05). Conclusions: Drugs considered potentially dangerous present fewer errors (Heparins, Corticoids), but more serious. Drugs with the highest prevalence of errors were Paracetamol and Inhibitors of proton pump but had a lower impact.Este estudio fue objeto de una beca FIS (Fondo de Investigación Sanitaria) con número PI051524, desarrollado durante 2 año

Analysis of the Interferon Gamma (rs2430561, +874T/A) Functional Gene Variant in Relation to the Presence of Cardiovascular Events in Rheumatoid Arthritis

OBJECTIVE: Rheumatoid arthritis (RA) is a chronic inflammatory disease associated with increased cardiovascular (CV) morbidity and mortality. Since interferon-gamma (IFN-γ) has a direct effect on inflammation, in this study we assessed the potential association of the IFNG functional gene variant rs2430561 with CV disease in patients with RA. METHODS: One thousand six hundred and thirty-five patients fulfilling the 1987 American College of Rheumatology classification criteria for RA were genotyped for the IFNG (rs2430561, +874T/A) gene polymorphism using TaqMan genotyping assay. Patients were stratified according to the presence of CV events or not. Logistic regression models to explain the presence of CV disease according to the IFNG rs2430561 allele distribution were performed. The potential influence of this variant in the development of subclinical atherosclerosis was also analyzed in a subgroup of patients with no history of CV events to determine carotid artery intima-media thickness (IMT) (n = 286) and presence of carotid plaques. Levels of the cytokine were determined in a subgroup of patients by ELISA. RESULTS: Adjusted logistic regression model disclosed that presence of the minor allele A was not associated with increased risk of suffering CV events in RA patients. Besides, differences did not achieve statistical significance regarding carotid IMT and presence of carotid plaques in RA patients carrying IFNG rs2430561 variant allele. Levels of IFN-γ were higher in patients who had suffered CV events compared to patients who did not. CONCLUSION: Our results do not support a role of IFNG rs2430561 (+874T/A) functional gene variant in the development of CV disease in RA patients

Probing quantum confinement within single core-multishell nanowires

Theoretically core-multishell nanowires under a cross-section of hexagonal geometry should exhibit peculiar confinement effects. Using a hard X-ray nanobeam, here we show experimental evidence for carrier localization phenomena at the hexagon corners by combining synchrotron excited optical luminescence with simultaneous X-ray fluorescence spectroscopy. Applied to single coaxial n-GaN/InGaN multiquantum-well/p-GaN nanowires, our experiment narrows the gap between optical microscopy and high-resolution X-ray imaging and calls for further studies on the underlying mechanisms of optoelectronic nanodevices. © 2012 American Chemical Society.The authors thank Irina Snigireva and Armando Vicente Sole for their assistance with the SEM measurements and data processing using PyMca, respectively. We thank Remi Tocoulou and Peter Cloetens for their help and the ESRF for the beam time allocated. We also thank Andrei Rogalev for the valuable discussions and Gary Admans for the critical reading of the manuscript. This work has been partially supported by the NANOWIRING Marie Curie ITN (EU project no. PITN-GA-2010-265073), as well as by the EPIC-NANOTICS (TEC2011-29120-C05-04) and Q&C-LIGHT (S2009ESP-1503) from Spanish MEC and CAM, respectively.Martínez Criado, G.; Homs Puron, AA.; Alen, B.; Sans Tresserras, JÁ.; Segura Ruiz, J.; Molina Sánchez, A.; Susini, J.... (2012). Probing quantum confinement within single core-multishell nanowires. Nano Letters. 12(11):5829-5834. https://doi.org/10.1021/nl303178uS58295834121

Silane-induced n-polarity in wires probed by a synchrotron nanobeam

Noncentrosymmetric one-dimensional structures are key driving forces behind advanced nanodevices. Owing to the critical role of silane injection in creating nanosized architectures, it has become a challenge to investigate the induced local lattice polarity in single GaN wires. Thus, if axial and radial structures are well-grown by a silane-mediated approach, an ideal model to study their polar orientations is formed. By combining synchrotron X-ray fluorescence and X-ray excited optical luminescence, we show here experimental evidence of the role of silane to promote the N-polarity, light emission, and elemental incorporation within single wires. In addition, our experiment demonstrates the ability to spatially examine carrier diffusion phenomena without electrical contacts, opening new avenues for further studies with simultaneous optical and elemental sensitivity at the nanoscale

Scanning x-ray excited optical luminescence microscopy in GaN

In this work, an imaging tool to investigate optical inhomogeneities with site and chemical sensitivities has been integrated in a hard x-ray microprobe. Freestanding GaN and epitaxially grown GaN:Mn on -Al2O3 are used to exploit the unprecedented scanning x-ray excited luminescence technique. Optical images of the radiative recombination channels are reported for several impurities and defect centers in sapphire and GaN compounds. Within the experimental accuracy, a visible nonuniformity characterizes the Mn centers in good correlation with former x-ray fluorescence map. Expanding the microprobe versatility, x-ray absorption spectroscopy in both photon collection modes (x-ray excited luminescence and x-ray fluorescence) is finally presented from a freestanding GaN layer.Special thanks are due to Martin Hermann, Martin Eickhoff, and Martin Stutzmann (Walter Schottky Institute) for providing the sample used in this study. The authors are also grateful to Remi Tucoulou as well as Sylvain Laboure for their useful help.Peer reviewe

The effect of reducing dimensionality on the excitonic recombination in InAs/InP heterostructures

In this work we study the exciton recombination of InAs/InP self-organized quantum dots by means of photolumincscence (PL) as a function of temperature and excitation density. Well defined islands, spatially separated in most cases, and with different size distribution, make localized exciton recombination the dominant contribution to the PL spectrum. From our experimental results, we propose the co-existence of two types of islands, one with small height whose contribution to the PL spectra is important in samples with low InAs coverage (below two monolayers), and the properly 3D islands, whose dimensions and sheet concentration increase with the InAs coverage. Good quality structures are obtained for an InAs coverage of about two to three monolayers, showing only one PL band centered around 1.11 eV with a reasonable luiewidth below 40 meV.Peer Reviewe

Formation of intermetallics in Pt/Al system as a function of Pt layer thickness

The properties of metals and alloys are of critical importance and bulk alloying is one of the possibilities to enhance their properties. An alternative method to improve their surface characteristics is surface coating. In the system of our interest, Pt/Al, the formation of intermetallics and their spatial distribution was investigated in thermally annealed systems as a function of coating thickness using intense synchrotron X-ray beams. Whereas the detection of intermetallics within depths was examined by synchrotron μ-X-ray diffraction, changes in coating morphology were studied by scanning electron microscopy. Our results show that the Al21Pt6, Al2Pt, Al3Pt2, AlPt, AlPt2 intermetallics were formed irrespectively of coating thickness. However, the formation of the most dominant phases was strongly influenced by the coating thickness. They also provide new routes to generate specific PtxAly phases with desirable properties based on controllable experimental conditions, opening directions towards properties tunability of a coated system.The authors acknowledge financial support from the National Research Foundation (NRF), South Africa, Grant number 73806

In operando x-ray imaging of nanoscale devices: Composition, valence, and internal electrical fields

We introduce a method for directly imaging depletion layers in operando with elemental specificity and chemical speciation at sub–100 nm spatial resolution applicable to today’s three-dimensional electronic architectures. These typically contain complex, multicomponent designs consisting of epitaxial heterostructures, buried domains, or nanostructures with different shapes and sizes. Although the variety of devices is immense, they commonly rely on carrier separation in a built-in potential induced by composition or strain gradients. To image these, we scanned a focused synchrotron x-ray nanobeam over a single semiconductor nanowire heterostructure and simultaneously measured the current through the device and the emitted characteristic x-rays as a function of the incoming hard x-ray energy. With these results, it is possible to identify the compositional and molecular structure as well as localize the electrical fields present under typical working conditions. This information allows us to draw an energy band diagram consistent with the elemental distribution and a high-resolution chemical speciation map.We acknowledge financial support by the Deutsche Forschungsgemeinschaft (DFG; RO 1198/14-1) and Austrian Science Fund (FWF; No. I 724-N16) under the auspices of the D-A-CH-project “Wiring quantum dots,” the German Ministry for Research and Technology (BMBF) within the project “nano@work” (05K16SJ1), and the ESRF for the allocated beam time. G.M.-C. thanks the partial financial support from Consejo Superior de Investigaciones Científicas through the project 201660I001.We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).Peer Reviewe