3,044 research outputs found

    InGaN nano-ring structures for high-efficiency light emitting diodes

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    A technique based on the Fresnel diffraction effect for the fabrication of nano-scale site-controlled ring structures in InGaN/GaN multi-quantum well structures has been demonstrated. The ring structures have an internal diameter of 500 nm and a wall width of 300 nm. A 1 cm-1 Raman shift has been measured, signifying substantial strain relaxation from the fabricated structure. The 9 nm blueshift observed in the cathodoluminescence spectra can be attributed to band filling and/or screening of the piezoelectric field. A light emitting diode based on this geometry has been demonstrated. © 2005 American Institute of Physics.published_or_final_versio

    A systematic comparison of polar and semipolar Si-doped AlGaN alloys with high AlN content

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    Abstract With a view to supporting the development of ultra-violet light-emitting diodes and related devices, the compositional, emission and morphology properties of Si-doped n-type Al x Ga1-x N alloys are extensively compared. This study has been designed to determine how the different Al x Ga1-x N crystal orientations (polar (0001) and semipolar (11–22)) affect group-III composition and Si incorporation. Wavelength dispersive x-ray (WDX) spectroscopy was used to determine the AlN mole fraction (x ≈ 0.57–0.85) and dopant concentration (3 × 1018–1 × 1019 cm−3) in various series of Al x Ga1-x N layers grown on (0001) and (11–22) AlN/sapphire templates by metalorganic chemical vapor deposition. The polar samples exhibit hexagonal surface features with Ga-rich boundaries confirmed by WDX mapping. Surface morphology was examined by atomic force microscopy for samples grown with different disilane flow rates and the semipolar samples were shown to have smoother surfaces than their polar counterparts, with an approximate 15% reduction in roughness. Optical characterization using cathodoluminescence (CL) spectroscopy allowed analysis of near-band edge emission in the range 4.0–5.4 eV as well as various deep impurity transition peaks in the range 2.7–4.8 eV. The combination of spatially-resolved characterization techniques, including CL and WDX, has provided detailed information on how the crystal growth direction affects the alloy and dopant concentrations.</jats:p

    Health care logistics: who has the ball during disaster?

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    In contemporary organizations, a wide gamut of options is available for sustaining and supporting health care operations. When disaster strikes, despite having tenable plans for routine replenishment and operations, many organizations find themselves ill-prepared, ill-equipped, and without effective mechanisms in place to sustain operations during the immediate aftermath of a crisis. Health care operations can be abruptly halted due to the non-availability of supply

    Analysis of defect-related inhomogeneous electroluminescence in InGaN/GaN QW LEDs

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    The inhomogeneous electroluminescence (EL) of InGaN/GaN quantum well light emitting diode structures was investigated in this study. Electroluminescence hyperspectral images showed that inhomogeneities in the form of bright spots exhibited spectrally blue-shifted and broadened emission. Scanning electron microscopy combined with cathodoluminescence (SEM-CL) was used to identify hexagonal pits at the centre of approximately 20% of these features. Scanning transmission electron microscopy imaging with energy dispersive X-ray spectroscopy (STEM-EDX) indicated there may be p-doped AlGaN within the active region caused by the presence of the pit. Weak beam dark-field TEM (WBDF-TEM) revealed the presence of bundles of dislocations associated with the pit, suggesting the surface features which cause the inhomogeneous EL may occur at coalescence boundaries, supported by trends in the number of features observed across the wafer.The European Research Council has provided financial support under the European Community’s Seventh Framework Programme/ ERC grant agreement no. 279361 (MACONS).This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.spmi.2016.03.03

    Football-induced fatigue in hypoxia impairs repeated sprint ability and perceptual-cognitive skills

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    The present study investigated the effects of football-induced fatigue during hypoxia on RS and perceptual-cognitive skills. Ten male semi-professional football players underwent four sessions; a control session (0-m) to quantify RS in a non-fatigued state; and three further sessions at hypoxia (0-m;1500-m;3000-m) examining RS and perceptual-cognitive skill responses for a given physical workload. Anticipation and decision-making accuracy were obtained at the 30-min mark of each half. The mean number of trials (%) in which the player made the correct response was used for analysis. HR, TC, RPE and % saturation of O2 were measured during the warm-up, football-induced fatigue and RS test. It was found that HR, RPE and % saturation of O2 were different between conditions (P<0.05; ES=0.44-6.13). Further, RS were affected by football-induced fatigue for DC (4.8%; P=0.019; ES=0.68) and AV (5.5%; P=0.006; ES=0.79). In hypoxia, it was observed that football-induced fatigue decreased by 6.5% in DC, 6.3% in AV and 3.1% in PV at 1500-m compared to 0-m (P<0.05). Further significant changes were found at 3000-m compared to 0-m decreasing 12.8% in DC, 12.8% in AV and 6.2% in PV (P<0.0005). More pronounced declines in perceptual-cognitive skills were found as altitude increased (5.0-12.5 %; P<0.05; ES=1.17-2.41) and between both halves (5.3-6.7 %; P<0.05). The data demonstrates that the RS test was highly sensitive to fatigue and hypoxia for a given physical load. Simulated matches in hypoxia revealed larger decreases, when compared to normoxia in RS and perceptual-cognitive skills, highlighting the need for optimal acclimatisation strategies, including physical and technical preparation, prior to playing a

    Selective Affimers Recognise the BCL‐2 Family Proteins BCL‐xL and MCL‐1 through Noncanonical Structural Motifs

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    The BCL‐2 family is a challenging group of proteins to target selectively due to sequence and structural homologies across the family. Selective ligands for the BCL‐2 family regulators of apoptosis are useful as probes to understand cell biology and apoptotic signalling pathways, and as starting points for inhibitor design. We have used phage display to isolate Affimer reagents (non‐antibody‐binding proteins based on a conserved scaffold) to identify ligands for MCL‐1, BCL‐xL, BCL‐2, BAK and BAX, then used multiple biophysical characterisation methods to probe the interactions. We established that purified Affimers elicit selective recognition of their target BCL‐2 protein. For anti‐apoptotic targets BCL‐xL and MCL‐1, competitive inhibition of their canonical protein‐protein interactions is demonstrated. Co‐crystal structures reveal an unprecedented mode of molecular recognition; where a BH3 helix is normally bound, flexible loops from the Affimer dock into the BH3 binding cleft. Moreover, the Affimers induce a change in the target proteins towards a desirable drug‐bound‐like conformation. These proof‐of‐concept studies indicate that Affimers could be used as alternative templates to inspire the design of selective BCL‐2 family modulators and more generally other protein‐protein interaction inhibitors

    Optical and structural properties of dislocations in InGaN

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    Threading dislocations in thick layers of InxGa1−xN (5% &amp;lt; x &amp;lt; 15%) have been investigated by means of cathodoluminescence, time-resolved cathodoluminescence, and molecular dynamics. We show that indium atoms segregate near dislocations in all the samples. This promotes the formation of In-N-In chains and atomic condensates, which localize carriers and hinder nonradiative recombination at dislocations. We note, however, that the dark halo surrounding the dislocations in the cathodoluminescence image becomes increasingly pronounced as the indium fraction of the sample increases. Using transmission electron microscopy, we attribute the dark halo to a region of lower indium content formed below the facet of the V-shaped pit that terminates the dislocation in low composition samples (x &amp;lt; 12%). For x &amp;gt; 12%, the facets of the V-defect featured dislocation bundles instead of the low indium fraction region. In this sample, the origin of the dark halo may relate to a compound effect of the dislocation bundles, of a variation of surface potential, and perhaps, of an increase in carrier diffusion length.ER-C Lindemann Trust Fellowshi
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