65 research outputs found
Imaging non-radiative point defects buried in quantum wells using cathodoluminescence
Crystallographic point defects (PDs) can dramatically decrease the efficiency
of optoelectronic semiconductor devices, many of which are based on quantum
well (QW) heterostructures. However, spatially resolving individual
non-radiative PDs buried in such QWs has so far not been demonstrated. Here,
using high-resolution cathodoluminescence (CL) and a specific sample design, we
spatially resolve, image, and analyse non-radiative PDs in InGaN/GaN QWs. We
identify two different types of PD by their contrasting behaviour with
temperature, and measure their densities from cm to as high as
cm. Our CL images clearly illustrate the interplay between PDs
and carrier dynamics in the well: increasing PD concentration severely limits
carrier diffusion lengths, while a higher carrier density suppresses the
non-radiative behaviour of PDs. The results in this study are readily
interpreted directly from CL images, and represent a significant advancement in
nanoscale PD analysis.Comment: Main text: 8 pages, 6 figures. Supplementary: 11 pages, 8 figure
Beyond cool: adapting upland streams for climate change using riparian woodlands
Managed adaptation could reduce the risks of climate change to the world's ecosystems, but there have been surprisingly few practical evaluations of the options available. For example, riparian woodland is advocated widely as shade to reduce warming in temperate streams, but few studies have considered collateral effects on species composition or ecosystem functions. Here, we use cross-sectional analyses at two scales (region and within streams) to investigate whether four types of riparian management, including those proposed to reduce potential climate change impacts, might also affect the composition, functional character, dynamics and energetic resourcing of macroinvertebrates in upland Welsh streams (UK). Riparian land use across the region had only small effects on invertebrate taxonomic composition, while stable isotope data showed how energetic resources assimilated by macroinvertebrates in all functional guilds were split roughly 50:50 between terrestrial and aquatic origins irrespective of riparian management. Nevertheless, streams draining the most extensive deciduous woodland had the greatest stocks of coarse particulate matter (CPOM) and greater numbers of ‘shredding’ detritivores. Stream-scale investigations showed that macroinvertebrate biomass in deciduous woodland streams was around twice that in moorland streams, and lowest of all in streams draining non-native conifers. The unexpected absence of contrasting terrestrial signals in the isotopic data implies that factors other than local land use affect the relative incorporation of allochthonous subsidies into riverine food webs. Nevertheless, our results reveal how planting deciduous riparian trees along temperate headwaters as an adaptation to climate change can modify macroinvertebrate function, increase biomass and potentially enhance resilience by increasing basal resources where cover is extensive (>60 m riparian width). We advocate greater urgency in efforts to understand the ecosystem consequences of climate change adaptation to guide future actions
A protocol for a trial of homeopathic treatment for irritable bowel syndrome
Background
Irritable bowel syndrome is a chronic condition with no known cure. Many sufferers seek complementary and alternative medicine including homeopathic treatment. However there is much controversy as to the effectiveness of homeopathic treatment. This three-armed study seeks to explore the effectiveness of individualised homeopathic treatment plus usual care compared to both an attention control plus usual care and usual care alone, for patients with irritable bowel syndrome.
Methods/design
This is a three-armed pragmatic randomised controlled trial using the cohort multiple randomised trial methodology. Patients are recruited to an irritable bowel syndrome cohort from primary and secondary care using GP databases and consultants lists respectively. From this cohort patients are randomly selected to be offered, 5 sessions of homeopathic treatment plus usual care, 5 sessions of supportive listening plus usual care or usual care alone. The primary clinical outcome is the Irritable Bowel Syndrome Symptom Severity at 26 weeks.
From a power calculation, it is estimated that 33 people will be needed for the homeopathic treatment arm and 132 for the usual care arm, to detect a minimal clinical difference at 80 percent power and 5 percent significance allowing for loss to follow up. An unequal group size has been used for reasons of cost. Analysis will be by intention to treat and will compare homeopathic treatment with usual care at 26 weeks as the primary analysis, and homeopathic treatment with supportive listening as an additional analysis.
Discussion
This trial has received NHS approval and results are expected in 2013.
Trial registration
Current Controlled Trials ISRCTN9065114
Protein and lipid metabolism adjustments in silver catfish (Rhamdia quelen) during different periods of fasting and refeeding
Characterisation of InGaN by Photoconductive Atomic Force Microscopy.
Nanoscale structure has a large effect on the optoelectronic properties of InGaN, a material vital for energy saving technologies such as light emitting diodes. Photoconductive atomic force microscopy (PC-AFM) provides a new way to investigate this effect. In this study, PC-AFM was used to characterise four thick (∼130 nm) In x Ga 1 - x N films with x = 5%, 9%, 12%, and 15%. Lower photocurrent was observed on elevated ridges around defects (such as V-pits) in the films with x ≤ 12 %. Current-voltage curve analysis using the PC-AFM setup showed that this was due to a higher turn-on voltage on these ridges compared to surrounding material. To further understand this phenomenon, V-pit cross sections from the 9% and 15% films were characterised using transmission electron microscopy in combination with energy dispersive X-ray spectroscopy. This identified a subsurface indium-deficient region surrounding the V-pit in the lower indium content film, which was not present in the 15% sample. Although this cannot directly explain the impact of ridges on turn-on voltage, it is likely to be related. Overall, the data presented here demonstrate the potential of PC-AFM in the field of III-nitride semiconductors
InGaN/GaN QWs on Si
<p>Dataset for the project of high TD density QWs grown on Si, published <a href="https://doi.org/10.3390/nano13182569">here</a>.</p><p>The different sub-datasets are named after:</p><ul><li>the measurement technique, from [ Atomic Force Microscopy (AFM) ; Cathodoluminescence (CL) mapping ; Power-dependent photoluminescence (PL) series (P-series) ; Scanning Electron Micrographs (SEM) ; Temperature-dependent P-series (T-P-series) ; Transmission Electron Microscopy (TEM) ; Time-resolved PL (TRPL) ];</li><li>the sample name, from [ R = A4286 ; U = A4287 ; V = A4289 ].</li></ul><p>Further relevant information can be found in the .zip folders, in README files.</p>
Investigation of the Impact of Point Defects in InGaN/GaN Quantum Wells with High Dislocation Densities
In this work, we report on the efficiency of single InGaN/GaN quantum wells (QWs) grown on thin (9 cm−2) is much lower than that of TD (2–3 × 1010 cm−2). Time-resolved photoluminescence and cathodoluminescence studies confirm the prevalence of point defects over TDs in QW efficiency. Interestingly, TD terminations lead to the formation of independent domains for carriers, thanks to V-pits and step bunching phenomena
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