The dissociation of (a+c) misfit dislocations at the InGaN/GaN interface

(a+c) dislocations in hexagonal materials are typically observed to be dissociated into partial dislocations. Edge (a+c) dislocations are introduced into (0001) nitride semiconductor layers by the process of plastic relaxation. As there is an increasing interest in obtaining relaxed InGaN buffer layers for the deposition of high In content structures, the study of the dissociation mechanism of misfit (a+c) dislocations laying at the InGaN/GaN interface is then crucial for understanding their nucleation and glide mechanisms. In the case of the presented plastically relaxed InGaN layers deposited on GaN substrates we observe a trigonal network of (a+c) dislocations extending at the interface with a rotation of 3 degrees from directions. High resolution microscopy studies show that these dislocations are dissociated into two Frank-Shockley 1/6 partial dislocations with the I1 BSF spreading between them. Atomistic simulations of a dissociated edge (a+c) dislocation revealed a 3/5 atom ring structure for the cores of both partial dislocations. The observed separation between two partial dislocations must result from the climb of at least one of the dislocations during the dissociation process, possibly induced by the mismatch stress in the InGaN layer.Comment: This is a submitted version of the manuscript published in Journal of Microscop

Segregation of In to dislocations in InGaN.

Dislocations are one-dimensional topological defects that occur frequently in functional thin film materials and that are known to degrade the performance of InxGa1-xN-based optoelectronic devices. Here, we show that large local deviations in alloy composition and atomic structure are expected to occur in and around dislocation cores in InxGa(1-x)N alloy thin films. We present energy-dispersive X-ray spectroscopy data supporting this result. The methods presented here are also widely applicable for predicting composition fluctuations associated with strain fields in other inorganic functional material thin films.This work was funded in part by the Cambridge Commonwealth trust, St. John’s College and the EPSRC. SKR is funded through the Cambridge-India Partnership Fund and Indian Institute of Technology Bombay via a scholarship. MAM acknowledges support from the Royal Society through a University Research Fellowship. Additional support was provided by the EPSRC through the UK National Facility for Aberration-Corrected STEM (SuperSTEM). The Titan 80- 200kV ChemiSTEMTM was funded through HM Government (UK) and is associated with the capabilities of the University of Manchester Nuclear Manufacturing (NUMAN) capabilities. SJH acknowledges funding from the Defence Treat Reduction Agency (DTRA) USA (grant number HDTRA1-12-1-0013).This is the accepted manuscript. The final version is available at http://pubs.acs.org/doi/abs/10.1021/nl5036513

Lagomorpha as a model morphological system

Due to their global distribution, invasive history, and unique characteristics, European rabbits are recognizable almost anywhere on our planet. Although they are members of a much larger group of living and extinct mammals [Mammalia, Lagomorpha (rabbits, hares, and pikas)], the group is often characterized by several well-known genera (e.g., Oryctolagus, Sylvilagus, Lepus, and Ochotona). This representation does not capture the extraordinary diversity of behavior and form found throughout the order. Model organisms are commonly used as exemplars for biological research, but there are a limited number of model clades or lineages that have been used to study evolutionary morphology in a more explicitly comparative way. We present this review paper to show that lagomorphs are a strong system in which to study macro- and micro-scale patterns of morphological change within a clade that offers underappreciated levels of diversity. To this end, we offer a summary of the status of relevant aspects of lagomorph biology.Brian Kraatz, Rafik Belabbas, Łucja Fostowicz-Frelik, De-Yan Ge, Alexander N. Kuznetsov, Madlen M. Lang ... et al

Energetics and core structure of the undissociated basal screw dislocation in wurtzite GaN

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Pressure induced phase transitions and elastic properties of CaCO3 polymorphs: a density functional theory study

First-principles calculations, based on density functional theory, were carried out to investigate phase transitions, structural and elastic properties of three polymorphs of calcium carbonate, in the pressure range up to 40 GPa. Our calculations led to the following stability sequence: calcite-IIIb → calcite-III → calcite-IIIb → calcite-VI, where phase transitions of the first order occur at 4.3 GPa, 14.9 GPa and 18.2 GPa, respectively. From 4.3 to 40 GPa, the elastic properties, the acoustic wave velocities and the Debye temperature of each polymorph exhibit a linear dependence over pressure. A nonlinear behavior is observed from 2.0 to 4.3 GPa for the properties of calcite-IIIb. As there are no available experimental data on the elastic properties of calcite-III, calcite-IIIb, calcite-VI and their pressure dependence, our present findings can serve to a better understanding of the behavior of calcium carbonate in the Earth's mantle

Core properties and the role of screw dislocations in the bulk n-type conductivity in InN

International audienceFirst principles calculations, based on density functional theory, have been carried out to investigate the role of screw dislocations in the bulk n-type conductivity which is usually observed in indium nitride. Energetics, atomic and electronic structures of different core configurations of dislocations, running along the [0001] polar or along the [1120] non-polar direction, have been determined and compared. This enabled inspection of the modifications in the properties of screw dislocations when the growth direction is changed. For the c-type screw dislocation, the configuration with a double 6-atom ring, involving wrong bonds was revealed as a ground state configuration, and for the a-type screw dislocation, the shuffle configuration was found to be energetically favoured over glide ones. Unlike core configurations of the a-type screw dislocation, those of the c-type screw dislocation have their Fermi levels pinned in the conduction band and thus act as a source of non-intentional n-type conductivity. This demonstrates that eliminating the contribution of screw dislocations to the n-type conductivity can be achieved by growing wurtzite InN along the non-polar direction. © the Owner Societies

First-principles calculations of threading screw dislocations in AlN and InN

International audienceThe threading screw dislocation in AlN and InN, two technologically important nitride-based materials, has been studied using first-principles calculations. By performing a comprehensive search for the most stable core configuration, several original core structures have been obtained depending on experimental conditions. In Al-rich and In-rich conditions, screw dislocation cores exhibit a metalliclike character, predicted to provide pathways to leakage currents in III-N based electronic devices. Specifical to AlN, most stable core geometries in N-rich conditions are shown to contain nitrogen atoms organized like nitrogen molecules. Finally, our investigations revealed that in InN dislocation cores are associated to partial or complete closure of the gap and to the injection of electrons into the bulk conduction band

Colic malakoplakia : about a case with review of literature

La Malakoplakie est une affection inflammatoire chronique qui a surtout été décrite au niveau de l'appareil génito-urinaire. Nous rapportons le cas d'un patient âgé de 41 ans, en mauvais état général, ayant présenté depuis plusieurs années une diarrhée chronique mise sur le compte d'une colopathie fonctionnelle. Le reste de l'examen clinique était sans particularité et le bilan biologique montrait essentiellement une baisse modérée du fer sérique. La coloscopie met en évidence la présence de polypes et pseudo-polypes, d'ulcérations ct de pseudo-tumeurs disséminés au niveau de tout le cadre colique. L'examen histopathologique des multiples biopsies prélevées au niveau de ces différentes lésions révélaient une infiltration du chorion par des nappes constituées d'histiocytes macrophages abritant des corps de Michaelis Gutmann Von Kossa faiblement positifs et PAS fortement positifs. L'étude immuno-histochimique utilisant l'anticorps anti-CD68 montrait un immuno-marquage cytoplasmique au niveau de quelques histiocytes. Ces résultats confortent l'une des théories histopathogéniques de l'affection qui serait essentiellement due à une infection par une souche non-spécifique d'Escherichia coli et pourrait être secondaire à un défaut d'activité enzymatique phagocytaire des histiocytes. Le patient a très bien répondu au traitement par la ciprofloxacine. Il est actuellement sous surveillance régulière et bénéficiera éventuellement d'une coloscopie de contrôle. Les examens endoscopique et histopathologique ont donc été indispensables dans le diagnostic de cette affection qui a bien évolué sous traitement médical, ce qui a permis au patient de reprendre une vie normale

Microstructure analysis and mechanical properties by instrumented indentation of Charonia Lampas Lampas shell

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Core properties and mobility of the basal screw dislocation in wurtzite GaN: a density functional theory study

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