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Composition Fluctuations (composition + fluctuation)
Selected AbstractsDensity fluctuations in oxide glasses investigated by small-angle X-ray scatteringJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Claire Levelut The structure of glasses is characterized by the existence of density and composition fluctuations on the nanometre scale. We present three examples of the use of small-angle X-ray scattering to get information about these density fluctuations. The thermal history and OH content were observed to have a huge influence. The static compressibility decreases when the OH content or fictive temperature increase. We showed that temperature scanning small-angle X-ray scattering can provide an accurate description of the position, width and shape of the glass transition. [source] Quantitative evaluation of the atomic structure of defects and composition fluctuations at the nanometer scale inside InGaN/GaN heterostructuresPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004P. Ruterana Abstract Investigation is carried out by high-resolution electron microscopy on threading dislocations using data treatments with procedures that allow the extraction of the most likely atomic configurations. We also report In composition fluctuations inside InGaN/GaN quantum wells by coupling HRTEM, image simulation and Finite Element Modelling (FEM) of the thin foil relaxation. The results show that the indium content may be close to x = 1.0 in the clusters and this is much higher that was previously suggested by 2D FEM modelling. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of V/III flux ratio on AlInGaN/AlGaN quantum wells grown by atmospheric pressure MOCVDPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005R. J. Choi Abstract We investigated the structural and optical properties of AlInGaN/AlGaN quantum wells (QWs) and the quaternary AlInGaN epilayers as a function of V/III flux ratio (flow rate of NH3). From the photoluminescence and cathodoluminescence (CL) measurements, the emission wavelengths of the AlInGaN/AlGaN QWs linearly became blueshifted and the intensities decreased with increasing the flow rate of NH3. In the X-ray rocking curve, a pattern of the sample grown at lower NH3 flow rate gives an indication of the good crystalline quality of the films. The monochromated scanning CL image of the AlInGaN epilayers measured at around 80 K showed that more densely and uniformly distributed bright spot densities, indicating In segregation regions, increased at lower NH3 flow rate. Therefore, these results suggest that the relatively decrease of NH3 flow rate results in the increase of In composition fluctuations into the AlInGaN alloys, which generate exciton localized states, and thereby enhances the emission. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Size and shape of In rich clusters and InGaN QWs at the nanometer scalePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005P. Ruterana Abstract Following the need to accurately understand the In composition fluctuations and their role on the optical properties of the GaN based heterostructures, an investigation of MOCVD InGaN/GaN quantum wells is carried out. To this end, quantitative High Resolution Transmission Electron Microscopy (HRTEM) is coupled with image simulation and Finite Element Method (FEM) for the thin foil relaxation modelling. The results show that the indium content can reach x = 1 in the clusters inside the core. In these MOCVD QWs, we attempt to connect the Quantum dot density, composition, and shape to the growth conditions, in order to help the engineering process of highly efficient devices. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ab initio studies of indium separated phases in AlGaInN quaternary alloysPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005M. Marques Abstract In this work, ab initio total energy electronic structure calculations are combined with Monte Carlo simulations to study microscopically the indium separated phases taking place in AlxGayIn1,x,yN quaternary alloys. The presence of aluminum in the InGaN alloy is shown to enhance the phase separation process, compared to the InGaN ternary alloy with the same In compositions. We also observe that even in the stable region of the quaternay alloy there are composition fluctuations towards InGaN- and AlGaN-like alloys formation. From our findings the origin of the emissions which have been observed from AlGaInN quaternary is discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] FTIR microspectroscopy study of composition fluctuations in extruded amylopectin,gelatin blendsBIOPOLYMERS, Issue 4 2001Z. Mousia Abstract The spatial variation in the composition of nonexpanded biopolymer blends prepared by extrusion of mixtures of gelatin with either native or pregelatinized waxy maize starch was studied using a 30-,m aperture FTIR microspectroscopy technique. The ratio of the areas of the "saccharide" bands (953,1180 cm,1) and the amide I and II bands (1483,1750 cm,1) was used to monitor the relative distributions of the two components of the blend. Two calibration methods were used to obtain amylopectin concentration values from the ratios of the IR bands. The results suggested a high degree of heterogeneity in these blends, despite the thorough mixing expected by twin-screw extrusion processing. The concentration fluctuations were greater for the blends produced by extruding gelatin and native waxy maize starch mixtures. This was in agreement with the reduced degree of conversion of the starch granules when extruded in the presence of gelatin. The FTIR 2-dimensional maps obtained suggested that in the blends produced from either native or pregelatinized starch at all concentrations studied (25/75, 50/50, and 75/25 amylopectin/gelatin) the gelatin constituted the continuous phase. The effect of the spatial resolution on the FTIR microspectroscopy results was considered and the proposed interpretation was verified by the use of polarized light microscopy and FTIR microspectroscopy acquired at higher spatial resolution (10 ,m). © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 208,218, 2001 [source] | |||||||||||||