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Crystal Defects (crystal + defect)
Selected AbstractsProcess induced disorder in crystalline materials: Differentiating defective crystals from the amorphous form of griseofulvinJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2008Tao Feng Abstract This research investigates milling induced disorder in crystalline griseofulvin. Griseofulvin was subjected to cryogenic milling for various lengths of time. For comparison, the amorphous form of griseofulvin was also prepared by the quench melt method. Different analytical techniques were used to study the differences between the cryomilled, amorphous and crystalline forms of the drug. Cryogenic milling of griseofulvin progressively reduces the crystallinity of the drug by inducing crystal defects, rather than amorphous materials. Raman analysis provides evidence of structural differences between the two. The differences between the defective crystals produced by milling and the amorphous form are significant enough as to be measurable in their bulk thermal properties. Defective crystals show significant decrease in the heat of fusion as a function of milling time but do not exhibit a glass transition nor recrystallization from the amorphous form. Crystal defects undergo recrystallization upon heating at temperatures well below the glass transition temperature (Tg) in a process that is separate and completely independent from the crystallization of the amorphous griseofulvin, observed above Tg. Physical mixtures of defective crystals and amorphous drug demonstrate that the thermal events associated with each form persist in the mixtures, unaffected by the presence of the other form. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97: 3207,3221, 2008 [source] Three-dimensional visualization of the inner structure of single crystals by step-scanning white X-ray section topographyJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2006Taihei Mukaide Visualization of the three-dimensional distribution of the crystal defects of large single crystals of calcium fluoride has been demonstrated by white X-ray section topography using sheet-like X-rays (BL28B2 at SPring-8). An image of the three-dimensional distribution of the crystal defects was reconstructed by stacking section topographs, which expressed the images of cross sections of the sample. The section topographs were recorded using a CMOS flat-panel imager or a CCD detector combined with scintillator (Gd2O2S:Tb) and relay lens system. The section topographs were measured by repeating cycles of exposure and sample translation along the direction perpendicular to the top face of the sample. Using high-brilliance and high-energy white X-rays (,60,keV) efficiently, visualization of the three-dimensional structure of subgrains of a sample of up to 60,mm in diameter was achieved. Furthermore, the three-dimensional distribution of the glide plane in the crystal was visualized by reconstructing the linear contrast of the glide plane. [source] Nanometric crystal defects in transmission electron microscopyMICROSCOPY RESEARCH AND TECHNIQUE, Issue 5 2006Robin Schäublin Abstract Transmission electron microscopy (TEM) is revisited in order to define methods for the identification of nanometric defects. Nanometric crystal defects play an important role as they influence, generally in a detrimental way, physical properties. For instance, radiation-induced damage in metals strongly degrades mechanical properties, rendering the material stronger but brittle. The difficulty in using TEM to identify the nature and size of such defects resides in their small size. TEM image simulations are deployed to explore limits and possible ways to improve on spatial resolution and contrast. The contrast of dislocation loops, cavities, and a stacking fault tetrahedra (SFT) are simulated in weak beam, interfering reflections (HRTEM), and scanned condensed electron probe (STEM) mode. Results indicate that STEM is a possible way to image small defects. In addition, a new objective aperture is proposed to improve resolution in diffraction contrast. It is investigated by simulations of the weak beam imaging of SFT and successfully applied in experimental observations. Microsc. Res. Tech. 69:305,316, 2006. © 2006 Wiley-Liss, Inc. [source] Electron microscopy of InGaN nanopillars spontaneously grown on Si(111) substratesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2010Th. Kehagias Abstract The mopholological, structural and chemical properties of InxGa1,xN nanopillars directly grown on Si (111) substrates, by molecular beam epitaxy, were investigated employing transmission electron microscopy related techniques. Single crystalline, single phase nanopillars were observed exhibiting a low density of crystal defects, which contribute to good crystal quality. Initial nanostructures merge through subgrain boundaries to form final nanopillars. Energy dispersive X-ray analysis revealed a very low InN mole fraction near the interface with the substrate, owing to high desorption rates from the elevated growth temperature, and gradually higher In incorporation rates near the tips of the nanopillars. This compositional fluctuation is maintained due to poor segregation of indium adatoms along the c-axis of the nanopillars towards the Si interface. A second species of long and narrow nanopillars was found In-free. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synchrotron microscopy and spectroscopy for analysis of crystal defects in siliconPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2009Winfried Seifert Abstract The paper discusses the synchrotron-based microprobe techniques XBIC (X-ray beam induced current), ,-XRF (X-ray fluorescence microscopy) and ,-XAS (X-ray absorption microspectroscopy) and their application for studying electrical activity of defects and precipitation of transition metals in Si materials. Investigations were performed on samples of block-cast multicrystalline Si and on model samples cut from a bonded monocrystalline wafer. To analyze the precipitation sites, Ni, Cu and Fe were introduced intentionally into the samples. The detected precipitates were found to consist of silicides. Evidence for metal precipitates was also found in virtually uncontaminated as-grown block-cast Si. Besides Ni precipitates detected at a recombination active grain boundary, particles containing one or several metals (Cu, Fe, Ti, V) were observed. Unexpectedly, these particles seem to exhibit low only recombination activity. Further studies are necessary to identify their nature. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Non-periodicity in nanoparticles with close-packed structuresACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2010Andrey Rempel Experimentally it is observed that nanomaterials from II,VI compounds like CdS have a high density of stacking faults. It is argued that these are not crystal defects but rather that they represent a characteristic feature of nanomaterials. [source] Excitons in AgI,oxide particle composites: AgI,SrTiO3PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2006Fumito Fujishiro Abstract We fabricated (x)AgI,(1,x)SrTiO3 fine particle composites over a wide composition range of 0,100 mol% AgI. It is found that the dispersion of SrTiO3 fine particles enhances the ionic conductivity and (0.6)AgI,(0.4)SrTiO3 has the highest ionic conductivity (1.68 × 10,4 S/cm which is two hundreds times in comparison with that of pristine AgI), for the first time. In order to clarify such ionic conductivity enhanced by dispersing SrTiO3 fine particles into AgI, the photoluminescence measurements were carried out at different temperatures between 10 K and room temperature under different photoexcitation intensities, together with the structural and morphological studies (X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray fluorescence spectroscopy). The spectra consist of free exciton luminescence band and several broad luminescence bands due to the excitons trapped at crystal defects and residual impurities. The free exciton luminescence band almost disappears at x = 0.6, which may suggest the existence of considerable number of non-radiative traps (crystal defects) at the AgI/SrTiO3 particle interfaces. Such crystal defects may act as ionic pathways. The structural and morphological studies confirm the randomly-stacked ,AgI/,AgI heterostructures at the AgI/SrTiO3 particle interfaces. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The effect of Ge doping for lattice-mismatched InGaP/InP (100) with epitaxial lateral overgrowthPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006Kenichi Higuchi Abstract We have proposed the use of 1.3 ,m InGaAs/InGaP laser on an InP (100) substrate to reduce the leakage current. Because of the lattice-mismatch between InP and InGaP, epitaxial lateral overgrowth (ELO) technique is used. Ge doping is an effective way of increasing the amount of lateral growth in InP/InP lattice-matched ELO. In the InGaP/InP lattice-mismatched ELO, the crystal defects of the Ge-doped InGaP layer decrease compared to undoped sample. The Ge doping is effective for growing InGaP/InP with high crystalline quality by ELO. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Integration of CdSe quantum dots with GaN optoelectronic materialsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005J. G. Pagan Abstract Material structures on the nanoscale can enable enhancement of optoelectronic device performance. For example, in the InGaN active layers of MOCVD grown blue light emitting diodes, indium segregation plays a critical role in the interplay between blue luminescent channels and non-radiative recombination centers such as crystal defects. Unfortunately, high efficiency luminescence of InGaN does not extend into the "deep green" spectral region, around the wavelength of peak human eye response. We are investigating whether commercially available luminescent nanostructures such as CdSe quantum dots can be incorporated into III-nitride devices to extend their high-efficiency performance into the "deep green". Surfactant stabilized CdSe particles in liquid dispersions are drop-cast onto HVPE grown GaN. Physical properties of resultant CdSe surface structures are examined. Luminescence is reported before and after subsequent growth of GaN. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Quantitative evaluation of shunts in solar cells by lock-in thermographyPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 8 2003O. Breitenstein Abstract Infrared lock-in thermography allows to image shunts very sensitively in all kinds of solar cells and also to measure dark currents flowing in certain regions of the cell quantitatively. After a summary of the physical basis of lock-in thermography and its practical realization, four types of quantitative measurements are described: local I,V characteristics measured thermally up to a constant factor (LIVT); the quantitative measurement of the current through a local shunt; the evaluation of the influence of shunts on the efficiency of a cell as a function of the illumination intensity; and the mapping of the ideality factor n and the saturation current density J0 over the whole cell. The investigation of a typical multicrystalline solar cell shows that the shunts are predominantly responsible for deterioration of the low-light-level performance of the cell, and that variations of the injection current density related to crystal defects are predominantly determined by variation of J0 rather than of n. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||