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Planar Defects (planar + defect)
Selected AbstractsHigh Purity GaAs Nanowires Free of Planar Defects: Growth and Characterization,ADVANCED FUNCTIONAL MATERIALS, Issue 23 2008Hannah J. Joyce Abstract We investigate how to tailor the structural, crystallographic and optical properties of GaAs nanowires. Nanowires were grown by Au nanoparticle-catalyzed metalorganic chemical vapor deposition. A high arsine flow rate, that is, a high ratio of group V to group III precursors, imparts significant advantages. It dramatically reduces planar crystallographic defects and reduces intrinsic carbon dopant incorporation. Increasing V/III ratio further, however, instigates nanowire kinking and increases nanowire tapering. By choosing an intermediate V/III ratio we achieve uniform, vertically aligned GaAs nanowires, free of planar crystallographic defects, with excellent optical properties and high purity. These findings will greatly assist the development of future GaAs nanowire-based electronic and optoelectronic devices, and are expected to be more broadly relevant to the rational synthesis of other III,V nanowires. [source] Building Nanocrystalline Planar Defects within Self-Assembled Photonic Crystals by Spin-Coating,ADVANCED MATERIALS, Issue 9 2006R. Pozas A new type of 2D defect within artificial opals is presented. Sequential deposition of a colloidal crystal by convective self-assembly and a slab of oxide nanocrystals by spin-coating gives rise to heterostructures (as shown in the figure). The nanocrystalline layer behaves as an optical dopant, opening transmission windows within the forbidden frequency interval of the lattice, as can be seen in the superimposed transmittance spectra. [source] Dielectric Planar Defects in Colloidal Photonic Crystal Films,ADVANCED MATERIALS, Issue 4 2004N. Tétreault A straightforward synthetic route to produce colloidal photonic crystals containing dielectric planar defects of controlled thickness (see Figure) is presented. Allowed states that arise within the stop band as a result of this doping greatly modify the reflectance properties of the crystals, in good agreement with theoretical predictions. [source] Structural Analysis on Planar Defects Formed in WC Platelets in Ti-Doped WC,CoJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006Sabine Lay Platelet-reinforced WC,Co alloys are processed by liquid-phase sintering from very fine-grained WC powders in the presence of small amounts of TiC. Large and flat WC grains develop in the material. The microstructure of these platelets is investigated by high-resolution electron microscopy in order to obtain information on their formation mechanism. Inside the grains, an extended defect parallel to the basal plane is observed. It can be described by a pair of stacking faults with a shear vector equal to 1/3 ,0-110, occurring in two successive (0001) planes. At the level of the faults, the plane spacing is slightly reduced. The defect area is similar to a thin cubic layer about 0.5 nm thick at the interior of the platelet. The enhanced grain growth of the platelets is likely related to the presence of the defect area. [source] Variational approach to the free-discontinuity problem of inverse crack identificationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2008R. TsotsovaArticle first published online: 17 DEC 200 Abstract This work presents a computational strategy for identification of planar defects (cracks) in homogenous isotropic linear elastic solids. The underlying strategy is a regularizing variational approach based on the diffuse interface model proposed by Ambrosio and Tortorelli. With the help of this model, the sharp interface problem of crack identification is split into two coupled elliptic boundary value problems solved using the finite element method. Numerical examples illustrate the application of the proposed approach for effective reconstruction of the position and the shape of a single crack using only the information collected on the surface of the analyzed body. Copyright © 2007 John Wiley & Sons, Ltd. [source] Dielectric Planar Defects in Colloidal Photonic Crystal Films,ADVANCED MATERIALS, Issue 4 2004N. Tétreault A straightforward synthetic route to produce colloidal photonic crystals containing dielectric planar defects of controlled thickness (see Figure) is presented. Allowed states that arise within the stop band as a result of this doping greatly modify the reflectance properties of the crystals, in good agreement with theoretical predictions. [source] X-ray Diffraction Investigations of Microstructure of Calcium Hydroxide Crystallites in the Interfacial Transition Zone of ConcreteJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2003Valeri S. Harutyunyan This work presents theoretical and experimental X-ray diffractometry investigations of the morphology and deformation state of calcium hydroxide (Ca(OH)2, CH) crystallites in the interfacial transition zone of concrete. Based on the developed theoretical approach, the distributions of CH crystallites and their coherent domains over strains and sizes are reconstructed. The average amounts of planar defects, cracks, and possible stacking faults within a CH crystallite are estimated. A comparative analysis is conducted for the morphology of CH texture depending on the type of aggregate particles (granite and smoky quartz) used. [source] Fabrication of high performance 3C-SiC vertical MOSFETs by reducing planar defectsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2008Hiroyuki Nagasawa Abstract The planar defect density of 3C-SiC can be reduced by growing it on undulant-Si substrates. However, specific stacking faults (SFs) remain, that expose the Si-face on the (001) surface. These residual SFs increase the leakage current in devices made with 3C-SiC. They can be eliminated using an advanced SF-reduction method called switch-back epitaxy (SBE) that combines polarity conversion with homoepitaxial growth. Vertical metal,oxide,semiconductor field-effect-transistors (MOSFETs) are fabricated on 3C-SiC with SBE, varying in size from a single cell with an area of (30 × 30) ,m2 to 12,000 hexagonal cells on a (3 × 3) mm2 chip. The MOSFET characteristics suggest that currents greater than 100 A are realistic for blocking voltages of 600,1,200 V by increasing the number of cells with reduced cell-pitch. The combination of blocking voltage capability with a demonstrable high current capacity shows that 3C-SiC is well-suited for use in vertical MOSFETs for high- and medium-power electronic applications. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spontaneous stratification of InGaN layers and its influence on optical propertiesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Z. Liliental-Weber Abstract Transmission Electron Microscopy, high resolution X-ray diffraction and reciprocal space maps, Rutherford Back Scattering and photoluminescence were applied to study InGaN layers grown by MOCVD with increasing layer thickness (100 nm to 1000 nm) and nominally constant In concentration of 10%. Spontaneous stratification of the layer has been found. A strained layer with lower than nominal In content was found in direct contact with the underlying GaN followed by relaxed layers with a nominal or higher In concentration. A high density of randomly distributed stacking faults as well as domains with cubic structure and closely distributed stacking faults (polytype-like) were present in the thicker layers. Strong corrugation of the thicker sample surface was observed. The appearance of multiple photoluminescence line positions was related not only to the spontaneously formed layers with different In content, but also to the structural planar defects formed in the thicker layers. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structure of Ce2RhIn8: an example of complementary use of high-resolution neutron powder diffraction and reciprocal-space mapping to study complex materialsACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2006J. L. Sarrao The room-temperature crystal structure of the heavy fermion antiferromagnet Ce2RhIn8, dicerium rhodium octaindide, has been studied by a combination of high-resolution synchrotron X-ray reciprocal-space mapping of single crystals and high-resolution time-of-flight neutron powder diffraction. The structure is disordered, exhibiting a complex interplay of non-periodic, partially correlated planar defects, coexistence and segregation of polytypic phases (induced by periodic planar `defects'), mosaicity (i.e. domain misalignment) and non-uniform strain. These effects evolve as a function of temperature in a complicated way, but they remain down to low temperatures. The room-temperature diffraction data are best represented by a complex mixture of two polytypic phases, which are affected by non-periodic, partially correlated planar defects, differ slightly in their tetragonal structures, and exhibit different mosaicities and strain values. Therefore, Ce2RhIn8 approaches the paracrystalline state, rather than the classic crystalline state and thus several of the concepts of conventional single-crystal crystallography are inapplicable. The structural results are discussed in the context of the role of disorder in the heavy-fermion state and in the interplay between superconductivity and magnetism. [source] | |||||||||||||