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Atomic Scale (atomic + scale)
Selected AbstractsStrain Mapping at the Atomic Scale in Highly Mismatched Heterointerfaces,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2007M. Sánchez Abstract A complete characterization of dislocation network in a highly mismatched interface with high spatial resolution has been performed. The interface between InN quantum dots and a (0001) GaN substrate contains three noninteracting sets of regularly-spaced misfit dislocations lying along <110> directions. The network has a "Star of David" form, with each star bounding a hexagonal region which is pseudomorphic. These misfit dislocations form a threading dislocation network at the island edges due to free surface forces. [source] Cover Picture: From atomic scale to macroscopic scale: an experimental and theoretical challenge. (Adv. Eng.ADVANCED ENGINEERING MATERIALS, Issue 12 2006Mater. No abstract is available for this article. [source] Revealing the Design Principles of High-Performance Biological Composites Using Ab initio and Multiscale Simulations: The Example of Lobster CuticleADVANCED MATERIALS, Issue 4 2010Svetoslav Nikolov Natural materials are hierarchically structured nanocomposites. A bottom-up multiscale approach to model the mechanical response of the chitin-based mineralized cuticle material of Homarus americanus is presented, by combining quantum-mechanical ab initio calculations with hierarchical homogenization. The simulations show how the mechanical properties are transferred from the atomic scale through a sequence of specifically designed microstructures to realize optimal stiffness. [source] Dynamic Processes at Solid-liquid InterfacesIMAGING & MICROSCOPY (ELECTRONIC), Issue 1 2006Video-STM Images Nanoscale Dynamics Scanning tunnelling microscopy (STM) not only provides unsurpassed resolution, enabling real-space imaging of individual surface atoms, but also is capable to operate in a wide range of environments, ranging from ultrahigh vacuum to gases and liquids. The latter allows studies of processes at solidliquid interfaces with a time resolution that can be as low as some 10 msec. in modern instruments. This is sufficiently fast to study elementary transport processes at these interfaces, such as surface diffusion or crystal growth, directly on the atomic scale. [source] Cover Picture: Acceleration of Calcite Kinetics by Abalone Nacre Proteins (Adv. Mater.ADVANCED MATERIALS, Issue 22 200522/2005) Abstract Abalone utilizes a system of macromolecular matrices and soluble proteins to produce beautiful and mechanically robust shells. The cover shows work by Qiu and co-workers reported on p.,2678, in which AP8 proteins isolated from the shell of red abalone are shown to alter the growth of calcite both by accelerating the rate and modifying the shape from the simple rhombohedra seen in the upper left of the scheme to the more complex form seem in the lower right. The changes are made manifest at an atomic scale through alterations in the growth speed and shape of the atomic steps that form the growth hillocks (background). [source] Accessing Time,Varying Forces on the Vibrating Tip of the Dynamic Atomic Force Microscope to Map Material CompositionISRAEL JOURNAL OF CHEMISTRY, Issue 2 2008Ozgur Sahin In dynamic atomic force microscopes the primary physical quantities being measured are the amplitude/phase or amplitude/frequency of the vibrating force probe. Topographic images with spatial resolutions down to the atomic scale can be obtained by mapping these measurements across the sample surface under feedback control. During the imaging process the vibrating tip is observing tip,sample interaction potentials (force,distance relationships) at every point on the surface. The interaction potential is a superposition of short- and long,distance interactions of various origins determined by the material compositions of the tip, sample, and the medium of imaging. In principle, measurement of tip,sample interaction potential should allow determination and mapping of material composition of the sample. However, a single measurement of amplitude/phase or amplitude/frequency in dynamic atomic force microscopes is not enough to characterize a complicated tip,sample interaction potential. Recent developments in the understanding of dynamics of the vibrating force probe (cantilever), together with specially designed cantilevers that utilize torsional vibrations in addition to conventional vertical vibrations, enable the recovery of tip,sample interaction potentials at a timescale less than a millisecond. Here, with theory and experiments, we discuss how these cantilevers recover the information about the tip,sample interaction forces and give an example of compositional mapping on a polymeric material system. [source] Examination of whewellite kidney stones by scanning electron microscopy and powder neutron diffraction techniquesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2009Michel Daudon Kidney stones made of whewellite, i.e. calcium oxalate monohydrate, exhibit various morphological aspects. The crystalline structure of whewellite at the atomic scale was revisited through a single-crystal neutron study at room temperature using a four-circle automated diffractometer. The possible relationships between the various morphological types of whewellite stones and their structural characteristics were examined at the mesoscopic scale by the use of scanning electron microscopy and at the nanometric scale by powder neutron diffraction. All types of whewellite stones displayed a similar structure at the nanometric scale. However, significant differences were found at the mesoscopic scale. In particular, the crystallites in kidney stones resulting from a genetic hyperoxaluria exhibited a peculiar structure. There was a close relationship between stone morphology and crystallite organization at the mesoscopic level and the effectiveness of extracorporeal shockwave lithotripsy. [source] Analytical SuperSTEM for extraterrestrial materials researchMETEORITICS & PLANETARY SCIENCE, Issue 10 2009John P. Bradley The improved technical capabilities enable analyses previously not possible. Mineral structures can be directly imaged and analyzed with single-atomic-column resolution, liquids, and implanted gases can be detected, and UV-VIS optical properties can be measured. Detection limits for minor/trace elements in thin (<100 nm thick) specimens are improved such that quantitative measurements of some extend to the sub-500 ppm level. Electron energy-loss spectroscopy (EELS) can be carried out with 0.10,0.20 eV energy resolution and atomic-scale spatial resolution such that variations in oxidation state from one atomic column to another can be detected. Petrographic mapping is extended down to the atomic scale using energy-dispersive X-ray spectroscopy (EDS) and energy-filtered transmission electron microscopy (EFTEM) imaging. Technical capabilities and examples of the applications of SuperSTEM to extraterrestrial materials are presented, including the UV spectral properties and organic carbon K-edge fine structure of carbonaceous matter in interplanetary dust particles (IDPs), X-ray elemental maps showing the nanometer-scale distribution of carbon within GEMS (glass with embedded metal and sulfides), the first detection and quantification of trace Ti in GEMS using EDS, and detection of molecular H2O in vesicles and implanted H2 and He in irradiated mineral and glass grains. [source] Atomic scale defect analysis in the scanning transmission electron microscope,MICROSCOPY RESEARCH AND TECHNIQUE, Issue 5 2006Ilke Arslan Abstract Z-contrast imaging and electron energy loss spectroscopy in the scanning transmission electron microscope provide the ability to investigate the structure,composition,property relationship at individual defects on the atomic scale. In this article, the main principles behind the techniques will be described. The application of these methods to the analysis of individual dislocations in GaN will also be discussed. In this case, the atomic scale methods indicate that many of the structural and electronic properties of dislocations are modified by the presence of impurities, such as oxygen. Microsc. Res. Tech 69:330,342, 2006. Published 2006 Wiley-Liss, Inc. [source] Investigation of InN layers grown by MOCVD using analytical and high resolution TEM: The structure, band gap, role of the buffer layersPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2006P. Ruterana Abstract In this work we investigate the microstructure of InN layers grown by MOCVD on different buffer layers using TEM (InN, GaN). The large mismatch between the various lattices (InN, sapphire or GaN) leads to particular interface structures. Our local analysis allows to show that at atomic scale, the material has the InN lattice parameters and that no metallic In precipitates are present, meaning that the PL emission below 0.8 eV is a genuine property of the InN semiconductor. It is also shown that the N polar layers, which exhibit a 2D growth, have poorer PL emission than In polar layers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Kinetic and strain-driven growth phenomena on Si(001)PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2004C. Schelling Abstract Self-organization phenomena in semiconductors are usually based on strain-driven island growth during hetero epitaxial layer deposition. However, kinetic phenomena can become important and even dominating at the low growth temperatures usually employed during molecular beam epitaxy. We report on kinetic step bunching on Si(001), and identify the driving mechanism on the atomic scale via kinetic Monte Carlo simulations. Another phenomena discussed is facet formation during annealing of SiO2 -covered Si(001) nanostructures at the relatively low temperatures usually employed for oxide desorption. Both phenomena are combined to facilitate perfect ordering of self-assembled Ge dots on facetted Si(001) nanostructure templates. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Multiscale simulation of polycrystal mechanics of textured ,-Ti alloys using ab initio and crystal-based finite element methodsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2008D. Ma Abstract Crystal-based finite element methods (FEM) are versatile continuum approaches for predicting mechanical properties and deformation-induced crystallographic textures. They can be applied to both, elastic,plastic and elastic problems. The methodology is based on (i) a detailed understanding of the underlying crystal deformation mechanisms and (ii) a number of constitutive material parameters that are often difficult to measure. First principle calculations, that take into account the discrete nature of matter at the atomic scale, are an alternative way to study mechanical properties of single crystals without using empirical parameters. In this study we demonstrate how to combine these two well-established modeling tools, viz., ab initio modeling and crystal mechanical FEM, for an improved approach to design of polycrystalline materials. The combination is based on (i) the determination of basic thermodynamic and elastic parameter trends in metallurgical alloy design using density-functional (DFT) calculations (P. Hohenberg and W. Kohn, Phys. Rev. 136, B864 (1964), W. Kohn and L. J. Sham, Phys. Rev. 140, A1133 (1965) [1, 2], respectively) and (ii) the up-scale transfer of these results into crystal-based finite element simulations which take into account the anisotropic nature of the elastic,plastic deformation of metals. The method is applied to three body-centered cubic (bcc, ,) Ti,Nb alloys for bio-medical applications. The study addresses two technological processes, namely, the prediction of texture evolution during cold rolling (elastic-plastic problem) and elastic bending of textured polycrystals (elastic problem). (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Generalized Wannier functions: An efficient way to construct ab-initio tight-binding parameters for group-III nitridesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2006M. Wahn Abstract An ab-initio tight-binding (TB) parametrization has successfully been accomplished for the group-III nitrides GaN and InN as well as for GaAs. The approach allows for multi-scale electronic structure calculations while conserving the accuracy of the atomic scale. The method has been implemented into the plane-wave pseudopotential code S/PHI/nX (http://www.sfhingx.de [1]). Based on it we have performed careful checks of the efficiency (number of non-vanishing matrix elements of the TB Hamiltonian) and the accuracy (description of the bandstructure in comparison to the plane-wave basis). The effect of different exchange-correlation functionals (LDA, EXX) has also been investigated. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Studies of electric field induced structural and electron-density modifications by X-ray diffractionACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2004Niels K. Hansen During the last two decades, a number of X-ray diffraction studies on the response of a crystal to an applied electric field have been carried out. In a few cases, the electron-density polarizations could be determined. The analysis of the induced variations of the structural properties on an atomic scale are of prime importance in order to acquire a better understanding of physical properties like the piezoelectric and dielectric properties of crystals. This article reviews the experimental technique used and the modelling methods of the Bragg scattering variations induced by the field. Some noteworthy results are presented that illustrate the possibility of detecting subtle structural changes, for example as small as 0.1° in bond angles arising from applying a strong field, 10,40,kV,cm,1, as well as the pitfalls of such an approach for clarifying the relevance of the structural properties in physical mechanisms. [source] Systematic formulations for electronegativity and hardness and their atomic scales within density functional softness theoryINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2006Mihai V. Putz Abstract A unified Mulliken valence with Parr ground-state electronegativity picture is presented. It provides a useful analytical tool on which the absolute hardness as well ionization potential and electron affinity functionals are based. For all these chemical reactivity indices, systematic approximate density functionals are formulated within density functional softness theory and are applied to atomic systems. For the absolute hardness, a special relationship with the new electronegativity ansatz and a particular atomic trend paralleling the absolute electron affinity are established that should complement and augment the earlier finite-difference energetic approach. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] | |||||||||||||||||||