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  • Articles  (876)
  • 2010-2014  (876)
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  • Articles  (876)
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  • 11
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    Atomic resolution tomography reconstruction of tilt series based on a GPU accelerated hybrid input–output algorithm using polar Fourier transform (2014)
    Elsevier
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    Publication Date: 2014-12-19
    Description: Publication date: February 2015 Source: Ultramicroscopy, Volume 149 Author(s): Xiangwen Lu , Wenpei Gao , Jian-Min Zuo , Jiabin Yuan Advances in diffraction and transmission electron microscopy (TEM) have greatly improved the prospect of three-dimensional (3D) structure reconstruction from two-dimensional (2D) images or diffraction patterns recorded in a tilt series at atomic resolution. Here, we report a new graphics processing unit (GPU) accelerated iterative transformation algorithm (ITA) based on polar fast Fourier transform for reconstructing 3D structure from 2D diffraction patterns. The algorithm also applies to image tilt series by calculating diffraction patterns from the recorded images using the projection-slice theorem. A gold icosahedral nanoparticle of 309 atoms is used as the model to test the feasibility, performance and robustness of the developed algorithm using simulations. Atomic resolution in 3D is achieved for the 309 atoms Au nanoparticle using 75 diffraction patterns covering 150° rotation. The capability demonstrated here provides an opportunity to uncover the 3D structure of small objects of nanometers in size by electron diffraction.
    Print ISSN: 0304-3991
    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
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  • 12
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    Dynamic scattering of electron vortex beams – A Bloch wave analysis (2014)
    Elsevier
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    Publication Date: 2014-12-19
    Description: Publication date: February 2015 Source: Ultramicroscopy, Volume 149 Author(s): B.G. Mendis Two important applications of electron vortex beams are in electron magnetic chiral dichroism (EMCD) measurements and nanoparticle manipulation. In both cases orbital angular momentum (〈 L z 〉) transfer between the vortex beam and the specimen due to dynamic scattering is critical. In general the 〈 L z 〉 pendellösung consists of short and long wavelength oscillations. The former is due to interference between the tightly bound 1s and more dispersive non-1s Bloch states, while the latter is due to interference between the non-1s states. For EMCD experiments with ± ħ angular momentum beams, momentum transfer can be minimised by selecting the appropriate aperture size, so that the probe wavefunction approximately matches that of the 2p-type Bloch states. For manipulating nanoparticles with large angular momentum beams small apertures are required to excite the 1s state and thereby enhance the short wavelength oscillations in 〈 L z 〉. This enables efficient momentum transfer to the specimen, provided the nanoparticle dimension corresponds to a minimum in the 〈 L z 〉 pendellösung.
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    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
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  • 13
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    Towards denoising XMCD movies of fast magnetization dynamics using extended Kalman filter (2014)
    Elsevier
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    Publication Date: 2014-12-19
    Description: Publication date: January 2015 Source: Ultramicroscopy, Volume 148 Author(s): M. Kopp , S. Harmeling , G. Schütz , B. Schölkopf , M. Fähnle The Kalman filter is a well-established approach to get information on the time-dependent state of a system from noisy observations. It was developed in the context of the Apollo project to see the deviation of the true trajectory of a rocket from the desired trajectory. Afterwards it was applied to many different systems with small numbers of components of the respective state vector (typically about 10). In all cases the equation of motion for the state vector was known exactly. The fast dissipative magnetization dynamics is often investigated by x-ray magnetic circular dichroism movies (XMCD movies), which are often very noisy. In this situation the number of components of the state vector is extremely large (about 10 5 ), and the equation of motion for the dissipative magnetization dynamics (especially the values of the material parameters of this equation) is not well known. In the present paper it is shown by theoretical considerations that – nevertheless – there is no principle problem for the use of the Kalman filter to denoise XMCD movies of fast dissipative magnetization dynamics.
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    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
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  • 14
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    Imaging collagen type I fibrillogenesis with high spatiotemporal resolution (2014)
    Elsevier
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    Publication Date: 2014-12-19
    Description: Publication date: February 2015 Source: Ultramicroscopy, Volume 149 Author(s): Dimitar R Stamov , Erik Stock , Clemens M Franz , Torsten Jähnke , Heiko Haschke Fibrillar collagens, such as collagen type I, belong to the most abundant extracellular matrix proteins and they have received much attention over the last five decades due to their large interactome, complex hierarchical structure and high mechanical stability. Nevertheless, the collagen self-assembly process is still incompletely understood. Determining the real-time kinetics of collagen type I formation is therefore pivotal for better understanding of collagen type I structure and function, but visualising the dynamic self-assembly process of collagen I on the molecular scale requires imaging techniques offering high spatiotemporal resolution. Fast and high-speed scanning atomic force microscopes (AFM) provide the means to study such processes on the timescale of seconds under near-physiological conditions. In this study we have applied fast AFM tip scanning to study the assembly kinetics of fibrillar collagen type I nanomatrices with a temporal resolution reaching eight seconds for a frame size of 500 nm. By modifying the buffer composition and pH value, the kinetics of collagen fibrillogenesis can be adjusted for optimal analysis by fast AFM scanning. We furthermore show that amplitude-modulation imaging can be successfully applied to extract additional structural information from collagen samples even at high scan rates. Fast AFM scanning with controlled amplitude modulation therefore provides a versatile platform for studying dynamic collagen self-assembly processes at high resolution.
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    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
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  • 15
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    Electron imaging with an EBSD detector (2014)
    Elsevier
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    Publication Date: 2014-12-19
    Description: Publication date: January 2015 Source: Ultramicroscopy, Volume 148 Author(s): Stuart I. Wright , Matthew M. Nowell , René de Kloe , Patrick Camus , Travis Rampton Electron Backscatter Diffraction (EBSD) has proven to be a useful tool for characterizing the crystallographic orientation aspects of microstructures at length scales ranging from tens of nanometers to millimeters in the scanning electron microscope (SEM). With the advent of high-speed digital cameras for EBSD use, it has become practical to use the EBSD detector as an imaging device similar to a backscatter (or forward-scatter) detector. Using the EBSD detector in this manner enables images exhibiting topographic, atomic density and orientation contrast to be obtained at rates similar to slow scanning in the conventional SEM manner. The high-speed acquisition is achieved through extreme binning of the camera—enough to result in a 5×5 pixel pattern. At such high binning, the captured patterns are not suitable for indexing. However, no indexing is required for using the detector as an imaging device. Rather, a 5×5 array of images is formed by essentially using each pixel in the 5×5 pixel pattern as an individual scattered electron detector. The images can also be formed at traditional EBSD scanning rates by recording the image data during a scan or can also be formed through post-processing of patterns recorded at each point in the scan. Such images lend themselves to correlative analysis of image data with the usual orientation data provided by and with chemical data obtained simultaneously via X-Ray Energy Dispersive Spectroscopy (XEDS).
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    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
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  • 16
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    Enhanced quantification for 3D SEM–EDS: Using the full set of available X-ray lines (2014)
    Elsevier
    Details
    Publication Date: 2014-12-19
    Description: Publication date: January 2015 Source: Ultramicroscopy, Volume 148 Author(s): Pierre Burdet , S.A. Croxall , P.A. Midgley An enhanced method to quantify energy dispersive spectra recorded in 3D with a scanning electron microscope (3D SEM–EDS) has been previously demonstrated. This paper presents an extension of this method using all the available X-ray lines generated by the beam. The extended method benefits from using high energy lines, that are more accurately quantified, and from using soft X-rays that are highly absorbed and thus more surface sensitive. The data used to assess the method are acquired with a dual beam FIB/SEM investigating a multi-element Ni-based superalloy. A high accelerating voltage, needed to excite the highest energy X-ray line, results in two available X-ray lines for several elements. The method shows an improved compositional quantification as well as an improved spatial resolution.
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    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
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  • 17
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    Multislice Algorithms Revisited: Solving the Schrödinger Equation Numerically for Imaging with Electrons (2014)
    Elsevier
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    Publication Date: 2014-12-19
    Description: Publication date: Available online 17 December 2014 Source: Ultramicroscopy Author(s): C. Wacker , R.R. Schröder For a long time, the high-energy approximation was sufficient for any image simulation in electron microscopy. This changed with the advent of aberration correctors that allow high-resolution imaging at low electron energies. To deal with this fact, we present a numerical solution of the exact Schrödinger equation that is novel in the field of electron microscopy. Furthermore, we investigate systematically the advantages and problems of several multislice algorithms, especially the real-space algorithms.
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    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
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  • 18
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    Analytic solution for a quartic electron mirror (2014)
    Elsevier
    Details
    Publication Date: 2014-12-19
    Description: Publication date: January 2015 Source: Ultramicroscopy, Volume 148 Author(s): Jack C. Straton A converging electron mirror can be used to compensate for spherical and chromatic aberrations in an electron microscope. This paper presents an analytical solution to a diode (two-electrode) electrostatic mirror including the next term beyond the known hyperbolic shape. The latter is a solution of the Laplace equation to second order in the variables perpendicular to and along the mirror׳s radius ( z 2 − r 2 / 2 ) to which we add a quartic term ( k λ z 4 ). The analytical solution is found in terms of Jacobi cosine-amplitude functions. We find that a mirror less concave than the hyperbolic profile is more sensitive to changes in mirror voltages and the contrary holds for the mirror more concave than the hyperbolic profile.
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    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
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  • 19
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    Modeling of temperature profiles in an environmental transmission electron microscope using computational fluid dynamics (2014)
    Elsevier
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    Publication Date: 2014-12-19
    Description: Publication date: Available online 16 December 2014 Source: Ultramicroscopy Author(s): Peter Mølgaard Mortensen , Thomas Willum Hansen , Jakob Birkedal Wagner , Anker Degn Jensen The temperature and velocity field, pressure distribution, and the temperature variation across the sample region inside an environmental transmission electron microscope (ETEM) have been modeled by means of computational fluid dynamics (CFD). Heating the sample area by a furnace type TEM holder gives rise to temperature gradients over the sample area. Three major mechanisms have been identified with respect to heat transfer in the sample area: radiation from the grid, conduction in the grid, and conduction in the gas. A parameter sensitivity analysis showed that the sample temperature was affected by the conductivity of the gas, the emissivity of the sample grid, and the conductivity of the grid. Ideally the grid should be polished and made from a material with good conductivity, e.g. copper. With hydrogen gas, which has the highest conductivity of the gases studied, the temperature difference over the TEM grid is less than 5 ° C, at what must be considered typical conditions, and it is concluded that the conditions on the sample grid in the ETEM can be considered as isothermal during general use.
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    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
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  • 20
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    Novel lift-off technique for Transmission Electron Microscopy imaging of block copolymer films (2014)
    Elsevier
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    Publication Date: 2014-12-19
    Description: Publication date: Available online 15 December 2014 Source: Ultramicroscopy Author(s): Fergus J.M. Roache , Mazdak Radjainia , David E. Williams , Juliet A. Gerrard , Jadranka Travas-Sejdic , Jenny Malmstrӧm We have developed a simple technique to allow for the lift-off and subsequent transfer of poly(styrene- block -ethylene glycol) films to Transmission Electron Microscopy (TEM) grids. The block copolymer is spin coated onto carbon coated mica and annealed. After the thin film is produced it can easily be floated onto water and picked up by a TEM grid. This method offers better control over film processing than dip coating the TEM grid and is also a significant improvement over methods using etchants such as hydrofluoric acid.
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    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
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