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Ultramicroscopy

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https://www.readbyqxmd.com/read/28343726/rapid-measurement-of-low-order-aberrations-using-fourier-transforms-of-crystalline-ronchigrams
#1
Koji Kimoto, Kazuo Ishizuka
The aberrations of the objective lens should be measured and adjusted to realize high spatial resolution in scanning transmission electron microscopy (STEM). Here we report a method of measuring low-order aberrations using the Fourier transforms of Ronchigrams of an arbitrary crystal such as a specimen of interest. We have applied this technique to measure first- and second-order geometrical aberrations using typical standard specimens. Focus and twofold astigmatism are measured using two Ronchigrams obtained under different foci...
March 18, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28341554/structure-and-chemistry-of-epitaxial-ceria-thin-films-on-yttria-stabilized-zirconia-substrates-studied-by-high-resolution-electron-microscopy
#2
Robert Sinclair, Sang Chul Lee, Yezhou Shi, William C Chueh
We have applied aberration-corrected transmission electron microscopy (TEM) imaging and electron energy loss spectroscopy (EELS) to study the structure and chemistry of epitaxial ceria thin films, grown by pulsed laser deposition onto (001) yttria-stabilized zirconia (YSZ) substrates. There are few observable defects apart from the expected mismatch interfacial dislocations and so the films would be expected to have good potential for applications. Under high electron beam dose rate (above about 6000 e(-)/Å(2)s) domains of an ordered structure appear and these are interpreted as being created by oxygen vacancy ordering...
March 18, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28341557/cathodoluminescence-in-the-scanning-transmission-electron-microscope
#3
M Kociak, L F Zagonel
Cathodoluminescence (CL) is a powerful tool for the investigation of optical properties of materials. In recent years, its combination with scanning transmission electron microscopy (STEM) has demonstrated great success in unveiling new physics in the field of plasmonics and quantum emitters. Most of these results were not imaginable even twenty years ago, due to conceptual and technical limitations. The purpose of this review is to present the recent advances that broke these limitations, and the new possibilities offered by the modern STEM-CL technique...
March 16, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28341553/spin-polarisation-with-electron-bessel-beams
#4
P Schattschneider, V Grillo, D Aubry
The theoretical possibility to use an electron microscope as a spin polarizer is studied. It turns out that a Bessel beam passing a standard magnetic objective lens is intrinsically spin polarized when post-selected on-axis. In the limit of infinitely small detectors, the spin polarisation tends to 100%. Increasing the detector size, the polarisation decreases rapidly, dropping below 10(-4) for standard settings of medium voltage microscopes. For extremely low voltages, the Figure of Merit increases by two orders of magnitude, approaching that of existing Mott detectors...
March 16, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28341556/advanced-electron-holography-techniques-for-in-situ-observation-of-solid-state-lithium-ion-conductors
#5
Tsukasa Hirayama, Yuka Aizawa, Kazuo Yamamoto, Takeshi Sato, Hidekazu Murata, Ryuji Yoshida, Craig A J Fisher, Takehisa Kato, Yasutoshi Iriyama
Advanced techniques for overcoming problems encountered during in situ electron holography experiments in which a voltage is applied to an ionic conductor are reported. The three major problems encountered were 1) electric-field leakage from the specimen and its effect on phase images, 2) high electron conductivity of damage layers formed by the focused ion beam method, and 3) chemical reaction of the specimen with air. The first problem was overcome by comparing experimental phase distributions with simulated images in which three-dimensional leakage fields were taken into account, the second by removing the damage layers using a low-energy narrow Ar ion beam, and the third by developing an air-tight biasing specimen holder...
March 15, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28341555/enhanced-thermal-stability-of-a-polymer-solar-cell-blend-induced-by-electron-beam-irradiation-in-the-transmission-electron-microscope
#6
Olof Bäcke, Camilla Lindqvist, Amaia Diaz de Zerio Mendaza, Stefan Gustafsson, Ergang Wang, Mats R Andersson, Christian Müller, Per Magnus Kristiansen, Eva Olsson
We show by in situ microscopy that the effects of electron beam irradiation during transmission electron microscopy can be used to lock microstructural features and enhance the structural thermal stability of a nanostructured polymer:fullerene blend. Polymer:fullerene bulk-heterojunction thin films show great promise for use as active layers in organic solar cells but their low thermal stability is a hindrance. Lack of thermal stability complicates manufacturing and influences the lifetime of devices. To investigate how electron irradiation affects the thermal stability of polymer:fullerene films, a model bulk-heterojunction film based on a thiophene-quinoxaline copolymer and a fullerene derivative was heat-treated in-situ in a transmission electron microscope...
March 15, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28334576/stemsalabim-a-high-performance-computing-cluster-friendly-code-for-scanning-transmission-electron-microscopy-image-simulations-of-thin-specimens
#7
Jan Oliver Oelerich, Lennart Duschek, Jürgen Belz, Andreas Beyer, Sergei D Baranovskii, Kerstin Volz
We present a new multislice code for the computer simulation of scanning transmission electron microscope (STEM) images based on the frozen lattice approximation. Unlike existing software packages, the code is optimized to perform well on highly parallelized computing clusters, combining distributed and shared memory architectures. This enables efficient calculation of large lateral scanning areas of the specimen within the frozen lattice approximation and fine-grained sweeps of parameter space.
March 10, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28340394/assessment-of-engineered-surfaces-roughness-by-high-resolution-3d-sem-photogrammetry
#8
L C Gontard, J D López-Castro, L González-Rovira, J M Vázquez-Martínez, F M Varela-Feria, M Marcos, J J Calvino
We describe a methodology to obtain three-dimensional models of engineered surfaces using scanning electron microscopy and multi-view photogrammetry (3DSEM). For the reconstruction of the 3D models of the surfaces we used freeware available in the cloud. The method was applied to study the surface roughness of metallic samples patterned with parallel grooves by means of laser. The results are compared with measurements obtained using stylus profilometry (PR) and SEM stereo-photogrammetry (SP). The application of 3DSEM is more time demanding than PR or SP, but it provides a more accurate representation of the surfaces...
March 7, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28314155/optimizing-experimental-parameters-for-the-projection-requirement-in-haadf-stem-tomography
#9
R Aveyard, Z Zhong, K J Batenburg, B Rieger
Tomographic reconstruction algorithms offer a means by which a tilt-series of transmission images can be combined to yield a three dimensional model of the specimen. Conventional reconstruction algorithms assume that the measured signal is a linear projection of some property, typically the density, of the material. Here we report the use of multislice simulations to investigate the extent to which this assumption is met in HAADF-STEM imaging. The use of simulations allows for a systematic survey of a range of materials and microscope parameters to inform optimal experimental design...
March 7, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28292687/x-ray-absorption-in-pillar-shaped-transmission-electron-microscopy-specimens
#10
H Bender, F Seidel, P Favia, O Richard, W Vandervorst
The dependence of the X-ray absorption on the position in a pillar shaped transmission electron microscopy specimen is modeled for X-ray analysis with single and multiple detector configurations and for different pillar orientations relative to the detectors. Universal curves, applicable to any pillar diameter, are derived for the relative intensities between weak and medium or strongly absorbed X-ray emission. For the configuration as used in 360° X-ray tomography, the absorption correction for weak and medium absorbed X-rays is shown to be nearly constant along the pillar diameter...
March 7, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28292686/effects-of-small-angle-mistilts-on-dopant-visibility-in-adf-stem-imaging-of-nanocrystals
#11
Jacob T Held, Samuel Duncan, K Andre Mkhoyan
Quantitative ADF-STEM imaging paired with image simulations has proven to be a powerful technique for determining the three dimensional location of substitutionally doped atoms in thin films. Expansion of this technique to lightly-doped nanocrystals requires an understanding of the influence of specimen mistilt on dopant visibility due to the difficulty of accurate orientation determination in such systems as well as crystal movement under the beam. In this study, the effects of specimen mistilt on ADF-STEM imaging are evaluated using germanium-doped silicon nanocrystals as model systems...
March 7, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28334577/on-the-achievable-field-sensitivity-of-a-segmented-annular-detector-for-differential-phase-contrast-measurements
#12
Felix Schwarzhuber, Peter Melzl, Josef Zweck
Differential phase contrast microscopy measures minute deflections of the electron probe due to electric and/or magnetic fields, using a position sensitive device. Although recently, pixelated detectors have become available which also serve as a position sensitive device, the most frequently used detector is a four-segmented annular semiconducting detector ring (or variations thereof), where the difference signals of opposing detector elements represent the components of the deflection vector. This deflection vector can be used directly to quantitatively determine the deflecting field, provided the specimen's thickness is known...
March 4, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28314556/simulation-in-elemental-mapping-using-aberration-corrected-electron-microscopy
#13
L J Allen
Elemental mapping at the atomic scale in aberration-corrected electron microscopes is becoming increasingly widely used. In this paper we describe the essential role of simulation in understanding the underlying physics and thus in correctly interpreting these maps, both qualitatively and quantitatively.
March 2, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28285731/excitonic-vibrational-and-van-der-waals-interactions-in-electron-energy-loss-spectroscopy
#14
T Mizoguchi, T Miyata, W Olovsson
The pioneer, Ondrej L. Krivanek, and his collaborators have opened up many frontiers for the electron energy loss spectroscopy (EELS), and they have demonstrated new potentials of the EELS method for investigating materials. Here, inspired by those achievements, we show further potentials of EELS based on the results of theoretical calculations, that is excitonic and van der Waals (vdW) interactions, as well as vibrational information of materials. Concerning the excitonic interactions, we highlight the importance of the two-particle calculation to reproduce the low energy-loss near-edge structure (ELNES), the Na-L2,3 edge of NaI and the Li-K edge of LiCl and LiFePO4...
March 2, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28284705/characterization-of-misfit-dislocations-in-si-quantum-well-structures-enabled-by-stem-based-aberration-correction
#15
Philip E Batson, Maureen J Lagos
The success of aberration correction techniques at the end of the 20th century came at a time of increasing need for atomic resolution imaging to better understand known structural defects that influence semiconductor device operation, and to advance the search for new structures and behavior that will form the basis for devices in the future. With this in mind, it is a pleasure to recognize the contributions of Ondrej Krivanek to the success of aberration correction techniques, and his extension of aberration techniques to EELS equipment that further promises to unite structural studies with characterization of behavior from meV to keV energies in the STEM...
March 2, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28284704/manipulating-low-dimensional-materials-down-to-the-level-of-single-atoms-with-electron-irradiation
#16
Toma Susi, Jannik C Meyer, Jani Kotakoski
Recent advances in scanning transmission electron microscopy (STEM) instrumentation have made it possible to focus electron beams with sub-atomic precision and to identify the chemical structure of materials at the level of individual atoms. Here we discuss the dynamics that are observed in the structure of low-dimensional materials under electron irradiation, and the potential use of electron beams for single-atom manipulation. As a demonstration of the latter capability, we show how momentum transfer from the electrons of a 60-keV Ångström-sized STEM probe can be used to move silicon atoms embedded in the graphene lattice with atomic precision...
March 2, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28284703/high-resolution-monochromated-electron-energy-loss-spectroscopy-of-organic-photovoltaic-materials
#17
Jessica A Alexander, Frank J Scheltens, Lawrence F Drummy, Michael F Durstock, Fredrik S Hage, Quentin M Ramasse, David W McComb
Advances in electron monochromator technology are providing opportunities for high energy resolution (10 - 200meV) electron energy-loss spectroscopy (EELS) to be performed in the scanning transmission electron microscope (STEM). The energy-loss near-edge structure in core-loss spectroscopy is often limited by core-hole lifetimes rather than the energy spread of the incident illumination. However, in the valence-loss region, the reduced width of the zero loss peak makes it possible to resolve clearly and unambiguously spectral features at very low energy-losses (<3eV)...
March 2, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28284706/a-short-story-of-imaging-and-spectroscopy-of-two-dimensional-materials-by-scanning-transmission-electron-microscopy
#18
Juan C Idrobo, Wu Zhou
Here we present a short historical account of when single adatom impurities where first identified in two-dimensional materials by scanning transmission electron microscopy (STEM). We also present a study of the graphene low-loss (below 50eV) response as a function of number of layers using electron energy-loss spectroscopy (EELS). The study shows that as few as three layers of graphene behave as bulk graphite for losses above 10eV We also show examples of how point and extended defects can easily be resolved and structural dynamics can be readily capture by using aberration-corrected STEM imaging...
March 1, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28284057/effects-of-accelerating-voltage-and-specimen-thickness-on-the-spatial-resolution-of-transmission-electron-backscatter-diffraction-in-cu
#19
Jhih-Wun Shih, Ka-Wei Kuo, Jui-Chao Kuo, Tsung-Yuan Kuo
A quantitative approach was proposed to determine the spatial resolution of transmission electron backscatter diffraction (t-EBSD) and to understand the limits of spatial resolution of t-EBSD. In this approach, Cu bicrystals and digital image correlation were employed. The effects of accelerating voltage and specimen thickness on the spatial resolution of t-EBSD were also investigated. t-EBSD specimens with 8μm×10μm dimensions and different thicknesses were prepared using focused ion beam milling. The optimized quality of Kikuchi pattern was achieved at a working distance of 12mm and a tilting angle of 20°...
March 1, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28314154/streamlined-approach-to-mapping-the-magnetic-induction-of-skyrmionic-materials
#20
Jordan J Chess, Sergio A Montoya, Tyler R Harvey, Colin Ophus, Simon Couture, Vitaliy Lomakin, Eric E Fullerton, Benjamin J McMorran
Recently, Lorentz transmission electron microscopy (LTEM) has helped researchers advance the emerging field of magnetic skyrmions. These magnetic quasi-particles, composed of topologically non-trivial magnetization textures, have a large potential for application as information carriers in low-power memory and logic devices. LTEM is one of a very few techniques for direct, real-space imaging of magnetic features at the nanoscale. For Fresnel-contrast LTEM, the transport of intensity equation (TIE) is the tool of choice for quantitative reconstruction of the local magnetic induction through the sample thickness...
February 28, 2017: Ultramicroscopy
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