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Mark J McLean, William A Osborn
Compared to more commonly used strain measurement techniques, electron backscatter diffraction (EBSD) offers improved spatial resolution and measurement sensitivity. Additionally, EBSD can provide the full deformation tensor, whereas other techniques, such as digital image correlation (DIC), are limited to only in-plane strains and rotations. In this work, EBSD was used to measure strains and rotations in-situ during testing of a single-crystal silicon micromechanical test specimen. The theta-like specimen geometry was chosen due to the complex and spatially-varying strain states that exist in the circular frame of the sample during testing, as well as the nominally uniform strains in the central web...
November 14, 2017: Ultramicroscopy
Travis M Rampton, Stuart I Wright, Michael P Miles, Eric R Homer, Robert H Wagoner, David T Fullwood
Twin detection via EBSD can be particularly challenging due to the fine scale of certain twin types - for example, compression and double twins in Mg. Even when a grid of sufficient resolution is chosen to ensure scan points within the twins, the interaction volume of the electron beam often encapsulates a region that contains both the parent grain and the twin, confusing the twin identification process. The degradation of the EBSD pattern results in a lower image quality metric, which has long been used to imply potential twins...
November 10, 2017: Ultramicroscopy
Lennart Duschek, Andreas Beyer, Jan Oliver Oelerich, Kerstin Volz
Knowledge of the microscopic elemental composition of multinary III/V semiconductor materials is crucial to the development of functionalized opto-electronic devices. Well-proven composition analysis methods, such as high resolution X-ray diffraction (HRXRD), fail to determine the elemental composition when more than three atomic species are involved. In this work we propose a procedure for the composition analysis of multinary III/V semiconductors at atomic resolution using high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) image simulations...
November 9, 2017: Ultramicroscopy
Debabrata Biswas, Gaurav Singh, Shreya G Sarkar, Raghwendra Kumar
The field enhancement factor at the emitter tip and its variation in a close neighbourhood determines the emitter current in a Fowler-Nordheim like formulation. For an axially symmetric emitter with a smooth tip, it is shown that the variation can be accounted by a cosθ˜ factor in appropriately defined normalized co-ordinates. This is shown analytically for a hemiellipsoidal emitter and confirmed numerically for other emitter shapes with locally quadratic tips.
October 31, 2017: Ultramicroscopy
Zhichao Zhong, Richard Aveyard, Bernd Rieger, Sara Bals, Willem Jan Palenstijn, K Joost Batenburg
HAADF-STEM tomography is a common technique for characterizing the three-dimensional morphology of nanomaterials. In conventional tomographic reconstruction algorithms, the image intensity is assumed to be a linear projection of a physical property of the specimen. However, this assumption of linearity is not completely valid due to the nonlinear damping of signal intensities. The nonlinear damping effects increase w.r.t the specimen thickness and lead to so-called "cupping artifacts", due to a mismatch with the linear model used in the reconstruction algorithm...
October 30, 2017: Ultramicroscopy
Johannes Jobst, Jaap Kautz, Maria Mytiliniou, Rudolf M Tromp, Sense Jan van der Molen
In a lot of systems, charge transport is governed by local features rather than being a global property as suggested by extracting a single resistance value. Consequently, techniques that resolve local structure in the electronic potential are crucial for a detailed understanding of electronic transport in realistic devices. Recently, we have introduced a new potentiometry method based on low-energy electron microscopy (LEEM) that utilizes characteristic features in the reflectivity spectra of layered materials [1]...
October 25, 2017: Ultramicroscopy
J Huang, M Loeffler, U Muehle, W Moeller, J J L Mulders, L F Tz Kwakman, W F Van Dorp, E Zschech
A Ga focused ion beam (FIB) is often used in transmission electron microscopy (TEM) analysis sample preparation. In case of a crystalline Si sample, an amorphous near-surface layer is formed by the FIB process. In order to optimize the FIB recipe by minimizing the amorphization, it is important to predict the amorphous layer thickness from simulation. Molecular Dynamics (MD) simulation has been used to describe the amorphization, however, it is limited by computational power for a realistic FIB process simulation...
October 25, 2017: Ultramicroscopy
A Quesada, R Gargallo-Caballero, Y Montaña, M Foerster, L Aballe, J F Fernández, J de la Figuera
High aspect-ratio Fe nanostrips are known to reversibly switch from a single-domain magnetic state to a multidomain diamond pattern as a function of temperature (T) and width. This magnetic bistability can be understood by the temperature-dependent balance between magnetocrystalline, shape and magnetoelastic anisotropies and has potential applications in magnetic logic devices. However, as Fe nanostructures easily oxidize, protecting the surface with capping layers may be required, which could largely affect the anisotropy balance...
October 24, 2017: Ultramicroscopy
Yan Zhang, G M Dilshan Godaliyadda, Nicola Ferrier, Emine B Gulsoy, Charles A Bouman, Charudatta Phatak
Analytical electron microscopy and spectroscopy of biological specimens, polymers, and other beam sensitive materials has been a challenging area due to irradiation damage. There is a pressing need to develop novel imaging and spectroscopic imaging methods that will minimize such sample damage as well as reduce the data acquisition time. The latter is useful for high-throughput analysis of materials structure and chemistry. In this work, we present a novel machine learning based method for dynamic sparse sampling of EDS data using a scanning electron microscope...
October 23, 2017: Ultramicroscopy
Yi Wang, Michael R S Huang, Ute Salzberger, Kersten Hahn, Wilfried Sigle, Peter A van Aken
Electron energy-loss spectroscopy and energy-dispersive X-ray spectroscopy are two of the most common means for chemical analysis in the scanning transmission electron microscope. The marked progress of the instrumentation hardware has made chemical analysis at atomic resolution readily possible nowadays. However, the acquisition and interpretation of atomically resolved spectra can still be problematic due to image distortions and poor signal-to-noise ratio of the spectra, especially for investigation of energy-loss near-edge fine structures...
October 21, 2017: Ultramicroscopy
Jiří Zelinka, Martin Oral, Tomáš Radlička
We present a comprehensive numerical method for iterative computation of electron optical systems influenced by space charge which can accurately describe all effects in an optical system, including areas near a cathode tip and all crossovers. We use two different algorithms of evaluating the space charge distribution in different parts of the system. The Monte-Carlo based particle-in-cell method is used in the vicinity of the cathode. The algorithm based on the calculation of the current density distribution from an aberration polynomial is used for the rest of the system...
October 20, 2017: Ultramicroscopy
Hang-Eun Joe, Won-Sup Lee, Martin B G Jun, No-Cheol Park, Byung-Kwon Min
A method for interface detection is proposed for focused ion beam (FIB) processes of multilayered targets. As multilayers have emerged as promising structures for nanodevices, the FIB machining of multilayers has become a challenging issue. We proposed material interface detection by monitoring secondary electron (SE) images captured during the FIB process. The average of the gray-levels and the skewness coefficient of gray-level histograms of the SE images were evaluated to recognize endpoints for the FIB processes...
October 20, 2017: Ultramicroscopy
Tim Grieb, Moritz Tewes, Marco Schowalter, Knut Müller-Caspary, Florian F Krause, Thorsten Mehrtens, Jean-Michel Hartmann, Andreas Rosenauer
The chemical composition of four Si1-xGex layers grown on silicon was determined from quantitative scanning transmission electron microscopy (STEM). The chemical analysis was performed by a comparison of the high-angle annular dark field (HAADF) intensity with multislice simulations. It could be shown that amorphous surface layers originating from the preparation process by focused-ion beam (FIB) at 30 kV have a strong influence on the quantification: the local specimen thickness is overestimated by approximately a factor of two, and the germanium concentration is substantially underestimated...
October 13, 2017: Ultramicroscopy
I G C Weppelman, R J Moerland, J P Hoogenboom, P Kruit
We present a new method to create ultrashort electron pulses by integrating a photoconductive switch with an electrostatic deflector. This paper discusses the feasibility of such a system by analytical and numerical calculations. We argue that ultrafast electron pulses can be achieved for micrometer scale dimensions of the blanker, which are feasible with MEMS-based fabrication technology. According to basic models, the design presented in this paper is capable of generating 100 fs electron pulses with spatial resolutions of less than 10 nm...
October 13, 2017: Ultramicroscopy
Ken Vidar Falch, Carsten Detlefs, Anatoly Snigirev, Ragnvald H Mathiesen
Analytical expressions for the transmission cross-coefficients for x-ray microscopes based on compound refractive lenses are derived based on Gaussian approximations of the source shape and energy spectrum. The effects of partial coherence, defocus, beam convergence, as well as lateral and longitudinal chromatic aberrations are accounted for and discussed. Taking the incoherent limit of the transmission cross-coefficients, a compact analytical expression for the modulation transfer function of the system is obtained, and the resulting point, line and edge spread functions are presented...
October 13, 2017: Ultramicroscopy
J F M van Rens, W Verhoeven, J G H Franssen, A C Lassise, X F D Stragier, E R Kieft, P H A Mutsaers, O J Luiten
We present a theoretical description of resonant radiofrequency (RF) deflecting cavities in TM110 mode as dynamic optical elements for ultrafast electron microscopy. We first derive the optical transfer matrix of an ideal pillbox cavity and use a Courant-Snyder formalism to calculate the 6D phase space propagation of a Gaussian electron distribution through the cavity. We derive closed, analytic expressions for the increase in transverse emittance and energy spread of the electron distribution. We demonstrate that for the special case of a beam focused in the center of the cavity, the low emittance and low energy spread of a high quality beam can be maintained, which allows high-repetition rate, ultrafast electron microscopy with 100 fs temporal resolution combined with the atomic resolution of a high-end TEM...
October 12, 2017: Ultramicroscopy
T Friedrich, A Bochmann, J Dinger, S Teichert
In this paper an alternative method of off-line Kikuchi pattern centre calibration and orientation mapping, utilising the cross-correlation between entire experimental patterns and dynamical simulated patterns is applied and evaluated. To demonstrate the improvement in angular resolution compared to Hough transform based methods, EBSD datasets of a silicon monocrystal were analysed using both, classical and the presented cross-correlation based method, which revealed significant enhancement of angular resolution for the refined method...
October 12, 2017: Ultramicroscopy
Wenquan Ming, Jianghua Chen, Christopher S Allen, Shiyun Duan, Ruohan Shen
In a transmission electron microscope, electron illumination beam tilt, or the degree of deviation of electron beam from its optical axis, is an important parameter that has a significant impact on image contrast and image interpretation. Although a large beam tilt can easily be noticed and corrected by the standard alignment procedure, a small residual beam tilt is difficult to measure and, therefore, difficult to account for quantitatively. Here we report a quantitative method for measuring small residual beam tilts, including its theoretical schemes, numerical simulation testing and experimental verification...
October 12, 2017: Ultramicroscopy
Sung-Il Baik, Dieter Isheim, David N Seidman
Atom-probe tomography (APT) is a unique analysis tool that enables true three-dimensional (3-D) analyses with sub-nano scale spatial resolution. Recent implementations of the local-electrode atom-probe (LEAP) tomograph with ultraviolet laser pulsing have significantly expanded the research applications of APT. The small field-of-view of a needle-shaped specimen with a less than 100 nm diam. is, however, a major limitation for analyzing materials. The systematic approaches for site-specific targeting of an APT nanotip in a transmission electron microscope (TEM) of a thin sample are introduced to solve the geometrical limitations of a sharpened APT nanotip...
October 12, 2017: Ultramicroscopy
Ken Vidar Falch, Mikhail Lyubomirsky, Daniele Casari, Anatoly Snigirev, Irina Snigireva, Carsten Detlefs, Marco Di Michiel, Ivan Lyatun, Ragnvald H Mathiesen
The current work represents the first implementation of Zernike phase contrast for compound refractive lens based x-ray microscopy, and also the first successful Zernike phase contrast experiment at photon energies above 12 keV. Phase contrast was achieved by fitting a compound refractive lens with a circular phase plate. The resolution is demonstrated to be sub-micron, and can be improved using already existing technology. The possibility of combining the technique with polychromatic radiation is considered, and a preliminary test experiment was performed with positive results...
October 3, 2017: Ultramicroscopy
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