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Avi Auslender, Mahdi Halabi, George Levi, Oswaldo Diéguez, Amit Kohn
The mean inner potential (MIP) of a single crystal α-Al2 O3 sapphire was measured using off-axis electron holography. To measure the MIP, we use mechanically polished wedge specimens for transmission electron microscopy (TEM). This approach also enabled us to measure the plasmon mean free path for inelastic scattering (IMFP). The wedge specimen, chosen here at an angle of approximately 45°, allows to determine the MIP by measuring the gradient of phase variations of the reconstructed electron wave over extended regions across the sample...
December 30, 2018: Ultramicroscopy
Benjamin Berkels, Christian H Liebscher
Aberration corrected scanning transmission electron microscopes (STEM) enable to determine local strain fields, composition and bonding states at atomic resolution. The precision to locate atomic columns is often obstructed by scan artifacts limiting the quantitative interpretation of STEM datasets. Here, a novel bias-corrected non-rigid registration approach is presented that compensates for fast and slow scan artifacts in STEM image series. The bias-correction is responsible for the correction of the slow scan artifacts and based on a explicit coupling of the deformations of the individual images in a series via a minimization of the average deformation...
December 24, 2018: Ultramicroscopy
T Ickler, H Meckbach, F Zeismann, A Brückner-Foit
The magnetic properties of non-oriented electrical steel (NOES) used in an electrical engine play an important role in the transformation process from electric to mechanic energy. In this process the NOES is subjected to cyclic loading and strong tensile forces. Until now the dependence of the magnetic properties with respect to a through stress changing microstructure is not fully understood. In this paper a setup for a quasi-static in situ deformation experiment with a SEM is presented in which the surface magnetic domains of a NOES were captured by revealing type 2 magnetic contrast with forescatter diodes, the crystallographic texture was mapped through EBSD and the local relative strains and rotations were calculated with CrossCourt...
December 24, 2018: Ultramicroscopy
N Klingner, R Heller, G Hlawacek, S Facsko, J von Borany
A helium ion microscope, known for high resolution imaging and modification with helium or neon ions, has been equipped with a time-of-flight spectrometer for compositional analysis. Here we report on its design, implementation and show first results of this powerful add-on. Our design considerations were based on the results of detailed ion collision cascade simulations that focus on the physically achievable resolution for various detection limits. Different secondary ion extraction geometries and spectrometer types are considered and compared with respect to the demands and limitations of the microscope...
December 24, 2018: Ultramicroscopy
Shang Yan, Aderonke Adegbule, Tohren C G Kibbey
Scanning electron microscopy is important across a wide range of machine vision applications, and the ability to detect shadows in images could provide an important tool for evaluating attributes of the surfaces being imaged, such as the presence of defects or particulate impurities. One example where the presence of shadows can be important is in the reconstruction of elevation maps from stereo-pair scanning electron microscopy (SEM) images. Shadows can both interfere with determination of matching points for stereoscopic calculations, and confuse shape-from-shading algorithms which rely on pixel intensity gradients to calculate surface slope, leading to inaccurate reconstructions...
December 24, 2018: Ultramicroscopy
Nicolas Brodusch, Hendrix Demers, Alexandra Gellé, Audrey Moores, Raynald Gauvin
A commercial electron energy-loss spectrometer (EELS) attached to a high-resolution cold-field emission scanning electron microscope in transmission mode (STEM) is evaluated and its potential for characterizing materials science thin specimens at low accelerating voltage is reviewed. Despite the increased beam radiation damage at SEM voltages on sensitive compounds, we describe some potential applications which benefit from lowering the primary electrons voltage on less-sensitive specimens. We report bandgap measurements on several dielectrics which were facilitated by the lack of Cherenkov radiation losses at 30 kV...
December 24, 2018: Ultramicroscopy
Yang Yang, Zhengqian Fu, Xiao Zhang, Yan Cui, Fangfang Xu, Tie Li, Yuelin Wang
This research is aimed at the development of an in situ tensile device which is suitable for standard double-tilt electrical TEM holders. The device contains a hexagonal electrostatic chip with a diameter of 1.8 mm. The chip has 706 pairs of combs, which provides an effective tensile displacement larger than 1 µm. To demonstrate the device performance, in situ tensile testing for penta-twinned silver nanowire is conducted in a high-resolution TEM. Experimental results show that the device can fulfill a tilt angle of 10° around both X and Y axes when performing in situ tensile testing experiments...
December 17, 2018: Ultramicroscopy
H G Brown, R Ishikawa, G S Anchez-Santolino, N Shibata, Y Ikuhara, L J Allen, S D Findlay
Most reconstructions of the electrostatic potential of a specimen at atomic resolution assume a thin and weakly scattering sample, restricting accurate quantification to specimens only tens of Ångströms thick. We demonstrate that using large-angle-illumination scanning transmission electron microscopy (STEM)-a probe forming aperture with convergence angle larger than about 50 mrad-allows us to better meet the weak phase object approximation and thereby accurately reconstruct the electrostatic potential in samples thicker than the order of 100 Å...
December 17, 2018: Ultramicroscopy
Karunakar R Pothula, Daryna Smyrnova, Gunnar F Schröder
Helical protein polymers are often dynamic and complex assemblies, with many conformations and flexible domains possible within the helical assembly. During cryo-electron microscopy reconstruction, classification of the image data into homogeneous subsets is a critical step for achieving high resolution, resolving different conformations and elucidating functional mechanisms. Hence, methods aimed at improving the homogeneity of these datasets are becoming increasingly important. In this paper, we introduce a new algorithm that uses results from 2D image classification to sort 2D classes into groups of similar helical polymers...
December 17, 2018: Ultramicroscopy
A J M Hubert, R Römer, R Beanland
We use semi-automated data acquisition and processing to produce digital large angle CBED (D-LACBED) patterns. We demonstrate refinements of atomic coordinates and isotropic Debye-Waller factors for well-known materials using simulations produced with a neutral, spherical independent atom model. We find that atomic coordinate refinements in Al2 O3 have sub-pm precision and accuracy. Isotropic DWFs are accurate for Cu, a simple fcc metal, but do not agree with X-ray measurements of GaAs or Al2 O3 . This lack of agreement is probably caused by bonding and change transfer between atoms...
December 15, 2018: Ultramicroscopy
O L Krivanek, N Dellby, J A Hachtel, J-C Idrobo, M T Hotz, B Plotkin-Swing, N J Bacon, A L Bleloch, G J Corbin, M V Hoffman, C E Meyer, T C Lovejoy
Electron energy loss spectroscopy (EELS) in the electron microscope has progressed remarkably in the last five years. Advances in monochromator and spectrometer design have improved the energy resolution attainable in a scanning transmission electron microscope (STEM) to 4.2 meV, and new applications of ultrahigh energy resolution EELS have not lagged behind. They include vibrational spectroscopy in the electron microscope, a field that did not exist 5 years ago but has now grown very substantially. Notable examples include vibrational mapping with about 1 nm spatial resolution, analyzing the momentum dependence of vibrational states in very small volumes, determining the local temperature of the sample from the ratio of energy gains to energy losses, detecting hydrogen and analyzing its bonding, probing radiation-sensitive materials with minimized damage by aloof spectroscopy and leap-frog scanning, and identifying biological molecules with different isotopic substitutions...
December 11, 2018: Ultramicroscopy
Nicolas Lobato-Dauzier, Matthieu Denoual, Takaaki Sato, Saeko Tachikawa, Laurent Jalabert, Hiroyuki Fujita
Micro-Electro-Mechanical-System (MEMS) devices associated to Transmission Electron Microscopes (TEM) have demonstrated their high potential for atomic resolution imaging of specimen while applying stress for mechanical testing. This paper introduces a novel actuation principle for the MEMS device in TEM relying on the internal magnetic field of the TEM and current flow through the device. The actuation principle is experimentally demonstrated in TEM and entirely modeled in the case of a silicon beam. The model is validated through static and dynamic experimental studies...
December 6, 2018: Ultramicroscopy
Christopher A Mizzi, Pratik Koirala, Ahmet Gulec, Laurence D Marks
Although charging is ubiquitous in electron microscopy, its effects are typically avoided or ignored. However, avoiding charging is not possible in some materials, e.g. lanthanide scandates with well-ordered surfaces positively charge immensely under electron beam illumination because of their electronic structure, and ignoring charging can leave new science undiscovered. In this work, a combination of rapidly acquired electron energy loss spectra and cross-correlation were used to understand and overcome charging effects in DyScO3 ...
December 6, 2018: Ultramicroscopy
K H W van den Bos, L Janssens, A De Backer, P D Nellist, S Van Aert
The atomic lensing model has been proposed as a promising method facilitating atom-counting in heterogeneous nanocrystals [1]. Here, image simulations will validate the model, which describes dynamical diffraction as a superposition of individual atoms focussing the incident electrons. It will be demonstrated that the model is reliable in the annular dark field regime for crystals having columns containing dozens of atoms. By using the principles of statistical detection theory, it will be shown that this model gives new opportunities for detecting compositional differences...
December 6, 2018: Ultramicroscopy
Lan-Hsuan Lee, Chia-Hao Yu, Chuan-Yu Wei, Pei-Chin Lee, Jih-Shang Huang, Cheng-Yen Wen
Using the focused ion beam (FIB) to prepare plan-view transmission electron microscopy (TEM) specimens is beneficial for obtaining structural information of two-dimensional atomic layer materials, such as graphene and molybdenum disulfide (MoS2 ) nanosheets supported on substrates. The scanning electron microscopy (SEM) image in a dual-beam FIB-SEM can accurately locate an area of interest for specimen preparation. Besides, FIB specimen preparation avoids damages and hydrocarbon contamination that are usually produced in other preparation methods, in which chemical etching and polymer adhesion layers are used...
December 5, 2018: Ultramicroscopy
Seyedeh Zahra Mohammadi, Majid Moghaddam, Hossein Nejat Pishkenari
Dynamical lumped modeling of Trolling-mode AFM in manipulation of bio-samples is presented. The combination of high accuracy and compatibility with physiological conditions makes AFM a unique tool for studying biological materials in liquid medium. However, AFM microcantilever suffers from severe sensitivity degradation and noise intensification while operating in liquid; the large hydrodynamic drag between the cantilever and the surrounding liquid overwhelms the tip-sample interaction forces that are important in controlling the process...
December 5, 2018: Ultramicroscopy
H Rose, A Nejati, H Müller
Aberration correction in transmission electron microscopy has proven feasible and useful over a large range of acceleration voltages. The spherical aberration has been corrected for beam energies from 15 kV [1] up to 1.2 MeV [2] while the correction of the chromatic aberration has been achieved for beam energies ranging from 20 kV[3] up to 300 kV[4]. Above this threshold the conventional correction principle based on mixed electric and magnetic focusing elements becomes infeasible with present technology [5]...
November 29, 2018: Ultramicroscopy
Cheng Zhang, William Cantara, Youngmin Jeon, Karin Musier-Forsyth, Nikolaus Grigorieff, Dmitry Lyumkis
Single-particle electron cryo-microscopy and computational image classification can be used to analyze structural variability in macromolecules and their assemblies. In some cases, a particle may contain different regions that each display a range of distinct conformations. We have developed strategies, implemented within the Frealign and cisTEM image processing packages, to focus-classify on specific regions of a particle and detect potential covariance. The strategies are based on masking the region of interest using either a 2-D mask applied to reference projections and particle images, or a 3-D mask applied to the 3-D volume...
November 29, 2018: Ultramicroscopy
P W Hawkes
No abstract text is available yet for this article.
November 24, 2018: Ultramicroscopy
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