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Ultramicroscopy

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https://www.readbyqxmd.com/read/28806543/200%C3%A2-kev-cold-field-emission-source-using-carbon-cone-nanotip-application-to-scanning-transmission-electron-microscopy
#1
Shuichi Mamishin, Yudai Kubo, Robin Cours, Marc Monthioux, Florent Houdellier
We report the use of a pyrolytic carbon cone nanotip as field emission cathode inside a modern 200 kV dedicated scanning transmission electron microscope. We show an unprecedented improvement in the probe current stability while maintaining all the fundamental properties of a cold field emission source such as a small angular current density together with a high brightness. We have also studied the influence of the low extraction voltage, as enabled by the nanosized apex of the cones, on the electron optics properties of the source that prevent the formation of a virtual beam cross-over of the gun...
August 9, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28797951/subsampling-and-inpainting-approaches-for-electron-tomography
#2
Toby Sanders, Christian Dwyer
With the aim of addressing the issue of sample damage during electron tomography data acquisition, we propose a number of new reconstruction strategies based on subsampling (which uses only a subset of a full image) and inpainting (recovery of a full image from subsampled one). We point out that the total-variation (TV) inpainting model commonly used to inpaint subsampled images may be inappropriate for 2D projection images of typical TEM specimens. Thus, we propose higher-order TV (HOTV) inpainting, which accommodates the fact that projection images may be inherently smooth, as a more suitable image inpainting scheme...
August 3, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28783580/evaluation-of-high-quality-image-reconstruction-techniques-applied-to-high-resolution-z-contrast-imaging
#3
G Bárcena-González, M P Guerrero-Lebrero, E Guerrero, A Yañez, D Fernández-Reyes, D González, P L Galindo
High-quality image reconstruction techniques allow the generation of high pixel density images from a set of low-resolution micrographs. In general, these techniques consist of two main steps, namely, accurate registration, and formulation of an appropriate forward image model via some restoration method. There exist a wide variety of algorithms to cope with both stages and depending on their practical applications, some methods can outperform others, since they can be sensitive to the assumed data model, noise, drift, etc...
July 31, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28780142/probing-the-effect-of-electron-channelling-on-atomic-resolution-energy-dispersive-x-ray-quantification
#4
Katherine E MacArthur, Hamish G Brown, Scott D Findlay, Leslie J Allen
Advances in microscope stability, aberration correction and detector design now make it readily possible to achieve atomic resolution energy dispersive X-ray mapping for dose resilient samples. These maps show impressive atomic-scale qualitative detail as to where the elements reside within a given sample. Unfortunately, while electron channelling is exploited to provide atomic resolution data, this very process makes the images rather more complex to interpret quantitatively than if no electron channelling occurred...
July 31, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28780143/imaging-the-potential-distribution-of-individual-charged-impurities-on-graphene-by-low-energy-electron-holography
#5
Tatiana Latychevskaia, Flavio Wicki, Conrad Escher, Hans-Werner Fink
While imaging individual atoms can routinely be achieved in high resolution transmission electron microscopy, visualizing the potential distribution of individually charged adsorbates leading to a phase shift of the probing electron wave is still a challenging task. Low-energy electrons (30 - 250 eV) are sensitive to localized potential gradients. We employed low-energy electron holography to acquire in-line holograms of individual charged impurities on free-standing graphene. By applying an iterative phase retrieval reconstruction routine we recover the potential distribution of the localized charged impurities present on free-standing graphene...
July 29, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28780141/quantitative-electric-field-mapping-in-thin-specimens-using-a-segmented-detector-revisiting-the-transfer-function-for-differential-phase-contrast
#6
Takehito Seki, Gabriel Sánchez-Santolino, Ryo Ishikawa, Scott D Findlay, Yuichi Ikuhara, Naoya Shibata
Differential phase contrast in scanning transmission electron microscopy can visualize local electromagnetic fields inside specimens. The contrast derived from first moments, the so-called center of mass, of the diffraction patterns for each probe position can be quantitatively related to the local electromagnetic field under the phase object approximation. While only approximate first moments can be obtained with a segmented detector, in weak phase objects the fields can be accurately quantified on the basis of a phase contrast transfer function...
July 26, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28779615/three-dimensional-visualization-of-dislocations-in-a-ferromagnetic-material-by-magnetic-field-free-electron-tomography
#7
Kana L Hasezaki, Hikaru Saito, Takumi Sannomiya, Hiroya Miyazaki, Takashi Gondo, Shinsuke Miyazaki, Satoshi Hata
In conventional transmission electron microscopy, specimens to be observed are placed in between the objective lens pole piece and therefore exposed to a strong magnetic field about 2 T. For a ferromagnetic specimen, magnetization of the specimen causes isotropic and anisotropic defocusing, deflection of the electron beam as well as deformation of the specimen, which all become more severe when the specimen tilted. Therefore electron tomography on a ferromagnetic crystalline specimen is highly challenging because tilt-series data sets must be acquired without changing the excitation condition of a specific diffraction spot...
July 26, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28763761/feedforward-neural-network-methodology-to-characterize-thin-films-by-electrostatic-force-microscopy
#8
M Konomi, G M Sacha
The contribution of the present paper is in introducing a numerical method to improve the automatic characterization of thin films by increasing the effectiveness of numerical methods that take into account the macroscopic shape of the tip. To achieve this objective, we propose the combination of different feedforward neural networks architectures adapted to the specific requirements of the physical system under study. First, an Adaline architecture is redefined as a linear combination of Green functions obtained from the Laplace equation...
July 26, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28734230/simultaneous-scanning-tunneling-microscopy-and-synchrotron-x-ray-measurements-in-a-gas-environment
#9
Rik V Mom, Willem G Onderwaater, Marcel J Rost, Maciej Jankowski, Sabine Wenzel, Leon Jacobse, Paul F A Alkemade, Vincent Vandalon, Matthijs A van Spronsen, Matthijs van Weeren, Bert Crama, Peter van der Tuijn, Roberto Felici, Wilhelmus M M Kessels, Francesco Carlà, Joost W M Frenken, Irene M N Groot
A combined X-ray and scanning tunneling microscopy (STM) instrument is presented that enables the local detection of X-ray absorption on surfaces in a gas environment. To suppress the collection of ion currents generated in the gas phase, coaxially shielded STM tips were used. The conductive outer shield of the coaxial tips can be biased to deflect ions away from the tip core. When tunneling, the X-ray-induced current is separated from the regular, 'topographic' tunneling current using a novel high-speed separation scheme...
July 14, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28728044/atomic-force-microscopy-study-of-morphological-modifications-induced-by-different-decontamination-treatments-on-escherichia-coli
#10
Florina Lucica Zorila, Cristina Ionescu, Liviu Stefan Craciun, Bogdan Zorila
In this paper we used atomic force microscopy (AFM) to investigate the surface morphology of Escherichia coli, after being subjected to decontamination treatments, at sub-MICs levels (minimal inhibitory concentrations), with different disinfectants used in hospitals, pharmaceutical, food industry and even in our home, as an essential means to prevent the spreading of microorganisms. This article focuses on different morphological modifications adopted by E. coli cells as responses to the different modes of action of these substances...
July 14, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28715668/spatial-resolution-and-cathodoluminescence-intensity-dependence-on-acceleration-voltage-in-electron-beam-excitation-assisted-optical-microscopy-using-y2o3-eu-3-film
#11
Yu Masuda, Masashi Kamiya, Atsushi Sugita, Wataru Inami, Yoshimasa Kawata, Hiroko Kominami, Yoichiro Nakanishi
This study presents relationship between acceleration voltage and spatial resolution of electron-beam assisted (EXA) optical microscope. The nanometric illumination light sources of the present EXA microscope was red-emitting cathodoluminescence (CL) in the Y2O3:Eu(3+) thin film excited by focused electron beam. Our experimental results demonstrated that the spatial resolutions of the EXA microscope were higher as the acceleration voltage was higher. We managed to make images of the scattered gold particles with approximately 90 nm-resolutions at the voltages higher than 20 kV...
July 13, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28728043/autofocus-on-moving-object-in-scanning-electron-microscope
#12
Andrey V Kudryavtsev, Sounkalo Dembélé, Nadine Piat
The sharpness of the images coming from a Scanning Electron Microscope (SEM) is a very important property for many computer vision applications at micro- and nanoscale. It represents how much object details are distinctive in the images: the object may be perceived sharp or blurred. Image sharpness highly depends on the value of focal distance, or working distance in the case of the SEM. Autofocus is the technique allowing to automatically adjust the working distance to maximize the sharpness. Most of the existing algorithms allows working only with a static object which is enough for the tasks of visualization, manual microanalysis or microcharacterization...
July 12, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28711769/unmixing-hyperspectral-data-by-using-signal-subspace-sampling
#13
Jakob Spiegelberg, Shunsuke Muto, Masahiro Ohtsuka, Kristiaan Pelckmans, Ján Rusz
This paper demonstrates how Signal Subspace Sampling (SSS) is an effective pre-processing step for Non-negative Matrix Factorization (NMF) or Vertex Component Analysis (VCA). The approach allows to uniquely extract non-negative source signals which are orthogonal in at least one observation channel, respectively. It is thus well suited for processing hyperspectral images from X-ray microscopy, or other emission spectroscopies, into its non-negative source components. The key idea is to resample the given data so as to satisfy better the necessity and sufficiency conditions for the subsequent NMF or VCA...
July 10, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28712555/space-charge-effects-and-aberrations-on-electron-pulse-compression-in-a-spherical-electrostatic-capacitor
#14
Lei Yu, Haibo Li, Weishi Wan, Zheng Wei, Krzysztof P Grzelakowski, Rudolf M Tromp, Wen-Xin Tang
The effects of space charge, aberrations and relativity on temporal compression are investigated for a compact spherical electrostatic capacitor (α-SDA). By employing the three-dimensional (3D) field simulation and the 3D space charge model based on numerical General Particle Tracer and SIMION, we map the compression efficiency for a wide range of initial beam size and single-pulse electron number and determine the optimum conditions of electron pulses for the most effective compression. The results demonstrate that both space charge effects and aberrations prevent the compression of electron pulses into the sub-ps region if the electron number and the beam size are not properly optimized...
July 6, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28705441/spin-filtered-time-of-flight-k-space-microscopy-of-ir-towards-the-complete-photoemission-experiment
#15
G Schönhense, K Medjanik, S Chernov, D Kutnyakhov, O Fedchenko, M Ellguth, D Vasilyev, A Zaporozhchenko-Zymaková, D Panzer, A Oelsner, C Tusche, B Schönhense, J Braun, J Minár, H Ebert, J Viefhaus, W Wurth, H J Elmers
The combination of momentum microscopy (high resolution imaging of the Fourier plane) with an imaging spin filter has recently set a benchmark in k-resolution and spin-detection efficiency. Here we show that the degree of parallelization can be further increased by time-of-flight energy recording. On the quest towards maximum information (in earlier work termed "complete" photoemission experiment) we have studied the prototypical high-Z fcc metal iridium. Large partial bandgaps and strong spin-orbit interaction lead to a sequence of spin-polarized surface resonances...
July 6, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28697383/on-the-loss-of-information-in-pca-of-spectrum-images
#16
Pavel Potapov
Principal Component Analysis (PCA) can drastically denoise STEM spectrum-images but might distort or cut off the important variations in data. The present paper analyzes various approaches to estimate such deviations and compares them with the simulated data. A spiked covariance model by Nadler (2008) appears to be most appropriated for application in STEM spectrum-imaging.
July 6, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28709084/aberration-measurement-of-the-probe-forming-system-of-an-electron-microscope-using-two-dimensional-materials
#17
Hidetaka Sawada, Christopher S Allen, Shanshan Wang, Jamie H Warner, Angus I Kirkland
The geometric and chromatic aberration coefficients of the probe-forming system in an aberration corrected transmission electron microscope have been measured using a Ronchigram recorded from monolayer graphene. The geometric deformations within individual local angular sub-regions of the Ronchigram were analysed using an auto-correlation function and the aberration coefficients for the probe forming lens were calculated. This approach only requires the acquisition of a single Ronchigram allowing rapid measurement of the aberration coefficients...
July 5, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28692935/a-direct-comparison-of-experimental-methods-to-measure-dimensions-of-synthetic-nanoparticles
#18
P Eaton, P Quaresma, C Soares, C Neves, M P de Almeida, E Pereira, P West
Nanoparticles have properties that depend critically on their dimensions. There are a large number of methods that are commonly used to characterize these dimensions, but there is no clear consensus on which method is most appropriate for different types of nanoparticles. In this work four different characterization methods that are commonly applied to characterize the dimensions of nanoparticles either in solution or dried from solution are critically compared. Namely, transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and dynamic light scattering (DLS) are compared with one another...
July 5, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28692933/contrast-enhancement-of-nanomaterials-using-phase-plate-stem
#19
Hiroki Minoda, Takayuki Tamai, Yuya Ohmori, Hirofumi Iijima
Visualizing materials composed of light elements is difficult, and the development of an imaging method that enhances the phase contrast of such materials has been of much interest. In this study, we demonstrate phase-plate scanning transmission electron microscopy (P-STEM), which we developed recently, and its application to nanomaterials. An amorphous carbon film with a small hole in its center was used to control the phase of incident electron waves, and the phase-contrast transfer function (PCTF) was modified from sine-type to cosine-type...
July 4, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28692934/measuring-nanometre-scale-electric-fields-in-scanning-transmission-electron-microscopy-using-segmented-detectors
#20
H G Brown, N Shibata, H Sasaki, T C Petersen, D M Paganin, M J Morgan, S D Findlay
Electric field mapping using segmented detectors in the scanning transmission electron microscope has recently been achieved at the nanometre scale. However, converting these results to quantitative field measurements involves assumptions whose validity is unclear for thick specimens. We consider three approaches to quantitative reconstruction of the projected electric potential using segmented detectors: a segmented detector approximation to differential phase contrast and two variants on ptychographical reconstruction...
July 3, 2017: Ultramicroscopy
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