Description: Publication date: Available online 14 April 2018 Source: Ultramicroscopy Author(s): Priya Dwivedi, Sander Konijnenberg, Silvania Pereira, Paul Urbach Ptychography, a form of Coherent Diffractive Imaging, is used with short wavelengths (e.g. X-rays, electron beams) to achieve high-resolution image reconstructions. One of the limiting factors for the reconstruction quality is the accurate knowledge of the illumination probe positions. Recently, many advances have been made to relax the requirement for the probe positions accuracy. Here, we analyse and demonstrate a straightforward approach that can be used to correct the probe positions with sub-pixel accuracy. Simulations and experimental results with visible light are presented in this work.

Description: Publication date: Available online 13 April 2018 Source: Ultramicroscopy Author(s): P. Schattschneider, S. Löffler Interaction of the probe with the specimen in an electron microscope inevitably leads to entanglement between the probe and the scatterer. In spite of the importance of entanglement in many areas of modern physics, this subject has not been touched in the literature. Here, we develop some ideas about entanglement in electron microscopy for a number of scattering mechanisms. The relationship between entropy, density matrices, and coherence is discussed. In addition, we explore the questions “Why is Bragg scattering coherent and energy loss incoherent?” and “When does decoherence play a role?” It turns out that it seems to be possible to measure decoherence on extremely short timescales of ∼ 10 − 8 s . This is especially important in view of recent developments in ultrafast electron microscopy.

Description: Publication date: Available online 13 April 2018 Source: Ultramicroscopy Author(s): Se-Ho Kim, Phil Woong Kang, O Ok Park, Jae-Bok Seol, Jae-Pyoung Ahn, Ji Yeong Lee, Pyuck-Pa Choi We present a new method of preparing needle-shaped specimens for atom probe tomography from freestanding Pd and C-supported Pt nanoparticles. The method consists of two steps, namely electrophoresis of nanoparticles on a flat Cu substrate followed by electrodeposition of a Ni film acting as an embedding matrix for the nanoparticles. Atom probe specimen preparation can be subsequently carried out by means of focused-ion-beam milling. Using this approach, we have been able to perform correlative atom probe tomography and transmission electron microscopy analyses on both nanoparticle systems. Reliable mass spectra and three-dimensional atom maps could be obtained for Pd nanoparticle specimens. In contrast, atom probe samples prepared from C-supported Pt nanoparticles showed uneven field evaporation and hence artifacts in the reconstructed atom maps. Our developed method is a viable means of mapping the three-dimensional atomic distribution within nanoparticles and is expected to contribute to an improved understanding of the structure-composition-property relationships of various nanoparticle systems.

Description: Publication date: Available online 12 April 2018 Source: Ultramicroscopy Author(s): Tim Grieb, Florian F. Krause, Marco Schowalter, Dennis Zillmann, R. Sellin, Knut Müller-Caspary, Christoph Mahr, Thorsten Mehrtens, D. Bimberg, Andreas Rosenauer Strain analyses from experimental series of nano-beam electron diffraction (NBED) patterns in scanning transmission electron microscopy are performed for different specimen tilts. Simulations of NBED series are presented for which strain analysis gives results that are in accordance with experiment. This consequently allows to study the relation between measured strain and actual underlying strain. A two-tilt method which can be seen as lowest-order electron beam precession is suggested and experimentally implemented. Strain determination from NBED series with increasing beam convergence is performed in combination with the experimental realization of a probe-forming aperture with a cross inside. It is shown that using standard evaluation techniques, the influence of beam convergence on spatial resolution is lower than the influence of sharp rings around the diffraction disc which occur at interfaces and which are caused by the tails of the intensity distribution of the electron probe.

Description: Publication date: June 2018 Source: Ultramicroscopy, Volume 189 Author(s): Hussein Banjak, Thomas Grenier, Thierry Epicier, Siddardha Koneti, Lucian Roiban, Anne-Sophie Gay, Isabelle Magnin, Françoise Peyrin, Voichita Maxim Fast tomography in Environmental Transmission Electron Microscopy (ETEM) is of a great interest for in situ experiments where it allows to observe 3D real-time evolution of nanomaterials under operating conditions. In this context, we are working on speeding up the acquisition step to a few seconds mainly with applications on nanocatalysts. In order to accomplish such rapid acquisitions of the required tilt series of projections, a modern 4K high-speed camera is used, that can capture up to 100 images per second in a 2K binning mode. However, due to the fast rotation of the sample during the tilt procedure, noise and blur effects may occur in many projections which in turn would lead to poor quality reconstructions. Blurred projections make classical reconstruction algorithms inappropriate and require the use of prior information. In this work, a regularized algebraic reconstruction algorithm named SIRT-FISTA-TV is proposed. The performance of this algorithm using blurred data is studied by means of a numerical blur introduced into simulated images series to mimic possible mechanical instabilities/drifts during fast acquisitions. We also present reconstruction results from noisy data to show the robustness of the algorithm to noise. Finally, we show reconstructions with experimental datasets and we demonstrate the interest of fast tomography with an ultra-fast acquisition performed under environmental conditions, i.e. gas and temperature, in the ETEM. Compared to classically used SIRT and SART approaches, our proposed SIRT-FISTA-TV reconstruction algorithm provides higher quality tomograms allowing easier segmentation of the reconstructed volume for a better final processing and analysis.

Description: Publication date: May 2018 Source: Ultramicroscopy, Volume 188 Author(s): Elena Pascal, Saransh Singh, Patrick G. Callahan, Ben Hourahine, Carol Trager-Cowan, Marc De Graef

Description: Publication date: May 2018 Source: Ultramicroscopy, Volume 188 Author(s): Tyson C. Back, Andreas K. Schmid, Steven B. Fairchild, John J. Boeckl, Marc Cahay, Floor Derkink, Chen Gong, Ali Sayir

Description: Publication date: May 2018 Source: Ultramicroscopy, Volume 188

Description: Publication date: Available online 6 April 2018 Source: Ultramicroscopy Author(s): João M. Medeiros, Désirée Böck, Gregor L. Weiss, Romain Kooger, Roger A. Wepf, Martin Pilhofer Electron cryotomography is able to visualize macromolecular complexes in their cellular context, in a frozen-hydrated state, and in three dimensions. The method, however, is limited to relatively thin samples. Cryo-focused ion beam (FIB) milling is emerging as a powerful technique for sample thinning prior to cryotomography imaging. Previous cryo-FIB milling reports utilized custom-built non-standard equipment. Here we present a workflow and the required commercially available instrumentation to either implement the method de novo , or as an upgrade of pre-existing dual beam milling instruments. We introduce two alternative protocols and the respective sample holders for milling. The “bare grid holder” allows for milling on plain grids, having the advantage of enabling relatively shallow milling angles for wedge geometries. The “Autogrid holder” is designed for milling grids clamped into a mechanical support ring (Autogrid), resulting in increased stability for lamella geometries. We applied the workflow to prepare samples and record high-quality tomograms of diverse model organisms, including infected and uninfected HeLa cells, amoebae, yeast, multicellular cyanobacteria, Pseudomonas aeruginosa and Escherichia coli cells. The workflow will contribute to the dissemination of electron cryotomography of cryo-FIB milled samples in the biological sciences.

Description: Publication date: Available online 6 April 2018 Source: Ultramicroscopy Author(s): Patrick Trampert, Faysal Bourghorbel, Pavel Potocek, Maurice Peemen, Christian Schlinkmann, Tim Dahmen, Philipp Slusallek In scanning electron microscopy, the achievable image quality is often limited by a maximum feasible acquisition time per dataset. Particularly with regard to three-dimensional or large field-of-view imaging, a compromise must be found between a high amount of shot noise, which leads to a low signal-to-noise ratio, and excessive acquisition times. Assuming a fixed acquisition time per frame, we compared three different strategies for algorithm-assisted image acquisition in scanning electron microscopy. We evaluated (1) raster scanning with a reduced dwell time per pixel followed by a state-of-the-art Denoising algorithm, (2) raster scanning with a decreased resolution in conjunction with a state-of-the-art Super Resolution algorithm, and (3) a sparse scanning approach where a fixed percentage of pixels is visited by the beam in combination with state-of-the-art inpainting algorithms. Additionally, we considered increased beam currents for each of the strategies. The experiments showed that sparse scanning using an appropriate reconstruction technique was superior to the other strategies.