Torrents Abad, Oscar | Wheeler, Jeffrey M. | Michler, Johann | Schneider, Andreas S. | Arzt, Eduard
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The strength of metals increases with decreasing sample size, a trend known as the size effect. In particular, focused ion beam-milled body-centered cubic (BCC) micropillars exhibit a size effect known to scale with the ratio of the test temperature to the critical temperature (Tc) of the BCC metal, a measure of how much the yield stress is governed by the lattice resistance. In this paper, this effect is systematically studied by performing high-temperature compression tests on focused ion beam-manufactured Ta and W single crystal pillars ranging in diameter from 500 nm to 5 μm at temperatures up to 400 °C, and discussed in the context of bulk strength and size dependent stresses. Both metals show larger size effects at higher temperatures, reaching values that are in the range of FCC metals at temperatures near Tc. However, it is demonstrated that size effects can be considerably affected by material parameters such as dislocation density and lattice friction, as well as by the yield criterion used. Furthermore, for W, a change from uniform wavy deformation to localized deformation is observed with increasing temperature and pillar size, further indicating that the temperature ratio strongly influences the relative motion of screw and edge dislocations.
Bachmaier, Andrea | Schmauch, Jörg | Aboulfadl, Hisham | Verch, Andreas | Motz, Christian
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In this study, dual phase CuCo composites with a total immiscibility in the solid state and a very different initial phase strength are deformed by severe plastic deformation. Nanocrystalline supersaturated solid solutions are reached in all CuCo composites independent of the initial composition. The deformation and mechanical mixing process is studied thoroughly by combining scanning electron microscopy, transmission electron microscopy, three-dimensional atom probe tomography and nanoindentation. The indentation hardness of the Cu and Co phase and its evolution as a function of the applied strain is linked to deformation and mechanical mixing process to gain a better understanding how the phase strength mismatch of the Cu and Co phase effects the amount of co-deformation and deformation-induced mixing. Our results show that co-deformation is not a necessary requirement to achieve mechanical mixing.
Dahmen, Tim | Engstler, Michael | Pauly, Christoph | Trampert, Patrick | de Jonge, Niels | Mücklich, Frank | Slusallek, Philipp
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A new method for the image acquisition in scanning electron microscopy (SEM) was introduced. The method used adaptively increased pixel-dwell times to improve the signal-to-noise ratio (SNR) in areas of high detail. In areas of low detail, the electron dose was reduced on a per pixel basis, and a-posteriori image processing techniques were applied to remove the resulting noise. The technique was realized by scanning the sample twice. The first, quick scan used small pixel-dwell times to generate a first, noisy image using a low electron dose. This image was analyzed automatically, and a software algorithm generated a sparse pattern of regions of the image that require additional sampling. A second scan generated a sparse image of only these regions, but using a highly increased electron dose. By applying a selective low-pass filter and combining both datasets, a single image was generated. The resulting image exhibited a factor of ~ ‰3 better SNR than an image acquired with uniform sampling on a Cartesian grid and the same total acquisition time. This result implies that the required electron dose (or acquisition time) for the adaptive scanning method is a factor of ten lower than for uniform scanning.
Dahmen, Tim | Trampert, Patrick | de Jonge, Niels | Slusallek, Philipp
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Three-dimensional (3D) scanning transmission electron microscopy (STEM) has become one of the primary tools for analytical characterization in materials science and also finds increasing use in the life sciences. A number of different recording schemes exist for the acquisition of 3D data using STEM, each capturing different spatial frequencies and, thus, different information about the shape of a specimen. In this article, we present and compare different sampling approaches based on images with both large and small depth of field. We highlight the latest contribution to 3D data acquisition, the combined tilt, and focal series. This recording scheme combines the advantages of tilt series-based tomography with 3D data acquisition using a focal series and is particularly beneficial for imaging specimens with a thickness of 1 µm or greater.
Dahmke, Indra N. | Hermannsdörfer, Justus | Weatherup, Robert | Hofmann, Stephan | Peckys, Diana B. | de Jonge, Niels
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DOI:de Jonge, Niels | Mølhave, Kristian | Alloyeau, Damien
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DOI:de Jonge, Niels | Peckys, Diana B.
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Electron microscopy of biological cells in liquid provides unique nanoscale information. A highly attractive idea is the capability to also study physiological processes of live cells with electron microscopy. However, this idea seems unrealistic because the minimal needed electron dose to obtain contrast is already many orders of magnitude above the lethal dose known to cause reproductive-cell death. We show here that claims of electron microscopy of viable cells in recent reports are based on a questionable interpretation of the used fluorescence live/dead assay. A practical alternative to study biological processes is correlative light and electron microscopy.
de Jonge, Niels | Ross, Frances M. | Wang, Chongmin
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DOI:Peckys, Diana | Korf, Ulrike | Wiemann, Stefan | de Jonge, Niels
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DOI:Peckys, Diana B. | Alansary, Dalia | Niemeyer, Barbara A. | de Jonge, Niels
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