Thomas Slater

Research Articles
Joseph P. Patterson, Lucas R. Parent, Joshua Cantlon, Holger Eickhoff, Guido Bared, James E. Evans, Nathan C. Gianneschi
Microscopy and Microanalysis,FirstView Article(s), 8 pages

Abstract

Publication date: August 2016
Source:Ultramicroscopy, Volume 167
Author(s): Raynald Gauvin, Samantha Rudinsky
A universal equation for computing the beam broadening of incident electrons in thin films is presented. This equation is based on the concepts of anomalous diffusion with the Hurst exponent H. When the thickness to elastic mean free path ratio, t / λ , is greater than 1, the Hurst exponent goes to 0.5 and this random walk behavior leads to the Goldstein et al. [1] beam broadening equation when non-relativistic screened Rutherford elastic cross-sections are used. When t / λ ≪ 1 , the lack of elastic collisions for the electron trajectories gives an H exponent of 1 and a different beam broadening equation is obtained. A general equation to compute the beam broadening that takes into account the variation of H with t / λ is presented and this equation was fitted and validated with Monte Carlo simulations of electron trajectories in thin films.

Nature Materials. doi:10.1038/nmat4620

Authors: Tarun C. Narayan, Andrea Baldi, Ai Leen Koh, Robert Sinclair & Jennifer A. Dionne

Publication date: July 2016
Source:Ultramicroscopy, Volume 166
Author(s): Timothy S. English, J Provine, Ann F. Marshall, Ai Leen Koh, Thomas W. Kenny
Specimen preparation remains a practical challenge in transmission electron microscopy and frequently limits the quality of structural and chemical characterization data obtained. Prevailing methods for thinning of specimens to electron transparency are serial in nature, time consuming, and prone to producing artifacts and specimen failure. This work presents an alternative method for the preparation of plan-view specimens using isotropic vapor-phase etching with integrated etch stops. An ultrathin amorphous etch-stop layer simultaneously serves as an electron transparent support membrane whose thickness is defined by a controlled growth process such as atomic layer deposition with sub-nanometer precision. This approach eliminates the need for mechanical polishing or ion milling to achieve electron transparency, and reduces the occurrence of preparation induced artifacts. Furthermore, multiple specimens from a plurality of samples can be thinned in parallel due to high selectivity of the vapor-phase etching process. These features enable dramatic reductions in preparation time and cost without sacrificing specimen quality and provide advantages over wet etching techniques. Finally, we demonstrate a platform for high-throughput transmission electron microscopy of plan-view specimens by combining the parallel preparation capabilities of vapor-phase etching with wafer-scale micro- and nanofabrication.

Research Articles
Robert Estivill, Guillaume Audoit, Jean-Paul Barnes, Adeline Grenier, Didier Blavette
Microscopy and Microanalysis,FirstView Article(s), 7 pages

Abstract

Research Articles
Jong Seok Jeong, K. Andre Mkhoyan
Microscopy and Microanalysis,FirstView Article(s), 8 pages

Abstract

Publication date: 15 May 2016
Source:Acta Materialia, Volume 110
Author(s): Yiqiang Chen, R. Prasath babu, Thomas J.A. Slater, Mingwen Bai, Robert Mitchell, Octav Ciuca, Michael Preuss, Sarah J. Haigh
The anomalous cyclic coarsening behaviour of γ′ precipitates after ageing at 1073 K has been investigated for the low misfit commercial powder metallurgy (PM) Ni-based superalloy RR1000. Using scanning transmission electron microscope (STEM) imaging combined with absorption-corrected energy-dispersive X-ray (EDX) spectroscopy, the elemental segregation as a function of coarsening behaviour has been experimentally observed for secondary γ′ precipitates. Elemental EDX spectrum imaging has revealed nanoscale enrichment of Co and Cr and a depletion of Al and Ti within the γ matrix close to the γ-γʹ interface. Our experimental results, coupled with complementary modelling and synchrotron X-ray diffraction analysis, demonstrate the importance of elastic strain energy resulting from local compositional variations for influencing precipitate morphology. In particular, elemental inhomogeneities, as a result of complex diffusive interactions within both matrix and precipitates, play a crucial role in determining the rate of coarsening. Our findings provide important new evidence for understanding the microstructural evolution observed for advanced superalloys when they are exposed to different heat treatment regimes.

Graphical abstract

Publication date: May 2016
Source:Ultramicroscopy, Volume 164
Author(s): Daniele Zanaga, Thomas Altantzis, Jonathan Sanctorum, Bert Freitag, Sara Bals
It is very challenging to measure the chemical composition of hetero nanostructures in a reliable and quantitative manner. Here, we propose a novel and straightforward approach that can be used to quantify energy dispersive X-ray spectra acquired in a transmission electron microscope. Our method is based on a combination of electron tomography and the so-called ζ-factor technique. We will demonstrate the reliability of our approach as well as its applicability by investigating Au-Ag and Au-Pt hetero nanostructures. Given its simplicity, we expect that the method could become a new standard in the field of chemical characterization using electron microscopy.

Publication date: May 2016
Source:Ultramicroscopy, Volume 164
Author(s): W. Xu, J.H. Dycus, X. Sang, J.M. LeBeau
Here we report a numerical approach to model a four quadrant energy dispersive X-ray spectrometer in the transmission electron microscope. The model includes detector geometries, specimen position and absorption, shadowing by the holder, and filtering by the Be carrier. We show that this comprehensive model accurately predicts absolute counts and intensity ratios as a function of specimen tilt and position. We directly compare the model to experimental results acquired with a FEI Super-X EDS four quadrant detector. The contribution from each detector to the sum is investigated. The program and source code can be downloaded from https://github.com/subangstrom/superAngle.

Abstract

Excessive corrosion of silver nanoparticles is a significant impediment to their use in a variety of potential applications in the biosensing, plasmonic and antimicrobial fields. Here we examine the environmental degradation of triangular silver nanoparticles (AgNP) in laboratory air. In the early stages of corrosion, transmission electron microscopy shows that dissolution of the single-crystal, triangular, AgNP (side lengths 50–120 nm) is observed with the accompanying formation of smaller, polycrystalline Ag particles nearby. The new particles are then observed to corrode to Ag₂S and after 21 days nearly full corrosion has occurred, but some with minor Ag inclusions remaining. In contrast, a bulk Ag sheet, studied in cross section, showed an adherent corrosion layer of only around 20–50 nm in thickness after over a decade of being exposed to ambient air. The results have implications for antibacterial properties and ecotoxicology of AgNP during corrosion as the dissolution and reformation of Ag particles during corrosion will likely be accompanied by the release of Ag⁺ ions.

Electron microscopes, particularly those with aberration correction, can view materials at the subnanometer scale. Additional improvements make it possible to obtain images at lower – [Read More]

Research Articles
Zheng-Yu Yan, Xiao-Xia Ai, Yi-Long Su, Xin-Ying Liu, Xiao-Hui Shan, Sheng-Mei Wu
Microscopy and Microanalysis,FirstView Article(s), 9 pages

Abstract

Automated data collection is an integral part of modern workflows in single particle electron microscopy (EM) research. This review surveys the software packages available for automated single particle EM data collection. The degree of automation at each stage of data collection is evaluated, and the capabilities of the software packages are described. Finally, future trends in automation are discussed.

Publication date: February 2016
Source:Ultramicroscopy, Volume 161
Author(s): Julien Guyon, Nathalie Gey, Daniel Goran, Smail Chalal, Fabián Pérez-Willard
A new setup for automatic 3D EBSD data collection in static mode has been developed using a conventional FIB–SEM system. This setup requires no stage or sample movements between the FIB milling and EBSD mapping. Its capabilities were tested experimentally on a coherent twin boundary of an INCONEL sample. Our result demonstrates that this static setup holds many advantages in terms of data throughput and quality as compared with other ones requiring stage/sample movements. The most important advantages are the better slice alignment and an improved orientation precision in 3D space, both being prerequisite for a reliable grain boundary characterization.

Publication date: February 2016
Source:Ultramicroscopy, Volume 161
Author(s): Tim Dahmen, Lukas Marsalek, Nico Marniok, Beata Turoňová, Sviatoslav Bogachev, Patrick Trampert, Stefan Nickels, Philipp Slusallek
We present a novel software package for the problem “reconstruction from projections” in electron microscopy. The Ettention framework consists of a set of modular building-blocks for tomographic reconstruction algorithms. The well-known block iterative reconstruction method based on Kaczmarz algorithm is implemented using these building-blocks, including adaptations specific to electron tomography. Ettention simultaneously features (1) a modular, object-oriented software design, (2) optimized access to high-performance computing (HPC) platforms such as graphic processing units (GPU) or many-core architectures like Xeon Phi, and (3) accessibility to microscopy end-users via integration in the IMOD package and eTomo user interface. We also provide developers with a clean and well-structured application programming interface (API) that allows for extending the software easily and thus makes it an ideal platform for algorithmic research while hiding most of the technical details of high-performance computing.

Nature Nanotechnology 10, 994 (2015). doi:10.1038/nnano.2015.284

Author: Maksym V. Kovalenko

Although research into colloidal quantum dots has led to promising results for the realization of photovoltaic devices, a better understanding of the robustness and stability of these devices is necessary before commercial competiveness can be claimed.

Nature Nanotechnology 10, 1001 (2015). doi:10.1038/nnano.2015.288

Author: Arto Nurmikko

Synthesis of semiconductor colloidal quantum dots by low-cost, solution-based methods has produced an abundance of basic science. Can these materials be transformed to high-performance light emitters to disrupt established photonics technologies, particularly semiconductor lasers?

Publication date: February 2016
Source:Ultramicroscopy, Volume 161
Author(s): T.L. Burnett, R. Kelley, B. Winiarski, L. Contreras, M. Daly, A. Gholinia, M.G. Burke, P.J. Withers
Ga⁺ Focused Ion Beam-Scanning Electron Microscopes (FIB-SEM) have revolutionised the level of microstructural information that can be recovered in 3D by block face serial section tomography (SST), as well as enabling the site-specific removal of smaller regions for subsequent transmission electron microscope (TEM) examination. However, Ga⁺ FIB material removal rates limit the volumes and depths that can be probed to dimensions in the tens of microns range. Emerging Xe⁺ Plasma Focused Ion Beam-Scanning Electron Microscope (PFIB-SEM) systems promise faster removal rates. Here we examine the potential of the method for large volume serial section tomography as applied to bainitic steel and WC–Co hard metals. Our studies demonstrate that with careful control of milling parameters precise automated serial sectioning can be achieved with low levels of milling artefacts at removal rates some 60× faster. Volumes that are hundreds of microns in dimension have been collected using fully automated SST routines in feasible timescales (<24h) showing good grain orientation contrast and capturing microstructural features at the tens of nanometres to the tens of microns scale. Accompanying electron back scattered diffraction (EBSD) maps show high indexing rates suggesting low levels of surface damage. Further, under high current Ga⁺ FIB milling WC–Co is prone to amorphisation of WC surface layers and phase transformation of the Co phase, neither of which have been observed at PFIB currents as high as 60nA at 30kV. Xe⁺ PFIB dual beam microscopes promise to radically extend our capability for 3D tomography, 3D EDX, 3D EBSD as well as correlative tomography.

This is a brief account of the earlier history of single-particle cryo-EM of biological molecules lacking internal symmetry, which goes back to the mid-seventies. The emphasis of this review is on the mathematical concepts and computational approaches. It is written as the field experiences a turning point in the wake of the introduction of digital cameras capable of single electron counting, and near-atomic resolution can be reached even for smaller molecules.