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  • 1.
    Ali, Hasan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Eriksson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, FREIA. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Li, Hu
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jafri, S. Hassan M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kumar, M. S. Sharath
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Ögren, Jim
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Ziemann, Volker
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    An electron energy loss spectrometer based streak camera for time resolved TEM measurements2017In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 176, p. 5-10Article in journal (Refereed)
    Abstract [en]

    We propose an experimental setup based on a streak camera approach inside an energy filter to measure time resolved properties of materials in the transmission electron microscope (TEM). In order to put in place the streak camera, a beam sweeper was built inside an energy filter. After exciting the TEM sample, the beam is swept across the CCD camera of the filter. We describe different parts of the setup at the example of a magnetic measurement. This setup is capable to acquire time resolved diffraction patterns, electron energy loss spectra (EELS) and images with total streaking times in the range between 100 ns and 10 μs.

  • 2.
    Ali, Hasan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Warnatz, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Xie, Ling
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Quantitative EMCD by use of a double aperture for simultaneous acquisition of EELS2019In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 196, p. 192-196Article in journal (Refereed)
    Abstract [en]

    The weak signal strength in electron magnetic circular dichroism (EMCD) measurements remains one of the main challenges in the quantification of EMCD related EELS spectra. As a consequence, small variations in peak intensity caused by changes of background intervals, choice of method for extraction of signal intensity and equally differences in sample quality can cause strong changes in the EMCD signal. When aiming for high resolution quantitative EMCD, an additional difficulty consists in the fact that the two angular resolved EELS spectra needed to obtain the EMCD signal are taken at two different instances and it cannot be guaranteed that the acquisition conditions for these two spectra are identical.  Here, we present an experimental setup where we use a double hole aperture in the transmission electron microscope to obtain the EMCD signal in a single acquisition. This geometry allows for the parallel acquisition of the two electron energy loss spectra (EELS) under exactly the same conditions. We also compare the double aperture acquisition mode with the qE acquisition mode which has been previously used for parallel acquisition of EMCD. We show that the double aperture mode not only offers better signal to noise ratio as compared to qE mode but also allows for much higher acquisition times to significantly improve the signal quality which is crucial for quantitative analysis of the magnetic moments.

    The full text will be freely available from 2020-10-20 18:43
  • 3.
    Boll, T.
    et al.
    Chalmers, Dept Appl Phys, SE-41296 Gothenburg, Sweden..
    Thuvander, M.
    Chalmers, Dept Appl Phys, SE-41296 Gothenburg, Sweden..
    Koch, S.
    Chalmers, Dept Appl Phys, SE-41296 Gothenburg, Sweden..
    Wagner, J. N.
    Karlsruhe Inst Technol, KNMF, DE-76344 Eggenstein Leopoldshafen, Germany..
    Nedfors, N.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Stiller, K.
    Chalmers, Dept Appl Phys, SE-41296 Gothenburg, Sweden..
    An APT investigation of an amorphous Cr-B-C thin film2015In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 159, p. 217-222Article in journal (Refereed)
    Abstract [en]

    A magnetron sputtered amorphous Cr-B-C thin film was investigated by means of atom probe tomography (APT). The film is constituted of two phases; a Cr-rich phase present as a few nanometer large regions embedded in a Cr-poor phase (tissue phase). The Cr-rich regions form columnar chains oriented parallel to the growth direction of the film. It was found that the Cr-rich regions have a higher B:C ratio than the Cr-poor regions. The composition of the phases was determined as approximately 35Cr-33B-30C and 15Cr-40B-42C (at%), respectively. The results suggest that this type of nanocomposite films has a more complex structure than previously anticipated, which may have an importance for the mechanical and electrical properties.

  • 4. Calmels, Lionel
    et al.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Momentum-resolved EELS and EMCD spectra from the atomic multiplet theory: application to magnetite2010In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 110, no 8, p. 1042-1045Article in journal (Refereed)
    Abstract [en]

    While the energy loss near edge structures of metallic crystals can be calculated with a good accuracy using density functional theory based codes, core-level spectra of transition metal oxides show pronounced multiplet effects which are better described by atomic multiplet codes. We describe the formalism which allows to calculate momentum-resolved electron energy loss spectra in the electric dipole approximation from the atomic multiplet theory, and we apply this formalism to the calculation of energy loss magnetic chiral dichroic spectra of magnetic transition metal oxides. Explicit results are given for magnetite Fe3O4.

  • 5.
    Forsberg, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Englund, Carl-Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Duda, Laurent
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    A versatile soft x-ray transmission system for time resolved in situ microscopy with chemical contrast2009In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 109, no 9, p. 1157-1163Article in journal (Refereed)
    Abstract [en]

    We present the design and operation of a versatile soft X-ray   transmission system for time resolved in situ microscopy with chemical   contrast. The utility of the setup is demonstrated by results from   following a corrosion process of iron in saline environment, subjected   to a controlled humid atmosphere. The system includes a transmission   flow-cell reactor that allows for in situ microscopic probing with soft   X-rays. We employ a full field technique by using a nearly collimated   X-ray beam that produces an unmagnified projection of the transmitted   soft X-rays (below 1.1 keV) which is magnified and recorded by an   optical CCD camera. Time lapse series with chemical contrast allow us   to follow and interpret the chemical processes in detail. The   obtainable lateral resolution is a few mu m, sufficient to detect   filiform corrosion on iron.

     

     

     

  • 6.
    Grandfield, Kathryn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Palmquist, Anders
    Dept of Biomaterials, Sahlgrenska Academy at University of Gothenburg, Göteborg.
    Engqvist, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Three-dimensional structure of laser-modified Ti6Al4V and bone interface revealed with STEM tomography2013In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 127, p. 48-52Article in journal (Refereed)
    Abstract [en]

    The early interaction between an implant's surface and bone is a leading factor for implant success, where multiple surface properties contribute to improved bone anchorage. An important parameter is surface topography, both on the micron and nanoscale. Laser-modification has been performed in the thread valleys of Ti6Al4V screws to alter their surface chemistry and topography to form a nanostructured surface titanium-dioxide. Implants were placed in the rabbit tibia, removed with surrounding bone after 8 weeks, fixated, dried and resin embedded. Focused ion beam milling (FIB) was used to prepare specimens from the resin blocks for transmission electron microscopy (TEM). Z-contrast electron tomography offered the possibility to explore the interfacial structure with high-resolution in three-dimensions. With this technique, collagen fibers of the surrounding bone appear to have been laid down parallel to the implant surface. Accordingly, visualization of the laser-modified interface with nanoscale three-dimensional resolution, as offered by Z-contrast electron tomography, gives new insights into bone bonding mechanisms between roughened titanium-dioxide surfaces and bone.

  • 7. Hebert, C.
    et al.
    Schattschneider, P.
    Rubino, S.
    Novak, P.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Stoeger-Pollach, M.
    Magnetic circular dichroism in electron energy loss spectrometry2008In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 108, no 3, p. 277-284Article in journal (Refereed)
    Abstract [en]

    The measurement of circular dichroism in the electron microscope is a new, emerging method and, as such, it is subject to constant refinement and improvement. Different ways can be envisaged to record the signal. We present an overview of the key steps in the energy-loss magnetic chiral dichroism (EMCD) experiment as well as a detailed review of the methods used in the intrinsic way where the specimen is used as a beam splitter. Lateral resolution up to 20-30 nm can be achieved, and the use of convergent beam techniques leads to an improved SIN ratio. Dichroic effects are shown for Ni and Co single crystal; as a counterexample, measurements were carried also for a non-magnetic (Ti) sample, where no dichroic effect was found.

  • 8.
    Lidbaum, Hans
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Rusz, Ján
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rubino, Stefano
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Liebig, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Reciprocal and real space maps for EMCD experiments2010In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 110, no 11, p. 1380-1389Article in journal (Refereed)
    Abstract [en]

    Electron magnetic chiral dichroism (EMCD) is an emerging tool for quantitative measurements of magnetic properties using the transmission electron microscope (TEM), with the possibility of nanometer resolution. The geometrical conditions, data treatment and electron gun settings are found to influence the EMCD signal. In this article, particular care is taken to obtain a reliable quantitative measurement of the ratio of orbital to spin magnetic moment using energy filtered diffraction patterns. For this purpose, we describe a method for data treatment, normalization and selection of mirror axis. The experimental results are supported by theoretical simulations based on dynamical diffraction and density functional theory. Special settings of the electron gun, so called telefocus mode, enable a higher intensity of the electron beam, as well as a reduction of the influence from artifacts on the signal. Using these settings, we demonstrate the principle of acquiring real space maps of the EMCD signal. This enables advanced characterization of magnetic materials with superior spatial resolution.

  • 9.
    Löfgren, André
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Zeiger, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kocevski, Vancho
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rusz, Ján
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Influence of nuclear quantum effects on frozen phonon simulations of electron vortex beam HAADF-STEM images.2016In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 164, p. 62-69Article in journal (Refereed)
    Abstract [en]

    We have evaluated atomic resolution high-angle annular dark field images with ordinary beams and electron vortex beams for thin crystals of bcc iron, explicitly considering the atomic vibrations using molecular dynamics. The shape of the image representing an atomic column depends on the orbital angular momentum, sample thickness and temperature. For electron vortex beams we observe characteristic doughnut-shaped images of atomic columns. It is shown how the thermal diffuse scattering reduces the depth of their central minima, which get further smeared by finite source size effects. In addition, it is shown that in calculations of HAADF-STEM images at low temperatures one has to explicitly consider the nuclear quantum effects (zero point vibrations), otherwise the effect of atomic vibrations is strongly underestimated.

  • 10.
    Maia, Filipe R.N.C.
    et al.
    Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA.
    Yang, Chao
    Marchesini, Stefano
    Compressive auto-indexing in femtosecond nanocrystallography2011In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 111, no 7, p. 807-811Article in journal (Refereed)
    Abstract [en]

    Ultrafast nanocrystallography has the potential to revolutionize biology by enabling structural elucidation of proteins for which it is possible to grow crystals with 10 or fewer unit cells on the side. The success of nanocrystallography depends on robust orientation-determination procedures that allow us to average diffraction data from multiple nanocrystals to produce a three-dimensional (3D) diffraction data volume with a high signal-to-noise ratio. Such a 3D diffraction volume can then be phased using standard crystallographic techniques. “Indexing” algorithms used in crystallography enable orientation determination of diffraction data from a single crystal when a relatively large number of reflections are recorded. Here we show that it is possible to obtain the exact lattice geometry from a smaller number of measurements than standard approaches using a basis pursuit solver.

  • 11. Muto, S.
    et al.
    Tatsumi, K.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Parameter-free extraction of EMCD from an energy-filtered diffraction datacube using multivariate curve resolution2013In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 125, p. 89-96Article in journal (Refereed)
    Abstract [en]

    We present a parameter-free method of extraction of the electron magnetic circular dichroism spectra from energy-filtered diffraction patterns measured on a crystalline specimen. The method is based on a multivariate curve resolution technique. The main advantage of the proposed method is that it allows extraction of the magnetic signal regardless of the symmetry and orientation of the crystal, as long as there is a sufficiently strong magnetic component of the signal in the diffraction plane. This method essentially overcomes difficulties in extraction of the EMCD signal caused by complexity of dynamical diffraction effects.

  • 12. Pohl, Darius
    et al.
    Schneider, Sebastian
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rellinghaus, Bernd
    Electron vortex beams prepared by a spiral aperture with the goal to measure EMCD on ferromagnetic films via STEM2015In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 150, p. 16-22Article in journal (Refereed)
    Abstract [en]

    X-ray magnetic circular dichroism is a well established method to study element specific magnetic properties of a material, while electron magnetic circular dichroism (EMCD), which is the electron wave analogue to XMCD, is scarcely used today. Recently discovered electron vortex beams, that carry a discrete orbital angular momentum (OAM) L, are also predicted to reveal dichroic signals. Since electron beams can be easily focused down to sub-nanometer diameters, this novel technique promises the possibility to quantitatively determine local magnetic properties with unrivalled lateral resolution. As the spiralling wave front of the electron vortex beam has an azimutally growing phase shift of up to 2 pi and a phase singularity in its axial center, specially designed apertures are needed to generate such non-planar electron waves. We report on the preparation and successful implementation of spiral apertures into the condenser lens system of an aberration-corrected FEL Titan(3) 80-300 transmission electron microscope (TEM). This setup allows to perform scanning TEM (STEM) with vortex beams carrying user-selected OAM. First experiments on the interaction of the vortex beam with a poly-crystalline sample are presented. Within the achieved signal to noise ratio no EMCD signal has been detected. This finding is supported by simulations of inelastic scattering of a beam generated by spiral aperture.

  • 13.
    Rusz, Jan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Muto, Shunsuke
    Tatsumi, Kazuyoshi
    New algorithm for efficient Bloch-waves calculations of orientation-sensitive ELNES2013In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 125, p. 81-88Article in journal (Refereed)
    Abstract [en]

    We discuss in detail the Bloch waves method for the calculation of energy and orientation dependent scattering cross-section for inelastic scattering of electrons on crystals. Convergence properties are investigated and a new algorithm with superior timing and accuracy is described. The new method is applied to calculations of intensity of weakly excited spots, maps of magnetic signal, and tilt series from zone axis orientation towards three-beam orientation.

  • 14.
    Rusz, Ján
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Modified automatic term selection v2: A faster algorithm to calculate inelastic scattering cross-sections2017In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 177, p. 20-25Article in journal (Refereed)
    Abstract [en]

    We present a new algorithm for calculating inelastic scattering cross-section for fast electrons. Compared to the previous Modified Automatic Term Selection (MATS) algorithm (Rusz et al. [18]), it has far better convergence properties in zone axis calculations and it allows to identify contributions of individual atoms. One can think of it as a blend of MATS algorithm and a method described by Weickenmeier and Kohl [10].

  • 15.
    Schneider, Sebastian
    et al.
    IFW Dresden, Inst Metall Mat, POB 270116, D-01171 Dresden, Germany.;Tech Univ Dresden, Inst Festkorperphys, D-01062 Dresden, Germany..
    Pohl, Darius
    IFW Dresden, Inst Metall Mat, POB 270116, D-01171 Dresden, Germany..
    Loeffler, Stefan
    TU Wien, Univ Serv Ctr Electron Microscopy, Wiedner Hauptstr 8-10, A-1040 Vienna, Austria.;McMaster Univ, Dept Mat Sci & Engn, 1280 Main St West, Hamilton, ON L8S 4L8, Canada..
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kasinathan, Deepa
    Max Planck Inst Chem Phys Fester Stoffe, Dept Phys Correlated Matter, Nothnitzer Str 40, D-01187 Dresden, Germany..
    Schattschneider, Peter
    TU Wien, Univ Serv Ctr Electron Microscopy, Wiedner Hauptstr 8-10, A-1040 Vienna, Austria.;TU Wien, Inst Solid State Phys, Wiedner Hauptstr 8-10, A-1040 Vienna, Austria..
    Schultz, Ludwig
    IFW Dresden, Inst Metall Mat, POB 270116, D-01171 Dresden, Germany.;Tech Univ Dresden, Inst Festkorperphys, D-01062 Dresden, Germany..
    Rellinghaus, Bernd
    IFW Dresden, Inst Metall Mat, POB 270116, D-01171 Dresden, Germany..
    Magnetic properties of single nanomagnets: Electron energy-loss magnetic chiral dichroism on FePt nanoparticles2016In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 171, p. 186-194Article in journal (Refereed)
    Abstract [en]

    Electron energy-loss magnetic chiral dichroism (EMCD) allows for the quantification of magnetic properties of materials at the nanometer scale. It is shown that with the support of simulations that help to identify the optimal conditions for a successful experiment and upon implementing measurement routines that effectively reduce the noise floor, EMCD measurements can be pushed towards quantitative magnetic measurements even on individual nanoparticles. With this approach, the ratio of orbital to spin magnetic moments for the Fe atoms in a single Ll(0) ordered FePt nanoparticle is determined to be m(l)/m(s) = 0.08 +/- 0.02. This finding is in good quantitative agreement with the results of XMCD ensemble measurements. (C) 2016 Elsevier B.V. All rights reserved.

  • 16.
    Song, Dongsheng
    et al.
    Tsinghua Univ, Natl Ctr Electron Microscopy Beijing, Key Lab Adv Mat MOE, Sch Mat Sci & Engn, Beijing 100084, Peoples R China.;Tsinghua Univ, State Key Lab New Ceram & Fine Proc, Sch Mat Sci & Engn, Beijing 100084, Peoples R China..
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cai, Jianwang
    Chinese Acad Sci, Beijing Natl Lab Condensed Matter Phys, Inst Phys, Beijing 100190, Peoples R China..
    Zhu, Jing
    Tsinghua Univ, Natl Ctr Electron Microscopy Beijing, Key Lab Adv Mat MOE, Sch Mat Sci & Engn, Beijing 100084, Peoples R China.;Tsinghua Univ, State Key Lab New Ceram & Fine Proc, Sch Mat Sci & Engn, Beijing 100084, Peoples R China..
    Detection of electron magnetic circular dichroism signals under zone axial diffraction geometry2016In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 169, p. 44-54Article in journal (Refereed)
    Abstract [en]

    EMCD (electron magnetic circular dichroism) technique provides us a new opportunity to explore magnetic properties in the transmission electron microscope. However, specific diffraction geometry is the major limitation. Only the two-beam and three-beam case are demonstrated in the experiments until now. Here, we present the more general case of zone axial (ZA) diffraction geometry through which the EMCD signals can be detected even with the very strong sensitivity to dynamical diffraction conditions. Our detailed calculations and well-controlled diffraction conditions lead to experiments in agreement with theory. The effect of dynamical diffraction conditions on EMCD signals are discussed both in theory and experiments. Moreover, with the detailed analysis of dynamical diffraction effects, we experimentally obtain the separate EMCD signals for each crystallographic site in Y3Fe5O12, which is also applicable for other materials and cannot be achieved by site-specific EMCD and XMCD technique directly. Our work extends application of more general diffraction geometries and will further promote the development of EMCD technique.

  • 17.
    Spiegelberg, Jakob
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Idrobo, Juan Carlos
    Oak Ridge National Laboratory, Center for Nanophase Materials Sciences, Oak Ridge, TN 37831, USA.
    Herklotz, Andreas
    Oak Ridge National Laboratory, Materials Sciences and Technology Division, Oak Ridge, TN 37831, USA.
    Ward, Thomas Zac
    Oak Ridge National Laboratory, Materials Sciences and Technology Division, Oak Ridge, TN 37831, USA.
    Zhou, Wu
    School of Physical Sciences, CAS Key Laboratory of Vacuum Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
    Rusz, Ján
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Local low rank denoising for enhanced atomic resolution imaging2018In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 187, p. 34-42Article in journal (Refereed)
    Abstract [en]

    Atomic resolution imaging and spectroscopy suffers from inherently low signal to noise ratios often prohibiting the interpretation of single pixels or spectra. We introduce local low rank (LLR) denoising as tool for efficient noise removal in scanning transmission electron microscopy (STEM) images and electron energy-loss (EEL) spectrum images. LLR denoising utilizes tensor decomposition techniques, in particular the multilinear singular value decomposition (MLSVD), to achieve a denoising in a general setting largely independent of the signal features and data dimension, by assuming that the signal of interest is of low rank in segments of appropriately chosen size. When applied to STEM images of graphene, LLR denoising suppresses statistical noise while retaining fine image features such as scan row-wise distortions, possibly related to rippling of the graphene sheet and consequent motion of atoms. When applied to EEL spectra, LLR denoising reveals fine structures distinguishing different lattice sites in the spinel system CoFe2O4.

  • 18.
    Spiegelberg, Jakob
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Muto, Shunsuke
    Nagoya Univ, Inst Mat & Syst Sustainabil, Adv Measurement Technol Ctr, Chikusa Ku, Nagoya, Aichi 4648603, Japan..
    Ohtsuka, Masahiro
    Nagoya Univ, Grad Sch Engn, Chikusa Ku, Nagoya, Aichi 4648603, Japan..
    Pelckmans, Kristiaan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Unmixing hyperspectral data by using signal subspace sampling2017In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 182, p. 205-211Article in journal (Refereed)
    Abstract [en]

    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. Results obtained both on an artificial simulation study as well as based on experimental data from electronmicroscopy are reported. 

  • 19.
    Spiegelberg, Jakob
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    A multislice theory of electron scattering in crystals including backscattering and inelastic effects2015In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 159, p. 11-18Article in journal (Refereed)
    Abstract [en]

    In the framework of the slice transition operator technique, a general multislice theory for electron scattering in crystals is developed. To achieve this generalization, we combine the approaches for inelastic scattering derived by Yoshioka [J. Phys. Soc. Jpn. 12, 6 (1957)] and backscattering based on the formalism of Chen and Van Dyck [Ultramicroscopy 70, 29-44 (1997)]. A computational realization of the obtained equations is suggested. The proposed computational scheme is tested on elastic backscattering of electrons, where we consider single backscattering in analogy to the computational scheme proposed by Chen and Van Dyck.

  • 20.
    Spiegelberg, Jakob
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Can we use PCA to detect small signals in noisy data?2017In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 172, p. 40-46Article in journal (Refereed)
    Abstract [en]

    Principal component analysis (PCA) is among the most commonly applied dimension reduction techniques suitable to denoise data. Focusing on its limitations to detect low variance signals in noisy data, we discuss how statistical and systematical errors occur in PCA reconstructed data as a function of the size of the data set, which extends the work of Lichtert and Verbeeck, (2013) [16]. Particular attention is directed towards the estimation of bias introduced by PCA and its influence on experiment design. Aiming at the denoising of large matrices, nullspace based denoising (NBD) is introduced.

  • 21.
    Spiegelberg, Jakob
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    LEIFER, KLAUS
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Thersleff, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    The usage of data compression for the background estimation of electron energy loss spectra2017In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 181, p. 117-122Article in journal (Refereed)
    Abstract [en]

    Quantitative analysis of noisy electron spectrum images requires a robust estimation of the underlying background signal. We demonstrate how modern data compression methods can be used as a tool for achieving an analysis result less affected by statistical errors or to speed up the background estimation. In particular, we demonstrate how a multilinear singular value decomposition (MLSVD) can be used to enhance elemental maps obtained from a complex sample measured with energy electron loss spectroscopy. Furthermore, the usage of vertex component analysis (VCA) for a basis vector centered estimation of the background is demonstrated. Arising computational benefits in terms of model accuracy and computational costs are studied.

  • 22.
    Spiegelberg, Jakob
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pelckmans, Kristiaan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Tensor decompositions for the analysis of atomic resolution electron energy loss spectra2017In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 175, p. 36-45Article in journal (Refereed)
  • 23.
    Spiegelberg, Jakob
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thersleff, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Pelckmans, Kristiaan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Analysis of electron energy loss spectroscopy data using geometric extraction methods2017In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 174, p. 14-26Article in journal (Refereed)
  • 24.
    Spiegelberg, Jakob
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Song, Dongsheng
    Dunin-Borkowski, Rafal
    Zhu, Jing
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Blind identification of magnetic signals in electron magnetic chiral dichroism using independent component analysis2018In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 195, p. 129-135Article in journal (Refereed)
    Abstract [en]

    Electron magnetic chiral dichroism (EMCD) is a promising technique to investigate local magnetic structures in the electron microscope. However, recognition of the EMCD signal, or also finding optimal parameter settings for given materials and sample orientations typically requires extensive simulations to aid the experiment. Here, we discuss how modern data processing techniques, in particular independent component analysis, can be used to identify magnetic signals in an unsupervised manner from energy filtered transmission electron microscopy (EFTEM) images. On the background of the recent advent of 4D scanning transmission electron microscopy, we discuss how this data processing may enable simultaneous tracking of all three spatial components of the magnetic momenta for arbitrary materials and several sample orientations without the previous need of complementary simulations.

  • 25. Verbeeck, J.
    et al.
    Hebert, C.
    Rubino, S.
    Novak, P.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Houdellier, F.
    Gatel, C.
    Schattschneider, P.
    Optimal aperture sizes and positions for EMCD experiments2008In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 108, no 9, p. 865-872Article in journal (Refereed)
    Abstract [en]

    The signal-to-noise ratio (SNR) in energy-loss magnetic chiral dichroism (EMCD)-the equivalent of Xray magnetic circular dichroism (XMCD) in the electron microscope-is optimized with respect to the detector shape, size and position. We show that an important increase in SNR over previous experiments can be obtained when taking much larger detector sizes. We determine the ideal shape of the detector but also show that round apertures are a good compromise if placed in their optimal position. We develop the theory for a simple analytical description of the EMCD experiment and then apply it to dynamical multibeam Bloch wave calculations and to an experimental data set. In all cases it is shown that a significant and welcome improvement of the SNR is possible.

1 - 25 of 25
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