Ultramicroscopy (ULTRAMICROSCOPY)

Publications in this journal

• Article: XEDS STEM tomography for 3D chemical characterization of nanoscale particles

  Arda Genc §, Libor Kovarik ⊥, Meng Gu ⊥, Huikai Cheng §, Paul Plachinda §, Lee Pullan §, Bert
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  ABSTRACT: We present a tomography technique which couples scanning transmission electron microscopy (STEM) and X-ray energy dispersive spectrometry (XEDS) to resolve 3D distribution of elements in nanoscale materials. STEM imaging when combined with XEDS mapping using a symmetrically arranged XEDS detector design around the specimen overcomes many of the obstacles in 3D chemical imaging of nanoscale materials and successfully elucidates the 3D chemical information in a large field of view of the transmission electron microscopy (TEM) sample. We employed this technique to investigate 3D distribution of Nickel (Ni), Manganese (Mn) and Oxygen (O) in a Li1.2Ni0.2Mn0.6O2 (LNMO) nanoparticle used as a cathode material in Lithium (Li) ion batteries. For this purpose, 2D elemental maps were acquired for a range of tilt angles and reconstructed to obtain 3D elemental distribution in an isolated LNMO nanoparticle. The results highlight the strength of this technique in 3D chemical analysis of nanoscale materials by successfully resolving Ni, Mn and O elemental distributions in 3D and discovering the new phenomenon of Ni surface segregation in this material. Furthermore, the comparison of simultaneously acquired high angle annular dark filed (HAADF) STEM and XEDS STEM tomography results show that XEDS STEM tomography provides additional 3D chemical information of the material especially when there is low atomic number (Z) contrast in the material of interest.
  Ultramicroscopy 04/2013;
• Article: Controlling mechanisms for field-induced electron emission from diamond-like carbon films

  S.R.P Silva, Richard G Forbes
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  ABSTRACT: A diamond-like carbon film is a possible electron emitter for electronic displays, but the mechanism of electron emission is not well established. A central issue is: “What is the current-limiting process, and where does this occur?” This paper surveys various hypotheses about the nature of the controlling emission mechanism, using (where relevant) data obtained by Fowler-Nordheim analyses of emission from nitrogen-containing hydrogenated amorphous carbon films. Our conclusion is that, in the present state of the theory, none of the hypotheses examined can provide a complete explanation of the experimental results. There is a need for more detailed theoretical analyses and for extra forms of experimental information.
  Ultramicroscopy 02/2013;
• Article: Meanwhile, towards the end of the decade,...

  P.W. hawkes
  Ultramicroscopy 02/2013; 20:189–194.
• Article: An alternative definition of Gabor focus

  P.W. Hawkes
  Ultramicroscopy 02/2013; 41:441.
• Article: Discrete Tomography of Demanding Samples Based on a Modified SIRT Algorithm

  Andreas Zürner, Markus Döblinger, Valentina Cauda, Ruoshan Wei, Thomas Bein
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  ABSTRACT: The 3D structure of three particularly challenging samples was reconstructed by electron tomography. Due to sample limitations resulting in a large missing wedge and large tilt increments respectively the 3D structure could not be reconstructed by standard iterative algorithms; even a recently developed discrete algorithm failed until the input parameters for discrete reconstruction were improved. These challenges were addressed by adding a mask in each step of the preceding standard iterative reconstruction, setting all voxels known to be vacuum as zero, thus improving the segmentation and the 3D starting model. The position of these vacuum voxels is obtained from TEM images or other measurement data.
  Ultramicroscopy 04/2012; 115:41-49.
• Article: TEM and electron holography analyses of granular and thin layered Cu-Co magnetic materials

  B Dubiel, D Wolf, A Czyrska-Filemonowicz
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  ABSTRACT: The paper shows the examples of application of transmission electron microscopy (TEM) techniques for characterization of two types of copper-cobalt magnetic nanomaterials: Cu-10 wt% Co granular giant magnetoresistance (GMR) thin ribbons and thin nanocrystalline Co films deposited on Cu substrate. Quantitative TEM microstructural analyses were used for determination of Co particle size distributions in GMR ribbons. It was demonstrated that the relative resistivity depends on the mean diameter of the cobalt nanoparticles. For nanocrystalline thin Co layers, off-axis electron holography was used to investigate their magnetic structure. The mean in-plane component of the magnetic field in cobalt was calculated from the phase gradient.
  Ultramicroscopy 01/2010; 110:433.
• Article: Nature's infinite books of secrecy.

  Peter Hawkes
  Ultramicroscopy 07/2009;
• Article: "Ab initio" structure solution from electron diffraction data obtained by a combination of automated diffraction tomography and precession technique.

  E Mugnaioli, T Gorelik, U Kolb
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  ABSTRACT: Using a combination of our recently developed automated diffraction tomography (ADT) module with precession electron technique (PED), quasi-kinematical 3D diffraction data sets of an inorganic salt (BaSO(4)) were collected. The lattice cell parameters and their orientation within the data sets were found automatically. The extracted intensities were used for "ab initio" structure analysis by direct methods. The data set covered almost the complete set of possible symmetrically equivalent reflections for an orthorhombic structure. The structure solution in one step delivered all heavy (Ba, S) as well as light atoms (O). Results of the structure solution using direct methods, charge flipping and maximum entropy algorithms as well as structure refinement for three different 3D electron diffraction data sets were presented.
  Ultramicroscopy 06/2009; 109(6):758-65.
• Article: Near-grain-boundary characterization by atomic force microscopy.

  A K Pramanick, A Sinha, G V S Sastry, R N Ghosh
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  ABSTRACT: Characterization of near-grain boundary is carried out by atomic force microscopy (AFM). It has been observed to be the most suitable technique owing to its capability to investigate the surface at high resolution. Commercial purity-grade nickel processed under different conditions, viz., (i) cold-rolled and annealed and (ii) thermally etched condition without cold rolling, is considered in the present study. AFM crystallographic data match well with the standard data. Hence, it establishes two grain-boundary relations viz., plane matching and coincidence site lattice (CSL Sigma=9) relation for the two different sample conditions.
  Ultramicroscopy 06/2009; 109(6):741-7.
• Article: A model of secondary electron imaging in the helium ion scanning microscope.

  Ranjan Ramachandra, Brendan Griffin, David Joy
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  ABSTRACT: A combination of the 'semi-empirical' model for secondary electron production and the TRIM routines which describe ion stopping power, scattering, and transport, has been used to construct a Monte Carlo simulation (IONiSE) that can quantitatively interpret the generation of secondary electrons (SE) from materials by fast helium ions. This approach requires that the parameters of the semi-empirical model be determined by fitting to experimental yield data but has the merit that, unlike more fundamental models, it can be applied with equal ease to both pure elements and complex compounds. The application of the model to predict the topographic yield variation of helium generated SE as a function of energy and material, and to investigate the ratio between SE generated by incident and backscattered ions, is demonstrated.
  Ultramicroscopy 06/2009; 109(6):748-57.
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  Available from: 144.206.159.178

  Article: Burgers vector determination in deformed perovskite and post-perovskite of CaIrO(3) using thickness fringes in weak-beam dark-field images.

  Nobuyoshi Miyajima, Nicolas Walte
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  ABSTRACT: The thickness-fringe method [Ishida et al., Philosophical Magazine 42 (1980) 453] for complete determination of the character of a dislocation Burgers vector has been performed in CaIrO(3) perovskite and post-perovskite deformed at high pressures and high temperatures. By selecting several main zone axes and determining the number of terminating thickness fringes at the extremity of a dislocation from a wedge-shaped thin-foil specimen in weak-beam dark-field transmission electron microscope (TEM) images, the Burgers vectors were unambiguously determined. The results demonstrate that [100] screw and edge dislocations on the (010) slip plane are dominant in the post-perovskite phase. Curved [100] and [010] dislocations and straight 110 screw dislocations on a potential (001) slip plane were identified in the perovskite phase as well as a high density of {110} twins. Low-angle tilt boundaries consisting of different groups of parallel edge dislocations on the {110} and (001) planes indicate diffusion-assisted climb in perovskite at high temperatures. The differences in dislocation microstructures could be due to activations of limited numbers of slip systems for post-perovskite and of a large number of multiple slip systems for perovskite, which may result in the strong crystallographic preferred orientation (CPO) in post-perovskite and the lack of CPO in deformed perovskite.
  Ultramicroscopy 06/2009; 109(6):683-92.
• Article: Is the frozen phonon model adequate to describe inelastic phonon scattering?

  D Van Dyck
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  ABSTRACT: It is proven in a rigorous way that the frozen phonon model that is currently used to account for phonon scattering in multislice calculations, is equivalent to a full quantum-mechanical treatment of the inelastic phonon scattering process.
  Ultramicroscopy 06/2009; 109(6):677-82.
• Source

  Available from: arxiv.org

  Article: Imaging flux vortices in type II superconductors with a commercial transmission electron microscope.

  J C Loudon, P A Midgley
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  ABSTRACT: Flux vortices in superconductors can be imaged using transmission electron microscopy because the electron beam is deflected by the magnetic flux associated with the vortices. This technique has a better spatial and temporal resolution than many other imaging techniques and is sensitive to the magnetic flux density within each vortex, not simply the fields at the sample surface. Despite these advantages, only two groups have successfully employed the technique using specially adapted instruments. Here we demonstrate that vortices can be imaged with a modern, commercial transmission electron microscope operating at 300kV equipped with a field emission gun, Lorentz lens and a liquid helium cooled sample holder. We introduce superconductivity for non-specialists and discuss techniques for simulating and optimising images of flux vortices. Sample preparation is discussed in detail as the main difficulty with the technique is the requirement for samples with very large (>10microm), flat areas so that the image is not dominated by diffraction contrast. We have imaged vortices in superconducting Bi(2)Sr(2)CaCu(2)O(8-delta) and use correlation functions to investigate the ordered arrangements they adopt as a function of applied magnetic field.
  Ultramicroscopy 05/2009; 109(6):700-29.
• Article: The morphology of secondary-hardening carbides in a martensitic steel at the peak hardness by 3DFIM.

  J Akré, F Danoix, H Leitner, P Auger
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  ABSTRACT: The morphology and composition of secondary-hardening M(2)C carbides in a complex steel under non-isothermal tempering condition has been investigated with three-dimensional field ion microscopy and atom-probe tomography. The technical set-up and the condition of investigations have been developed. We will reveal for the first time, a virtually non-biased image of the so-called secondary-hardening microstructure, consisting in a very fine dispersion of nanometer-sized needles, idiomorphs and blocky carbides. Needles precipitate with a large number density at the maximum hardness peak. We have found out that this mixture of shape could be explained by the onset of coarsening, but the role of local factors have been evidenced: variation of composition among the carbides and even local strain effects due to the precipitation of a second phase can play a role in changing the growth conditions.
  Ultramicroscopy 05/2009; 109(5):518-23.