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Lewys Jones, Sigurd Wenner, Magnus Nord, Per Harald Ninive, Ole Martin Løvvik, Randi Holmestad, Peter D Nellist
Annular dark-field scanning transmission electron microscopy is a powerful tool to study crystal defects at the atomic scale but historically single slow-scanned frames have been plagued by low-frequency scanning-distortions prohibiting accurate strain mapping at atomic resolution. Recently, multi-frame acquisition approaches combined with post-processing have demonstrated significant improvements in strain precision, but the optimum number of frames to record has not been explored. Here we use a non-rigid image registration procedure before applying established strain mapping methods...
April 15, 2017: Ultramicroscopy
C Moussa, M Bernacki, R Besnard, N Bozzolo
Electron BackScatter Diffraction (EBSD) is often used for semi-quantitative analysis of dislocations in metals. In general, disorientation is used to assess Geometrically Necessary Dislocations (GNDs) densities. In the present paper, we demonstrate that the use of disorientation can lead to inaccurate results. For example, using the disorientation leads to different GND density in recrystallized grains which cannot be physically justified. The use of disorientation gradients allows accounting for measurement noise and leads to more accurate results...
April 14, 2017: Ultramicroscopy
C Kisielowski, H A Calderon, F R Chen, S Helveg, J R Jinschek, P Specht, D Van Dyck
No abstract text is available yet for this article.
April 6, 2017: Ultramicroscopy
Laurène Donati, Masih Nilchian, Sylvain Trépout, Cédric Messaoudi, Sergio Marco, Michael Unser
A central challenge in scanning transmission electron microscopy (STEM) is to reduce the electron radiation dosage required for accurate imaging of 3D biological nano-structures. Methods that permit tomographic reconstruction from a reduced number of STEM acquisitions without introducing significant degradation in the final volume are thus of particular importance. In random-beam STEM (RB-STEM), the projection measurements are acquired by randomly scanning a subset of pixels at every tilt view. In this work, we present a tailored RB-STEM acquisition-reconstruction framework that fully exploits the compressed sensing principles...
April 6, 2017: Ultramicroscopy
A A Ünal, A Parabas, A Arora, J Ehrler, C Barton, S Valencia, R Bali, T Thomson, F Yildiz, F Kronast
The antiferromagnetic to ferromagnetic phase transition in FeRh can be induced globally by either heating the material above its phase transition temperature or applying a combination of external stimuli (such as mechanical strain, electric/magnetic fields) on the material preheated close to its transition temperature. On the other hand, to locally induce this phase transition is more desirable for applications and requires a confined source of energy such as a focused laser beam. Here we combine laser excitation with X-ray magnetic imaging to determine the effect of laser heating on the local and transient magnetization of FeRh using time-resolved photoelectron emission microscopy...
April 4, 2017: Ultramicroscopy
Quentin M Ramasse
Nearly two decades have passed since the Electron Microscopy and Analysis Group (EMAG) Conference was held in Cambridge in 1997, during which two seminal lectures were delivered that would influence the future of the U.K. electron microscopy community. With "Aberration correction in the STEM", O.L. Krivanek and co-workers ushered in the era of probe-corrected scanning transmission electron microscopy, a powerful technology that L.M. Brown urged the community at large to embrace, arguing that it would be akin to placing "A Synchrotron in a Microscope"...
April 1, 2017: Ultramicroscopy
Xiuguang Jin, Masao Suzuki, Tsuneo Yasue, Takanori Koshikawa, Yoshikazu Takeda
We demonstrate a new method of cleaning superlattice (SL) photocathodes using atomic hydrogen that allows an increased number of repeat activations. GaAs/GaAsP SL photocathodes were activated with either conventional heat cleaning or atomic hydrogen cleaning. Repeated heat cleaning was found to gradually lower the quantum efficiency (QE) of the photocathodes, while a relatively constant QE was maintained over repeated atomic hydrogen cleaning. These results show that atomic hydrogen cleaning allows a greater number of photocathode cleanings without a loss of performance...
March 30, 2017: Ultramicroscopy
M Kociak, A Gloter, O Stéphan
The new generation of spectromicroscopes opens up new fields of nanophysics. Beyond the impressive spatial and spectral resolutions delivered by these new instruments - an obvious example being the Hermes machine conceived, designed and built by O. L. Krivanek, who is honoured in this journal issue - here we wish to address the motivations and conditions required to get the best out of them. We first coarsely sketch the panorama of physical excitations worth motivating the use of ultra-high resolution spectroscopy techniques in STEMs...
March 29, 2017: Ultramicroscopy
Tom Wren, Robb Puttock, Boris Gribkov, Sergey Vdovichev, Olga Kazakova
We present the use of custom-made multilayer (ML) magnetic probes in magnetic force microscopy (MFM) for imaging soft magnetic structures, i.e. nickel submicron disks of different dimensions. One of the main advantages of a custom-made ML probe is that it can be controllably switched between standard (parallel) and low moment (antiparallel) states. We demonstrate that the predicted vortex and stripe domain states in the disks are observed when using the ML probes both in the antiparallel and parallel states...
March 28, 2017: Ultramicroscopy
A S Trifonov, D E Presnov, I V Bozhev, D A Evplov, V Desmaris, V A Krupenin
We report on the new active tip for scanning probe microscopy allowing the simultaneous measurements of surface topography and its potential profile. We designed and fabricated a field-effect transistor with nanowire channel located on the apex of silicon-on-insulator small chip. The field-effect transistor with nanowire channel was selected due to its extremely high electric field sensitivity even at room temperature. We developed the scanning probe operated in the tuning fork regime and demonstrated its reasonable spatial and field resolution...
March 28, 2017: Ultramicroscopy
Peter Knittel, Nicolas Hibst, Boris Mizaikoff, Steffen Strehle, Christine Kranz
In this study, high-aspect ratio silicon nanowire (SiNW) - modified atomic force microscopy (AFM) probes are fabricated using focused ion beam (FIB) microfabrication technology and vapor-solid-solid synthesis. Commercially available soft silicon nitride probes are used for localized nanowire growth yielding soft high-aspect ratio AFM probes. The SiNW-modified cantilevers are used here for imaging in PeakForce Tappingۛ (PFT) mode, which offers high force control along with valuable information about tip-sample adhesion...
March 28, 2017: Ultramicroscopy
Mingjian Wu, Erdmann Spiecker
We present a correlative micro-diffraction and differential phase contrast (DPC) study within scanning transmission electron microscopy (STEM) on the determination of mean inner potential (MIP) and explain the origin of subtle beam-specimen interactions at the edge of wedge-shaped crystals using both experiment and simulation. Our measurement of MIP of Si and GaAs resulted in 12.48 ± 0.22 V and 14.15 ± 0.22 V, respectively, from directly evaluating beam refraction in micro-diffraction mode. DPC-STEM measurements gave very similar values...
March 28, 2017: Ultramicroscopy
K M Yu, A Locatelli, M S Altman
A theoretical understanding of image formation in cathode lens microscopy can facilitate image interpretation. We compare Fourier Optics (FO) and Contrast Transfer Function (CTF) approaches that were recently adapted from other realms of microscopy to model image formation in low energy electron microscopy (LEEM). Although these two approaches incorporate imaging errors from several sources similarly, they differ in the way that the image intensity is calculated. The simplification that is used in the CTF calculation advantageously leads to its computational efficiency...
March 24, 2017: Ultramicroscopy
André L F Cauduro, Roberto Dos Reis, Gong Chen, Andreas K Schmid, Horst-Günter Rubahn, Morten Madsen
The knowledge of the structural and electronic surface morphology is imperative to fully understand the charge transfer at interfaces of electronic devices, such as in photovoltaic (PV) cells. To this aim, here, we use low-energy electron microscopy to probe the unoccupied states of post-annealed MoOx thin-films grown in oxygen excess (x∼3.16) and deficient (x∼2.57) environments. 2D work function maps are correlated with the surface topography extracted by mirror electron microscopy (MEM) mode, which show homogenous surface morphology and electronic levels for the specimen with x∼2...
March 23, 2017: Ultramicroscopy
Daniel M Gottlob, Eugénie Martinez, Claire Mathieu, Christophe Lubin, Nicolas Chevalier, Munique Kazar Mendes, Christelle Charpin, Eric Jalaguier, Olivier Renault, Nicholas Barrett
HfO2-based resistive oxide memories are studied by core-level spectromicroscopy using a laboratory-based X-ray photoelectron emission microscope (XPEEM). After forming, the top electrode is thinned to about 1 nm for the XPEEM analysis, making the buried electrode/HfO2 interface accessible whilst preserving it from contamination. The results are obtained in the true photoemission channel mode from individual memory cells (5 × 5 µm) excited by low-flux laboratory X-rays, in contrast to most studies employing the X-ray absorption channel using potentially harmful bright synchrotron X-rays...
March 23, 2017: Ultramicroscopy
Myung-Geun Han, Joseph A Garlow, Matthew S J Marshall, Amanda L Tiano, Stanislaus S Wong, Sang-Wook Cheong, Frederick J Walker, Charles H Ahn, Yimei Zhu
The ability to map out electrostatic potentials in materials is critical for the development and the design of nanoscale electronic and spintronic devices in modern industry. Electron holography has been an important tool for revealing electric and magnetic field distributions in microelectronics and magnetic-based memory devices, however, its utility is hindered by several practical constraints, such as charging artifacts and limitations in sensitivity and in field of view. In this article, we report electron-beam-induced-current (EBIC) and secondary-electron voltage-contrast (SE-VC) with an aberration-corrected electron probe in a transmission electron microscope (TEM), as complementary techniques to electron holography, to measure electric fields and surface potentials, respectively...
March 23, 2017: Ultramicroscopy
Daniel Knez, Philipp Thaler, Alexander Volk, Gerald Kothleitner, Wolfgang E Ernst, Ferdinand Hofer
We report the transformation of nickel clusters into NiO rings by an electron beam induced nanoscale Kirkendall effect. High-purity nickel clusters consisting of a few thousand atoms have been used as precursors and were synthesized with the superfluid helium droplet technique. Aberration-corrected, analytical scanning transmission electron microscopy was applied to oxidise and simultaneously analyse the nanostructures. The transient dynamics of the oxidation could be documented by time lapse series using high-angle annular dark-field imaging and electron energy-loss spectroscopy...
March 23, 2017: Ultramicroscopy
R F Egerton
We discuss the delocalization of the inelastic scattering of 60-300keV electrons in a thin specimen, for energy losses below 50eV where the delocalization length exceeds atomic dimensions. Analytical expressions are derived for the point spread function (PSF) that describes the radial distribution of this scattering, based on its angular distribution and a dielectric representation of energy loss. We also compute a PSF for energy deposition, which is directly related to the radiolysis damage created by a small-diameter probe...
March 22, 2017: Ultramicroscopy
Alan J Craven, Hidetaka Sawada, Sam McFadzean, Ian MacLaren
Ray tracing is used to find improved set-ups of the projector system of a JEOL ARM 200CF TEM/STEM for use in coupling it to a Gatan 965 Quantum ER EELS system and to explain their performance. The system has a probe aberration corrector but no image corrector. With the latter, the problem would be more challenging. The agreement between the calculated performance and that found experimentally is excellent. At 200kV and using the 2.5mm Quantum entrance aperture, the energy range over which the collection angle changes by a maximum of 5% from that at zero loss has been increased from 1...
March 20, 2017: Ultramicroscopy
Renata Rychtáriková, Tomáš Náhlík, Kevin Shi, Daria Malakhova, Petr Macháček, Rebecca Smaha, Jan Urban, Dalibor Štys
Current biological and medical research is aimed at obtaining a detailed spatiotemporal map of a live cell's interior to describe and predict cell's physiological state. We present here an algorithm for complete 3-D modelling of cellular structures from a z-stack of images obtained using label-free wide-field bright-field light-transmitted microscopy. The method visualizes 3-D objects with a volume equivalent to the area of a camera pixel multiplied by the z-height. The computation is based on finding pixels of unchanged intensities between two consecutive images of an object spread function...
March 18, 2017: Ultramicroscopy
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