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Jiří Škvarla, Juraj Škvarla
A procedure is introduced for measuring the radius of spherical colloid particles from the curvature of upper parts of their central cross-sectional profiles obtained by atomic force microscopy (AFM). To minimize the possible compression and displacement of the spheres, AFM is operated in a mode rendering a constant ultralow pN force on the tip. The procedure allows us to evaluate the mean radius of nearly monodisperse submicrometer spheres of silica in their natively hydrated state in aqueous electrolyte solutions, irrespective of whether they are coagulated or not...
May 16, 2017: Ultramicroscopy
Johannes Jobst, Jaap Kautz, Maria Mytiliniou, Rudolf M Tromp, Sense Jan van der Molen
In a lot of systems, charge transport is governed by local features rather than being a global property as suggested by extracting a single resistance value. Consequently, techniques that resolve local structure in the electronic potential are crucial for a detailed understanding of electronic transport in realistic devices. Recently, we have introduced a new potentiometry method based on low-energy electron microscopy (LEEM) that utilizes characteristic features in the reflectivity spectra of layered materials [1]...
May 13, 2017: Ultramicroscopy
A Quesada, R Gargallo-Caballero, Y Montaña, M Foerster, L Aballe, J F Fernández, J de la Figuera
High aspect-ratio Fe nanostrips are known to reversibly switch from a single-domain magnetic state to a multidomain diamond pattern as a function of temperature (T) and width. This magnetic bistability can be understood by the temperature-dependent balance between magnetocrystalline, shape and magnetoelastic anisotropies and has potential applications in magnetic logic devices. However, as Fe nanostructures easily oxidize, protecting the surface with capping layers may be required, which could largely affect the anisotropy balance...
May 13, 2017: Ultramicroscopy
A V Kondratov, O Y Rogov, R V Gainutdinov
A significant part of the optical metamaterial phenomena has the plasmonic nature and their investigation requires very accurate knowledge of the fabricated structures shape with a focus on the periodical features. We describe a consistent approach to the shape reconstruction of the plasmonic nanostructures. This includes vertical and tilted spike AFM probes fabrication, AFM imaging and specific post-processing. We studied a complex-shaped chiral metamaterial and conclude that the described post-processing routine extends possibilities of the existing deconvolution algorithms in the case of periodical structures with known rotational symmetry, by providing valuable information about periodical features...
May 11, 2017: Ultramicroscopy
Y R Niu, A A Zakharov, R Yakimova
The Sn intercalation into a buffer layer graphene grown on 4H-SiC(0001) substrate has been studied with spectroscopic photoemission and low energy electron microscope. Both SnSix and SnOx interfacial layers are found to form below the buffer layer, converting it into a quasi-free-standing monolayer graphene. Combining the various operation modes of the microscope allows a detailed insight into the formation processes of the interlayers and their thermal stability. In particular, at the interface we observed a reversible transition from silicide to oxide after exposure to ambient pressure and subsequent annealing...
May 10, 2017: Ultramicroscopy
J A Pollock, M Weyland, D J Taplin, L J Allen, S D Findlay
Position-averaged convergent beam electron diffraction patterns are formed by averaging the transmission diffraction pattern while scanning an atomically-fine electron probe across a sample. Visual comparison between experimental and simulated patterns is increasingly being used for sample thickness determination. We explore automating the comparison via a simple sum square difference metric. The thickness determination is shown to be accurate (i.e. the best-guess deduced thickness generally concurs with the true thickness), though factors such as noise, mistilt and inelastic scattering reduce the precision (i...
May 10, 2017: Ultramicroscopy
J I Flege, J-O Krisponeit, J Höcker, M Hoppe, Y Niu, A Zakharov, A Schaefer, J Falta, E E Krasovskii
The complex structure and morphology of ultrathin praseodymia films deposited on a ruthenium(0001) single crystal substrate by reactive molecular beam epitaxy is analyzed by intensity-voltage low-energy electron microscopy in combination with theoretical calculations within an ab initio scattering theory. A rich coexistence of various nanoscale crystalline surface structures is identified for the as-grown samples, notably comprising two distinct oxygen-terminated hexagonal Pr2O3(0001) surface phases as well as a cubic Pr2O3(111) and a fluorite PrO2(111) surface component...
May 10, 2017: Ultramicroscopy
J M de Voogd, M A van Spronsen, F E Kalff, B Bryant, O Ostojić, A M J den Haan, I M N Groot, T H Oosterkamp, A F Otte, M J Rost
Within the last three decades Scanning Probe Microscopy has been developed to a powerful tool for measuring surfaces and their properties on an atomic scale such that users can be found nowadays not only in academia but also in industry. This development is still pushed further by researchers, who continuously exploit new possibilities of this technique, as well as companies that focus mainly on the usability. However, although imaging has become significantly easier, the time required for a safe approach (without unwanted tip-sample contact) can be very time consuming, especially if the microscope is not equipped or suited for the observation of the tip-sample distance with an additional optical microscope...
May 10, 2017: Ultramicroscopy
Tyson C Back, Andreas K Schmid, Steven B Fairchild, John J Boeckl, Marc Cahay, Floor Derkink, Gong Chen, Ali Sayir
With its low work function and high mechanical strength, the LaB6/VB2 eutectic system is an interesting candidate for high performance thermionic emitters. For the development of device applications, it is important to understand the origin, value, and spatial distribution of the work function in this system. Here we combine thermal emission electron microscopy and low energy electron microscopy with Auger electron spectroscopy and physical vapor deposition of the constituent elements to explore physical and chemical conditions governing the work function of these surfaces...
May 10, 2017: Ultramicroscopy
Kellie Pearce, Francis Schuknecht, Christian Späth, Benjamin Duschner, Florian Richter, Ulf Kleineberg
We use photoemission electron microscopy (PEEM) with single- and two-photon excitation to study the properties of surface plasmon polaritons (SPPs) in tapered silver stripe waveguides. Arrays of waveguides with different widths, grating coupler geometries, and taper angles are fabricated using electron beam lithography (EBL) on Si and indium-tin-oxide (ITO)-covered glass substrates. The presence of propagating SPP modes is indicated by modulations of the non-linear photoemission intensity which run along the length of the waveguide - the result of interfering SPPs reflected from the edges...
May 10, 2017: Ultramicroscopy
Tomáš Duchoň, Johanna Hackl, Jan Höcker, Kateřina Veltruská, Vladimír Matolín, Jens Falta, Stefan Cramm, Slavomír Nemšák, Claus M Schneider, Jan Ingo Flege, Sanjaya D Senanayake
Proper consideration of length-scales is critical for elucidating active sites/phases in heterogeneous catalysis, revealing chemical function of surfaces and identifying fundamental steps of chemical reactions. Using the example of ceria thin films deposited on the Cu(111) surface, we demonstrate the benefits of multi length-scale experimental framework for understanding chemical conversion. Specifically, exploiting the tunable sampling and spatial resolution of photoemission electron microscopy, we reveal crystal defect mediated structures of inhomogeneous copper-ceria mixed phase that grow during preparation of ceria/Cu(111) model systems...
May 10, 2017: Ultramicroscopy
M Mankos, K Shadman, B J Siwick
An electron mirror-based pulse compressor design has been developed for improving the temporal resolution of dynamic/ultrafast transmission electron microscopes and ultrafast electron diffraction cameras. The improvement will enable electron microscopes and diffraction cameras to better resolve the dynamics of reactions in the areas of solid state physics, chemistry, and biology. The design utilizes a combination of mirror optics and a magnetic beam separator, which exploits the symmetry inherent in reversing the electron trajectory in the mirror in order to compress the pulse...
May 10, 2017: Ultramicroscopy
Tim Grieb, Florian F Krause, Christoph Mahr, Dennis Zillmann, Knut Müller-Caspary, Marco Schowalter, Andreas Rosenauer
Nano-beam electron diffraction (NBED) is a method which can be applied to measure lattice strain and polarisation fields in strained layer heterostructures and transistors. To investigate precision, accuracy and spatial resolution of such measurements in dependence of properties of the specimen as well as electron optical parameters, simulations of NBED patterns are required which allow to predict the result of common disc-detection algorithms. In this paper we demonstrate by focusing on the detection of the central disc in crystalline silicon that such simulations require to take several experimental characteristics into account in order to obtain results which are comparable to those from experimental NBED patterns...
May 3, 2017: Ultramicroscopy
Matthew J Young, Jared C Carson, Peter H Pfromm, Mary E Rezac, Bruce M Law
Dynamic observation of hydrogen on catalytic metal surfaces is a challenging aspect of studying liquid-phase heterogeneous catalysis. Current methods suffer from one or more of the following limitations: the requirement to observe the surface in high vacuum, the inability to provide nanometer-level spatial resolution, the inability to deal with opaque catalysts and/or liquid immersion phase, the lack of real-time scanning of the surface area, and the inability to assess pronounced topographies or mixed materials...
April 29, 2017: Ultramicroscopy
Kentaro Soma, Stan Konings, Ryotaro Aso, Naoto Kamiuchi, Genki Kobayashi, Hideto Yoshida, Seiji Takeda
An apparatus is developed for transmission electron microscopy (TEM) to acquire image and spectral data, such as TEM images, electron holograms, and electron energy loss spectra, synchronized with the measurement of the dynamic response of a specimen under an applied alternating current (AC) electric potential (voltage, denoted VAC). From a VAC of frequency f, a shutter pulse signal is generated to open and close a pre-specimen shutter in a base TEM apparatus. A pulse is generated per VAC cycle from the targeted phase Φ to Φ +∆Φ with phase width ∆Φ (∆Φ <2π)...
April 29, 2017: Ultramicroscopy
Andreas Beyer, Lennart Duschek, Jürgen Belz, Jan Oliver Oelerich, Kakhaber Jandieri, Kerstin Volz
Surface relaxation of thin transmission electron microscopy (TEM) specimens of strained layers results in a severe bending of lattice planes. This bending significantly displaces atoms from their ideal channeling positions which has a strong impact on the measured annular dark field (ADF) intensity. With the example of GaAs quantum wells (QW) embedded in a GaP barrier, we model the resulting displacements by elastic theory using the finite element (FE) formalism. Relaxed and unrelaxed super cells served as input for state of the art frozen phonon simulation of atomic resolution ADF images...
April 29, 2017: Ultramicroscopy
Farangis Ram, Stuart Wright, Saransh Singh, Marc De Graef
The efficacy of the dictionary approach to Electron Back-Scatter Diffraction (EBSD) indexing was evaluated through the analysis of the error in the retrieved crystal orientations. EBSPs simulated by the Callahan-De Graef forward model were used for this purpose. Patterns were noised, distorted, and binned prior to dictionary indexing. Patterns with a high level of noise, with optical distortions, and with a 25 × 25 pixel size, when the error in projection center was 0.7% of the pattern width and the error in specimen tilt was 0...
April 29, 2017: Ultramicroscopy
Young-Min Kim, Stephen J Pennycook, Albina Y Borisevich
Octahedral tilt behavior is increasingly recognized as an important contributing factor to the physical behavior of perovskite oxide materials and especially their interfaces, necessitating the development of high-resolution methods of tilt mapping. There are currently two major approaches for quantitative imaging of tilts in scanning transmission electron microscopy (STEM), bright field (BF) and annular bright field (ABF). In this paper, we show that BF STEM can be reliably used for measurements of oxygen octahedral tilts...
April 29, 2017: Ultramicroscopy
Florian F Krause, Andreas Rosenauer, Dirk Van Dyck
A relatively simple yet accurate analytical model for the image formation in the imaging scanning TEM (ISTEM) imaging mode, which implements partial spatial incoherence using a combination of scanning illumination and conventional imaging, is presented. Based on an object function approximation the ISTEM intensity can be divided into a constant, a linear and a nonlinear term. Under certain conditions, which are discussed, the formation of both linear and nonlinear terms can be expressed by convolutions with point spread functions...
April 25, 2017: Ultramicroscopy
Juri Barthel, Markus Lentzen, Andreas Thust
In a recent article [1] we examined the influence of the applied electron dose rate on the magnitude of the image contrast in high-resolution transmission electron microscopy (HRTEM). We concluded that the magnitude of the image contrast is not substantially affected by the applied electron dose rate. This result is in obvious contradiction to numerous earlier publications by Kisielowski and coworkers [2-7], who commented our recent article due to this contradiction. The present short communication is a response to the comment of Kisielowski and coworkers on our recent article, where we provide additional arguments supporting our initial findings and conclusions on the magnitude of the image contrast in HRTEM...
April 21, 2017: Ultramicroscopy
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