1,720,985 research outputs found
Pattern recognition in high-resolution electron microscopy of complex materials
No full textStructural features like defects or heterointerfaces in crystals or amorphous phases give rise to different local patterns in high-resolution electron micrographs or object wave functions. Pattern recognition techniques can be used to identify these typical patterns that constitute the image itself, as was already demonstrated for compositional changes in isostructural heterostructures, where the patterns within unit cells of the lattice were analyzed. To extend such analyses to more complex materials, we examined patterns in small circular areas centered on intensity maxima of the image. Nonsupervised clustering, namely, Ward's clustering method, was applied to these patterns. In two examples, a highly defective ZnMnTe layer on GaAs and a tunnel magneto resistance device, we demonstrate how typical patterns are identified by this method and how these results can be used for a further investigation of the microstructural properties of the sample
Nanofabrication of spin-transfer torque devices by a polymethylmethacrylate mask one step process: Giant magnetoresistance versus single layer devices
No full textWe present a method to prepare magnetic spin torque devices of low specific resistance in a one step lithography process. The quality of the pillar devices is demonstrated for a standard magnetic double layer device. For single layer devices, we found hysteretic switching and a more complex dynamical excitation pattern in higher fields. A simple model to explain the resistance spikes is presented. (c) 2007 American Institute of Physics
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Off-Axis Electron Holographic Focal Series of GaN
No full textThis is a high resolution off-axis electron hologram series obtained with a transmission electron microscope of a Gallium Nitride (GaN) crystal in zoneaxis orientation at atomic resolution. It contains the raw data of two holographic focal series obtained under equal conditions (no strong changes in illumination or microscope setup) a few minutes apart. The first series is a focal series of object holograms,
where the GaN-crystal was located in one of the partial waves. The second
series is taken with object removed from the field of view. The MTF of the camera is also supplied
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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Three-Dimensional Composition and Electric Potential Mapping of III–V Core–Multishell Nanowires by Correlative STEM and Holographic Tomography
Full text linkThe
nondestructive characterization of nanoscale devices, such as those
based on semiconductor nanowires, in terms of functional potentials
is crucial for correlating device properties with their morphological/materials
features, as well as for precisely tuning and optimizing their growth
process. Electron holographic tomography (EHT) has been used in the
past to reconstruct the total potential distribution in three-dimension
but hitherto lacked a quantitative approach to separate potential
variations due to chemical composition changes (mean inner potential,
MIP) and space charges. In this Letter, we combine and correlate EHT
and high-angle annular dark-field scanning transmission electron microscopy
(HAADF-STEM) tomography on an individual ⟨111⟩ oriented
GaAs–AlGaAs core–multishell nanowire (NW). We obtain
excellent agreement between both methods in terms of the determined
Al concentration within the AlGaAs shell, as well as thickness variations
of the few nanometer thin GaAs shell acting as quantum well tube.
Subtracting the MIP determined from the STEM tomogram, enables us
to observe functional potentials at the NW surfaces and at the Au–NW
interface, both ascribed to surface/interface pinning of the semiconductor
Fermi level
Microstructural investigations of Manganese-doped Gallium Nitride by modern methods of high resolution and analytical transmission electron microscopy
No full textIn einem verdünnten magnetischen Halbleiter hängen die magnetischen Eigenschaften von der Mikrostruktur des Materials ab. In dieser Arbeit wird Mn-dotiertes GaN mittels Transmissionselektronenmikroskopie in Hinblick auf den Einbau des Mn und die auftretenden Kristalldefekte untersucht.Durch Anwendung der Objektwellenrekonstruktion ergibt sich eine neue Art und Weise der Abbildung ausgedehnter Defekte. So werden in dieser Arbeit die Kernstrukturen verschiedener Defekte beobachtet und auch ihre Verzerrungsfelder mittels geometrischer Phasenanalyse gemessen.Durch analytische Methoden werden GaMn3N-Ausscheidungen in diesem Material identifiziert. Desweiteren wird erstmals eine inhomogene Verteilung des gelösten Mn in ausscheidungsfreiem Material beobachtet. Auch das Verhältnis von substitutionellem zu interstitiellem Einbau des Mn wurde mittels winkelabhängiger Röntgenspektroskopie untersucht und ein vorwiegend substitutioneller Einbau nachgewiesen.The magnetic properties of a diluted magnetic semiconductor depend on the microstructure of the material. In this work transmission electron microscopy was applied to Mn-doped GaN to investigate the incorporation of Mn and the occurring crystal defects.The novel method of object wave reconstruction was used for the imaging of extended defects. This technique allowed the observation of core structures of various defects. The strain fields of these defects were measured using geometric phase analysis.Precipitates of GaMn3N were identified by analytical measurements. A further investigation of material free of precipitates revealed an inhomogeneous distribution of the Mn, which is reported for the first time. The ratio between substitutional and interstitial incorporation of Mn was measured by angular resolved X-ray spectroscopy. The Mn was found predominantly on the substitutional site
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