245 research outputs found
Phase retrieval from 4-dimensional electron diffraction datasets
We present a computational imaging mode for large scale electron microscopy
data, which retrieves a complex wave from noisy/sparse intensity recordings
using a deep learning approach and subsequently reconstructs an image of the
specimen from the Convolutional Neural Network (CNN) predicted exit waves. We
demonstrate that an appropriate forward model in combination with open data
frameworks can be used to generate large synthetic datasets for training. In
combination with augmenting the data with Poisson noise corresponding to
varying dose-values, we effectively eliminate overfitting issues. The U-NET
based architecture of the CNN is adapted to the task at hand and performs well
while maintaining a relatively small size and fast performance. The validity of
the approach is confirmed by comparing the reconstruction to well-established
methods using simulated, as well as real electron microscopy data. The proposed
method is shown to be effective particularly in the low dose range, evident by
strong suppression of noise, good spatial resolution, and sensitivity to
different atom types, enabling the simultaneous visualisation of light and
heavy elements and making different atomic species distinguishable. Since the
method acts on a very local scale and is comparatively fast it bears the
potential to be used for near-real-time reconstruction during data acquisition.Comment: Accepted conference paper of IEEE ICIP 202
Fast generation of calculated ADF-EDX scattering cross-sections under channelling conditions
Advanced materials often consist of multiple elements which are arranged in a
complicated structure. Quantitative scanning transmission electron microscopy
is useful to determine the composition and thickness of nanostructures at the
atomic scale. However, significant difficulties remain to quantify mixed
columns by comparing the resulting atomic resolution images and spectroscopy
data with multislice simulations where dynamic scattering needs to be taken
into account. The combination of the computationally intensive nature of these
simulations and the enormous amount of possible mixed column configurations for
a given composition indeed severely hamper the quantification process. To
overcome these challenges, we here report the development of an incoherent
non-linear method for the fast prediction of ADF-EDX scattering cross-sections
of mixed columns under channelling conditions. We first explain the origin of
the ADF and EDX incoherence from scattering physics suggesting a linear
dependence between those two signals in the case of a high-angle ADF detector.
Taking EDX as a perfect incoherent reference mode, we quantitatively examine
the ADF longitudinal incoherence under different microscope conditions using
multislice simulations. Based on incoherent imaging, the atomic lensing model
previously developed for ADF is now expanded to EDX, which yields ADF-EDX
scattering cross-section predictions in good agreement with multislice
simulations for mixed columns in a core-shell nanoparticle and a high entropy
alloy. The fast and accurate prediction of ADF-EDX scattering cross-sections
opens up new opportunities to explore the wide range of ordering possibilities
of heterogeneous materials with multiple elements
Mapping electronic reconstruction at the metal/insulator interfaces in \ce{LaVO_3/SrVO_3} heterostructures
A \ce{(LaVO_3)_6/(SrVO_3)_3} superlattice is studied with a combination of
sub-{\AA} resolved scanning transmission electron microscopy and monochromated
electron energy-loss spectroscopy. The V oxidation state is mapped with atomic
spatial resolution enabling to investigate electronic reconstruction at the
\ce{LaVO_3}/\ce{SrVO_3} interfaces. Surprisingly, asymmetric charge
distribution is found at adjacent chemically symmetric interfaces. The local
structure is proposed and simulated with double channeling calculation which
agrees qualitatively with our experiment. We demonstrate that local strain
asymmetry is the likely cause of the electronic asymmetry of the interfaces.
The electronic reconstruction at the interfaces extends much further than the
chemical composition, varying from 0.5 to 1.2 nm. This distance corresponds to
the length of charge transfer previously found in the
\ce{(LaVO_3)_m}/\ce{(SrVO_3)_n} metal/insulating and the
\ce{(LaAlO_3)_m}/\ce{(SrTiO_3)_n} insulating/insulating interfaces.Comment: 6 pages, 5 figures. Physical Review B, 201
In-situ Plasma Studies using a Direct Current Microplasma in a Scanning Electron Microscope
Microplasmas can be used for a wide range of technological applications and
to improve our understanding of fundamental physics. Scanning electron
microscopy, on the other hand, provides insights into the sample morphology and
chemistry of materials from the mm-down to the nm-scale. Combining both would
provide direct insight into plasma-sample interactions in real-time and at high
spatial resolution. Up till now, very few attempts in this direction have been
made, and significant challenges remain. This work presents a stable direct
current glow discharge microplasma setup built inside a scanning electron
microscope. The experimental setup is capable of real-time in-situ imaging of
the sample evolution during plasma operation and it demonstrates localized
sputtering and sample oxidation. Further, the experimental parameters such as
varying gas mixtures, electrode polarity, and field strength are explored and
experimental - curves under various conditions are provided. These
results demonstrate the capabilities of this setup in potential investigations
of plasma physics, plasma-surface interactions, and materials science and its
practical applications. The presented setup shows the potential to have several
technological applications, e.g., to locally modify the sample surface (e.g.,
local oxidation and ion implantation for nanotechnology applications) on the
m-scale.Comment: LG, DC, and RDM contributed equally to this work. The videos
mentioned in the manuscript can be found in the Zenodo repository linked in
the pape
Direct Observation of Ferrielectricity at Ferroelastic Domain Boundaries in CaTiO3 by Electron Microscopy
High-resolution aberration-corrected transmission electron microscopy aided by statistical parameter estimation theory is used to quantify localized displacements at a (110) twin boundary in orthorhombic CaTiO3. The displacements are 3–6 pm for the Ti atoms and confined to a thin layer. This is the first direct observation of the generation of ferroelectricity by interfaces inside this material which opens the door for domain boundary engineering.\ud
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Graphical Abstract: http://onlinelibrary.wiley.com/store/10.1002/adma.201103717/asset/image_m/mcontent.jpg?v=1&s=833d8771f847e356acb7c65dffc61a359098e66
Synthesis of diarylamines in the benzo[b]thiophene series bearing electron donating or withdrawing groups by Buchwald–Hartwig C–N coupling
Diarylamines in the benzo[b]thiophene series bearing electron donating or withdrawing groups, were prepared by Buchwald–
Hartwig C–N coupling in moderate to high yields. The conditions used were Pd(OAc)2 (3 mol%), BINAP as ligand (4 mol%) and Cs2CO3 as
base (1.4 equiv.), in toluene at 1008C, being 6-bromo or amino benzo[b]thiophenes coupled, respectively, with substituted anilines or
phenylbromides. The 6-aminobenzo[b]thiophene derivatives were also prepared by palladium catalyzed C–N coupling of the corresponding
6-bromo compounds with benzophenone imine, followed by acidic hydrolysis of the imino derivatives. When 4-nitrobromobenzene and
4-bromobenzonitrile were used as coupling components, triarylamines were also isolated in small amounts. The presence of a fluorine atom
on the phenylbromide highly increases the diarylamine yield
Interface Pattern Engineering in Core-Shell Upconverting Nanocrystals: Shedding Light on Critical Parameters and Consequences for the Photoluminescence Properties
Advances in controlling energy migration pathways in core-shell lanthanide (Ln)-based hetero-nanocrystals (HNCs) have relied heavily on assumptions about how optically active centers are distributed within individual HNCs. In this article, it is demonstrated that different types of interface patterns can be formed depending on shell growth conditions. Such interface patterns are not only identified but also characterized with spatial resolution ranging from the nanometer- to the atomic-scale. In the most favorable cases, atomic-scale resolved maps of individual particles are obtained. It is also demonstrated that, for the same type of core-shell architecture, the interface pattern can be engineered with thicknesses of just 1 nm up to several tens of nanometers. Total alloying between the core and shell domains is also possible when using ultra-small particles as seeds. Finally, with different types of interface patterns (same architecture and chemical composition of the core and shell domains) it is possible to modify the output color (yellow, red, and green-yellow) or change (improvement or degradation) the absolute upconversion quantum yield. The results presented in this article introduce an important paradigm shift and pave the way toward the emergence of a new generation of core-shell Ln-based HNCs with better control over their atomic-scale organization
Preventing cation intermixing enables 50% quantum yield in sub-15 nm short-wave infrared-emitting rare-earth based core-shell nanocrystals
Short-wave infrared (SWIR) fluorescence could become the new gold standard in optical imaging for biomedical applications due to important advantages such as lack of autofluorescence, weak photon absorption by blood and tissues, and reduced photon scattering coefficient. Therefore, contrary to the visible and NIR regions, tissues become translucent in the SWIR region. Nevertheless, the lack of bright and biocompatible probes is a key challenge that must be overcome to unlock the full potential of SWIR fluorescence. Although rare-earth-based core-shell nanocrystals appeared as promising SWIR probes, they suffer from limited photoluminescence quantum yield (PLQY). The lack of control over the atomic scale organization of such complex materials is one of the main barriers limiting their optical performance. Here, the growth of either homogeneous (α-NaYF) or heterogeneous (CaF) shell domains on optically-active α-NaYF:Yb:Er (with and without Ce co-doping) core nanocrystals is reported. The atomic scale organization can be controlled by preventing cation intermixing only in heterogeneous core-shell nanocrystals with a dramatic impact on the PLQY. The latter reached 50% at 60 mW/cm; one of the highest reported PLQY values for sub-15 nm nanocrystals. The most efficient nanocrystals were utilized for in vivo imaging above 1450 nm
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