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Amongst the impressive improvements in high-resolution electron microscopy, the Cs-corrector also has significantly enhanced the capabilities of off-axis electron holography. Recently, it has been shown that the signal above noise in the reconstructable phase can be significantly improved by combining holography and hardware aberration correction. Additionally, with a spherical aberration close to zero, the traditional optimum focus for recording high-resolution holograms ("Lichte's defocus") has become less stringent and both, defocus and spherical aberration, can be selected freely within a certain range. This new degree of freedom can be used to improve the signal resolution in the holographically reconstructed object wave locally, e.g. at the atomic positions. A brute force simulation study for an aberration corrected 200. kV TEM is performed to determine optimum values for defocus and spherical aberration for best possible signal to noise in the reconstructed atomic phase signals. Compared to the optimum aberrations for conventional phase contrast imaging (NCSI), which produce "bright atoms" in the image intensity, the resulting optimum values of defocus and spherical aberration for off-axis holography enable "black atom contrast" in the hologram. However, they can significantly enhance the local signal resolution at the atomic positions. At the same time, the benefits of hardware aberration correction for high-resolution off-axis holography are preserved. It turns out that the optimum is depending on the object and its thickness and therefore not universal. © 2012 Elsevier B.V. Source

Lyatti M.,Julich Research Center | Savenko A.,FEI Electronic Optics BV | Savenko A.,Julich Research Center | Poppe U.,CEOS GmbH
Superconductor Science and Technology | Year: 2016

Despite impressive progress in the development of superconducting nanowire single-photon detectors (SNSPD), the main obstacle for the widespread use of such detectors is the low operating temperature required for low-temperature superconductors. The very attractive idea of increasing the operating temperature using high-temperature superconductors for SNSPD fabrication is problematic due to the insufficient quality of ultra-thin films from high-temperature superconductors, which is one of the key requirements for the single-photon detection by superconducting nanowires. In this work, we demonstrate the possibility of fabricating ultra-thin YBa2Cu3O7-x films on SrTiO3 substrates with a surface flatness of ± 1 unit cell and a high critical current density up to 14 MA cm-2 at T = 78 K. The critical current density of ultra-thin films had very low value in the first three unit cell layers adjacent to the substrate and reached nearly the bulk value at the fifth layer. 97% of the superconducting current is carried by only two upper layers of a 5-unit-cell thick YBa2Cu3O7-x film. Due to such superconducting current distribution over the film thickness and good surface flatness 5-unit-cell thick YBa2Cu3O7-x films could be promising for the fabrication of single-photon detectors. © 2016 IOP Publishing Ltd. Source

Schultheiss K.,Karlsruhe Institute of Technology | Zach J.,CEOS GmbH | Gamm B.,Karlsruhe Institute of Technology | Dries M.,Karlsruhe Institute of Technology | And 3 more authors.
Microscopy and Microanalysis | Year: 2010

A promising novel type of electrostatic phase plate for transmission electron microscopy (TEM) is presented. The phase plate consists of a single microcoaxial cable-like rod with its electrode exposed to the undiffracted electrons. The emerging field is used to shift the phase of the undiffracted electrons with respect to diffracted electrons. The design overcomes the drawback of the spatial frequency-blocking ring electrode of the Boersch phase plate. First, experimental phase-contrast images are presented for PbSe and Pt nanoparticles with clearly varying phase contrast, which depends on the applied voltage and resulting phase shift of the unscattered electrons. With the new phase-plate design, we show for the first time the reconstruction of an object wave function based on a series of only three experimental phase-contrast TEM images obtained with an electrostatic phase plate. © Microscopy Society of America 2010. Source

Gibb A.L.,University of California at Berkeley | Gibb A.L.,Lawrence Berkeley National Laboratory | Alem N.,University of California at Berkeley | Alem N.,Lawrence Berkeley National Laboratory | And 12 more authors.
Journal of the American Chemical Society | Year: 2013

Grain boundaries are observed and characterized in chemical vapor deposition-grown sheets of hexagonal boron nitride (h-BN) via ultra-high-resolution transmission electron microscopy at elevated temperature. Five- and seven-fold defects are readily observed along the grain boundary. Dynamics of strained regions and grain boundary defects are resolved. The defect structures and the resulting out-of-plane warping are consistent with recent theoretical model predictions for grain boundaries in h-BN. © 2013 American Chemical Society. Source

Erni R.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Rossell M.D.,ETH Zurich | Nguyen M.-T.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Blankenburg S.,Empa - Swiss Federal Laboratories for Materials Science and Technology | And 10 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Chromatic and spherical aberration-corrected atomic-resolution transmission electron microscopy combined with density-functional theory calculations is employed to elucidate the stability and dynamics of admolecules on suspended graphene. The results presented provide evidence that the interaction between the molecules and hydrogen adatoms leads to a mutual trapping. These "symbiotic" configurations can explain the presence of stable admolecules on graphene at ambient temperature. It is proposed to exploit these configurations to functionalize and dope graphene. © 2010 The American Physical Society. Source

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