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Lugg N.R.,University of Tokyo | Kothleitner G.,University of Graz | Kothleitner G.,Center for Electronic Microscopy | Shibata N.,University of Tokyo | Ikuhara Y.,University of Tokyo
Ultramicroscopy | Year: 2015

Chemical mapping using energy dispersive X-ray spectroscopy (EDS) in scanning transmission electron microscopy (STEM) has recently shown to be a powerful technique in analyzing the elemental identity and location of atomic columns in materials at atomic resolution. However, most applications of EDS STEM have been used only to qualitatively map whether elements are present at specific sites. Obtaining calibrated EDS STEM maps so that they are on an absolute scale is a difficult task and even if one achieves this, extracting quantitative information about the specimen - such as the number or density of atoms under the probe - adds yet another layer of complexity to the analysis due to the multiple elastic and inelastic scattering of the electron probe. Quantitative information may be obtained by comparing calibrated EDS STEM with theoretical simulations, but in this case a model of the structure must be assumed a priori. Here we first theoretically explore how exactly elastic and thermal scattering of the probe confounds the quantitative information one is able to extract about the specimen from an EDS STEM map. We then show using simulation how tilting the specimen (or incident probe) can reduce the effects of scattering and how it can provide quantitative information about the specimen. We then discuss drawbacks of this method - such as the loss of atomic resolution along the tilt direction - but follow this with a possible remedy: precession averaged EDS STEM mapping. Highlights: © 2014 Elsevier B.V.

Parlinska-Wojtan M.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Parlinska-Wojtan M.,Center for Electronic Microscopy | Meier S.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Patscheider J.,Empa - Swiss Federal Laboratories for Materials Science and Technology
Thin Solid Films | Year: 2010

Plastic deformation of TiN5 nm/SiN0.5 nm multilayers by nanoindentation was investigated by transmission electron microscopy in order to identify deformation mechanisms involved in film failure resulting from severe plastic deformation. The TiN layers exhibited a crystalline fcc structure with a [002] preferential orientation; further crystal growth was interrupted by the amorphous SiNx layers. After severe plastic deformation collective vertical displacement of slabs of several TiN/SiNx- bilayers, which resulted from shear sliding at TiN/TiN grain boundaries, was observed. They are, together with horizontal fractures along the SiNx layers, vertical cracks under the indenter tip following the TiN grain boundaries and delamination from the substrate, the predominant failure mechanisms of these coatings. The deformation behaviour of these films provides an experimental support for the absence of dislocation activity in grains of 5 nm size. © 2010 Elsevier B.V. All rights reserved.

Winkler R.,Center for Electronic Microscopy | Fowlkes J.,Oak Ridge National Laboratory | Szkudlarek A.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Utke I.,Empa - Swiss Federal Laboratories for Materials Science and Technology | And 4 more authors.
ACS Applied Materials and Interfaces | Year: 2014

The gas flux direction in focused electron beam induced processes can strongly destabilize the morphology on the nanometer scale. We demonstrate how pattern parameters such as position relative to the gas nozzle, axial rotation, scanning direction, and patterning sequence result in different growth modes for identical structures. This is mainly caused by nanoscale geometric shadowing, particularly when shadowing distances are comparable to surface diffusion lengths of (CH3)3-Pt-CpCH3 adsorbates. Furthermore, two different adsorbate replenishment mechanisms exist and are governed by either surface diffusion or directional gas flux adsorption. The experimental study is complemented by calculations and dynamic growth simulations which successfully emulate the observed morphology instabilities and support the proposed growth model. © 2014 American Chemical Society.

Lapresta-Fernandez A.,Friedrich - Schiller University of Jena | Lapresta-Fernandez A.,University of Seville | Doussineau T.,Friedrich - Schiller University of Jena | Doussineau T.,CNRS Laboratory of Ionic and Molecular Spectrometry | And 5 more authors.
Nanotechnology | Year: 2011

This paper describes the preparation of nanoparticles composed of a magnetic core surrounded by two successive silica shells embedding two fluorophores, showing uniform nanoparticle size (50-60nm in diameter) and shape, which allow ratiometric pH measurements in the pH range 5-8. Uncoated iron oxide magnetic nanoparticles (∼10nm in diameter) were formed by the coprecipitation reaction of ferrous and ferric salts. Then, they were added to a water-in-oil microemulsion where the hydrophilic silica shells were obtained through hydrolysis and condensation of tetraethoxyorthosilicate together with the corresponding silylated dye derivatives - a sulforhodamine was embedded in the inner silica shell and used as the reference dye while a pH-sensitive fluorescein was incorporated in the outer shell as the pH indicator. The magnetic nanoparticles were characterized using vibrating sample magnetometry, dynamic light scattering, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. The relationship between the analytical parameter, that is, the ratio of fluorescence between the sensing and reference dyes versus the pH was adjusted to a sigmoidal fit using a Boltzmann type equation giving an apparent pKa value of 6.8. The fluorescence intensity of the reference dye did not change significantly (∼3.0%) on modifying the pH of the nanoparticle dispersion. Finally, the proposed method was statistically validated against a reference procedure using samples of water and physiological buffer with 2% of horse serum, indicating that there are no significant statistical differences at a 95% confidence level. © IOP Publishing Ltd.

Kolb F.,University of Graz | Kolb F.,Center for Electronic Microscopy | Schmoltner K.,NanoTecCenter Weiz Forschungsgesellschaft mbH | Huth M.,Goethe University Frankfurt | And 7 more authors.
Nanotechnology | Year: 2013

The development of simple gas sensing concepts is still of great interest for science and technology. The demands on an ideal device would be a single-step fabrication method providing a device which is sensitive, analyte-selective, quantitative, and reversible without special operating/reformation conditions such as high temperatures or special environments. In this study we demonstrate a new gas sensing concept based on a nanosized PtC metal-matrix system fabricated in a single step via focused electron beam induced deposition (FEBID). The sensors react selectively on polar H2O molecules quantitatively and reversibly without any special reformation conditions after detection events, whereas non-polar species (O 2, CO2, N2) produce no response. The key elements are isolated Pt nanograins (2-3 nm) which are embedded in a dielectric carbon matrix. The electrical transport in such materials is based on tunneling effects in the correlated variable range hopping regime, where the dielectric carbon matrix screens the electric field between the particles, which governs the final conductivity. The specific change of these dielectric properties by the physisorption of polar gas molecules (H2O) can change the tunneling probability and thus the overall conductivity, allowing their application as a simple and straightforward sensing concept. © 2013 IOP Publishing Ltd.

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