Biomedical subjects

Günter Möbus

Publications and source records attributed to Günter Möbus.

3 recordsLinked to original sources

PubMed2005

IMAGE-WARP: a real-space restoration method for high-resolution STEM images using quantitative HRTEM analysis.

We have developed a new method for processing distorted high-resolution scanning transmission electron microscopy (STEM) images. The method is based on finding the displaced vertices in the experimental STEM image and warping to geometrically correct reference grid of the object. As a reference grid for warping a structural model obtained using a high-resolution transmission electron microscopy (HRTEM) analysis of the area of interest is utilised. Combined with quantitative HRTEM analysis the IMAGE-WARP method provides a real-space restoration of high-resolution high-angle annular dark-field (HAADF) STEM images without affecting the original Z-contrast information. The method can be applied to extract valuable compositional atomic-column data from any HAADF-STEM image of any kind of bulk crystals with local occupancy or chemistry fluctuations, stacking faults, special grain boundaries or interfaces, for which we have an available structural model. After the warping, distortion-corrected images can be further enhanced using conventional image-filtering techniques, and finally quantified with HAADF-STEM image simulations. The applicability of the IMAGE-WARP method was illustrated using experimental HAADF-STEM images of a strontium titanate crystal disrupted with a Ruddlesden-Popper-type antiphase boundary.

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PubMed2003

Nanobeam propagation and imaging in a FEGTEM/STEM.

Atomic resolution information by EELS can only be obtained by careful control of the propagation and spreading of the beam within the sample. A multislice calculation is used to estimate 3D-intensity distributions in sapphire illuminated with beams of 0.1-0.3 nm diameter, with the focus, Cs-value, and specimen thickness as the variables. The 3D-intensity pattern is then used to predict spatially resolved ELNES signals, interpreted as a convolution of the atomically projected density of states (DOS) with an elastic excitation envelope. The site-and-momentum projected DOS functions are calculated using local density function theory, applied to a rhombohedral grain boundary in sapphire. Finally, experimental difficulties in directly imaging the beam exit wave of a nanobeam-illuminated specimen are demonstrated. Calculation and experiments are for a typical modern high-resolution 300 kV FEGTEM.

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PubMed2003

Spectroscopic electron tomography.

The elemental mapping techniques in analytical transmission electron microscopy (TEM), energy filtered imaging (EFTEM) and EDX-mapping, are shown to provide new routes for tomographic reconstructions of 3D chemical maps on the nanoscale. The inelastic scattering does not only provide chemical sensitivity but also improves the linear projection relationship between mass density and image intensity, which often fails in bright field TEM of crystalline materials due to diffraction contrast. Instrumental requirements and artefact sources within the contrast formation mechanisms and within the numerical reconstruction are assessed.

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