Biomedical subjects

M Ohler

Publications and source records attributed to M Ohler.

4 recordsLinked to original sources

PubMed2002

X-ray diffraction topography using a diffractometer with a bendable monochromator at a synchrotron radiation source.

The different properties of laboratory- and synchrotron-based double-crystal setups for X-ray topographic applications are discussed as a basis for the realization of a versatile instrument allowing the investigation of all kinds of crystals with high strain sensitivity and without any reduction in image size. It appears that the use of a bendable highly perfect monochromator (silicon) achieves this goal, through the local adaptation of Bragg angles, to compensate either dispersion or a bending of the sample.

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PubMed2000

A conical slit for three-dimensional XRD mapping.

Traditionally, depth resolution in diffraction experiments is obtained by inserting pinholes in both the incoming and diffracted beam. For materials science investigations of local strain and texture properties this leads to very slow data-acquisition rates, especially when characterization is performed on the level of the individual grains. To circumvent this problem a conical slit has been manufactured by wire-electrodischarge machining. The conical slit has six 25 microm-thick conically shaped openings matching six of the Debye-Scherrer cones from a face-centred-cubic powder. By combining the slit with a microfocused incoming beam of hard X-rays, an embedded gauge volume is defined. Using a two-dimensional detector, fast and complete information can be obtained regarding the texture and strain properties of the material within this particular gauge volume. The average machining and assemblage errors of the conical slit are found both to be of the order of 5 microm. An algorithm for alignment of the slit is established, and the potential of the technique is illustrated with an example of grain mapping in a 4.5 mm-thick Cu sample.

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PubMed1999

Theory of moiré fringes on X-ray diffraction topographs of bicrystals.

The theory of moiré fringes on X-ray diffraction topographs of bicrystals is derived from the dynamical theory of X-ray diffraction for the reflection (Bragg) and the transmission (Laue) case. The influence on the moiré fringes of the diffraction geometry, of the geometry of the sample, of its optical properties and of the topographic method is investigated. The perfect-crystal theory is also expanded to weakly deformed bicrystals.

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PubMed1999

X-ray diffraction moiré topography as a means to reconstruct relative displacement fields in weakly deformed bicrystals.

X-ray diffraction topographs of wafers produced by separation by implanted oxygen (SIMOX) show moiré fringes in both reflection and transmission geometry. These fringes reveal deformations of the order of 10(-6) to 10(-8) between the layer and the substrate of the SIMOX material. A new method for a quantitative analysis of moiré fringes is developed and allows reconstruction with a high sensitivity of the three components of the relative displacement field between layer and substrate directly from a set of topographs. This method is used for the interpretation of moiré topographs of entire 4 in SIMOX wafers and of regions around crystal defects. Finally, the capabilities of an analysis of moiré fringes are compared with those of the usual diffraction topo-graphy.

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