Alain Soyer

Three-dimensional computer reconstructions from serial sections of cell nuclei

The analysis of ultrathin serial sections as 3‐dimensional (3D) information requires interpretation and display of a large amount of data. We suggest a simple way to solve this problem; it permits presentation of a series of sections as a 3D color image of good quality. It involves a picture system with specialized hardware and software written for this purpose.

Experimental and computer simulation study of the variation with depth of the X-ray section topograph images of a dislocation

A systematic study of the variations of the contrast of a dislocation in silicon on section topographs with the depth of the line was performed both experimentally and with computer simulations. Mo Kα1 radiation and 33{\bar 3} and {\bar 3}{\bar 3}3 symmetric reflections were used. The crystal thickness was 440 μm so that the value of μt was 0.64. The influence of the orientation of the dislocation was studied for values of the angle between the line and its Burgers vector ranging between 60 and 90° in the glide plane. It was observed that when the dislocation lies close to the entrance surface, whatever its orientation, its image is centred around the trace of the plane of incidence passing through the intersection of the dislocation with the direct beam while when the dislocation lies close to the exit surface its image is centred around the projection of the dislocation on the section pattern. The variation of the orientation of the image for intermediate depths of the dislocation is interpreted by means of the geometrical construction of the dynamical image. The values of the orientation of the image calculated according to this simple model are in good agreement with those measured on both experimental and simulated topographs. The same geometrical model enables the difference in the relative positions of the direct and dynamic images of stereo pairs to be explained. A new feature was observed in the simulated images and several of the experimental ones, namely a concentration of intensity along the projection of the dislocation in the reflected direction. Slit width was taken into account in the simulations for a better fit with experimental topographs but not polarization, which was taken to be normal to the plane of incidence. Because of the small value of the crystal thickness and of μt, the variation of the contrast with the Burgers vector is very small, making its determination very difficult.

The Use of an Array Processor for the Simulation of X-ray Topographs

The use of a varying-step algorithm now allows the simulation of traverse topographs and of section topographs taking into account the real width of the incident beam. However, computation time remains a critical factor in practical use. With an array processor it is possible to decrease the computation time significantly. It is shown that pictures of good quality may be obtained in a reasonable time using local facilities. The influence of various parameters on the accuracy of the simulations is discussed. It is demonstrated that local machines can be more useful, in crystallography, than giant computers often difficult to reach through the network of communications.

Simulation of X‐ray traverse topographs by means of a computer

The precision of the numerical algorithm used is the critical factor in computing traverse topographs. The varying-step algorithm allows such a computation. Images have been computed simulating the real experiment, i.e. by the addition of the intensities of individual section topographs. Results are in good agreement with experiments: it has been possible to characterize dislocations fully by the study of the fine details of their contrast. This may be of practical interest whenever section topographs cannot be used, as, for instance, in the case of thin crystals.

X-ray standing waves in a heterostructure: application to a Zn1−xCoxO epilayer on ZnO(00.\bar 1)–O substrate

X-ray standing waves (XSW) in a thin epitaxic film are treated in the framework of the dynamical theory. It is demonstrated that the fluorescence yield around the main peak of the rocking curve has essentially the same characteristics as that of the usual XSW on a bulk crystal surface. Thus, XSW provide a direct method to probe the atom position in a thin film. The method was applied to an epilayer of the diluted magnetic semiconductor Zn0.94Co0.06O, in order to determine the Co-atom position. The XSW established that Co atoms occupy the substitutional Zn site in the ZnO matrix, although their coherent fraction, which measures the degree of order, is rather low. Moreover, the measurement of the Zn fluorescence in the film gives approximately the same value for the coherent fraction of the Zn atoms. Besides, by using the substrate rocking curve, it is shown that the XSW signal of the Zn atoms in the substrate can be detected through the film. This interesting approach allows the coherent fraction of an element of a substrate below an interface to be probed in situ. For the Zn fluorescence, the coherent fraction is lower near the interface than in the bulk. These results should relate to strains and defects on both sides of the interface.

Fourier Filtering of Synchrotron White-Beam Topographs

Numerical image treatment has been used for the enhancement and the analysis of synchrotron white-beam topographs. Images are recorded either during the experiment by means of an X-ray-sensitive camera or after the experiment from photographic films. Filters are designed to avoid artefacts such as the Gibbs effect. Filtering has been applied to the study of the propagation of surface acoustic waves in piezoelectric materials and ferromagnetic domains in Fe-Si crystals, illustrating the interest of Fourier filtering for a deep analysis of X-ray topographs.

Observation of surface acoustic waves using synchrotron radiation X-ray topography

Progressive surface acoustic waves (SAW) are well imaged using synchronous X-ray topography. We show that using large synchrotron radiation X-ray beams it is possible to obtain much information about the waves existing in various devices including filters and delay lines. To better understand the mechanism of formation of these images, section topographs were made and compared to simulated images. It appears that the section images contain more intricate contrasts than expected that, in fact, give new information about the SAW and explain the mechanism of formation of the translation images.

Time resolved synchrotron radiation X-ray topography study of surface acoustic waves propagation.

The purpose of this contribution is to study several phenomena influencing the formation of X-rays diffraction images of SAW propagating on crystals so to be able to use them to obtain further information about the SAW. We consider particularly new contrasts appearing in white beam section topographs made with low or large amplitude SAW. The first ones can bring information about propagation at different depth and the second allows a measurement of the amplitude of the SAW.

Images Of Serial Sectioning In Electron Microscopy : 3D Visualisation Of Objects Of Biological Interest

In the case of serial sections observed by the means of an electron microscope, it is possible to rebuild an image of an object, using the local intelligence of an image work-station without the need of a powerful computer. We will explain the basic principles of a program that we have written and explain its further developments.

Image treatment of synchrotron topographs

Various techniques of images treatment such as Fourier filtering or maximum entropy were used to enhance images of X-ray topography recorded with synchrotron radiation.