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Coherent Diffraction (coherent + diffraction)
Selected AbstractsObservation of interference effects in coherent diffraction of nanocrystals under X-ray standing-wave illuminationJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2007Piotr Gryko Coherent X-ray diffraction is a useful technique for understanding the structure of compact objects including those which can be represented as phase objects. X-rays are highly penetrating and have wavelengths very close to atomic spacing. In this work, gold nanocrystals (on a reflecting substrate) were imaged at the Advanced Photon Source and found to produce a novel double diffraction pattern. Simulations were carried out to explain the experimental diffraction pattern in terms of reflection of the incident beam from the substrate to produce a standing wave. The experimental data were then phased to produce a two-dimensional real-space image of the gold. It is expected that the standing-wave illumination may be a useful tool to aid the convergence of the phasing algorithms for nanocrystals. [source] Imaging of quantum array structures with coherent and partially coherent diffractionJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2003I. A. Vartanyants Recent achievements in experimental and computational methods open the possibility of measuring and inverting the diffraction pattern from a finite object of submicrometer size. In this paper the possibilities of such experiments for two-dimensional arrays of quantum dots are discussed. The diffraction pattern corresponding to coherent and partial coherent illumination of a sample was generated. Test calculations based on the iterative algorithms were applied to reconstruct the shape of the individual islands in such a quantum structure directly from its diffraction pattern. It is demonstrated that, in the case of coherent illumination, the correct shape and orientation of an individual island can be obtained. In the case of partially coherent illumination, the correct shape of the particle can be obtained only when the coherence of the incoming beam is reduced to match the size of the island. [source] X-ray diffraction from rectangular slitsJOURNAL OF SYNCHROTRON RADIATION, Issue 4 2002D. Le Bolloc'h It is shown that for micrometre-sized beams the X-ray diffraction from slits is a source of strong parasitic background, even for slits of high quality. In order to illustrate this effect, the coherent diffraction from rectangular slits has been studied in detail. A large number of interference fringes with strong visibility have been observed using a single set of slits made of polished cylinders. For very small apertures, asymmetrical slits generate asymmetrical patterns. This pattern is calculated from the theory of electromagnetic field propagation and compared with experiment in the far-field regime. The use of guard slits to remove Fraunhofer diffraction from the beam-defining slits is treated theoretically. Numerical simulations yield the optimum aperture of the guard slits with respect to the distance to the primary slits. Diffraction theory is shown to be essential to understand how to reduce the background-to-signal ratio in high-resolution experiments. [source] The fine structure of X-ray diffuse scattering in the vicinity of high-angle superlattice Bragg reflectionsACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2003Fine structure of X-ray diffuse scattering Triple-axis X-ray diffractometry was used to study diffuse scattering from an AlAs/GaAs superlattice grown on an [001]-oriented GaAs substrate by molecular beam epitaxy. Reciprocal-space maps were obtained around the 002 reflection from the superlattice and its low-angle first-order satellite. The data obtained reveal quasi-Bragg diffuse-scattering sheets caused by conformal behavior of interfacial roughness as well as amplification of diffuse scattering when the incoming or outgoing angle is nearly equal to the Bragg angle of the superlattice or substrate. The observed features of diffuse-scattering fine structure are explained within the framework of the distorted-wave Born approximation. Nevertheless, this approximation is shown to be incorrect for quantitative analysis of diffuse scattering. In particular, the observed domination in intensity of the incoming Bragg features over the outgoing ones is shown to reflect the decay rate of the coherent X-ray field through the diffuse-scattering channel, which is not negligible relative to the coherent diffraction. [source] | ||||||||||