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Abstract: X-ray microanalysis of materials by synchrotron radiation has generated an increasing demand for advanced multilayer based X-ray optical elements that can be used in beam-lines as monochromators of small or large spectral bandwidth, or in components for shaping high-intensity X-ray beams with highest reflectivities. Modern thin film technologies allow the fabrication of appropriate multilayer systems with reproducible control of layer thicknesses and resulting excellent reflectivity properties that are well adjusted to the requirements. Aperiodic multilayer systems combine the advantage of large bandwidths and decent reflectivity values. Their development necessitates quantitative control of the processing and of the resulting microstructures on the nanometer scale. We have investigated aperiodic multilayer systems consisting of W/B4C bi-layers on silicon, with single layer thicknesses ranging from about 1nm to 2nm. The microstructure and the bi-layer and single layer thickness are characterized quantitatively on cross-sectional samples by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The thickness of bi-layers is determined by geometric phase analysis and that of single layers by evaluation of STEM intensity line profiles. Comparisons with nominal thickness values and with those derived from X-ray reflectivity scans show very good agreement. [Copyright &y& Elsevier]

Abstract: Wavefront preservation of reflective X-ray optics, i.e., homogeneity and coherence properties of the reflected beam, are of crucial importance for their application in combination with high-brilliance synchrotron light sources. In order to compare the performance of optical elements in a quantitative manner, a protocol has been established using the Talbot effect to access the coherence properties of the reflective beam as well as long propagation distance imaging to study its homogeneity. The basic idea is to operate in a single-bounce geometry: a high-resolution imaging detector translated at short propagation distances along the beam is used to measure the visibility of a diffraction grating in transmission geometry placed close to the mirror under study. The change of the fringe visibility as a function of distance between the grating and the detector gives access to the angular source size. A second high-resolution imaging detector at longer propagation distances of up to several meters allows one to measure the homogeneity of the beam. This article outlines the concept as realized at beamline ID19 of the European Synchrotron Radiation Facility, gives insight into some of the technical details to be considered for implementation at other facilities and ends with an example application: the study of a multilayer mirror. [Copyright &y& Elsevier]

Abstract: A round-robin between the multilayer deposition laboratories of the Advanced Photon Source, the European Synchrotron Radiation Facility and the National Synchrotron Light Source II has been initiated in order to study standard W/B4C multilayer mirrors produced by the different facilities. The use of such multilayer mirrors for hard X-ray monochromatisation represents an important alternative to crystal-based devices when greater photon flux density is desirable for, e.g., X-ray imaging applications and other photon-intensive techniques. Currently, knowledge about the potential degradation of the wavefront in terms of beam profile distortion and coherence properties due to reflection on a multilayer mirror is limited. In order to address this issue, the beam profile and coherence properties of a monochromatic synchrotron beam reflected by the individual mirrors were studied at the Advanced Photon Source insertion device beamline 32-ID. The results indicate that by using the same coating material, commercially available high quality substrates and a similar coating technique, mirrors with comparable performance can be produced with quite different multilayer deposition facilities. Furthermore, no wave-optical formalism is available at this time which relates the influence of a multilayer reflection on the wavefront to the structural quality of the mirror. Hence, the experimental studies presented are highly targeted in order to identify parameters which have a potential influence on the wavefront preservation properties of a multilayer. [Copyright &y& Elsevier]

Abstract: Larger spectral bandwidth and higher photon flux density are the major advantages of multilayer monochromators over crystal-based devices. Especially for synchrotron-based hard X-ray microimaging applications the increased photon flux density is important in order to achieve high contrast and resolution in space and/or time. However, the modifications on the beam profile induced by reflection on a multilayer are a drawback which can seriously harm the performance of such a monochromator. A recent study [A. Rack, T. Weitkamp, M. Riotte, D. Grigoriev, T. Rack, L. Helfen, T. Baumbach, R. Dietsch, T. Holz, M. Krämer, F. Siewert, M. Meduňa, P. Cloetens, E. Ziegler, J. Synchrotron Radiat. 17 (2010) 496–510] has shown that the modifications in terms of beam flatness and coherence preservation can be influenced via the material composition of the multilayer coating. The present article extends this knowledge by studying further material compositions used on a daily basis for hard X-ray monochromatization at the beamline ID19 of the European Synchrotron Radiation Facility. [Copyright &y& Elsevier]