Multilayer Monochromator Research Articles

Dual energy-band excitation from a low power Rh anode X-ray tube for the simultaneous determination of low Z and high Z elements (Na-U) using total-reflection X-ray fluorescence analysis (TXRF).

This article presents results from an experimental setup for a dual energy-band vacuum spectrometer for total-reflection X-ray fluorescence analysis allowing simultaneous efficient excitation of low, medium, and high Z elements. The spectrometer is equipped with an air-cooled 35 W low power Rh X-ray tube and a 17 mm2 silicon drift detector with a thin 8 µm beryllium window. A Pd/B4C multilayer monochromator is used at the same time as a Bragg reflector for Rh-Kα radiation and as a high-energy cut-off reflector above 5 keV, where the characteristic Rh-L radiation is totally reflected and present in the spectrum of the exciting radiation. This leaves one broad low energy band below 5 keV and one high energy band around the energy of Rh-Kα. As Rh-L radiation would be absorbed on its path through air, a new beam entrance system was designed in order to guide the Rh-L photons into the vacuum chamber for efficient excitation of low Z elements. With this setup, elements down to sodium (Z = 11, E = 1.04 keV) could be detected. First results are presented, and spectra obtained in air as well as in vacuum are compared and discussed. Detection limits in the range of 1000 µg/kg for Na and around 140 µg/kg for Mg were achieved using the NIST SRM 1640 (trace elements in water).

IN13 Neutron guide and primary spectrometer upgrade

We discuss the proposed upgrade of the IN13 neutron backscattering spectrometer at the Institut Laue-Langevin (Grenoble, France) and the resulting changes in instrument performance. The effect of using a temperature gradient monochromator on instrument flux and resolution is presented and reproduced using a multi-layer monochromator model for the Monte Carlo neutron ray tracing package McStas. Simulations of the combined effect of varying crystal mosaicity in conjunction with the gradient monochromator on supermirror guides are also shown.

Spectral tailoring of nanoscale EUV and soft x-ray multilayer optics

Extreme ultraviolet and soft X-ray (XUV) multilayer optics have experienced significant development over the past few years, particularly on controlling the spectral characteristics of light for advanced applications like EUV photolithography, space observation, and accelerator- or lab-based XUV experiments. Both planar and three dimensional multilayer structures have been developed to tailor the spectral response in a wide wavelength range. For the planar multilayer optics, different layered schemes are explored. Stacks of periodic multilayers and capping layers are demonstrated to achieve multi-channel reflection or suppression of the reflective properties. Aperiodic multilayer structures enable broadband reflection both in angles and wavelengths, with the possibility of polarization control. The broad wavelength band multilayer is also used to shape attosecond pulses for the study of ultrafast phenomena. Narrowband multilayer monochromators are delivered to bridge the resolution gap between crystals and regular multilayers. High spectral purity multilayers with innovated anti-reflection structures are shown to select spectrally clean XUV radiation from broadband X-ray sources, especially the plasma sources for EUV lithography. Significant progress is also made in the three dimensional multilayer optics, i.e., combining micro- and nanostructures with multilayers, in order to provide new freedom to tune the spectral response. Several kinds of multilayer gratings, including multilayer coated gratings, sliced multilayer gratings, and lamellar multilayer gratings are being pursued for high resolution and high efficiency XUV spectrometers/monochromators, with their advantages and disadvantages, respectively. Multilayer diffraction optics are also developed for spectral purity enhancement. New structures like gratings, zone plates, and pyramids that obtain full suppression of the unwanted radiation and high XUV reflectance are reviewed. Based on the present achievement of the spectral tailoring multilayer optics, the remaining challenges and opportunities for future researches are discussed.

Interfacial mechanics of carbonaceous reinforcements in electrophoretically deposited nickel coatings

Electrophoretically deposited nickel and its composite coatings are extensively used in aerospace and automotive industry for steel plating, super mirror, multilayer monochromator due to superior corrosion resistance and mechanical properties. The present article proposes a systematic approach of comparing the elastic modulus of electrophoretically deposited Ni with diamond, carbon nanotubes (CNT) and graphene reinforcements. Dynamic modulus mapping of electrophoretically deposited coatings exhibited an increased elastic modulus on the addition of diamond, CNT and graphene (259.8GPa, 217.6GPa and 210.7GPa, respectively) than that of pure Ni (167.7GPa). This conflicting effect on the elastic modulus arises due to the difference in reinforcement's morphology, which is further examined using the rule of mixture (ROM), combined Voigt-Reuss model (V-R) and Hashin-Shtrikman model (H-S). Closer prediction of elastic modulus via V-R model indicates that volume fraction plays the more dominant role than the aspect ratio of the reinforcements. In ROM and H-S model, the values of elastic modulus of CNT and graphene reinforcements are closer to the lower bound, while with diamond reinforcement, elastic modulus value approaches in between the upper and lower bound, ascertaining strong interfacial anchoring of diamond with matrix than CNT and graphene. Reinforcement factor (Rf) has also confirmed this strong mechanical interlocking of diamond with the matrix which was ~1.7 and ~3.0 times higher than CNT and graphene, respectively.

Time- and spatial-resolved XAFS spectroscopy in a single shot: new analytical possibilities for in situ material characterization.

A new concept that comprises both time- and lateral-resolved X-ray absorption fine-structure information simultaneously in a single shot is presented. This uncomplicated set-up was tested at the BAMline at BESSY-II (Berlin, Germany). The primary broadband beam was generated by a double multilayer monochromator. The transmitted beam through the sample is diffracted by a convexly bent Si (111) crystal, producing a divergent beam. This, in turn, is collected by either an energy-sensitive area detector, the so-called color X-ray camera, or by an area-sensitive detector based on a CCD camera, in θ-2θ geometry. The first tests were performed with thin metal foils and some iron oxide mixtures. A time resolution of lower than 1 s together with a spatial resolution in one dimension of at least 50 µm is achieved.

Structural characterization and low-temperature properties of Ru/C multilayer monochromators with different periodic thicknesses.

Ru/C multilayer monochromators with different periodic thicknesses were investigated using X-ray grazing-incidence reflectivity, diffuse scattering, Bragg imaging, morphology testing, etc. before and after cryogenic cooling. Quantitative analyses enabled the determination of the key multilayer structural parameters for samples with different periodic thicknesses, especially the influence from the ruthenium crystallization. The results also reveal that the basic structures and reflection performance keep stable after cryogenic cooling. The low-temperature treatment smoothed the surfaces and interfaces and changed the growth characteristic to a low-frequency surface figure. This study helps with the understanding of the structure evolution of multilayer monochromators during cryogenic cooling and presents sufficient experimental proof for using cryogenically cooled multilayer monochromators in a high-thermal-load undulator beamline.

Thermal stress prediction in mirror and multilayer coatings.

Multilayer optics for X-rays typically consist of hundreds of periods of two types of alternating sub-layers which are coated on a silicon substrate. The thickness of the coating is well below 1 µm (tens or hundreds of nanometers). The high aspect ratio (∼10(7)) between the size of the optics and the thickness of the multilayer can lead to a huge number of elements (∼10(16)) for the numerical simulation (by finite-element analysis using ANSYS code). In this work, the finite-element model for thermal-structural analysis of multilayer optics has been implemented using the ANSYS layer-functioned elements. The number of meshed elements is considerably reduced and the number of sub-layers feasible for the present computers is increased significantly. Based on this technique, single-layer coated mirrors and multilayer monochromators cooled by water or liquid nitrogen are studied with typical parameters of heat-load, cooling and geometry. The effects of cooling-down of the optics and heating of the X-ray beam are described. It is shown that the influences from the coating on temperature and deformation are negligible. However, large stresses are induced in the layers due to the different thermal expansion coefficients between the layer and the substrate materials, which is the critical issue for the survival of the optics. This is particularly true for the liquid-nitrogen cooling condition. The material properties of thin multilayer films are applied in the simulation to predict the layer thermal stresses with more precision.

Realtime X-ray reflectometry to see changes at buried interfaces

X-ray reflectometry is powerful in determining internal structure of multilayered thin films, such as thickness and density of each layer, as well as the roughness of surface and interfaces [1]. The measurement requires some precise angular scans near the critical angle with monochromatic parallel X-rays, and therefore it has not been thought that the technique is basically suitable to see changes. However, even without any angular scans, it is possible to obtain essentially the same data by using wide angular dispersion of the incident X-ray beam. The principle is basically known as Naudon's pioneering concept [2]. The system has been improved further by employing a monochroator, which was not used by Naudon's work. A multilayer monochromator was placed at very narrow limited space between a rotating anode X-ray source and the sample stage [3]. Use of a fast Si strip detector also contributed to improve the time-resolution. One can obtain an X-ray reflectivity curve with 4.5 decades even in 1 sec. It is possible to measure the curve down to 10-6, if 20 sec accumulation is allowed. Another advantage of the present instrument is fairly wide angular divergence, which ensures simultaneous data collection for 2 deg range. One of our recent successful applications of this method is the measurement of thermal expansion factor of the polymer thin film. It was also possible to see melting and freezing surfaces. In the presentation, such practical application will be demonstrated, in addition to the detailed description of our instruments.

Feasibility study of total reflection X-ray fluorescence analysis using a liquid metal jet X-ray tube

Total reflection X-ray spectroscopy (TXRF) is a powerful analytical technique for qualitative and quantitative analysis of trace and ultratrace elements in a sample with lower limits of detection (LLDs) of pg/g to ng/g in concentration and absolute high fg levels are attainable. Several X-ray sources, from low power (few W), 18kW rotating anodes to synchrotron radiation, are in use for the excitation and lead accordingly to their photon flux delivered on the sample the detection limits specified. Not only the power, but also the brilliance and focal shape are of importance for TXRF. A microfocus of 50–100μm spot size or the line focus of diffraction tubes is best suited. Excillum developed a new approach in the design of a source: the liquid metal jet anode. In this paper the results achieved with this source are described. A versatile TXRF spectrometer with vacuum chamber designed at Atominstitut was used for the experiments. A multilayer monochromator selecting the intensive Ga-Kα radiation was taken and the beam was collimated by 50μm slits. Excellent results regarding geometric beam stability, high fluorescence intensities and low background were achieved leading to detection limits in the high fg range for Ni. A 100mm2 silicon drift detector (SDD) collimated to 80mm2 was used to collect the fluorescence radiation. The results from measurements on single element samples are presented.

A robust tool for photon source geometry measurements using the fractional Talbot effect

A reliable measurement of beam coherence is important for optimal performance of a number of coherence methods being utilized at third-generation synchrotrons and free-electron lasers. Various approaches have been proposed in the past for determining the source size, and hence the degree of coherence; however they often require complex setups with perfect optics and suffer from undefined uncertainties. We present a robust tool for X-ray source characterization with a full quantitative uncertainty analysis for fast on-the-fly coherence measurements. The influence of three multilayer monochromator crystals on the apparent source size is evaluated using the proposed method.

Optimization of the cooling system in a double multilayer monochromator

This paper presents the results of heat transfer and deformation analyses of the first of two monochromator crystals installed in a DMM (double multilayer monochromator) for SAXS (small angle X-ray scattering) beamline at the Pohang Light Source (PLS). The DMM was developed to allow precise rotational and linear motion of the crystal. The two crystals have independent driving systems and can be rotated simultaneously, but the first crystal absorbs most of the heat power, so we used the ANSYS program to calculate the temperature distribution and the deformation in the first crystal and in the crystal holder. When the contact geometry between the crystal and the crystal holder is changed, the surface slope error coming from thermal deformation varies. With these analyses of deformation and slope error, an optimized cooling system was designed for the first crystal holder.

A dedicated micro-CT beamline for the Australian Synchrotron and the Remote-CT project

A dedicated micro-CT beamline is planned for the Australian Synchrotron which will extend the synchrotron's imaging and tomography capability down to the smaller scale, incorporating phase-contrast and absorption-contrast, and an additional focussing-based mode for high-resolution. The beamline will use multi-layer mirror monochromators for enhanced flux, and will focus particularly on dynamic and high throughput studies in both monochromatic and pink-beam mode. Together with the existing Imaging and Medical beamline, this beamline will produce numerous large datasets of 10 GB or more, providing a significant data-processing challenge. The Remote-CT project addresses this by combining the "MASSIVE" supercomputing GPU cluster with XLI / X-TRACT software, developed at CSIRO. This software has extensive functionality for both processing and simulation of absorption and phase-contrast tomography data and has now been modified for parallel operation on a GPU cluster to take maximum advantage of the speed-up this enables.

Upgraded ESRF BM29 beamline for SAXS on macromolecules in solution

Small-angle X-ray scattering (SAXS) measurements of proteins in solution are becoming increasingly popular with biochemists and structural biologists owing to the presence of dedicated high-throughput beamlines at synchrotron sources. As part of the ESRF Upgrade program a dedicated instrument for performing SAXS from biological macromolecules in solution (BioSAXS) has been installed at the renovated BM29 location. The optics hutch has been equipped with new optical components of which the two principal elements are a fixed-exit double multilayer monochromator and a 1.1 m-long toroidal mirror. These new dedicated optics give improved beam characteristics (compared with the previous set-up on ID14-3) regarding the energy tunability, flux and focusing at the detector plane leading to reduced parasitic scattering and an extended s-range. User experiments on the beamline have been successfully carried out since June 2012. A description of the new BioSAXS beamline and the set-up characteristics are presented together with examples of obtained data.

Analysis and design of multilayer structures for neutron monochromators and supermirrors

A relatively simple and accurate analytical model for studying the reflectivity of neutron multilayer monochromators and supermirrors is proposed. Design conditions that must be fulfilled in order to reach the maximum reflectivity are considered. The question of the narrowest bandwidth of a monochromator is discussed and the number of layers required to build such a monochromator is derived. Finally, we propose a new and efficient algorithm for synthesis of a supermirror with specified parameters and discuss some inherent restrictions on an attainable reflectivity.

New generation mirror systems for the ESRF upgrade beamlines

The construction of new beamlines defined in the ESRF upgrade program, requires high performance optics, for which thermal and mechanical stability will be of the utmost importance. Solutions for optimizing drifts and thermal gradients, as well as vibration free positioning have been analysed. This has lead to new opto-mechanical engineering able to implement generic solutions for the optics, such as new architecture for flat or bent mirrors, multilayer monochromators, and a new generation hexapod for toroidal mirrors. Vertical incidence fine tuning within 200 nrad, as well as horizontal reflection resolution in the range of 50 nrad, has lead to the development of different movers and positioning mechanisms. A review is presented, considering the different design validation stages and laboratory commissioning and showing performance achieved on the very first upgrade beamlines.

SAXS/WAXS Capability and Absolute Intensity Measurement Study at the SAXS Beamline of the Siam Photon Laboratory

A Small Angle X-ray Scattering (SAXS) beamline has been constructed at the Siam Photon Laboratory of the Synchrotron Light Research Institute (SLRI), Thailand. The beamline was commissioned and opened for users in March 2011. In order to maximize the photon flux, a Double Multilayer Monochromator was adopted to monochromatize synchrotron x-rays within the energy range of 6-9 keV. The experimental station is equipped with a CCD detector for SAXS measurements and an Image Plate for wide angle x-ray scattering (WAXS) measurements. Apparatus for in-situ measurements have been developed to enable studies of nano structural changes during temperature and tensile variation. Capability for scattering measurements in absolute unit has been investigated. This work reports the current status of the beamline and results from dispersed Au nanoparticles measurements.

Small d-spacing WSi2/Si multilayers for X-ray monochromators

A WSi2/Si multilayer, with 300 bi-layers and a 2.18-nm d-spacing, is designed for X-ray monochromator application. The multilayer is deposited using direct current magnetron sputtering technology. The reflectivity of the 1st-order Bragg peak measured at E=8.05 keV is 38%, and the angular resolution (\Delta \theta/\theta) is less than 1.0%. Fitting results of the reflectivity curve indicate a layer thickness drift of 1.6%, mainly accounting for the broadening of the Bragg peaks. The layer morphology is further characterized by transmission electron microscopy, and a well-ordered multilayer structure with sharp interfaces is observed from the substrate to the surface. The material combination of WSi2/Si is a promising candidate for the fabrication of a high-resolution multilayer monochromator in the hard X-ray region.

3D elemental distribution images in biological samples by XRFµCT

An X-ray transmission microtomography (CT) system combined with an X-ray fluorescence microtomography (XRFµCT) system was implemented in the Brazilian Synchrotron Light Laboratory (LNLS), Campinas, Brazil. The aim of this work was to determine the elemental distribution in biological samples (breast, prostate and lung samples) in order to verify the concentration of some elements correlated with characteristics and pathology of each tissue observed by the transmission CT. The experiments were performed at the X-ray fluorescence beamline (D09B-XRF) of the Brazilian Synchrotron Light Laboratory, Campinas, Brazil. A quasi-monochromatic beam produced by a multilayer monochromator was used as an incident beam. The sample was placed on a high-precision goniometer and translation stages that allow rotating as well as translating it perpendicularly to the beam. The fluorescence photons were collected with an energy dispersive HPGe detector placed at 90° to the incident beam, while transmitted photons were detected with a fast Na(Tl) scintillation counter placed behind the sample on the beam path. The CT images were reconstructed using a filtered-back projection algorithm and the XRFµCT images were reconstructed using a filtered-back projection algorithm with absorption corrections. The 3D images were reconstructed using the 3D-DOCTOR software. Results from the 3D visualization showed that the distribution of iron, copper and zinc is different and heterogeneous from the analyzed samples. Copyright © 2011 John Wiley & Sons, Ltd.

Coherence preservation and beam flatness of a single-bounce multilayer monochromator (beamline ID19—ESRF)

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. Kramer, 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.

A SAXS/WAXS/GISAXS Beamline with Multilayer Monochromator

We discuss the construction of a new SAXS/WAXS beamline at the Advanced Light Source at Lawrence Berkeley Laboratory. The beamline is equipped with a multilayer monochromator in order to obtain a high X-ray flux. The detrimental effects that the increased bandwidth transmitted by this monochromator could have on the data quality of the SAXS and WAXS patterns is shown to be negligible for the experimental program intended to be operated on this beamline.