X-ray nanometer focusing at the SSRF basing on multi-layer Laue lens

Content Provider	Semantic Scholar
Author	Chkhalo, Nikolai I. Nechay, A. N. Pariev, D. E. Polkovnikov, Vladimir N. Salashchenko, Nikolai N. Schaefers, Franz Sokolov, Andrey Svechnikov, Mikhail V. Vainer, Yu. A. Zorina, M. V. Zuev, S. Yu.
Copyright Year	2016
Abstract	Cr/Sc multilayer systems can be used as near-normal incidence mirrors for the water window spectral range. We show that a detailed characterization of these multilayer systems with 400 bilayers of Cr and Sc each with individual layer thicknesses below < 1 nm is attainable by the combination of several analytic techniques. We used EUVand X-ray reflectance measurements, resonant EUV reflectance across the Sc L-edge as well as X-ray standing wave fluorescence measurements. The parameters of our multilayer model were determined based on a particle swarm optimizer and validated using a Markov-chain Monte Carlo maximum likelihood approach. For the determination of the interface roughness diffuse scattering measurements were conducted. Reconstruction of interfaces of periodic multilayer structures using model independent GIXR and XSW techniques. PXRNMS , University of Twente, Enschede, 10-11 November 2016 I. A. Makhotkin1, C.P. Hendrikx1, A. Zameshin1, R.W.E. van de Kruijs1, A.E. Yakshin1 , E. Louis1, S.N. Yakunin2 and Fred Bijkerk1 Industrial Focus Group XUV Optics, MESA+ Institute for Nanotechnology, University of Twente, Drienerlolaan 5, Enschede, 7522 NB, The Netherlands NRC Kurchatov Institute, Moscow, Russian Federation Development of the state-of-the-art periodic multilayer structures requires advanced interface engineering. Grazing Incidence X-ray Reflectivity (GIXR) is a widely used analysis method sensitive to the structure of interfaces in multilayers. However, conventional so-called model-based approaches of structural reconstruction from GIXRR data are lacking analytical power when dealing with multilayers where interface thicknesses are comparable to total thickness of multilayer period . We have developed the free-form approach that allows to analyze the GIXR data without the need for a priori assumptions on layer or interface parameters. The application of this approach will be demonstrated on the example of analysis of La/B multilayer structures1. To study the multilayers with inter-diffusion barriers with a higher precision an atomic-sensitive technique is often required. The ideal candidate is the X-Ray Standing Wave technique (XSW). The X-ray standing wave formed at the Bragg reflection condition in a periodic multilayer structure modulates atom-specific X-ray fluorescence. Previously2 we have shown that atomic profiles can be recalculated directly from measured X-ray fluorescence yields modulated by XSW. This calculations require the knowledge of the optical constant profile obtained from GIXR analysis. We have demonstrated that, obtained by free-form analysis of GIXR, optical constant profile can be used as an input to calculation of atomic profiles from XSW data, what significantly simplifies the advanced characterization of the structure of periodic multilayers. 1. A. Zameshin, I. A. Makhotkin, et. al., Journal of Applied Crystallography 49 (4), 1300-1307 (2016). 2. S. N. Yakunin, I. A. Makhotkin, et. al., J. Appl. Phys. 115 (13), (2014). X-ray at-wavelength metrology of multi-layered surfaces Sebastien Berujon1), Pierre Piault 1), Eric Ziegler1) European Synchrotron Radiation Facility, CS 40220, 38043 Grenoble cedex 9, France Multilayer-coated mirrors are widely used as optical elements to handle the X-ray beam produced by sources such as synchrotrons, notably for spectroscopy and imaging applications. Their assets are a wide and tuneable spectral bandwidth transmission, an optical behaviour free from chromatic aberration, a high reflectivity efficiency and the possibility to use them at incidence angles larger than for mirrors operating at the total reflection angle, thus increasing the optical aperture and lowering the diffraction limit. On the other hand, their performances are limited by the surface shape errors and roughness. While well-known methods such as reflectivity and diffuse scattering permit to assess statistical characteristics of the multi-layered material along the growth direction [1], the full topological description of the surface is only accessible at the cost of greater experimental efforts [2]. For Xray imaging applications using coherent light such metrology information is of significant importance since the height errors in the mirror deposition process are responsible for unwanted large intensity modulation of the X-ray beam through an interference process. The challenge in characterizing these defects lies in the fact that such error amplitudes can be as small as the light wavelength, i.e. in the order of a few nanometers for spatial periods in the millimeter range and above. This presentation will introduce the methods available for measuring and analysing small spatial frequency aberrations in a beam upon reflection on a multilayer-coated mirror surface. The interest in measuring the wavefront of the X-ray reflected beam is to infer the surface optical defects and to map out the layer deposition errors. Theoretical and experimental implementation of these characterization methods using hard X-ray light produced by a synchrotron source will be given, especially the ones based on interferometry and speckle. This metrology will eventually permit to better understand the origin of the wavefront intensity modulation generated by multilayer mirrors and enable the development of multilayer manufacturing process strategies capable of minimizing surface defects and preserve a highly uniform X-ray wavefront. [1] Kozhevnikov I. V., Peverini L., Ziegler E., “Development of a self-consistent free-form approach for studying the three-dimensional morphology of a thin film”, Physical Review B, 85, p. 125439, (2012). [2] Berujon S., Wang H., Alcock S., Sawhney K., “At-wavelength metrology of hard X-ray mirror using near field speckle”, Optics Express, 22, pp. 6438-46, (2014). Self-consistent optical-constant of materials for EUV multilayer coatings Juan I. Larruquert, Luis V. Rodríguez-de Marcos, José A. Méndez, José A. Aznárez GOLD, Instituto de Optica-CSIC, Madrid The preparation of multilayer coatings relies on the availability of precise optical constants of thin-film materials. When these are available, often they are not selfconsistent, because they are obtained either on a narrow spectral range or by aggregation of data from different sources. Self-consistency requires that n and k be connected with the Kramers-Kronig (KK) relations. At GOLD we have been obtaining self-consistent optical constants of several thin-film materials, mostly following two procedures: a) Transmittance measurements versus energy in a broad spectral range for various film thicknesses. This provides k at each photon energy, and n is calculated with KK analysis. b) Combinations of measurements including transmittance, reflectance, and ellipsometry in spectral intervals jointly covering a broad spectral range. Starting with these measurements, an iterative double Kramers-Kronig analysis procedure is followed: a first one on reflectance and its phase and a second one on k and n. Measurements from the near infrared down to a wavelength of 30 nm (up to 41 eV) in the EUV can be performed at GOLD, as well as ellipsometry in the 190-950 nm range. To cover shorter wavelengths (larger energies), we have used BEAR-Elettra and 6.3.2ALS synchrotron beamlines in collaboration with various groups in Italy and USA. Self-consistency of n-k data generated with either procedure is tested with the use of two sum rules. Typically, the self-consistency of optical-constants is globally evaluated over the whole spectrum with these sum rules. We have generalized this evaluation to obtain also the local consistency of the optical constants at each photon energy range through a novel sum-rule method which includes window functions. With the above procedures, various sets of materials have been characterized, including a long series of lanthanide and alkaline-earth metals, along with various carbides, fluorides, oxides, and boron. We will display examples of optical constants and selfconsistency tests of interesting materials for multilayers in the EUV and adjacent ranges. DFT simulations of surfaces, interfaces and multilayers
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