Ultra-precision fabrication of 500 mm long and laterally graded Ru/C multilayer mirrors for X-ray light sources

Abstract

X-ray mirrors are needed for beam shaping and monochromatization at advanced research light sources, for instance, free-electron lasers and synchrotron sources. Such mirrors consist of a substrate and a coating. The shape accuracy of the substrate and the layer precision of the coating are the crucial parameters that determine the beam properties required for various applications. In principal, the selection of the layer materials determines the mirror reflectivity. A single layer mirror offers high reflectivity in the range of total external reflection, whereas the reflectivity is reduced considerably above the critical angle. A periodic multilayer can enhance the reflectivity at higher angles due to Bragg reflection. Here, the selection of a suitable combination of layer materials is essential to achieve a high flux at distinct photon energies, which is often required for applications such as microtomography, diffraction, or protein crystallography. This contribution presents the current development of a Ru/C multilayer mirror prepared by magnetron sputtering with a sputtering facility that was designed in-house at the Helmholtz-Zentrum Geesthacht. The deposition conditions were optimized in order to achieve ultra-high precision and high flux in future mirrors. Input for the improved deposition parameters came from investigations by transmission electron microscopy. The X-ray optical properties were investigated by means of X-ray reflectometry using Cu- and Mo-radiation. The change of the multilayer d-spacing over the mirror dimensions and the variation of the Bragg angles were determined. The results demonstrate the ability to precisely control the variation in thickness over the whole mirror length of 500 mm thus achieving picometer-precision in the meter-range.

Surface and interface characterization of Ru/C/Ru trilayer structure using grazing incidence X‐ray reflectivity and X‐ray fluorescence

“…16,17 Ru has been used in multilayers in combination with Si as an analyser for polarization measurements 18 and with carbon and boron carbide as multilayer mirror in soft X-ray region 18 and as multilayer monochromators in hard X-ray region. 1,19 In the present work, we have studied Ru/C/Ru trilayer structure as a potential waveguide system for 8-to 20-keV X-ray energy regions. Carbon has been used as a barrier layer in multilayers to reduce interdiffusion at the interfaces and improve the reflectivity performance of the multilayers.…”

“…For X-ray optics applications, major challenge in the fabrication of multilayered systems is to achieve the precise thickness of all the layers. 1 In addition, film uniformity and interface quality is of paramount importance from application point of view. The quality of film and the interfaces formed by different layers are highly dependent on the deposition techniques.…”

1 m long multilayer-coated deformable piezoelectric bimorph mirror for adjustable focusing of high-energy X-rays

“…The application of multilayer coating techniques to optical components of increasing size continues to make progress. Störmer et al [4] have reported the fabrication of a 500 mm long, laterally graded Ru/C multilayer mirror and its successful testing with Cu Kα 1 (8.048 keV) and Mo Kα 1 (17.48 keV) X-rays. The coating of silicon substrates with boron carbide has been carried up to a 1500 mm length by Störmer et al [5].…”

Development of a glue-free bimorph mirror for use in vacuum chambers

“…[9][10][11] At SPring-8, a compensation optical system was developed that uses a bimorph mirror to realize an ultimate beam size of 7 nm. In this work, the diffraction-limited operation was realized in a compensational way, although the employed multi-layer coated 12,13 Kirkpatrick-Baez (KB) mirrors [14][15][16][17][18][19] did not fully satisfy the Rayleigh criterion. 20 Furthermore, a two-stage focusing optical system was used at SPring-8 to change the beam size, in which diffraction-limited performances were realized at all beam sizes.…”