Microstructure evolution and hard x-ray reflectance of ultrathin Ru/C multilayer mirrors with different layer thicknesses

Abstract

Nanoscale Ru/C multilayers are essential reflective optics in the hard x-ray region of 7–20 keV. To understand the layer growth behavior and develop ultrathin Ru/C multilayer mirrors with periods smaller than 3.0 nm, multilayers with different periods of 6.2–1.5 nm were fabricated and studied. It is found that the average interface width started to increase obviously when the period became smaller than 2.5 nm while the surface roughness of different multilayers remained almost the same. The intrinsic stress of the multilayer gradually decreased with decreasing period and reached a very low value of −82 MPa at d = 2.3 nm. High reflectance of 54% and 65% (at E = 8.04 keV) were demonstrated for the multilayers with periods of 2.5 nm and 3.0 nm, respectively, whereas that for 1.9 nm period was significantly lower. To further analyze the layer microstructure, x-ray diffraction and transmission electron microscopy were used. The polycrystallized structure of Ru remained similar for the multilayers with period less than 2.5 nm, while a non-continuous layer growth and severe intermixing between Ru and C were observed for the multilayer with period of 1.9 nm. The increased intermixing between Ru and C was found to be the main reason for the larger interface width and lower reflectance of the multilayers with period smaller than 2.5 nm. It also indicated that the layer thickness threshold for a Ru/C multilayer growing with good layer quality is 1.0–1.2 nm.

Role of C and B4C barrier layers in controlling diffusion propagation across the interface of Cr/Sc multilayers

“…This is a good assumption and a standard practice in the study of this kind of multilayers. 56 It should also be noted that the deposition process we used, i.e. , ion beam sputtering, is a very consistent process and during deposition the process parameters remain more or less the same throughout the multilayer.…”

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

“…22 The investigations on surface-interface properties of Ru/C multilayers deposited using DC magnetron have also been carried out by various groups. 23,24 However, no studies are available for ion beam sputtering (IBS)-deposited Ru/C interfaces.…”

Background Pressure Induced Structural and Chemical Change in NiV/B4C Multilayers Prepared by Magnetron Sputtering

“…Thus, it is widely used in advanced imaging, spectroscopy, and monochromator systems for synchrotron radiation facilities and astronomical observation projects [1][2][3]. As photon energy requirement of synchrotron radiation facilities and space telescopes extends to several tens of kiloelectron volts, the multilayer working at such wavelength region requires an extremely small d-spacing which is less than 3.0 nm [4][5][6][7]. This makes the x-ray reflectance very sensitive to the interface and surface quality of the multilayer, which also needs the more precise control of fabrication and the more suitable selection of materials.…”