Study of the X-ray Optical and Mechanical Characteristics of C/Si and B4C/Si Multilayer Mirrors

• Published in: Surface investigation, x-ray, synchrotron and neutron techniques x-ray, synchrotron and neutron techniques, 2023-12, Vol.17 (6), p.1350-1355
• Main Authors: Smertin, R. M., Barysheva, M. M., Garakhin, S. A., Zorina, M. V., Zuev, S. Yu, Polkovnikov, V. N., Chkhalo, N. I., Radishchev, D. B.
• Format: Article
• Language: English
• Subjects: Blistering; Boron carbide; Chemistry and Materials Science; Deposition; Electrical resistivity; Materials Science; Mechanical properties; Microelectromechanical systems; Mirrors; Multilayers; Optical components; Optical properties; Reflectance; Reflection; Residual stress; Silicon substrates; Surfaces and Interfaces; Thin Films; X-rays
• ISSN: 1027-4510; 1819-7094
• DOI: 10.1134/S1027451023060459

The X-ray optical and mechanical properties of dielectric multilayer mirrors based on pairs of C/Si and B 4 C/Si materials are synthesized and studied. The mirrors are optimized for a wavelength of 13.5 nm. Parameters of the deposition process that simultaneously ensure the fulfillment of three conditions are found: relatively high reflection coefficients at the operating wavelength, near-zero mechanical stresses in the film, and the absence of electrical conductivity. At zero internal stresses, the reflection coefficient of C/Si multilayer mirrors deposited onto superpolished silicon substrates at an operating wavelength of 13.5 nm is R = 11% and the spectral bandwidth is Δλ = 0.33 nm. The B 4 C/Si mirror provides the following characteristics: R  = 8.2%, spectral bandwidth of Δλ = 0.3 nm. However, blistering is found in B 4 C/Si multilayer mirrors, i.e., the appearance of bubbles on the film due to the accumulation of hydrogen inside, which excludes their use for deposition onto commercially available microelectromechanical systems of micromirrors. The deposition of a C/Si coating made it possible for the first time to obtain an efficient microelectromechanical system that reflects X-rays at an operating wavelength of 13.5 nm. The reflection coefficient is about R ~ 3%. The low value of the reflection coefficient is due to the high, about 2 nm, microroughness of the surface of the microelectromechanical-system micromirrors. The study performed indicates the fundamental possibility of creating a matrix X-ray optical element for modulating the spatial and temporal characteristics of X-ray beams.