The diamond–silicon carbide composite Skeleton^® as a promising material for substrates of intense X-ray beam optics

The paper considers the possibility of using the diamond-silicon carbide composite Skeleton^® with a technological coating of polycrystalline silicon as a substrate for X-ray mirrors used with powerful synchrotron radiation sources (third+ and fourth generation). Samples were studied after polishing to provide the following surface parameters: root-mean-square flatness ≃ 50 nm, micro-roughness on the frame 2 µm × 2 µm σ ≃ 0.15 nm. The heat capacity, thermal conductivity and coefficient of linear thermal expansion were investigated. For comparison, a monocrystalline silicon sample was studied under the same conditions using the same methods. The value of the coefficient of linear thermal expansion turned out to be higher than that of monocrystalline silicon and amounted to 4.3 × 10^-6 K^-1, and the values of thermal conductivity (5.0 W cm^-1 K^-1) and heat capacity (1.2 J K^-1 g^-1) also exceeded the values for Si. Thermally induced deformations of both Skeleton^® and monocrystalline silicon samples under irradiation with a CO₂ laser beam have also been experimentally studied. Taking into account the obtained thermophysical constants, the calculation of thermally induced deformation under irradiation with hard (20 keV) X-rays showed almost three times less deformation of the Skeleton^® sample than of the monocrystalline silicon sample.