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

The X-ray optical and mechanical properties of dielectric multilayer mirrors based on pairs of C/Si and B4C/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 Delta lambda = 0.33 nm. The B4C/Si mirror provides the following characteristics: R = 8.2%, spectral bandwidth of Delta lambda = 0.3 nm. However, blistering is found in B4C/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 similar to 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.