In situ GISAXS study on the temperature-dependent performance of multilayer monochromators from the liquid nitrogen cooling temperature to 600 °C

Abstract With the extensive demands of high-flux beamlines for current or planned synchrotron radiation sources, it is important to use multilayer monochromators for beamlines with insertion devices to select required quasi-monochromatic beams. Few studies have reported the interface evolution of multilayer monochromators in the liquid nitrogen (LN2) cooling environment under intense white beam irradiation. In this research, an in situ grazing-incidence small-angle X-ray scattering (GISAXS) setup was designed to monitor different interface characteristics of Ru/C, Cr/C, W/Si, and Ni/Ti multilayers from the LN2 temperature to 600 °C. The temperature treatment was executed in three steps — (i) the long-term low-temperature treatment, (ii) the quick temperature variation treatments, and (iii) the high-temperature treatment. A surface profiler was also used to determine the lower-frequency surface roughness after different temperature treatments. The temperature-dependent performances of multilayers were analyzed along the layer deposition direction and the out-of-plane direction. Scattering along the deposition direction reveals different interface features of the multilayers based on their thermal expansions. The power spectral density curve fitting proves that the fractal exponent is very sensitive to temperature change. Most of multilayers have a lower fractal exponent at the LN2 temperature. Moreover, clear interfacial changes were observed in Ru/C and Ni/Ti multilayers during high-temperature treatments.