STUDIES OF THE MULTILAYER MIRROR REFLECTIVITY IN SOFT-X-RAY REGION

Four factors (the interface roughness, the monotonous thickness drift, the interdiffusion between two layers and the change of extinction co efficients) which may affect the multilayer mirror reflectivity in sof t X-ray region are investigated. Some conclusions are obtained by our theoretical analysis. In long wavelength region (lambda > 12 nm), the change of extinction coefficients is the main cause reducing the multi layer mirror reflectivity and others (excluding the interface roughnes s) only shift the peak position. In short wavelength region (lambda < 10 nm), all the four factors affect the reflectivity. In addition, the two factors, monotonous thickness drift and interdiffusion between tw o layers, shift the peak position. To check these conclusions, the mea surement of a Nb/Si multilayer mirror fabricated by our magnet sputter ing system is performed on an X-ray generator and a reflectometer inst alled on the Beijing Synchrotron Radiation Facility. The experimental results are in good agreement with our calculations, and the reflectiv ity up to 32% of the Nb/Si multilayer mirror (with 41 layers and at wa velength 17.59 nm) is attained.