Investigation in the interface roughness of DC-sputtered Mo/B4C multilayer mirrors with variable layer pairs for 7-nm soft X-ray polarizers

The surface and interface roughness of Mo/B4C multilayer mirrors for 7-nm soft X-ray polarizer with variable layer pairs (N = 50, 70, 90 and 110), fabricated by DC sputtering technique is investigated by atomic force microscopy and X-ray scattering and reflecting. The experimental results present that the surface and interface roughness of Mo/B4C multilayer mirrors increase layer by layer from its substrate as its Mo layer thickness greater than 2 nm, and the roughness grown tendency could be characterized by a quadratic function.