Microstructure of Multilayer Fresnel Zone Plate for X-ray Focusing

We have been fabricated the multilayer Fresnel zone plate (FZP) for hard X-ray focusing. The multilayer FZP consists of a series of concentric multilayer of low-Z (Al) zone and high-Z (Cu) zone, alternatively. The spatial resolution of the multilayer FZP is related with the outermost zone width and the smoothness of the multilayer. In case of the concentric multilayer FZP, the undulations were often observed. The smoothness of the multilayer is strongly related with he optical resolution. In this study we reported the microscopic structure of the multilayer FZP with a scanning transmission electron microscope (STEM) observation and discussed the seed of the undulation.