First-principle of Sc / Cr multilayers for x-ray mirrors applications

Abstract: In order to produce x-ray mirrors the Thin Film Physics group at IFM grows Cr/Sc multilayers, with a typical thickness of the individual layers in the range 5-20 Å, and with as many periods as possible (a few hundred). The quality of the multilayer interfaces is crucial for their performance as mirrors. For thick layers poly-crystalline multilayers form with an interface quality that is too poor for the use as x-ray mirrors. For thinner layers, however, amorphous layers are formed with a much better quality of the interface. The goal of this project was to understand the formation of amorphous multilayers. Unfortunately it is impossible with the present day's theoretical tools to determine the structure of amorph interfaces. It is also impossible to calculate the interface structure for elements with large mismatch in size. So we have to construct interface models that are both simple and based on physical arguments.