Introduction of Zr in nanometric periodic Mg/Co multilayers

We study the introduction of a third material, namely Zr, within a nanometric periodic Mg/Co structure designed to work as optical component in the extreme UV (EUV) spectral range. Mg/Co, Mg/Zr/Co, Mg/Co/Zr and Mg/Zr/Co/Zr multilayers are designed, and then characterized in terms of structural quality and optical performances through X-ray and EUV reflectometry measurements, respectively. For the Mg/Co/Zr structure, the reflectance value is equal to 50% at 25.1 nm and 45° of grazing incidence and reaches 51.3% upon annealing at 200°C. Measured EUV reflectivity values of tri-layered systems are discussed in terms of material order within a period and compared to the predictions of the theoretical model of Larruquert. Possible applications are pointed out.