Ultrasmooth Ge/Mo₂C multilayers with low interface diffusion at 46.5 nm

Until now, only the Sc-based multilayer has been developed for solar transition observation at 46.5 nm, which has a high reflectivity and a narrow bandwidth. However, Sc is chemically reactive, which poses a potential threat to the mirror's stability. Here, a Ge/Mo₂C multilayer for 46.5 nm was proposed for high stability, long lifetime payloads. The generation and impact of Mo₂C nanocrystals were discussed. Experimental results showed that the multilayer structure with a Ge seed layer, owing to the wetting properties of Ge, achieved an interface diffusion of 0.8 nm and an RMS surface roughness of 0.18 nm, which resulted in a high reflectivity of 30.3% at 46.5 nm. Our job provides a good candidate material pair for the EUV optical system at 46.5 nm.