Normal-incidence x-ray mirror for 7 nm

Multilayer (ML) structures composed of alternating, ultrathin layers of Ru and B(4)C have been grown by dc magnetron sputtering. The ML microstructure has been characterized using x-ray diffraction and highresolution transmission electron microscopy, and the normal-incidence reflectivity has been measured using synchrotron radiation. It is found that, under optimum deposition conditions, the ML structures exhibit smooth and compositionally abrupt interfaces, with a normal-incidence reflectivity as high as 20% at 7.2 nm. The reflectivity decreases when the ML structures are annealed at 500 degrees C owing to interdiffusion and com-pound formation at the interfaces.