Ni50Nb50/C amorphous multilayers for “water window” soft X-rays – structure and stability

Abstract

Amorphous Ni50Nb50/C multilayers with a period of 2.4 nm for the water window soft X-rays were prepared by pulsed laser ablation deposition. The structural stability of these multilayers was studied by grazing incidence X-ray scattering. The multilayers were found to be highly stable at room temperature for periods as long as 3 years. However, the Ni50Nb50 layer was found to undergo an amorphous – crystalline disorder – order transformation due to annealing while the carbon layer remained unchanged. The crystalline phase after transformation could be identified as the NiNb phase. The vertical layered structure, however, was found to be highly stable even after annealing the multilayers at 473 and 593 K under vacuum. The multilayer period remains unchanged till 473 K and increases by 7% on annealing at 593 K