Thermal stability of 2.4 nm period Ni-Nb/C multilayer x-ray mirror

The structure of Ni-Nb/C multilayers as a function of annealing at 200 and 320 degreesC has been studied. The layered structure is found to be extreme ly stable even after annealing at 320 degreesC. The interdiffused layer pre sent at the two interfaces Ni1/2Nb1/2/C and C/Ni1/2Nb1/2 before annealing u ndergoes a reverse diffusion on annealing leading to an increase in repeat unit thickness as well as reflectivity enhancement. The repeat unit thickne ss increases from 2.36 to 2.56 nm and the reflectivity at the first order p eak increases by 5 times after annealing at 320 degreesC. Only the Ni1/2Nb1 /2 layers in the multilayer undergo a crystalline transformation into an eq uilibrium NiNb compound without increasing the interface roughness. (C) 200 0 American Institute of Physics. [S0003-6951(00)01748-4].