Investigation of the thermal stability of Ni/C multilayers by X-ray methods.

Microstructural properties of Ni/C multilayers prepared by PLD (pulsed laser deposition) have been investigated after heat treatment in vacuum at temperatures in the range of 50 degrees C to 500 degrees C. X-ray diffractometry, X-ray reflectometry, fluorescence EXAFS (extended X-ray absorption fine structure) and HREM (high resolution transmission electron microscopy) have been applied to characterize samples in the initial state and after annealing. The multilayer reflectivity remained unchanged or increased at temperatures below 400 degrees C due to sharpening of the interfaces caused by the formation of alpha-nickel and nickel carbide. The reflectivity decreased at temperatures above 400 degrees C because of the fragmentation of the nickel layers. It can be shown, that both chemical and mechanical driving forces are responsible for the observed modifications of the initial specimen state.