THERMAL AGING OF NI/C MULTILAYERS PREPARED BY PULSED-LASER DEPOSITION

Ni/C multilayers are prepared by pulsed laser deposition with different laser wavelengths. Specimens providing different interface constitutions are investigated in the initial state and after an annealing time of 20 min at temperatures between 50 and 400-degrees-C. X-ray reflectometry and X-ray diffraction at grazing incidence of the radiation are applied for the characterization of the samples. An increase of the double layer thickness with increasing temperature is observed for all multilayer samples. Generally this process starts at temperatures between 100 and 250-degrees-C, but the sample with graded interfaces remain stable up to higher temperatures than those with abrupt interfaces. After heating at 400-degrees-C the initially almost amorphous nickel layers crystallize in a thermodynamically stable f.c.c. lattice structure. For the sample with abrupt interfaces intermixing of nickel and carbon during deposition leads to the formation of crystalline nickel carbide between 200 and 300-degrees-C.