Microstructure and Vickers hardness of Co/Cu multilayers fabricated by electrodeposition

In order to investigate thermal stability of Co/Cu multilayers fabricated by electrodeposition, Vickers hardness tests and microstructure observations were conducted on both as-deposited and annealed Co/Cu multilayers having a layer thickness of 100 nm. The multilayers were annealed at temperatures ranging from 473 to 1,273 K for 1 h. It is confirmed that even after the annealing at 1,023 K, the multilayer maintained the high hardness (Hv231) which was comparative to that of the as-deposited Co/Cu multilayer. When the annealing temperature was higher than 1,073 K, the hardness decreased rapidly with increasing temperature. Scanning electron microscopy (SEM) observation revealed that the multilayered structures were still maintained without any layer damages after the annealing at the temperatures less than 873 K. At the cross sections of the Co/Cu multilayers annealed at T > 923 K, several copper layers were fragmented. The layered structure finally disappeared by the annealing at 1,273 K. The rapid decrease in the hardness at T > 1,073 K is simply understood from the annihilation of the Co/Cu interfaces.