Evolution of interfacial structures and creep behavior of Cu/Ta multilayers at room temperature

The evolution of interfacial structures and creep behavior of Cu/Ta multilayers at room temperature were investigated as the individual layer thickness (hL) varies from 2.5 to 100nm. The interface structures exhibit different configurations at different length scales. The main crystal phase in Ta layers changes from α-Ta to β-Ta with the increase of hL from 5 to 10nm, and amorphous regions appear at the interface when hL=25nm. These variations affect the creep behaviors deeply. The creep stress exponent (n) increases with the decreasing hL and reaches maximum at hL=5nm. According to the variation of n values, the creep behavior is dominated by the dislocation climb from the grain boundaries in Cu layers to the heterogeneous interfaces between two constituent when decreasing the hL. In addition, the change of Ta phases also contributes a lot to the stress exponent at several nanometer scale.