Annealing Induced Interdiffusion And Microstructure Evolution

In this thesis, Cu/Ni multilayers prepared by sputter deposition on silicon substrate were annealed. TEM, STEM, XPS, nano-hardness were introduced to study the evolution of microstructure, concentration gradient, and the hardness of Cu/Ni multilayers after annealing. In addition, the interdiffusion process was simulated to study the effect of the difference of diffusivities, vacancy sources and coherency stress to interdiffusion.The polycrystalline structure of the multilayer is evident from the columns that extend through the multilayer thickness. Single layer thickness affects the regularity of the microstructure: the lower, the more regular. The quadruple junctions appear in the intersection of grain boundaries and phase interfaces. However, the movements of quadruple junctions are out of expectation and do not balance at quadruple junctions after annealing,∑γ= 0.The nano-hardness results reveal that the hardness values decrease as the increase of the annealing temperature and time. XPS results show that the concentration gradient is related to the nano-hardness value. The higher concentration gradient accords to the higher hardness.Our diffusion models firstly consider the effect of coherency stress to interdiffuison coefficient. In Cu/Ni multilayer, the copper layer is under compression, the vacancy concentration decreases, and then the interdiffuison is inhibited; the nickel layer is under tension, the vacancy concentration increases, and then the interdiffuison is promoted. For both Darken model and Nernst-Plank model, the coherency stress accelerates the homogenization process of the multilayer.