Effect of deposition substrates on surface topography, interface roughness and phase transformation of the Al/Ni multilayers

The Al/Ni multilayers with modulation periods of 50, 250, and 500 nm were deposited on AlN, AlNi3, Si, and Al2O3, respectively. Surface topography, interface roughness and phase transformation show strong dependence on the substrates. The substrate roughness can much increase the interface roughness, and this effect can accumulate for the later layers. The severely roughened surface of the AlN substrate causes much rougher interfaces, poorer surface flatness, and hence low compactness of the as-deposited multilayers. Phase transformation varies with the modulation period below 673 K. The stable AlNi preferentially formed in the 500 nm period multilayers instead of in smaller period samples at 773 K, which was related to the interface roughness. The roughened interface facilitates atomic interdiffusion to meet the nucleation requirement at the initial stage. The pre-formed intermetallic phase layers would hinder the diffusion of Ni and finally slower the formation of AlNi when annealing at 773 K. Substrates could also affect the intermixing region at interfaces. Larger hardness combined with smaller thermal conductivity coefficient of Al2O3 gives rise to clearer and sharper interfaces and finally leads to slower phase transformation in 500 nm period multilayers. This result suggests that substrates may provide advantages to tailor the performance of multilayers.