Minimization of interface roughness in laser deposited Fe/MgO multilayers

The physical properties of multilayers with layer periods in the nanometer range crucially depend on the nature of their interfaces. In this contribution we show how the interfacial roughness of multilayers consisting of two materials with a high difference in specific surface free energy (here MgO/Fe) and thus different growth modes (Volmer–Weber island growth for Fe and layer-by-layer growth for MgO) can be minimized. For this, the layer thickness of the island former has to be large enough that almost all island zipping processes have already occurred. At this thickness the layer is just closed and the intrinsic roughness is at a minimal value. To determine this optimal thickness, in-situ stress measurements as performed in this work are one method of choice. The layer-by-layer growth of the other material with lower surface free energy additionally leads to a further smoothening of the surface. Due to this alternating roughening and smoothing processes, cumulative roughness can be avoided and overall a minimal roughness of the multilayer structure is obtained.