Ab Initio Guided Low Temperature Synthesis Strategy for Smooth Face-Centred Cubic FeMn Thin Films

The sputter deposition of FeMn thin films with thicknesses in the range of hundred nanometres and beyond requires relatively high growth temperatures for the formation of the face-centred cubic (fcc) phase, which results in high thin film roughness. A low temperature synthesis strategy, based on local epitaxial growth of a 100 nm thick fcc FeMn film as well as a Cu nucleation layer on an alpha-Al2O3 substrate at 160 degrees C, enables roughness values (R-a) as low as similar to 0.6 nm, which is in the same order of magnitude as the pristine substrate (similar to 0.1 nm). The synthesis strategy is guided by ab initio calculations, indicating very strong interfacial bonding of the Cu nucleation layer to an alpha-Al2O3 substrate (work of separation 5.48 J/m(2))-which can be understood based on the high Cu coordination at the interface-and between fcc FeMn and Cu (3.45 J/m(2)). Accompanied by small lattice misfits between these structures, the strong interfacial bonding is proposed to enable the local epitaxial growth of a smooth fcc FeMn thin film. Based on the here introduced synthesis strategy, the implementation of fcc FeMn based thin film model systems for materials with interface dominated properties such as FeMn steels containing kappa-carbide precipitates or secondary phases appears meaningful.