Modeling of metastable phase formation diagrams for sputtered thin films

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Due to kinetically limited vapor phase condensation processes, metastable phases are commonly obtained during synthesis of thin films, which makes prediction of their structures and properties rather demanding. By applying theoretical means like CALPHAD and ab initio calculations, phase stability of the thin film systems has extensively been investigated. As a typical example, the metastable solubility limits of AlN in c-Ti1-xAlxN thin films are well described using these means. However, for efficient thin film materials design the knowledge of metastable phase formation diagrams is essential. To date, modeling of metastable phase formation diagrams for sputtered thin films has not been reported.In preliminary work a modelling strategy to predict metastable phase formation diagrams (containing Bcc and Fcc phases) for the immiscible Cu-W and Cu-V systems has been proposed and the calculations agree well with experimental data.In the here proposed project, the industrially relevant systems Ti-Al-N and Zr-Al-N, focusing on the TiN-AlN and ZrN-AlN pseudo-binary sections, will be studied using a correlative experimental and theoretical approach.Stoichoimetric nitride thin films (i.e., Ti1-xAlxN1 and Zr1-xAlxN1) will be synthesized using a combinatorial approach to obtain the metastable phase formation data. Ab initio calculations will be used to acquire enthalpy of formation and surface diffusion activation barriers of the Ti1-xAlxN1 and Zr1-xAlxN1 phases. Thermodynamic descriptions of the ternary Ti-Al-N and Zr-Al-N systems will be obtained using the CALPHAD approach.The proposed methodology will be validated by modeling the metastable phase formation diagrams for the TiN-AlN and ZrN-AlN thin films. A comprehensive strategy will be obtained to study the thermodynamics and kinetics of the sputtered thin films aiming to formulate metastable phase formation diagrams (non-equilibrium) for sputtered thin films, as well as phase diagrams (equilibrium) for the entire material system. The proposed strategy is expected to be applicable to other systems, allowing for understanding the composition-structure-property relationships for thin films more efficiently and hence provide a solid basis for the future design of thin film materials.