Modeling of metastable phase formation diagrams for sputtered thin films

由于动力学受限的气相冷凝过程，在薄膜合成过程中通常会产生亚稳相，这使得对其结构和性能的预测变得相当困难。应用CALPHAD和从头计算等理论手段，对薄膜体系的相稳定性进行了广泛的研究。作为一个典型的例子，用这些方法很好地描述了AlN在c-Ti1-xAlxN薄膜中的亚稳溶解极限。然而，对于高效的薄膜材料设计来说，亚稳态相形成图的知识是必不可少的。到目前为止，对溅射薄膜亚稳态相形成图的模拟还没有报道。在初步工作中，我们提出了一种预测不相容的铜-钨和铜-钒系统亚稳态相形成图(包括体心立方相和面心立方相)的模拟策略，计算结果与实验数据吻合较好。在本项目中，工业上相关的系统，主要是TiN-AlN和ZrN-AlN伪二元截面，将用相关的实验和理论方法研究。化学计量氮化物薄膜(即，将使用组合方法合成Ti1-xAlxN1和ZR1-xAlxN1)，以获得亚稳相的形成数据。用从头算方法计算了Ti1-xAlxN1和Zr1-xAlxN1相的生成热和表面扩散活化势垒。用CALPHAD方法得到了Ti-Al-N和Zr-Al-N三元系的热力学描述，并通过模拟TiN-AlN和ZrN-AlN薄膜的亚稳相形成图对所提出的方法进行了验证。对溅射薄膜的热力学和动力学的研究将得到一个全面的策略，旨在建立溅射薄膜的亚稳相形成图(非平衡)以及整个材料系统的相图(平衡)。该策略可望应用于其他体系，从而能够更有效地理解薄膜的组成-结构-性能关系，从而为未来薄膜材料的设计提供坚实的基础。

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.