Numerical vs Experimental Sputtering Deposition Phase formation prediction in magnetron sputtered Cu(Ti)Zn thin films : Numerical vs Experimental approaches
Résumé
In this work we evaluated the ability of three numerical methods to predict the phase formation in Cu-Zn binary and Cu-Ti-Zn ternary alloy thin films deposited by DC-magnetron sputter deposition. Molecular dynamics simulations were carried out to simulate the growth of the alloy film and study the organization at the atomic level. A Machine Learning (ML) approach trained with a recently published bulk HEA (high entropy alloy) database was used to determine the presence of an amorphous phase, solid solutions or/and intermetallics. Finally, CALPHAD (CALculation of PHAse Diagrams) thermodynamic modeling based on Gibbs energy calculations allows to simulate the phase diagrams. This was done taking the experimental energy distribution functions of film forming species as inputs for the calculations. In this paper we discuss both agreements and limits of each method depending on their starting hypotheses and expected domains of validity. Crystalline phases formed in experimental films were investigated by grazing incidence X-ray diffraction (GIXRD). Comparison with CALPHAD results highlight that for pure Ti or binary Cu-Zn films, the thermodynamically stable phases are formed in the films. Less agreement was found at low or high percentage of Ti introduced in the Cu-Zn system, and drastic differences were observed for compositions close to equimolarity. In those cases, the out of equilibrium nature of the magnetron sputtering deposition technique is evidenced. The very limited agreement between GIXRD and ML approach is explained by the available database which is exclusively based on bulk alloys. Chemical composition of the alloy does not itself determine the stabilized phases: elaboration techniques are to be taken into account too. Molecular Dynamics (MD) simulations bring information on a possible segregation of the Zn element to the surface and grain boundaries. An interesting result is the very good agreement evidenced between the diffraction patterns calculated on the simulated films and that experimentally measured GIXRD
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