Correlating the optical property evolution in the Au-Ni binary thin films: From metastable solid solution to phase separated alloy

In this study, the optical properties of Au1-xNix alloy thin films are investigated by employing a combinatorial sputtering approach. The dielectric function is measured using spectroscopic ellipsometry and is correlated to the composition, determined by energy dispersive spectroscopy, and phases present, determined via x-ray diffraction. As-deposited alloys form a metastable solid solution, however, annealed alloys exhibited phase separation into Au-rich and Ni-rich phases due to the large miscibility gap in the Au-Ni material system. The optical properties are then rationalized by modeling the dielectric function of the solid solution alloys with a Drude-Critical Point analytical model. Lastly, the efficacy of the model is demonstrated which shows that the dielectric function of the phase separated alloys can be approximated using a composition-weighted average of two solid solution dielectric functions. (C) 2019 Elsevier B.V. All rights reserved.