Investigation of Solid‐State Interface Reactions Between the Compositionally Complex Solid Solution Noble Metal Alloy Ag‐Au‐Pd‐Pt and Si

Abstract Studying the stability of polyelemental systems such as compositionally complex solid solutions (CCSS) on the atomic scale against thermal decomposition or reaction with other elements is necessary to evaluate their suitability for applications. For this, the combinatorial processing platform approach is used to report on the stability of an exemplary noble metal CCSS thin film system (Ag‐Au‐Pd‐Pt). The thin film is sputter‐deposited at room temperature on flat and pre‐sharpened Si microtip array surfaces, protected solely by their native oxide. The as‐deposited film is a fcc solid solution which is subjected to sequential annealing up to 400 °C. Up to 300 °C, the native Si oxide is a sufficient reaction barrier. However, after annealing at 400 °C solid‐state reactions between the noble metal film and the Si substrate occur, forming mainly a ternary Pd‐Pt‐Si silicide with a crystal structure of Pd₂Si (space group P6̅m2), as revealed by a semi‐correlative APT/TEM analysis. Removal of Pd and Pt from the thin film causes partial decomposition of the initial fcc solid solution, with the formation of a Ag‐Au‐rich phase. Moreover, the interaction of the quaternary alloy system with Si is compared to that of pure Pt/Pd with Si. From this, information of preferential silicide formation is derived.