Thin metal films deposited on metal-oxide substrates tend to undergo solid-state dewetting when annealed at elevated temperatures but below their melting point. While this behavior is a major problem in microelectronics due to the failure of thin-film devices, the process is nowadays more and more often used as a tool to fabricate a variety of nanostructures in a cost-effective and environmentally friendly manner. Especially the fabrication of magnetic, optical, or catalytic alloyed nanostructures has recently attracted great interest [1]–[3]. In both cases, thermal stability and fabrication of nanostructures, understanding and controlling the kinetics of the dewetting process is of outmost importance.
In this work, the binary AuNi system as a model system for a high misfit alloy as well as AuAg alloys as a reference system with negligible misfit was used to study the influence of the atomic size mismatch on the process of solid-state dewetting. Therefore, AuNi and AuAg bilayers were deposited on α-Al2O3, Si/SiO2, and Si/AlOx substrates via e-beam evaporation. Rapid thermal annealing above the miscibility gap of the AuNi system at 890°C for 120s in a reducing atmosphere was conducted to investigate the influence of the Au concentration on the thermal stability of binary alloy films. A correlative approach of X-ray diffraction and electron microscopy reveals the influence of Au concentration on the texture and structure evolution as well as the thermal stability of the binary alloys.
XRD out-of-plane (OOP) reveals that all samples show the well-known <111> OOP texture. Furthermore, the left-shift of the diffraction peaks (Fig1a) indicates the alloyed state of the AuNi particles, which is in addition confirmed by STEM-EDX (Fig.1b).
Ex-situ SEM studies revealed  enhanced dewetting kinetics in a Au concentration range between ~50 to 70at% independent of the substrate for the NiAu system (Fig.2a,b). In contrast, no such region could be identified in the absence of a large atomic size mismatch (AgAu) (Fig. 2a and c) . We explain the enhanced kinetics in AuNi by the introduction of an additional strain energy and disorder due the high atomic mismatch. This strain influences the Mullins coefficient by adding additional energy to the surface free energy of the film.
Overall we demonstrate that alloying of thin films provide additional energy contributions to the total energy balance and therefore significantly tailors the thermal stability and thus dewetting kinetics of thin bimetallic films.

[1]    L. Wang et al., “Magnetic-plasmonic Ni@Au core-shell nanoparticle arrays and their SERS properties,” RSC Adv., vol. 10, no. 5, pp. 2661–2669, 2020, doi: 10.1039/c9ra10354f.
[2]    D. Wang and P. Schaaf, “Plasmonic nanosponges,” Adv. Phys. X, vol. 3, no. 1, p. 1456361, Jan. 2018, doi: 10.1080/23746149.2018.1456361.
[3]    H. W. Lee et al., “Solid-solution alloying of immiscible Pt and Au boosts catalytic performance for H2O2 direct synthesis,” Acta Mater., vol. 205, p. 116563, 2021, doi: 10.1016/j.actamat.2020.116563.