Solid-State Thermal Dewetting of Just-Percolated Gold Films Evaporated on Glass: Development of the Morphology and Optical Properties

Solid-state thermal dewetting of just-percolated gold films of nominal thicknesses in the range 10-16 nm, prepared by evaporation on glass slides and annealing, was systematically studied. The kinetics of thermal dewetting and transition from a percolated film to isolated islands were monitored using in situ transmission localized surface plasmon resonance (LSPR) spectroscopy combined with ex situ high-resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and selected-area electron diffraction (SAED) to correlate between evolution of the film morphology and development of the optical properties. Annealing at 550 degrees C results in transformation of the as-evaporated, percolated polycrystalline films, with mean crystallite dimensions close to the film nominal thickness, to (111) textured films comprising large separated single-crystalline islands. The dewetting scenario depends on the initial morphology of the unannealed, just-percolated Au film, in particular on the structure of the voids at the metal-ambient and metal-glass interfaces. Dewetting of films of <13 nm (nominal thickness), the latter exhibiting a majority of voids which are open at both interfaces (denoted type I films), shows faster kinetics than in-plane grain growth. In films of >13 nm (nominal thickness), in which the majority of voids do not protrude through the entire film and are closed at the metal-glass interface (denoted type II films), grain growth presents faster kinetics than dewetting. The annealed films display discrete single-crystalline Au islands with flat, (111) textured top surfaces. Island diameters range from <100 nm to submicrometer, while the surface plasmon extinction band varies over >300 nm for different average island sizes.