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

Abstract

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 <i>in situ</i> transmission localized surface plasmon resonance (LSPR) spectroscopy combined with <i>ex situ</i> 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 °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