Ag Nanostructures on GaN (0001): Morphology Evolution Controlled by the Solid State Dewetting of Thin Films and Corresponding Optical Properties

Silver (Ag) nanostructures have demonstrated the feasibility of being utilized in various optoelectronic, catalytic, biomedical, and sensor devices due to their excellent surface plasmon resonance characteristics. The geometrical structure, spacing, and spatial arrangement of nanostructures are crucial for controlling the properties and device performance. Herein, we demonstrate the fabrication of various configurations of self-assembled Ag nanostructures on GaN (0001) by the systematic control of deposition thickness and annealing duration. The surface morphology evolution is thoroughly investigated, and the corresponding influence on optical properties is probed. The evolution of Ag nanostructures in response to thermal annealing is described based on the dewetting of thin films, Volmer-Weber growth model, coalescence growth, and surface energy minimization mechanism. For the deposition amount variation between 1 and 100 nm, the Ag nanostructures show gradual morphological transitions such as small nanoparticles (NPs) to enlarged NPs between 1 and 7 nm, elongated nanostructures to cluster networks between 10 and 30 nm, and void evolution with layered nanostructures between 40 and 100 nm. In addition, the annealing duration effect has been studied between 0 and 3600 s, where the Ag nanostructures exhibit the evolution of network-like, elongated and isolated irregular shapes, ascribed to Ostwald's ripening along with Ag sublimation. Furthermore, corresponding Raman, photoluminescence, and reflectance spectra reveal the morphology-dependent behaviors and are discussed based on the phonon, emission band, scattering, absorption, and surface plasmon effect.