Morphological and Optical Evolution of Silver Nanoparticles on Sapphire (0001) Along with the Concurrent Influence of Diffusion, Ostwald's Ripening, and Sublimation

Silver nanoparticles (Ag NPs) have found a number of applications in various fields such as optoelectronics, sensors, and catalysts, and the optical, physical, and chemical properties of Ag NPs can be modified by the control of size, density, and configuration as well as their spacing. Therefore, in this paper, we demonstrate the size, shape, and spacing control of Ag NPs by the systematic control of annealing duration between 0 and 3600 s on sapphire (0001) (Al₂O₃). The Ag NPs show a sharp distinction in morphology along with the controlled duration at 20 and 14 nm thickness, and the evolution trend is systematically discussed based on the concurrent influence of surface diffusion, Ostwald's ripening, and sublimation. With the relatively thicker film of 20 nm, the fabrication of irregular and round NPs is demonstrated along with the gradually reduced size up on the annealing at 750 °C for the duration between 0 and 900 s. Between 1800 and 3600 s, tiny grain-like particles result as a consequence of an extensive sublimation. Meanwhile, with the film thickness of 14 nm at 400 °C, densely packed small NPs are resulted between 0 and 3600 s due to the limited surface diffusion. At the same time, the optical characterizations such as Raman and reflectance spectroscopy show a distinctive trend of spectra, i.e., intensity, peak position, and FWHM, based on the evolution of Ag NPs and are discussed in conjunction with the specific morphology and surface coverage of the Ag NPs.