Controlled Formation of Nanoislands During Microwave Annealing of Au Thin Films

We present a systematic study on the fabrication of gold nanoislands by microwave-assisted annealing, a rapid and energy-efficient alternative to conventional thermal treatments. Gold thin films with nominal thicknesses of 4, 5, 6, 8, and 10 nm are deposited by thermal evaporation directly onto BK7 glass substrates, with and without a 3 nm chromium adhesion layer. The samples are subsequently annealed in a microwave kiln, where microwave irradiation is absorbed and converted to heat within the graphite-coated cavity (kiln), allowing the substrate temperature to exceed 550 °C, the threshold required for film dewetting. This process induces a controlled morphological evolution from continuous thin films to well-defined nanoislands, with the final size distribution strongly dependent on the initial film thickness. Compared with oven-based annealing, microwave treatment promotes faster and more uniform heating, which enhances atomic diffusion and accelerates dewetting while reducing the risk of substrate deformation or excessive coalescence. The resulting nanoislands exhibit tailored size-dependent plasmonic properties, with clear correlations between film thickness, crystallite size, and optical absorption features. Importantly, the method is cost-efficient, requiring shorter processing times and lower energy input, while enabling reproducible fabrication of high-quality plasmonic nanostructures on inexpensive glass substrates, suitable for applications in sensing, photonics, and nanophotonics.