Ag droplets nano-shape design on SiC: Study on wetting and energetics

This work describes the effect of the annealing temperature on the size and wetting of nanostructures obtained on 4H–SiC substrate by the dewetting process of a deposited nanoscale-thick Ag film. The work focuses, in particular, on the difference between solid-state dewetting (below Ag melting temperature) and liquid-state dewetting (above Ag melting temperature). Following the deposition of a 58 nm-thick Ag film on the SiC substrate, annealings were perfomed at 800 °C, 850 °C and 885 °C so to induce the Ag film solid-state dewetting. In addition, annealing at 1040 °C was performed so to induce the Ag film liquid-state dewetting. The dewetting processes led to the formation of nanostructures on the SiC surface. Plan-view and cross-view scanning electron microscopy analyses were carried out to quantify the evolution of the average planar size and of the average contact angle (to the SiC surface) of the Ag nanostructures versus the annealing temperature. These analyses allowed us to extract information on the wetting behavior of the nanostructures on the SiC surface by calculating the temperature-dependent adhesion work. In fact, the nanostructures obtained by the 800 °C and 850 °C processes show mean contact angle of 118,9° and 117,4°, respectively, and mean work of adhesion of 0,45 and 0,48 J/m2, respectively. On the other hand, the nanostructures obtained by the 885 °C and 1040 °C show mean contact angle of 48,3° and 52,2° respectively, and work of adhesion of 1,45 and 1,40 J/m2, respectively. The variation of the wetting properties is identified in Si diffusion from the SiC substrate to the Ag nanostructures at the higher temperatures, as confirmed by energy dispersive x-ray analyses. Finally, the optical properties of the Ag nanostructures/SiC systems were probed by absorbance and transmittance measurements allowing to recognize the occurrence of a peak around 460 nm which is attributed to localized surface plasmon resonances due to the Ag nanostructures.