Au nanoparticles decorated SiO2 nanowires by dewetting on curved surfaces: facile synthesis and nanoparticles-nanowires sizes correlation

We report a solid-state synthesis for SiO2 nanowires (NWs) (up to 20 microns in length and from about 40 to about 150 nm in diameter) coated by Au nanoparticles (NPs) (from about 20 to about 80 nm in diameter). This protocol is based on three steps: (1) large area production of very long SiO2 NWs on a Si surface exploiting a simple Au/Si solid-state reaction at high temperature; (2) coating of the SiO2 NWs by a Au film of desired thickness using sputtering depositions; and (3) a thermal process to induce a dewetting process of the Au-film coating the SiO2 NWs to obtain Au NPs on the curved surface of the NWs. The morphology evolution of the SiO2 NWs was followed, in each step, by scanning electron microscopy analyses. They allowed to correlate the evolution of the NPs size with the NWs sizes for different thicknesses of the starting Au-film coating the NWs and different annealing temperatures of the dewetting process. Some theoretical concepts, related to the dewetting process of a film on a curved surface were used to describe the experimental data. The main advantages of the proposed protocols include: (i) simplicity and low-cost (it is based only on sputtering depositions and thermal processes), and (ii) versatility based on the possibility of tuning Au-film thickness and annealing temperature to tune the NPs-NWs sizes ratio. These advantages can make this technique suitable for the mass production of Au NPs-coated SiO2 NWs toward applications in electronic devices, biosensors, and nanoscale optical devices.