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 (up to 20 microns in length and from about 40 to about 150 nm in diameter) coated by Au nanoparticles (from about 20 to about 80 nm in diameter). This protocol is based on three steps: 1) large area production of very long SiO2 nanowires on a Si surface exploiting a simple Au/Si solid state reaction at high temperature; 2) coating of the SiO2 nanowires by a Au film of desired thickness using sputtering depositions; 3) a thermal process to induce a dewetting process of the Au film coating the SiO2 nanowires to obtain Au nanoparticles on the curved surface of the nanowires. The morphology evolution of the SiO2 nanowires was followed, in each step, by scanning electron microscopy analyses. They allowed to correlate the evolution of the nanoparticles size with the nanowires sizes for different thicknesses of the starting Au film coating the nanowires 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), (ii) versatility based on the possibility of tuning Au film thickness and annealing temperature to tune the nanoparticles-nanowires sizes ratio. These advantages can make this technique suitable for the mass production of Au nanoparticles coated SiO2 nanowires towards applications in electronic devices, biosensors, nanoscale optical devices.