Coating of gold nanoparticles made by pulsed laser ablation in liquids with silica shells by simultaneous chemical synthesis.

Coating of gold nanoparticles with silica shells by the well known Stöber-method requires the use of additional coupling agents to seed the growth of the shell as gold does not form a native oxide. Here we report a novel single-step process to create the gold nanoparticles directly into a mixture of tetraethyl orthosilicate and a catalyst by means of pulsed laser ablation in liquids. We observe that good silica shells are achieved only when all of the reagents are present during the production of the nanoparticles. Experiments with two different laser wavelengths: 515 nm and 1030 nm, show that the formation of the shell is efficient only with the laser wavelength close to the plasmon resonance of the gold nanoparticles. We propose a model indicating that the shell formation is initiated by laser-induced heating of the particles.