LOCALIZED GROWTH OF GOLD NANOPARTICLES FROM Au(I) AND Au(III) PRECURSORS USING LASER IRRADIATION

When embedded in transparent solid matrices, the nonlinear optical properties of gold nanoparticles (GNPs) make them attractive for applications such as optical telecommunications, data storage, optical computing and information processing. Whereas a large number of synthetic routes have been developed to obtain GNPs in the liquid phase with controlled sizes and shapes, their inclusion in solid host matrices is not at all a trivial task. In the present work, a direct and space-selective formation of GNPs was obtained within a transparent mesoporous silica host matrix post-doped with appropriate Au(III) and Au(I) precursors. This synthesis was carried out using laser irradiation which provided a localized growth of the GNPs. The choice of these precursors made it possible to obtain reproducible microarrays of spherical and non-aggregated GNPs without the addition of either reducing or capping agents to the system. The synthesis method described consists of three steps: impregnation of the sol-gel-derived matrices with the gold precursors, irradiation and then removal of the precursors from the matrices by washing. The different phases of the process were followed spectroscopically by means of Raman spectroscopy, TEM, UV-vis absorption spectroscopy, x-ray diffraction and transmission electron microscopy. The irradiations were carried out with both continuous wave lasers ( = 266 and 532 nm) and a pulsed laser ( =800 nm; pulse: 120 fs; repetition rate: 1 KHz), which made it possible to fabricate 2D and 3D microarrays of gold nanoparticles, respectively. The presence of GNPs in the irradiated sample was confirmed by UV-vis absorption spectroscopy and xray diffraction and the gradual change in the matrix and in the chemical precursors were followed using micro Raman spectroscopy. TEM analysis showed that the GNPs obtained are spherical and that clustering is avoided thanks to the mesoporous nature of the matrix. The washed samples were tested for thermal resistance: it was shown that the GNP microarrays obtained are able to resist until up to at least 500°C with no observable gold diffusion outside the irradiated areas. The evolution of the Localized Surface Plasmon resonance band with temperature was followed using UV-visible spectroscopy.