Odile Cristini-Robbe

Synthesis and nonlinear optical properties of zirconia-protected gold nanoparticles embedded in sol–gel derived silica glass

A new approach to dope a silica glass with gold nanoparticles (GNPs) is presented. It consisted in embedding zirconia-coated GNPs in a silica sol to form a doped silica gel. Then, the sol-doped nanoporous silica xerogel is densified leading to the formation of a glass monolith. The spectral position and shape of the surface plasmon resonance (SPR) reported around 520 nm remain compatible with small spherical GNPs in a silica matrix. The saturable absorption behavior of this gold/zirconia-doped silica glass has been evidenced by Z-scan technique. A second-order nonlinear absorption coefficient β of about −13.7 cm GW−1 has been obtained at a wavelength near the SPR of the GNPs.

Synthesis of gold nanoparticles within silica monoliths through irradiation techniques using Au(I) and Au(III) precursors

The formation of gold nanoparticles (GNPs) within mesoporous silica matrices by means of irradiation techniques is reported. The xerogels were impregnated with solutions of two different gold precursors: (Ph3P)AuCl for Au(I) and [nBu4N]AuCl4 for Au(III). The irradiations were performed with two continuous wave laser sources (266 and 532 nm), with a femtosecond pulsed laser (800 nm), and with a mercury vapour lamp emitting in the UV region. It has been shown that no reducing agent was ever required to obtain GNP formation. XRD data exhibited the typical patterns of fcc gold, except for two cases involving the Au(I)-doped matrices, where a preferential crystallographic orientation was observed. Excluding the case of the UV irradiations performed on Au(III)-doped samples, we always obtained the formation of roughly spherical and well dispersed GNPs of relatively small size (6–60 nm). The gold-reduction mechanisms proposed depend on the chosen irradiation technique. Moreover, when laser sources are employed, GNP formation can be selectively limited to the irradiated areas, thus making it possible to obtain reproducible patterns of GNPs.

Zirconia coating for enhanced thermal stability of gold nanoparticles

This paper describes a rapid, simple and one-step method for the preparation of 2–4 nm diameter zirconia-coated gold nanoparticles at room temperature. These nanoparticles were synthesized by two simultaneous processes: the chemical reduction of tetrachloroauric acid with sodium borohydride and the formation of zirconia sol–gel matrices. All the gold nanoparticle sols were characterized by UV–visible absorption and transmission electron microscopy to determine the nanoparticle size and shape. The synthesis method is a combination of a polymeric structure of the amorphous zirconia and the use of a strong reducing agent, and it yields to very small quasi-spherical gold nanoparticles at room temperature. The thermal stability up to 1200 °C of the coated nanoparticles was studied by x-ray diffraction. The metastable tetragonal phase of the zirconia coating was obtained at 400 °C, and a progressive transformation from tetragonal to monoclinic phases of the zirconia coating was observed up to 1100 °C. After the heat treatment at 400 °C, the crystallite size of the gold nanoparticles was about 29 nm, and it remained unchanged from 400 °C to 1200 °C. These results are promising for the development of such materials as doping elements for optical fiber applications.

Combination of porous silica monolith and gold thin films for electrode material of supercapacitor

An all-solid electrical double layer supercapacitor was prepared, starting from a porous silica matrix coated with a gold thin-film. The metallization of the silica xerogel was performed by an original wet chemical process, based on the controlled growth of gold nanoparticles on two opposite faces of the silica monolith as a seed layer, followed by an electroless deposition of a continuous gold thin film. The thickness of the metallic thin film was assessed to be 700 nm. The silica plays two major roles: (1) it is used as a porous matrix for the gold electrode, creating a large specific surface area, and (2) it acts as a separator (non-metallized part of the silica). The silica monolith was soaked in a polyvinyl alcohol and phosphoric acid mixture which is used as polymer electrolyte. Capacitance effect was demonstrated by cyclic voltammetry experiments. The specific capacitance was found to be equal to 0.95 mF cm− 2 (9.5 F g−1). No major degradation occurs within more than 3000 cycles.