Mike Schmitt

Synthesis of Ag-colloids in sol-gel derived SiO2-coatings on glass

Ag colloid-containing coatings on soda lime glass and fused silica are prepared via the sol-gel process. To incorporate Ag+-ions in the coatings homogeneously, they are stabilized by a functionalised silane (aminosilane) and then mixed with the basic sol prepared from 3-glycidoxypropyl trimethoxysilane (GPTS) and tetraethoxysilane (TEOS). Crack-free and transparent coatings with a thickness of 0.5 to 1.2 μm, are obtained by heat treatment between 120°C and 600°C. The Ag-colloid formation was monitored by UV-VIS spectroscopy as a function of temperature. The investigations reveal that the substrate has a deciding influence on the Ag-colloid formation caused by alkali diffusion from the substrate into the coating. High resolution transmission electron microscopy (HRTEM) investigations prove that poly-crystalline AgxOy-nanoparticles are formed during thermal densification in the coatings and that this change is accompanied by a vanishing of the yellow colour of the coatings. A post-heat treatment in a reducing atmosphere (90% N2, 10% H2) turns back the yellow colour and single-crystalline Ag-colloids can be detected by HRTEM. A suitable choice of the temperature and time conditions allows the control of the colloid size during heat treatment in a reducing atmosphere. For comparison, ion-exchange experiments have been carried out which showed that a spontaneous Ag-colloid formation was achieved in the soda lime substrate at 400°C. Since Ag containing SiO2-coatings remained colourless after thermal treatment between 400°C and 600°C in air, on soda lime substrates, a remarkable diffusion of Ag+ into the substrate was excluded.

Colored coatings on eye glass lenses by noble metal colloids

Abstract Metal colloids in glass coatings are suitable for preparation of colored transparent coatings with thicknesses of about 0.2 to l μm due to their high molar coefficient of absorbance (≈ 10 6 l/(mol cm)). The absorbance of these metallic particles in a dielectric environment is caused by a surface plasmon resonance effect of the conductive electrons of the colloids. Therefore, it is characteristic for the metal, but can be affected by the dielectric properties of the surrounding matrix. Glass sol—gel coatings have been developed for the preparation of 0.2 to 0.4 μm thick, transparent colored coatings on silicate eye glass lenses by incorporation of Au-, Ag- and Pd-colloids into an 87 mol% SiO 2 —13 mol% PbO glass. A functionalized silane has been used as a complex forming agent for the appropriate noble metal ions to control the nucleation and growth processes of the colloids during the thermal densification of the coatings. By mixing different noble metal salts and addition of Co 2+ ions, pink, brown, green and grey colors with optical densities ≤ 6 have been obtained. By variation of the glass composition the refractive index of the coating can be adapted to that of different types of substrate glasses ( n D from 1.52 to 1.6) to obtain coatings with desirable optical performance. In a similar manner the transformation temperature ( T g ) of the coatings can be less than the substrate, allowing a complete thermal densification of the coatings at about 500°C. The coatings show glass like chemical durability and mechanical stability. Due to the optical and thermomechanical properties of the colored coatings and due to the thermal and UV-stability of the colloids these coatings were applied to eye glass lenses.

Investigations of the electronic structure of nanoscaled gold-colloids in sol-gel-coatings

Abstract The electronic structure of nano-scaled Au-colloids embedded in thin glass-like sol—gel coatings on glass substrates was investigated by small-angle X-ray scattering (SAXS) in grazing incidence and by UV-VIS spectroscopy as a function of the densification temperature of the coatings and of kind and concentration of the stabilizer used in the sol. Special interest was concentrated on the structure of the interface between matrix and colloids. It was found that the structure of this interface changes with the preparation of the coatings. Depending on densification temperature and stabilizer, it was observed that the structure of the surface of the colloids or the interface region between matrix and colloids is changing continuously from a structure similar to a fractal surface to a sharp phase boundary. Further densification leads partially to a ‘fuzzy’ colloid surface which is supposed to be due to the formation of a highly densified shell around the colloids caused by the ligands.

Gold colloids in sol-gel derived SiO2 coatings on glass and their linear and nonlinear optical properties

An organic-inorganic synthesis route to Au-colloid containing, transparent SiO2 coatings has been developed, using four different types of functionalized silanes as stabilizing ligands for the Au. By variation of the kind and the concentration of the stabilizing silane in the sol the onset temperature for the colloid formation varies between 100 and 300 degree(s)C and the final colloid radii can be controlled in a range between 3 and 30 nm after densification of the composite coatings on glass at 500 degree(s)C. The third order polarizability (Chi) m(3) in the metal particles is one order of magnitude higher than in glass composites and exhibits a strong dependence on the ligand.

SiO2 coatings on glass containing copper colloids using the sol-gel technique

A sol-gel method for the preparation of transparent copper nano particle-containing SiO2 coatings on glass has been developed. The sol is synthesized from alkoxysilanes and tetra ethyl orthosilicate with copper ammine complexes, prepared from Cu2+ salts and amino alkoxy silanes. Glass substrates are coated by dipping and layers up to 1 micrometers in thickness are obtained after thermal densification at temperatures between 200 degree(s) - 500 degree(s)C. The Cu colloid formation can be achieved using a reducing atmosphere during densification. Thus reddish-brown colored coatings on glass with optical densities between 0.5 and 2 are obtained. Under ambient air the color turns from reddish-brown to dark green. This process is reversible and by re-heating under reducing conditions the reddish-brown color can be re- established. UV-VIS absorbance measurements and structural investigations by WAXS, TEM, ESCA and SNMS show that the green color is due to an oxide layer at the colloidal interface.