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 synthesised from alkoxysilanes and tetra ethyl orthosilicate with copper ammine complexes, prepared from Cu²+ salts and amino alkoxy silames. Glass substrates are coated by dipping and layers up to 1 µm in thickness are obtained after thermal densification at temperatures between 200°-500°C. The Cu colloid formation can be achieved using a reducing atmosphere during densification. Thus reddish-brown coloured coatings on glass with optical densities between 0.5 and 2 are obtained. Under ambient air the colour turns from reddish-brown to dark green. This process is reversible and by re-heating under reducing conditions the reddish-brown colour can be re-establised. UV-VIS absorbance measurements and structural investigations by WAXS, TEM, ESCA and SNMS show that the green colour is due to an oxide layer at the colloidal interface

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

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 \u27fuzzy\u27 colloid surface which is supposed to be due to the formation of a highly densified shell around the colloids caused by the ligands

Small-angle x-ray scattering experiments in grazing incidence on sol-gel coatings containing nano-scaled gold colloids : a new technique for investigating thin coatings and films

Small-angle X-ray scattering (SAXS) is generally not applicable to thin (∼­1 µm) films and coatings because of their weak scattering signal in conventional transmission experiments. This restriction can be overcome by working in grazing incidence, with an angle of incidence α slightly above the critical angle of total reflection φc, in order to augment the effective X-ray path in the sample. The possibilities of this technique are demonstrated by preliminary results obtained on glass-like solgel coatings containing nano-scaled gold colloids. The scattering of the gold colloids was identified by variations of the X-ray energy near the absorption edge of gold (anomalous SAXS). It showed the theoretically predicted variation of intensity with energy. The recorded scattering spectra were corrected for absorption and refraction effects, whose influences on the spectra are discussed. Calculated size distributions of the colloids from SAXS in grazing incidence were compared with results from high-resolution transmission electron microscopy (HTEM) investigations and optical UV-visible spectroscopy