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Bulk borosilicate glasses were prepared by the sol-gel process and doped with gold nanoparticles. First, a sol of the host glass (with nominal molar composition of 10% B 2 O 3 -90% SiO 2 ) was prepared, and then gold was introduced into the sol by means of a solution of a Au 3+ complex. The resulting gels were dried at 60 °C and then heated in air at various temperatures up to 600 °C to nucleate the gold particles and sinter the glass matrix. Various gold ligands were tested, and thiourea was found to be the most effective ligand in preventing fast gold reduction and precipitation to the gel surface during drying. A model based on the formation of insoluble gold species during drying of the gel is discussed to explain the phenomenon of gold precipitation to the sample surface. The heated gels were studied by measurements of the BET specific surface area and of the apparent density, showing the densification of the matrix during the heat treatments. UV-vis optical absorption spectroscopy was used to monitor the formation of Au nanoparticles that was effective after heating the gel at 300 °C in air. TEM studies revealed that two kinds of Au particles were present, with mean sizes of 10 and 30 nm. The smaller particles have a lattice spacing corresponding to face-centered cubic Au, whereas electron nanodiffraction patterns of the larger particles exhibit features of orthorhombic Au 3 Si.

A systematic investigation of the effects of thermal annealing on the optical absorption and structure of evaporated GaSe thin films is reported. The optical gap is determined in films annealed at various temperatures and for different periods of time. The variation of the optical gap is tentatively explained as due to the annealing of the unsaturated bonds present in the amorphous solid. An electron microscopic investigation shows that a gradual amorphous-polycrystalline transformation occurs in films treated at temperatures higher than 500 K.