Sol-gel synthesis and characterization of Ag2S nanocrystallites in silica thin film glasses

Silver sulfide particles embedded in thin coatings of transparent and homogeneous silica glass are promising materials for the development of optical devices. The optical properties are strongly dependent on the elemental composition and morphology of the coatings as well as on the size distribution of the nanoclusters. A sol-gel route has been used to achieve good control over film composition and morphology. The dip-coating procedure from alcoholic solutions containing tetraethoxysilane [Si(OEt)(4)] and silver diethylthiourea complexes [Ag(EtNHCSNHEt)(n)](+) has been adopted. The silver sulfide particles were directly generated in silica by decomposition of the silver complexes upon heating the coatings. Annealing was performed in a nitrogen atmosphere in order to prevent sulfide oxidation to sulfate. The sol-gel method has been shown to be a suitable procedure for controlling the size of the metal sulfide particles. Evolution of the system under heating has been studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), secondary-ion mass spectrometry (SIMS) and atomic force microscopy (AFM).