Sol-gel synthesis of Zn-thiourea-SiO2 thin films from (EtO)3Si(CH2)3NHC(=S)NHPh as molecular precursor

In order to study new and convenient sol–gel syntheses to homogeneous nanocomposites systems based on zinc sulphide clusters embedded in films of silica glass, a thiourea-functionalized silane ((EtO)3Si(CH2)3NHC(S)NHPh, SilTu) was investigated as starting precursor. Electrospray ionization mass spectrometry (ESI-MS), FT-IR and NMR spectroscopies clearly evidence that SilTu coordinates Zn2+ ions in solution through the thiourea function. Both zinc acetate (Zn(CH3COO)2) and zinc chloride (ZnCl2) were used as zinc source. The SilTuZn2+ complex is also stable under sol–gel conditions. Alcoholic solutions of SilTu, zinc acetate and tetraethoxysilane Si(OEt)4 (TEOS) were used to prepare the thin films by dip-coating. Transparent, homogeneous and crack-free layers were obtained under annealing up to 600 °C. The samples were investigated by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). Beside ZnS formation, the presence of oxygenated zinc species was observed inside the silica matrix.