Synthesis of tin and tin oxide nanoparticles of low size dispersity for application in gas sensing

Nanocomposite core-shell particles that consist of a Sn-0 core surrounded b y a thin layer of tin oxides have been prepared by thermolysis of [(Sn(NMe2 )(2))(2)] in anisole that contains small, controlled amounts of water. The particles were characterized by means of electronic microscopies (TEM, HRTE M, SEM), X-ray diffraction (XRD) studies, photoelectron spectroscopy (XPS), and Mossbauer spectroscopy. The TEM micrographs show spherical nanoparticl es, the size and size distribution of which depends on the initial experime ntal conditions of temperature, time, water concentration, and tin precurso r concentration. Nanoparticles of 19 nm median size and displaying a narrow size distribution have been obtained with excellent yield in the optimized conditions. HRTEM, XPS, XRD and Mossbauer studies indicate the composite n ature of the particles that consist of a well-crystallized tin beta core of approximate to 11 nm covered with a layer of approximate to 4 nm of amorph ous tin dioxide and which also contain quadratic tin monoxide crystallites. The thermal oxidation of this nanocomposite yields well-crystallized nanop articles of SnO2. without coalescence or size change. XRD patterns show tha t the powder consists of a mixture of two phases: the tetragonal cassiterit e phase, which is the most abundant, and an orthorhombic phase. In agreemen t with the small SnO2 particle size, the relative intensity of the adsorbed dioxygen peak observed on the XPS spectrum is remarkable, when compared wi th that observed in the case of larger SnO2 particles. This is consistent w ith electrical conductivity measurements, which demonstrate that this mater ial is highly sensitive to the presence of a reducing gas such as carbon mo noxide.