Synthesis of Tin and Tin Oxide Nanoparticles of Low Size Dispersity for Application in Gas Sensing CeÂline Nayral, [a] Eric Viala, [a] Pierre Fau, [b] François Senocq, [c] Jean-Claude Jumas, [d] Andre Maisonnat,* [a] and Bruno Chaudret* [a] Abstract: Nanocomposite core ± shell particles that consist of a Sn 0 core surrounded by a thin layer of tin oxides have been prepared by thermolysis of [{SnNMe 2 ) 2 } 2 ] in anisole that contains small, controlled amounts of water. The particles were characterized by means of electronic microscopies TEM, HRTEM, SEM), X-ray diffraction XRD) studies, photoelectron spectros- copy XPS), and Mössbauer spectros- copy. The TEM micrographs show spherical nanoparticles, the size and size distribution of which depends on the initial experimental conditions of tem- perature, time, water concentration, and tin precursor concentration. Nanoparti- cles 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 Mössbauer studies indicate the composite nature of the particles that consist of a well-crystallized tin b core of  11 nm covered with a layer of  4 nm of amorphous tin dioxide and which also contain quadratic tin mon- oxide crystallites. The thermal oxidation of this nanocomposite yields well-crys- tallized nanoparticles of SnO 2 without coalescence or size change. XRD pat- terns show that the powder consists of a mixture of two phases: the tetragonal cassiterite phase, which is the most abundant, and an orthorhombic phase. In agreement with the small SnO 2 par- ticle size, the relative intensity of the adsorbed dioxygen peak observed on the XPS spectrum is remarkable, when compared with that observed in the case of larger SnO 2 particles. This is consis- tent with electrical conductivity meas- urements, which demonstrate that this material is highly sensitive to the pres- ence of a reducing gas such as carbon monoxide. Keywords: colloids ´ nanostructures ´ semiconductors ´ sensors ´ tin Introduction The optical and electrical properties of polycrystalline semi- conducting oxides depend strongly on the surface states of the individual grains, and on the distribution and the nature of the grain boundaries. Thus, the non-linear resistivity of zinc oxide varistors is partially explained in terms of chemisorption and diffusion of dioxygen to the grain boundaries, [1±3] a phenom- enon which is generally treated as an electronic process in which charge transfer occurs between the adsorbed species and the oxide. [4, 5] Similarly, the changes in electric conduc- tivity of the semiconducting oxide gas sensors involve redox processes that result from the interaction of reducing gases with surface oxygens. This gives rise to a measurable signal. [6±8] In nanosized materials, since the surface to volume ratio is much larger than that commonly found for semiconductor materials, both the surface properties and the grain-boundary distribution become predominant. This renders these materi- als as good candidates for applications that will take advantage of the high surface/volume ratio, such as chemical sensors [9±12] or luminescent semiconducting sensors. [13] The precise control of the morphology of semiconducting oxide materials at a nanometric scale is consequently of basic importance and, given the industrial and commercial de- mands, requires reproducible low-cost synthetic methods that can be implemented in microelectronic processes. Concerning tin dioxide, the oxide material most widely used as the sensitive layer of chemical sensors, [6±8] several synthetic [a] Dr. A. Maisonnat, Dr. B. Chaudret, Dr. C. Nayral, E. Viala [] Laboratoire de Chimie de Coordination du CNRS, UPR 8241 205 route de Narbonne, 31077 Toulouse Cedex 04 France) Fax:  33) 561-55-30-03 E-mail : maisonat@lcc-toulouse.fr chaudret@lcc-toulouse.fr [b] Dr. P. Fau MicroChemical System SA, 15 rue de Porcena Corcelles, 2035 Switzerland) [c] Dr. F. Senocq Laboratoire Interface et Mate riaux Ecole Nationale SupeÂrieure de Chimie, INPT 118, route de Narbonne, 31077 Toulouse Cedex 04 France) [d] Dr. J.-C. Jumas Laboratoire des AgreÂgats Mole culaires et Mate riaux Inorganiques ESA 5072 CNRS) Universite Montpellier II Sciences et Technologies du Languedoc, Case Courrier 015 Place E. Bataillon, 34095 Montpellier Cedex 5 France) [  ] E.V. on leave from Motorola Semiconductors SA, le Mirail, BP 1029, 31023 Toulouse Cedex 4 France) FULL PAPER  WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000 0947-6539/00/0622-4082 $ 17.50+.50/0 Chem. Eur. J. 2000, 6, No. 22 4082