Tailored nanoparticle films from monosized tin oxide nanocrystals: Particle synthesis, film formation, and size-dependent gas-sensing properties

In order to investigate the change of gas-sensitive properties of undoped tin oxide nanoparticle films depending on particle size, a thin film synthesis technique has been developed. Well-defined tin oxide nanoparticles have been prepared using a gas-phase condensation method. Pure SnO was used as starting material and was evaporated at T=820degreesC. The resulting particles were sintered and crystallized in-flight at T=650degreesC. Size-selected nanoparticles ranging from 10 to 35 nm were produced to form a nanoparticle film by means of electrostatic precipitation or low pressure impaction. The effect of in-flight oxidation, sintering, and crystallization on the structure, size, and size distribution of nanoparticles have been studied in detail. The samples show n-type semiconductors' behavior like bulk SnO2. The influence of particle size on gas sensitivity and response behavior is investigated for C2H5OH at operating temperatures 200-300degreesC using silicon substrates having an interdigitated contact pattern and an integrated heating system. In the range of 10-35 nm it has been shown unambiguously that decreasing the particle size of tin oxide particles leads to an increase of the sensitivity and a more rapid response on changing gas conditions. The effect is especially clear for films with a particle size of 20 nm or smaller. (C) 2003 American Institute of Physics.