Surface oxidation of monodisperse SnOx nanoparticles

Monodisperse tin oxide nanoparticles of size from 10 to 25 nm with different initial oxygen stoichiometry are prepared by a gas-phase condensation technique. Auger electron spectroscopy is used to study the stoichiometric changes of the particle surfaces processed under different conditions. Annealing the as-deposited SnOx particles at 300 °C for 1 h in synthetic air leads to an intermediate phase of tin oxide and on further annealing, an equilibrium phase is stabilized. The annealing treatments oxidize the particle surface nearly to stoichiometric SnO2, depending on the initial oxygen content. In the case of pre-oxidized particles in the gas phase, an under-stoichiometric phase, with the surface composition of SnO1.8, is observed even after multiple heat treatments whereas the SnO particles, that are not pre-oxidized, transform into SnO2 after annealing twice at 300 °C. The surface stoichiometry is not found to change with the particle size.