Synthesis of SnO2−x nanoparticles tuned between 0 ⩽ x ⩽ 1 in a premixed low pressure H2/O2/Ar flame

The transition from tin monoxide to tin dioxide is investigated by doping a low pressure premixed H2/O2/Ar flame with dilute concentrations of tetramethyl tin (TMT) Sn(CH3)4. The H2/O2 ratio was varied between 1.97 and 0.97; the reactor pressure was set to 30 mbar. The inlet gas velocity was kept constant and the precursor concentration was varied between 200 and 700 ppm. Mean particle diameters between 3 nm ⩽ dp ⩽ 7 nm were measured using a particle mass spectrometer (PMS), while X-ray diffraction (XRD) and transmission electron microscope (TEM) analysis revealed information on crystal structure as well as morphology of the synthesized oxides. A gray SnO film was observed in the reactor at low oxygen concentrations, while for higher oxygen concentrations light yellow sub-stoichiometric tin oxides and white SnO2 were obtained. Further analysis of the sub-stoichiometric oxides, using atomic electron spectroscopy AES revealed that SnO2−x (0.2 ⩽ x ⩽ 0.6) was obtained. Furthermore, electrical characterization of all materials, deposited on interdigital capacitors, showed a decrease in the conductivity of the nanoparticles with increasing oxidation (decreasing x).