Gas phase synthesis of SnOx nanoparticles and characterization

Tin oxide nanoparticles with an average size ranging from 4 to 80 nm were synthesized by oxidation of tin vapor in a low vacuum (10–40 mbar) reactor containing an Ar/O2 gas mixture. The effect of oxygen and argon partial pressure on the phase formation, size characteristics and morphology of the particles was studied by transmission electron microscopy (TEM) and X-ray diffraction (XRD) method. Electron spectroscopy chemical analysis (ESCA) was used to study the state of the particle surfaces. It was shown that with increasing the oxygen partial pressure, coarser SnOx particles were synthesized. The ESCA shift for the tin 3d5/2 line was 2 eV and the separation between this line and the oxygen 1s line was 44 eV. The oxygen 1s line was narrow and symmetric without the OH tail, indicating clean surface. The O/Sn ratios were estimated by using the areas of the tin and oxygen lines, and it was found that the oxidized tin vapor consisted of both SnO and SnO2. At the oxygen concentration of 50 vol% and the total pressure of 10 mbar, the surface composition was estimated to be SnO1.2. The particles were transformed to tetragonal SnO2 after heat treatment at 350 °C for 24 h in air.