Plasma treatment of SnO2 nanocolumn arrays deposited by liquid injection plasma-enhanced chemical vapor deposition for gas sensors

SnO2 nanocolumn arrays have been grown on 4 in. SiO2/Si substrates by liquid injection plasma-enhanced chemical vapor deposition. The nanocolumns are well-crystallized and aligned without any additional substrate heating and catalysts. Effects of the thermal annealing and O2 plasma treatment on the sensing response to CO and H2 gas were comparatively studied. It was found that the sensing response of the SnO2 nanocolumn arrays was greatly enhanced by O2 plasma treatment. The oxygen species and the stoichiometry of the as-deposited, annealed and plasma-treated samples were comparatively analyzed by X-ray photoelectron spectroscopy. The average composition ratio [O]lattice/[Sn] increased continuously after annealing and O2 plasma treatment. Plenty of oxygen species were chemisorbed on the surface of the SnO2 nanocolumns during O2 plasma treatment, resulting in the shift of binding energy O 1s for the plasma-treated sample to a higher value of 532.3 eV. The improvement in the sensing properties of the O2 plasma-treated sample is closely related with the chemisorbed oxygen on the surface and obvious aging effects on the sensitivity were also observed on this sample.