Comparison of CO and CO2 rf plasma treatment of SnO2 nanoparticles for gas sensing materials

Abstract

CO and CO2 plasmas were used to modify SnO2 nanoparticles (NPs) to understand the role of key gas-phase species and to explore a potential route for improving these materials as solid-state gas sensors. Excited state species in both plasmas were monitored using optical emission spectroscopy and the NP were analyzed after plasma exposure with x-ray photoelectron spectroscopy. These studies reveal that in the CO2 plasma, CO2 decomposes to CO and O, leading to etching of the SnO2 lattice. Conversely, in the CO plasma, very little O is formed, leading to the deposition of a carbonaceous film on the SnO2 NP. Sensors fabricated with the CO2 modified SnO2 NP demonstrate a higher response to CO, benzene, and ethanol and improved response and recovery behavior when compared with untreated devices. CO plasma modification, however, had a detrimental effect on the gas sensing performance of this material.