Failure Study of Sno2 Room Temperature Gas Sensors Fabricated on Nanospike Substrates

SnO2 gas sensors were fabricated on polyurethane (PU) polymer surfaces with nanospike structures. These nanospikes are replicated with a low-cost soft nanolithography method from silicon nanospike surfaces formed by femtosecond pulsed laser irradiation. The hydrophobicity of the sensing surface was enhanced by a monolayer coating of silane (1H,1H,2H,2H-perfluorooctyltrichlorosilane, PFOTS). The resulting self-cleaning behavior enabled sensing in environments with high moisture and heavy particulate content, while performing cleaning-in-place operations to prolong the lifetime of the sensors. Failure studies were performed to quantify the effects on the sensitivity of water washing. Contact angle measurements showed that the hydrophobicity was weakened after many cycles of droplet washing due to wear of the PFOTS film and/or damage of the nanoscale spike structure. It was also found that the baseline signal increased with droplet washing, while the sensitivity changed randomly within about 7.5%, so that the sensitivity of the gas sensor remained at a constant level after several thousand cycles of water washing.