20-Nm-Nanogap Oxygen Gas Sensor With Solution-Processed Cerium Oxide

Pt-based nanogap electrodes with a gap separation of 20 nm were prepared by electron-beam lithography (EBL). These electrodes were employed to fabricate nanogap gas sensors by combining solution-processed cerium oxide (ceria, CeO2) as the sensing material. Two types (bottom- and top-contact) of nanogap gas sensors were prepared by alternating the EBL and the solution process. Oxygen gas responses were investigated as functions of the gap separation, ceria film thicknesses, and operating temperatures. The sensor response strongly depended on the gap separation and the nanostructure of the cerium oxide film. In the cases of the small gap separation below 35 nm, the nanogap gas sensor exhibits a fast response time of 10 s at a relatively low operating temperature of 573 K; this response time is approximately three orders of magnitude shorter than that exhibited by a microgap sensor under the same measurement conditions. The nanogap gas sensor could also be in use at 1 atm. The improved sensor performance is attributed to the extremely small gap separation of the nanogap electrodes; the reduced gap separation facilitates electron hopping conduction in the ceria film. The proposed approach for fabricating robust and ultrafine nanogap electrodes together with a facile coating method for forming the sensing layer opens up possibilities to develop various nanogap gas sensors with a fast response time.