Design of a highly sensitive and selective C ₂H ₅OH sensor using p-type Co ₃O ₄ nanofibers

The Co ₃O ₄ nanofibers were prepared by electrospinning and their gas sensing characteristics were investigated. The Co ₃O ₄ sensors prepared by heat treatment of as-spun precursor fibers at 500 and 600 °C showed well-developed one-dimensional morphologies and exhibited high responses to 100 ppm C ₂H ₅OH (R _g/R _a = 51.2 and 45.3; R _g, resistance in gas; R _a, resistance in air) at 301 °C with negligible cross-responses to 100 ppm CO, C ₃H ₈, and H ₂ (R _g/R _a = 1.02-2.7). In contrast, the most of one-dimensional morphology of the Co ₃O ₄ specimen was lost and the response to 100 ppm C ₂H ₅OH became significantly lower when the heat treatment temperature was increased to 700 °C or when the nanofibers were ultrasonically disintegrated into primary particles. The significant decrease of the gas response was explained and discussed in relation to the gas sensing mechanism of a p-type semiconductor, the morphology of specimens, and the connecting configuration between nanoparticles and nanofibers.