Fig. 6.

Sensor responses of various samples towards 50 ppm ethanol vapor. a Gas responses of the six types of sensors, based on annealed 50-nm-thick SnO₂:NiO network as-deposit 50-nm-thick SnO₂:NiO network, annealed continuous 50-nm-thick SnO₂:NiO film, as-deposit continuous 50-nm-thick SnO₂:NiO film, annealed 20-nm-thick SnO₂:NiO network, and annealed 100-nm-thick SnO₂:NiO network, respectively. b Gas responses of the sensors fabricated at different plasma etching time