Zinc oxide thin films for a room temperature dual carbon dioxide and carbon monoxide sensor

Zinc oxide was grown onto glass substrates by the spray-pyrolysis technique in order to obtain thin films of different thicknesses to test their sensing characteristics towards CO₂ and CO at room temperature (21 °C). The different films showed a diverse surface reactivity towards these gases due to the dominant crystallographic orientation of grains. The working temperature allows the sensor to operate without the need of maintaining the film heated, greatly reducing its energy needs and building costs. A 2% signal decrease to 2000 ppm of CO₂ is achieved within 120 s (t₅₀ time) with a recovery time of approximately 290 s. The detection limit is estimated to be at 400 ppm. This sensor can also detect harmful concentration of CO (above 50 ppm) since its response can be clearly differentiated from its CO₂ response, thus behaving as a dual sensor.