The gas-sensing measurements were made on the films deposited on top of alumina substrates with platinum interdigitated electrodes (for electrical measurements). A platinum heater was printed on the backside of the substrate. The gas-sensing measurements were carried out in the environmental test chamber shown in Fig. 1. The desired concentration of probe gas was prepared by mixing CO with air in the gas mixing chamber. Then, the mixture was injected into the measurement chamber through an MKS flow control valve connected to a gas mixing system (MKS 47X). The concentration of CO was varied in the range 500–50,000 ppm. The volume of gas to be injected was controlled by the duration (dwell time) of valve opening and its flow rate. The temperature of the sensor was controlled with a programmable power supply (BK1700), a K-type thermocouple (feedback element) and a PC PID temperature controller. The sensor temperature was varied in the range 300–600
C. The sensor current (under a given bias voltage) was measured using a source measure unit (Keithly 238). The resistance of the films was calculated as the ratio between the applied bias voltage and the measured current. A personal computer was used to control all the operations (gas injection, temperature measurement and control, and current measurement) using LABVIEW via a GPIB interface