Fig. 2 shows the resistance change of ZnO nanorods at various temperatures and concentrations of test gases.
It shows that resistance is very high at low temperature and it decreases with increasing testing temperature.
This generally happens due to the increase of electron concentration on the surface of ZnO nanorods with increasing temperature.
Furthermore, the response increased and recovery time decreased with increasing testing temperature as well as gas concentration in case of CO gas while in case of ethanol and acetaldehyde, response as well as recovery time both increased.
These ZnO nanorods show response as low as 100 °C for CO and ethanol gas but for acetaldehyde it does not show response below 200 °C (resistance change for CO and ethanol at 100 °C is shown in Fig. S2).
Although, the concentration of ethanol is lower than the CO gas but it shows better response at almost every test temperature.
However, recovery time for CO is better than the ethanol at every testing temperature.
Furthermore, reproducibility is an important factor for gas sensor and it is checked by repeating the test three times at every test temperature for 1000 ppm of CO and 250 ppm of ethanol as well as acetaldehyde.
As can be seen from Fig. 2, ZnO nanorods show good reproducibility at every testing temperature for these gases.