Fig. 1. (Color online) XRD patterns of (a) the Au samples, and (b) the Au–CuO and pure CuO samples.

Fig. 2. SEM micrographs of (a,b) the CuO nanomaterial, (c) the Au nanoparticles, and (d) the Au-loaded CuO nanomaterial.

Fig. 3. (Color online) (a) Relation of the gas response with operating temperature for the pure CuO, and 0.5‰, 1.0‰, and 2.0‰ Au-loaded CuO gas sensors to 500 ppm of ethanol. (b) The response of the sensors based on pure CuO and Au-loaded CuO to different concentrations of ethanol at 160 ºC.

Fig. 4. (Color online) (a, b) Response and recovery behavior of the gas sensors based on pure CuO and 1.0‰ Au-loaded CuO to different concentrations of ethanol at 160 ºC. (c, d) The response time (T_res) and the recovery time (T_rec) of the gas sensors based on pure CuO and 1.0‰ Au-loaded CuO to 400 ppm of ethanol at 160 ºC.

Fig. 5. (Color online) Equivalent diagram of the resistance of the Au-loaded CuO nanosheet.

Fig. 6. (Color online) Response of the gas sensors based on the pure CuO and 0.5‰, 1.0‰, and 2.0‰ Au-loaded CuO to 400 ppm of various test gases at 160 ºC.

Fig. 7. (Color online) Response of the gas sensors based on the pure CuO and 0.5‰, 1.0‰, and 2.0‰ Au-loaded CuO to different concentrations of formaldehyde at 160 ºC.

Fig. 8. (Color online) Seven cycles of response-recovery to 300 ppm of ethanol of the 2.0‰ Au-loaded CuO gas sensor at 160 ºC.

Table 1. Comparison of gas-sensing properties of other metal oxide nanostructures toward ethanol gas.