Conflict of interest

with response magnitude of 1.84. Doped ZnO nanobelts also get its optimal operating point at 200°C. Its response magnitude was obtained at 2.06. The best sensing signal response of CH4 was found at 200°C. The sensing response at 50, 100, and 150°C (not shown) was comparatively negligible. The sensing response of undoped ZnO nanowires and Mg-doped ZnO nanobelts was found to be 1.84 and 2.06 at 200° C for the same concentration, respectively. The enhanced sensitivity response was observed for the ZnO nanostructures as shown in Figure 10(b). Large amount of oxygen molecules and atoms are adsorbed on Mg-doped ZnO nanobelts due to large surface area (i.e., large defects are created) due to which interaction chance of CH4 gas increases as compared to undoped ZnO nanostructures [60, 61]. On exposing the surface of the ZnO nanostructures to air, oxygen is adsorbed at the ZnO nanostructures surface by capturing an electron from conduction band of surface sites of undoped and Mg-doped ZnO nanostructures [62, 63]. Reactive O2 (oxygen molecules) are chemisorbed or trapped by these ZnO nanostructures from the air,

(a) CH4 gas sensing response of undoped ZnO nanowires (S1). (b) CH4 gas sensing response of Mg-doped ZnO

takes place, due to which a wide space charge is formed that results in a decrease in carrier concentration due to which the resistance of the material is increased.

Growth of 1-D ZnO nanostructures was presented in the present chapter. Vaporliquid-solid mechanism has been employed for the synthesis of ZnO nanostructures. It was found that the morphologies tuned with change in temperature which leads to the formation of nanowires at 850°C, nanorods at 900°C, nanobelts at 950°C, and nanobelts with needle-like ends at 1030°C. The dimensions of the morphologies have been measured by SEM. The length of the structures from 2.93 to 319.48 μm, thickness of the structures from 0.05 to 1.88 μm, and diameter of the structures from 0.95 to 12.66 μm have been obtained successfully. XRD peaks show that the crystallinity and intensity increase with increase in temperature. Doping of magnesium acetate (0.05 g) in ZnO through vapor transport method was successfully achieved. The sensing response of doped ZnO nanostructures for UV light at room temperature and CH4 gas at 200°C has increased. ZnO nanowires show great selectivity response toward different volatile organic compounds (ethanol, methanol, and acetone). At the same concentration and temperature, the ZnO nanowires show

and O; as a result transformation of electrons

forming active oxygen species O2

5. Conclusions

118

Figure 10.

Gas Sensors

nanobelts.

There is no conflict of interest in this chapter.
