4.7 Morphology analysis

the magnesium acetate [Mg(CH3COO)24H2O] weight was 0.08 g, and the sample

(a) SEM image of undoped ZnO nanorods (S2). (b) SEM images of Mg-doped ZnO nanobelts. (c) SEM image of undoped ZnO nanowires (S1). (d) SEM images of Mg-doped ZnO nanobelts. (e) and (f) show EDX analysis

of undoped and Mg-doped ZnO nanowires and nanobelts, respectively.

The collected Mg-doped ZnO nanostructure sample characterization was carried out for crystallinity, morphology and elemental composition, and optical properties. Optical and gas sensing response of the respective Mg-doped ZnO nanostructures was carried out by measuring respective resistances by two probe methods using a

distance from the source material was 12 cm.

multimeter (Keithly 2100).

Gas Sensors

Figure 9.

116

Mg-doped ZnO nanostructure morphology was probed by means of SEM. Figure 9(a) shows the SEM image of undoped ZnO nanorods (S2) with average diameter and length of 12.66 3.72 μm and 319.48 93.50 μm, respectively. Figure 9(b) shows SEM images of Mg-doped (0.05 g) ZnO nanobelts. The average thickness of 1.88 0.70 μm, average width of 4.7 1.04 μm, and average length of 72.03 18.84 μm of the Mg-doped ZnO nanobelts were measured. Figure 9(c) shows the SEM image of undoped typical ZnO nanowires (S1) with different dimensions, having average diameter and average length of 0.95 0.11 μm and 35.59 9.90 μm, respectively. Figure 9(d) shows the respective EDX analysis spectrum of the undoped ZnO nanowires (S1). The EDX spectra show the attachment of O (oxygen) and Zn (zinc) in the ratio O/Zn which was found to be 32:58, respectively. These composition analyses clearly showed that no impurity peak was observed, showing the purity of ZnO nanostructures. The aspect ratio of undoped and doped ZnO nanorods and nanobelts was found to be 25 and 51, respectively. Figure 9(e) shows the Mg-doped (0.08 g) ZnO nanobelts having average thickness of 0.05 0.009 μm, average width of 0.28 0.02 μm, and average length of 2.93 0.87 μm. The corresponding elemental compositions of the synthesized ZnO nanobelts were confirmed by EDX spectroscopy. Figure 9(f) shows the corresponding EDX analysis of the doped ZnO nanobelts, showing the presence of oxygen, magnesium, and zinc in the ratio O/Mg/Zn which was found to be 28:0.35:72 respectively. EDX analysis confirmed that the compositions of the products are Mg-doped ZnO without impurity. The aspect ratio of undoped ZnO nanowires and Mg-doped ZnO nanobelts was found to be 37 and 38, respectively. The possible reason for the formation of thin and transparent nanobelts is due to the morphology tuning from nanorods and nanowires to nanobelts by Mg doping, because doping of definite elements plays a key role in the alteration of the dimensions of nanostructures [52–58]. Growth rates and polar surfaces can provoke the asymmetric growth. Formation of nanobelts was explained as continuous process of 1-D branching and subsequent 2-D interspace filling.

Polar surfaces of wurtzite crystals of oxide semiconductors can induce asymmetric growth which leads to the diverse nanostructures, e.g., nanocombs, nanobrushes, needle-like belts/rods, etc. [59].
