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the SEM and TEM pictures of ZnO nanobelts.The nanoparticles were chemically synthesized from SnCl4 by inverse microemulsion using non-ionic surfactant, and have an average size of 10 nm and are highly agglomerated.Figure 4.7 shows SEM images of the synthesized ZnO nanobelt helical nanostructures, 20

Liu et al.21 synthesized SnO2 nanorods by converting nanoparticles at elevated temperatures.10 Kong and Wang 20 further demonstrated that by controlling growth kinetics, left-handed helical nanostructures and nano-rings can be formed by rolling up single crystal ZnO nanobelts.In (0001) facet-dominated single crystal nanobelts, positive and negative ionic charges are sponta- neously established on the zinc- and oxygen-terminated +-(0001) surfaces, respectively.Various oxide nanowires, such as ZnO, Ga2O3 and MgO, and CuO were synthesized by such evaporation-condensationNanobelts of other oxides such as Ga2O3 with a crystal structure of monoclinic and PbO2 (rutile) were also synthe- sized by the same technique.The growth of nanobelts cannot be attributed to either screw dislocation induced anisotropic growth, nor impurity inhib- ited growth.17 The typical thickness and width-to-thickness ratios of the ZnO nanobelts are in the range of 10 to 30 nm and ~5 to 10, respectively.No screw dislocation was found throughout the entire length of the nanobelt, except a single stacking fault parallel to the growth axis in the nanobelts grown along [0110] direction.

the SEM and TEM pictures of ZnO nanobelts. 17 The typical thickness and width-to-thickness ratios of the ZnO nanobelts are in the range of 10 to 30 nm and ~5 to 10, respectively. Two growth directions were observed: [0001] and [0110]. No screw dislocation was found throughout the entire length of the nanobelt, except a single stacking fault parallel to the growth axis in the nanobelts grown along [0110] direction. The surfaces of the nanobelts are clean, atomically sharp and free of any sheathed amorphous phase. Their further TEM analysis also revealed the absence of amorphous globules on the tip of nanobelts. The above observations imply that the growth of nanobelts is not due to the VLS mechanism, which will be dis- cussed later in this chapter. The growth of nanobelts cannot be attributed to either screw dislocation induced anisotropic growth, nor impurity inhib- ited growth. Furthermore, since four oxides in question all have different crystal structures, it is not likely that the growth of nanobelts is directly related to their crystal structures. Nanobelts of other oxides such as Ga2O3 with a crystal structure of monoclinic and PbO2 (rutile) were also synthe- sized by the same technique. 18 It seems worthwhile to note that the shape of nanowires and nanobelts may also depend on growth temperature. Early work showed that single crystal mercury grown at different temperatures would have either a platelet shape or a whisker form. 9,19 CdS ribbons were

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also grown by evaporation-condensation method. 10 Kong and Wang 20 further demonstrated that by controlling growth kinetics, left-handed helical nanostructures and nano-rings can be formed by rolling up single crystal ZnO nanobelts. This phenomenon is attributed to a consequence of minimizing the total energy attributed by spontaneous polarization and elasticity. The spontaneous polarization results from the noncentrosymmetric ZnO crystal structure. In (0001) facet-dominated single crystal nanobelts, positive and negative ionic charges are sponta- neously established on the zinc- and oxygen-terminated ±(0001) surfaces, respectively. Figure 4.7 shows SEM images of the synthesized ZnO nanobelt helical nanostructures, 20

Liu et al.21 synthesized SnO2 nanorods by converting nanoparticles at elevated temperatures. The nanoparticles were chemically synthesized from SnCl4 by inverse microemulsion using non-ionic surfactant, and have an average size of 10 nm and are highly agglomerated. SnO2 nanoparticles are likely to be amorphous. When heated to temperatures ranging from 780°C to 820°C in air, single crystal SnO2 nanorods with rutile structure were formed. Nanorods are straight and have uniform diameters ranging from 20 to 90 nm and lengths from 5 to 10 µm, depending on annealing temperature and time. Various oxide nanowires, such as ZnO, Ga2O3 and MgO, and CuO were synthesized by such evaporation-condensation