THESIS
2016
ix, 97 pages : illustrations ; 30 cm
Abstract
The polarity of zinc oxide nanostructures is crucial to modern electronic devices in terms of
electrical and optical properties. However, it is still unclear whether the growth direction which
affects the polarity of zinc oxide nanorods in hydrothermal processes is Zn-, O- or mix-polar.
Earlier studies suggested it should be Zn-polar based on the thermodynamic calculation. Later,
studies proposed that the nanorods are O-polar, i.e., less stable than Zn-polar, resulting in the
formation of nanotubes by KOH etching. Recently, the possibility of the co-existence of both
Zn- and O-polar has been demonstrated. Therefore, we investigated the polarity issue by
fabricating two types of ZnO nanorods in acidic and alkaline growth conditions. The as-grown
and etched morphologies of these t...[
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The polarity of zinc oxide nanostructures is crucial to modern electronic devices in terms of
electrical and optical properties. However, it is still unclear whether the growth direction which
affects the polarity of zinc oxide nanorods in hydrothermal processes is Zn-, O- or mix-polar.
Earlier studies suggested it should be Zn-polar based on the thermodynamic calculation. Later,
studies proposed that the nanorods are O-polar, i.e., less stable than Zn-polar, resulting in the
formation of nanotubes by KOH etching. Recently, the possibility of the co-existence of both
Zn- and O-polar has been demonstrated. Therefore, we investigated the polarity issue by
fabricating two types of ZnO nanorods in acidic and alkaline growth conditions. The as-grown
and etched morphologies of these two types of nanorods are obviously different. Valence band
x-ray photoemission spectroscopy (VB-XPS) has been employed to determine the polarity. We
found that nanorods from both conditions are Zn-polar. This led us to find out the formation of
nanotubes is determined by the surface energy on the Zn-polar face of heterogeneously grown
nanorods. The surface energy of ZnO nanorods can be controlled by a second acidic chemical
bath, as long as the surface is not annealed. Furthermore, the thermodynamics of the process
was studied to investigate the possible growth mechanism after the confirmation of polarity.
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