Abstract
One dimensional ZnO nanostructures prepared by favorable and simple solution growth methods are at the forefront of this research. Vertically oriented ZnO nanorods with uniform physical properties require high-quality seed layers with a narrow size distribution of the crystallites, strong c-axis orientation, and low surface roughness and porosity. It has been shown that high quality seed layers can be prepared by the sol–gel process. The sol–gel process involves three essential steps: preparation of the sol, its deposition by dip coating, and thermal treatment comprising preheating and annealing. We put emphasis on the investigation of the heat treatment on the properties of the seed layers and on the vertical alignment of the nanorods. It was demonstrated that for the vertical alignment of the nanorods, the preheating step is crucial and that the temperatures reported in the literature have been too low. With higher preheating temperatures, conditions for the vertical alignment of the nanorods were achieved in both investigated annealing atmospheres in air and in argon.
Highlights
Zinc oxide, in the form of nanostructures, has been studied enormously for its advantageous properties such as a direct wide band-gap, high exciton binding energy (60 meV), high electron mobility, and high piezoelectric constants [1]
We investigated the effect of the heat treatment on the properties of the ZnO seed layers prepared by the sol–gel process and on the vertical alignment of the ZnO nanorods grown by chemical bath deposition
It was further demonstrated that for the most frequently used chemical solutions, the preheating temperature should be higher than the typically reported values below 300 ◦ C, because the low preheating temperature is insufficient to decompose all of the organic by-products of the deposited xerogel
Summary
In the form of nanostructures, has been studied enormously for its advantageous properties such as a direct wide band-gap (band-gap energy 3.37 eV), high exciton binding energy (60 meV), high electron mobility, and high piezoelectric constants [1]. These properties open space for a broad range of applications including UV photodetectors and light-emitting devices, piezoelectric nanogenerators, solar cells, and chemical sensors [2]. Zinc oxide typically crystalizes in the most thermodynamically stable wurtzite structure in a hexagonal crystal system that exhibits asymmetry, which is caused by the absence of a center of inversion along the c-direction [3].
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