Abstract
In this work, we have modified the experimental setup for a vapor-solid (VS) process to synthesize Zinc oxide (ZnO) microtubes (MTs) with lengths up to 3 mm during a 90-min growth period. The critical idea behind this modification is to control the distribution of Zn vapor along the Si substrates. The morphology evolution of ZnO structures with the increasing reaction time was particularly explored. We found that, within the 90-min growth period, four different types of ZnO microstructures appeared in this synthesis process: microrods (MRs), short MTs, two-tier structures, and long MTs. Growth mechanisms were proposed to interpret the formation of these structures.
Highlights
Zinc oxide (ZnO), one of the most important functional materials, has attracted wide attention because of its unique semiconducting, piezoelectric, and optoelectronic properties, which have promising applications in electronics [1], optoelectronics [2], photodetectors [3,4], power generators [5] and microfluidic devices [6], to name a few
ZnO seeds appeared on the Si substrates from around 900 °C
The production of MR in the first step and the emergence of MWs in the third step are both induced by the situation that Zn vapors around the sidewalls of ZnO structures are less than, or just comparable to, those on the top surfaces of these structures, while the formation of the MTs in the second step and the merging of MWs in the fourth step are caused by much higher Zn concentrations around the sidewalls of ZnO structures in comparison with those on the tops of these structures
Summary
Zinc oxide (ZnO), one of the most important functional materials, has attracted wide attention because of its unique semiconducting, piezoelectric, and optoelectronic properties, which have promising applications in electronics [1], optoelectronics [2], photodetectors [3,4], power generators [5] and microfluidic devices [6], to name a few. Solution-phase methods have been widely proposed and employed to construct precise morphology due to their low growth temperatures and good potential for scale-up. Due to their low growth rates (because of low synthesis temperatures), long ZnO microstructures are difficult to achieve using these approaches [23,24,25]. The vapor-phase approaches are often applied to grow long ZnO microstructures, which are employed in this work. To circumvent the limitations of the existing methods in synthesizing long ZnO MTs, we have developed a modified vapor-phase setup in this work
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