ZnO nanorod arrays were synthesized by hydrothermal method under different growth times. The effect of growth time on nanorods morphology was investigated systematically. Results illustrate that ZnO nanorods with hexagonal wurtzite structure grow vertically on the Si substrates. The length of the ZnO nanorods increases with increasing growth time. In our experiments, quenching stage plays a key role in forming the tips of nanorods. With growth time no more than 1h, the solution is in a continuous heating state and doesn’t reach the set temperature 180oC. Therefore, longer growth time means higher solution temperature which in turn increases cooling rate during quenching stage, as a consequence, to a smaller mean crystal size in the nanorods tips.
In this work, we study the field emission properties of a single vertical carbon nanotube with cathode radius changing. The carbon nanotube is considered as purely perfect conductor, and the anode and cathode are modeled as discs. The radius of anode is kept as 24m, then the radius of cathode is changed from 24 m to 1 m. The emitter of that CNT consists of a hemispherical cap of 4 nm radius (r) on top of a cylinder height of 2 m (h). The distance from anode to cathode is w=h+20m. The overall surface area of the CNT and cathode are all grounded, and the anode plate has a constant potential value of 100 V. The distribution of potential and electric field, field emission current are obtained by simulating with the help of COMSOL Multiphysics 4.3b electrostatics module. We find that with cathode radius decrease, the electric field strength over the surface of carbon nanotube (CNT) strengthening and field emission current increase.
The ZnO nanorods with sharp tip have been fabricated via water cooling treatment during the hydrothermal growth. The morphology and crystal structure of the zinc oxide nanostructure were examined by field-emission scanning electron microscopy and x-ray diffraction, respectively. The structural characterizations revealed that the as-synthesized nanorods were single crystalline, with a hexagonal phase. It has been demonstrated that the cooling rate is the critical factor of the synthesis of the sharp tip ZnO nanorods by comparing the different cooling conditions. The growth mechanism for the sharp tip ZnO nanorods has been proposed on the basis of the different crystallographic habits of wurtzite hexagonal ZnO crystals.
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