RESUMO
We report the melting behaviours of ZnO nanowire by heating ZnO-Al(2)O(3) core-shell heterostructures to form Al(2)O(3) nanotubes in an in situ ultrahigh vacuum transmission electron microscope (UHV-TEM). When the ZnO-Al(2)O(3) core-shell nanowire heterostructures were annealed at 600 °C under electron irradiation, the amorphous Al(2)O(3) shell became single crystalline and then the ZnO core melted. The average vanishing rate of the ZnO core was measured to be 4.2 nm s(-1). The thickness of the Al(2)O(3) nanotubes can be precisely controlled by the deposition process. Additionally, the inner geometry of nanotubes can be defined by the initial ZnO core. The result shows a promising method to obtain the biocompatible Al(2)O(3) nanotubes, which may be applied in drug delivery, biochemistry and resistive switching random access memory (ReRAM).
RESUMO
In this article, ZnO nanostructures were synthesized via the hydrothermal method which used ZnCl(2) and HMTA mixed solution as the precursor. A multistep growth was adopted to improve the growth restriction of a closed system, not only the length but also the aspect ratio were increased with steps of growth, and the shape of nanorods maintained integrity. Furthermore, photoluminescence spectra which have the near-band-edge-emission (â¼3.37 eV) and defect-related emission show the optical properties of ZnO nanostructures. The defect-related emission intensity was greatly enhanced with the increasing surface area of ZnO nanowires. The level of the OH group was attributed to the yellow-light emission (â¼580 nm) and the red-shift phenomenon. In addition, we fabricated two types of ultraviolet photodetectors: a single nanowire device and a nanowire-array device, operating at a low bias (less than 5 mV). With the lower energy consumption and the weaker persistent photoconductive effect, our ultraviolet photodetectors have better performance, exhibiting a short response time and higher sensitivity.