Gas-phase Synthesis And Characterization Of ZnO Nanostructures

As a new direct wide-bandgap semiconductor material, ZnO have similar bandgap and latticeconstant with GaN, attracting more and more attention. ZnO is a good photoelectrictransformation material, as well as the only material which have both piezoelectric andsemiconducting properties. ZnO has wide development space in terms of micro- and nano-electronic devices. It has wide application value at many areas, such as ultraviolet laser,photoelectric detector, capacitor, solar battery, gas sensor, field emission display and so on.Researchers have synthesized ZnO nanostructures with various shapes, such as nanowires,nanobelts, nanorods, nanorings, nanobelts, and tetrapod nanostructures, all of them can beensynthesized at 700℃-1400℃. Several approaches have been developed for the synthesis of ZnOnanostructures, including gas reaction method, solid state reaction method, sol-gel-templatemethod, hydrothermal method and pulsed laser deposition (PLD). Nonetheless, the experimentalconditions of the ZnO nanostructure cannot be controlled, and the morphology and properties ofthe products are uncertain. Also, the growth mechanism has not been understood in deep.Therefore, it’s still an important task for researchers to study the fabrication of ZnOnanostructures in long time.This paper reviews the nature of ZnO, fabrication methods, and testing methods. The Zn filmwas deposited on Si (111) by laser molecular beam epitaxy(LMBE). ZnO nanostructures withdifferent shapes have been synthesized by thermal evaporation process and carbon thermalreduction deposition process on Zn film which provided sites and catalyst for the growth ofnanosructures. The morphologies, crystalline qualities, composition and optical characteristics ofZnO nanostructures were investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM),transmission electron microscopy (TEM), high-resolution transmission electronmicroscopy (HRTEM) and photoluminescence (PL), respectively. The details are as follows:1. The Zn film was deposited on Si (111) by laser molecular beam epitaxy. ZnO whiskerswith different shapes have been synthesized on Zn film under different flow rates of O2, growthtemperatures and growth times by simple thermal evaporation.2. The morphology of the as-synthesized ZnO whiskers were characterized by scanningelectron microscopy (SEM), transmission electron microscopy (TEM) and high-resolutiontransmission electron microscopy (HRTEM). The crystalline qualities and composition wereinvestigated by X-ray diffraction (XRD), electron dispersive spectrum (EDS), and Fouriertransform infrared spectrum (FTIR). For the optical property, the measurement of PL spectrum was performed with a Xe lamp as the excitation source (wavelength was 280 nm) at roomtemperature. We conclude that the green emission would be a result of the existence of theoxygen vacancies in the ZnO nanostructures. According to the results, we have discussed thegrowth mechanism of ZnO whiskers which grew under different experimental conditions. Theeffect of each growth factor has been analyzed.3. The Zn film was deposited on Si (111) by laser molecular beam epitaxy. ZnO nanoparticlesand ZnO nanorods have been successfully fabricated on Si (111) substrates and substrates withzinc film respectively via a carbon thermal reduction deposition process.4. The morphology, crystalline qualities and composition of ZnO nanorods were investigatedby scanning electron microscopy(SEM), transmission electron microscopy (TEM),high-resolution transmission electron microscopy (HRTEM), X-ray diffraction(XRD), and X-rayphotoelectron spectroscopy (XPS), respectively. Results show that Zn atoms in the Zn film havebeen oxidized totally, confirming that the as-prepared nanorods were ZnO with hexagonalwurtzite structure. The growth mechanism was discussed in brief.