The Synthesis And Application Of Different ZnO Nanostructures With Macroscale In Appearance

ZnO is an important wide band semiconductor with a band gap of 3.37 eV and exciton binding energy of 60 meV at room temperature,which makes it a promising material for electronic and optical devices.ZnO nanostructures have some different properties that are different from the bulk materials in physics and chemistry,so the research on it becomes one of the most important works.As inspired by macroscopical long Carbon Nanotube,we introduce the synthesis and characterization of different ZnO nanostructures with macroscale in appearance in this article.At the same time,the application of them in optics,sensor and laser has also been studied. Main concludes and results are as follows:1.ZnO nanostructures with macroscale in shape have been synthesized via conventional thermal evaporation method with metal catalyst.This method provides simple route for the preparation of ZnO macroscopical nanostructure,which has low cost and good reproducibility.Except ultra-long ZnO nanocombs,the ultra-long nanorods and nanobelts with diameters and thicknesses are only several hundreds nanometers were synthesized for the first time,but their lengthes are several millimeters,even centimeters.At same time,the fractal ZnO nanostructures with macroscopical shape,viz.,ZnO dendrites and feathers,have also been synthesized, which are composed of well-oriented nanorods with diameters of several hundreds nanometers and possess high surface-to-volume ratio.To the best of our knowledge, these unique fractal structures of ZnO have never been reported.These as-grown ZnO nanostructures possess macroscopical shape and properties of nanomaterials,hence, they are fabricated facilely in conventional way under macroscopical condition avoiding from complex microfabrication technologies,such as fabrication by atomic force microscope(AFM)and scanning electron microscopy(SEM),and then applied in optoelectronic devices.Moreover,we used Energy dispersive x-ray spectroscopy (EDXS),scanning electron microscopy(SEM),and transmission electron microscopy (TEM)respectively to investigate the morphology,crystal structure and composition of the as-grown products,and studied formation mechanism of the products.We found that Cu and CuO as catalyst plays an important role in the evolution from ZnO nanostructures to macroscale in shape. 2.As inspired by fractal ZnO nanostructures with macroscopical shape(dendrites and feathers)possessing high surface-to-volume ratio,we fabricated new gas and humidity sensor based on a single dendrite and feather.The sensing characteristics of the gas sensor were carefully studied in various gases,i.e.NH₃,H₂,H₂S,and NO₂. We found that the ZnO dendrite-based gas sensor has high sensitivity to H₂S gas and large change of its resistance.Then we describe theoretically the origin of the high sensitivity.Moreover,we found that theâ… -â…¤curve of the ZnO feather-based humidity sensor exhibits good linear behavior in any RH atmosphere.But the sensitivities of the humidity sensor are slightly fluctuated at high humidity.Finally,we give some discussions about the phenomena of the sensitivity of the nonlinear behavior at high humidity.3.As inspired by the formation of Schottky contact due to Fermi surface alignment between the metals and ZnO,we successfully fabricated ZnO-based Schottky barrier diodes(SBDs)using Ag metal and ultra-long ZnO nanorods with large-size diameters.This new processing technique for SBDs solves the problem that nanobelts or nanowires with large-size widths or diameters could result in the poor contacts on both electrodes.The resulting current-voltage(â… -â…¤)characteristics of the SBD exhibit a good rectifying behavior.In addition,the detailedâ… -â…¤characteristics have been investigated in different temperature and in NH₃ gas environment.It can be found that the SBDs have good thermal stability and high sensitivity to NH₃ gas.In finally,we give some discussions about the rectifying mechanism of ZnO SBDs.4.Based on the unique optical and electrical properties,we fabricated a new ZnO laser based on a single ultra-long nanobelts.After hydrogen plasma treating the ZnO nanobelt,surface-emitting lasing action from the nanobelt was observed for the first time under electrical excitation.Though the laser has already been achieved in ZnO powders and ZnO heterojunctions by electrical excitation,to the best of our knowledge,the laser has not been reported in single-crystal n-type ZnO nanostructures after hydrogen plasma treatment.It can be measured that the lasing emission spectrum is dominated by emission band in the ultraviolet and blue region. This phenomenon of the ultraviolet emission may be attributed to random lasing with coherent feedback.It is worthwhile to mention that three sharp peaks emerge particularly in the blue region of the emission spectra,and the three independent peaks show some regularity.We also found that the surface-emitting lasing action can be observed twice even many times from the ZnO laser in the hydrogen gas ambience. We simply analyse the lasing mechanism of the ZnO laser,and then believe that hydrogen play an important role in the appearance of such remarkable blue lasing action from the nanobelt.