Study On The Fabrication Control And Properties Modulation Of 1-Dimensional ZnO Nanostructures

A tremendous upsurge has seen the studies on the preparation and properties of ZnO 1-dimensional(1-D)nanostructures in recent years.Besides the common virtues addressed on 1-D nanomaterials,ZnO 1-D nanostructures possess many extraordinary, fascinating properties thus have been regarded as one of the most promising inorganic functional nanomaterials.If ZnO 1-D nanostructures are prepared in a controllable way during which the morphology,size,microstructure,composition,orientation(as well as spatial alignment),and properties can be well controlled,it will be ideal for people to investigate the physics in mesoscopic,quantum-confined,low dimensional, polarized systems,and this is also the prerequisite of putting ZnO-based nanodevices in practice.However,despite the remarkable progresses that have been made in the fabrication of ZnO 1-D nanostructures,most of the present preparation methods are still lack of control.Besides,the studies as well as the understandings on how to efficiently tailor the properties of ZnO 1-D nanostructures are still quite limited.In this paper,efforts will be focused on the fabrication control and properties tailoring of ZnO 1-D nanostructures during vapor phase synthesis process.The framework will be arranged in the order of "local control←→overall control","fabrication control properties modulation",and "binary system→ternary system".The main contents and conclusions can be summarized as the following:1.Controlled synthesis and properties of well-aligned ZnO 1D nanoarraysWell-aligned,single-crystalline ZnO nanoprobe arrays with different tip-shapes were controllably fabricated and the radius of curvature at these tips can be less than 2 nm.The as-grown nanoprobes possess good optical and electrical properties which can be tuned readily by simple air-annealing.Perfectly-aligned,single-crystalline ZnO nanorod arrays with excellent c-axial and in-plane alignment were synthesized controllably.It is found that the quality of alignment of these nanoarrays is as good as the single-crystalline c-GaN epi-layer on which the nanoarrays have grown epitaxially,and is better than any other result on ZnO nanoarrays so far.These perfectly-aligned nanoarrays are excellent candidates for low-threshold,room temperature lasing.2.Strong size effect on the luminescence of individual ZnO nanorodsSingle-crystalline,tapered ZnO nanorods with diameter shrinking smoothly and gradually from several hundred nanometers to～20 nm have been grown controllably. Spatially-resolved cathodoluminescence spectra were collected at spots with different diameters on a series of individual nanorods to study 1)the size-dependent surface effect,and 2)size-induced optical band-gap shift within a non-quantum-confinement region.It is found that the deep level(DE)emission of the nanorods is mainly originated from surface-related recombination process instead of internal defects.As the nanorod diameter continuously shrinks,DL emission becomes more and more dominant while the near band edge(NBE)emission is severely suppressed,with the integral intensity ratio(the ratio of DL to NBE emission)increases superlinearly.These observations can be well-described by an improved surface-recombination-layer approximation.It is found that the injection by electron-beam significantly modulates the optical band-gap in the nanorods.As the nanorod diameter continuously reduced,the peak position of NBE emission shifts anomalously and remarkably.This can be understood by consideration of both Burstein-Moss and Band Gap Narrowing effects which have been observed earlier in those heavily-doped semiconductor systems.3.Morphology dependent field-emission from vertically well-aligned ZnO nanoprobe arraysVertically-aligned single-crystalline ZnO nanoprobe arrays with three different tip-shapes,tapered,abruptly sharpened and flat one,were controllably prepared with wafer size uniformity.The field-emission properties of these nanoprobe arrays were investigated comparatively with the stress on how the geometrical factors such as the tip-shape,radius of curvature at the tip and the density of the nanoprobes affect their field-emission performance.It is found that abruptly sharpened nanoprobe possesses the best field-emission property.Discussion is given on how the screening effect and field enhancement is modulated by the emitter's shape,which helps us optimize the performance of the nano-emitter via a novel multi-segment design.4.Controlled fabrication and properties of highly-oriented,hierarchical nanobelt-nanopillar arrays from self-assembled ternary oxide Zn-In-OHighly-oriented,hierarchical 3-D nanoarrays of self-assembled ZnO:In nanobelt -(ZnO)_m-In₂O₃(m=2,3,4,5)superstructured nanopillar were grown successfully and repeatably.The morphology,microstructure,composition and optical property are characterized in details.Efforts are made to trace their formation mechanism on the basis of a series of fabrication control processes.