Preparation And Research Of Optical Properties Of ZnO Nanostructures

Nanoscale scientific technology is an emerging research area with interdisciplinary and cutting-edge characteristic, at present, the contents of its theory and experiment cover not only many basic subjects, such as chemistry and physics, but also about engineering subjects and medical subjects which are relating to human life closely. At room temperature, the band gap and exciton binding energy of zinc oxide (ZnO) are 3.37eV and 60meV respectively, ZnO is a kind of direct band-gap semiconductor material with piezoelectric, thermoelectric and optoelectronic properties. Study confirmed that ZnO nano-materials have a broad space for development in optical devices, electrical devices, sensors, and so on.The preparations of ZnO nano-materials have been widely reported, we mainly used thermal evaporation and chemical vapor deposition, and MBE method, two methods. Among them, the thermal evaporation and chemical vapor deposition method is a kind of vapor deposition method, which is widely used in the preparation of nanostructures; MBE method is a high-cleaning degree, precisely controlled vapor deposition method. This paper introduces the preparation method, optical properties and the growth mechanism of ZnO nanostructures prepared by the above two methods. The main research results are concluded as follows:1. Bat-like ZnO nanostructures were synthesized on silicon substrate by thermal evaporation of zinc powders in a near ambient atmosphere. The SEM results show that each nanobat is composed of a hexagonal head, a continuous neck and a thin handle. The diameters of the heads are 1-2 micrometers,100-300 nanometers of the handles, and the lengths are several micrometers. The SAED and HRTEM results show that the ZnO nanobat grows along [0001] c-axis direction. The room-temperature PL result illustrates that the ZnO nanowires have a strong emission peak at 383nm near ultraviolet. The peak occurs on account of a wide band-gap edge emission resulted from exciton recombination processes, belonging to the intrinsic emission peak. This illustrates the ZnO sample has few defects, with good crystal quality and optical properties. Through HRTEM analysis, we propose three growth sections of a nanobat:dynamic control section, metastable section and thermodynamic equilibrium section, which can interpret the formation of the ZnO nanobats reasonably. Regarding to the multi-branch junction, it is proposed that the growth process of branch-structure can be summarized into polyhedron nucleation and radical growth.2. In terms of vapor-liquid-solid (VLS) growth mechanism, in the oxygen plasma-assisted molecular beam epitaxy (PA-MBE) system, ZnO thin films and nanowires were achieved on Si (111) substrates coated with lnm Zn and Au catalysts respectively. Through FE-SEM observation, the density and particle size of ZnO thin films are closely related to temperature and growth time; ZnO nanowires were grown on the substrare orderly, neatly and densely, with a diameter of about 30nm, and a length of about 140nm. The XRD patterns indicate that the ZnO thin films and nanowires possess high crystallinity and grow along [0001] c-axis direction. This paper explains the VLS growth mechanism and the growth process of ZnO thin films and nanowires reasonably.