| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 93 === Abstract
The growth and optical properties of In-doped ZnO nanodisks grown via carbothermal reduction of ZnO/In2O3 powders at a temperature of 900-1000℃ in flowing Ar as functions of cooling rate, oxygen partical pressure into the Ar flow, and carbon concentration in the (ZnO,In2O3)/carbon powders were studied. The hexagonal ZnO nanodisks enclosed by {10-10} facets and twelve-sided ones enclosed by {10-10} and {11-20} facets were grown at a temperature of 900-970℃. At 1000℃ only hexagonal nanodisks were formed. The growth temperature and In doping act as important roles in determining the morphology of ZnO nanostructures. For ZnO nanodisks grown in Ar and then subjected to air cooling green emission was enhanced due to the oxygen vacancies and defects induced by In doping. Furnace cooling allowed the equilibrium concentration of oxygen vacancies at room temperature to be readily reached, resulting in the decrease of oxygen vacancies in the ZnO nanodisks as compared with the air-cooled samples, and thus increased the ultra-violet (UV)/green emission ratio. However, the intensity of UV emission was concurrently decreased because of the formation of amorphous zinc oxides in the samples. Upon growth and subsequent furnace cooling in the Ar/O2 flow with the O2 concentration in the range of 0.5-10% the UV intensity and UV/green ratio were significantly increased. The reasons can be attributed to the decrease of oxygen vacancies, the larger grain size, and enhanced growth of ZnO nanodisks. With the O2 concentration above 25% no ZnO nanodisks were grown. The UV/green ratio first increased with the O2 concentration in the range of 0.5-1% and then decreased in the range of 2-10%. The introduction of O2 in the Ar flow during growth can decrease the oxygen vacancies in the ZnO nanodisks; however, higher O2 concentration can induce the formation of zinc vacancies and thus enhance green emission. Higher carbon concentration in the (ZnO,In2O3)/carbon powders decreased the UV/green ratio of ZnO nanodisks because of the reduction of grain size and the formation of more CO2.
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