Abstract
AbstractThis thesis is mainly focused on the various oxygen vacancies density in the Fe2O3 nanowires and related measurements at magnetic and field-emission behaviors where the Fe2O3 nanowires are synthesized from Fe-Ni alloy substrate via tip-growth mechanism in three zone furnace.The Fe2O3 nanowires are grown at different temperatures of 350, 400, 500, 550, and 600 ℃, respectively. Subsequently, all the nanowires are examined by TEM in order to systematically discuss the oxygen vacancies inside the Fe2O3 nanowires. The long rang ordering phenomenon can be found inside the Fe2O3 nanowires at growth temperature above 450 to 600 ℃ whose periodic length is ten time of (3,-3,0) plane by investigated the high resolution TEM in detail whereas the periodic length is decreased from ten to six times of (3,-3,0) planes as the growth temperature is decreased to 400 ℃, indicating that the density of oxygen ordering inside the Fe2O3 is increased. However, this ordering phenomenon will disappear when the growth temperature is below 350 ℃.On the other hand, we expect that the finding at ordering phenomenon inside the Fe2O3 is caused by oxygen vacancies owing to two factors. Fist, the iron cations can be enforced to diffuse from alloy substrate to react with oxygen atom by surface and internal diffusion during the growth of Fe2O3 nanowries in which the whole growth are suffered an oxygen deficient ambient. Second, the formation of energy for oxygen vacancies is smaller than that of the iron vacancies. In addition, it is found that the density of oxygen vacancies is increased as the synthesized temperature is decreased, which is proved by measurements of energy dispersive spectrum (EDS) and electron energy loss spectrometry (EELS). The similar results regarding the oxygen vacancies are found in Al2O3 (Corundum) materials where the five kinds of oxygen vacancies migration mechanisms are proposed. As the result, by comparing with the five kinds of oxygen vacancies migration mechanisms inside the Al2O3 and atomic simulation, the oxygen vacancies is suggested to be easily existed at the coordinated corner of octahedron, which is consistent with results found at the high resolution TEM as well.Besides, it is of interesting that the different oxygen deficiencies inside the Fe2O3 nanowres caused by different synthesized temperature may influence the magnetic properties. Herein, the magnetic properties are investigated at measurements of field-cooling and zero field-cooling, namely, magnetization as the function of the different temperature without and with magnetic field, for two kinds of deficiencies inside the Fe2O3 nanowires synthesized at temperature of 350, 500 and 600 ℃, respectively. For the field-emission properties, current density as the function of the different applied voltage at the different synthesized temperatures and different measured distance between surface of nanowires and anode are measured and discussed systematically.