三氧化二鐵奈米線之氧缺陷濃度及其特性研究

Characterization of Iron Oxide Nanowires with Oxygen Vacancies Tuning

梁家綺(Jia-Qi Liang)

指導教授 ： 周立人

國立清華大學/工學院/材料科學工程學系/碩士(2006年)

https://doi.org/10.6843/NTHU.2006.00615

摘要

摘要
在本實驗中，我們利用三區爐管藉由尖端成長機制在鐵鎳合金上成長三氧化二鐵之奈米線，主要研究不同溫度成長之三氧化二鐵奈米線氧缺陷的變化及其相關性質分析。
我們分別在350℃、400℃、450℃、500℃、550℃及 600℃成長三氧化二鐵奈米線。經由穿透式電子顯微鏡的分析，研究其三氧化二鐵結構中氧缺陷，我們發現在450℃以上至600℃成長之奈米線會存在長程序化的缺陷，其週期為10層(3-30)的平面。而當成長溫度降至400℃時，奈米線中長程序化的缺陷週期降到6層，有缺陷濃度增加的趨勢。不過當溫度低於350℃時，此現象會傾向消失。
在成長三氧化二鐵奈米線的過程中，因為處於稀少氧的氣氛下，且鐵是從基板藉由表面擴散與內部擴散至頂端與氛圍中的氧結合，再加上在三氧化二鐵中形成氧缺陷的能量會低於鐵缺陷，因此我們推斷三氧化二鐵中的長程序化缺陷為氧缺陷所構成，且氧缺陷含量會隨成長溫度變低而增加，此推斷可藉由EDS與EELS分析證明。此外，經由五種氧缺陷在金剛砂結構中擴散機制比較，我們推測氧缺陷容易存在於八偶體的邊界，再以此推測進行模擬，結果與HETEM影像一致。
此外，比較有趣的是三氧化二鐵的磁性質會不會受到養缺陷含量的影響，因此我們分別對350℃、500℃與600℃成長之三氧化二鐵奈米線，做加場冷卻與不加場冷卻之磁化量與溫度之關係研究。場發射性質方面，我們量測不同成長溫度之試片與不同量測距離對三氧化二鐵奈米線之場發射性質影響。

關鍵字

三氧化二鐵 ； 氧缺陷 ； 氧化鐵

並列摘要

Abstract
This 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.

並列關鍵字

Fe2O3 ； oxygen vacacies ； Iron oxide

參考文獻

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