在本實驗中，我們成功地利用α-Fe2O3粉末合成具有方向性排列的α-Fe2O3奈米線，同時，我們也在矽基板上進行選擇性成長α-Fe2O3的奈米結構。實驗結果發現，材料的成長情形隨基板組成、溫度、氣體流量、以及相對位置而變化。根據TEM及EELS的分析結果，α-Fe2O3奈米線內部存有軸向排列的長週期氧缺陷結構。我們認為此缺陷結構在材料成長時扮演著協助鐵原子進行內部擴散的角色。此外，磁性質方面，由磁滯曲線我們發現到α-Fe2O3奈米線表現出明顯的晶體異向性。場發射現象上，α-Fe2O3奈米線的場發射遵守F-N行為且其β值在低電場時約為560，在高電場時為1500。
接著，我們利用氫、氬混合氣體將α-Fe2O3奈米線還原成為Fe3O4奈米線，還原的機制主要是藉由改變氧離子沿最密堆積方向的堆積順序來達成。實驗中發現Fe3O4不傾向以奈米線的形式存在，在高溫時材料會崩毀變形。我們推測這應該是由於Fe3O4本身的等向性cubic結構所導致。關於材料的磁性質，Fe3O4奈米線表現出了強烈的形狀異向性。
藉由還原α-Fe2O3奈米線的過程中引入Si或Ge，我們成功地合成了氧化物包覆Fe3O4奈米線的一維核-殼結構。其中包覆層的氧化是根源於內層奈米線還原時所釋放出的氧。
最後，經in-situ TEM的分析，驗證了α-Fe2O3在高溫且缺乏氧氛圍的情況下會還原為Fe3O4。同時，也進ㄧ步肯定了Fe3O4奈米線在高溫時不穩定的事實。

In present study, aligned α-Fe2O3 nanowires were synthesized successfully by using of α-Fe2O3 commercial powder. And 1-D α-Fe2O3 nanostructures were also selectively grown on Si wafer. According to experiment results, composition of substrate, temperature, gas flow, and relative position were the factors could cause various morphologies of α-Fe2O3 nanomaterials. TEM and EELS analysis indicated that there were axial long-range ordered oxygen vacancies inside the nanowire. The defects were considered as the channels for internal diffusion of iron atoms during growth. In addition, significant magnetocrystalline anisotropy was obtained by SQUID measurement. The field-emission of α-Fe2O3 nanowires was following F-N behavior with β value of 560 at low electrical field and of 1500 at high electrical field.

Fe3O4 nanowires were synthesized by reduction of α-Fe2O3 nanowires with gas mixed of H2 and Ar. The reduction mechanism was based on modifying the stacking sequence of oxygen ions along the close packed direction. It was found that Fe3O4 nanowires were unstable at higher temperature, which would owing to the isotropic cubic structure of Fe3O4. About the magnetic properties, Fe3O4 nanowires displayed significant shape anisotropy.

Introducing of gaseous Si or Ge during reduction process, the Fe3O4/oxide core-shell nanowires could be synthesized. And the oxidization of shell was due to the release of oxygen from inner nanowire during reduction.

According to the observation from in-situ TEM, reduction of α-Fe2O3 to Fe3O4 at higher temperature in environment without oxygen was evidenced. Furthermore, the result demonstrated that the Fe3O4 naowires was unstable at high temperature.

Chapter 1
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