本研究中，我們針對過渡性金屬氧化物奈米線進行了一系列的電性量測與結果探討，包含了氧化鎢（WO3）奈米線與氧化鐵（α-Fe2O3和Fe3O4）奈米線。首先藉由兩點探針的方法來求得奈米線的電壓-電流特性，但是從量測的結果發現，由於接觸電阻的影響，兩點探針的量測方式並不能真正求得奈米線本身的電阻值。通常而言，量測所得的電阻值不只是包括奈米線本身的阻值，也包括了金屬電極與奈米線接觸部分的阻值。為了避免接觸阻值的影響，我們利用四點量測的方式經由計算來求得奈米線本身真正的阻值。除此以外，由於我們利用有機溶劑將奈米線轉移到量測用的晶片上，所以表面會有殘留物引發漏電流的現象導致元件無法導通。
由於它們都屬於半導體材料，因此它們的場效特性是相當令人期待的。對於氧化鎢（WO3）奈米線的電性量測中，在閘極電壓的施加下（從-20伏特到+20伏特），並沒有出現任何的場效特性。而且在低溫（T = 4K）的量測下，計算出來的活化能大約為0.02電子伏特。我們推測是由於氧化鎢奈米線本身具有相當大的能隙，在電性表現上比較接近本質半導體的行為。
至於氧化鐵（α-Fe2O3）奈米線的部分，我們利用四點探針的方法求得奈米線本身真正的阻值。藉由施加不同的閘極電壓，可以量測到氧化鐵奈米線具有p型和n型半導體的特性。我們推測可能是由於在不同的氣氛底下成長，以及內部氧缺陷濃度不同導致這種現象的產生。
而在另外一種氧化鐵（Fe3O4）奈米線量測的部分，施加不同的閘極電壓（從-20伏特到+20伏特），並沒有出現任何的場效特性。而在低溫（T = 4K）的量測下，可以計算出活化能大約為0.214電子伏特。此值大於Fe3O4與MgO的同軸結構（0.1電子伏特），推測是由於使用的金屬電極不同所導致的結果。而且從阻值與溫度的關係曲線中，我們可以在122K處發現所謂的Verwey溫度。

In this study, a series of electrical property measurements and discussions about metal oxide nanowires were carried out, including tungsten oxide (WO3) and iron oxide (α-Fe2O3 and Fe3O4) nanowires. There was a large discrepancy in the two-probe measured resistance from various two-probe devices. In general, a total measured resistance containing both of the contact resistance and the wire resistance were obtained by the two-probe measurement technique. In order to avoid the influence of contact resistance, the four-probe measurement technique was utilized to get the real resistance of α-Fe2O3 nanowire. In addition, due to the solution dispersing method utilized for transferring nanowires onto the chips, there were residual solvent contaminants on the chips to induce leakage current even the devices not work.
Due to the semiconducting behavior of tungsten oxide and iron oxide nanowires, their field effect characteristics are interesting. In the measurement of tungsten oxide nanowires, there was no field effect when applying high gate voltage from +20 volt to -20 volt. In addition, by measuring at lower temperature (T~4K), the activation energy can be calculated as 0.02 eV caused by the high bandgap and more intrinsic transport property of the WO3 nanowires.
In the case of α-Fe2O3 nanowires, the four-probe measurement technique was utilized to get the real resistance in nature. In addition, the p-type behavior for semiconductor was first measured, and then the n-type character for semiconductor was measured. The appearance of different atmosphere and the existence of oxygen vacancy are explained.
In the study of Fe3O4 nanowires, the field-effect can’t be found from the Fe3O4 nanowires even through the gate voltage is increased to ±20 volt and the source-drain bias is also increased to ±2 V, the I-V characteristic almost remains unchanged. Moreover, by measuring at lower temperature (T~4K), the activation energy can be calculated as 0.214 eV higher than the value of Fe3O4 core-shell structure (0.1eV). This could be explained by the different work functions between metal electrodes we chose and nanowires. From the curve of resistance versus temperature, the Verwey temperature about 122 K can be found.

Contents I
Acknowledgements III
List of Acronyms and Abbreviations IV
Abstracts VI

Chapter 1 Introduction
1-1 Nanotechnology 01
1-2 Metal Oxide 02
1-3 Tungsten Oxide 03
1-3-1 Tungsten Oxide Nanowire 03
1-3-2 Fabricating of Tungsten Oxide Nanowire 04
1-3-3 Electrical property of Tungsten Oxide
Nanowire 05
1-4 Iron Oxide 05
1-4-1 Iron Oxide Nanowire 07
1-4-2 Fabrication of Iron Oxide Nanowire 08
1-4-3 Electrical property of Iron Oxide
Nanowire 09
1-5 Electrical Property Measurement 13
1-6 Motivation 14
Chapter 2 Experiment Procedures
2-1 Chip cleaning and sample preparation 16
2-2 Locating positions of nanowires 16
2-3 Defining the contact electrodes and side-gate
electrodes 17
2-4 Photoresist spin coating and soft backing 17
2-5 Electron beam lithography 17
2-6 Development 18
2-7 Thermal evaporation 18
2-8 Lift off process 18
2-9 Device evaluation 18
2-10 I-V measurement 19
2-11 Field-effect characteristic measurement 19
Chapter 3 Results and Discussions
Part I Tungsten Oxide Nanowires
3-1 I-V measurement at room temperature 20
3-2 Lower temperature (T = 4K) electronic property 23
Part II Iron Oxide (α-Fe2O3) Nanowires
3-3 Different growth conditions 25
3-4 I-V measurement at room temperature 27
3-5 N- to P- type transition of α-Fe2O3 nanowire 28
3-6 Four-probe measurement technique 30
Part III Iron Oxide (Fe3O4) Nanowires
3-7 I-V measurement at room temperature 32
3-8 Lower temperature (T = 4K) electronic property 32
Chapter 4 Summary and Conclusions 36

Reference 38
Table Captions 50
Figure Captions 51
Tables 56
Figures 58

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