臺灣博碩士論文加值系統

在本論文中，我們運用過渡金屬硫化法在藍寶石基板上成長出大面積的二維材料如二硫化鉬及二硫化鎢，透過控制過渡金屬的濺鍍時間，我們可以達到對過渡金屬二硫化層數的精準控制，並且使用此法在三個原子層內完成二硫化鎢/二硫化鉬/二硫化鎢雙異質接面的結構。而透過低功率氧電漿的處理，我們除了可增加元件的場效應載子遷移率之外，我們還可運用相同的低功率氧電漿來達成過渡金屬二硫化物之原子層刻蝕 (Atomic layer etching; ALE）。在多層二硫化鉬經過低功率氧電漿處理後，最上層的二硫化鉬會被氧化，由於鉬氧化物與二硫化鉬表面較弱的吸引力將導致鉬氧化物從下層的二硫化鉬脫離，最後，通過蝕刻後的再硫化步驟，殘留在下層被部分氧化的二硫化鉬可以被修復回完整的二硫化鉬薄膜。在原子層蝕刻製程之後，二硫化鉬薄膜的光學和電特性都不會有所影響。通過重複相同的原子層蝕刻製程，可以對二硫化鉬進行逐層蝕刻，最終我們可以藉此技術達成過渡金屬二硫化物異質結構之等效選擇性刻蝕 (Equivalent Selective Etching)。

In this thesis, we have demonstrated that by using the growth technique of sulfurizing pre-deposited transition metals, large-area transition metal disulfides such as MoS2 and WS2 can be grown on sapphire substrates. Good layer number controllability can be achieved for MoS2 down to single layer by controlling the Mo sputtering times. With sequential transition metal deposition and following sulfurization procedures, a WS2/MoS2/WS2 double hetero-structure can be established in 3-layer 2D crystal thickness. By using the low-power oxygen plasma treatment, a significant increase in field-effect mobility in the fabricated MoS2 transistors was observed. By using the same low-power oxygen plasma treatment, atomic layer etching of MoS2 can be achieved. After the low-power oxygen plasma treatment, the topmost MoS2 layer of multi-layer MoS2 film will be fully oxidized. The weaker adhesion of Mo oxides with MoS2 surfaces would lead to the de-attachment of the topmost oxidized MoS2 layer from the underlying MoS2 films. With the re-sulfurization procedure after the etching process, the partially oxidized MoS2 film remained on the substrate can be recovered back to a complete MoS2 film. Both optical and electrical characteristics of the MoS2 films can be maintained after the ALE procedure. By repeating the same ALE procedures, the equivalent selective etching of TMD hetero-structures is demonstrated.

致謝......I
摘要......II
Abstract......III
Table of contents......IV
List of Figures......VII
List of Tables......XV
Chapter 1. Introduction......1
1.1. Crystal structure and properties of molybdenum disulfide......6
1.2. The Raman spectrum of molybdenum disulfide......6
1.3. The PL spectrum of molybdenum disulfide......10
1.4. Preparation of molybdenum disulfide......14
1.4.1. The Mechanical Exfoliation......16
1.4.2. The Chemical Vapor Deposition......16
1.5. The Thesis Organization......18
Chapter 2. Experimental Instruments......22
2.1. The procedure and systems for 2D material growth......22
2.1.1. The growth of molybdenum disulfide......22
2.1.2. The substrate pretreatment......23
2.1.3. The deposition of molybdenum film......23
2.1.4. The sulfurization of the molybdenum film......26
2.2. The material characterization systems for the 2D materials......29
2.2.1. The Raman measurement system......29
2.2.2. The photoluminescence measurement system......31
2.2.3. X-ray photoelectron spectrometer (XPS)......32
2.2.4. Ultraviolet photoelectron spectroscopy (UPS)......32
2.2.5. Transmission Electron Microscope (TEM)......35
2.2.6. Atomic Force Microscope (AFM)......36
2.3. The instruments for device processing......39
2.3.1. The Reactive-Ion Etching (RIE) System......39
2.3.2. The Atomic Layer Deposition (ALD) System......39
2.3.3. The oxygen plasma etching system......44
Chapter 3. The Preparation of Large-area Transition Metal Dichalcogenides for Device Applications......46
3.1. Layer number control of MoS2 through the pre-deposited Mo film thicknesses......46
3.1.1. The Raman measurements of MoS2 films with different sputtering times......46
3.1.2. The PL measurements of MoS2 films with different sputtering times......51
3.1.3. The cross-sectional high-resolution transmission electron microscopy images of MoS2 films with different sputtering times......53
3.1.4. The Raman peak difference and the actual MoS2 layer numbers......56
3.2. Multi-layer MoS2 transistors and the layer number controllability of transition metal disulfides......58
3.2.1. The characterizations of MoS2 films......58
3.2.2. The fabrication of MoS2 transistors......64
3.2.3. Double WS2/MoS2/WS2 hetero-structures......67
3.3. Summary......69
Chapter 4. The Application of Oxygen Plasma for 2D Material Devices......73
4.1. Enhancing the mobility of bottom-gate MoS2 transistors by using the oxygen plasma treatment......73
4.1.1. The preparation of the multi-layer MoS2 and the device fabrication procedure......73
4.1.2. The device performances of the MoS2 transistors......77
4.1.3. The effect of oxygen plasma treatment of the MoS2 transistors......84
4.2. The Atomic layer etching of transition metal disulfides by using the low-power oxygen plasma treatment......87
4.2.1. The background of the MoS2 atomic layer etching......87
4.2.2. The atomic layer etching of MoS2 by using the low-power oxygen plasma treatment......88
4.2.3. The mechanisms of MoS2 atomic layer etching by using the low-power oxygen plasma treatment......97
4.2.4. The equivalent selective etching of WS2/MoS2 hetero-structures......102
4.3. Summary......111
Chapter 5. Conclusion......114
References......116
Publication List......122
Journal Articles......122
Conference Papers......123
Future Work......124

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