臺灣博碩士論文加值系統

二維材料中由石墨烯、六方氮化硼和過渡金屬二硫族化物等組成的異質結構，開啟了新穎材料科學領域，此類以凡得瓦力組合而成的材料，可藉由更換組成分子或控制堆疊結構，進而調製其電子及光學特性。層狀二硒化鈀(PdSe2)是過渡金屬二硫族化物的新興材料，其能隙會隨層數調變，具有高度可變之特性。本論文將討論以化學氣相沉積法成長的層狀二硒化鈀，如何透過偏振拉曼光譜和二次諧波，來識別層狀二硒化鈀的層數和晶體異向性。由於層狀二硒化鈀的層間具有強交互作用，在低頻拉曼光譜中強度與位置皆與層數呈正相關，可以透過校正過的線性鏈模型來描述。層數可以通過二次諧波成像進一步確認，其可於非中心對稱結構的偶數層二硒化鈀晶體中觀察到較強二次諧波信號。偏振拉曼和二次諧波測量還揭示了異向性，且與穿透式電子顯微鏡呈現的晶軸一致。另外在垂直堆疊的二硫化鎢/二硫化鉬(WS2/MoS2)雙層異質結構，其電子與光學性質亦與層間堆疊方式相關，我們使用低頻拉曼光譜分析垂直堆疊之雙層二硫化鎢/二硫化鉬異質結構的堆疊方式，通過分析層間剪切(shear)和呼吸(breathing)拉曼振動模式，嘗試辨別層間扭角0度和60度時的堆疊配置。

Vertically stacked heterostructures made of atomically thin two-dimensional (2D) layered materials, such as graphene, boron nitride, and transition metal dichalcogenides (TMDs), have recently attracted much attention due to their versatility in creating functional artificial materials. Replacing the constituent materials and controlling the structure pave the way for future designing of heterostructure devices. 2D PdSe2 crystal is a member of 2D TMDs, featuring a unique puckered pentagonal structure with in-plane anisotropy, and is theoretically predicted to exhibit a widely tunable bandgap. In this thesis, we demonstrate that the layer number and crystal anisotropy of 2D PdSe2 can be identified by polarization-resolved Raman spectroscopy and second harmonic generation (SHG). The strong interlayer interaction in 2D PdSe2 is revealed by measuring the interlayer breathing mode in low-frequency Raman spectroscopy, which can be well predicted by the conventional linear chain model corrected by the minor interlayer restoring forces. The layer number is further confirmed by SHG, where a strong SHG signal can be observed in the even-layer PdSe2 non-centrosymmetric, and a nearly vanished SHG in odd-layer PdSe2. Polarization-resolved Raman and SHG measurements also reveal in-plane anisotropy, which is consistent with the crystallographic axes determined by transmission electron microscopy. On the other hand, we also demonstrate that the low-frequency Raman spectroscopy can be used to identify the stacking configuration of WS2/MoS2 heterobilayers. WS2/MoS2 heterobilayer formed by vertical CVD grown of WS2 on MoS2. Since its electronic and optical properties strongly depend on the stacking configuration due to the symmetry-dependent interlayer coupling, we found that the stacking configuration of TMD heterobilayers can be characterized by low-frequency (< 60 cm-1) shear and breathing Raman modes, corresponding to in-plane and out-of-plane layer vibrations, respectively.

摘要 i
Abstract ii
誌謝 iii
目錄 iv
圖目錄 vii
第一章 簡介 1
1.1 過渡金屬二硫族化物 1
1.2 研究動機 3
第二章 理論介紹 4
2.1 拉曼光譜學(Raman spectroscopy) 4
2.1.1 拉曼光譜原理 4
2.1.2 層狀二硒化鈀的拉曼選擇定則(Raman selection rule) 6
2.2 二次諧波(Second harmonic generation, SHG) 9
2.2.1 二次諧波原理 9
2.2.2 二階非線性極化率 10
第三章 樣品介紹與實驗架設 16
3.1 樣品結構與製備 16
3.1.1 層狀二硒化鈀 16
3.1.2 垂直堆疊二硫化鎢/二硫化鉬異質結構 17
3.2 拉曼光譜顯微系統(Raman spectroscopy) 19
3.2.1 高頻拉曼系統 19
3.2.2 低頻拉曼系統 19
3.3 二次諧波系統(Second harmonic generation, SHG) 21
3.3.1 二次諧波顯微系統 21
3.3.2 二次諧波角度解析系統 21
第四章 實驗結果與討論 23
4.1 同質堆疊層狀二硒化鈀的光學性質 23
4.1.1 高頻拉曼光譜分析 23
4.1.2 低頻拉曼光譜分析 25
4.1.3 方位角解析之二次諧波量測分析(Azimuthal angle dependent SHG) 28
4.1.4 角度解析之二次諧波量測分析 (Angle-resolved SHG) 30
4.2 垂直堆疊二硫化鎢/二硫化鉬異質結構的光學性質 31
4.2.1 低頻拉曼光譜分析 31
4.2.2 角度解析二次諧波量測分析 (Angle-resolved SHG) 33
第五章 結論 34
參考文獻 35
附錄一 二硒化鈀之DFT理論計算 38
附錄二 偶數層二硒化鈀之二次諧波極化圖 39
附件三 低頻拉曼光譜截止波長的不對稱問題 40

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