二維（2D）材料因其獨特的性質和在電子學中的潛在應用而成為納米材料科學家們關注的焦點。二維材料的有趣表面和電子特性已被廣泛研究並應用於各種器件。過渡金屬二硫化物 材料（TMD）最近在二維材料中引起了極大的興趣，二維材料由夾在兩個硫屬元素原子之間的過渡金屬原子組成。
我們研究的樣品是高度取向的熱解石墨（HOPG）上的二硫化鉬。來自杜鹤芸博士（NTU）並採用化學氣相沉積（CVD）方法製備。根據以前的研究結果，二硫化鉬中的硫空位有助於增強HER催化活性。在這裡，我們觀察到二硫化鉬具有特徵偏差依賴性的不同類型的結構缺陷。論文中將展示不同層上的微分電導（I / V曲線）的測量。除此之外，我們還採用STM來研究原子影像，二硫化鉬的大面積STM圖像，晶界和其他表徵。

Two-dimensional (2D) materials have become the focus of scientists working on nanomaterials because of its unique properties and potential applications in electronics. The interesting surface and electronic properties of 2D materials have been widely studied and applied to variety of devices. Transition metal dichalcogeniades materials (TMD) currently attract much interest recently in 2D materials which consist of transition-metal atoms sandwiched between two chalcogen atoms.
The sample we studied is Molybdenum disulfide grown on highly oriented pyrolytic graphite (HOPG). It's from Dr.Du He-yun (NTU) and was directly grown on a graphite substrate with chemical vapor deposition (CVD) method. According to previous work, sulfur vacancies in MoS2 contribute significantly to the enhancement of hydrogen evolution reaction (HER) catalytic activity. Here, we observed different types of structural defects with characteristic bias dependences. The measurement of the differential conductance (I/V curves) on different layers of MoS2 will be presented in the thesis. Besides that, we also employed STM to investigate the atomic resolution, large area STM images of MoS2 grain boundaries and other characterization.

1 Introduction 3
2 Theory 5
2.1 Scanning Tunneling Microscopy . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Quantum tunneling . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Scanning Tunneling Spectroscopy . . . . . . . . . . . . . . . . . . . 7
3 Instrument 8
3.1 Chambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2 Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2.1 Rotary pump . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2.2 Turbomolecular pump . . . . . . . . . . . . . . . . . . . . . 11
3.2.3 Ion pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3 Bakeout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.4 Residual Gas Analyzer . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.5 Cooling system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.6 Sample heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4 STM Repair 18
4.1 Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.1.1 Problem description . . . . . . . . . . . . . . . . . . . . . . 19
4.1.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2 Tip holder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.2.1 Problem description . . . . . . . . . . . . . . . . . . . . . . 21
4.2.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.3 Sample holder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.3.1 Problem description . . . . . . . . . . . . . . . . . . . . . . 24
4.3.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.4 Contact Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.4.1 Problem description of sample stage . . . . . . . . . . . . . . 25
4.4.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.4.3 Problem description of tip stage . . . . . . . . . . . . . . . . 26
4.4.4 Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.5 Z-shift control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.5.1 Problem description . . . . . . . . . . . . . . . . . . . . . . 27
4.5.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.6 Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5 Literature Review 31
5.1 Di_erent types of defects on MoS2 surface . . . . . . . . . . . . . . 31
5.2 Point defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6 Experiment Result 40
6.1 Large scans of MoS2 . . . . . . . . . . . . . . . . . . . . . . . . . . 40
6.2 Bias e_ect of large scanning area . . . . . . . . . . . . . . . . . . . 44
6.3 Atomic resolution of MoS2 . . . . . . . . . . . . . . . . . . . . . . . 47
6.4 Variety of defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
6.5 Bias e_ect of defects under di_erent voltages . . . . . . . . . . . . . 55
6.6 Bandgap of di_erent layers of MoS2 . . . . . . . . . . . . . . . . . 56
7 Conclusion 59
Reference 61

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