二硫化鉬屬於層狀半導體中的過渡金屬二硫族化物，可透過層數改變其能隙大小，且層跟層之間屬於凡得瓦力作用，我們可以輕易地透過機械剝離來產生新的可研究的表面，一直以來都是電子元件的熱門材料。
本次實驗我們在超高真空的環境下，利用掃描穿隧顯微鏡觀察天然二硫化鉬塊材的表面型態以及電性在四種情況下的變化，分別是機械剝離前的原始表面、機械剝離後的新鮮表面、機械剝離後曝氧8小時的表面以及機械剝離後置於大氣下7個月的表面。我們將二硫化鉬進行機械剝離後可以觀察到大量電子空乏的現象，此現象經過曝氧以及置於大氣下後幾乎退去。我們再來探討二硫化鉬的表面電性，曝氧後的二硫化鉬與置於大氣下的表面電性除了導帶的移動具有相似度以外，其表面態的特徵也吻合，藉此可以了解大氣中的氧氣是影響二硫化鉬表面電性的重要因素之一。
透過本次實驗，我們了解表面缺陷以及環境的變化可以影響二硫化鉬的表面能帶結構，這將成為我們如何考量天然二硫化鉬作為半導體材料的重要調控條件之一。

Molybdenum disulfide is a transition metal dichalcogenide in layered semiconductors. The energy gap can be changed by the number of layers, and the interaction between the layers is Van der Waals's force. We can easily generate a new surface for the study through mechanical exfoliation. Molybdenum disulfide has always been a popular material for electronic components.
In this work, we used a scanning tunneling microscope to observe the surface morphology and electrical changes of natural bulk molybdenum disulfide in an ultra-high vacuum environment. We control the bulk molybdenum disulfide in four situations, which are the original surface before mechanical exfoliation, the fresh surface just after the mechanical exfoliation, the surface exposed to oxygen for 8 hours after mechanical exfoliation, and the surface exposed to the atmosphere for 7 months after mechanical exfoliation. We can observe rich electron depletion after mechanically peeling molybdenum disulfide. This phenomenon almost disappears after exposure to oxygen and under the atmosphere for a long time. We discuss the surface electrical properties of molybdenum disulfide. In addition to the similar movement of the conduction band for both molybdenum disulfide exposed to oxygen and under the atmosphere, their characteristics of the surface state are also consistent. The oxygen in the atmosphere plays an important role that affects the surface electrical properties of molybdenum disulfide.
Through this experiment, we understand that surface defects and environmental changes can influence the surface energy band structure of molybdenum disulfide, which will become one of the important regulatory conditions for how we consider natural molybdenum disulfide as a semiconductor material.

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