氣相沉積生成在高定向熱解石墨上的二硫化鉬之掃描穿隧顯微鏡表面型態與莫列條紋尺度掃描穿隧能譜之研究

Abstract

二硫化鉬和二硒化鎢是擁有半導體特性的典型層狀過渡金屬硫屬化合物。我們利用低溫掃描穿隧式顯微鏡研究以化學氣相沉積長在高定向熱解石墨上二硫化鉬的表面型態。從原子力顯微鏡影像可知，二硫化鉬趨向形成大面積的三角形島狀結構，並且表現出與高定向熱解石墨台階邊緣相稱的特定生成方向。分析原子尺度的掃描穿隧式顯微鏡影像後，硫原子與莫列條紋的單位晶胞向量可被決定。經由六方晶格陣列重疊的對稱分析，我們可以得知二硫化鉬與高定向熱解石墨之間的旋轉角很小，也就是說二硫化鉬與石墨的晶格幾乎平行。結合晶格定向模型分析，在原子力顯微鏡影像中觀察到的三角形島狀結構的特定生成方向可以被解釋。此外，我們量測到莫列條紋尺度的單層二硫化鉬在高定向熱解石墨上的掃描穿隧能譜。在此情況下，莫列條紋主要來自電子態的起伏。原子莫列條紋模型顯示硫和碳原子的排列情況造成電子態在空間上的起伏。另外，我們量測到一個侷限在莫列條紋局部極大區域的電子態，而此電子態來自硫原子和碳原子軌域的交互作用。

Molybdenum disul de (MoS2) and tungsten diselenide (WSe2) are typical layered transition-metal dichalcogenide 2D materials with semiconductor properties. In this work, we investigate the topography of the chemical vapor deposition (CVD) grown MoS2 on HOPG by low temperature STM. In atomic force microscopy (AFM) data, MoS2 islands tend to form large domain triangular islands and show some preferred growing direction compared to the HOPG edge. From scanning tunneling microscopy (STM) atom-resolved image, the unit cell vector of the sulfur atoms and the superstructure moir e pattern can be determined. Through the symmetry analysis of the hexagonal array overlapping, we can figure out the angle of orientation di fference is small through the MoS2 domains we found, which means that MoS2 and HOPG lattice are almost parallel. Combining the edge orientation model analysis, the preferred direction of the triangular islands observed in AFM topography can be explained. Additionally, we obtain highly resolved scanning tunneling spectroscopy (STS) of monolayer MoS2 on HOPG in moir e-pattern resolution. The moir e pattern is mainly related to the corrugation of electronic states under this situation. A atom model of moir e pattern is made to reveal that the atomic arrangement between sulfur and carbon atoms causes the corrugation of electronic states. Moreover, we observe the state localized in the local maximum of moir e pattern, which may be originated from the orbital interaction between sulfur and carbon atoms.