掃描穿隧式電子顯微術於臺階引發之少數層二硫化鉬結及邊界之研究

自從石墨烯成功被製造出來，一系列的二維材料不斷的被發現並因其優異的特性吸引大量的研究關注，二硫化鉬屬於二維過度金屬二硫屬化物，因其具有半導體帶隙而成為其中被廣泛研究的材料之一。其帶隙隨著厚度而改變的性質，使得人們可以根據同種材料組成平面異質結，並且應用於電子或光電元件中。在此篇論文中，我們利用掃描穿隧式電子顯微術探討化學氣相沉積成長於高定向熱解石墨的二硫化鉬樣品，並且發現兩種二硫化鉬的多層結構:三角螺旋結構與層狀三角結構，兩者同時存在於樣品表面，藉由分析表面缺陷方向，我們確認三角螺旋具有三方的堆疊結構。此外，多層結構的存在也表示有可能在樣品中找到平面異質結。在這裡我們呈現出三個二硫化鉬系統的空間分布電子結構，分別是單層-雙層-三層的不連續系統、雙層-單層-雙層的連續系統以及單層二硫化鉬橫跨高定向熱解石墨臺階的系統。其中第二個系統的單層-雙層接面由滑邊組成，顯現出不同於傳統半導體接面的帶排列特性，考慮到二硫化鉬單層內的傳輸特性以及其較高的常溫遷移率，我們認為這類新型的結可以為電子及光電元件提供實際的應用。

關鍵字

二硫化鉬；平面異質結；帶排列；螺旋結構；掃描式穿隧電子顯微鏡

並列摘要

Since the first successful exfoliation of graphene, a great variety of 2D materials have been found and attracted much attention for their appealing properties. One of which is MoS2, belonging to a branch called transition metal dichalocogenides (TMDs) and well known for its intrinsic semiconducting bandgap. As MoS2 bandgap is sensitive to thickness, lateral heterojunctions (HJs) base on the same material are achievable and play an important role in applications in electronic/optoelectronic devices. In this thesis, MoS2 multilayer structures were found on a chemical vapor deposition (CVD) grown MoS2 on highly oriented pyrolytic graphite (HOPG) substrates and investigated by the techniques of scanning tunneling microscope (STM) and spectroscopy (STS). Triangular spiral structure and layer-by-layer (LBL) triangular structure coexist on this sample. Analysis on defect orientation confirms the stacking configuraion of the spiral as rhombohedral (2R/3R). Furthermore, the existence of multilayer structure also implies we could found lateral heterojunctions (HJs). Here we show the real space imaging of electronic structures in lateral monolayer (ML)-bilayer (BL)- tri-layer (TL) HJs, continuous BL- ML-BL HJs and a comparison case of monolayer MoS2 across a HOPG step. The second system consisting of slipped edges is different from conventional semiconductor in band alignments. Considering the in-plane transport property and high MoS2 mobility at room temperatue, we expect that this novel class of junctions could provide us a feasible solution for novel electronic and optoelectronic devices.

並列關鍵字

MoS2 ； lateral heterojunction ； band alignment ； spiral ； scanning tunneling microscopy

參考文獻

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[3] Q. H. Wang, K. Kalantar-Zadeh, A. Kis, J. N. Coleman and M. S. Strano. Electronics and optoelectronics of two-dimensional transition metal dichalco-genides. Nat. Nanotechnol. 27, 699 (2012).

[4] M. Chhowalla, H. S. Shin, G. Eda, L. J. Li, K. P. Loh and H.Zhang. The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets. Nat. Chem. 5, 263 (2013).

[5] M. X. Sun, D. Xie, Y. L. Sun, W. W. Li, C. J. Tseng and J. L. Xu. Lateral multilayer/monolayer MoS2 heterojunction for high performance photodetector applications. Sci. Reports 7, 4505 (2017).

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掃描穿隧式電子顯微術於臺階引發之少數層二硫化鉬結及邊界之研究

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