臺灣博碩士論文加值系統

本論文探討奈米多層結構的二硫化鉬(MoS2)層狀半導體之表面電子聚集效應及其電傳輸特性。本實驗利用機械剝離法產生MoS2奈米結構，發現其電導率與塊材相比高出幾個數量級。透過變溫電導率量測觀察到奈米結構MoS2擁有比塊材低的活化能，結合電導率結果可推測MoS2表面有著較材料內部高的導電特性。由transfer length method (TLM)分析發現MoS2表現出二維的電傳輸特性，並排除可能的接觸電阻效應。MoS2塊材原始表面(non-fresh surface)藉由掃描式穿隧顯微鏡(STM)量測證明了表面具有電子聚集的特性。擁有新撕開的新鮮表面(fresh surface)的塊材從STM量測並無發現表面電子聚集。放置大氣下4個月後由STM量測可得到與原始表面的塊材相同的結果。奈米結構fresh surface的MoS2量測到接近塊材等級的電導率。此外，亦對相近厚度但具有不同電導率的MoS2奈米結構做活化能量測，分析活化能機制與表面態的變化。利用場效應電晶體(FET)量測，可發現fresh surface的MoS2奈米結構相對於non-fresh surface的樣品表現出較高的電子遷移率與較低的電子濃度。推測non-fresh surface的MoS2奈米結構可能存在著較強的表面散射機制。

Surface electron accumulation (SEA) and thickness-dependent electric properties in the molybdenum disulfide (MoS2) two-dimensional (2D) nanostructures have been observed and investigated. The MoS2 nanoflakes fabricated by mechanical exfoliation exhibit several orders of magnitude higher conductivity than their bulk counterparts. The carrier activation energy of nanostructures is lower than that of the bulk counterparts. The transfer length method was used to determine the current transport in MoS2 following a 2D behavior rather than the conventional 3D mode. Scanning tunneling microscopy measurements confirmed the presence of surface electron accumulation (SEA) in this layer material. Notably, the pronounced n-doping characteristic can be easily removed by producing a fresh surface through mechanical exfoliation. Long-term exposure to air can transform the intrinsic fresh surface into a metallic-like surface, indicating that SEA is not inherent. The FET measurement indicates that the MoS2 nanoflakes with fresh surface exhibit higher mobility and lower electron concentration compare to the nanoflakes with non-fresh surface. A more significant surface scattering in the non-fresh MoS2 nanoflakes was proposed.

中文摘要
Abstract
致謝
目錄
圖目錄
表目錄
第一章 緒論
第二章 實驗方法
2.1 二硫化鉬單晶介紹
2.2 二硫化鉬層狀半導體之形貌、結構特性檢測
2.3 二硫化鉬層狀半導體元件製作
2.4 奈米材料元件之暗電導特性
第三章 結果與討論
3.1 二硫化鉬層狀半導體單晶之形貌與結構分析
3.2 二硫化鉬層狀半導體元件
3.3 二硫化鉬奈米結構暗電導
3.4 由STM觀察表面電子聚集效應
3.5 奈米結構本質電導率量測
3.6奈米結構新撕表面的樣品之活化能分析
3.7 電子遷移率與表面電子濃度
第四章 結論
參考文獻

[1] Novoselov, K. S. et al. Two-dimensional gas of massless Dirac fermions in graphene. Nature 438, 197-200 (2005).
[2] Geim, A. K. Graphene: Status and prospects. Science 324, 1530-1534 (2004).
[3] Yazyev, O. V., Kis, A. MoS2 and semiconductors in the flatland. Mater. Today 18, 20-30 (2015).
[4] Butler, S. Z. et al. Challenges, and opportunities in two-dimensional materials beyond graphene. ACS Nano 7, 2898-2926 (2013).
[5] Wang, Q. H., Kalantar-Zadeh, K., Kis, A., Coleman, J. N., Strano, M. S. Electronics and optoelectronics of two-dimensional transition metal dichalcogenides. Nat Nanotechnol. 7, 699-712 (2012).
[6] Mak, K. F., Lee, C., Hone, J., Shan, J., Heinz, T. F. Atomically thin MoS2: A new direct-gap semiconductor. Phys. Rev. Lett. 105, 136805 (2010).
[7] Splendiani, A. et al. Emerging photoluminescence in monolayer MoS2. Nano Lett. 10, 1271-1275 (2010).
[8] Geim, A. K., Grigorieva, I. V. Van der Waals heterostructures. Nature 499, 419-425 (2013).
[9] Withers, F. et al. Light-emitting diodes by band-structure engineering in van der Waals heterostructures. Nat Mater. 14, 301-306 (2015).
[10] Roy, K. et al. Graphene-MoS2 hybrid structures for multifunctional photoresponsive memory devices. Nat Nanotechnol. 8, 826-830 (2013).
[11] Zhang, W., Chuu, C. P., Huang, J. K., Chen, C.H., Tsai, M. L., Chang, Y. H., Liang, C. T., Chen, Y. Z., Chueh, Y. L., He, J. H., Chou, M. Y., Li, L. J. Ultrahigh-gain photodetectors based on atomically thin Graphene-MoS2 heterostructures. Sci Rep. 4, 3826 (2014)
[12] Liu, C. J. et al. Facile synthesis of MoS2/graphene nanocomposite with high catalytic activity toward triiodide reduction in dye-sensitized solar cells. J. Mater. Chem. 22, 21057-21064 (2012).
[13] Min, S., Lu, G. Sites for High efficient photocatalytic hydrogen evolution on a limited-layered MoS2 cocatalyst confined on graphene sheets-The role of graphene. J. Phys. Chem. C 116, 25415-25424 (2012).
[14] Xiang, Q., Yu, J., Jaroniec, M. Synergetic effect of MoS2 and graphene as cocatalysts for enhanced photocatalytic H2 production activity of TiO2 nanoparticles. J. Am. Chem. Soc. 134, 6575-6578 (2012).
[15] Radisavljevic, B., Radenovic, A., Brivio, J., Giacometti, V., Kis, A. Single-layer MoS2 transistors. Nat Nanotechnol. 6, 147-150 (2011).
[16] Radisavljevic, B., Kis, A. Mobility engineering and a metal-insulator transition in monolayer MoS2. Nat Mater. 12, 815-820 (2013).
[17] Liu, H., Neal, A. T., Ye, P. D. Channel length scaling of MoS2 MOSFETs. ACS Nano 6, 8563-8569 (2012).
[18] Wu, W. et al. High mobility and high on/off ratio field-effect transistors based on chemical vapor deposited single-crystal MoS2 grains. Appl. Phys. Lett. 102, 142106 (4 pages) (2013).
[19] Zhang, Y., Ye, J., Matsuhashi, Y., Iwasa, Y. Ambipolar MoS2 thin flake transistors. Nano Lett. 12, 1136-1140 (2012).
[20] Park, W. et al. Oxygen environmental and passivation effects on molybdenum disulfide field effect transistors. Nanotechnology 24, 095202 (5 pages) (2013).
[21] Tiong, K. K., Liao, P. C., Ho, C. H., Huang, Y. S. Growth and characterization of rhenium-doped MoS2 single crystals. J. Crystal Growth 205, 543-547 (1999).
[22] Novoselov, K. S. et al. Two-dimensional atomic crystals. Proc. Natl. Acad. Sci. U. S. A. 102, 10451-10453 (2005).
[23] Flewitt, P. E. J., Wild, R. K. Physical methods for materials characterization. IOP Publishing, Bristol (1994).
[24] Cullity, B. D., Stock, S. R. Elements of X-ray diffraction. Prentice Hall, New Jersey (2001).
[25] Tseng, A. A., Chen, K., Chen, C. D., Ma, K. J. Electron Beam Lithography in Nanoscale Fabrication: Recent Development. IEEE Trans. Electron. Packag. Manuf. 26, 141–149 (2003).
[26] Tseng, A. A. Recent developments in micromilling using focused ion beam technology. J. Micromech. Microeng. 14, 15–34 (2004).
[27] Tseng, A. A. Recent Developments in Nanofabrication using Focused Ion Beams. Small 1, 924–939 (2005).
[28] Braet, F., De Zanger, R., Wisse, E. Drying cells for SEM, AFM and TEM by hexamethyldisilazane: a study on hepatic endothelial cells. Journal of Microscopy. 186, 84–87 (1997).
[29] Chang, Y. M., Kim, H., Lee, J. H., Song, Y. W. Multilayered graphene efficiently formed by mechanical exfoliation for nonlinear saturable absorbers in fiber mode-locked lasers. Appl. Phys. Lett. 97, 211102 (3papers) (2010).
[30] Nam, C. Y., Tham, D., Fischer, J. E. Disorder effects in focused-ion-beam-deposited Pt contacts on GaN nanowires. Nano Lett. 5, 2029-2033 (2005)
[31] Li, H., Zhang, Q., Yap, C. C. R., Tay, B. K., Edwin, T. H. T., Olivier, A., Baillargeat, D. From bulk to monolayer MoS2: Evolution of Raman scattering. Adv. Funct. Mater. 22, 1385-1390 (2012)
[32] Chen, R. S., Tang, C. C., Shen, W. C., Huang, Y. S. Thickness-dependent electrical conductivities and ohmic contacts in transition metal dichalcogenides multilayers. Nanotechnology 25, 415706 (9 pages) (2014).
[33] 沈韋竹. 二硫化鉬及二硫化鎢層狀半導體奈米結構之厚度相依電傳輸特性. 國立台灣科技大學學位論文系統 (2015).
[34] Dolui, K., Rungger, I., Sanvito, S. Origin of the n-type and p-type conductivity of MoS2 monolayers on a SiO2 substrate. Phys. Rev. B. 87, 7 (2013)
[35] Mahboob, I., Veal, T. D., McConville, C. F. Intrinsic Electron accumulation at clean InN surfaces. Phys. Rev. Lett. 92, 36804 (2004).
[36] Peelaers, H., Van de Walle, C. G. Effects of strain on band structure and effective masses in MoS2. Phys. Rev. B 86, 241401 (2012).