近年來，二維層狀半導體材料，被許多科學家及實驗室研究團隊積極開發，像是石墨烯(graphene)及層狀金屬硫族化物(layer metal dichalcogenides)。石墨烯隨著奈米碳材熱門研究與發展下，由於其取得容易、市價便宜，且表現出十分優異的物理特性，包括高導電、高導熱性質。但在半導體特性上，缺乏明顯的能隙，導致石墨烯在電子及光電元件上限制了其應用端的表現。因此，我們將研究著重在有能隙的層狀金屬硫族化物半導體材料-二硫化錫(SnS2)。二硫化錫為n-型半導體，具有2-2.6電子伏特之薄膜厚度相關的間接能隙、開關電流比102及載子移動率可高達0.1~1 cm2/Vs，使得應用在場效電晶體、光電感測器、可撓式元件、太陽能電池應用上，受到了高度關注跟重視。
以機械剝離法將三維塊材製備成層狀二硫化錫薄膜，即可簡易又快速得到高品質單晶材料，但此法難以控制材料大小及薄膜層數是難以改善的缺點。而利用化學氣相沉積合成法，可製備大面積兼具高品質二硫化錫奈米薄膜。本研究中，使用草酸錫(SnC2O4)及硫粉(S)作為實驗前驅物，通入氬氣(Ar)於石英管中反應，在高溫爐中成功以化學氣相沉積法(chemical vapor deposition, CVD)，利用由下往上(bottom-up)的沉積方式，將二硫化錫奈米薄膜成長於p-型矽基板上，為了擴大面積，減少成核密度(nucleation density)，我們嘗試了各種方法，包含增加腔體內部氣體流速的調整和減少前驅物的使用量。並藉由光學顯微鏡、拉曼光譜儀、原子力顯微鏡、掃描式電子顯微鏡、高解析穿透式電子顯微鏡、X-光晶格繞射、來進一步鑑定我們合成的二硫化錫奈米薄膜。
我們隨著科技進步，人們對於高性能之電子產品，需求日益增高。如可撓式、輕薄式之電子基板等，也因此具有壓電壓阻高機械強度的二維半導體材料成了熱門研究主題。本研究以機械剝離法將二硫化錫轉置在聚對苯二甲酸(polyethylene terephthalate, PET)薄膜上，製成可撓式電子元件，並架設一個壓電感測平台，以量測二硫化錫電晶體在上下彎折時，拉伸與擠壓應力產生的電流起伏變化。未來，可進一步應用在可撓式的電子產品，人體脈動量測，或是其他新穎二維材料壓電鑑定上。

關鍵字：二硫化錫、化學氣相沉積、拉曼光譜儀、原子力顯微鏡、場效電晶體、壓電效應、可撓式元件

In recent years, two-dimensional layer semiconductor materials, such as graphene and layered metal dichalcogenides (LMDs) have been actively developed by many scientists and laboratory research teams. Graphene showed excellent physical properties, but the lack of obvious energy bandgap causes the limit of graphene for electronic and optoelectronic applications. Therefore, we focus on the LMD semiconductor with energy bandgaps, such as tin disulfide (SnS2). SnS2 is an n-type semiconductor with the film thickness dependent indirect energy bandgap of 2-2.6 eV, high on-off ratio of 102 and carrier mobility of up to 0.1~1 cm2/Vs and is suitable for fabrication of advanced high-performance field-effect transistors, photodetectors. Therefore, high-quality monolayered or few-layered tin disulfides hold great potential for future electronic applications.
Using a mechanical exfoliation method to prepare SnS2 is difficult to control the number of layers and the size of flakes. However, using a chemical vapor deposition (CVD) can be used to synthesize high-quality monolayered SnS2 with a large-scale area. In this research, we successfully used tin oxalate (SnC2O4) and sulfur powder (S) as precursors to synthesize SnS2 films on a silicon wafer in CVD reaction. In order to increase the area and reduce the nucleation density, we tried various adjustment, such as increasing the gas flow rate in the chamber and reducing the amount of precursors. Subsequently, we used an optical microscopy, Raman spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD) to identify the as-synthesized SnS2 films.
In future, smart electronic systems are expected to afford arbitrary form factors, robust elasticity, high-speed charge transport, and low-power consumption. With these characteristics, 2D layered semiconductors with high mechanical and piezotronic properties have attracted much attention in research. In this work, we fabricated a device with SnS2 nanosheets on a flexible, bendable polyethylene terephthalate (PET) thin film to examine the change of the electric transport in the device as the film was subject to tensile and compressive strains. With this capability, this SnS2-based device can be employed as a vessel pulsation sensor. Accordingly, other novel 2D materials-based piezotronics devices can be characterized by the same ways as this thesis demonstrated.

Keyword：tin disulfide, chemical vapor deposition, Raman spectroscopy, atomic force microscopy, field-effect transistor, piezoelectricity, flexible transistor

(1) Tekinderdogan, B.Engineering Connected Intelligence : A Socio-Technical Perspective; 2016.
(2) Fiori, G.; Bonaccorso, F.; Iannaccone, G.; Palacios, T.; Neumaier, D.; Seabaugh, A.; Banerjee, S. K.; Colombo, L.Electronics Based on Two-Dimensional Materials. Nat. Nanotechnol. 2014, 9 (10), 768–779.
(3) Lv, R.; Robinson, J. A.; Schaak, R. E.; Sun, D.; Sun, Y.; Mallouk, T. E.; Terrones, M.Transition Metal Dichalcogenides and beyond: Synthesis, Properties, and Applications of Single- and Few-Layer Nanosheets. Acc. Chem. Res. 2015, 48 (1), 56–64.
(4) Chang, R. J.; Tan, H.; Wang, X.; Porter, B.; Chen, T.; Sheng, Y.; Zhou, Y.; Huang, H.; Bhaskaran, H.; Warner, J. H.High-Performance All 2D-Layered Tin Disulfide: Graphene Photodetecting Transistors with Thickness-Controlled Interface Dynamics. ACS Appl. Mater. Interfaces 2018, 10 (15), 13002–13010.
(5) Plutnar, J.; Pumera, M.; Sofer, Z.Chemistry of CVD Graphene. J. Mater. Chem. C 2018.
(6) Vorobiev, Y.V; Mexicano, A.; García, A. G.Graphene Synthesis Using a CVD Reactor and a Discontinuous Feed of Gas Precursor at Atmospheric Pressure. Hindawi J. Nanomater. 2018, 2018, 1–10.
(7) Chen, X.; Zhang, L.; Chen, S.Large Area CVD Growth of Graphene. Synth. Met. 2015, 210, 95–108.
(8) Pumera, M.; Loo, A. H.Layered Transition-Metal Dichalcogenides (MoS2 and WS2) for Sensing and Biosensing. TrAC - Trends Anal. Chem. 2014, 61, 49–53.
(9) Huang, Y.; Sutter, E.; Sadowski, J. T.; Cotlet, M.; Monti, O. L. a; Racke, D. a; Neupane, M. R.; Wickramaratne, D.; Lake, R. K.; Parkinson, B. a; et al.Tin Disulfide- An Emerging Layered Metal Dichalcogenide Semiconductor : Materials Properties and Device Characteristics. ACS Nano 2014, 8 (10), 10743–10755.
(10) Ye, G.; Gong, Y.; Lei, S.; He, Y.; Li, B.; Zhang, X.; Jin, Z.; Dong, L.; Lou, J.; Vajtai, R.; et al.Synthesis of Large-Scale Atomic-Layer SnS2 through Chemical Vapor Deposition. Nano Res. 2017, 10 (7), 2386–2394.
(11) Gonzalez, J. M.; Oleynik, I. I.Layer-Dependent Properties of SnS2 and SnSe2 Two-Dimensional Materials. Phys. Rev. B 2016, 94 (12).
(12) Ahn, J. H.; Lee, M. J.; Heo, H.; Sung, J. H.; Kim, K.; Hwang, H.; Jo, M. H.Deterministic Two-Dimensional Polymorphism Growth of Hexagonal n-Type SnS2 and Orthorhombic p-Type SnS Crystals. Nano Lett. 2015, 15 (6), 3703–3708.
(13) Burton, L. A.; Whittles, T. J.; Hesp, D.; Linhart, W. M.; Skelton, J. M.; Hou, B.; Webster, R. F.; O’Dowd, G.; Reece, C.; Cherns, D.; et al.Electronic and Optical Properties of Single Crystal SnS2 : An Earth-Abundant Disulfide Photocatalyst. J. Mater. Chem. A 2016, 4 (4), 1312–1318.
(14) Burton, L. A.; Walsh, A.Phase Stability of the Earth-Abundant Tin Sulfides SnS, SnS2, and Sn2S3. J. Phys. Chem. C 2012, 116 (45), 24262–24267.
(15) Samad, L.; Bladow, S. M.; Ding, Q.; Zhuo, J.; Jacobberger, R. M.; Arnold, M. S.; Jin, S.Layer-Controlled Chemical Vapor Deposition Growth of MoS2 Vertical Heterostructures via van Der Waals Epitaxy. ACS Nano 2016, 10 (7), 7039–7046.
(16) Yang, S. Y.; Shim, G. W.; Seo, S. B.; Choi, S. Y.Effective Shape-Controlled Growth of Monolayer MoS2 Flakes by Powder-Based Chemical Vapor Deposition. Nano Res. 2017, 10 (1), 255–262.
(17) Mohamed, E. F.Nanotechnology: Future of Environmental Air Pollution Control. Environ. Manag. Sustain. Dev. 2017, 6 (2), 429.
(18) Fugallo, G.; Cepellotti, A.; Paulatto, L.; Lazzeri, M.; Marzari, N.; Mauri, F.Thermal Conductivity of Graphene and Graphite: Collective Excitations and Mean Free Paths. Nano Lett. 2014, 14 (11), 6109–6114.
(19) Marinho, B.; Ghislandi, M.; Tkalya, E.; Koning, C. E.; deWith, G.Electrical Conductivity of Compacts of Graphene, Multi-Wall Carbon Nanotubes, Carbon Black, and Graphite Powder. Powder Technol. 2012, 221, 351–358.
(20) Li, D.; Shao, Z.-G.; Hao, Q.; Zhao, H.Intrinsic Carrier Mobility of a Single-Layer Graphene Covalently Bonded with Single-Walled Carbon Nanotubes. J. Appl. Phys. 2014, 115 (23), 233701.
(21) Brown, M. A.; Crosser, M. S.; Leyden, M. R.; Qi, Y.; Ethan, D.Measurement of High Carrier Mobility in Graphene in an Aqueous Electrolyte Environment. 1919.
(22) Hirai, H.; Tsuchiya, H.; Kamakura, Y.; Mori, N.; Ogawa, M.Electron Mobility Calculation for Graphene on Substrates. J. Appl. Phys. 2014, 116 (8).
(23) Bolotin, K. I.; Sikes, K. J.; Jiang, Z.; Klima, M.; Fudenberg, G.; Hone, J.; Kim, P.; Stormer, H. L.Ultrahigh Electron Mobility in Suspended Graphene. Solid State Commun. 2008, 146 (9–10), 351–355.
(24) Papageorgiou, D. G.; Kinloch, I. A.; Young, R. J.Mechanical Properties of Graphene and Graphene-Based Nanocomposites. Prog. Mater. Sci. 2017, 90, 75–127.
(25) Akinwande, D.; Brennan, C. J.; Bunch, J. S.; Egberts, P.; Felts, J. R.; Gao, H.; Huang, R.; Kim, J. S.; Li, T.; Li, Y.; et al.A Review on Mechanics and Mechanical Properties of 2D Materials—Graphene and Beyond. Extrem. Mech. Lett. 2017, 13, 42–77.
(26) Socolar, J. E. S.; Lubensky, T. C.; Kane, C. L.Mechanical Graphene. New J. Phys. 2017, 19 (2).
(27) Singh, E.; Meyyappan, M.; Nalwa, H. S.Flexible Graphene-Based Wearable Gas and Chemical Sensors. ACS Appl. Mater. Interfaces 2017, 9 (40), 34544–34586.
(28) Jang, H.; Park, Y. J.; Chen, X.; Das, T.; Kim, M. S.; Ahn, J. H.Graphene-Based Flexible and Stretchable Electronics. Adv. Mater. 2016, 28 (22), 4184–4202.
(29) Lee, S. M.; Kim, J. H.; Ahn, J. H.Graphene as a Flexible Electronic Material: Mechanical Limitations by Defect Formation and Efforts to Overcome. Mater. Today 2015, 18 (6), 336–344.
(30) Kim, H.; Ahn, J. H.Graphene for Flexible and Wearable Device Applications. Carbon N. Y. 2017, 120, 244–257.
(31) Han, T. H.; Kim, H.; Kwon, S. J.; Lee, T. W.Graphene-Based Flexible Electronic Devices. Mater. Sci. Eng. R Reports 2017, 118, 1–43.
(32) Mokhtar Mohamed, M.; Mousa, M. A.; Khairy, M.; Amer, A. A.Nitrogen Graphene: A New and Exciting Generation of Visible Light Driven Photocatalyst and Energy Storage Application. ACS Omega 2018, 3 (2), 1801–1814.
(33) Tabish, T. A.; Zhang, S.; Winyard, P. G.Developing the next Generation of Graphene-Based Platforms for Cancer Therapeutics: The Potential Role of Reactive Oxygen Species. Redox Biol. 2018, 15 (November 2017), 34–40.
(34) Kim, S.; Shin, S.; Kim, T.; Du, H.; Song, M.; Kim, K. S.; Cho, S.; Lee, S. W.; Seo, S.A Reliable and Controllable Graphene Doping Method Compatible with Current CMOS Technology and the Demonstration of Its Device Applications. Nanotechnology 2017, 28 (17).
(35) Kuc, A.Low-Dimensional Transition-Metal Dichalcogenides. Chem. Model. 2015, 11, 1–29.
(36) Li, H.; Li, Y.; Aljarb, A.; Shi, Y.; Li, L.-J.Epitaxial Growth of Two-Dimensional Layered Transition-Metal Dichalcogenides: Growth Mechanism, Controllability, and Scalability. Chem. Rev. 2017, acs.chemrev.7b00212.
(37) Huang, W.; Gan, L.; Li, H.; Ma, Y.; Zhai, T.2D Layered Group IIIA Metal Chalcogenides: Synthesis, Properties and Applications in Electronics and Optoelectronics. CrystEngComm 2016, 18 (22), 3968–3984.
(38) Zhou, X.; Zhang, Q.; Gan, L.; Li, H.; Xiong, J.; Zhai, T.Booming Development of Group IV–VI Semiconductors: Fresh Blood of 2D Family. Adv. Sci. 2016, 3 (12).
(39) Hu, Z.; Wu, Z.; Han, C.; He, J.; Ni, Z.; Chen, W.Two-Dimensional Transition Metal Dichalcogenides: Interface and Defect Engineering. Chem. Soc. Rev. 2018, 47 (9), 3100–3128.
(40) Splendiani, A.; Sun, L.; Zhang, Y.; Li, T.; Kim, J.; Chim, C. Y.; Galli, G.; Wang, F.Emerging Photoluminescence in Monolayer MoS2. Nano Lett. 2010, 10 (4), 1271–1275.
(41) Mouri, S.; Miyauchi, Y.; Matsuda, K.Tunable Photoluminescence of Monolayer MoS2 via Chemical Doping. Nano Lett. 2013, 13 (12), 5944–5948.
(42) Chhowalla, M.; Shin, H. S.; Eda, G.; Li, L. J.; Loh, K. P.; Zhang, H.The Chemistry of Two-Dimensional Layered Transition Metal Dichalcogenide Nanosheets. Nat. Chem. 2013, 5 (4), 263–275.
(43) Mitzi, D. B.; Kosbar, L. L.; Murray, C. E.; Copel, M.; Afzali, A.High-Mobility Ultrathin Semiconducting Films Prepared by Spin Coating. Nature 2004, 428 (6980), 299–303.
(44) Britt, J.; Ferekides, C.Thin-Film CdS/CdTe Solar Cell with 15.8% Efficiency. Appl. Phys. Lett. 1993, 62 (22), 2851–2852.
(45) Binnewies, M.; Glaum, R.; Schmidt, M.; Schmidt, P.Chemical Vapor Transport Reactions. 2012.
(46) Wang, G.; Peng, J.; Zhang, L.; Zhang, J.; Dai, B.; Zhu, M.; Xia, L.; Yu, F.Two-Dimensional SnS2 PANI Nanoplates with High Capacity and Excellent Stability for Lithium-Ion Batteries. J. Mater. Chem. A 2015, 3 (7), 3659–3666.
(47) Xia, J.; Zhu, D.; Wang, L.; Huang, B.; Huang, X.; Meng, X. M.Large-Scale Growth of Two-Dimensional SnS2 Crystals Driven by Screw Dislocations and Application to Photodetectors. Adv. Funct. Mater. 2015, 25 (27), 4255–4261.
(48) Fan, C.; Li, Y.; Lu, F.; Deng, H. X.; Wei, Z.; Li, J.Wavelength Dependent UV-Vis Photodetectors from SnS2 Flakes. RSC Adv. 2015, 6 (1), 422–427.
(49) Zhou, T.; Pang, W. K.; Zhang, C.; Yang, J.; Chen, Z.; Liu, H. K.; Guo, Z.Enhanced Sodium-Ion Battery Performance by Structural Phase Transition from Two-Dimensional Hexagonal-SnS2 to Orthorhombic-SnS. ACS Nano 2014, 8 (8), 8323–8333.
(50) Wang, Z.; Pang, F.In-Plane Growth of Large Ultra-Thin SnS2 Nanosheets by Tellurium-Assisted Chemical Vapor Deposition. RSC Adv. 2017, 7 (46), 29080–29087.
(51) Hu, Y.; Chen, T.; Wang, X.; Ma, L.; Chen, R.; Zhu, H.; Yuan, X.; Yan, C.; Zhu, G.; Lv, H.; et al.Controlled Growth and Photoconductive Properties of Hexagonal SnS2 nanoflakes with Mesa-Shaped Atomic Steps. Nano Res. 2017, 10 (4), 1434–1447.
(52) Baskaran, S.Structure and Regulation of Yeast Glycogen Synthase STRUCTURE AND REGULATION OF YEAST GLYCOGEN SYNTHASE Sulochanadevi Baskaran Submitted to the Faculty of the University Graduate School in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Department of Biochemistry and Molecular Biology Indiana University. 2014, No. May.
(53) Wang, Y.; Huang, L.; Wei, Z.Photoresponsive Field-Effect Transistors Based on Multilayer SnS2 Nanosheets. J. Semicond. 2017, 38 (3), 1–6.
(54) Zhang, Z.; Yates, J. T.Band Bending in Semiconductors: Chemical and Physical Consequences at Surfaces and Interfaces. Chem. Rev. 2012, 112 (10), 5520–5551.
(55) Wang, Y.; Huang, L.; Wei, Z.Photoresponsive Field-Effect Transistors Based on Multilayer SnS2 Nanosheets. J. Semicond. 2017, 38 (3).
(56) Zhou, X.; Zhang, Q.; Gan, L.; Li, H.; Zhai, T.Large-Size Growth of Ultrathin SnS2 Nanosheets and High Performance for Phototransistors. Adv. Funct. Mater. 2016, 26 (24), 4405–4413.
(57) Duerloo, K. A. N.; Ong, M. T.; Reed, E. J.Intrinsic Piezoelectricity in Two-Dimensional Materials. J. Phys. Chem. Lett. 2012, 3 (19), 2871–2876.
(58) Alyörük, M. M.; Aierken, Y.; Çaklr, D.; Peeters, F. M.; Sevik, C.Promising Piezoelectric Performance of Single Layer Transition-Metal Dichalcogenides and Dioxides. J. Phys. Chem. C 2015, 119 (40), 23231–23237.
(59) Wu, W.; Wang, L.; Li, Y.; Zhang, F.; Lin, L.; Niu, S.; Chenet, D.; Zhang, X.; Hao, Y.; Heinz, T. F.; et al.Piezoelectricity of Single-Atomic-Layer MoS2 for Energy Conversion and Piezotronics. Nature. 2014, 514 (7523), 470–474.
(60) Qi, J.; Lan, Y. W.; Stieg, A. Z.; Chen, J. H.; Zhong, Y. L.; Li, L. J.; Chen, C. D.; Zhang, Y.; Wang, K. L.Piezoelectric Effect in Chemical Vapour Deposition-Grown Atomic-Monolayer Triangular Molybdenum Disulfide Piezotronics. Nat. Commun. 2015, 6 (May), 1–8.
(61) Huang, Y.; Sutter, E.; Sadowski, J. T.; Cotlet, M.; Monti, O. L. A.; Racke, D. A.; Neupane, M. R.; Wickramaratne, D.; Lake, R. K.; Parkinson, B. A.; et al.Tin Disulfide-an Emerging Layered Metal Dichalcogenide Semiconductor: Materials Properties and Device Characteristics. ACS Nano 2014, 8 (10), 10743–10755.
(62) Huang, Y.; Deng, H.-X.; Xu, K.; Wang, Z.-X.; Wang, Q.-S.; Wang, F.-M.; Wang, F.; Zhan, X.-Y.; Li, S.-S.; Luo, J.-W.; et al.Highly Sensitive and Fast Phototransistor Based on Large Size CVD-Grown SnS2 Nanosheets. Nanoscale 2015, 7 (33), 14093–14099.
(63) Park, J. C.; Lee, K. R.; Heo, H.; Kwon, S.-H.; Kwon, J.-D.; Lee, M.-J.; Jeon, W.; Jeong, S.-J.; Ahn, J.-H.Vapor Transport Synthesis of Two-Dimensional SnS2 Nanocrystals Using a SnS2 Precursor Obtained from the Sulfurization of SnO2. Cryst. Growth Des. 2016, 16 (7), 3884–3889.
(64) Choi, H.; Lee, J.; Shin, S.; Lee, J.; Lee, S.; Park, H.; Kwon, S.; Lee, N.; Bang, M.; Lee, S.-B.; et al.Fabrication of High Crystalline SnS and SnS2 thin Films, and Their Switching Device Characteristics. Nanotechnology. 2018, 29 (21).
(65) Manzeli, S.; Allain, A.; Ghadimi, A.; Kis, A.Piezoresistivity and Strain-Induced Band Gap Tuning in Atomically Thin MoS2. Nano Lett. 2015, 15 (8), 5330–5335.