本研究利用膠體合成法成功合成出具備豐富少數層之二碲化鎢奈米球狀粒子，且同時具備最穩定之半金屬相。於此之外，我們利用此材料進行亞甲基藍有機水溶液的降解實驗以及產生氫氣。原理以二碲化鎢之非對稱結構而具備壓電效應為基礎，在施加機械能於暗環境下展現壓電觸媒之特性。 在施予機械能後，材料中產生的內在電場導致電子電洞對分離，並於此同時和水分子反應產生氫氧自由基，而激進的氫氧自由基則貢獻於分解有機物與產生氣體產物。在實驗中，90% 過氧化氫配製而成的40ppm亞甲基藍可以在暗條件下於15秒內被完全降解，相對應的反應速率常數為~0.3ppm s-2 .尤其加入些許過氧化氫更能有效提升不論降解汙染物以其產生能源之效率。過氧化氫不只具備極性分子，更能與分離之電子再生成氫氧自由基。對於二碲化鎢之特性分析，掃描式電子顯微鏡與壓電響應分析儀證明了材料具備高表面積之奈米形貌以及對應形貌的壓電響應(外加偏壓3V下,反應~25mV)。在應用端重要的是利用螢光光譜儀與順磁共振儀證實了在受到機械震盪與添加些許過氧化氫的情形下，大量的氫氧自由基被產生與偵測到。此外，利用高解析穿隧式電子顯微鏡證實所合成之二碲化鎢為半金屬相，包括其原子排列以及繞射圖形；而主要參與反應的豐富少數層更為完美的單晶結構。在高濃度降解實驗中，200ppm亞甲基藍可以再添加90% 過氧化氫的條件下達到完全降解於一分鐘內，反應速率常數為~0.12ppm s-2；同樣在產氫實驗中可以大幅提升其效率。這是第一個成功使用半金屬相二碲化鎢奈米粒子透過過氧化氫強化壓電效應之應用於暗環境下的研究。

We have demonstrated an ultrafast degradation efficiency for decomposing the methylene blue (MB) dye and hydrogen gas production by applying mechanical force to the 1T distorted WTe2 (Td-WTe2) microspheres in a dark situation. The non-centrosymmetric structure and the Td phase of WTe2 microspheres can provide piezo-catalyst effect and the most stable phase for corresponding applications, respectively.
Hydroxyl radicals (OH•) were created from Td-WTe2 microspheres through piezoelectric spontaneous polarization and further decomposed polar molecules for gas generation. Moreover, the production of OH radicals can be enhanced with hydrogen peroxide molecules. Due to polar characteristic and loose O-O bond of hydrogen peroxide, OH• can be induced by piezo-catalytic Td-WTe2 microspheres in a H2O2-asisted system. Based on experiment, 200ppm MB dye solution with 90% H2O2 can be completely decomposed within 1 minutes, and the related reaction rate constant is ~ 0.12 ppm s-2.
To certify the Td-WTe2 microspheres exhibit highly piezoelectricity with elimination of particle size and morphology, the piezoresponse force microscopy (PFM), redox reactions with the measurement of X-ray photoelectron spectroscopy (XPS), and the dye degradation and absorption experiments were utilized to compare with the annealing powder. Based on the fluorescence (FL) spectra and the electron paramagnetic resonance (EPR) spin trapping with 5,5-dimethylpyrroline-1-oxide (DMPO) spectra, the evidence indicates Td-WTe2 microspheres can indeed emerge hydroxyl radicals during vibration in the dark. Furthermore, the amount of hydroxyl radicals were considerably improved with the assistance of hydrogen peroxide. The evidence that the efficiency of dye degradation and hydrogen production highly depends on the concentration of both Td-WTe2 microspheres and hydrogen peroxide can be observed clearly in the experiments of applications. This is the first work to demonstrate that Td-WTe2 microspheres can be significantly utilized on not only ultrafast
dye degradation but also hydrogen gas generation through H2O2-assisted piezo-catalyst effect in the dark.

Abstract
Acknowledgements
Contents
Chapter 1 Introduction------------------------------------------1
1.1 Preface-----------------------------------------------------1
1.2 Motivation--------------------------------------------------2
Chapter 2 Literature Review-------------------------------------5
2.1 2D Materials------------------------------------------------5
2.1.1 Graphene------------------------------------------------5
2.1.2 2D Transition Metal Dichalcogenide----------------------6
2.1.3 Synthesis of 2D Transition Metal Dichalcogenide---------7
1. Mecahnical and Liquid Exfoliation------------------------7
2. Chemical Vapor Deposition--------------------------------8
3. Hydrothermal Synthesis-----------------------------------9
4. Colloidal Synthesis-------------------------------------11
2.2 Photocatalyst----------------------------------------------13
2.2.1 Traditional Photocatalyst------------------------------13
2.2.2 Heterostructure Photocatalyst--------------------------15
2.2.3 Piezo-enhanced Photocatalyst---------------------------17
2.3 Piezoelectric effect---------------------------------------19
2.3.1 Origin and Mechanisn of Piezoelectricity---------------19
2.3.2 Piezoelectricity of Transition Metal Dichalcogenide----22
2.3.3 Piezocatalyst------------------------------------------25
2.3.4 Piezocatalytic Performance of MoS2 Nanoflower----------27
2.4 Tungsten Ditelluride--------------------------------------33
2.4.1 Synthsis of Tungsten Ditelluride-----------------------34
1.Chemical Vapor Deposition--------------------------------34
2.Chemical Vapor Transport---------------------------------35
3.Mechanical and Liquid Exfoliation------------------------36
2.4.2 Relative Discovery of Tungsten Ditelluride------------37
Chapter 3 Experimental Methods and Process---------------------38
3-1 Production of Precursors-----------------------------------39
3-2 Colloidal Synthesis, Annealing Process and PDMS------------40
3-3 Characterization-------------------------------------------43
3.3.1 Scanning Electron Microscopy---------------------------43
3.3.2 WAG X-ray Diffractometer-------------------------------44
3.3.3 High-resolution Transmission Electron Microscpe--------44
3.3.4 X-ray Photoelectron Spectroscopy & Redox Reactions-----45
3.3.5 Raman Spectra------------------------------------------46
3.3.6 Piezorespose Force Microscopy--------------------------47
3.3.7 Electron Paramagnetic Resonance------------------------48
3.3.8 Fluorescence Photoluminescence Spectrophotometer-------49
3.3.9 Piezocatalytic Experiments – Dye Degradation-----------49
3.3.10 Piezocatalytic Experiments – Hydrogen Evolution-------50
Chapter 4 Results and Discussion-------------------------------52
4-1 Surface Morphology-----------------------------------------52
4.2 X-ray Diffractional Pattern--------------------------------53
4.3 Raman Vibrational Mode-------------------------------------55
4.4 Crystal Structure------------------------------------------56
4.5 Binding Energy & Redox Reaction----------------------------59
4.6 Piezoresponse----------------------------------------------61
4.7 Radical Generation-----------------------------------------63
4.8 Analysis of Piezocatalytic Experiments---------------------65
4.8.1 Surface Modification-----------------------------------65
4.8.2 Dye Degradation & Absorption---------------------------67
4.8.3 Hydrogen Evolution-------------------------------------71
4.8.4 Mechanism----------------------------------------------73
Chapter 5 Conclusion-------------------------------------------75
Chapter 6 Future Work------------------------------------------76
Reference------------------------------------------------------77

[1] C.H. Lee, E.C. Silva, and L. Calderin, “Tungsten Ditelluride: a layered semimetal,” Sci. Rep., 10013 (2015).
[2] F.Schwierz, “Graphene transistors,” Nat. Publ. Gr., 487–496 (2013).
[3] J.Q. He, D.W. He, Y.S. Wang, and H. Zhao, “Photocarrier dynamics in transition metal dichalcogenide alloy Mo0.5W0.5S2,” Opt. Express, 33370–33377 (2015).
[4] N.P. Lõpez, A.L. Elías, and A. Berkdemir,“Photosensor device based on few-layered WS2 films,” Adv. Funct. Mater. 5511–5517 (2013).
[5] J.Guo, X.Chen, Y.Yi, W.Li, and C.Liang, “Layer-controlled synthesis of graphene-like MoS2 from single source organometallic precursor for Li-ion batteries,” RSC Adv., 16716–16720 (2014).
[6] D.K. Nandi, U.K. Sen, D. Choudhury, S. Mitra, and S.K. Sarkar, “Atomic layer deposited MoS2 as a carbon and binder free anode in Li-ion battery,” Electrochim. Acta, 706–713 (2014).
[7] W.Wu, L. Wang, Y. Li, F. Zhang, and L. Lin “Piezoelectricity of single-atomic-layer MoS2 for energy conversion and piezotronics,” Nature, 470–474 (2014).
[8] J. Kibsgaard, Z. Chen, B.N. Reinecke, and T.F. Jaramillo, “Engineering the surface structure of MoS2 to preferentially expose active edge sites for electrocatalysis,” Nat. Mater., 963–969 (2012).
[9] Q. Tang and D. Jiang, “Mechanism of Hydrogen Evolution Reaction on 1T MoS2 from First Principles,” ACS Catal., 01211 (2016).
[10] J. Yang, D. Voiry, S.J. Ahn, and D. Kang, “Two-dimensional hybrid nanosheets of tungsten disulfide and reduced graphene oxide as catalysts for enhanced hydrogen evolution,” Angew. Chemie Int. Ed., 13751–13754 (2013).
[11] N.T. Shelke and B.R. Karche, “Hydrothermal synthesis of WS2/RGO sheet and their application in UV photodetector,” J. Alloys Compd., 298–303 (2015).
[12] Z.Yin, H Li, L Jiang, and Y Shi, “Single-layer MoS2 phototransistors,” ACS Nano, 74–80 (2012).
[13] K. Nakata and A. Fujishima, “TiO2 photocatalysis: Design and applications,” J. Photochem. Photobiol. C Photochem. 169–189 (2012).
[14] J.M. Wu, W.E. Chang, Y.T. Chang, and C.K. Chang, “Piezo-Catalytic Effect on the Enhancement of the Ultra-High Degradation Activity in the Dark by Single- and Few
-Layers MoS2 Nanoflowers,” Adv. Mater., 3718–3725 (2016).
[15] A. Fujishima, X. Zhang, and D.A. Tryk, “TiO2 photocatalysis and related surface phenomena,” Surf. Sci. Rep., 515–582 (2008).
[16] Y. Lai, M. Meng, Y. Yu, X. Wang, and T. Ding, “Photoluminescence and photocatalysis of the flower-like nano-ZnO photocatalysts prepared by a facile hydrothermal method with or without ultrasonic assistance,” Appl. Catal. B Environ., 335–345 (2011).
[17] L.F. Chiang and R.A. Doong, “Enhanced photocatalytic degradation of sulfamethoxazole by visible-light-sensitive TiO2 with low Cu addition,” Sep. Purif. Technol., 1003–1010 (2015).
[18] R. Asahi, T. Morikawa, T. Ohwaki, and Y. Taga, “Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides,” Science, 269–271 (2001).
[19] S.Gu, “Facile synthesis of CeO2 nanoparticle sensitized CdS nanorod photocatalyst with improved visible-light photocatalytic degradation of rhodamine B,” RSC Adv., 79556–79564 (2015).
[20] C. Sun, Y. Fu, Q. Wang, L. Xing, B. Liu, and X. Xue, “Ultrafast piezo-photocatalytic degradation of organic pollutions by Ag2O/tetrapod-ZnO nanostructures under ultrasonic/UV exposure,” RSC Adv., 87446–87453 (2016).
[21] A.H. Zyoud, “CdS-sensitized TiO2 in phenazopyridine photo-degradation: Catalyst efficiency, stability and feasibility assessment,” J. Hazard. Mater. 318–325 (2010).
[22] L. Wang, S. Liu, Z. Wang, Y. Zhou, Y. Qin, and Z.L. Wang, “Piezotronic Effect Enhanced Photocatalysis in Strained Anisotropic ZnO/TiO2 Nanoplatelets via Thermal Stress,” ACS Nano, 2636–2643 (2016).
[23] H. Li, “Enhanced Ferroelectric-Nanocrystal-Based Hybrid Photocatalysis by Ultrasonic-Wave-Generated Piezophototronic Effect,” Nano Lett., 2372– 2379 (2015).
[24] D.Hong, “High Piezo-photocatalytic Efficiency of CuS/ZnO Nanowires Using Both Solar and Mechanical Energy for Degrading Organic Dye,” ACS Appl. Mater. Interfaces, vol. 8, no. 33, pp. 21302–21314, 2016.
[25] M. B.Starr and X.Wang, “Fundamental analysis of piezocatalysis process on the surfaces of strained piezoelectric materials.” Sci. Rep., 2160 (2013).

[26] H.Lin, Z.Wu, Y.Jia, W.Li, R. K.Zheng, and H.Luo, “Piezoelectrically induced mechano-catalytic effect for degradation of dye wastewater through vibrating Pb(Zr0.52Ti0.48)O3 fibers,” Appl. Phys. Lett., 1–5 (2014).
[27] H.P. Komsa and A.V. Krasheninnikov, "Electronic structures and optical properties of realistic transition metal dichalcogenide heterostructures from first principles," Physical Review B, 88 (2013).
[28] K.F. Mak and J. Shan, "Photonics and optoelectronics of 2D semiconductor transition metal dichalcogenides," Nature Photonics, 216 (2016)/
[29] K. Kośmider and J. Fernández-Rossier, "Electronic properties of the MoS2-WS2 heterojunction," Physical Review B, 075451 (2013).
[30] H. Liu, N. Han, and J. Zhao, "Atomistic insight into the oxidation of monolayer transition metal dichalcogenides: from structures to electronic properties," Rsc Advances, 17572-17581 (2015).
[31] K. Kaasbjerg, K. S. Thygesen, and A.P. Jauho, "Acoustic phonon limited mobility in two-dimensional semiconductors: Deformation potential and piezoelectric scattering in monolayer MoS2 from first principles," Physical Review B, 235312 (2013).
[32] Y.Y. Hui, X. Liu, W. Jie, N.Y. Chan, J. Hao, Y.T. Hsu, et al., "Exceptional tunability of band energy in a compressively strained trilayer MoS2 sheet," ACS nano, 7126-7131 (2013)
[33] D. Voiry, J. Yang, and M. Chhowalla, "Recent strategies for improving the catalytic activity of 2D TMD nanosheets toward the hydrogen evolution reaction," Advanced Materials, 6197-6206 (2016).
[34] A. Ambrosi, Z. Sofer, and M. Pumera, "2H→ 1T phase transition and hydrogen evolution activity of MoS2, MoSe2, WS2 and WSe2 strongly depends on the MX2 composition," Chemical Communications, 8450-8453 (2015).
[35] J. Chen, X. J. Wu, L. Yin, B. Li, X. Hong, and Z. Fan,"One‐pot Synthesis of CdS Nanocrystals Hybridized with Single‐Layer Transition‐Metal Dichalcogenide Nanosheets for Efficient Photocatalytic Hydrogen Evolution," Angewandte Chemie International Edition, 1210-1214 (2015).
[36] S. Mao, Z. Wen, S. Ci, X. Guo, K. K. Ostrikov, and J. Chen, "Perpendicularly oriented MoSe2/graphene nanosheets as advanced electrocatalysts for hydrogen evolution," Small, 414-419 (2015).
[37] P. Yu, W. Fu, Q. Zeng, J. Lin, C. Yan, and Z. Lai, "Controllable Synthesis of Atomically Thin Type‐II Weyl Semimetal WTe2 Nanosheets: An Advanced Electrode Material for All‐Solid‐State Flexible Supercapacitors," Advanced Materials, 29 (2017).
[38] L. Cao, S. Yang, W. Gao, Z. Liu, Y. Gong, and L. Ma, "Direct Laser‐Patterned Micro‐Supercapacitors from Paintable MoS2 Films," Small, 2905-2910 (2013).
[39] M. Pumera, Z. Sofer, and A. Ambrosi, "Layered transition metal dichalcogenides for electrochemical energy generation and storage," Journal of Materials Chemistry A, 8981-8987 (2014).
[40] J.H. Lin, Y.H. Tsao, M.H. Wu, T.M. Chou, Z.H. Lin, and J.M. Wu, "Single-and few-layers Mos2 nanocomposite as piezo-catalyst in dark and self-powered active sensor," Nano Energy, 575-581 (2017).
[41] Y. Wu, M. Xu, X. Chen, S. Yang, H. Wu, and J. Pan, "CTAB-assisted synthesis of novel ultrathin MoSe2 nanosheets perpendicular to graphene for the adsorption and photodegradation of organic dyes under visible light," Nanoscale, 440-450 (2016).
[42] K. Santosh, C. Zhang, S. Hong, R. M. Wallace, and K. Cho, "Phase stability of transition metal dichalcogenide by competing ligand field stabilization and charge density wave," 2D Materials, 035019 (2015).
[43] E. Torun, H. Sahin, S. Cahangirov, A. Rubio, and F. Peeters, "Anisotropic electronic, mechanical, and optical properties of monolayer WTe2," Journal of Applied Physics, 074307 (2016).
[44] C.H. Naylor, W.M. Parkin, Z. Gao, H. Kang, M. Noyan, and R.B. Wexler, "Large-area synthesis of high-quality monolayer 1T’-WTe2 flakes," 2D Materials, 021008 (2017).
[45] M. K. Jana, A. Singh, D. J. Late, C. R. Rajamathi, K. Biswas,and C. Felser, "A combined experimental and theoretical study of the structural, electronic and vibrational properties of bulk and few-layer Td-WTe2," Journal of Physics: Condensed Matter, 285401 (2015).
[46] F. Zheng, C. Cai, S. Ge, X. Zhang, X. Liu,and H. Lu, "On the Quantum Spin Hall Gap of Monolayer 1T’‐WTe2," Advanced Materials, 4845-4851 (2016).
[47] Y. Zhang, Y. Liu, and Z. L. Wang, "Fundamental theory of piezotronics," Advanced Materials, 3004-3013 (2011).
[48] J. Song, J. Zhou, and Z. L. Wang, "Piezoelectric and semiconducting coupled powegenerating process of a single ZnO belt/wire. A technology for harvesting electricity from the environment," Nano letters, 1656-1662 (2006).
[49] Z.L. Wang and W.Wu, "Piezotronics and piezo-phototronics: fundamentals and applications," National Science Review, 62-90 (2013).
[50] J.M. Wu, W.E. Chang, Y.T. Chang, and C.K. Chang, "Piezo‐Catalytic Effect on the Enhancement of the Ultra‐High Degradation Activity in the Dark by Single‐and Few‐Layers MoS2 Nanoflowers," Advanced Materials, 3718-3725 (2016).
[51] M.H. Wu, J.T. Lee, Y.J. Chung, M. Srinivaas, and J.M. Wu, "Ultrahigh efficient degradation activity of single-and few-layered MoSe2 nanoflowers in dark by piezo-catalyst effect," Nano Energy, 369-375 (2017).
[52] J. M. Wu, Y.G. Sun, W.E. Chang, and J.T. Lee, "Piezoelectricity induced water splitting and formation of hydroxyl radical from active edge sites of MoS2 nanoflowers," Nano Energy, 372-382 (2018).
[53] C. Dai, E. Qing, Y. Li, Z. Zhou, C. Yang,and X. Tian, "Novel MoSe2 hierarchical microspheres for applications in visible-light-driven advanced oxidation processes," Nanoscale, 19970-19976 (2015).
[54] E. S. Elmolla and M. Chaudhuri, "Photocatalytic degradation of amoxicillin, ampicillin and cloxacillin antibiotics in aqueous solution using UV/TiO2 and UV/H2O2/TiO2 photocatalysis," Desalination, 46-52 (2010).
[55] A.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang1, Y. Zhang1, SV. Dubonos, and I. V. Grigorieva1, “Electric Field Effect in Atomically Thin Carbon Films,” Science, 20–23 (2004).
[56] L. M.Xie, “Two-dimensional transition metal dichalcogenide alloys: preparation characterization and applications,” Nanoscale, 18392–18401 (2015).
[57] K. S.Novoselov, “Two-dimensional gas of massless Dirac fermions in graphene,” Nature, 197–200 (2005).
[58] F.Bonaccorso, Z.Sun, T.Hasan, and A. C.Ferrari, “Graphene Photonics and Optoelectronics,” Nat. Photonics, 611–622 (2010).
[59] A. H.Castro Neto, F.Guinea, N. M. R.Peres, K. S.Novoselov, and A. K.Geim, “The electronic properties of graphene,” Rev. Mod. Phys., 109–162 (2009).
[60] K. S.Novoselov, “Two-dimensional atomic crystals,” Proc. Natl. Acad. Sci. U.S.A., 10451–10453 (2005).
[61] Y.Zhu, “Graphene and graphene oxide: Synthesis, properties, and applications,” Adv. Mater., 3906–3924 (2010).
[62] K. N.Duerloo, M. T.Ong, and E. J.Reed, “Intrinsic Piezoelectricity in 2D Materials,” Environment, 2871–2876 (2012).
[63] J.Zhou, “Large-area and high-quality 2D transition metal telluride,” arXiv,122-113 (2016).
[64] M.-W.Lin., “Room-temperature high on/off ratio in suspended graphene nanoribbon field-effect transistors.” Nanotechnology, 265201 (2011).
[65] X.Li, X.Wang, L.Zhang, S.Lee, and H.Dai, “Chemically Derived Ultramooth Graphene Nanoribbon Semiconductors,” Science, 1229–1232 (2008).
[66] M.Y.Han, B.Özyilmaz, Y.Zhang, and P.Kim, “Energy Band-Gap Engineering of Graphene Nanoribbons,” Phys. Rev. Lett., 206805 (2007).
[67] R.Balog, “Bandgap opening in graphene induced by patterned hydrogen adsorption,” Nat. Mater., 315–319 (2010).
[68] Y.Zhang, “Direct observation of a widely tunable bandgap in bilayer graphene,” Nature, 820–823 (2009).
[69] J.A.Wilson and A. D.Yoffe, “The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties,” Adv. Phys., 193–335 (1969).
[70] C.H.Lee, “Tungsten Ditelluride: a layered semimetal,” Sci. Rep., 10013 (2015).
[71] N.Alem, R.Erni, C.Kisielowski, M. D.Rossell, W.Gannett, and A.Zettl, “Atomically thin hexagonal boron nitride probed by ultrahigh-resolution transmission electron microscopy,” Phys. Rev. B - Condens. Matter Mater. Phys., 1–7 (2009).
[72] C.R.Dean, “Boron nitride substrates for high-quality graphene electronics.” Nat. Nanotechnol., 722–726 (2010).
[73] K.Kalantar-Zadeh, A.Vijayaraghavan, M. H.Ham, H.Zheng, M.Breedon, and M. S.Strano, “Synthesis of atomically thin WO3 sheets from hydrated tungsten trioxide,” Chem. Mater., 5660–5666 (2010).
[74] M.Osada and T.Sasaki,“Two-dimensional dielectric nanosheets: Novel nanoelectronic from nanocrystal building blocks,” Adv. Mater., 210–228 (2012).
[75] S.Bertolazzi, J.Brivio, and A.Kis, “Stretching and breaking of ultrathin MoS2,” ACS Nano, 9703–9709 (2011).
[76] B.Radisavljevic, M. B.Whitwick, and A.Kis, “Integrated circuits and logic operations based on single-layer MoS2,” ACS Nano, 9934–9938 (2011).
[77] A.Splendiani, “Emerging photoluminescence in monolayer MoS2,” Nano Lett., 1271–1275 (2010).
[78] K. F.Mak, C.Lee, J.Hone, J.Shan, and T. F.Heinz, “Atomically thin MoS2: A new direct-gap semiconductor,” Phys. Rev. Lett., 2–5 (2010).
[79] C.Lee, H.Yan, L. E.Brus, T. F.Heinz, J.Hone, and S.Ryu, “Anomalous lattice vibrations of single- and few-layer MoS2,” ACS Nano, 2695–2700 (2010).
[80] W.Lu, “Thin tungsten telluride layer preparation by thermal annealing,” Nanotechnology, 414006 (2016).
[81] G.Eda, H.Yamaguchi, D.Voiry, T.Fujita, M.Chen, and M.Chhowalla, “Photoluminescence from chemically exfoliated MoS2,” Nano Lett., 5111–5116 (2011).
[82] R. A.Gordon, D.Yang, E. D.Crozier, D. T.Jiang, and R. F.Frindt, “Structures of exfoliated single layers of WS2, MoS2, and MoSe2 in aqueous suspension,” Phys. Rev. B - Condens. Matter Mater. Phys., 1254071–1254079 (2002).
[83] G. L.Frey, K. J.Reynolds, R. H.Friend, H.Cohen, and Y.Feldman, “Solution-processed anodes from layer-structure materials for high-efficiency polymer light-emitting diodes,” J. Am. Chem. Soc., 5998–6007 (2003).
[84] M. B.Dines, “Lithium intercalation via -Butyllithium of the layered transition metal dichalcogenides,” Mater. Res. Bull., 287–291 (1975).
[85] P.Joensen, R. F.Frindt, and S. R.Morrison, “Single-layer MoS2,” Mater. Res. Bull., 457–461 (1986).
[86] Y.Kim, Y. I.Jhon, J.Park, J. H.Kim, S.Lee, and Y. M.Jhon, “Anomalous Lattice Dynamics of Mono-, Bi-, and Tri-layer WTe2,” arXiv, 1–26 (2015).
[87] A. Y. S.Eng, A.Ambrosi, Z.Sofer, P.Šimek, and M.Pumera, “Electrochemistry of transition metal dichalcogenides: Strong dependence on the metal-to-chalcogen composition and exfoliation method,” ACS Nano, 12185–12198 (2014).
[88] S.Kirmayer, E.Aharon, E.Dovgolevsky, M.Kalina, and G. L.Frey, “Self-assembled lamellar MoS2, SnS2 and SiO2 semiconducting polymer nanocomposites.” Philos. Trans A. Math. Phys. Eng. Sci., 1489–1508 (2007).
[89] G.Cunningham, “Solvent Exfoliation of Transition Metal Dichalcogenides : Dispersability of Exfoliated Nanosheets Varies Only Weakly Between Compounds Solvent Exfoliation of Transition Metal Dichalcogenides : Dispersability of Exfoliated Nanosheets Varies Only Weakly Bet,” ACS Nano, 3468–3480 (2012).
[90] V.Nicolosi, M.Chhowalla, M. G.Kanatzidis, M. S.Strano, and J. N.Coleman, “Liquid Exfoliation of Layered Materials,” Science, 1226419 (2013).
[91] J. N.Coleman, “Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials,” Science 568–571 (2011).
[92] K.K.Liu, “Growth of large-area and highly crystalline MoS2 thin layers on insulating substrates,” Nano Lett., 1538–1544 (2012).
[93] Y.Zhan, Z.Liu, S.Najmaei, P. M.Ajayan, and J.Lou, “Large-area vapor-phase growth and characterization of MoS2 atomic layers on a SiO2 substrate,” Small, 966–971 (2012).
[94] Y.H.Lee,“Synthesis of large-area MoS2 atomic layers with chemical vapor deposition,” Adv. Mater., 2320–2325 (2012).
[95] C.Jung, “Highly Crystalline CVD-grown Multilayer MoSe2 Thin Film Transistor for Fast Photodetector.,” Sci. Rep., 15313 (2015).
[96] X.Wang, “Chemical vapor deposition growth of crystalline monolayer MoSe2,” ACS Nano, 5125–5131 (2014).
[97] K. M.McCreary, A. T.Hanbicki, G. G.Jernigan, J. C.Culbertson, and B. T.Jonker, “Synthesis of Large-Area WS2 monolayers with Exceptional Photoluminescence,” Sci. Rep., 19159 (2016).
[98] Y.Zhang, “Controlled Growth of High-Quality Monolayer WS 2 Layers on Sapphire,” ACS Nano, 8963–8971 (2013).
[99] K.Xu, Z.Wang, X.Du, M.Safdar, C.Jiang, and J.He, “Atomic-layer triangular WSe2 sheets: synthesis and layer-dependent photoluminescence property,” Nanotechnology, 465705 (2013).
[100] J.Xie, “Defect-rich MoS2 ultrathin nanosheets with additional active edge sites for enhanced electrocatalytic hydrogen evolution,” Adv. Mater., 5807– 5813 (2013).
[101] J.Xie, “Controllable disorder engineering in oxygen-incorporated MoS2 ultrathin nanosheets for efficient hydrogen evolution,” J. Am. Chem. Soc., 17881–17888
(2013).
[102] X.Yang, F.Yang, M.Xue, X.Zhang, and G.Luo, “Hydrothermal synthesis and
tribological properties of MoSe2 nanoflowers,” Nano Lett., 339–342 (2015).
[103] H.Tang, K.Dou, C.Kaun, Q.Kuang, and S.Yang, “MoSe nanosheets and their graphene hybrids: synthesis, characterization and hydrogen evolution reaction studies,” Mater. Chem. A, 360–364 (2014).
[104] S.Ratha and C. S.Rout, “Supercapacitor electrodes based on layered tungsten disulfide- reduced graphene oxide hybrids synthesized by a facile hydrothermal method,” ACS Appl. Mater. Interfaces, 11427–11433 (2013).
[105] W.Li, “Synthesis and tribological properties of Mo-doped WSe2 Nanolamellars,” Cryst. Res. Technol., 876–881 (2012).
[106] M.H. Wu, J.T. Lee, Y.J. Chung, M. Srinivaas, J.M. Wu,”Ultrahigh efficient degradation activity of single- and few-layered MoSe2 nanoflowers in dark by piezo-catalyst effect”, Nano Energy, 369–375 (2017).
[107] M. Srinivaas, Y.C. Hu, Z.H. Lin, S.W. Chan, T.M. Chou, J.M. Wu,”High efficient degradation of dye molecules by PDMS embedded abundant single-layer tungsten disulfide and their antibacterial performance’” Nano Energy, 338–346 (2018).
[108] M.Bouroushian,“Wet-chemical synthesis and applications of non-layer structured two-dimensional nanomaterials,” Electrochemistry of Metal Chalcogenides, 104-108 (2010).
[109] G. A.Somorjai and J. Y.Park, “Colloid science of metal nanoparticle catalysts in 2D and 3D structures. Challenges of nucleation, growth, composition, particle shape, size control and their influence on activity and selectivity,” Top. Catal. 126–135 (2008).
[110] S. G.Kwon and T.Hyeon, “Formation mechanisms of uniform nanocrystals via hot- injection and heat-up methods,” Small, 2685–2702 (2011).
[111] D.V.Talapin, J.-S.Lee, M.V.Kovalenko, and E.V.Shevchenko, “Prospects of Colloidal Nanocsrystals for Electronic and Optoelectronic Applications,” Chem. Rev., 389–458, (2010).
[112] J.VanEmbden, A. S. R.Chesman, and J. J.Jasieniak, “The heat-up synthesis of colloidal nanocrystals,” Chem. Mater., 2246–2285 (2015).
[113] M.Nasilowski, B.Mahler, E.Lhuillier, S.Ithurria, and B.Dubertret, “Two-Dimensional Colloidal Nanocrystals,” Chem. Rev., 10934–10982 (2016).
[114] X.Li, A.Tang, J.Li, L.Guan, G.Dong, and F.Teng, “Heating-up Synthesis of MoS2 Nanosheets and Their Electrical Bistability Performance,” Nanoscale Res. Lett., 171 (2016).
[115] D.Sun, S.Feng, M.Terrones, and R. E.Schaak, “Formation and interlayer decoupling of colloidal MoSe2 nanoflowers,” Chem. Mater., 3167–3175 (2015).
[116] X.Zhou, “Fast colloidal synthesis of scalable Mo-rich hierarchical ultrathin MoSe 2−x nanosheets for high-performance hydrogen evolution,” Nanoscale, 11046–11051 (2014).
[117] B.Mahler, V.Hoepfner, K.Liao, and G. A.Ozin, “Colloidal synthesis of 1T-WS2 and 2H-WS2 nanosheets: Applications for photocatalytic hydrogen evolution,” Am. Chem. Soc., 14121–14127 (2014).
[118] W.Jung, “Colloidal Synthesis of Single-Layer MSe2 (M = Mo, W) Nanosheets via Anisotropic Solution-Phase Growth Approach,” Am. Chem. Soc., 7266–7269 (2015).
[119] P. D.Antunez, D. H.Webber, and R. L.Brutchey, “Solution-Phase Synthesis of Highly Conductive Tungsten Diselenide Nanosheets,” Appl. Chem., 2–7 (2013).
[120] D.Yeh, M.Kim, S.Jeong, J.Han, and J.Cheon, “Chemical synthetic strategy for single- layer transition-metal chalcogenides,” J. Am. Chem. Soc., 14670–14673 (2014).
[121] C.D.Sang, “Well-Defined Colloidal 2D Layered Transition-Metal Chalcogenide Nanocrystals via Generalized Synthetic Protocols,”Small, 1–4 (2012).
[122] Y.Kim, Y. I.Jhon, J.Park, J. H.Kim, S.Lee, and Y. M.Jhon, “Anomalous Lattice Dynamics of Mono-, Bi-, and Tri-layer WTe2,” arXiv. 1–26 (2015).
[123] W.Ren, Z.Ai, F.Jia, L.Zhang, X.Fan, and Z.Zou, “Low temperature preparation and visible light photocatalytic activity of mesoporous carbon-doped crystalline TiO2,” Appl. Catal. B Environ. 138–144 (2007).
[124] D.Mao, “Nonlinear Saturable Absorption of Liquid-Exfoliated Molybdenum / Tungsten Ditelluride Nanosheets,” Small, 1489–1497 (2016).
[125] S. A.Han, R.Bhatia, and S.-W.Kim, “Synthesis, properties and potential applications of two-dimensional transition metal dichalcogenides,” Nano Converg., 17 (2015).
[126] R.Lee, “Transition metal dichalcogenides and beyond: Synthesis, properties, and applications of single- and few-layer nanosheets,” Acc. Chem. Res. 56– 64 (2015).
[127] Z.Zeng, “An effective method for the fabrication of few-layer-thick inorganic nanosheets,” Angew. Chemie - Int. Ed., 9052–9056 (2012).
[128] X.Xue, “Piezo-potential enhanced photocatalytic degradation of organic dye using ZnO nanowires,” Nano Energy, 414–422 (2015).
[129] Z.Zeng, “Single-layer semiconducting nanosheets: High-yield preparation and device fabrication,” Angew. Chemie - Int. Ed., 11093–11097 (2011).
[130] H.K. Hahn, “Crystallographic and noncrystallographic point groups, in International Tables for Crystallography Volume A: Space-group symmetry”, Editor (2002).
[131] A. Kumara, and P.K. Ahluwalia, “Electronic structure of transition metal dichalcogenides monolayers 1H-MX2 (M = Mo, W; X = S, Se, Te) from ab-initio theory: New direct band gap semiconductors,” Eur. Phys. J. B, 18–22 (2012).
[132] Q.Feng, “Growth of large-area 2D MoS2 (1-x) Se2x semiconductor alloys,” Adv. Mater. 2648–2653 (2014).
[133] M. Alyörük, Y. Aierken, D. Çaklr, M. Peeters, and C. Sevik, “Promising Piezoelectric Performance of Single Layer Transition-Metal Dichalcogenides and Dioxides,” J. Phys. Chem. C, 23231–23237 (2015).
[134] X. Wu, “Controlled Growth of High-Quality Monolayer WS2 Layers on Sapphire,” ACS Nano, 8963–8971 (2013).
[135] H.Lin, Z.Wu, Y.Jia, W.Li, R. K.Zheng, and H.Luo, “Piezoelectrically induced mechano-catalytic effect for degradation of dye wastewater through vibrating Pb(Zr0.52Ti0.48)O3 fibers,” Appl. Phys. Lett., 1–5 (2014).
[136] J.M. Wu, W.E. Chang, Y.T. Chang, and C.K. Chang, “Piezo-Catalytic Effect on the Enhancement of the Ultra-High Degradation Activity in the Dark by Single- and Few-Layers MoS2 Nanoflowers,” Adv. Mater., 3718–3725 (2016).
[137] S. Yang, L. Zhang, W. Wang, X. Li, Y. Zhang, and D. Shaoa, “Enhanced H2 evolution based on ultrasoundassisted piezo-catalysis of modified MoS2”, J. Mater. Chem. A, 11909 (2018).
[138] J. A.Champion, “Some properties of (Mo, W) (Se, Te)2,” Appl. Phys. 1035–1037 (1965).
[139] L. H.Brixner, “Preparation and properties of the single crystalline AB2-type selenides and tellurides of niobium, tantalum, molybdenum and tungsten,” Nucl. Chem., 257–263, (1962).
[140] Z. Jiadong, “Large-area and high-quality 2D transition metal telluride,” arXiv (2016).
[141] U. Albert and J. Jacimovic, “Chloride-Driven Chemical Vapor Transport Method for Crystal Growth of Transition Metal Dichalcogenides,” Cryst. Growth Des. 4453–4459, (2013).
[142] W.Lu, “Thin tungsten telluride layer preparation by thermal annealing,” Nanotechnology, 414006 (2016).
[143] M. Dong, “Nonlinear Saturable Absorption of Liquid-Exfoliated Molybdenum / Tungsten Ditelluride Nanosheets,” Small, 1489–1497 (2016).
[144] S.Mazhar, “Electrical Properties of Tungsten-Ditelluride WTe2,” Journal of the Physical Society of Japan, 945–948 (1966).
[145] K. DeFen, W.Lu, D.Shao, and Y.Liu, “Perfect charge compensation in WTe2 for the extraordinary magnetoresistance: From bulk to monolayer,” Xiv. Prepr., 37004 (2014).
[146] Y. Kim, Y. I. Jhon, J. Park, J. H. Kim, S. Lee, and Y. M. Jhon, "Anomalous Raman scattering and lattice dynamics in mono-and few-layer WTe2," Nanoscale, 2309-2316 (2016).
[147] M. K. Jana, A. Singh, D. J. Late, C. R. Rajamathi, K. Biswas, C. Felser, "A combined experimental and theoretical study of the structural, electronic and vibrational properties of bulk and few-layer Td-WTe2," Journal of Physics: Condensed Matter, 285401 (2015).
[148] C. H. Naylor, W. M. Parkin, Z. Gao, H. Kang, M. Noyan, and R. B. Wexler, "Large-area synthesis of high-quality monolayer 1T’-WTe2 flakes," 2D Materials, 021008 (2017).
[149] Y. Sun, K. Fujisawa, M. Terrones, and R. E. Schaak, "Solution synthesis of few-layer WTe2 and Mo x W1− x Te2 nanostructures," Journal of Materials Chemistry C, 11317-11323 (2017).
[150] N. Lu, C. Zhang, C.-H. Lee, J. P. Oviedo, M. A. T. Nguyen, and X. Peng, "Atomic and Electronic Structures of WTe2 Probed by High Resolution Electron Microscopy and ab Initio Calculations," The Journal of Physical Chemistry C, 8364-8369 (2016).
[151] F. Ye, J. Lee, J. Hu, Z. Mao, J. Wei, and P. X. L. Feng, "Environmental Instability
and Degradation of Single‐and Few‐Layer WTe2 Nanosheets in Ambient Conditions," Small, 5802-5808 (2016).
[152] J. Li, M. Hong, L. Sun, W. Zhang, H. Shu, and H. Chang, "Enhanced electrocatalytic hydrogen evolution from large scale, facile prepared, highly crystalline WTe2 nanoribbon with Weyl semimetallic phase," ACS applied materials & interfaces, 1064 (2017).
[153] D. S. Dalavi, R. S. Devan, R. A. Patil, R. S. Patil, Y.-R. Ma, and S. B. Sadal, "Efficient electrochromic performance of nanoparticulate WO 3 thin films," Journal of Materials Chemistry C, 3722-3728 (2013).
[154] C. An, J. Wang, W. Jiang, M. Zhang, X. Ming, and S. Wang, "Strongly visible-light responsive plasmonic shaped AgX: Ag (X= Cl, Br) nanoparticles for reduction of CO2 to methanol," Nanoscale, 5646-5650 (2012).
[155] H. Kanai, M. Yoshiki, M. Hayashi, R. Kuwae, and Y. Yamashita, "Grain‐Boundary‐Phase Identification of a Lead‐Based Relaxor by X‐ray Photoelectron Spectroscopy," Journal of the American Ceramic Society, 2229-2231 (1994).
[156] H. Ogi, M. Fukunaga, M. Hirao, and H. Ledbetter, "Elastic constants, internal friction, and piezoelectric coefficient of α− TeO2," Physical Review B, 024104 (2004).
[157] C. Dai, E. Qing, Y. Li, Z. Zhou, C. Yang, and X. Tian, "Novel MoSe2 hierarchical microspheres for applications in visible-light-driven advanced oxidation processes," Nanoscale, 19970-19976 (2015).
[158] S. Li, I. Timoshkin, M. Maclean, S. MacGregor, M. Wilson, and M. Given, "Fluorescence detection of hydroxyl radicals in water produced by atmospheric pulsed discharges," IEEE Transactions on Dielectrics and electrical insulation, 1856-1865 (2015).
[159] T. Charbouillot, M. Brigante, G. Mailhot, P. R. Maddigapu, C. Minero, and D. Vione, "Performance and selectivity of the terephthalic acid probe for OH as a function of temperature, pH and composition of atmospherically relevant aqueous media," Journal of Photochemistry and Photobiology A: Chemistry, 70-76 (2011).
[160] S.Chang, P.Y. Yang, C.M. Lai, S.C. Lu, G.A. Li, W.C. Chang and H.Y. Tuan, “Synthesis of Cu/ZnO core/shell nanocomposites and their use as efficient photocatalysts,” CrystEngComm, 616–621 (2016).