單元素層狀二維(2D)材料，因優異特性，如:拓樸絕緣及光電特性，以及獨特的異向性特徵，吸引了科學家的注意。近年，單元素二維材料，如矽烯(Silicene)、磷烯(Phosphorene)，已經成功被製備出。碲(Tellurium)由於有Z軸的優選性，過往以奈米線型態存在，直到2017年首次成功利用化學溶液法，製造出二維結構，並展現出許多優異半導體特性，如可調式能隙、高載子遷移率、光響應性以及環境穩定性，但也伴隨著無法大面積製造、尺寸不均以及耗時等問題。
本研究利用化學氣相沉積法(CVD)，搭配氯化物輔助製程的進行，成功在各種基板上沉積出層狀碲薄片。實驗中發現，兩種前驅物TeCl4和TeO2的比例對於碲合成出的形貌有很直接的影響，TeCl4的量多時，形貌以一維為主，唯有特定比例才有碲烯的成長。本研究利用氯化物可以控制化物易於達到高飽和蒸汽壓的特性，成功製備材料於無論是在單晶基板或非晶型基板，尺寸可到8 µm，並達到10奈米到70奈米的厚度控制，並展現出長達一個月的穩定度。此製程方法可以直接應用在各式基板，並省略可能損害到材料的轉移步驟，以進行後續電晶體以及光電感測器的應用，達到縮短製程時間及降低成本的目的，並期待實現在其他單元素材料中，以探索更多半導體材料特性。

In this topic, we introduce new growth approach that enable to directly synthesize Te nanoflake on anbitrary substrates with the aid of chloride. Moreover, Systematic studies of growth at varying material powder ratio or flow rates demonstrate the control in thickness from over 70 nm down to 10 nm. Highly air-stability can also be found via unchanged layered-structure and good crystalline. We also investigate the thermal property of tellurene by using Scanning Thermal Microscope (SThM). The surprising thermal mapping shows the thermal property will significantly affected by morphology and has a minor connection with thickness under 30 nm. The chloride-assisted strategy may provide a new approach for synthesizing other high quality 2D elementary materials.

[1] L. Zhou et al., "Role of Molecular Sieves in the CVD Synthesis of Large‐Area 2D MoTe2," Adv. Funct. Mater., vol. 27, no. 3, p. 1603491, 2017.
[2] X. Xu et al., "Scaling-up Atomically Thin Coplanar Semiconductor–Metal Circuitry via Phase Engineered Chemical Assembly," Nano letters, vol. 19, no. 10, pp. 6845-6852, 2019.
[3] M. J. Allen, V. C. Tung, and R. B. Kaner, "Honeycomb carbon: a review of graphene," Chemical reviews, vol. 110, no. 1, pp. 132-145, 2010.
[4] K. S. Novoselov et al., "Electric field effect in atomically thin carbon films," science, vol. 306, no. 5696, pp. 666-669, 2004.
[5] W. Cai et al., "Thermal transport in suspended and supported monolayer graphene grown by chemical vapor deposition," Nano letters, vol. 10, no. 5, pp. 1645-1651, 2010.
[6] B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti, and A. Kis, "Single-layer MoS 2 transistors," Nature nanotechnology, vol. 6, no. 3, pp. 147-150, 2011.
[7] N. R. Glavin et al., "Emerging applications of elemental 2D materials," Advanced Materials, vol. 32, no. 7, p. 1904302, 2020.
[8] L. Li et al., "Black phosphorus field-effect transistors," Nature nanotechnology, vol. 9, no. 5, p. 372, 2014.
[9] S. Balendhran, S. Walia, H. Nili, S. Sriram, and M. Bhaskaran, "Elemental analogues of graphene: silicene, germanene, stanene, and phosphorene," small, vol. 11, no. 6, pp. 640-652, 2015.
[10] M. Houssa, E. Scalise, K. Sankaran, G. Pourtois, V. Afanas’ Ev, and A. Stesmans, "Electronic properties of hydrogenated silicene and germanene," Applied Physics Letters, vol. 98, no. 22, p. 223107, 2011.
[11] C. L. Kane and E. J. Mele, "Quantum spin Hall effect in graphene," Physical review letters, vol. 95, no. 22, p. 226801, 2005.
[12] B. A. Bernevig, T. L. Hughes, and S.-C. Zhang, "Quantum spin Hall effect and topological phase transition in HgTe quantum wells," science, vol. 314, no. 5806, pp. 1757-1761, 2006.
[13] C.-C. Liu, W. Feng, and Y. Yao, "Quantum spin Hall effect in silicene and two-dimensional germanium," Physical review letters, vol. 107, no. 7, p. 076802, 2011.
[14] L. Meng et al., "Buckled silicene formation on Ir (111)," Nano letters, vol. 13, no. 2, pp. 685-690, 2013.
[15] L. Tao et al., "Silicene field-effect transistors operating at room temperature," Nature nanotechnology, vol. 10, no. 3, pp. 227-231, 2015.
[16] C. Grazianetti et al., "Silicon nanosheets: crossover between multilayer silicene and diamond-like growth regime," ACS nano, vol. 11, no. 3, pp. 3376-3382, 2017.
[17] F.-f. Zhu et al., "Epitaxial growth of two-dimensional stanene," Nature materials, vol. 14, no. 10, pp. 1020-1025, 2015.
[18] J. Deng et al., "Epitaxial growth of ultraflat stanene with topological band inversion," Nature materials, vol. 17, no. 12, pp. 1081-1086, 2018.
[19] Q. Wei and X. Peng, "Superior mechanical flexibility of phosphorene and few-layer black phosphorus," Applied Physics Letters, vol. 104, no. 25, p. 251915, 2014.
[20] H. Liu et al., "Phosphorene: an unexplored 2D semiconductor with a high hole mobility," ACS nano, vol. 8, no. 4, pp. 4033-4041, 2014.
[21] M. A. Huber et al., "Femtosecond photo-switching of interface polaritons in black phosphorus heterostructures," Nature nanotechnology, vol. 12, no. 3, pp. 207-211, 2017.
[22] A. N. Abbas et al., "Black phosphorus gas sensors," ACS nano, vol. 9, no. 5, pp. 5618-5624, 2015.
[23] J. Sun et al., "Entrapment of polysulfides by a black‐phosphorus‐modified separator for lithium–sulfur batteries," Advanced materials, vol. 28, no. 44, pp. 9797-9803, 2016.
[24] A. Castellanos-Gomez et al., "Isolation and characterization of few-layer black phosphorus," 2D Materials, vol. 1, no. 2, p. 025001, 2014.
[25] Z. Guo et al., "From black phosphorus to phosphorene: basic solvent exfoliation, evolution of Raman scattering, and applications to ultrafast photonics," Adv. Funct. Mater., vol. 25, no. 45, pp. 6996-7002, 2015.
[26] W. Zhao, Z. Xue, J. Wang, J. Jiang, X. Zhao, and T. Mu, "Large-scale, highly efficient, and green liquid-exfoliation of black phosphorus in ionic liquids," ACS applied materials & interfaces, vol. 7, no. 50, pp. 27608-27612, 2015.
[27] F. Xia, H. Wang, and Y. Jia, "Rediscovering black phosphorus as an anisotropic layered material for optoelectronics and electronics," Nature communications, vol. 5, no. 1, pp. 1-6, 2014.
[28] J. Wu et al., "Colossal ultraviolet photoresponsivity of few-layer black phosphorus," ACS nano, vol. 9, no. 8, pp. 8070-8077, 2015.
[29] M. Engel, M. Steiner, and P. Avouris, "Black phosphorus photodetector for multispectral, high-resolution imaging," Nano letters, vol. 14, no. 11, pp. 6414-6417, 2014.
[30] S. Zhang, Z. Yan, Y. Li, Z. Chen, and H. Zeng, "Atomically thin arsenene and antimonene: semimetal–semiconductor and indirect–direct band‐gap transitions," Angewandte Chemie, vol. 127, no. 10, pp. 3155-3158, 2015.
[31] S. Zhang et al., "Semiconducting group 15 monolayers: a broad range of band gaps and high carrier mobilities," Angewandte Chemie, vol. 128, no. 5, pp. 1698-1701, 2016.
[32] Y. Chen et al., "Black arsenic: a layered semiconductor with extreme in‐plane anisotropy," Advanced Materials, vol. 30, no. 30, p. 1800754, 2018.
[33] M. Zhong et al., "Thickness‐dependent carrier transport characteristics of a new 2D elemental semiconductor: black arsenic," Adv. Funct. Mater., vol. 28, no. 43, p. 1802581, 2018.
[34] Y. Hu et al., "van der Waals epitaxial growth and interfacial passivation of two-dimensional single-crystalline few-layer gray arsenic nanoflakes," Chemistry of Materials, vol. 31, no. 12, pp. 4524-4535, 2019.
[35] A. Koma, "Van der Waals epitaxy—a new epitaxial growth method for a highly lattice-mismatched system," Thin Solid Films, vol. 216, no. 1, pp. 72-76, 1992.
[36] L. A. Walsh and C. L. Hinkle, "van der Waals epitaxy: 2D materials and topological insulators," Applied Materials Today, vol. 9, pp. 504-515, 2017.
[37] G. Pizzi, M. Gibertini, E. Dib, N. Marzari, G. Iannaccone, and G. Fiori, "Performance of arsenene and antimonene double-gate MOSFETs from first principles," Nature communications, vol. 7, p. 12585, 2016.
[38] Y. Du et al., "One-dimensional van der Waals material tellurium: Raman spectroscopy under strain and magneto-transport," Nano letters, vol. 17, no. 6, pp. 3965-3973, 2017.
[39] J. Chen, Y. Dai, Y. Ma, X. Dai, W. Ho, and M. Xie, "Ultrathin β-tellurium layers grown on highly oriented pyrolytic graphite by molecular-beam epitaxy," Nanoscale, vol. 9, no. 41, pp. 15945-15948, 2017.
[40] Z. Liu et al., "Shape-controlled synthesis and growth mechanism of one-dimensional nanostructures of trigonal tellurium," New Journal of Chemistry, vol. 27, no. 12, pp. 1748-1752, 2003.
[41] H.-S. Qian, S.-H. Yu, J.-Y. Gong, L.-B. Luo, and L.-f. Fei, "High-quality luminescent tellurium nanowires of several nanometers in diameter and high aspect ratio synthesized by a poly (vinyl pyrrolidone)-assisted hydrothermal process," Langmuir, vol. 22, no. 8, pp. 3830-3835, 2006.
[42] Y. Wang et al., "Field-effect transistors made from solution-grown two-dimensional tellurene," Nature Electronics, vol. 1, no. 4, pp. 228-236, 2018, doi: 10.1038/s41928-018-0058-4.
[43] W.-J. Lan, S.-H. Yu, H.-S. Qian, and Y. Wan, "Dispersibility, stabilization, and chemical stability of ultrathin tellurium nanowires in acetone: morphology change, crystallization, and transformation into TeO2 in different solvents," Langmuir, vol. 23, no. 6, pp. 3409-3417, 2007.
[44] C. Zhao et al., "Evaporated tellurium thin films for p-type field-effect transistors and circuits," Nature nanotechnology, vol. 15, no. 1, pp. 53-58, 2020.
[45] X. Zhang et al., "Hydrogen-Assisted Growth of Ultrathin Te Flakes with Giant Gate-Dependent Photoresponse," (in English), Adv. Funct. Mater., Article vol. 29, no. 49, p. 9, Dec 2019, Art no. 1906585, doi: 10.1002/adfm.201906585.
[46] L. Tong et al., "Stable mid-infrared polarization imaging based on quasi-2D tellurium at room temperature," Nature communications, vol. 11, no. 1, pp. 1-10, 2020.
[47] A. A. Balandin et al., "Superior thermal conductivity of single-layer graphene," Nano letters, vol. 8, no. 3, pp. 902-907, 2008.
[48] Z. Luo et al., "Measurement of in-plane thermal conductivity of ultrathin films using micro-Raman spectroscopy," Nanoscale and Microscale Thermophysical Engineering, vol. 18, no. 2, pp. 183-193, 2014.
[49] S. Huang et al., "Anisotropic thermal conductivity in 2D tellurium," 2D Materials, vol. 7, no. 1, p. 015008, 2019.
[50] D. Buckley et al., "Anomalous low thermal conductivity of atomically thin InSe probed by scanning thermal microscopy," Adv. Funct. Mater., p. 2008967.
[51] X. Xu et al., "Length-dependent thermal conductivity in suspended single-layer graphene," Nature communications, vol. 5, no. 1, pp. 1-6, 2014.
[52] L. Cui et al., "Study of radiative heat transfer in Ångström-and nanometre-sized gaps," Nature communications, vol. 8, no. 1, pp. 1-9, 2017.
[53] G. Wielgoszewski et al., "Microfabricated resistive high-sensitivity nanoprobe for scanning thermal microscopy," Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, vol. 28, no. 6, pp. C6N7-C6N11, 2010.
[54] Y. Zhang, W. Zhu, F. Hui, M. Lanza, T. Borca‐Tasciuc, and M. Muñoz Rojo, "A review on principles and applications of scanning thermal microscopy (SThM)," Adv. Funct. Mater., vol. 30, no. 18, p. 1900892, 2020.
[55] Q. Wang, M. Safdar, K. Xu, M. Mirza, Z. Wang, and J. He, "Van der Waals epitaxy and photoresponse of hexagonal tellurium nanoplates on flexible mica sheets," ACS nano, vol. 8, no. 7, pp. 7497-7505, 2014.
[56] R. A. Yadav, N. Padma, S. Sen, K. Chandrakumar, H. Donthula, and R. Rao, "Anomalous vibrational behavior of two dimensional tellurium: Layer thickness and temperature dependent Raman spectroscopic study," Applied Surface Science, vol. 531, p. 147303, 2020.
[57] E. Bianco et al., "Large-area ultrathin Te films with substrate-tunable orientation," Nanoscale, vol. 12, no. 23, pp. 12613-12622, 2020.
[58] D. K. Sang et al., "Electronic and optical properties of two-dimensional tellurene: from first-principles calculations," Nanomaterials, vol. 9, no. 8, p. 1075, 2019.
[59] J. Cao, M. Safdar, Z. Wang, and J. He, "High-performance flexible supercapacitor electrodes based on Te nanowire arrays," Journal of Materials Chemistry A, vol. 1, no. 34, pp. 10024-10029, 2013.
[60] M. Safdar et al., "Site-specific nucleation and controlled growth of a vertical tellurium nanowire array for high performance field emitters," Nanotechnology, vol. 24, no. 18, p. 185705, 2013.
[61] B. Wu et al., "Self-organized graphene crystal patterns," NPG Asia Materials, vol. 5, no. 2, pp. e36-e36, 2013.
[62] X. Zhai et al., "Enhanced optoelectronic performance of CVD-grown metal–semiconductor NiTe2/MoS2 heterostructures," ACS applied materials & interfaces, vol. 12, no. 21, pp. 24093-24101, 2020.
[63] S. B. Abu, V. Moiseyenko, M. Dergachov, A. Yevchik, and G. Dovbeshko, "Manifestation of metastable gamma-TeO2 phase in the Raman spectrum of crystals grown in synthetic opal pores," Ukrainian journal of physical optics, no. 14,№ 3, pp. 119-124, 2013.
[64] L. D'Alessio, D. Ferro, and V. Piacente, "Sublimation study of tellurium tetrachloride and tetraiodide from their vapour pressure measurements," Journal of alloys and compounds, vol. 209, no. 1-2, pp. 207-212, 1994.
[65] F. Arab, M. Mousavi-Kamazani, and M. Salavati-Niasari, "Facile sonochemical synthesis of tellurium and tellurium dioxide nanoparticles: Reducing Te (IV) to Te via ultrasonic irradiation in methanol," Ultrasonics sonochemistry, vol. 37, pp. 335-343, 2017.
[66] C. Arnaboldi et al., "Production of high purity TeO2 single crystals for the study of neutrinoless double beta decay," Journal of Crystal Growth, vol. 312, no. 20, pp. 2999-3008, 2010.
[67] Z. Gao, F. Tao, and J. Ren, "Unusually low thermal conductivity of atomically thin 2D tellurium," Nanoscale, vol. 10, no. 27, pp. 12997-13003, 2018.
[68] S. Lin, W. Li, Z. Chen, J. Shen, B. Ge, and Y. Pei, "Tellurium as a high-performance elemental thermoelectric," Nature communications, vol. 7, no. 1, pp. 1-6, 2016.
[69] C. Metzke et al., "On the limits of scanning thermal microscopy of ultrathin films," Materials, vol. 13, no. 3, p. 518, 2020.
[70] N.-W. Park, S.-I. Park, and S.-K. Lee, "Effect of thickness of single-phase antimony and tellurium thin films on their thermal conductivities," Journal of nanoscience and nanotechnology, vol. 15, no. 9, pp. 6729-6733, 2015.