Abstract
Chemical vapor deposition (CVD) has been proved to be the most useful method to produce two-dimensional (2D) materials, including tungsten disulfide (WS2). However, the existence of inhomogeneity of strain, doping, and defects in the CVD-grown WS2 monolayers may significantly influence the optical and electronic properties of the materials, thus affecting their device applications. In this work, we systematically characterized the inhomogeneity of strain, doping, and nonradiative defect centers in mesoscopic-size, triangular-shape monolayer WS2 grown by CVD on sapphire substrate by using spatially resolved micro-Raman and photoluminescence (PL) spectroscopy. We performed correlative analyses on the variations of the pertinent spectral parameters (i.e., peak position, intensity, and full width at half maximum) of Raman and PL signatures in two physical scales: (1) the complete-data-set level, including the data of the whole sample, and (2) the sub-data-set level for individual special regions (e.g., apexes, edges, center) that exhibit distinctly different strain, doping, and defect states. This study reveals and explains the inhomogeneous strain, doping, and defects across the WS2 monolayer. Additionally, we find the inhomogeneity substantially diminishes when a mesoscopic-size triangle structure expands into a continuous film. Our work demonstrates that the correlative analyses, supported with physics insights, can offer comprehensive understanding on the underlying mechanisms of the inhomogeneity and guidance for optimizing the growth process and device processing of 2D materials.
摘要
化学气相沉积(CVD)已被证明是生产二维材料(包括二硫化钨(WS2))最有效的方法. 然而, CVD生长的WS2单层中存在的应变、 掺杂和缺陷的不均匀性会显著影响材料的光学和电子特性, 从而影响其器件应用. 在本研究中, 我们通过CVD方法在蓝宝石衬底上生长了介观尺寸的三角形单层WS2, 并利用空间分辨的显微拉曼和光致发光(PL)光谱技术系统地表征了单层WS2中的应变、 掺杂和非辐射缺陷中心的不均匀性. 我们从全域(整个单层WS2三角形)和分区域(如顶点、 边缘、 中心)两个维度对其拉曼和PL光谱的相关参数(即峰值位置、 强度和半峰宽)随位置的变化进行了相关性分析, 发现单层WS2三角形的不同区域往往表现出明显不同的应变、 掺杂和缺陷状态. 这项研究揭示并解释了单层WS2应变、 掺杂和缺陷的不均匀性. 此外, 我们发现当介观尺寸的三角形结构扩展到连续薄膜时, 不均匀性大大降低. 我们的工作表明, 对光谱特征的相关性分析并辅以对物理机制的了解有助于全面理解材料生长带来的不均匀性, 并为优化二维材料的生长过程和器件加工提供指导.
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References
Fu Q, Han J, Wang X, et al. 2D transition metal dichalcogenides: Design, modulation, and challenges in electrocatalysis. Adv Mater, 2021, 33: 1907818
Chen B, Chao D, Liu E, et al. Transition metal dichalcogenides for alkali metal ion batteries: Engineering strategies at the atomic level. Energy Environ Sci, 2020, 13: 1096–1131
Liang Q, Zhang Q, Zhao X, et al. Defect engineering of two-dimensional transition-metal dichalcogenides: Applications, challenges, and opportunities. ACS Nano, 2021, 15: 2165–2181
Partoens B, Peeters FM. From graphene to graphite: Electronic structure around the K point. Phys Rev B, 2006, 74: 075404
Wang C, Yang F, Gao Y. The highly-efficient light-emitting diodes based on transition metal dichalcogenides: From architecture to performance. Nanoscale Adv, 2020, 2: 4323–4340
Phan NAN, Noh H, Kim J, et al. Enhanced performance of WS2 field-effect transistor through mono and bilayer h-BN tunneling contacts. Small, 2022, 18: 2105753
Pei Y, Chen R, Xu H, et al. Recent progress about 2D metal dichalcogenides: Synthesis and application in photodetectors. Nano Res, 2021, 14: 1819–1839
Ozdemir B, Barone V. Thickness dependence of solar cell efficiency in transition metal dichalcogenides MX2 (M: Mo, W; X: S, Se, Te). Sol Energy Mater Sol Cells, 2020, 212: 110557
Zhang Q, Mei L, Cao X, et al. Intercalation and exfoliation chemistries of transition metal dichalcogenides. J Mater Chem A, 2020, 8: 15417–15444
Yu Y, Li C, Liu Y, et al. Controlled scalable synthesis of uniform, high-quality monolayer and few-layer MoS2 films. Sci Rep, 2013, 3: 1866
Su L, Zhang Y, Yu Y, et al. Dependence of coupling of quasi 2-D MoS2 with substrates on substrate types, probed by temperature dependent Raman scattering. Nanoscale, 2014, 6: 4920–4927
Su L, Yu Y, Cao L, et al. Effects of substrate type and material-substrate bonding on high-temperature behavior of monolayer WS2. Nano Res, 2015, 8: 2686–2697
Buscema M, Steele GA, van der Zant HSJ, et al. The effect of the substrate on the Raman and photoluminescence emission of single-layer MoS2. Nano Res, 2014, 7: 561–571
Yu Y, Yu Y, Xu C, et al. Engineering substrate interactions for high luminescence efficiency of transition-metal dichalcogenide monolayers. Adv Funct Mater, 2016, 26: 4733–4739
Su L, Yu Y, Cao L, et al. In situ monitoring of the thermal-annealing effect in a monolayer of MoS2. Phys Rev Appl, 2017, 7: 034009
Tang L, Tan J, Nong H, et al. Chemical vapor deposition growth of two-dimensional compound materials: Controllability, material quality, and growth mechanism. Acc Mater Res, 2021, 2: 36–47
Qin Z, Loh L, Wang J, et al. Growth of Nb-doped monolayer WS2 by liquid-phase precursor mixing. ACS Nano, 2019, 13: 10768–10775
Zhang P, Cheng N, Li M, et al. Transition-metal substitution-induced lattice strain and electrical polarity reversal in monolayer WS2. ACS Appl Mater Interfaces, 2020, 12: 18650–18659
Gutiérrez HR, Perea-López N, Elías AL, et al. Extraordinary room-temperature photoluminescence in triangular WS2 monolayers. Nano Lett, 2013, 13: 3447–3454
Shang J, Shen X, Cong C, et al. Observation of excitonic fine structure in a 2D transition-metal dichalcogenide semiconductor. ACS Nano, 2015, 9: 647–655
Wang XH, Ning JQ, Su ZC, et al. Photoinduced doping and photoluminescence signature in an exfoliated WS2 monolayer semiconductor. RSC Adv, 2016, 6: 27677–27681
Wang Y, Cong C, Yang W, et al. Strain-induced direct–indirect bandgap transition and phonon modulation in monolayer WS2. Nano Res, 2015, 8: 2562–2572
Tongay S, Suh J, Ataca C, et al. Defects activated photoluminescence in two-dimensional semiconductors: Interplay between bound, charged and free excitons. Sci Rep, 2013, 3: 2657
Zhou W, Zou X, Najmaei S, et al. Intrinsic structural defects in monolayer molybdenum disulfide. Nano Lett, 2013, 13: 2615–2622
Kim JY, Gelczuk Ł, Polak MP, et al. Experimental and theoretical studies of native deep-level defects in transition metal dichalcogenides. npj 2D Mater Appl, 2022, 6: 75
Liu Z, Amani M, Najmaei S, et al. Strain and structure heterogeneity in MoS2 atomic layers grown by chemical vapour deposition. Nat Commun, 2014, 5: 5246
Lu AY, Martins LGP, Shen PC, et al. Unraveling the correlation between Raman and photoluminescence in monolayer MoS2 through machine-learning models. Adv Mater, 2022, 34: 2202911
Yu Y, Hu S, Su L, et al. Equally efficient interlayer exciton relaxation and improved absorption in epitaxial and nonepitaxial MoS2/WS2 heterostructures. Nano Lett, 2015, 15: 486–491
Kotsakidis JC, Zhang Q, Vazquez de Parga AL, et al. Oxidation of monolayer WS2 in ambient is a photoinduced process. Nano Lett, 2019, 19: 5205–5215
Berkdemir A, Gutiérrez HR, Botello-Méndez AR, et al. Identification of individual and few layers of WS2 using Raman spectroscopy. Sci Rep, 2013, 3: 1755
Zhu B, Chen X, Cui X. Exciton binding energy of monolayer WS2. Sci Rep, 2015, 5: 9218
Dadgar AM, Scullion D, Kang K, et al. Strain engineering and Raman spectroscopy of monolayer transition metal dichalcogenides. Chem Mater, 2018, 30: 5148–5155
Chakraborty B, Bera A, Muthu DVS, et al. Symmetry-dependent phonon renormalization in monolayer MoS2 transistor. Phys Rev B, 2012, 85: 161403
Rathod UP, Egede J, Voevodin AA, et al. Extrinsic p-type doping of few layered WS2 films with niobium by pulsed laser deposition. Appl Phys Lett, 2018, 113: 062106
Wang F, Li S, Bissett MA, et al. Strain engineering in monolayer WS2 and WS2 nanocomposites. 2D Mater, 2020, 7: 045022
Peimyoo N, Yang W, Shang J, et al. Chemically driven tunable light emission of charged and neutral excitons in monolayer WS2. ACS Nano, 2014, 8: 11320–11329
Yim WM, Paff RJ. Thermal expansion of AlN, sapphire, and silicon. J Appl Phys, 1974, 45: 1456–1457
Zobeiri H, Xu S, Yue Y, et al. Effect of temperature on Raman intensity of nm-thick WS2: Combined effects of resonance Raman, optical properties, and interface optical interference. Nanoscale, 2020, 12: 6064–6078
Wang S, Robertson A, Warner JH. Atomic structure of defects and dopants in 2D layered transition metal dichalcogenides. Chem Soc Rev, 2018, 47: 6764–6794
Zhang F, Lu Y, Schulman DS, et al. Carbon doping of WS2 monolayers: Bandgap reduction and p-type doping transport. Sci Adv, 2019, 5: eaav5003
Iqbal MW, Shahzad K, Hussain G, et al. Gate dependent phonon shift in tungsten disulfide (WS2) field effect transistor. Mater Res Express, 2019, 6: 115909
del Corro E, Botello-Méndez A, Gillet Y, et al. Atypical exciton–phonon interactions in WS2 and WSe2 monolayers revealed by resonance Raman spectroscopy. Nano Lett, 2016, 16: 2363–2368
Feng J, Qian X, Huang CW, et al. Strain-engineered artificial atom as a broad-spectrum solar energy funnel. Nat Photon, 2012, 6: 866–872
Chen Q, McKeon BS, Zhang SY, et al. Impact of individual structural defects in GaAs solar cells: A correlative and in operando investigation of signatures, structures, and effects. Adv Opt Mater, 2021, 9: 2001487
Lee C, Jeong BG, Yun SJ, et al. Unveiling defect-related Raman mode of monolayer WS2 via tip-enhanced resonance Raman scattering. ACS Nano, 2018, 12: 9982–9990
Shu H, Chen X, Ding F. The edge termination controlled kinetics in graphene chemical vapor deposition growth. Chem Sci, 2014, 5: 4639–4645
Liu Z, Liu B, Ren F, et al. Atomic-scale mechanism of spontaneous polarity inversion in AlN on nonpolar sapphire substrate grown by MOCVD. Small, 2022, 18: 2200057
Duan X, Wang C, Pan A, et al. Two-dimensional transition metal dichalcogenides as atomically thin semiconductors: Opportunities and challenges. Chem Soc Rev, 2015, 44: 8859–8876
Acknowledgements
Su L acknowledges the support of the Natural Science Foundation of Zhejiang Province (LQ21A050004), and Zhang Y acknowledges the support of the Bissell Distinguished Professorship.
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Author contributions Zhang Y conceived the idea and supervised this work. Yu Y and Cao L performed the CVD-growth of the samples. Su L conducted the experiments and analyzed the data. Su L and Zhang Y wrote the paper with support from Yu Y and Cao L. All authors contributed to the general discussion.
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Liqin Su is an assistant professor at the College of Optical and Electronic Technology, China Jiliang University. He received his PhD degree in 2015 from the University of North Carolina at Charlotte. His research interests focus on two-dimensional materials and optical spectroscopy.
Yong Zhang is a Bissell Distinguished Professor at the Electrical and Computer Engineering Department, UNC-Charlotte. He received his BS and MS degrees from Xiamen University and PhD degree from Dartmouth College. He was a postdoc and later a Senior Scientist at the National Renewable Energy Laboratory. His research interests include electronic and optical properties of semiconductors, organic-inorganic hybrid materials, impurity and defects in semiconductors, and novel materials and device architectures for applications in optoelectronics, energy, and electronic-photonic integrated circuits.
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Su, L., Yu, Y., Cao, L. et al. Correlative spectroscopic investigations of the mechanisms of inhomogeneity in CVD-grown monolayer WS2. Sci. China Mater. 66, 3949–3957 (2023). https://doi.org/10.1007/s40843-023-2616-x
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DOI: https://doi.org/10.1007/s40843-023-2616-x