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Uniform nucleation and epitaxy of bilayer molybdenum disulfide on sapphire

Nature volume 605, pages 69–75 (2022)Cite this article

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Abstract

Two-dimensional transition-metal dichalcogenides (TMDs) are of interest for beyond-silicon electronics1,2. It has been suggested that bilayer TMDs, which combine good electrostatic control, smaller bandgap and higher mobility than monolayers, could potentially provide improvements in the energy-delay product of transistors3,4,5. However, despite advances in the growth of monolayer TMDs6,7,8,9,10,11,12,13,14, the controlled epitaxial growth of multilayers remains a challenge15. Here we report the uniform nucleation (>99%) of bilayer molybdenum disulfide (MoS2) on c-plane sapphire. In particular, we engineer the atomic terrace height on c-plane sapphire to enable an edge-nucleation mechanism and the coalescence of MoS2 domains into continuous, centimetre-scale films. Fabricated field-effect transistor (FET) devices based on bilayer MoS2 channels show substantial improvements in mobility (up to 122.6 cm2 V−1 s−1) and variation compared with FETs based on monolayer films. Furthermore, short-channel FETs exhibit an on-state current of 1.27 mA μm−1, which exceeds the 2028 roadmap target for high-performance FETs16.

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Fig. 1: Thermodynamic analysis on the monolayer versus bilayer MoS2 growth on c-plane sapphire.
Fig. 2: Step-edge nucleation of bilayer MoS2 on c-plane sapphire.
Fig. 3: Uniform growth of bilayer MoS2 domains and continuous films.
Fig. 4: The epitaxial relationship between bilayer MoS2 and c-plane sapphire.
Fig. 5: The interlayer stacking of bilayer MoS2.
Fig. 6: FET performance of bilayer MoS2.

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References

  1. Akinwande, D. et al. Graphene and two-dimensional materials for silicon technology. Nature 573, 507–518 (2019).

    Article  ADS  CAS  PubMed  Google Scholar 

  2. Liu, C. et al. Two-dimensional materials for next-generation computing technologies. Nat. Nanotechnol. 15, 545–557 (2020).

    Article  ADS  CAS  PubMed  Google Scholar 

  3. Szabó, Á., Rhyner, R. & Luisier, M. Ab initio simulation of single- and few-layer MoS2 transistors: effect of electron-phonon scattering. Phys. Rev. B 92, 035435 (2015).

    Article  ADS  Google Scholar 

  4. Cao, W., Kang, J., Sarkar, D., Liu, W. & Banerjee, K. 2D semiconductor FETs—projections and design for sub-10 nm VLSI. IEEE Trans. Electron Devices 62, 3459–3469 (2015).

    Article  ADS  CAS  Google Scholar 

  5. Agarwal, T. et al. Benchmarking of MoS2 FETs with multigate Si-FET options for 5 nm and beyond. IEEE Trans. Electron Devices 62, 4051–4056 (2015).

    Article  ADS  Google Scholar 

  6. Yang, P. et al. Epitaxial growth of centimeter-scale single-crystal MoS2 monolayer on Au(111). ACS Nano 14, 5036–5045 (2020).

    Article  CAS  PubMed  Google Scholar 

  7. Wang, Q. et al. Wafer-scale highly oriented monolayer MoS2 with large domain sizes. Nano Lett. 20, 7193–7199 (2020).

    Article  ADS  CAS  PubMed  Google Scholar 

  8. Choi, S. H. et al. Epitaxial single-crystal growth of transition metal dichalcogenide monolayers via the atomic sawtooth Au surface. Adv. Mater. 33, 2006601 (2021).

    Article  CAS  Google Scholar 

  9. Zhou, J. et al. A library of atomically thin metal chalcogenides. Nature 556, 355–359 (2018).

    Article  ADS  CAS  PubMed  Google Scholar 

  10. Kang, K. et al. High-mobility three-atom-thick semiconducting films with wafer-scale homogeneity. Nature 520, 656–660 (2015).

    Article  ADS  CAS  PubMed  Google Scholar 

  11. Chubarov, M. et al. Wafer-scale epitaxial growth of unidirectional WS2 monolayers on sapphire. ACS Nano 15, 2532–2541 (2021).

    Article  CAS  PubMed  Google Scholar 

  12. Aljarb, A. et al. Ledge-directed epitaxy of continuously self-aligned single-crystalline nanoribbons of transition metal dichalcogenides. Nat. Mater. 19, 1300–1306 (2020).

    Article  ADS  CAS  PubMed  Google Scholar 

  13. Poh, S. M. et al. Molecular beam epitaxy of highly crystalline MoSe2 on hexagonal boron nitride. ACS Nano 12, 7562–7570 (2018).

    Article  CAS  PubMed  Google Scholar 

  14. Zhang, X. et al. Defect-controlled nucleation and orientation of WSe2 on hBN: a route to single-crystal epitaxial monolayers. ACS Nano 13, 3341–3352 (2019).

    Article  CAS  PubMed  Google Scholar 

  15. Ye, H. et al. Toward a mechanistic understanding of vertical growth of van der Waals stacked 2D materials: a multiscale model and experiments. ACS Nano 11, 12780–12788 (2017).

    Article  CAS  PubMed  Google Scholar 

  16. Vyas, A. A. et al. International Roadmap for Devices and Systems 2020 (IEEE, 2020); https://irds.ieee.org/images/files/pdf/2020/2020IRDS_MM.pdf

  17. Ahmed, Z. et al. Introducing 2D-FETs in device scaling roadmap using DTCO. In 2020 IEEE International Electron Devices Meeting (IEDM) 22.25.21–22.25.24 (IEEE, 2021); https://doi.org/10.1109/IEDM13553.2020.9371906

  18. Yu, Z. et al. Realization of room-temperature phonon-limited carrier transport in monolayer MoS2 by dielectric and carrier screening. Adv. Mater. 28, 547–552 (2016).

    Article  CAS  PubMed  Google Scholar 

  19. Allain, A., Kang, J., Banerjee, K. & Kis, A. Electrical contacts to two-dimensional semiconductors. Nat. Mater. 14, 1195–1205 (2015).

    Article  ADS  CAS  PubMed  Google Scholar 

  20. Das, S., Chen, H.-Y., Penumatcha, A. V. & Appenzeller, J. High performance multilayer MoS2 transistors with scandium contacts. Nano Lett. 13, 100–105 (2013).

    Article  ADS  CAS  PubMed  Google Scholar 

  21. Liu, Y. et al. Approaching the Schottky–Mott limit in van der Waals metal–semiconductor junctions. Nature 557, 696–700 (2018).

    Article  ADS  CAS  PubMed  Google Scholar 

  22. Shen, P.-C. et al. Ultralow contact resistance between semimetal and monolayer semiconductors. Nature 593, 211–217 (2021).

    Article  ADS  CAS  PubMed  Google Scholar 

  23. Wang, Y. et al. Van der Waals contacts between three-dimensional metals and two-dimensional semiconductors. Nature 568, 70–74 (2019).

    Article  ADS  CAS  PubMed  Google Scholar 

  24. Gao, Q. et al. Scalable high performance radio frequency electronics based on large domain bilayer MoS2. Nat. Commun. 9, 4778 (2018).

    Article  ADS  PubMed  PubMed Central  Google Scholar 

  25. Xia, M. et al. Spectroscopic signatures of AA′ and AB stacking of chemical vapor deposited bilayer MoS2. ACS Nano 9, 12246–12254 (2015).

    Article  CAS  PubMed  Google Scholar 

  26. Zhang, X. et al. Transition metal dichalcogenides bilayer single crystals by reverse-flow chemical vapor epitaxy. Nat. Commun. 10, 598 (2019).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  27. Kang, K. et al. Layer-by-layer assembly of two-dimensional materials into wafer-scale heterostructures. Nature 550, 229–233 (2017).

    Article  ADS  PubMed  Google Scholar 

  28. Jin, G. et al. Heteroepitaxial van der Waals semiconductor superlattices. Nat. Nanotechnol. 16, 1092–1098 (2021).

    Article  ADS  CAS  PubMed  Google Scholar 

  29. Li, T. et al. Epitaxial growth of wafer-scale molybdenum disulfide semiconductor single crystals on sapphire. Nat. Nanotechnol. 16, 1201–1207 (2021).

    Article  ADS  CAS  PubMed  Google Scholar 

  30. Farmanbar, M. & Brocks, G. First-principles study of van der Waals interactions and lattice mismatch at MoS2 interfaces. Phys. Rev. B 93, 085304 (2016).

    Article  ADS  Google Scholar 

  31. Shang, S.-L. et al. Lateral versus vertical growth of two-dimensional layered transition-metal dichalcogenides: thermodynamic insight into MoS2. Nano Lett. 16, 5742–5750 (2016).

    Article  ADS  CAS  PubMed  Google Scholar 

  32. Chen, L. et al. Step-edge-guided nucleation and growth of aligned WSe2 on sapphire via a layer-over-layer growth mode. ACS Nano 9, 8368–8375 (2015).

    Article  CAS  PubMed  Google Scholar 

  33. Cuccureddu, F. et al. Surface morphology of c-plane sapphire (α-alumina) produced by high temperature anneal. Surf. Sci. 604, 1294–1299 (2010).

    Article  ADS  CAS  Google Scholar 

  34. Zhang, Z. & Lagally, M. G. Atomistic processes in the early stages of thin-film growth. Science 276, 377–383 (1997).

    Article  CAS  PubMed  Google Scholar 

  35. Verre, R. et al. Equilibrium faceting formation in vicinal Al2O3 (0001) surface caused by annealing. Surf. Sci. 606, 1815–1820 (2012).

    Article  ADS  CAS  Google Scholar 

  36. Xiang, Y. et al. Monolayer MoS2 on sapphire: an azimuthal reflection high-energy electron diffraction perspective. 2D Mater. 8, 025003 (2021).

    Article  CAS  Google Scholar 

  37. Van, L. P., Kurnosikov, O. & Cousty, J. Evolution of steps on vicinal (0001) surfaces of α-alumina. Surf. Sci. 411, 263–271 (1998).

    Article  ADS  Google Scholar 

  38. Chubarov, M., Choudhury, T. H., Zhang, X. & Redwing, J. M. In-plane x-ray diffraction for characterization of monolayer and few-layer transition metal dichalcogenide films. Nanotechnology 29, 055706 (2018).

    Article  ADS  PubMed  Google Scholar 

  39. Liu, K. et al. Evolution of interlayer coupling in twisted molybdenum disulfide bilayers. Nat. Commun. 5, 4966 (2014).

    Article  ADS  CAS  PubMed  Google Scholar 

  40. Weston, A. et al. Atomic reconstruction in twisted bilayers of transition metal dichalcogenides. Nat. Nanotechnol. 15, 592–597 (2020).

    Article  ADS  CAS  PubMed  Google Scholar 

  41. Wang, L. et al. Correlated electronic phases in twisted bilayer transition metal dichalcogenides. Nat. Mater. 19, 861–866 (2020).

    Article  ADS  CAS  PubMed  Google Scholar 

  42. Zhao, X. et al. Strain modulation by van der Waals coupling in bilayer transition metal dichalcogenide. ACS Nano 12, 1940–1948 (2018).

    Article  CAS  PubMed  Google Scholar 

  43. Nalin Mehta, A. et al. Grain-boundary-induced strain and distortion in epitaxial bilayer MoS2 lattice. J. Phys. Chem. C 124, 6472–6478 (2020).

    Article  CAS  Google Scholar 

  44. Jiang, T. et al. Valley and band structure engineering of folded MoS2 bilayers. Nat. Nanotechnol. 9, 825–829 (2014).

    Article  ADS  CAS  PubMed  Google Scholar 

  45. Li, W. et al. High-performance CVD MoS2 transistors with self-aligned top-gate and Bi contact. In 2021 IEEE International Electron Devices Meeting (IEDM) 37.3.1–37.3.4 (IEEE, 2021); https://doi.org/10.1109/IEDM19574.2021.9720595

  46. Dorow, C. et al. Advancing monolayer 2D NMOS and PMOS transistor integration from growth to van der Waals interface engineering for ultimate CMOS scaling. In 2021 Symposium on VLSI Technology 1–2 (IEEE, 2021); https://ieeexplore.ieee.org/document/9508732.

  47. Xu, K. et al. Sub-10 nm nanopattern architecture for 2D material field-effect transistors. Nano Lett. 17, 1065–1070 (2017).

    Article  ADS  CAS  PubMed  Google Scholar 

  48. Xie, L. et al. A facile and efficient dry transfer technique for two-dimensional van der Waals heterostructure. Chin. Phys. B 26, 087306 (2017).

    Article  ADS  Google Scholar 

  49. Li, N. et al. Atomic layer deposition of Al2O3 directly on 2D materials for high-performance electronics. Adv. Mater. Interfaces 6, 1802055 (2019).

    Article  Google Scholar 

  50. Yu, L. et al. Enhancement-mode single-layer CVD MoS2 FET technology for digital electronics. In 2015 IEEE International Electron Devices Meeting (IEDM) 32.33.31–32.33.34 (IEEE, 2016); https://doi.org/10.1109/IEDM.2015.7409814

  51. Yu, L. et al. Design, modeling, and fabrication of chemical vapor deposition grown MoS2 circuits with E-mode FETs for large-area electronics. Nano Lett. 16, 6349–6356 (2016).

    Article  ADS  CAS  PubMed  Google Scholar 

  52. Sun, L. et al. Concurrent synthesis of high-performance monolayer transition metal disulfides. Adv. Funct. Mater. 27, 1605896 (2017).

    Article  Google Scholar 

  53. Liu, H. et al. Statistical study of deep submicron dual-gated field-effect transistors on monolayer chemical vapor deposition molybdenum disulfide films. Nano Lett. 13, 2640–2646 (2013).

    Article  ADS  CAS  PubMed  Google Scholar 

  54. Kappera, R. et al. Phase-engineered low-resistance contacts for ultrathin MoS2 transistors. Nat. Mater. 13, 1128–1134 (2014).

    Article  ADS  CAS  PubMed  Google Scholar 

  55. Sebastian, A., Pendurthi, R., Choudhury, T. H., Redwing, J. M. & Das, S. Benchmarking monolayer MoS2 and WS2 field-effect transistors. Nat. Commun. 12, 693 (2021).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  56. English, C. D., Smithe, K. K. H., Xu, R. L. & Pop, E. Approaching ballistic transport in monolayer MoS2 transistors with self-aligned 10 nm top gates. In 2016 IEEE International Electron Devices Meeting (IEDM) 5.6.1–5.6.4 (IEEE, 2017); https://doi.org/10.1109/IEDM.2016.7838355

  57. Yu, Z. et al. Toward high-mobility and low-power 2D MoS2 field-effect transistors. In 2018 IEEE International Electron Devices Meeting (IEDM) 22.24.21–22.24.24 (IEEE, 2019); https://doi.org/10.1109/IEDM.2018.8614644

  58. Xie, L. et al. Graphene-contacted ultrashort channel monolayer MoS2 transistors. Adv. Mater. 29, 1702522 (2017).

    Article  Google Scholar 

  59. Daus, A. et al. High-performance flexible nanoscale transistors based on transition metal dichalcogenides. Nat. Electron. 4, 495–501 (2021).

    Article  CAS  Google Scholar 

  60. McClellan, C. J., Yalon, E., Smithe, K. K. H., Suryavanshi, S. V. & Pop, E. High current density in monolayer MoS2 doped by AlOx. ACS Nano 15, 1587–1596 (2021).

    Article  CAS  PubMed  Google Scholar 

  61. Wachter, S., Polyushkin, D. K., Bethge, O. & Mueller, T. A microprocessor based on a two-dimensional semiconductor. Nat. Commun. 8, 14948 (2017).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  62. Fang, M. et al. Controlled growth of bilayer-MoS2 films and MoS2-based field-effect transistor (FET) performance optimization. Adv. Electron. Mater. 4, 1700524 (2018).

    Article  Google Scholar 

  63. Li, X. et al. Performance potential and limit of MoS2 transistors. Adv. Mater. 27, 1547–1552 (2015).

    Article  CAS  PubMed  Google Scholar 

  64. Liu, Y. et al. Pushing the performance limit of sub-100 nm molybdenum disulfide transistors. Nano Lett. 16, 6337–6342 (2016).

    Article  ADS  CAS  PubMed  Google Scholar 

  65. Lin, J. et al. High-current MoS2 transistors with non-planar gate configuration. Sci. Bull. 66, 777–782 (2021).

    Article  CAS  Google Scholar 

  66. Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 50, 17953–17979 (1994).

    Article  ADS  Google Scholar 

  67. Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).

    Article  ADS  CAS  PubMed  Google Scholar 

  68. Kresse, G. & Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169 (1996).

    Article  ADS  CAS  Google Scholar 

  69. Grimme, S., Antony, J., Ehrlich, S. & Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 132, 154104 (2010).

    Article  ADS  PubMed  Google Scholar 

  70. Ma, L. & Zeng, X. C. Catalytic directional cutting of hexagonal boron nitride: the roles of interface and etching agents. Nano Lett. 17, 3208–3214 (2017).

    Article  ADS  CAS  PubMed  Google Scholar 

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Acknowledgements

This work is supported by the National Key Research and Development Program of China (grant no. 2017YFA0204800, 2021YFA0715600, 2021YFA1500700); the Leading-edge Technology Program of Jiangsu Natural Science Foundation (grant no. BK20202005); the National Natural Science Foundation of China (grant nos. 61927808, 61734003, 61851401, 91964202, 61861166001, 22033002, 21903014); the Strategic Priority Research Program of Chinese Academy of Sciences (grant no. XDB30000000); the “Shuang Chuang” Talent Program (JSSCRC2021489); the Basic Research Program of Jiangsu Province (grant no. BK20190328); Key Laboratory of Advanced Photonic and Electronic Materials, Collaborative Innovation Center of Solid-State Lighting and Energy-Saving Electronics and the Fundamental Research Funds for the Central Universities, China.

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  1. These authors contributed equally: Lei Liu, Taotao Li, Liang Ma, Weisheng Li, Si Gao, Wenjie Sun, Ruikang Dong

Authors and Affiliations

  1. National Laboratory of Solid State Microstructures, School of Electronic Science and Engineering and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China

    Lei Liu, Taotao Li, Weisheng Li, Xilu Zou, Dongxu Fan, Liangwei Shao, Ningxuan Dai, Xuecou Tu, Yi Shi & Xinran Wang

  2. School of Physics, Southeast University, Nanjing, China

    Liang Ma, Ruikang Dong & Jinlan Wang

  3. National Laboratory of Solid State Microstructures, Jiangsu Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China

    Si Gao, Wenjie Sun, Chenyi Gu, Yuefeng Nie & Peng Wang

  4. College of Electronic and Optical Engineering, Nanjing University of Posts and Telecommunications, Nanjing, China

    Zhihao Yu

  5. Key Laboratory of Light Field Manipulation and Information Acquisition, Ministry of Industry and Information Technology and Shaanxi Key Laboratory of Optical Information Technology, School of Physical Science and Technology, Northwestern Polytechnical University, Xi’an, China

    Xiaoqing Chen

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  1. Lei Liu
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Contributions

X.W. and T.L. conceived and supervised the project. L.L. performed CVD growth, with assistance from T.L., N.D. and X.Z. W.S., C.G. and Y.N. performed RHEED, LEED and in-plane XRD test and data analysis. L.M., R.D. and J.W. performed DFT calculations. S.G. and P.W. performed the transmission electron microscopy characterization and data analysis. X.C. and L.L. contributed to spectral characterizations, including PL, Raman, absorption and SHG. W.L., D.F., Z.Y., L.S., X.T. and Y.S. contributed to transistor fabrication, measurements and data analysis. T.L., L.M., J.W. and X.W. co-wrote the manuscript, with input from the other authors. All authors contributed to discussions.

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Correspondence to Taotao Li, Liang Ma, Jinlan Wang or Xinran Wang.

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Extended data figures and tables

Extended Data Fig. 1 Schematic of monolayer versus bilayer MoS2 flakes on c-plane sapphire.

a, 3R configuration. b, 2H configuration. c, The DFT calculated free energy variation of monolayer versus 2H bilayer MoS2 triangle domains presented in b. d, The calculated step-height-dependent formation energy between 2H bilayer MoS2 and sapphire terraces. Note 1: extra S atoms were introduced to passivate the edged Mo atoms. Note 2: the free energies are normalized by the number of Mo atoms with the consideration of the chemical potential of extra S atoms.

Extended Data Fig. 2 Edge-aligned bilayer MoS2 is energetically more preferable than the edge-misaligned bilayers.

a–c, The top and side views of atomic structures of 3R bilayer MoS2 with different edge misalignment distance (ΔL) on c-plane sapphire. The edge-aligned case (a) corresponds to ΔL = 0. d, The formation energy difference (ΔEf) as the function of ΔL for 3R bilayers, in which the edge-aligned case is the most energetically preferred one. This is attributed to the fact that the aligned edge can enhance the interaction of the edged S atoms between two neighbouring sides from two individual layers and, thereby, relieve the strained bonds of the edged and self-passivated S2 dimers of the top layer. e, Atomic-resolved HAADF-STEM image of edge alignment of bilayer MoS2 domain. Scale bar, 2 nm. f, The formation energy difference (ΔEf) as the function of ΔL, in which the edge-aligned case is the most energetically preferred for the 2H configuration.

Extended Data Fig. 3 Nucleation of monolayer and bilayer MoS2 and EELS characterization at the MoS2/sapphire interface.

a, AFM image of monolayer MoS2 at the initial growth stage on sapphire annealed at 1,000 °C. Scale bar, 1 μm. b, c, Atomic-resolved HAADF-STEM image of the cross section of monolayer MoS2 at the bistep nucleation point (b) and on the sapphire surface (c). Scale bars, 1 nm in b, 2 nm in c. d, Optical image of uniform continuous film on sapphire. Scale bar, 10 μm. e, f, AFM height and phase images showing the nucleation of bilayer MoS2 along the high steps. Scale bars, 500 nm. g, h, Annular dark-field images and EELS characterization of the bilayer MoS2/sapphire cross section, suggesting a S-passivation layer at the MoS2/sapphire interface.

Extended Data Fig. 4 Optical microscope images show the uniform growth of bilayer MoS2 domains on the substrate with high steps.

All domains with recognized orientation exhibit unidirectional alignment. The images a–c are from different samples. The substrate was annealed at 1,350 °C for 4 h. Scale bars, 10 μm.

Extended Data Fig. 5 Uniformity of continuous bilayer MoS2 film.

a, Optical microscope images from the same sample in different areas shows excellent uniformity in thickness and continuity of bilayer film. b–d, Raman mapping of the peak difference Δ(A1g-E12g) (b), E12g intensity (c) and A1g intensity (d). e, f, Distribution statistics of peak position and full width at half maximum of E12g (e) and A1g (f). Scale bar, 10 μm in a–d. h, STEM-HAADF characterization of the coalescence region near the steps. Scale bars, 5 nm. i, Scanning electron microscopy images showing the uniformity of the fully covered bilayer MoS2 films.

Extended Data Fig. 6 The epitaxial relationship between bilayer MoS2 and sapphire.

a, Cross-sectional HAADF-STEM image viewed in the sapphire <\(11\bar{2}0\)> direction. Scale bar, 1 nm. The measured lattice constant ratio between MoS2 and sapphire is 0.158 nm/0.412 nm = 0.38, which closely matches the R30° epitaxy relationship viewed along the sapphire <\(11\bar{2}0\)> direction. b, RHEED pattern obtained along the sapphire <\(11\bar{2}0\)> direction. The spots and the stripes, as marked in orange and white lines, respectively, stand for signals from MoS2 and sapphire. The RHEED intensity spectrum is overlapped on the top of the diffraction pattern. c, Schematic of the epitaxial relationship of bilayer MoS2 on sapphire (0001) viewed along the sapphire <\(11\bar{2}0\)> direction.

Extended Data Fig. 7 DFT calculations on the stacking order of bilayer MoS2 and the epitaxial relationship between bilayer MoS2 and c-plane sapphire.

a, The formation energy of 3R bilayer MoS2 on c-plane sapphire as a function of the angle between the <\(11\bar{2}0\)> orientations of MoS2 and sapphire, in which the R30° epitaxial configuration is the most energetically preferred. b, c, The atomic illustrations of the R0° and R30° epitaxial configurations of 3R bilayer MoS2 on c-plane sapphire. d, The formation energy of bilayer MoS2 as a function of the twist angle, which is defined as the angle between the <\(11\bar{2}0\)> orientations of the two individual layers. The 3R (0°) and 2H (60°) stacking orders are the two energetically degenerate and most stable configurations of bilayer MoS2. e, f, The atomic illustrations of the 3R and 2H stacking orders of bilayer MoS2. g, The epitaxial relationship between bilayer MoS2/sapphire with S-passivation, in which the R30° configuration is still the most energetically preferred. h, Free energy of monolayer versus bilayer MoS2 growth on S-passivated c-plane sapphire. A similar dependence on step height as without S-passivation was observed.

Extended Data Fig. 8 Spectral, structural and electrical characterization of grain boundary between 2H and 3R domains.

a, b, Optical microscope and SHG mapping showing the coalescence of the 3R and 2H domains. c, d, Atomic-resolved HAADF-STEM characterization of GBs between the 2H and 3R domains. The left 3R bilayer domain and the right 2H bilayer domain merge with shared atoms, and the boundaries exist in the form of four-membered rings. Scale bars, 5 nm in c, 1 nm in d. e, f, Electrical characteristics of FETs across a GB. e, Optical image and SHG mapping of a typical device. D1 and D3 are 2H and 3R phases, and D2 is across the GB. f, Transfer characteristics of the three devices. The mobilities of D1, D2 and D3 are 93, 74 and 102 cm2 V−1 s−1, respectively.

Extended Data Fig. 9 Electronic performance of bilayer MoS2 FETs.

a, Typical Ids–Vgs curves of a bilayer MoS2 FET at various temperatures from 45 K to 300 K. Vds = 0.5 V. Inset, the intrinsic field-effect mobility of the bilayer MoS2 FET as a function of temperature. b, Arrhenius plot at different Vgs of the same device as in a. c, Vgs dependence of the Schottky barrier height for a bilayer MoS2 FET with Bi/Au contact, showing a negligible contact barrier. Inset shows the linear output curves of the bilayer MoS2 FET at a low temperature of 45 K, exhibiting the ideal ohmic contact behaviour between bilayer MoS2 and Bi/Au electrodes. d, Transfer characteristics of Bi-contacted bilayer MoS2 FETs with various Lch at Vds = 0.1 V for the TLM study. e, Plots of total device resistance Rtot versus Lch for the bilayer MoS2 FETs at Vgs = 10 V, from which the total contact resistance (2Rc) can be extracted from the y-axis intercepts. Black symbols are experimental data and the red line is linear fits in i. f, Output characteristics of a 40-nm-channel-length bilayer MoS2 FET. From bottom to up, Vgs = −15 to 19 V with a step of 4 V. Inset shows the scanning electron microscopy image of the device. Scale bar, 200 nm. g–i, High-performance bilayer MoS2 top-gate transistor on sapphire. g, Cross-sectional schematic of a self-aligned top-gate bilayer MoS2 FET. h, Transfer characteristics of a top-gate bilayer MoS2 FET with a short gate length of 80 nm at Vds = 10, 50 and 100 mV, respectively. Inset is the scanning electron microscopy image of the device. Scale bar, 1 μm. i, Output characteristics of the same top-gate bilayer MoS2 FET with a short Lg of 80 nm at Vtg from −2 V to 5 V with a step of 0.5 V. The maximum Ion reaches 760 μA μm−1 at Vtg = 5 V and Vds = 2 V.

Extended Data Fig. 10 Uniform growth of bilayer WS2.

a, b, Optical microscopy images of the as-grown bilayer WS2 domains on sapphire substrate. Scale bars, 15 μm. c, d, PL and Raman spectra of bilayer WS2, respectively. e, AFM image of the bilayer WS2 domains. The height of 1.26 nm was shown, corresponding to the thickness of bilayer WS2. f, g, Optical microscope and SHG mapping at the same zone shows the existence of 2H and 3R stacking. The domains marked by the dashed line are of the 2H configuration, which shows extinction of SHG. Scale bars, 5 μm. h, SHG spectra of the 2H and 3R stacking domains.

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Liu, L., Li, T., Ma, L. et al. Uniform nucleation and epitaxy of bilayer molybdenum disulfide on sapphire. Nature 605, 69–75 (2022). https://doi.org/10.1038/s41586-022-04523-5

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