Abstract
Phase engineering is of vital importance for determining the material functionalities and expanding the material library. However, the controllable and scalable phase transition of transition metal chalcogenides remains extremely challenging. The microscopic observation of the phase evolution pathway is an essential prerequisite for understanding the phase transition mechanism. Here we atomically observe a non-stoichiometric phase evolution process in large-scale superconducting PdTe2 films under heating through in situ scanning transmission electron microscopy. The unprecedented phase transition from PdTe2 to PdTe via atomic reconstruction is evidenced and theoretically verified by our machine learning molecular dynamics simulations. In particular, forming the intermediate state of PdTe2/PdTe heterostructure during the phase transition robustly generates giant-helicity-dependent terahertz emission due to inversion symmetry breaking. Our results not only provide insights into the atomic reconstruction in transition metal chalcogenides but also offer a general strategy for the fabrication of large-area transition metal monochalcogenide films and heterostructures, potentially applicable for various device applications.
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The data that support the plots within this paper are available in the Article or its Supplementary Information. The other findings of this study are available from the corresponding authors upon request. Source data are provided with this paper.
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Acknowledgements
This work was supported by the National Natural Science Foundation of China (grant numbers 62525406, T2394473, 624B2070 and 62274085), the National Key R&D Program of China (grant number 2022YFA1402404) and the Innovation Program for Quantum Science and Technology of China (grant number 2024ZD0301300). W.Z. acknowledges the National Natural Science Foundation of China (grant number U23A6015) and the CAS Project for Young Scientists in Basic Research (grant number YSBR-003). T.Y. acknowledges the National Key R&D Program of China (grant number 2022YFA1203900) and the National Natural Science Foundation of China (grant number 52031014). J.G. acknowledges the National Key R&D Program of China (grant number 2024YFA1409600) and the National Natural Science Foundation of China (grant number 12374253). F.S. acknowledges the National Natural Science Foundation of China (grant numbers 12025404, 92161201 and T2221003). Y.H. acknowledges the Key R&D Program of Jiangsu Province (grant number BE2023009-2) and the Natural Science Foundation of Jiangsu Province (grant number BK20243014). F.D. acknowledges the National Natural Science Foundation of China (grant number 22461160283) and the research program from Suzhou Laboratory (grant number SK-1502-2024-055). This work also benefitted from the resources and support from the Electron Microscopy Center at the University of Chinese Academy of Sciences.
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Xuefeng Wang conceived the study and proposed the strategy. Xuefeng Wang and R.Z. supervised the project. Z.C., R.X., K.X., X.L. and Y.Z. developed the PLD method, grew the samples and performed the XRD and X-ray photoelectron spectroscopy measurements. Z.C. and D.T. carried out the THz emission measurements. Z.C. and Y.H. performed the AFM measurement. J.-a.S. and W.Z. carried out the electron microscopy characterization. J.H., S.A. and T.Y. conducted the first-principles calculations. Y.C., J.G. and F.D. performed the machine learning MD simulations. Z.C., X.D., Z.D. and X.Z. fabricated the devices and performed the transport measurements. Z.C., G.L. and X.X. performed the Raman measurements. S.Z., F.F., L.H., Y.X., F.S., B.J., Xinran Wang, Y.S. and R.Z. contributed to the data analysis and discussion. Xuefeng Wang and Z.C. wrote the manuscript with input from all authors.
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Extended data
Extended Data Fig. 1 PLD growth of large-scale PdTe2 thin films.
a, Schematic illustration of PLD growth process of PdTe2 films on sapphire substrate. b, RHEED patterns obtained with different growth time. As the growth time increases, the RHEED pattern gradually evolves from bright dots to blurry stripes, and eventually to sharp stripes, indicating a layered growth mode.
Extended Data Fig. 2 Low-magnification STEM images of the phase transition from PdTe2 to PdTe.
a-c, The phase transition under the heating temperature at 20, 50, and 200 °C, respectively. The green and red dashed rectangles represent the dislocations near the substrate and the ordered PdTe phase, respectively. The scale bar is 2 nm. Notably, we can find that when the phase transition temperature increases, all dislocations become the ordered PdTe phase with a zigzag structure, which is consistent with the observation in Fig. 2b–f.
Extended Data Fig. 3 Thickness-dependent superconductivity of PdTe film.
a-g, R-T curves of the PdTe with the thickness ranging from 6 to 38 nm, respectively. TC is defined at 90% of the normal-state resistance. The data are normalized by the resistance at 7 K. h, Thickness-dependent TC of PdTe. The red dashed line represents the TC of the bulk PdTe.
Extended Data Fig. 4 Interface stability measurements.
a-c, The cross-sectional STEM images of the PdTe2/PdTe heterostructure under the heating temperature at 150 °C by the in situ STEM with the heating time of 20, 30, and 60 min, respectively. The red-colored rectangles indicate the PdTe phase. d, Transient THz waveforms of PdTe2/PdTe heterostructure under the linear polarized excitations. The heterostructure is obtained by annealing PdTe2 film at 300 °C for various time in the PLD system.
Extended Data Fig. 5 The multi-terminal electrode patterns for PdTe array on the Al2O3 substrate.
a, Schematic diagram of the fabrication procedure of the multi-terminal device. b, Photograph of a 2 × 2 multi-terminal device array. c, Optical image of multi-terminal PdTe device in (b). d, Various I-V curves of the multi-terminal device in (c), showing the perfect ohmic contact.
Extended Data Fig. 6 Thermally driven atomic reconstruction in PtTe2 thin film.
a, Schematic illustration of the thermally driven atomic reconstruction phase transition from PtTe2 to PtTe. The purple ball, yellow ball and red dashed circle represent Pt atom, Te atom, and VTe, respectively. b, Raman spectra of the PtTe2 film and the PtTe2/PtTe heterostructure annealed in the PLD system at 500 °C for 60 min. c,d, In situ STEM images of PtTe2 without heating and the partial phase transition from PtTe2 to PtTe under the heating temperature at 310 °C, respectively. The red-colored region in (d) indicates the PtTe phase. The scale bar is 2 nm. e,f, Magnified STEM images of the red and blue dashed rectangles in (c) and (d), respectively. The attached schematic atomic structures in (e) and (f) are PtTe2 and PtTe, respectively.
Supplementary information
Supplementary Information (download PDF )
Supplementary Figs. 1–31 and refs. 1 and 2.
Supplementary Video 1 (download GIF )
Thermally driven atomic reconstruction phase transition in PdTe2.
Supplementary Video 2 (download GIF )
MD simulation of the PdTe2/PdTe heterostructure under 700 K.
Supplementary Video 3 (download GIF )
MD simulation of the PdTe2/PdTe heterostructure under 500 K.
Supplementary Video 4 (download GIF )
MD simulation of the PdTe2/PdTe heterostructure with the VTe line defects in one layer far from the interface under 500 K.
Supplementary Video 5 (download GIF )
MD simulation of the PdTe2/PdTe heterostructure with the VTe line defects near the interface under 500 K.
Supplementary Video 6 (download GIF )
MD simulation of the PdTe2/PdTe heterostructure under 400 K.
Supplementary Video 7 (download GIF )
MD simulation of the PdTe2/PdTe heterostructure under 600 K.
Supplementary Video 8 (download GIF )
MD simulation of the PtTe2/PtTe heterostructure under 600 K.
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Chen, Z., Shi, Ja., Huang, J. et al. Large-area non-stoichiometric phase transition in transition metal chalcogenide films. Nat. Mater. 25, 573–580 (2026). https://doi.org/10.1038/s41563-025-02471-9
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DOI: https://doi.org/10.1038/s41563-025-02471-9
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