Large-area non-stoichiometric phase transition in transition metal chalcogenide films

Nature Materials (2026)Cite this article 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.This is a preview of subscription content, access via your institution Access Nature and 54 other Nature Portfolio journals Get Nature+, our best-value online-access subscription $32.99 / 30 days cancel any timeSubscribe to this journal Receive 12 print issues and online access $259.00 per yearonly $21.58 per issueBuy this articleUSD 39.95Prices may be subject to local taxes which are calculated during checkoutThe 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.Kappera, R. et al. 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A 31, 1695–1697 (1985).Article Google Scholar Download referencesThis 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.Sajjad AliPresent address: College of Humanities and Sciences, Prince Sultan University, Riyadh, Saudi ArabiaThese authors contributed equally: Zhongqiang Chen, Jin-an Shi, Jianqi Huang, Yuan Chang.State Key Laboratory of Spintronics, Jiangsu Provincial Key Laboratory of Third Generation Semiconductors and High Energy Efficiency Devices, School of Electronic Science and Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, ChinaZhongqiang Chen, Ruijie Xu, Kankan Xu, Xu Zhang, Xudong Liu, Yong Zhang, Xingze Dai, Liang He, Yongbing Xu, Xinran Wang, Yi Shi, Rong Zhang & Xuefeng WangSchool of Physical Sciences, University of Chinese Academy of Sciences, Beijing, ChinaJin-an Shi & Wu ZhouShenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, ChinaJianqi Huang, Sajjad Ali & Teng YangLiaoning Academy of Materials, Shenyang, ChinaJianqi Huang & Teng YangMOE Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Dalian, ChinaYuan Chang & Junfeng GaoResearch Institute of Superconductor Electronics, MOE Key Laboratory of Optoelectronic Devices and Systems with Extreme Performances, School of Electronic Science and Engineering, Nanjing University, Nanjing, ChinaDa Tian & Biaobing JinNational Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing, ChinaGan Liu, Zheng Dai, Shuai Zhang, Fucong Fei, Xiaoxiang Xi & Fengqi SongNational Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences, Nanjing University, Nanjing, ChinaYufeng HaoSuzhou Laboratory, Suzhou, ChinaJunfeng Gao, Feng Ding & Xinran WangNanjing Institute of Atomic Scale Manufacturing, Nanjing, ChinaFengqi Song & Xuefeng WangDepartment of Physics, Xiamen University, Xiamen, ChinaRong ZhangSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarXuefeng 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.Correspondence to Wu Zhou, Teng Yang, Junfeng Gao, Rong Zhang or Xuefeng Wang.The authors declare no competing interests.Nature Materials thanks Soon-Yong Kwon and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.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.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.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.Source dataa-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.Source dataa, 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.Source dataa, 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.Source dataSupplementary Figs. 1–31 and refs. 1 and 2.Thermally driven atomic reconstruction phase transition in PdTe2.MD simulation of the PdTe2/PdTe heterostructure under 700 K.MD simulation of the PdTe2/PdTe heterostructure under 500 K.MD simulation of the PdTe2/PdTe heterostructure with the VTe line defects in one layer far from the interface under 500 K.MD simulation of the PdTe2/PdTe heterostructure with the VTe line defects near the interface under 500 K.MD simulation of the PdTe2/PdTe heterostructure under 400 K.MD simulation of the PdTe2/PdTe heterostructure under 600 K.MD simulation of the PtTe2/PtTe heterostructure under 600 K.Source data for Fig. 1.Source data for Fig. 3.Source data for Fig. 4.Source data for Extended Data Fig. 3.Source data for Extended Data Fig. 4.Source data for Extended Data Fig. 5.Source data for Extended Data Fig. 6.Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.Reprints and permissionsChen, Z., Shi, Ja., Huang, J. et al. Large-area non-stoichiometric phase transition in transition metal chalcogenide films. Nat. Mater. (2026). https://doi.org/10.1038/s41563-025-02471-9Download citationReceived: 22 March 2025Accepted: 15 December 2025Published: 16 January 2026Version of record: 16 January 2026DOI: https://doi.org/10.1038/s41563-025-02471-9Anyone you share the following link with will be able to read this content:Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative