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Tunable free-electron X-ray radiation from van der Waals materials


Tunable sources of X-ray radiation are widely used for imaging and spectroscopy in fundamental science, medicine and industry. The growing demand for highly tunable, high-brightness laboratory-scale X-ray sources motivates research into new fundamental mechanisms of X-ray generation. Here, we demonstrate the ability of van der Waals materials to serve as a platform for tunable X-ray generation when irradiated by moderately relativistic electrons available, for example, from a transmission electron microscope. The radiation spectrum can be precisely controlled by tuning the acceleration voltage of the incident electrons, as well as by our proposed approach: adjusting the lattice structure of the van der Waals material. We present experimental results for both methods, observing the energy tunability of X-ray radiation from the van der Waals materials WSe2, CrPS4, MnPS3, FePS3, CoPS3 and NiPS3. Our findings demonstrate the concept of material design at the atomic level, using van der Waals heterostructures and other atomic superlattices, for exploring novel phenomena of X-ray physics.

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Fig. 1: Demonstration of free-electron radiation from vdW materials.
Fig. 2: Tunability of X-ray radiation from vdW materials.
Fig. 3: Spectral shaping of X-ray radiation via customized superlattices.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.

Code availability

The codes that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.


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We thank Y. Kauffmann for advice and discussions. This work was supported by the ERC (Starter Grant no. 851780), the ISF (Grant no. 830/19) and the European Commission via the Marie Skłodowska-Curie Action Phonsi (H2020-MSCA-ITN-642656). H.H.S. also acknowledges the support of Marie Skłodowska-Curie Actions (H2020-MSCA-IF-2018-843830). K.S.T. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant no. \773122, LIMA). The Center for Nanostructured Graphene is sponsored by the Danish National Research Foundation, Project DNRF103. F.H.L.K. acknowledges financial support from the Government of Catalonia through the SGR grant, and from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0522), and Explora Ciencia FIS2017-91599-EXP. F.H.L.K. also acknowledges support by Fundacio Cellex Barcelona, Generalitat de Catalunya through the CERCA program, and the Mineco grants Plan Nacional (FIS2016-81044-P) and the Agency for Management of University and Research Grants (AGAUR) 2017 SGR 1656. Furthermore, the research leading to these results has received funding from the European Union’s Horizon 2020 under grant agreement no. 785219 (Core2) and no. 881603 (Core3) Graphene Flagship, and no. 820378 (Quantum Flagship). This work was supported by the ERC TOPONANOP under grant agreement no. 726001. L.J.W. acknowledges the support of the Agency for Science, Technology and Research (A*STAR) Advanced Manufacturing and Engineering Young Individual Research Grant (A1984c0043), and the Nanyang Assistant Professorship Start-up Grant. F.J.G.A. acknowledges support from the Spanish MINECO (Grant nos. MAT2017-88492-R and SEV2015-0522), ERC (Advanced Grant no. 789104-eNANO), the Catalan CERCA Program and Fundació Privada Cellex. I.K. was also supported by an Azrieli Faculty Fellowship.

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M.S. spearheaded the project, designed and performed the electron microscopy experiments, prepared the samples, analysed the data and developed the superlattice theory. A.K.B. contributed to the measurements and performed electron microscopy experiments. A.K.B., H.H.S., M.B., Y.A., S.T., F.H.L.K. and E.L synthesized the vdW materials and prepared the TEM samples. R.D. and M.K. advised on experimental aspects. X.S., Y.K. and F.J.G.A. developed and executed the PXR simulations. M.K.S. and K.S.T. performed the DFT simulations. L.J.W. developed and executed the CBS simulations. F.J.G.A., L.J.W., X.S. and I.K. contributed to the discussion of the experimental results, to the comparative analysis of the different theoretical mechanisms and to the overall conclusions. M.S. and I.K. conceived the idea. I.K. supervised the project.

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Correspondence to Michael Shentcis or Ido Kaminer.

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Shentcis, M., Budniak, A.K., Shi, X. et al. Tunable free-electron X-ray radiation from van der Waals materials. Nat. Photonics 14, 686–692 (2020).

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