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5 9 I H I G H L I G H T S 2 0 2 5

PRINCIPAL PUBLICATION

Reactive Molecular Beam Epitaxy Growth of a 1T-FeS2 Single-Layer–Atomic Structure, Moiré, and Decoupling via Intercalation, M.K. Prabhu et al., ACS Nano 19(14), 13941-13951 (2025); https:/doi.org/10.1021/acsnano.4c17873

REFERENCES

[1] M. Gibertini et al., Nat. Nanotechnol. 14, 408-419 (2019). [2] K. Yang et al., Phys. Rev. B 109(1), 014431 (2024).

peaks in real time, providing direct feedback on the crystal phase, strain state, and interlayer spacing. This capability made it possible to adjust growth parameters dynamically and confirm the formation of the ABC stacking sequence characteristic of the 1T structure (Figure 45). The measurements also revealed that the 1T-FeS2 monolayer exhibits remarkable thermal stability across a broad temperature range, with no detectable conversion into the bulk pyrite phase even after prolonged annealing.

Further experiments demonstrated that the 2D layer can be decoupled from the catalytic Au substrate by gentle caesium alkali-metal intercalation, producing an almost free-standing sheet without structural degradation (Figure 46). This process confirms that 1T-FeS2 is not merely an interface-stabilised film but a genuine 2D material. These results establish

a reproducible synthesis pathway for FeS2 and potentially for other first-row transition-metal dichalcogenides, providing a foundation for studying their intrinsic magnetism and electronic correlations at the monolayer limit.

This work demonstrates a reliable route to form 2D materials from compounds that are not naturally layered. Stabilising 1T-FeS2 in a transferable form represents an important step towards realising room- temperature 2D ferromagnets for future spintronic and quantum technologies. The same growth strategy and X-ray methodology can be extended to other transition-metal systems, allowing direct observation of structural transitions and strain-induced effects. These findings open a pathway to designing magnetic and electronic properties through atomic-level control of crystal phase and interfaces.

Fig. 46: a) Experimental X-ray diffraction pattern of the FeS2 1T phase grown on Au(111) substrate. b) Experimentally determined atomic model showing the Fe layer between two S layers within the unit cell. c) Electron diffraction pattern after

caesium (Cs) metal intercalation, demonstrating the structural integrity of the detached monolayer.