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8 7 I H I G H L I G H T S 2 0 2 3

PRINCIPAL PUBLICATION AND AUTHORS

Superstructures, Commensurations and Rotation of Single-Layer TaS2 on Au(111) Induced by Cs Intercalation/De-Intercalation, X. Weng (a), P. David (b), V. Guisset (b), L. Martinelli (b), O. Geaymond (b), J. Coraux (b), G. Renaud (a), ACS Nano 17 (6), 5459-5471 (2023); https:/doi.org/10.1021/acsnano.2c10655 (a) UGA and CEA-IRIG/MEM, Grenoble (France) (b) UGA and CNRS, Institut Néel, Grenoble (France)

REFERENCES

[1] C.E. Sanders et al., Phys. Rev. B 94, 081404(R) (2016). [2] R. Sant et al., J. Phys. Chem. C, 124, 23, 12397-12408 (2020).

Intercalation has a second, unexpected effect: about 30% of the initial single layer, which is in the form of flakes, twists its lattice by 30° rotation with respect to the substrate lattice. These yield complex diffraction patterns, where the signatures of two new superstructures appear (Figure 67). One corresponds to a perfectly commensurate moiré between 30°-rotated TaS2 flakes and the Au substrate; the other to another kind of superstructure, within 30°-rotated TaS2 flakes. The latter has a supercell (6×6) times larger than the TaS2 unit cell, and has no simple coincidence with the substrate instead it almost coincides with (4√3×4√3) Au lattice parameters. This reconstruction s period is twice larger than that of the well-known (3×3) charge density found in bulk TaS2 at low temperature. It is suggested that this could be a new form of charge density wave, allowed because of the 30° rotation of some TaS2 flakes, itself allowed by the decoupling of the layer from its substrate.

Fig. 67: Artistic view of the different TaS2 structures (pink) on an Au(111) substrate (gold) with a portion of the corresponding reciprocal space (red and yellow peaks on blue background). Top left: TaS2 flakes coupled to the Au substrate with a 7x8 aligned moiré (see text). Bottom: TaS2 flakes without moiré, because of their decoupling from the substrate by intercalation of Cs species (green layer). Top right: TaS2 flakes after de- intercalation and thus re-coupling thanks to annealing under H2S, which results in some of the flakes being rotated by 30°, and displaying a new (6x6) superstructure, possibly linked to a charge density wave.