Bidirectional and reversible tuning of the interlayer spacing of two-dimensional materials

Interlayer spacing is expected to influence the properties of multilayer two-dimensional (2D) materials. However, the ability to non-destructively regulate the interlayer spacing bidirectionally and reversibly is challenging. Here we report the preparation of 2D materials with tunable interlayer spacing by introducing active sites (Ce ions) in 2D materials to capture and immobilize Pt single atoms. The strong chemical interaction between active sites and Pt atoms contributes to the intercalation behavior of Pt atoms in the interlayer of 2D materials and further promotes the formation of chemical bonding between Pt atom and host materials. Taking cerium-embedded molybdenum disulfide (MoS2) as an example, intercalation of Pt atoms enables interlayer distance tuning via an electrochemical protocol, leading to interlayer spacing reversible and linear compression and expansion from 6.546 ± 0.039 Å to 5.792 ± 0.038 Å (~11 %). The electronic property evolution with the interlayer spacing variation is demonstrated by the photoluminescence (PL) spectra, delivering that the well-defined barrier between the multilayer and monolayer layered materials can be artificially designed.


Interlayer spacing expansion of Ce-MoS 2
The interlayer spacing of MoS2 exhibits a linear increase with the Ce concentration due to the gradual weakening of interlayer coupling caused by the electron transferring to the S-Mo antibonding orbitals, as shown in Supplementary Figure 1. When the concentration of Ce increases from 0% to 0.995%, the interlayer spacing of MoS2 changes from 6.232 ± 0.024 Å to 6.546 ± 0.039 Å.

Interlayer spacing compression of Pt, Ce-MoS 2 with Pt intercalating
The monodispersed Pt atoms were intercalated into the interlamination of Ce−MoS2 via an electrochemical reaction to reduce the interlayer spacing. When the concentration of Pt increases from 0% to 2.31%, the interlayer spacing of MoS2 changes from 6.546 ± 0.039 Å to 5.792 ± 0.

Stacking model and HAADF−STEM image of Ce-MoS 2
The introduction of Ce ions will lead to the change of MoS2 stacking structure, which is manifested in Supplementary Figure 16. Ce−MoS2 exhibits AA stacking model, whose calculated interlayer spacing is 6.78 Å, larger than the value of intrinsic MoS2 (6.22 Å).

Interlayer spacing expansion of MoS 2 with direct intercalation of Pt
It can be found that the interlayer spacing of MoS2 will get expanded with the direct intercalation of Pt without Ce ions (Supplementary Figure 17), consisting with the literature 5 . For one thing, Pt atoms tend to aggregate into nanoparticles without the stabilization of Ce ions, in which the steric effect will result in the interlayer spacing expansion. For another thing, metal atom intercalation will also lead to the expansion of the interlayer spacing inevitably due to the introduction of free electrons that will increase Fermi energy levels and expand the band gaps.

PL spectra of MoS 2 with different Ce concentration
The interlayer spacing of MoS2 increases with the Ce concentration increasing, resulting that the PL A peak position of the MoS2 shifts from 668 nm to 658 nm (Supplementary Figure 25). The change of peak position means that the interlayer-spacing-enlarged multi-layer MoS2 behaved as monolayer-like MoS2, for which its optical band gap value is 1.899 eV that is close to the value for the band gap of monolayer MoS2 (1.90 eV) in the reported work 9 . In addition, the intensity of the PL A peak is also greatly enhanced. This interlayer decoupling effect is derived from the weakening of van der Waals interaction with the expanding of the interlayer spacing.

The fitting results of the EXAFS spectra of Pt, Ce-MoS 2
In order to investigate the structural information of the Pt, Ce−MoS2, extended X-ray absorption fine structure (EXAFS) measurements at Pt L3-edge were carried out. The data ranges used for data fitting in k space (Δk) and R space are 3.45-9.9 and 1.25-2.3 Å, respectively.

Absorption energy of Pt atom on Ce-MoS 2 by DFT calculation
The strong interaction between Ce ions and Pt atoms provides us an accessible approach to dispersing and stabilizing Pt single atoms. For Ce-MoS2, we calculated the absorption energy of Pt atoms on Ce-MoS2 at different sites. The Supplementary Figure 28 show the five situations.
We artificially set the absorption energy corresponding to Supplementary Figure 28a