Nanosheets exhibit high and anisotropic hydroxyl ion conductivity, promising potentials in energy or environment applications.

Fe 3 GeTe 2 has emerged as one of the most fascinating van der Waals crystals due to its two-dimensional (2D) itinerant ferromagnetism, topological nodal lines and Kondo lattice behavior. However, lattice dynamics, chirality of phonons and spin-phonon coupling in this material, which set the foundation for these exotic phenomena, have remained unexplored. Here we report the first experimental investigation of the phonons and mutual interactions between spin and lattice degrees of freedom in few-layerFe 3 GeTe 2 . Our results elucidate three prominent Raman modes at room temperature: two A 1g (Γ) and one E 2g (Γ) phonons. The doubly degenerate E 2g (Γ) mode reverses the helicity of incident photon, indicating the pseudo-angular momentum and chirality. Through analysis of temperature-dependent phonon energies and lifetimes, which strongly diverge from the anharmonic model below Curie temperature, we determine the spin-phonon coupling in Fe 3 GeTe 2 . Such interaction between lattice oscillations and spin significantly enhances the Raman susceptibility, allowing us to observe two additional Raman modes at the cryogenic temperature range. In addition, we reveal laser radiation induced degradation of Fe 3 GeTe 2 in ambient conditions and the corresponding Raman fingerprint. Our results provide the first experimental analysis of phonons in this novel 2D itinerant ferromagnet and their applicability for further fundamental studies and application development.

Two-dimensional (2D) layered materials with a high intercalation pseudocapacitance have long been investigated for Li-ion-based electrochemical energy storage. By contrast, the exploration of guest ions other than Li has been limited, although promising. The present study investigates intercalation/deintercalation behaviors of various metal ions in 2D layered MnO with various interlayer distances, K-birnessite nanobelt (K-MnO), its protonated form (H-MnO), and a freeze-dried sample of exfoliated nanosheets. Series of metal ions, such as monovalent Li, Na, and K and divalent Mg, exhibit reversible intercalation during charge/discharge cycling, delivering high-rate pseudocapacitances. In particular, the freeze-dried MnO of exfoliated nanosheets restacked with the largest interlayer spacing and a less compact 3D network exhibits the best rate capability and a stable cyclability over 5000 cycles. Both theoretical calculation and kinetic analysis reveal that the increased interlayer distance facilitates the fast diffusion of cations in layered MnO hosts. The results presented herein provide a basis for the controllable synthesis of layered nanostructures for high-rate electrochemical energy storage using various single- and multivalent ions.

Bandgap engineering with two-dimensional layered materials based heterostructures provides a new method for designing high-performance broadband photodetectors, modulators and lasers.