Sodium-ion batteries are a potentially low-cost and safe alternative to the prevailing lithium-ion battery technology. However, it is a great challenge to achieve fast charging and high power density for most sodium-ion electrodes because of the sluggish sodiation kinetics. Here we demonstrate a high-capacity and high-rate sodium-ion anode based on ultrathin layered tin(II) sulfide nanostructures, in which a maximized extrinsic pseudocapacitance contribution is identified and verified by kinetics analysis. The graphene foam supported tin(II) sulfide nanoarray anode delivers a high reversible capacity of ∼1,100 mAh g⁻¹ at 30 mA g⁻¹ and ∼420 mAh g⁻¹ at 30 A g⁻¹, which even outperforms its lithium-ion storage performance. The surface-dominated redox reaction rendered by our tailored ultrathin tin(II) sulfide nanostructures may also work in other layered materials for high-performance sodium-ion storage.

Light scattering by small particles has a long and interesting history in physics. Nonetheless, it continues to surprise with new insights and applications. This includes new discoveries, such as novel plasmonic effects, as well as exciting theoretical and experimental developments such as optical trapping, anomalous light scattering, optical tweezers, nanospasers, and novel aspects and realizations of Fano resonances. These have led to important new applications, including several ones in the biomedical area and in sensing techniques at the single-molecule level. There are additionally many potential future applications in optical devices and solar energy technologies. Here we review the fundamental aspects of light scattering by small spherical particles, emphasizing the phenomenological treatments and new developments in this field.

The grand challenge in the development of atomically dispersed metallic catalysts is their low metal-atom loading density, uncontrollable localization and ambiguous interactions with supports, posing difficulty in maximizing their catalytic performance. Here, we achieve an interface catalyst consisting of atomic cobalt array covalently bound to distorted 1T MoS₂ nanosheets (SA Co-D 1T MoS₂). The phase of MoS₂ transforming from 2H to D-1T, induced by strain from lattice mismatch and formation of Co-S covalent bond between Co and MoS₂ during the assembly, is found to be essential to form the highly active single-atom array catalyst. SA Co-D 1T MoS₂ achieves Pt-like activity toward HER and high long-term stability. Active-site blocking experiment together with density functional theory (DFT) calculations reveal that the superior catalytic behaviour is associated with an ensemble effect via the synergy of Co adatom and S of the D-1T MoS₂ support by tuning hydrogen binding mode at the interface.

The fabrication of epitaxial graphene (EG) on SiC substrate by annealing has attracted a lot of interest as it may speed up the application of graphene for future electronic devices. The interaction of EG and the SiC substrate is critical to its electronic and physical properties. In this work, the Raman spectroscopy was used to study the structure of EG and its interaction with SiC substrate. All the Raman bands of EG blueshift from that of bulk graphite and graphene made by micromechanical cleavage, which was attributed to the compressive strain induced by the substrate. A model containing $13\times 13$ honeycomb lattice cells of graphene on carbon nanomesh was constructed to explain the origin of strain. The lattice mismatch between graphene layer and substrate causes the compressive stress of $2.27\mathrm{GPa}$ on graphene. We also demonstrate that the electronic structures of EG grown on Si- and C-terminated SiC substrates are quite different. Our experimental results shed light on the interaction between graphene and SiC substrate, which are critical to the future applications of EG.

Structures, electronic properties, and phonon dispersions of monolayer $MX$${}_{2}$ ($M=$ Mo, W; $X=$ S, Se) under various types of mechanical strains are investigated with density functional calculations. By analyzing the orbitals near band gaps, we demonstrate that the $X$-$M$-$X$ bond angle, together with the $X$-$X$ distances, plays one of the most important roles in determining band gaps, as it is directly related to the coupling of $d$ orbitals of the $M$ atoms and $p$ orbitals of the $X$ atoms. It is found that the band gaps of monolayer $MX$${}_{2}$ are more sensitive to biaxial strains. This notion can be attributed to the fact that, under biaxial strains, $MX$${}_{2}$ tends to be stretched more significantly along the out-of-plane direction, resulting in greater changes in bond lengths/angles than uniaxial strains. While most theoretical reports suggested systematic reduction of band gaps under mechanical strains, we found that the direct band gaps can be robustly widened by applying compressive biaxial strains. Our results are of immediate importance for the recent experimental advances in applying compressive strains, which was not applicable before. On the other hand, the anisotropy of $X$-$M$-$X$ bond angles induced by uniaxial strains leads to splitting in the phonon dispersion, and is directly relevant to recent Raman spectroscopy results. As most transition-metal dichalcogenides share the same structural characters, we expect that the notions derived here are applicable to other layered transition-metal oxides/chalcogenides and open up new venues to engineer their properties.