18 Search Results

The ability to tune the local electronic transport properties of group VI transition metal dichalcogenide (TMD) monolayers by strain-induced structural phase transformations (“phase programming”) has stimulated much interest in the potential applications of such layers as ultrathin programmable and dynamically switchable nanoelectronics components. In this manuscript, we propose a new approach toward controlling TMD monolayer phases by employing macroscopic in-plane strains to amplify heterogeneous strains arising from tailored, spatially extended defects within the monolayer. Furthermore, the efficacy of our proposed approach is demonstrated via numerical simulations of emerging domains localized around arrays of holes, grain boundaries, and compositional heterointerfaces. Quantitativemore » relations between the macroscopic strains required, spatial resolution of domain patterns, and defect configurations are developed. In particular, the introduction of arrays of holes is identified as the most feasible phase programming route.« less

Abstract The integration of Li ₂ S ₆ within a poly(ethylene oxide) (PEO)‐based polymer electrolyte is demonstrated to improve the polymer electrolyte's ionic conductivity because the strong interplay between O ²⁻ _(PEO) and Li ⁺ from Li ₂ S ₆ reduces the crystalline volume within the PEO. The Li/electrolyte interface is stabilized by the in situ formation of an ultra‐thin Li ₂ S/Li ₂ S ₂ layer via the reaction between Li ₂ S ₆ and lithium metal, which increases the ionic transport at the interface and suppresses lithium dendrite growth. A symmetric Li/Li cell with the Li ₂ Smore » ₆ ‐integrated composite electrolyte has excellent cyclability and a high critical current density of 0.9 mA cm ⁻² at 40 °C. Impressive electrochemical performance is demonstrated with all‐solid‐state Li/LiFePO ₄ and high‐voltage Li/LiNi _0.8 Mn _0.1 Co _0.1 O ₂ cells at 40 °C.« less

Abstract The integration of Li ₂ S ₆ within a poly(ethylene oxide) (PEO)‐based polymer electrolyte is demonstrated to improve the polymer electrolyte's ionic conductivity because the strong interplay between O ²⁻ _(PEO) and Li ⁺ from Li ₂ S ₆ reduces the crystalline volume within the PEO. The Li/electrolyte interface is stabilized by the in situ formation of an ultra‐thin Li ₂ S/Li ₂ S ₂ layer via the reaction between Li ₂ S ₆ and lithium metal, which increases the ionic transport at the interface and suppresses lithium dendrite growth. A symmetric Li/Li cell with the Li ₂ Smore » ₆ ‐integrated composite electrolyte has excellent cyclability and a high critical current density of 0.9 mA cm ⁻² at 40 °C. Impressive electrochemical performance is demonstrated with all‐solid‐state Li/LiFePO ₄ and high‐voltage Li/LiNi _0.8 Mn _0.1 Co _0.1 O ₂ cells at 40 °C.« less

Transition-metal single-atom catalysts present extraordinary activity per metal atomic site, but suffer from low metal-atom densities (typically less than 5 wt% or 1 at.%), which limits their overall catalytic performance. Here we report a general method for the synthesis of single-atom catalysts with high transition-metal-atom loadings of up to 40 wt% or 3.8 at.%, representing several-fold improvements compared to benchmarks in the literature. Graphene quantum dots, later interweaved into a carbon matrix, were used as a support, providing numerous anchoring sites and thus facilitating the generation of high densities of transition-metal atoms with sufficient spacing between the metal atoms tomore » avoid aggregation. A significant increase in activity in electrochemical CO₂ reduction (used as a representative reaction) was demonstrated on a Ni single-atom catalyst with increased Ni loading.« less

Electrochemically converting nitrate, a widespread water pollutant, back to valuable ammonia is a green and delocalized route for ammonia synthesis, and can be an appealing and supplementary alternative to the Haber-Bosch process. However, as there are other nitrate reduction pathways present, selectively guiding the reaction pathway towards ammonia is currently challenged by the lack of efficient catalysts. Here we report a selective and active nitrate reduction to ammonia on Fe single atom catalyst, with a maximal ammonia Faradaic efficiency of ~ 75% and a yield rate of up to ~ 20,000 μg h^–1 mg_cat.^–1 (0.46 mmol h^–1 cm^–2). Our Femore » single atom catalyst can effectively prevent the N-N coupling step required for N₂ due to the lack of neighboring metal sites, promoting ammonia product selectivity. Density functional theory calculations reveal the reaction mechanisms and the potential limiting steps for nitrate reduction on atomically dispersed Fe sites.« less

The condensation of half-light half-matter exciton polaritons in semiconductor optical cavities is a striking example of macroscopic quantum coherence in a solid-state platform. Quantum coherence is possible only when there are strong interactions between the exciton polaritons provided by their excitonic constituents. Rydberg excitons with high principal value exhibit strong dipole–dipole interactions in cold atoms. However, polaritons with the excitonic constituent that is an excited state, namely Rydberg exciton polaritons (REPs), have not yet been experimentally observed. Here, we observe the formation of REPs in a single crystal CsPbBr ₃ perovskite cavity without any external fields. These polaritons exhibit strongmore » nonlinear behavior that leads to a coherent polariton condensate with a prominent blue shift. Furthermore, the REPs in CsPbBr ₃ are highly anisotropic and have a large extinction ratio, arising from the perovskite’s orthorhombic crystal structure. Our observation not only sheds light on the importance of many-body physics in coherent polariton systems involving higher-order excited states, but also paves the way for exploring these coherent interactions for solid-state quantum optical information processing.« less

Two-dimensional topological materials bearing time reversal-breaking magnetic fields support protected one-way edge modes. Normally, these edge modes adhere to physical edges where material properties change abruptly. However, even in homogeneous materials, topology still permits a unique form of edge modes - kink modes - residing at the domain boundaries of magnetic fields within the materials. This scenario, despite being predicted in theory, has rarely been demonstrated experimentally. Here, we report our observation of topologically-protected high-frequency kink modes - kink magnetoplasmons (KMPs) - in a GaAs/AlGaAs two-dimensional electron gas (2DEG) system. These KMPs arise at a domain boundary projected from an externally-patternedmore » magnetic field onto a uniform 2DEG. They propagate unidirectionally along the boundary, protected by a difference of gap Chern numbers in the two domains. They exhibit large tunability under an applied magnetic field or gate voltage, and clear signatures of nonreciprocity even under weak-coupling to evanescent photons.« less

Hydrogen assisted magnesiothermic reduction (HAMR) of TiO₂ is a promising new process developed recently to produce Ti metal with low cost and less energy consumption. Here this work focuses on the understanding and optimization of the reduction process to control the quality of the reduced product. TiO₂ precursor particles with different relative densities were prepared, and the effects of the relative densities on reduction by Mg in H₂ were studied. The changes of oxygen contents vs. reduction time at various temperatures were investigated. The phase transformations during the reduction were analyzed both theoretically and experimentally. The relationship between the morphologymore » of the reduced products and the relative densities of the TiO₂ precursors was analyzed by SEM characterization and the likely reason for the morphology evolution was discussed.« less