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Switchable optical trapping based on vortex-pair beams generated by a polarization-multiplexed dielectric metasurface.

Optical trapping is a state-of-the-art methodology that plays an integral role in manipulating and investigating microscopic objects but faces formidable challenges in multiparticle trapping, flexible manipulation, and high-integration applications. In this study, we propose and demonstrate a switchable optical scheme for trapping microparticles incorporating disparate vortex-pair beams generated by a polarization-multiplexed metasurface. The miniaturized all-dielectric metasurface, which comprises an array of titanium dioxide nanoposts, was manufactured and characterized to provide polarization-tuned two-fold vortex-pair beams. The profiles of the created vortices can be flexibly tailored by adjusting the combination of topological charges and the separation among phase singularities. Under transverse electric polarized light conditions, a vortex-pair beam with opposite topological charge combinations traps a single microparticle within one beam spot, while under transverse magnetic polarization conditions, two microparticles are captured simultaneously by a vortex-pair beam with the same topological charge signs. The proposed switchable trapping scheme (incorporating a vortex-pair light beam) is expected to feature enhanced integration and flexible manipulation of multiple particles with potential applications in biophysics, nanotechnology, and photonics.

Growth temperature induced changes of luminescence in epitaxial BN: from colour centres to donor-acceptor recombination.

Defects play a very important role in semiconductors and only the control over the defect properties allows the implementation of materials in dedicated applications. We present an investigation of the UV luminescence of defects in hexagonal boron nitride (h-BN) grown by Metal Organic Vapor Phase Epitaxy (MOVPE). Such intentionally introduced defects are important for applications like deep UV emission and quantum information. In this work, we performed photoluminescence and cathodoluminescence experiments on a set of h-BN layers grown by MOVPE at different growth temperatures (tgr). The obtained defect-related spectra in the ultraviolet range include well-known lines at about 230 nm (X230, hν = 5.4 eV) and 300 nm (C300 - the brightest one, hν = 4.14 eV) as well as a rarely observed band with a zero-phonon line at 380 nm (C380, hν = 3.24 eV). The C300 and C380 bands have the characteristic of a color centre showing sharp lines (0.6 nm width) at 5 K. These lines are most probably an internal transition of carbon-related defects. We show that for samples grown at high temperatures (tgr > 1200 °C), the lines related to the color centres C are replaced by broad bands at 330 nm and 400 nm, which we marked as D330 and D400, respectively. The D bands have similar central energies to the C bands but extend over a large energy range, so we propose that the D emission is due to a shallow donor to deep acceptor recombination. Time-resolved photoluminescence analysis determined the lifetimes of the individual lines in the range from 0.9 ns (C300), 1.8 ns (C380) to 4 ns (D400). The C300 and C380 color centre bands are composed of a series of characteristic lines that are due to the interaction with phonons. The E1u (198 meV) and A2u (93 meV) phonon replicas have been identified.

Open Access
Single-layer HNb3O8 with strong and nearby Lewis and Brønsted acid sites boosts amide bond hydrolysis for urease mimicking.

Urea pollution is a growing environmental concern, and its removal via catalytic hydrolysis is challenging due to the resonance-stabilized amide bonds. In nature, this reaction is catalyzed by ureases in many soil bacteria. However, the remedy of this problem with natural enzymes is not feasible as they are easily denatured and require high costs for both preparation and storage. Given this, the development of nanomaterials bearing enzyme-like activity (nanozymes) with advantages such as low production cost, simple storage, and pH/thermal stability has attracted much attention over the past decade. As inspired by the mechanism of urease-catalyzed urea hydrolysis, the co-presence of Lewis acid (LA) and Brønsted acid (BA) sites is imperative to proceed with this reaction. Herein, layered HNb3O8 samples with intrinsic BA sites were adopted for investigation. The layer reduction of this material to few-/single layers can expose Nb sites with various LA strengths depending on the degree of NbO6 distortion. Among the catalysts examined, single-layer HNb3O8 bearing strong LA and BA sites displays the best hydrolytic activity towards acetamide and urea. This sample with high thermal stability was found to outperform urease at temperatures higher than 50 °C. The acidity-activity correlation established in this study is believed to guide the future design of industrial catalysts to remediate urea pollution.

A quasi-solid polymer electrolyte initiated by two-dimensional functional nanosheets for stable lithium metal batteries.

Lithium-metal batteries (LMBs) are expected to serve as next-generation energy storage systems due to their high theoretical energy density. However, their practical application is largely impeded due to the safety risks that arise from the uncontrollable Li dendrite growth and the high reactivity between high flammability liquid organic electrolytes and metallic lithium. Here, we report a highly safe quasi-solid gel polymer electrolyte (GPE) to achieve stable cycling of lithium metal with high coulombic efficiency, and it is prepared by in situ polymerization of 1,3-dioxolane (DOL) assisted by multi-functional H3Sb3P2O14 sheets. H3Sb3P2O14 acts as an initiator and a functional additive simultaneously that promotes the formation of a stable solid electrolyte interface (SEI) layer, thereby regulating the uniform deposition of Li and improving the Li plating/stripping efficiency. The obtained quasi-solid GPE exhibits high ionic conductivity and enhanced oxidative stability, favoring a stabilized electrode/electrolyte interface. Using the GPE, the electrochemical performance of the quasi-solid-state LMB with a LiFePO4 cathode and a lithium metal anode is significantly improved, delivering a discharge capacity of 125.7 mA h g-1 even after 1000 cycles. Therefore, the high reversibility and remarkable battery cyclability suggest that such a GPE is a promising choice of electrolyte for LMBs, while its facile preparation makes its large-scale application possible in the future.