[en] Cycling performance and thermal stability of spinel LiMn₂O₄ cathode material synthesized by a sol–gel method are improved by surface modification with FeF₃ through chemical deposition method. The phase structures, components and morphologies of pristine and FeF₃-coated LiMn₂O₄ are investigated by X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM). The cycling performances are thoroughly investigated and compared at room and high temperatures. The FeF₃-coated LiMn₂O₄ electrodes display enhanced cycling stabilities compared with that of pristine LiMn₂O₄. Especially, the 5 wt.% FeF₃-coated LiMn₂O₄ demonstrates the best cycling performance, with the capacity retentions of 68.2% after 200 cycles at room temperature (25 °C) and 61.5% after 100 cycles at elevated temperature (55 °C), much better than those of the pristine materials, 49.8 and 40.2%. Cyclic voltammetry (CV) confirms that FeF₃ modification layer improves the structure stability of LiMn₂O₄. Electrochemical impedance spectroscopy (EIS) data illustrate that FeF₃ coating can suppress the fast growth of undesirable solid electrolyte interfacial (SEI) film. Differential scanning calorimetry (DSC) tests show that the existence of FeF₃ helps to enhance the thermal stability of LiMn₂O₄ cathode

[en] Highlights: •Hydrothermal method was firstly utilized to prepare Si/TiO₂ composite. •The Si/TiO₂ composite demonstrates a high reversible capacity after 50 cycles. •TiO₂ serves not only as buffer, but also contributes capacity in repeated cycling. -- Abstract: Si/TiO₂ composites as anode material for lithium ion batteries are synthesized by a simple hydrothermal method. X-ray diffraction, inductively coupled plasma and field-emission scanning electron microscopy are used to determine their phase structures, components and surface morphologies. The electrochemical properties of Si, TiO₂ and Si/TiO₂ composites are investigated and compared by galvanostatic cycling measurements, which exhibits the discharge capacities of 4, 121 and 395 mA h g⁻¹ at 0.1 C after 50 cycles, respectively. Cyclic voltammogram measurements are carried out to further clarify the origin of excellent electrochemical performances of the Si/TiO₂ composite. Surface morphologies of electrode plates after 10 cycles show that the Si/TiO₂ composite electrode has more structural retention compared with its Si counterpart. All the experimental observations indicate that the performance improvement of Si/TiO₂ composites could be attributed to TiO₂ which suppresses the volume change of Si particles. On the other hand, TiO₂ also contributes electrochemical activity in repeated cycling with relatively stable structure

[en] Nanoparticles supporting a distinct series of Mie resonances have enabled a new class of nanoantennas and provide efficient ways to manipulate light at the nanoscale. The ability to flexibly tune the optical resonances and scattering directionality are particularly essential for various applications ranging from biosensing to nanolasers. In this paper, we investigate the core-shell nanoparticles that support both electric and magnetic Mie resonances and for the first time systematically reveal the mode evolution from a pure high-index dielectric nanosphere to its plasmonic counterpart. Abrupt mode transition and hybridization of Mie resonances are found in Ag-dielectric core-shell spheres when core-shell ratio increases from 0.4 to 0.5. Furthermore, by engineering the electric and magnetic resonances, we demonstrate the unidirectional forward and backward scattering in such a system and reveal its tunability via geometric tuning. (paper)

[en] Nonradiating sources are nontrivial charge–current distributions that do not generate fields outside the source domain. The pursuit of their possible existence has fascinated several generations of physicists and triggered developments in various branches of science ranging from medical imaging to dark matter. Recently, one of the most fundamental types of nonradiating sources, named anapole states, has been realized in nanophotonics regime and soon spurred considerable research efforts and widespread interest. A series of astounding advances have been achieved within a very short period of time, uncovering the great potential of anapole states in many aspects such as lasing, sensing, metamaterials, and nonlinear optics. In this review, we provide a detailed account of anapole states in nanophotonics research, encompassing their basic concepts, historical origins, and new physical effects. We discuss the recent research frontiers in understanding and employing optical anapoles and provide an outlook for this vibrant field of research. (paper)

[en] We proposed a silicon-based monolithic integrated multi-wavelength InAs/GaAs quantum dot microring laser array with radially coupled waveguides. To achieve the stable multi-wavelength lasing of the laser array in the 1.3 μm band, the three-dimensional finite-difference time-domain method is used to numerically optimize structure parameters of the microring laser with a connected III–V waveguide. The results show that the microring laser can realize a stable mode TE${}_{50,1}$ with an outer-wall radius of 3.5 μm, a microring width of 1.0 μm, a cladding thickness of 1.50 μm, an etching depth of 5.255 μm and a waveguide width of 0.5 μm. The mode wavelength is 1302.43 nm with a quality factor of 20,093.6. The optical coupling efficiency from the laser to the waveguide is about 47.8%. Moreover, mode wavelengths can be adjusted by the microring radius. When the microring width is 1.0 μm, changing the outer-wall radius from 2.7 to 3.9 μm with an interval of 0.2 μm, the mode wavelength ranges from 1289.29 to 1307.28 nm with a step of about 3.00 nm. It is feasible to achieve multi-wavelength laser arrays for monolithic silicon integration, which facilitates the preparation of silicon-based III–V multi-wavelength integrated light sources for dense wavelength division multiplexing applications.

[en] We, first, demonstrate an optimized structure design and analyze the optical mode properties of 1.3 μm wavelength square microcavity lasers on silicon with InAs/InGaAs quantum-dot active region and mid-point output waveguides. Si-based square microcavities with whispering-gallery-like modes have been proposed for optimizing their quality factors (Q factors). Three-dimensional finite-difference time-domain method is used to numerically analyze the optical mode characteristics. The influences of the side-length of the microcavity, the output waveguide width, and the etching depth on the optical modes of the microcavity are investigated in detail. It indicates that the Q factor increases with increasing etching depth, and decreases rapidly as the waveguide width increases. The results show that with the side length of 18 μm, the waveguide width of 1.0 μm, and the etching depth of 3.5 μm, the Q factor is the highest, and the mode distribution is optimal. The mode wavelength and Q factor are 1305.9 nm and 4694.8, respectively. Advantages of more stable and evenly distributed mode profiles for Si-based square microcavity lasers have been demonstrated, and compared with the Si-based disk microcavity (microdisk) lasers. It promises a potential alternative laser structure for Si-based optoelectronic integration.

[en] Nanowelding of nanomaterials opens up an emerging set of applications in transparent conductors, thin-film solar cells, nanocatalysis, cancer therapy, and nanoscale patterning. Single point nanowelding (SPNW) is highly demanded for building complex nanostructures. In this letter, the precise control of SPNW of silver nanowires is explored in depth, where the nanowelding is laser-induced through the plasmonic resonance enhanced photothermal effect. It is shown that the illumination position is a critical factor for the nanowelding process. As an example of performance enhancement, output at wire end can be increased by 65% after welding for a plasmonic nanocoupler. Thus, single point nanowelding technique shows great potentials for high-performance electronic and photonic devices based on nanowires, such as nanoelectronic circuits and plasmonic nanodevices.

[en] A variety of combinations of Y${}_2$O${}_3$ and Al${}_2$O${}_3$ were used as sintering aids in the fabrication of Si${}_3$N${}_4$ ceramics via gas pressure sintering (GPS). Based on the prediction of the residual thermal stress at the interface, the influence of crystal phases on the wear properties of Si${}_3$N${}_4$ ceramics was analyzed. As a result, with the increase of Y${}_2$O${}_3$ addition from 1 to 9 wt%, there are four kinds of crystal phases being firmly discovered in the sample, Y${}_2$Si${}_2$O${}_7$, YSiO${}_2$N, Y${}_4$Si${}_2$O${}_7$N${}_2$, and Y${}_2$Si${}_3$O${}_3$N${}_4$. The crystal phases of Y${}_2$Si${}_2$O${}_7$, YSiO${}_2$N, and Y${}_4$Si${}_2$O${}_7$N${}_2$ inhibit the particle flaking during the friction process, which greatly inhibited the progress of the abrasive wear, and optimize the wear resistance of silicon nitride ceramics. According to Selsing's model, it can be predicted that the interface residual thermal stress caused by the intergranular phase Y${}_2$Si${}_3$O${}_3$N${}_4$ is 22-35% higher than that caused by the other three intergranular phases. The crystal phase Y${}_2$Si${}_3$O${}_3$N${}_4$ intensifies the shedding of grains during wear, and reduces the wear performance of silicon nitride ceramics. In addition, the silicon nitride ceramics with 5wt% Y${}_2$O${}_3$ show better wear resistance, and the wear rate is 1.8 × 10${}^{-<!--\; ???\; -->6}$ mm${}^3$ N${}^{-<!--\; ???\; -->1}$ m${}^{-<!--\; ???\; -->1}$.

[en] Dielectric nanoantennas have generated much interest in recent years owing to their low loss and optically induced electric and magnetic resonances. In this paper, we investigate the coupling between a single emitter and dielectric patch nanoantennas. For the coupled system involving non-spherical structures, analytical Mie theory is no longer applicable. A semi-analytical model is proposed instead to interpret the coupling mechanism and the radiation characteristics of the system. Based on the presented model, we demonstrate that the angular emission of the single emitter can be not only enhanced but also rotated using the dielectric patch nanoantennas

[en] We optimize the structure of a silicon-based InAs/InGaAs quantum dot square microcavity laser with an output waveguide structure. By designing a new laser structure, the emission wavelength is extended to 1550 nm. We investigate the structure parameters that affect the quality factor and optical mode of the square microcavity, including the side length of the microcavity, the width of the output waveguide, the cladding layer thickness and the etching depth. By connecting the output waveguide at the edge-midpoint of the square microcavity, both the unidirectional emission and mode selectivity can be obtained, which avoids mode competition. The 1550 nm wavelength single-mode laser is beneficial and has reat significance for the development of silicon-based optoelectronic integration. (paper)