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<jats:p>Perfect vector beams are a class of special vector beams with invariant radius and intensity profiles under changing topological charges. However, with the limitation of current devices, the generation of these vector beams is limited in the visible and infrared wavebands. Herein, we generate perfect vector beams in the ultraviolet region assisted by nonlinear frequency conversion. Experimental and simulation results show that the radius of the generated ultraviolet perfect vector beams remains invariant and is thus independent of the topological charge. Furthermore, we measure the power of the generated ultraviolet perfect vector beams with the change of their topological charges. This study provides an alternative approach to generating perfect vector beams for ultraviolet wavebands and may promote their application to optical trapping and optical communication.</jats:p>

<jats:p>We propose a scheme to generate stable vector spatiotemporal solitons through a Rydberg electromagnetically induced transparency (Rydberg-EIT) system. Three-dimensional vector monopole and vortex solitons have been found under three nonlocal degrees. The numerical calculation and analytical solutions indicate that these solitons are generated with low energy and can stably propagate along the axes. The behavior of vector spatiotemporal solitons can be manipulated by the local and nonlocal nonlinearities. The results show a memory feature as these solitons can be stored and retrieved effectively by tuning the control field.</jats:p>

<jats:p>Both boron nitride (BN) and carbon (C) have <jats:italic>sp</jats:italic>, <jats:italic>sp</jats:italic> <jats:sup>2</jats:sup> and <jats:italic>sp</jats:italic> <jats:sup>3</jats:sup> hybridization modes, thus resulting in a variety of BN and C polymorphs with similar structures, such as hexagonal BN (hBN) and graphite, cubic BN (cBN) and diamond. Here, five types of BN polymorph structures are proposed theoretically, inspired by the graphite-diamond hybrid structures discovered in a recent experiment. These BN polymorphs with graphite-diamond hybrid structures possess excellent mechanical properties with combined high hardness and high ductility, and also exhibit various electronic properties such as semi-conductivity, semi-metallicity, and even one- and two-dimensional conductivity, differing from known insulators hBN and cBN. The simulated diffraction patterns of these BN hybrid structures could account for the unsolved diffraction patterns of intermediate products composed of so-called “compressed hBN” and diamond-like BN, caused by phase transitions in previous experiments. Thus, this work provides a theoretical basis for the presence of these types of hybrid materials during phase transitions between graphite-like and diamond-like BN polymorphs.</jats:p>

<jats:p>Many mechanical, thermal and transport behaviors of polymers and metallic glasses are interpreted by the free-volume model, whereas their applications on thermal expansion behaviors of glasses is rarely seen. Metallic glass has a range of glassy states depending on cooling rate, making their coefficients of thermal expansion vary with the glassy states. Anharmonicity in the interatomic potential is often used to explain different coefficients of thermal expansion in crystalline metals or in different metallic-glass compositions. However, it is unclear how to quantify the change of anharmonicity in the various states of metallic glass of the same composition and to connect it with coefficient of thermal expansion. In the present work, isothermal annealing is applied, and the dimensional changes are measured for La<jats:sub>62</jats:sub>Al<jats:sub>14</jats:sub>Cu<jats:sub>11.7</jats:sub>Ag<jats:sub>2.3</jats:sub>Ni<jats:sub>5</jats:sub>Co<jats:sub>5</jats:sub> and Zr<jats:sub>52.5</jats:sub>Cu<jats:sub>17.9</jats:sub>Ni<jats:sub>14.6</jats:sub>Al<jats:sub>10</jats:sub>Ti<jats:sub>5</jats:sub> metallic glasses, from which changes in density and the coefficients of thermal expansion of the specimens are both recorded. The coefficients of thermal expansion linearly decrease with densification reflecting the role of free volume in thermal expansion. Free volume is found to have not only volume but also entity with an effective coefficient of thermal expansion similar to that of gases. Therefore, the local regions containing free volume inside the metallic glass are gas-like instead of liquid-like in terms of thermal expansion behaviors.</jats:p>

<jats:p>High-quality polycrystalline diamond films with dominated (100)-oriented grains are realized by combining the thermally oxidation and the homogeneous second growth processes. Moreover, we investigate the wettability property of the polycrystalline diamonds in various stages. Different surface structures (with various grain sizes, voids, and orientations, etc.) and terminations (hydrogen or oxygen) have significant effects on the wettability of polycrystalline diamond films. The wettability is further closely related to the polarity of solutions. By measuring the contact angle and calculating the dispersion and polarity components, we estimate the surface energy of polycrystalline diamond films, and explore the factors affecting the surface energy. The modulations in growth quality and wettability property of polycrystalline diamond films provide valuable data for development of diamond-based multiple devices in practical applications.</jats:p>

<jats:p>Twisted bilayer graphene (TBG), which has drawn much attention in recent years, arises from van der Waals materials gathering each component together via van der Waals force. It is composed of two sheets of graphene rotated relatively to each other. Moiré potential, resulting from misorientation between layers, plays an essential role in determining the band structure of TBG, which directly relies on the twist angle. Once the twist angle approaches a certain critical value, flat bands will show up, indicating the suppression of kinetic energy, which significantly enhances the importance of Coulomb interaction between electrons. As a result, correlated states like correlated insulators emerge from TBG. Surprisingly, superconductivity in TBG is also reported in many experiments, which drags researchers into thinking about the underlying mechanism. Recently, the interest in the atomic reconstruction of TBG at small twist angles comes up and reinforces further understandings of properties of TBG. In addition, twisted multilayer graphene receives more and more attention, as they could likely outperform TBG although they are more difficult to handle experimentally. In this review, we mainly introduce theoretical and experimental progress on TBG. Besides the basic knowledge of TBG, we emphasize the essential role of atomic reconstruction in both experimental and theoretical investigations. The consideration of atomic reconstruction in small-twist situations can provide us with another aspect to have an insight into physical mechanism in TBG. In addition, we cover the recent hot topic, twisted multilayer graphene. While the bilayer situation can be relatively easy to resolve, multilayer situations can be really complicated, which could foster more unique and novel properties. Therefore, in the end of the review, we look forward to future development of twisted multilayer graphene.</jats:p>

<jats:p>Dynamic cantilever magnetometry is a sensitive method that has been widely used in studying magnetic anisotropy in ferromagnetic materials and Fermi surface in quantum materials. We study a cobalt-iridium metal-metalloligand coordination polymer using dynamic cantilever magnetometry. The experimental data of dynamic cantilever magnetometry are well explained using the proposed model for Langevin paramagnetism with slow relaxation. Based on the proposed model, we calculate the magnetization and magnetic susceptibility of paramagnetic materials from frequency shifts of a cantilever. The extracted magnetization and magnetic susceptibility are consistent with those obtained from conventional DC and AC magnetometry. The proposed slow relaxation picture is probably a general model for explaining dynamic cantilever magnetometry data of paramagnetic materials, including previously observed dynamic cantilever magnetometry data of paramagnetic metals [Gysin <jats:italic>et al.</jats:italic> 2011 <jats:italic>Nanotechnology</jats:italic> <jats:bold>22</jats:bold> 285715].</jats:p>

<jats:p>Electroluminescence from a p-type GaAs(110) surface was induced by tunneling electrons in a scanning tunneling microscope under both polarities of bias voltage. The optical spectra exhibit a polarity-independent luminescence peak at 1.47 eV resulting from the exciton recombination. However, the quantum yield of photon emission at negative bias voltage is two orders of magnitude weaker than that at positive bias voltage. Moreover, the luminescence at negative bias voltage shows the linear dependence of bias voltage, distinct from the rapid rise due to resonant electron injection at positive bias. Furthermore, the threshold bias voltage for electroluminescence at negative bias is nearly twice the bandgap of GaAs, not simply satisfying the energy conservation for the creation of an electron-hole pair. Through theoretical calculation, we propose an impact ionization model to nicely explain the newly observed electroluminescence at negative bias voltage. We believe that this mechanism of impact ionization could be readily applied to other nanoscale optoelectronics including 2D semiconductors and 1D nanostructures.</jats:p>

<jats:p>Ni-rich layered oxide cathode materials, such as LiNi<jats:sub>0.83</jats:sub>Co<jats:sub>0.12</jats:sub>Mn<jats:sub>0.05</jats:sub>O<jats:sub>2</jats:sub> (NCM811), exhibit high specific capacity and low cost, and become cathode material preference of high-energy-density Li-ion batteries. However, these cathode materials are not stable and will form Li-poor reconstructed layers and alkaline compounds (Li<jats:sub>2</jats:sub>CO<jats:sub>3</jats:sub>, LiOH) on the surface during the storage and processing in humid air, resulting in serious deterioration of electrochemical properties. During the past two decades, the consensus on the surface instability mechanism during humid air storage has not been reached. The main controversy focuses on the unstable octahedron mechanism and the Li/H exchange mechanism. Herein, we investigate the instability mechanism in the humid air by conducting scanning electronic microscopy, scanning transmission electron microscopy, and x-ray photoelectron spectroscopy analysis on NCM811 samples stored in designed atmospheres, etc., and realize that the surface instability of the NCM811 during storage should be mainly originated from Li/H exchange when it contacts with moisture.</jats:p>

<jats:p>Beginning with precise data on the ratio of structure functions in deep inelastic scattering (DIS) from <jats:sup>3</jats:sup>He and <jats:sup>3</jats:sup>H, collected on the domain 0.19 ≤ <jats:italic>x</jats:italic> <jats:sub>B</jats:sub> ≤ 0.83, where <jats:italic>x</jats:italic> <jats:sub>B</jats:sub> is the Bjorken scaling variable, we employ a robust method for extrapolating such data to arrive at a model-independent result for the <jats:italic>x</jats:italic> <jats:sub>B</jats:sub> = 1 value of the ratio of neutron and proton structure functions. Combining this with information obtained in analyses of DIS from nuclei, corrected for target-structure dependence, we arrive at a prediction for the proton valence-quark ratio: <jats:italic>d<jats:sub>ν</jats:sub> </jats:italic>/<jats:italic>u<jats:sub>νq</jats:sub> </jats:italic> |<jats:sub> <jats:italic>x</jats:italic> <jats:sub>B</jats:sub> → 1</jats:sub> = 0.230 (57). Requiring consistency with this result presents a challenge to many descriptions of proton structure.</jats:p>