Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Metasurfaces incorporating graphene hold great promise for active manipulation of terahertz waves. However, it remains challenging to design a broadband graphene-based terahertz metasurface with switchable functionality of half-wave plate (HWP) and quarter-wave plate (QWP). Here, we propose a graphene-metal hybrid metasurface for achieving broadband switchable HWP/QWP in the terahertz regime. Simulation results show that, by varying the Fermi energy of graphene from 0 eV to 1 eV, the function of the reflective metasurface can be switched from an HWP with polarization conversion ratio exceeding 97% over a wide band ranging from 0.7 THz to 1.3 THz, to a QWP with ellipticity above 0.92 over 0.78-1.33 THz. The sharing bandwidth reaches up to 0.52 THz and the relative bandwidth is as high as 50%. We expect this broadband and dynamically switchable terahertz HWP/QWP will find applications in terahertz sensing, imaging, and telecommunications.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this paper, we develop a research of spin currents in a <jats:sup>23</jats:sup>Na spinor Bose-Einstein condensate (BEC) by applying a magnetic field gradient. The spin current is successfully induced by the spin-dependent force arising from the magnetic field gradient. The dynamics of the spin components under the magnetic force is investigated. The study is promising to be extended to produce a longer spin-coherence and enhance the sensitivity of the spin-mixing interferometry in a spinor BEC.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Although the significant roles of magnetic induction and electromagnetic radiation in the neural system have been widely studied, their influence on Parkinson’s disease (PD) has yet to be well explored. By virtue of the magnetic flux variable, this paper study the transition of firing patterns induced by magnetic induction and the regulation effect of external magnetic radiation on the firing activities of the subthalamopallidal network in basal ganglia. We find: (1) The network reproduces five typical waveforms corresponding to the severity of symptoms: weak cluster, episodic, continuous cluster, episodic, and continuous wave. (2) Magnetic induction is a double-edged sword for the treatment of PD. Although the increase of magnetic coeffcient may lead the physiological firing activity to transfer to pathological firing activity, it also can regulate the pathological intensity firing activity with excessive <jats:italic>β</jats:italic>-band power transferring to the physiological firing pattern with weak <jats:italic>β</jats:italic>-band power. (3) External magnetic radiation could inhibit continuous tremulous firing and <jats:italic>β</jats:italic>-band power of subthalamic nucleus (STN), which means the severity of symptoms weakened. Especially, the bi-parameter plane of the regulation region shows that a short pulse period of magnetic radiation and a medium level of pulse percentage can well regulate pathological oscillation. This work helps to understand the firing activity of the subthalamopallidal network under electromagnetic effect. It may also provide insights into the mechanisms behind the electromagnetic therapy of PD-related firing activity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Noble metal nanoparticles exhibit unique surface plasmon resonance dependent optical properties. On this basis, gold nanoparticles (AuNPs) encapsulated in metal-organic frameworks (MOFs) can form AuNPs@MOFs composites to modulate the optical properties of fluorescent molecules, which is less reported. In this paper, based on the fluorescence enhancement effect of AuNPs on 2-(2-Hydroxyphenyl)-1H-benzimidazole (HPBI) molecules, zeolitic imidazolate framework-8 (ZIF-8) crystals with structural stability were introduced. AuNPs@ZIF-8 exhibited a significantly pronounced fluorescence enhancement of the HPBI molecules. In addition, by comparing the fluorescence characteristics of the HPBI molecules adsorbed on AuNPs@ZIF-8 and the ones captured in AuNPs@ZIF-8, we found that the ZIF-8 can act as a spacer layer with highly effective near-field enhancement. All our preliminary results throw light on future research on the composite structures of noble metal particles and MOFs for fluorescent probes and sensing applications.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Na-ion batteries (NIBs), as one of the next-generation rechargeable battery systems, hold great potential in large-scale energy storage applications owing to the abundance and cost-effectiveness of sodium resources. Despite the extensive exploration of electrode materials, the relatively low attainable capacity of NIBs hinders their practical application. In recent years, the anionic redox reaction (ARR) in NIBs has been emerging as a new paradigm to deliver extra capacity and thus offers an opportunity to break through the intrinsic energy density limit. In this review, the fundamental investigation of the ARR mechanism and the latest exploration of cathode materials are summarized, in order to highlight the significance of reversible anionic redox and suggest prospective developing directions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The influences of off-state overdrive stress on the fluorine-plasma treated AlGaN/GaN high-electronic mobility transistors (HEMTs) are investigated. It is observed that the reverse leakage current between the gate and source decreases after the off-state stress, whereas that current between the gate and drain increases. By analyzing those changes of the reverse currents based on the Frenkel-Poole model, it is suggested that the ionization of fluorine ions occurs during the off-state stress. Furthermore, threshold voltage degradation is also observed after the off-state stress, but the degradations of AlGaN/GaN HEMTs treated with different F-plasma RF powers are different. By comparing the differences between those devices, we find that the F-ions incorporated in the GaN buffer layer play an important role in averting degradation. Lastly, suggestions to obtain a more stable fluorine-plasma treated AlGaN/GaN HEMT are put forwarded.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This review provides a discussion of the current state of research on sp-carbon chains synthesized by pulsed laser ablation in liquid. In recent years, pulsed laser ablation in liquid (PLAL) has been widely employed for polyynes synthesis thanks to its flexibility with varying laser parameters, solvents, and targets. This allows the control of sp-carbon chains properties as yield, length, termination and stability. Although many reviews related to PLAL have been published, a comprehensive work reporting the current status and advances related to the synthesis of sp-carbon chains by PLAL is still missing. Here we first review the principle of PLAL and the mechanisms of formation of sp-carbon chains. Then we discuss the role of laser fluence (i.e. energy density), solvent, and target for sp-carbon chains synthesis. Lastly, we report the progress related to the prolonged stability of sp-carbon chains by PLAL encapsulated in polymeric matrices. This review will be a helpful guide for researchers interested in synthesizing sp-carbon chains by PLAL.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>As concepts closely related to microwave absorption properties, impedance matching and phase matching were rarely combined with material parameters to regulate properties and explore related mechanisms. In this work, reduction diffusion method was innovatively applied to synthesize rare earth alloy Y<jats:sub>2</jats:sub>Fe<jats:sub>17</jats:sub>. In order to regulate the electromagnetic parameters of absorbers, the Y<jats:sub>2</jats:sub>Fe<jats:sub>17</jats:sub>N<jats:sub>3-δ</jats:sub> particles were coated with silica (Y<jats:sub>2</jats:sub>Fe<jats:sub>17</jats:sub>N<jats:sub>3-δ</jats:sub>@SiO<jats:sub>2</jats:sub>) and absorbers with different volume fractions were prepared. The relationship between impedance matching, matching thickness and the strongest reflection loss peak (<jats:italic>RL</jats:italic> <jats:sub> <jats:italic>min</jats:italic> </jats:sub>) was presented obviously. Compared to the microwave absorption properties of Y<jats:sub>2</jats:sub>Fe<jats:sub>17</jats:sub>N<jats:sub>3-δ</jats:sub>/PU absorber, Y<jats:sub>2</jats:sub>Fe<jats:sub>17</jats:sub>N<jats:sub>3-δ</jats:sub>@SiO<jats:sub>2</jats:sub>/PU absorbers are more conducive to the realization of microwave absorption material standards which are thin thickness, light weight, strong absorbing intensity and broad bandwidth. Based on microwave frequency bands, the microwave absorption properties of the absorbers were analyzed and the related parameters were listed. As an important parameter related to perfect matching, reflection factor ($\sqrt {{\varepsilon _r}/{\mu _r}} $) was discussed combined with microwave amplitude attenuation. According to the origin and mathematical model of bandwidth, the formula of EAB (RL&lt;-10 dB) was derived and simplified. The calculated bandwidths agreed well with the experimental results.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this letter, we demonstrate a novel Si-rich SiN bilayer passivation technology for AlGaN/GaN HEMTs with thin-barrier to minimize surface leakage current to enhance the breakdown voltage. The bilayer SiN with 20 nm Si-rich SiN and 100 nm Si<jats:sub>3</jats:sub>N<jats:sub>4</jats:sub> was deposited by plasma-enhanced chemical vapor deposition (PECVD) after removing 20 nm SiO<jats:sub>2</jats:sub> pre-deposition layer. Compared to traditional Si<jats:sub>3</jats:sub>N<jats:sub>4</jats:sub> passivation for thin-barrier AlGaN/GaN HEMTs, Si-rich SiN bilayer passivation can suppress the current collapse ratio from 18.54% to 8.40%. However, Si-rich bilayer passivation leads to a severer surface leakage current, so that it has a low breakdown voltage. 20nm SiO<jats:sub>2</jats:sub> pre-deposition layer can protect the surface of HEMTs in fabrication process and decrease Ga-O bonds, resulting in a lower surface leakage current. In contrast to passivating Si-rich SiN directly, devices with the novel Si-rich SiN bilayer passivation increase the breakdown voltage from 29 V to 85 V. RF small-signal characteristics show that HEMTs with the novel bilayer SiN passivation leads to <jats:italic>f</jats:italic> <jats:sub>T</jats:sub>/<jats:italic>f</jats:italic> <jats:sub>max</jats:sub> of 68 GHz/102 GHz. At 30 GHz and <jats:italic>V</jats:italic> <jats:sub>DS</jats:sub> = 20 V, devices obtain a maximum <jats:italic>P</jats:italic> <jats:sub>out</jats:sub> of 5.2 W/mm and a peak PAE of 42.2%. These results indicate that HEMTs with the novel bilayer SiN passivation can have potential applications in the millimeter-wave range.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this work, a series of nominal compositions MgAl<jats:sub>2-<jats:italic>x</jats:italic> </jats:sub>(Li<jats:sub>1/3</jats:sub>Ti<jats:sub>2/3</jats:sub>)<jats:sub> <jats:italic>x</jats:italic> </jats:sub>O<jats:sub>4</jats:sub> (<jats:italic>x</jats:italic> = 0, 0.04, 0.08, 0.12, 0.16 and 0.20) ceramics were successfully prepared via the conventional solid-state reaction route. The phase compositions, microstructures, and microwave dielectric properties were investigated. The results of X-ray diffraction (XRD) and Scanning electron microscopy (SEM) showed that a single phase ceramics of MgAl<jats:sub>2-<jats:italic>x</jats:italic> </jats:sub>(Li<jats:sub>1/3</jats:sub>Ti<jats:sub>2/3</jats:sub>)<jats:sub> <jats:italic>x</jats:italic> </jats:sub>O<jats:sub>4</jats:sub> with spinel structure were obtained at <jats:italic>x</jats:italic> ≤ 0.12, whereas the second phase MgTi<jats:sub>2</jats:sub>O<jats:sub>5</jats:sub> appeared when <jats:italic>x</jats:italic> &gt; 0.12. The cell parameters were obtained by XRD refinement. As the <jats:italic>x</jats:italic> values increased, the unit cell volume kept expanding. This phenomenon could be attributed to the partial substitution of (Li<jats:sub>1/3</jats:sub>Ti<jats:sub>2/3</jats:sub>)<jats:sup>3+</jats:sup> for Al<jats:sup>3+</jats:sup>. Results showed that (Li<jats:sub>1/3</jats:sub>Ti<jats:sub>2/3</jats:sub>)<jats:sup>3+</jats:sup> doping into MgAl<jats:sub>2</jats:sub>O<jats:sub>4</jats:sub> spinel ceramics effectively reduced the sintering temperature and improved the quality factor (Qf) values. Optimum microwave dielectric properties were achieved for sample at <jats:italic>x</jats:italic> = 0.20 sintering at 1500℃ in oxygen atmosphere for 4 h: dielectric constant (ε<jats:sub>r</jats:sub>) = 8.78, temperature coefficient of resonant frequency (τ<jats:sub>f</jats:sub>) = -85 ppm/ ℃, and Qf = 62,300 GHz. The Qf value of <jats:italic>x</jats:italic> = 0.20 sample was about two times higher than that of pure MgAl<jats:sub>2</jats:sub>O<jats:sub>4</jats:sub> ceramics (31600 GHz). Thus, MgAl<jats:sub>2-<jats:italic>x</jats:italic> </jats:sub>(Li<jats:sub>1/3</jats:sub>Ti<jats:sub>2/3</jats:sub>)<jats:sub> <jats:italic>x</jats:italic> </jats:sub>O<jats:sub>4</jats:sub> ceramics with excellent microwave dielectric properties can be applied to 5G communications.</jats:p>