Catálogo de publicaciones - revistas

<jats:p>We investigate the ultrafast spin dynamics of an antiferromagnet in a ferromagnet/antiferromagnet heterostructure Fe/GdFeO<jats:sub>3</jats:sub> via an all-optical method. After laser irradiation, the terahertz spin precession is hard to be excited in a bare GdFeO<jats:sub>3</jats:sub> without spin reorientation phase but efficiently in Fe/GdFeO<jats:sub>3</jats:sub>. Both quasi-ferromagnetic and impurity modes, as well as a phonon mode, are observed. We attribute it to the optical modification of interfacial exchange coupling between Fe and GdFeO<jats:sub>3</jats:sub>. Moreover, the excitation efficiency of dynamics can be modified significantly via the pump laser influence. Our results elucidate that the interfacial exchange coupling is a feasible stimulation to efficiently excite terahertz spin dynamics in antiferromagnets. It will expand the exploration of terahertz spin dynamics for antiferromagnet-based opto-spintronic devices.</jats:p>

<jats:p>Two-dimensional multiferroics, which simultaneously possess ferroelectricity and magnetism in a single phase, are well-known to possess great potential applications in nanoscale memories and spintronics. On the basis of first-principles calculations, a CrNCl<jats:sub>2</jats:sub> monolayer is reported as an intrinsic multiferroic. The CrNCl<jats:sub>2</jats:sub> has an antiferromagnetic ground state, with a Néel temperature of about 88 K, and it exhibits an in-plane spontaneous polarization of 200 pC/m. The magnetic moments of CrNCl<jats:sub>2</jats:sub> mainly come from the d5<jats:sub> <jats:italic>xy</jats:italic> </jats:sub> orbital of the Cr cation, but the plane of the d<jats:sub> <jats:italic>xy</jats:italic> </jats:sub> orbital is perpendicular to the direction of the ferroelectric polarization, which hardly suppresses the occurrence of ferroelectricity. Therefore, the multiferroic exits in the CrNCl<jats:sub>2</jats:sub>. In addition, like CrNCl<jats:sub>2</jats:sub>, the CrNBr<jats:sub>2</jats:sub> is an intrinsic multiferroic with antiferromagnetic-ferroelectric ground state while CrNI<jats:sub>2</jats:sub> is an intrinsic multiferroic with ferromagnetic-ferroelectric ground state. These findings enrich the multiferroics in the two-dimensional system and enable a wide range of applications in nanoscale devices.</jats:p>

<jats:p>A new frustrated triangular lattice antiferromagnet Na<jats:sub>2</jats:sub>BaNi(PO<jats:sub>4</jats:sub>)<jats:sub>2</jats:sub> was synthesized by high temperature flux method. The two-dimensional triangular lattice is formed by the Ni<jats:sup>2+</jats:sup> ions with <jats:italic>S</jats:italic> = 1. Its magnetism is highly anisotropic with the Weiss constants <jats:italic>θ</jats:italic> <jats:sub>CW</jats:sub> = –6.615 K (<jats:italic>H</jats:italic> ⊥ <jats:italic>c</jats:italic>) and –43.979 K (<jats:italic>H</jats:italic> ∥ <jats:italic>c</jats:italic>). However, no magnetic ordering is present down to 0.3 K, reflecting strong geometric spin frustration. Our heat capacity measurements show substantial residual magnetic entropy existing below 0.3 K at zero field, implying the presence of low energy spin excitations. These results indicate that Na<jats:sub>2</jats:sub>BaNi(PO<jats:sub>4</jats:sub>)<jats:sub>2</jats:sub> is a potential spin liquid candidate with spin-1.</jats:p>

<jats:p>Zn nano rods were produced on glass substrates using oblique angle deposition method at different deposition angles. For oxidation, the samples were placed in a furnace under oxygen flux. AFM and FESEM images were used to morphology analysis of the structures. The results showed that with increasing the angle of deposition, the grain size decreases and the porosity of the structures increases. XRD pattern and XPS depth profile analysis were used to crystallography and oxide thickness investigations, respectively. The XRD results confirmed oxide phase formation, and the XPS results analyzed the oxide layer thickness. The result showed that as the deposition angle of the nanorods increases, the thickness of the oxide layer increases. The reason for the increase in the thickness of the oxide layer with increasing deposition angle was investigated and attributed to the increase in the porosity of the thin films. The optical spectra of the structures for p polarized light at 10° incident light angle were obtained using single beam spectrophotometer in the 300 nm to 1000 nm wavelengths. The results showed that the formed structures although annealed in oxygen flux, tend to behave like metal. To calculate the optical constant of the structures, the reverse homogenization theory was used and the void fraction and complex refractive index of the structures were obtained. Finally, by calculating permittivity and optical conductivity of the structures, their changes with the deposition angle were investigated.</jats:p>

<jats:p>Optical fiber temperature sensors have been widely employed in enormous areas ranging from electric power industry, medical treatment, ocean dynamics to aerospace. Recently, graphene optical fiber temperature sensors attract tremendous attention for their merits of simple structure and direct power detecting ability. However, these sensors based on transfer techniques still have limitations in the relatively low sensitivity or distortion of the transmission characteristics, due to the unsuitable Fermi level of graphene and the destruction of fiber structure, respectively. Here, we propose a tunable and highly sensitive temperature sensor based on graphene photonic crystal fiber (Gr-PCF) with the non-destructive integration of graphene into the holes of PCF. This hybrid structure promises the intact fiber structure and transmission mode, which efficiently enhances the temperature detection ability of graphene. From our simulation, we find that the temperature sensitivity can be electrically tuned over four orders of magnitude and achieve up to ∼ 3.34 × 10<jats:sup>−3</jats:sup> dB/(cm⋅°C) when the graphene Fermi level is ∼ 35 meV higher than half the incident photon energy. Additionally, this sensitivity can be further improved by ∼ 10 times through optimizing the PCF structure (such as the fiber hole diameter) to enhance the light–matter interaction. Our results provide a new way for the design of the highly sensitive temperature sensors and broaden applications in all-fiber optoelectronic devices.</jats:p>

<jats:p>The different fluorescence behavior caused by the excited state proton transfer in 3-hydroxy-4-pyridylisoquinoline (2a) compound has been theoretically investigated. Our calculation results illustrate that the 2a monomer in tetrahydrofuran solvent would not occur proton transfer spontaneously, while the 2a complex in methanol (MeOH) solvent can undergo an asynchronous excited state intramolecular proton transfer (ESIPT) process. The result was confirmed by analyzing the related structural parameters, infrared vibration spectrum and reduced density gradient isosurfaces. Moreover, the potential curves revealed that with the bridging of single MeOH molecular the energy barrier of ESIPT was modulated effectively. It was distinctly reduced to 4.80 kcal/mol in 2a-MeOH complex from 25.01 kcal/mol in 2a monomer. Accordingly, the ESIPT process induced a fluorochromic phenomenon with the assistant of proton-bridge. The elucidation of the mechanism of solvent discoloration will contribute to the design and synthesis of fluorogenic dyes as environment-sensitive probes.</jats:p>

<jats:p>Design and simulation results of a novel multifunctional electronic calibration kit based on microelectromechanical system (MEMS) single-pole double-throw (SPDT) switches are presented in this paper. The short-open-load-through (SOLT) calibration states can be completed simultaneously by using the MEMS electronic calibration, and the electronic calibrator can be reused 10<jats:sup>6</jats:sup> times. The simulation results show that this novel electronic calibration can be used in a frequency range of 0.1 GHz–20 GHz, the return loss is less than 0.18 dB and 0.035 dB in short-circuit and open-circuit states, respectively, and the insertion loss in through (thru) state is less than 0.27 dB. On the other hand, the size of this novel calibration kit is only 6 mm × 2.8 mm × 0.8 mm. Our results demonstrate that the calibrator with integrated radio-frequency microelectromechanical system (RF MEMS) switches can not only provide reduced size, loss, and calibration cost compared with traditional calibration kit but also improves the calibration accuracy and efficiency. It has great potential applications in millimeter-wave measurement and testing technologies, such as device testing, vector network analyzers, and RF probe stations.</jats:p>

<jats:p>In blue quantum dot light emitting diodes (QLEDs), electron injection is insufficient, which would degrade device efficiency and stability. Herein, we employ chlorine passivated ZnO nanoparticles as electron transport layer to facilitate electron injection into QDs effectively. Moreover, it suppresses exciton quenching at the QD/ZnO interface by blocking charge transfer channel. As a result, the maximum external quantum efficiency of blue QLED was increased from 2.55% to 4.60%, and the operation lifetime of blue QLED was nearly 4 times longer than that of the control device. Our work indicates that election injection plays an important role in blue QLED efficiency and stability.</jats:p>

<jats:p>The special any-polar resistive switching mode includes the coexistence and stable conversion between the unipolar and the bipolar resistive switching mode under the same compliance current. In the present work, the any-polar resistive switching mode is demonstrated when thin Ti intercalations are introduced into both sides of Pt/HfO<jats:sub>2</jats:sub>/Pt RRAM device. The role of the Ti intercalations contributes to the fulfillment of the any-polar resistive switching working mechanism, which lies in the filament constructed by the oxygen vacancies and the effective storage of the oxygen ion at both sides of the electrode interface.</jats:p>

<jats:p>We propose a terahertz hybrid metamaterial composed of subwavelength metallic slits and graphene plasmonic ribbons for sensing application. This special design can cause the interaction between the plasmon resonances of the metallic slits and graphene ribbons, giving rise to a strong coupling effect and Rabi splitting. Intricate balancing in the strong coupling region can be perturbed by the carrier concentration of graphene, which is subject to the analyte on its surface. Thereby, the detection of analyte can be reflected as a frequency shift of resonance in terahertz transmission spectra. The result shows that this sensor can achieve a theoretical detection limit of 325 electrons or holes per square micrometer. Meanwhile, it also works well as a refractive index sensor with the frequency sensitivity of 485 GHz/RIU. Our results may contribute to design of ultra-micro terahertz sensors.</jats:p>