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In this paper, a transmissive reconfigurable polarization converter (RPC) based on an active metasurface is proposed, which can regulate the ideal plane wave and the spherical wave as a cladding of the horn antenna. The metasurface unit is composed of a single-layer F4B dielectric substrate and two double-cross metal strips with a p–i–n diode on the top and seven vertical metal strips on the bottom. One RPC prototype with 15 × 15 units has been fabricated and measured when it regulates an ideal plane wave. By controlling the states of diodes, the RPC can realize the linear-to-circular polarization conversion (LCPC) or the linear polarization maintaining (LPM) function from 2.5 to 3.64 GHz. Furthermore, the RPC is used as the cladding of a horn antenna for high integration in practical applications. The measured results show that this RPC-antenna system can still achieve LCPC or LPM function from 3.1 to 4.5 GHz. It is worth mentioning that the 3 dB axial ratio beam width of RPC can cover from −65° to 65° in LCPC. The proposal has advantages of a wideband, simple biasing network, and easy fabrication and integration, which can be widely applied in modern wireless communication systems. [ABSTRACT FROM AUTHOR]

Nb-doped ZnO (NbxZn1−xO, NZO) thin films with various Nb additions (x = 0, 0.2, 0.5, and 0.8 at. %) were deposited on Pt/TiO2/SiO2/Si substrates by radio frequency magnetron sputtering. The Nb doping concentration was found to affect the microstructure, the number of oxygen vacancies, and work function of the Pt/NZO/Pt structures. Among the various devices, the film with 0.5 at. % Nb addition showed a better switching-voltage stability [i.e., the optimal coefficient of variation (Cv) for reset (7.02%) and set (2.73%) operations, respectively], a high endurance (∼1000 cycles), and lower reset (0.57 V) and set (1.83 V) voltages due to a larger number of oxygen vacancies and a lower work function. In general, the results show that the present NZO thin films are promising candidates for stable and low power-consumption resistive random access memory applications. [ABSTRACT FROM AUTHOR]

Studies of spin current injection, transport, and interface control have drawn attention recently for efficient organic spintronic devices. In this study, we apply both spin pumping (SP) and the longitudinal spin Seebeck effect (LSSE) to inject spin currents into a π-conjugated organic semiconductor, perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), and characterize injection and transport by measuring inverse spin Hall voltage V ISHE in spin detectors. A normalization factor introduced to SP analysis eliminates a contribution provoked by deviation of spin sources and leads to a more accurate determination of the spin diffusion length in PTCDA. While SP with Permalloy as a spin source is effective in generating detectable V ISHE , the LSSE from yttrium iron garnet shows no convincing sign of spin injection. In addition, spin-flip scattering induced by hybrid states undermining electrical spin injection is negligible in SP. These results are attributed to interfaces between spin sources and PTCDA, indicative of the importance of injection methods and material choices. [ABSTRACT FROM AUTHOR]

ZnO thin film transistor with high-k NbLaO/SiO2 bilayer gate dielectric was fabricated by sputtering, and the temperature dependence of the electrical properties of the device was investigated in the temperature range of 293–353 K for clarifying thermally activated carrier generation and carrier transport mechanisms in the conducting channel. With the increase in the temperature, the transfer curve shifts toward the negative gate voltage direction with a negative shift of the threshold voltage, an increase in the off-state current and the subthreshold slope, and a significant increase in carrier mobility. The decrease in the threshold voltage is originated from the formation of oxygen vacancy and the release of free electrons in the ZnO channel, and the formation energy can be estimated to be approximately 0.3 eV. In both subthreshold and above-threshold regimes, the temperature dependence of the drain current shows Arrhenius-type dependence, and the activation energy is around 0.94 eV for a gate voltage of 2 V, reducing with the increase in the gate voltage. The temperature dependence of the ZnO film resistance also exhibits an Arrhenius-type behavior, indicating that the thermal activation conduction process is the dominant conduction mechanism in the ZnO film. Two types of thermal activation conduction processes are observed in the 303–373 K temperature range. This is explained in terms of the existence of two types of deep donors that are consecutively excited to the conduction band as the temperature increases. [ABSTRACT FROM AUTHOR]

The propagation dynamics of an azimuthally polarized dark hollow laser beam described by a first-order Bessel–Gauss laser beam in a parabolic plasma channel is investigated by adopting the weakly relativistic limit. By using the variational method, the evolution equation of the ring-beam radius is derived and the ring-beam width is proportional to and synchronous with the radius. It is found that the azimuthal polarization can weaken the vacuum diffraction effect and the propagation dynamics of the dark hollow laser beam may be classified into three types, i.e., propagation with a constant ring-beam radius and width, or synchronous periodic defocusing oscillation, or synchronous periodic focusing oscillation. Their corresponding critical conditions and characteristic quantities, such as the amplitudes and spatial wavelengths, are obtained. Further investigation indicates that, with the increase in the initial laser power or the ratio of initial ring-beam radius to channel radius, the dark hollow beam may experience a process from synchronous periodic defocusing oscillation to constant propagation and then to synchronous periodic focusing oscillation, in which the corresponding amplitudes decrease sharply to zero (constant propagation) and then increase gradually, while the spatial wavelength decreases continuously. The evolution type of this kind of dark hollow beam also depends on its initial amplitude but is insensitive to the initial laser profile which, however, has a large influence on the spatial wavelength. These results are well confirmed by the numerical simulation of the wave equation. A two-dimensional particle-in-cell simulation of an azimuthally polarized laser beam is performed finally and also reveals the main results. [ABSTRACT FROM AUTHOR]

The low-field dielectric responses of pure and 0.15 wt. % MnO-added (1-x)Pb(Fe2/3W1/3)O3–xPbTiO3 [(1-x)PFW–xPT] were investigated with the empirical model, the Curie–Weiss law and the spin-glass model. According to the experimental data and the fitting results, we conclude that (1) the lattice structure is changed and the electron compensation is induced with MnO addition. (2) The dielectric behaviors obey the Curie–Weiss law as the temperature is much far above Tm for all samples. (3) TCW, the temperature at which the dielectric behaviors deviate from the Curie–Weiss law, is higher and the diffuse phase characteristic is more obvious as decreasing PbTiO3 content or adding MnO. (4) The tailed temperature-dependent local order parameters, which are derived from the spin-glass model and the experimental results, for more diffuse phase transition relaxors show higher thermal stability in the spontaneous polarization microregions. (5) The temperature-dependent local ordering parameters change from a long-range-ordered ferroelectric state to a short-range-ordered relaxor with decreasing the PbTiO3 content or adding MnO. [ABSTRACT FROM AUTHOR]

Regarding the dielectric characteristics of the diffusion phase transition (DPT) in ferroelectric relaxor materials, several researchers have provided similar but different laws to explain these phenomenon. These laws, presented by Burfoot et al. and Eiras et al., have been proven to provide a better explanation, especially the dielectric diffusion phenomenon, of the incomplete DPT materials if compared with the models presented by Smolensky, and Isupov. However, the differences in fitting adaptability and the physical and mathematical meanings between these two laws have never been discussed. In this paper, we analyze these two laws in the (1-x)Pb(Fe2/3W1/3)-xPbTiO3 [(1-x)PFW-xPT] relaxor system using the statistical regression theory. We find that the laws of both Burfoot and Eiras demonstrate the same adaptability and provide smaller estimation bias on the samples than the models of Smolensky and Isupov, despite the complete or incomplete DPT characteristics. When x is smaller, the samples tend to be complete DPT phenomenon and the estimation bias of Smolensky and Isupov`s models is relatively smaller. However, when the samples show ferroelectric characteristics, the estimation bias will be increased. [ABSTRACT FROM AUTHOR]

In this paper, pure and 0.15 wt %MnO additives of (1-x)Pb(Fe2/3W1/3)O3–xPbTiO3 [(1-x)PFW-xPT] with x=0.1, 0.2, 0.3, and 0.4 were synthesized by the conventional solid state reaction method. The dielectric diffusion properties were investigated with the empirical law. The lattice structure was found to transfer from tetragonal to pseudocubic and the diffusion phase characteristic is more notable as decreasing PbTiO3 compositions or adding MnO additives. Moreover, the dielectric loss is improved and the space charge polarization effect is vanished as adding MnO additives in 0.7PFW-0.3PT compounds. We suggested it was probably due to the lead vacancy which is substituted by the manganese ions or the interstitial manganese ions intervene into the interstice between the positive and negative ions. [ABSTRACT FROM AUTHOR]

A series of three-coordinate octupolar compounds with varied centers (boron, aluminum, and nitrogen), which exhibit very large effective two-photon absorption cross sections have been theoretically studied. The ground state geometries and electronic structures are obtained using the density functional theory with the B3LYP functional and 6-31G(d) basis set, and the results are comparable to the available experimental determinations. Based on the correct geometrical and electronic structures, the one- and two-photon absorptions are predicted by the ZINDO-SOS method. Among these compounds, the boron (B) and aluminum (Al) centers act as acceptors, while the nitrogen center acts as donor according to the net charge changes during the excitation. It is found that (i) the compounds with boron and aluminum centers show two large two-photon absorption peaks, while the molecule with nitrogen center show only one two-photon absorption peak; (ii) the cross sections of the molecules with B or Al as centers are larger than that of the molecule with nitrogen as center; furthermore, the two-photon absorption cross section of the molecule with Al center is larger than that of the molecule with B center, from this point of view, our theoretical prediction provides for the experiment a good new candidate with large two-photon absorption cross section for further research; (iii) lengthening the conjugation bridge by inserting a benzene ring on the organoborane compounds (forming the investigated molecule B-2) enhances the two-photon absorption cross section, and keeping good transparency at the same time. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this work, a design of integrating ultrasonic transduction with live cell imaging chamber is introduced. The principle of a metal-incident-glass-output acoustic path was used to deliver a uniform energy profile into the imaging/incubation chamber in the form of leaky Lamb waves. The design was applied to examine living mouse mammary gland epithelial cells (EpH4). Significant changes in intracellular activities were observed even at a very low energy intensity level (1 MHz, ISATA = 1 mW/cm2, continuous wave). Live imaging with ultrasonic stimulation provides a different paradigm to interrogate cellular mechanosensitive responses in real time. [ABSTRACT FROM AUTHOR]

We discuss the development of the instability for electron acceleration and energy gain of electrons from laser waves in both homogeneous and inhomogeneous non-planar cylindrical plasma channels. We find that the instability (i.e., electron acceleration) in the cylindrical plasma channel can be developed more quickly and strongly than that in the planar two-dimensional plasma channel. Then, enhancement of energy gain and shortening of acceleration length in the cylindrical plasma channel are observed. For the cylindrical plasma channel, the electron in the inhomogeneous plasma channel can gain more energy from the laser and the acceleration length can be shortened by adjusting the width of the laser and the inhomogeneous charge density distributions. [ABSTRACT FROM AUTHOR]

We examine the electron acceleration in a two-dimensional plasma channel under the action of a laser field and an additional static electric field. We propose to design an appropriate additional electric field (its direction and location), in order to launch the electron onto an energetic trajectory. We find that the electron acceleration strongly depends on the coupled effects of the laser polarization, the direction, and location of the additional electric field. The additional electric field affects the electron dynamics by changing the dephasing rate. Particularly, a suitably designed additional electric field leads to a considerable energy gain from the laser pulse after the interaction with the additional electric field. The electron energy gain from the laser with the additional electric field can be much higher than that without the additional electric field. This engineering provides a possible means for producing high energetic electrons. [ABSTRACT FROM AUTHOR]

We study the laser-driven electron acceleration in a transversely inhomogeneous plasma channel. We find that, in inhomogeneous plasma channel, the developing of instability for electron acceleration and the electron energy gain can be controlled by adjusting the laser polarization angle and inhomogeneity of plasma channel. That is, we can short the accelerating length and enhance the energy gain in inhomogeneous plasma channel by adjusting the laser polarization angle and inhomogeneity of the plasma channel. [ABSTRACT FROM AUTHOR]

The nonlinear interaction of ultra-intense short laser beam and homogeneous/inhomogeneous electron-positron-ion (e-p-i) plasma is investigated. It is found that soliton solutions can exist in both homogeneous and inhomogeneous e-p-i plasma. The influence of the positron density, the phase velocity, the inhomogeneity nature, and the Hamiltonian of the system on the soliton structure is investigated. The evolution of envelope solitons in homogeneous e-p-i plasma is analyzed analytically by using a two-time-scale method and confirmed by numerical simulations. However, the soliton solutions can exist in inhomogeneous e-p-i plasma only when the positron density is high enough. Furthermore, the phase diagram for existing envelope soliton in positron density and phase velocity of the wave plane is obtained. [ABSTRACT FROM AUTHOR]

The unipolar resistive switching behavior of Pt/LixZn1-xO/Pt structures fabricated via radio-frequency magnetron sputtering is investigated. Various Li doping concentrations influence the defect types (i.e., VO, Lii, and LiZn) in LixZn1-xO films for adjustable resistance ratio. The resistance ratio reaches 108 due to the minimized leakage current in the high-resistance state (HRS) at 6 at. % Li dopants. The dominant conduction mechanisms are explained in terms of Ohmic behavior and Poole-Frenkel (PF) emission. The coefficient r of the PF emission in the HRS is evaluated to confirm that the total number of defects in LixZn1-xO films decreases with increasing Li content. [ABSTRACT FROM AUTHOR]

We investigated high catalytic activity of Ni/HZSM-5 catalysts synthesized by the impregnation method, which was successfully applied for low-temperature steam reforming of bio-oil. The influences of the catalyst composition, reforming temperature and the molar ratio of steam to carbon fed on the stream reforming process of bio-oil over the Ni/HZSM-5 catalysts were investigated in the reforming reactor. The promoting effects of current passing through the catalyst on the bio-oil reforming were also studied using the electrochemical catalytic reforming approach. By comparing Ni/HZSM-5 with commonly used Ni/Al2O3 catalysts, the Ni20/ZSM catalyst with Ni-loading content of about 20% on the HZSM-5 support showed the highest catalytic activity. Even at 450 °C, the hydrogen yield of about 90% with a near complete conversion of bio-oil was obtained using the Ni20/ZSM catalyst. It was found that the performance of the bio-oil reforming was remarkably enhanced by the HZSM-5 supporter and the current through the catalyst. The features of the Ni/HZSM-5 catalysts were also investigated via X-ray diffraction, inductively coupled plasma and atomic emission spectroscopy, hydrogen temperature-programmed reduction, and Brunauer-Emmett-Teller methods. [ABSTRACT FROM AUTHOR]

The approach to realize the optimal chirped probe pulse length for an arbitrary pulsed terahertz (THz) signal measured with the spectral-encoding technique was investigated by simulation. It was found that either the maximum positive peak or the absolute value of the strongest negative peak of the normalized difference between the probe spectrum modulated by THz signal and the background probe spectrum tended to be maximized when the probe pulse duration approached to the optimal value. The probe pulse length can be adjusted continuously with a pair of triangular dispersive prisms. THz signals from high-voltage biased air plasmas induced by femtosecond laser pulse were measured with minimum distortion using our simple method. [ABSTRACT FROM AUTHOR]

High-temperature superconductor GdBa2Cu3O7 thin films were epitaxially grown in situ on (100) oriented ytrrium-stabilized zirconia single-crystal substrates by dc magnetron sputtering using a single planar target. All samples prepared in continual 12 runs have zero-resistance transition temperature Tc0 more than 90 K and a transition width 1–2 K. The best films have a Tc0 of 92.5 K, a transition width of 0.7 K, and a critical current density of 1.4×106 A/cm2 at 77 K. The reproducibility is very good. X-ray diffraction spectra analysis in different geometries showed epitaxial growth with the c axis normal to the film surface. [ABSTRACT FROM AUTHOR]

We have measured the dielectric loss in SrTiO[sub 3] thin films grown on SrRuO[sub 3] electrode layers with thickness ranging from 25 nm to 2.5 μm. The loss depends strongly on the thickness but differently above and below Tapprox. 80 K: as the thickness increases, the loss decreases at high temperatures but becomes higher at low temperatures. Our result suggests that, in the high temperature regime, the interfacial dead layer effect dominates while, in the low temperature regime, the losses related to the structural phase transition and quantum fluctuations are important. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present low-frequency dielectric loss and nonlinearity measurements in SrTiO[sub 3] thin films grown by pulsed laser deposition on SrRuO[sub 3] electrode layers. A low loss tangent in the order of 10[sup -4], close to the level found in SrTiO[sub 3] single crystals, was observed. Combined with a large tunability, this resulted in a figure of merit for frequency and phase agile materials that can rival that observed in single crystals. The result is potentially significant for tunable microwave device applications, and it points to stress and interface effects as the possible causes for higher dielectric losses in thin films. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have used a metal–oxide bilayer Raman scattering technique to study lattice dynamics in SrTiO[sub 3] thin films. The SrTiO[sub 3] thin films were epitaxially grown on a conducting metal–oxide layer which reflects the exciting laser beam so that it does not enter the LaAlO[sub 3] substrate. Raman scattering from the SrTiO[sub 3] thin films was clearly observed, including the first-order Raman peaks forbidden by the cubic symmetry in single crystals. We suggest that strain exists in the films, which changes the crystal symmetry and will affect the dielectric properties of the SrTiO[sub 3] thin films. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]