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The dielectric properties of (Fe,Li)-codoped KTa1-xNbxO3 single crystals have been measured, and the origin of the dielectric abnormities was discussed in detail. In the low temperature range of 20–100K for each of the samples, the relaxation R1 is attributed to the electrons-activating/ freezing in the defect-dipoles while the dielectric abnormity is contributed by the relaxation R1 and the two phase transitions (PR-O and PO-T). The relaxation R2 in the range of 100–200K is likely due to the reorientation of the dipolar structure Fe3+-Oi 2- as well as the formation of a small number of non-localized polaronic particles. In the high temperature range of 200–450 K, controlling the temperature interval between the first-order phase transition P1 and the diffuse transition P2 could make permittivity tunable in values and thermal stability through simply changing the composition parameter x in the doped KTN single crystals. This work provides us an effective way to design optimal dielectric materials for research and applications. [ABSTRACT FROM AUTHOR]

In this study, the semiconducting single-walled carbon nanotube (semi-SWCNT) thin film transistors (TFTs) with high dielectric constant (κ) atomic layer deposited ZrAlOx gate insulator are fabricated by the drop-casted method. The hysteresis characteristic, negative gate voltage stress stability, and thermal stability are studied, and the semi-SWCNT TFTs with ZrAlOx gate insulators show a small hysteresis of 0.2 V, a little threshold voltage shift of 2.5V under the negative gate voltage stress, and a threshold voltage shift of 2V under the thermal stress. Such advantages are due to the amorphous structure and smooth surface of the atomic layer deposited ZrAlOx gate insulator, which induces less trap states. In addition, the thermal stress stability of semi-SWCNT TFTs is investigated. It is found that the behavior of semi-SWCNT TFTs under thermal stress obeys the thermally activated hopping model obviously. This model explains the threshold voltage shift of the device under thermal stress, which is very reasonable. [ABSTRACT FROM AUTHOR]

Silica (SiO2) islands with a dendritic structure were prepared on polycrystalline copper foil, using silane (SiH4) as a precursor, by annealing at high temperature. Assisted by copper vapor from bare sections of the foil, single-layer hexagonal graphene domains were grown directly on the SiO2 islands by chemical vapor deposition. Scanning electron microscopy, atomic force microscopy, Raman spectra, and X-ray photoelectron spectroscopy confirm that hexagonal graphene domains, each measuring several microns, were synthesized on the silica islands. [ABSTRACT FROM AUTHOR]

This work presents a strategy of nitrogen anion doping to suppress negative gate-bias illumination instability. The electrical performance and negative gate-bias illumination stability of the ZnSnON thin film transistors (TFTs) are investigated. Compared with ZnSnO-TFT, ZnSnON-TFT has a 53% decrease in the threshold voltage shift under negative bias illumination stress and electrical performance also progresses obviously. The stability improvement of ZnSnON-TFT is attributed to the reduction in ionized oxygen vacancy defects and the photodesorption of oxygen-related molecules. It suggests that anion doping can provide an effective solution to the adverse tradeoff between field effect mobility and negative bias illumination stability. [ABSTRACT FROM AUTHOR]

Memristive devices have been widely employed to emulate biological synaptic behavior. In these cases, the memristive switching generally originates from electrical field induced ion migration or Joule heating induced phase change. In this letter, the Ti/ZnO/Pt structure was found to show memristive switching ascribed to a carrier trapping/detrapping of the trap sites (e.g., oxygen vacancies or zinc interstitials) in ZnO. The carrier trapping/detrapping level can be controllably adjusted by regulating the current compliance level or voltage amplitude. Multi-level conductance states can, therefore, be realized in such memristive device. The spike-timing-dependent plasticity, an important Hebbian learning rule, has been implemented in this type of synaptic device. Compared with filamentary-type memristive devices, purely electronic memristors have potential to reduce their energy consumption and work more stably and reliably, since no structural distortion occurs. [ABSTRACT FROM AUTHOR]

This study investigates the effect of hafniumdoping on the density of states (DOSs) in HfZnSnO thin film transistors fabricated by dual-target magnetron co-sputtering system. The DOSs is extracted by temperature-dependent field-effect measurements, and they decrease from 1.1 × 1017 to 4.6 × 1016 eV/cm³ with increasing the hafnium concentrations. The behavior of DOSs for the increasing hafnium concentration HfZnSnO thin film transistors can be confirmed by both the reduction of ΔVT under bias stress and the trapping charges calculated by capacitance voltage measurements. It suggests that the reduction in DOSs due to the hafniumdoping is closely related with the bias stability and thermal stability. [ABSTRACT FROM AUTHOR]

We investigated the upper critical fields of Ca10(Pt4As8)(Fe1.8Pt0.2As2)5 superconducting whiskers. The whiskers consist of several wire-like grains with diameter of around 200 nm, joined by grain boundaries whose misorientation angles are less than 5°. The upper critical fields along c-axis and in ab-plane were observed as 49 T at 12K and 50 T at 22K, respectively, which can be extrapolated to 81 and ~133 T at 0 K. The whisker demonstrated weak anisotropic factor and almost constant value of ~2 below 15 K. The impressive transport properties of the whisker may find applications in fields like superconducting micro- and meso-structure systems. [ABSTRACT FROM AUTHOR]

We investigated the upper critical fields of Ca10(Pt4As8)(Fe2-xPtxAs2)5 superconducting whiskers. The whiskers consist of several wire-like grains with diameter of around 200 nm, joined by grain boundaries whose misorientation angles are less than 5°. The upper critical fields along c-axis and in ab-plane were observed as 49 T at 12 K and 50 T at 22 K, respectively, which can be extrapolated to ~81 and ~133 T at 0 K. The whisker demonstrated weak anisotropic factor and almost constant value of ~2 below 15 K. The impressive transport properties of the whisker may find applications in fields like superconducting micro- and meso-structure systems. [ABSTRACT FROM AUTHOR]

In this letter, we report on the resistive switching originating from the rupture/rejuvenation of single-crystalline Cu filaments in a nitrogen-doped porous carbon-based memristive device Cu/ CN0.15/Pt. Cu filaments are confined in conical nanopores in CN0.15 thin films. Dislocations exist in the Cu filaments, resulting in obvious crystal lattice distortions. The Cu/CN0.15/Pt device shows outstanding high temperature retention performance for both ON and OFF states, indicating that it is promising for resistance memory applications. Furthermore, continuous RESET (ON-to-OFF switching) and SET (OFF-to-ON switching) processes could be realized indicating the adaptive learning ability of Cu/CN0.15/Pt, which has potential applications in synaptic devices. [ABSTRACT FROM AUTHOR]

We investigated the superconducting transition temperature Tc of FeSe0.5Te0.5 single crystals, which can be enhanced up to 14% by attaching onto a commercial Scotch tape. The Scotch tape exhibits a large cooling shrinkage at low temperatures, which is considerably more pronounced than that of the metallic FeSe0.5Te0.5 single crystal, thus providing a compressive strain of 2.4 x 10-3 at 15 K. For such strain, we calculated that the lattice parameter of c/a can be increased to ~0.31%, which corresponds to the enhancement of the superconductivity. The present finding provides a rapid and simple method to examine the microstructure sensitive physical properties of the layered-structure materials by using the Scotch tape as strain generator. [ABSTRACT FROM AUTHOR]

Lead-free (1 -- x)BaTiO3-x(Na0.5Er0.5)TiO3 (0 ≤ x ≤ 0.15) ceramics were prepared by a solid state reaction method. Their structure and electric properties were analyzed. Rietveld refinements suggested that the ceramics crystallized in the tetragonal perovskite space group P4 mm at room temperature. With increasing x from 0 to 0.05, Na+/Er3+ co-substitution at Ba-site in BaTiO3 leads to the decrease of lattice parameters and unit cell volume. While minor secondary phase, Er2Ti2O7 and (TiO1.2)0.787, appears at x = 0.10 or above. A great enhancement of piezoelectric properties and other electric parameters was obtained in this system by properly moderating the compositions. For example, in the ceramics with composition x = 0.05, a large piezoelectric coefficient d33 (333 pm/V), a high remnant polarization Pr (14.3 μC/cm²), a good planar electromechanical coupling factor kp (0.391), a mechanical quality factor Qm (97.3), and a high Curie temperature (TC = 134°C) (higher than that of pure BaTiO3) were achieved. Our results show that (1 -- x)BaTiO3-x(Na0.5Er0.5)TiO3 ceramics are a good candidate of lead-free piezoelectric materials. [ABSTRACT FROM AUTHOR]

We fabricated polymer piezoelectric energy harvesters (PEHs) that can generate electric power at wind speed of less than 4.7m/s due to their high sensitivity to wind. In order to optimize their operating conditions, we evaluated three distinct PEH operation modes under the boundary conditions of single-side clamping. We found that a PEH connected to an external load of 120 kX shows the largest output power of 0.98 μW at 3.9 m/s, with wind incident on its side (mode I). We attribute this result to large bending and torsion involved in this operation mode. [ABSTRACT FROM AUTHOR]

A two-step polarization reversal process was identified in the pentacene/poly(vinylidene fluoride-trifluoroethylene) double-layer device. Displacement current measurement showed that three peaks generated non-symmetrically in the current-voltage characteristics. Accordingly, optical electric-field induced second-harmonic generation measurement displayed two hysteresis loops. A proposed model based on a two-step polarization reversal mechanism accounted for these results, and suggested that interaction of interfacial charge and ferroelectric polarization governed the mechanism. The proposed model is useful to explain the reduced remanent polarization in ferroelectric field-effect transistors, and will be helpful for developing organic devices with a ferroelectric layer. [ABSTRACT FROM AUTHOR]

We investigate the dependence of effective Q-factor on force sensitivity in Q-controlled phase-modulation atomic force microscopy. With Q-control, the phase noise density spectrum shows a characteristic dependence on modulation frequency (fm). The phase noise density spectrum is nearly constant in the low-fm region, whereas it decreases inverse-proportionally to fm in the high-fm region. Such a decrease enhances the force sensitivity. We demonstrate that force sensitivity can be markedly increased with Q-control to exceed the limit of force sensitivity without Q-control. [ABSTRACT FROM AUTHOR]

We demonstrate theoretically that electric field can drive a quantum phase transition between band insulator to topological insulator in CdTe/HgCdTe/CdTe quantum wells. The numerical results suggest that the electric field could be used as a switch to turn on or off the topological insulator phase, and temperature can affect significantly the phase diagram for different gate voltage and compositions. Our theoretical results provide us an efficient way to manipulate the quantum phase of HgTe quantum wells. [ABSTRACT FROM AUTHOR]

Electron resonance acceleration by an intense laser pulse in an inhomogeneous external magnetic field is investigated. The acceleration mechanism makes use of electron cyclotron resonance to increase the electron energy. By appropriately tailoring the radial gradient of the magnetic field, an electron in the rising front part of laser pulse will be attracted toward the cyclotron-resonance radius and be trapped there, so that it can gain much energy. It is shown that the electron net energy gain can be up to the GeV level. [ABSTRACT FROM AUTHOR]

We report measurements of the quantum capacitance of individual semiconducting and small band gap single walled carbon nanotubes (SWNTs). The observed quantum capacitance, 82 aF/μm for a semiconducting SWNT with chiral index (16,8) and 10.3 aF/μm for a small band gap SWNT upon Fermi level lying at the first subband are remarkably smaller than those originating from the density of states. We attribute the discrepancy to a strong electron correlation in SWNTs and derive the Luttinger parameter g of 0.25–0.3 for the (16,8) SWNT and of 0.32 for a small band gap SWNT. [ABSTRACT FROM AUTHOR]

The alloying effects of Nb, Zr, and/or Sn on the phase stability and elastic properties of Ti are investigated by using a first-principles method. Our calculation results indicate that a carefully designed Ti–Nb–Zr–Sn system can be a good candidate for low modulus biomedical materials. We find that the well-known correlation between the e/a ratio and both elastic and phase stabilities for Ti alloyed with transition metal elements breaks down for the Ti–Sn alloy. [ABSTRACT FROM AUTHOR]

The authors have developed phase modulation atomic force microscopy in constant excitation mode capable of simultaneously imaging the topography and energy dissipation of a sample surface in a liquid. This setup utilizes a fast, low-cost sample-and-hold technique to analyze the oscillation signals of a cantilever. The proposed circuitry allows us to measure the local energy dissipated by the tip-sample interaction during imaging. The energy dissipation image exhibits a material-specific contrast for a polymer-blend film. [ABSTRACT FROM AUTHOR]

Although the low-temperature specific heat in metallic nanocrystals has been extensively demonstrated to be always enhanced due to the surface phonon softening, it is revealed here to be anomalously depressed by the surface oxidation so that the excess specific heat can be either positive or negative as a function of temperature with respect to the counterparts of the bulk crystals. The background mechanism has been theoretically deduced to well explain these experimental phenomena by calculating and comparing the vibrational densities of states (VDOS) of face-centered cubic-aluminum (fcc-Al) and amorphous-alumina (a-Al2O3) nanoparticles. Different from fcc-Al nanocrystals, both the surface and volume VDOSs g(ω) of a-Al2O3 nanoparticles are scaled as g(ω) ~ ω1.5 at the low-frequency limit (ω). The effective spatial dimension for the a-Al2O3 surfaces and volume as well as the fcc-Al surfaces is thus assumed to be between 2D and 3D while it is 3D for the fcc-Al volume. The specific heat of a-Al2O3@Al nanoparticles is consequently revealed to show a different T-dependent feature from those of both pure metallic nanocrystals and bulk crystals at low temperatures. [ABSTRACT FROM AUTHOR]

This study reveals the contribution of hot electrons from the excited plasmonic nanoparticles in dye sensitized solar cells (DSSCs) by correlating the photoconductance of a core-shell Au@TiO2 network on a micro-gap electrode and the photovolatic properties of this material as photoanodes in DSSCs. The distinct wavelength dependence of these two devices reveals that the plasmon-excited hot electrons can easily overcome the Schottky barrier at Au/TiO2 interface in the whole visible wavelength range and transfer from Au nanoparticles into the TiO2 network. The enhanced charge carrier density leads to higher photoconductance and facilitates more efficient charge separation and photoelectron collection in the DSSCs. [ABSTRACT FROM AUTHOR]

Examines the theory of YBa[sub 2]Cu[sub 3]O[sub 7-x]/PrBa[sub 2]Cu[sub 3]O[sub 7-x] (PrBCO) superlattices as superconductor-insulator multilayers. Description of the CuO[sub 2] planes in PrBCO layer by the two-dimensional Mott-Hubbard insulator with Coulomb repulsion; Correlation between transition temperature and number of PrBCO unit cells.

In the superconductor of FeSe0.5Te0.5, the superconductivity is highly sensitive to variations of microstructure. Therefore, a fine manipulation of the microstructures will be crucial not only for a better understanding of the superconductivity but also for potential applications. Here, we demonstrate an approach to control the superconductivity in-situ by using a magnetostrictive substrate ZnCr2Se4 as the strain generator. By mounting an FeSe0.5Te0.5 single crystal onto a magnetostrictive substrate, we show that the magnetoresistance of FeSe0.5Te0.5 is directly coupled to the magnetostriction of ZnCr2Se4. The strain is fine-tuned in-situ by an external magnetic field, leading to the superconductivity of FeSe0.5Te0.5 correspondingly favored by compressive strain while suppressed by tensile strain. [ABSTRACT FROM AUTHOR]

A physical approach has been developed to in situ coat metal nanoparticles with a nanolayer of organic hydrocarbon film. Copper nanoparticles produced by the flow-levitation method were in situ coated with hydrocarbon films via a dielectric barrier discharge. The hydrocarbon-coated Cu nanoparticles have been analyzed by transmission electron microscopy and infrared absorption to determine the size distribution and dispersion of nanoparticles as well as the chemical components and thickness of the coatings. [ABSTRACT FROM AUTHOR]

We report the development of hybrid complementary inverters based on p-channel organic and n-channel metal oxide thin-film transistors (TFTs) both processed from solution at <200°C. For the organic TFTs, a ternary blend consisting of the small-molecule 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene, the polymer indacenodithiophene-benzothiadiazole (C16IDT-BT) and the p-type dopant C60F48 was employed, whereas the isotype In2O3/ZnO heterojunction was used for the n-channel TFTs. When integrated on the same substrate, p- and n-channel devices exhibited balanced carrier mobilities up to 10cm2/Vs. Hybrid complementary inverters based on these devices show high signal gain (>30V/V) and wide noise margins (70%). The moderate processing temperatures employed and the achieved level of device performance highlight the tremendous potential of the technology for application in the emerging sector of large-area microelectronics. [ABSTRACT FROM AUTHOR]

Organic water-gated transistors (OWGTs) have emerged as promising sensing architectures for biomedical applications and environmental monitoring due to their ability of in-situ detection of biological substances with high sensitivity and low operation voltage, as well as compatibility with various read-out circuits. Tremendous progress has been made in the development of p-type OWGTs. However, achieving stable n-type operation in OWGTs due to the presence of solvated oxygen in water is still challenging. Here, we report an ambipolar OWGT based on a bulk heterojunction active layer, which exhibits a stable hole and electron transport when exposed to aqueous environment. The device can be used as a photodetector both in the hole and electron accumulation regions to yield a maximum responsivity of 0.87A W-1. More importantly, the device exhibited stable static and dynamic photodetection even when operated in the n-type mode. These findings bring possibilities for the device to be adopted for future biosensing platforms, which are fully compatible with lowcost and low-power organic complementary circuits. [ABSTRACT FROM AUTHOR]

We report on the electrothermal behavior and the terahertz emission properties of a stand-alone Bi2Sr2CaCu2O8 intrinsic Josephson junction stack contacted in a three-terminal configuration. One terminal is used as a collective ground while the other two, contacting the stack from its right and left side, allow to vary the current injection profile. At high bias, a hot spot forms in the stack. Its appearance and position can be controlled by varying the ratios of the injected currents. Depending on this ratio, the emitted power can vary by an order of magnitude. Further, for a given total injection current, the device allows to vary the emission frequency on a 10% level by altering the injection profile. The overall tunability of the emission frequency, varying also the total bias current, is on the order of 20%. [ABSTRACT FROM AUTHOR]

The ultrafast terahertz (THz) modulation characteristic during photo-induced insulator-tometal transition (IMT) of undoped and tungsten (W)-doped VO2 film was investigated at picoseconds time scale using time-resolved THz spectroscopy. W-doping slows down the photo-induced IMT dynamic processes (both the fast non-thermal process and the slow metallic phase propagation process) in VO2 film and also reduces the pump fluence threshold of photo-induced IMT in VO2 film. Along with the observed broadening of phase transition temperature window of IMT in W-doped VO2, we conclude that W-doping prevents metallic phase domains from percolation. By further extracting carrier properties from photo-induced THz conductivity at several phase transition times, we found that the electron-electron correlation during IMT is enhanced in W-doped VO2. [ABSTRACT FROM AUTHOR]

The ultrafast terahertz (THz) modulation characteristic during photo-induced insulator-to-metal transition (IMT) of undoped and tungsten (W)-doped VO2 film was investigated at picoseconds time scale using time-resolved THz spectroscopy. W-doping slows down the photo-induced IMT dynamic processes (both the fast non-thermal process and the slow metallic phase propagation process) in VO2 film and also reduces the pump fluence threshold of photo-induced IMT in VO2 film. Along with the observed broadening of phase transition temperature window of IMT in W-doped VO2, we conclude that W-doping prevents metallic phase domains from percolation. By further extracting carrier properties from photo-induced THz conductivity at several phase transition times, we found that the electron-electron correlation during IMT is enhanced in W-doped VO2. [ABSTRACT FROM AUTHOR]

Field emission devices using a wet-processed composite cathode of carbon nanotube films coated with titanium dioxide exhibit outstanding field emission characteristics, including ultralow turn on field of 0.383 V μm-1 and threshold field of 0.657 V μm-1 corresponding with a very high field enhancement factor of 20000, exceptional current stability, and excellent emission uniformity. The improved field emission properties are attributed to the enhanced edge effect simultaneously with the reduced screening effect, and the lowered work function of the composite cathode. In addition, the highly stable electron emission is found due to the presence of titanium dioxide nanoparticles on the carbon nanotubes, which prohibits the cathode from the influence of ions and free radical created in the emission process as well as residual oxygen gas in the device. The high-performance solution-processed composite cathode demonstrates great potential application in vacuum electronic devices. [ABSTRACT FROM AUTHOR]

Field emission devices using a wet-processed composite cathode of carbon nanotube films coated with titanium dioxide exhibit outstanding field emission characteristics, including ultralow turn on field of 0.383 V μm-1 and threshold field of 0.657 V μm-1 corresponding with a very high field enhancement factor of 20000, exceptional current stability, and excellent emission uniformity. The improved field emission properties are attributed to the enhanced edge effect simultaneously with the reduced screening effect, and the lowered work function of the composite cathode. In addition, the highly stable electron emission is found due to the presence of titanium dioxide nanoparticles on the carbon nanotubes, which prohibits the cathode from the influence of ions and free radical created in the emission process as well as residual oxygen gas in the device. The high-performance solution-processed composite cathode demonstrates great potential application in vacuum electronic devices. [ABSTRACT FROM AUTHOR]

A surface potential measurement method using amplitude-modulation and heterodyne techniques is proposed. The effect of the stray capacitance between a cantilever and a sample in Kelvin probe force microscopy and the electrostatic force spectroscopy measurements are almost completely removed, because the distance (z) dependence of the modulated electrostatic force increases from 1/z to1/z2. This method improves the sensitivity of short range forces and reduces the surface potential measurement crosstalk that is induced by topographic feedback. This method has the advantage of high potential sensitivity due to the high cantilever Q value under vacuum. Quantitative surface potential measurements are demonstrated. [ABSTRACT FROM AUTHOR]

Electrical transport properties and photoresponse of individual TiO2-coated carbon nanofibers were studied in an attempt to elucidate the limiting factors of core-shell nanowire-based dye-sensitized solar cells (DSSC). The role of the semiconductor shell microstructure was investigated by comparing as grown and thermally annealed samples. Steady state I-V and transient photoconductivity measurements suggest that improving the microstructure leads to reduced resistivity and contact resistance, a decrease in charge traps, improved surface stoichiometry for dye adsorption, and reduced absorption of visible light by the semiconductor, all of which may improve nanowire-based DSSC performance. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate an enhanced four-wave mixing (FWM) based on atomic coherence in a Pr3+:Y2SiO5 crystal. By employing coherent population return and fractional stimulated Raman adiabatic passage to prepare maximum atomic coherence in the crystal, an efficient FWM signal can be generated. By measuring the generated FWM signal, the time-dependent atomic coherence is monitored. Such an enhanced FWM in solids may have practical applications in nonlinear optics and laser spectroscopy. [ABSTRACT FROM AUTHOR]

Using a nanowire-based templating approach, lithography-free fabrication of three-dimensional circular optical nanostructures with a minimum physical size of 20 nm is demonstrated. Regular circular gratings with alternating transparent and opaque annular zones and having discrete nanometer length scale separations can be easily achieved. These columnar optical nanostructures could potentially be used for direct integration with other optical components. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]