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The polycrystalline BaTiO3 (BTO) thin films were grown on F-doped SnO2 substrates by pulsed laser deposition. The devices show a rectification at a small voltage, while bipolar resistive switching (RS) and negative differential resistance (NDR) appear at a large voltage. Furthermore, RS remains and NDR disappears when no positive bias is applied, while both RS and NDR behaviors improve when increasing the positive bias. The electrons trapped/detrapped by interface states at Au/BTO interface are proposed to understand the above behaviors. [ABSTRACT FROM AUTHOR]

The discovery in 1986 of high-temperature superconductivity in cuprates above liquid nitrogen temperature brought about a new chapter in high-temperature superconductivity research, bringing applications that bit closer. However, how to further improve the superconducting transition temperature of high-temperature superconductors is a huge challenge in condensed matter physics and materials science. Recently, interface-enhanced high-temperature superconductivity in one-unit-cell FeSe film on a SrTiO3 substrate has created a new avenue for improving the superconducting transition temperature. Here, a transition from an originally non-superconducting state to a superconducting state triggered by the interfacial injection of charge carriers was observed in a PrBa2Cu3O7/Nb-doped SrTiO3 heterostructure, and the non-superconducting to superconducting transition temperature increases with increase in the injection current. Current–voltage characteristics indicate that several conduction mechanisms coexist. In the proposed mechanism, the injected electrons are self-trapped in an unstable quasiconduction band which has a direct influence on the intrinsic properties, such as resistance and superconductivity, of the PrBa2Cu3O7 film. Our findings offer an alternative strategy for manipulating the superconducting state in oxides by the injection of charge carriers through the oxide interfaces, and can also help us to understand the mechanism of high-temperature superconduction. [ABSTRACT FROM AUTHOR]

Although photosynthesis has been intensively studied during leaf senescence, it is unclear whether the changes of photosynthetic function in various mesophyll tissues can be detected using chlorophyll a fluorescence induction kinetics (CFI) in vivo. To clarify this question, leaf structure and CFI were carefully examined in senescent leaves. The results showed declines in chlorophyll content and photosynthetic rate in both cucumber and maize plants as leaves aged. In cucumber leaves, the number of chloroplasts decreased more rapidly in the palisade tissue compared to the sponge tissue as senescence progressed. Under various pulse light intensities, the enhancement of the relative variable fluorescence in the CFI curves measured on the adaxial side was larger than that on the abaxial side of senescent cucumber leaves, indicating senescence in the palisade tissue progressed more quickly than that in the sponge tissue. JIP-test parameters further showed that the loss of photosynthetic electron transport activity in palisade tissue was faster than that in sponge tissue. However, during leaf senescence in maize, there were no such dorsoventral differences. We therefore propose that the decline of photosynthesis in cucumber leaves is largely determined by the senescence of palisade tissue. The changes in photosynthesis in palisade and sponge tissues with leaf aging can be probed effectively by CFI measured on both sides of cucumber leaves in vivo. [ABSTRACT FROM AUTHOR]

ZnO thin films and (Bu4N)2(Ru)(dcbpyH)2(NCS)2 (called N719) sensitized ZnO thin films are grown on fluorine-doped tin oxide (FTO) conducting glass substrates using laser molecular beam epitaxy. Ultraviolet-visible absorption, photoluminescence (PL), surface photovoltage spectroscopy, and Raman scattering are employed to probe into the transition process of photogenerated charges and the interaction between ZnO and N719. The experimental results indicate that there is a significant electronic interaction between N719 and ZnO through chemiadsorption. The interaction greatly enhances the photogenerated charge separation and thus the photovoltaic response of the ZnO film but remarkedly weakens its radiative recombination, i.e., PL, implying strong energy and charge transfer occurring between N719 and ZnO. In addition, a new PL peak observed at about 720 nm in N719 sensitized ZnO/FTO is attributed to the electron-hole recombination of N719. [ABSTRACT FROM AUTHOR]

Arrays of highly ordered ZnO nanowires have been synthesized on polycrystalline Al-doped ZnO (AZO) buffer layers prepared on p-Si substrates (7–13 Ω cm) with assistance of a thermal deposition method. The diameter and interspacing of the nanowires have been controlled by the growth conditions and properties of AZO films. The optimized array of ZnO nanowires shows low turn-on and threshold fields (∼1.1 and ∼3.0 V/μm, respectively) and displays exceptional time stability of electron field emission. The time-fluctuation instability was found to be less than 0.6% at a current density of 10 mA/cm2, as measured for 500 min. The low turn-on and threshold fields as well as the stable electron emission current suggest that the arrays of ZnO nanowires could be considered in some electron field emission applications. [ABSTRACT FROM AUTHOR]

Undoped and Al-, Ga-, and In-doped Bi4Ti3O12 thin films were prepared on fused quartz substrates by chemical solution deposition. Their microstructures and optical properties were investigated by x-ray diffraction and UV-visible-NIR spectrophotometer, respectively. The optical band-gap energies, Urbach energies, and linear refractive indices of all the films are derived from the transmittance spectrum. Following the single oscillator model, the dispersion parameters such as the average oscillator energy (E0) and dispersion energy (Ed) are achieved. The energy band gap and refractive indices are found to decrease with introducing the dopants of Al, Ga, and In, which is useful for the band-gap engineering and optical waveguide devices. The refractive index dispersion parameter (E0/S0) increases and the chemical bonding quantity (β) decreases in all the films compared with those of bulk. It is supposed to be caused by the nanosize grains in films. [ABSTRACT FROM AUTHOR]

The anatase nanocrystalline TiO2 samples were synthesized by a sol-gel method with a thermal treatment under air and oxygen atmospheres at 500 °C and investigated by x-ray powder diffraction, ultraviolet-visible diffuse reflectance spectra (UV-vis DRSs), Raman spectra, and photoluminescence (PL) spectra, respectively. Compared to the sample calcined in air, there were slight differences in the lattice parameter and Raman line shape for the sample calcined in oxygen. UV-vis DRSs exhibited a visible redshift of the absorption edge, which could be understood by Burstein–Moss effect. Different calcination atmospheres led the obvious variations of intensity, position, and linewidth in the PL spectra, which could be attributed to the surface oxygen defect changes. [ABSTRACT FROM AUTHOR]

In-plane optical anisotropy (IPOA) in (001) GaAs/AlGaAs superlattice induced by uniaxial strain has been investigated by reflectance difference spectroscopy (RDS). Uniaxial strain on the order of 10-4 was introduced by bending a strip sample with a stress apparatus. The IPOA of all interband transitions shows a linear dependence on strain. The birefringence and dichroism spectra induced by strain are obtained by RDS on the basis of a three-phase model, which is in good agreement with the reported results. [ABSTRACT FROM AUTHOR]

Superior thermal stability of the phosphors is crucial to retain the light balance of phosphor-converted WLEDs. At present, the fundamental research on the development of the phosphors with high thermal stability remains a challenging task. In this work, a series of red-emitting phosphors Ca9Y(PO4)7(1−x)(VO4)7x:Eu3+ (x = 0 − 1), in which phosphate groups were gradually replaced by vanadate groups, were synthesized via a high temperature solid-state reaction method. Their XRD patterns, Raman spectra, photoluminescent excitation and emission spectra, as well as temperature dependent emission properties and decay curves were investigated. The results of XRD pattern and Raman spectra indicated that a solid solution formed in Ca9Y(PO4)7(1−x)(VO4)7x:Eu3+ from x = 0 to x = 1. The photoluminescent properties study revealed that emission intensity upon the excitation 393 nm decreased while that under the irradiation of 464 nm increased with the improvement of vanadate groups. Moreover, the substitution of vanadium ions can increase the red to orange intensity ratio values of Eu3+. Especially, a limited amount of vanadium in Ca9Y(PO4)7:Eu3+ will improve the luminescence thermal stability. This was confirmed by temperature dependent lifetime values for the phosphors with and without vanadium. The possible reason affecting the above properties have been considered in details. [ABSTRACT FROM AUTHOR]