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We study the quantum anomaly for the transverse Ward-Takahashi relations in the four-dimensional gauge theory QED by using Fujikawa's method in which the anomaly is fundamentally a variation of the functional integral measure under transformation. A regulator which leads to a finite result for the anomaly is proposed. It is shown that a novel anomaly associated with transverse Ward-Takahashi identity of pseudo-tensor current is derived due to a set of infinitesimal transverse transformation of field variables. [ABSTRACT FROM AUTHOR]

Cation distribution between tetrahedral and octahedral sites within the ZnMn2O4 spinel lattice, along with microstructural features, is affected greatly by the temperature of heat treatment. Inversion parameters can easily be tuned, from 5%–19%, depending on the annealing temperature. The upper limit of inversion is found for T = 400 °C as confirmed by x-ray powder diffraction and Raman spectroscopy. Excellent battery behavior is found for samples annealed at lower temperatures; after 500 cycles the specific capacity for as-prepared ZnMn2O4 is 909 mAh g−1, while ZnMn2O4 heat-treated at 300 °C is 1179 mAh g−1, which amounts to 101% of its initial capacity. Despite the excellent performance of a sample processed at 300 °C at lower charge/discharge rates (100 mAh g−1), a drop in the specific capacity is observed with rate increase. This issue is solved by graphene-oxide wrapping: the specific capacity obtained after the 400th cycle for graphene-oxide-wrapped ZnMn2O4 heat-treated at 300 °C is 799 mAh g−1 at a charge/discharge rate 0.5 A g−1, which is higher by a factor of 6 compared to samples without graphene -oxide wrapping. [ABSTRACT FROM AUTHOR]

Titania nanotubes were prepared by a simple hydrothermal route. Their electrochemical performance has been examined in detail and compared to TiO2(B) nanoparticles, TiO2 anatase and P25 titania nanoparticles. The cycling and rate performance of TiO2 nanotubes is superior to both types of nanoparticles, and it can be further improved by an in situ titanium precursor treatment, which results in the formation of TiO2 nanoparticles on/between the nanotubes. The obtained specific capacity after 200 cycles at 0.2 A g−1 charge/discharge rate remained above 130 mAh g−1. The enhanced lithium storage properties of these samples can be attributed to their unique morphology and crystal structure. [ABSTRACT FROM AUTHOR]

Transparent solutions of nanocrystals exhibit many unique properties, and are thus attractive materials for numerous applications. However, the synthesis of transparent nanocrystal solutions of magnesium hydroxide (MH) with wide applications is yet to be realized. Here, we report a facile two-step process, which includes a direct reactive precipitation in alcohol phase instead of aqueous phase combined with a successive surface modification, to prepare transparent alcohol solutions containing lamellar MH nanocrystals with an average size of 52 nm and an ultrathin thickness of 1–2 nm, which is the thinnest MH nanoplatelet reported in the literatures. Further, highly flexible and transparent nanocomposite films are fabricated with a solution mixing method by adding the transparent MH nanocrystal solutions into PVB solution. Considering the simplicity of the fabrication process, high transparency and good flexibility, this MH/polymer nanocomposite film is promising for flame-resistant applications in plastic electronics and optical devices with high transparency, such as flexible displays, optical filters, and flexible solar cells. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) has been shown as a powerful technique to build three-dimensional (3D) all-solid-state microbattery, because of its unique advantages in fabricating uniform and pinhole-free thin films in 3D structures. The development of solid-state electrolyte by ALD is a crucial step to achieve the fabrication of 3D all-solid-state microbattery by ALD. In this work, lithium phosphate solid-state electrolytes were grown by ALD at four different temperatures (250, 275, 300, and 325 °C) using two precursors (lithium tert-butoxide and trimethylphosphate). A linear dependence of film thickness on ALD cycle number was observed and uniform growth was achieved at all four temperatures. The growth rate was 0.57, 0.66, 0.69, and 0.72 Å/cycle at deposition temperatures of 250, 275, 300, and 325 °C, respectively. Furthermore, x-ray photoelectron spectroscopy confirmed the compositions and chemical structures of lithium phosphates deposited by ALD. Moreover, the lithium phosphate thin films deposited at 300 °C presented the highest ionic conductivity of 1.73 × 10−8 S cm−1 at 323 K with ∼0.51 eV activation energy based on the electrochemical impedance spectroscopy. The ionic conductivity was calculated to be 3.3 × 10−8 S cm−1 at 26 °C (299 K). [ABSTRACT FROM AUTHOR]

The performances of organic optoelectronic devices, such as organic light emitting diodes and polymer solar cells, have rapidly improved in the past decade. The stability of an organic optoelectronic device has become a key problem for further development. In this paper, we report one simple encapsulation method for organic optoelectronic devices with a parafilm, based on ternary polymer solar cells (PSCs). The power conversion efficiencies (PCE) of PSCs with and without encapsulation decrease from 2.93% to 2.17% and from 2.87% to 1.16% after 168-hours of degradation under an ambient environment, respectively. The stability of PSCs could be enhanced by encapsulation with a parafilm. The encapsulation method is a competitive choice for organic optoelectronic devices, owing to its low cost and compatibility with flexible devices. [ABSTRACT FROM AUTHOR]

We propose an efficient scheme for realizing quantum dense coding with three-particle GHZ state in separated low-Q cavities. In this paper, the GHZ state is first prepared with three atoms trapped, respectively, in three spatial separated cavities. Meanwhile, with the assistance of a coherent optical pulse and X-quadrature homodyne measurement, we can implement quantum dense coding with three-particle GHZ state with a higher probability. Our scheme can also be generalized to realize N-particle quantum dense coding. [ABSTRACT FROM AUTHOR]

High efficiency organic light-emitting diodes (OLEDs) strongly depend on the balanced injection and transport of charge carriers from electrodes. Here, an efficient method that utilizes a charge generation layer composed of 1,4,5,8,9,11-hexaazatriphenylene- hexacarbonitrile (HAT-CN)/1,1-bis[(di-4-tolyamino)phenyl]cyclohexane organic heterojunction (OHJ) simultaneously as electron and hole injectors was proposed. Attractively, the fabricated green, blue and red OLEDs show higher efficiency compared with the normal OLEDs without OHJ as charge injectors. The improvement in efficiency benefits from the more balanced generation and injection of electrons and holes from the OHJs. The capacitance–frequency and current density–voltage characteristic measurements were used to well demonstrate the injection properties of electrons generated from the OHJ and the effects of the introduced ultra-thin Al layer between HAT-CN and electron transport layer. It can be seen that the injection way of charge carriers generated by OHJ, only depending on the external electric field, is completely different from that of direct injection via electrodes. This is not only beneficial to the charge balance, but also far away from the unstable metal electrode interfaces, therefore, the high efficiency and long lifetime OLEDs could be expected. [ABSTRACT FROM AUTHOR]

A new oxide CaCr0.5Fe0.5O3 was prepared under high pressure and temperature conditions. It crystallizes in a B-site disordered Pbnm perovskite structure. The charge combination is determined to be Cr5+/Fe3+ with the presence of unusual Cr5+ state in octahedral coordination, although Cr4+ and Fe4+ occur in the related perovskites CaCrO3 and CaFeO3. The randomly distributed Cr5+ and Fe3+ spins lead to short-range ferromagnetic coupling, whereas an antiferromagnetic phase transition takes place near 50 K due to the Fe3+–O–Fe3+ interaction. In spite of the B-site Cr5+/Fe3+ disorder, the compound exhibits electrical insulating behavior. First-principles calculations further demonstrate the formation of charge combination, and the electron correlation effect of Fe3+ plays an important role for the insulting ground state. CaCr0.5Fe0.5O3 provides the first Cr5+ perovskite system with octahedral coordination, opening a new avenue to explore novel transition-metal oxides with exotic charge states. [ABSTRACT FROM AUTHOR]

We demonstrate the growth and optical characterization of semipolar (1 1 &2macr; 2) GaN light-emitting diodes (LEDs) on sapphire utilizing two distinct heteroepitaxial growth methodologies. The properties of semipolar (1 1 &2macr; 2) LEDs are analyzed by the simultaneous growth of LED structures on templates prepared by both two-step growth on m-sapphire and selective growth on etched r-plane sapphire. Typically, growth on m-sapphire yields a high density of microstructural defects and surface morphological features which complicate the understanding of emission properties in devices. In this study, we find improved spectral properties of devices grown on etched r-sapphire due to improved surface roughness and microstructural quality (x-ray diffraction rocking curves of 280-550 arcsec for on-axis (1 1 &2macr; 2) and off-axis (101n), n = 0-5 diffractions), and reveal that the commonly observed broad emission and sub-bandgap peak in semipolar LEDs on sapphire are caused by a tunneling-assisted radiative recombination mechanism. [ABSTRACT FROM AUTHOR]

The increasing demand for complementary metal-oxide-semiconductor integrated GaN-based optoelectronics and power electronics calls for wafer-scale crack-free and high quality GaN thick film grown on Si. However, the huge mismatch in both lattice constant and coefficient of thermal expansion between GaN and Si often causes a high density of threading dislocations (TDD, typically 109–1010 cm−2) and the formation of micro-crack networks, producing a poor-quality GaN film with a limited thickness (<6 µm). By virtue of a well-designed Al-composition step-graded AlN/AlGaN buffer, a wafer-scale crack-free 10 µm-thick successive GaN with a low TDD of 5.8  ×  107 cm−2 grown on Si was achieved for the first time. Detailed study on the depth-dependent strain and dislocation evolution shed light on the complex interplay between strain relaxation and defect reduction, as well as their influences on the GaN optical properties along the growth direction. This work paves the way for building high-performance GaN-based optoelectronics and power electronics on the Si platform. [ABSTRACT FROM AUTHOR]

An abnormal aging phenomenon is reported for GaN-based near-ultraviolet laser diodes (LDs). Under an electrical stress for several minutes, the threshold current of the LDs decreased, while the light output power and the operation voltage increased. The amplitude of the abnormal aging phenomena was found to be mainly related to the excess Mg concentration in the p-AlGaN electron blocking layer (EBL). It almost disappeared when the Mg concentration in the AlGaN EBL was reduced to 2  ×  1019 cm−3. We propose that this phenomenon was related to the Mg–VN–H complex defects formed in highly doped AlGaN EBL ([Mg]  >  3  ×  1019 cm−3). [ABSTRACT FROM AUTHOR]

AlGaN nanostructures have many applications because of their interesting and unique properties. Here we report a simple fabrication method of AlGaN nanostructures by nanolithography on ultraviolet (UV) LEDs grown on Si substrates. We also studied the effects of various AlGaN nanostructure arrays on the performance of the UV (370 nm) thin-film LEDs with an embedded n-type contact. The output power of the UV LEDs with nanostructures was enhanced by 3.9 times compared to the flat UV LEDs, while no penalty was induced for the electrical characteristics of the UV LEDs. Additionally, the far-field radiation pattern of the UV LEDs with nanostructures showed much better directionality and a much stronger intensity than the flat UV LEDs, which would be of great benefit to directional UV curing applications. [ABSTRACT FROM AUTHOR]

Thin AlN spacer layer is widely adopted in Al(In)GaN/AlN/GaN heterostructures to improve the mobility of two-dimensional electron gas (2DEG) by increasing the 2DEG confinement and reducing the remote alloy scattering. However, the nominal AlN spacer is found to be an AlGaN spacer mainly due to the unintentional incorporation of Ga from the decomposition of the underlying GaN channel during the growth of AlN spacer and the temperature ramping process from the GaN channel to the Al(In)GaN barrier. The growth conditions of AlN spacer layer were varied systematically to study their influences on the unintentional Ga incorporation and the 2DEG mobility of AlInGaN/AlN/GaN heterostructures. Interestingly, the nominal AlN spacer (or AlGaN spacer in fact) can still effectively reduce the remote alloy scattering and deliver a 2DEG mobility substantially higher than that of AlInGaN/GaN heterostructures with no spacer or an AlGaN spacer uniformly containing a Ga content similar to the average Ga composition of the nominal AlN spacer. A simplified microstructure of the nominal AlN spacer with an inhomogeneous Ga incorporation was proposed to discuss about the influence of the spacer on the 2DEG mobility. [ABSTRACT FROM AUTHOR]

Screened bonding (SB), screened antibonding (SA) and charge transfer plasmon (CTP) modes in the conductively connected nanorod heterodimer are studied in detail by simulation. All of the SB, SA and CTP modes can be observed in the extinction spectra of the conductively connected nanorod heterodimer. Also, the amplitudes of the three modes can be tuned by changing the radius of the cylinder conductive connection. Even the amplitude of the SA mode can be tuned to be higher than that of the SB mode, which is difficult to achieve in an unconnected nanorod heterodimer. Furthermore, the wavelengths of the three plasmon modes can be adjusted with a high degree of freedom, since the wavelength of the SB mode mainly depends on the length of the longer nanorod, the wavelength of the SA mode mainly depends on the length of the shorter nanorod and the wavelength of the CTP mode mainly depends on the total length of the nanorod heterodimer. Our study will be helpful for the design of plasmon enhancement devices, such as surface enhanced Raman scattering (SERS), plasmon enhanced fluorescence, plasmon rulers and so on. [ABSTRACT FROM AUTHOR]

Thin AlN spacer layer is widely adopted in Al(In)GaN/AlN/GaN heterostructures to improve the mobility of two-dimensional electron gas (2DEG) by increasing the 2DEG confinement and reducing the remote alloy scattering. However, the nominal AlN spacer is found to be an AlGaN spacer mainly due to the unintentional incorporation of Ga from the decomposition of the underlying GaN channel during the growth of AlN spacer and the temperature ramping process from the GaN channel to the Al(In)GaN barrier. The growth conditions of AlN spacer layer were varied systematically to study their influences on the unintentional Ga incorporation and the 2DEG mobility of AlInGaN/AlN/GaN heterostructures. Interestingly, the nominal AlN spacer (or AlGaN spacer in fact) can still effectively reduce the remote alloy scattering and deliver a 2DEG mobility substantially higher than that of AlInGaN/GaN heterostructures with no spacer or an AlGaN spacer uniformly containing a Ga content similar to the average Ga composition of the nominal AlN spacer. A simplified microstructure of the nominal AlN spacer with an inhomogeneous Ga incorporation was proposed to discuss about the influence of the spacer on the 2DEG mobility. [ABSTRACT FROM AUTHOR]

A solid solution of (HfSc)0.83W2.25P0.83O12−δ is synthesized by the high-temperature, solid-state reaction and fast-quenching method. It is shown that it possesses an orthorhombic structure with space group Pmmm (47) and exhibits negative thermal expansion (NTE) property with low anisotropy in thermal expansion. The coefficients of thermal expansion (CTEs) for a, b, and c axes are 1.41 × 10−6 K−1, −2.23× 10−6 K−1, and −1.87 × 10−6 K−1, respectively. This gives rise to volume and linear CTEs of −3.10 × 10−6 K−1 and −1.03 × 10−6 K−1, respectively. Besides, it exhibits also intense photoluminescence from 360 nm to about 600 nm. The mechanism of NTE and the correlation of the PL with axial thermal expansion property are discussed. [ABSTRACT FROM AUTHOR]

We propose, fabricate and characterize photonic integration of a InGaN/GaN multiple-quantum-well light-emitting diode (MQW-LED), waveguide, ring resonator and InGaN/GaN MQW-photodiode on a single chip, in which the photonic circuit is suspended by the support beams. Both experimental observations and simulation results illustrate the manipulation of in-plane light coupling and propagation by the waveguide and the ring resonator. The monolithic photonic circuit forms an in-plane data communication system using visible light. When the two suspended InGaN/GaN MQW-diodes simultaneously serve as the transmitter and the receiver, an in-plane full-duplex light communication is experimentally demonstrated with a transmission rate of 30 Mbps, and the superimposed signals are extracted using the self-interference cancellation method. The suspended photonic circuit creates new possibilities for exploring the in-plane full-duplex light communication and manufacturing complex GaN-based monolithic photonic integrations. [ABSTRACT FROM AUTHOR]

This work reports a significant improvement in efficiency by optimizing the via-like n-electrode architecture design of a GaN-based thin-film LED grown on a 6-inch silicon substrate. The external quantum efficiency of the as-fabricated 1.1 mm × 1.1 mm via-thin-film LED chip at 350 mA was increased by 11.3% compared to that of a vertical thin-film LED chip with a conventional finger-like n-electrode. Detailed analysis of encapsulation gain and false color emission patterns illustrated that the significantly improved LED performance was due to enhanced light extraction efficiency and more uniform current spreading, both of which can be attributed to the optimized via-thin-film chip structure. Minimizing the light loss at the periphery of the Ag mirror was demonstrated to be a critical factor for improving light extraction, rather than simply replacing the finger-like n-electrodes with via-like ones. After encapsulation, the median blue lamp power and the wall-plug efficiency of the via-thin-film LED at 350 mA reached 659 mW and 63.7%, respectively. [ABSTRACT FROM AUTHOR]

The atomic structure and transition properties of H-like Al embedded in hot and dense plasmas are investigated using modified GRASP2K code. The plasma screening effect on the nucleus is described using the self-consistent field ion sphere model. The effective nuclear potential decreases much more quickly with increasing average free electron density, but increases slightly with increasing electron temperature. The variations of the transition energies, transition probabilities, and oscillator strengths with the free electron density and electron temperature are the same as that of the effective nuclear potential. The results reported in this work agree well with other available theoretical results and are useful for plasma diagnostics. [ABSTRACT FROM AUTHOR]

A simple experiment for measuring the surface tension coefficient is proposed, which is well suited for teaching and learning the behavior of liquids in typical student laboratories. It is based on the pull-off method and the dynamometer used is the Jolly balance. The experiment requires inexpensive equipment but the methods allow for serious analysis of possible systematic errors, such as the impact of the state of the spring and wire on the experimental results, and the unusual movement of the engraved line on the mirror when pulling up the water film. [ABSTRACT FROM AUTHOR]

In this article, we demonstrate plasmonic-induced optical transparency (PIT) in a planar metamaterial consisting of a metallic regular triangle (RT) embedded in a ring nanostructure. The interference between the bright dipole mode of the RT and the dark quadrupole mode of the ring leads to the emergence of a transparent window in the visible regime. By combining nanostructures with different degrees of symmetry, the PIT transmission properties of our metamaterial remain stable with respect to the incident polarization, showing polarization-insensitivity to the incident wave. The transmission efficiency of the PIT peak for different polarizations can be maintained at greater than 95.77% with a fluctuation range of 0.01% in our calculation accuracy. [ABSTRACT FROM AUTHOR]

Based on the extended geometrical optics model, a theoretical study of the optical trapping force on a spherical particle with the absorption considered is presented. In this study, the numerical simulation on transverse trapping force is given. The results suggest that the absorption coefficient and the axial shift of the particle center from the focused Gaussian beam waist greatly influence the trapping properties. Spherical particles with weak absorption could be stably trapped on the optical axis of the Gaussian beam, and the stiffness of trapping decreases with the increasing absorption coefficient of the particle. A highly absorbing particle has more complex trapping characteristics. As the particle location changes from the upstream to the downstream direction of the beam, the stable trapping position may firstly locate on the beam axis, secondly be along a circular route centered on the beam axis, and finally vanish. If the stable trapping position is along a circular route, the stiffness of trapping increases with the increasing absorption coefficient. [ABSTRACT FROM AUTHOR]