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For the purpose of introducing a high work-function layer to improve the implied voltage in asymmetric silicon-based heterojunction photovoltaic devices, molybdenum oxide (MoOx, 0 < x < 3) is applied to the device. However, besides the role of extracting holes on one side, another singularity behavior presented itself in the nonequilibrium state, i.e. a worsened photovoltaic peformance (an 'S-shape') of current density versus voltage (J–V) was revealed with an inappropriate chemical state of the MoOx film. The source of the 'S-shaped' behavior of an MoOx/a-Si: H(i)/n-Si heterojunction device was co-analyzed by x-ray photoelectron spectroscopy with depth profiling, ultraviolet photoelectron spectroscopy, current density-voltage representation, a minority carrier lifetime survey and automat for simulation of heterostructures software simulation. It was found that an amorphous SiOx interlayer was spontaneously formed during the deposition of MoOx film onto a-Si: H(i)/n-Si substrate, blocking the transport of holes. The decrease in the work-function of the MoOx layer is attributed to an oxidation reaction at the MoOx/a-Si: H(i) boundary zone, which results in the decline of hole selectivity. A rising O/Si ratio in the SiOx interlayer induces an augmentation of valence band offsets, which could be the best interpretation of the 'S-shaped' response, because of a barrier that hinders the thermionic emission of holes. Meanwhile, the thicker (>4 nm) SiOx layer leads to a lower tunneling probability for holes. The characteristic analysis of the MoOx/a-Si: H(i)/n-Si heterojunction device deepens the understanding of the hole transport mechanism of the device. [ABSTRACT FROM AUTHOR]

Threading dislocations that are of a type were observed to form locally in InGaN layers and wells containing 7%-15% indium. Direct correlations between a type dislocations and stacking faults in InGaN layers and wells were observed. The formation of these dislocations is attributed to the dissociation of Shockley partials bounding the stacking faults. [ABSTRACT FROM AUTHOR]

We report the bandgap and electronic properties of wurtzite ZnO doped with elements IIA or/and IIIA, investigated using both theoretical and experimental methods. With wurtzite ZnO co-doped with B and Mg (denoted as ZnO:[B,Mg]) grown via metalorganic chemical vapor deposition, we have observed that both the bandgap and the conductivity can be widely tunable with the doping levels. From first-principles calculations of wurtzite ZnO:Mg, we show that IIA doping elements have a great impact on the widening of the bandgap. Also, from a newly developed calculation method for investigating the electronic properties of wurtzite ZnO:Al, we have found that IIIA doping elements play an important role in tailoring the conductivity. [ABSTRACT FROM AUTHOR]

We investigated the spin-transfer switching in a full-Heusler Co2FeAl0.5Si0.5 alloy spin-valve nanopillar through micromagnetic simulation. A two-step switching hysteresis loop due to the fourfold in-plane magnetocrystalline anisotropy of Co2FeAl0.5Si0.5 layers was obtained. The simulation explains the experimental result of the resistance versus current hysteresis loop and yields good agreement with the measured critical current. Furthermore, the magnetization trajectory and magnetization distribution were shown and analyzed to elucidate the different characters of two-step switching. [ABSTRACT FROM AUTHOR]

Predicting the domain structures and properties in both bulk single crystal and thin film ferroelectrics using the phase-field approach requires the knowledge of fundamental mechanical, electrical, and electromechanical coupling properties of a single-domain state. In this work, the elastic properties and structural parameters of cubic single crystals as well as tetragonal, orthorhombic, and rhombohedral BaTiO3 single domain states are obtained using first-principles calculations under the local density approximation. The calculated lattice constants, bulk modulus, and elastic constants are in good agreement with experiments for both the cubic paraelectric phase and the low-temperature ferroelectric phases. Spontaneous polarizations for all three ferroelectric phases and the electrostrictive coefficients of cubic BaTiO3 are also computed using the Berry’s phase approach, and the results agree well with existing experimentally measured values. [ABSTRACT FROM AUTHOR]

A complete surface reconstruction takes place after a local connection between two crossed tubes is established, leading to the creation of an extended X-shaped junction constituted by topological defects with smooth negative curvature. Molecular-dynamics simulations show that the surface reconstructions occur through (1) generalized Stone-Wales transformation and (2) the movement of sp and sp3 atoms and their transformation to sp2 atoms by bond rearrangement. Based on both the principle of energy minimization and a generalized Euler’s rule, it is demonstrated that the most stable structure for X junctions contains only 12 heptagons. The annealing temperature influences the topological structure and stability of junctions. [ABSTRACT FROM AUTHOR]

The temperature- and growth-dependent Urbach band-tail characteristics in polysilicon wafers have been investigated both experimentally and theoretically for the improvement of solar cells. The band-tail parameter in polysilicon has been obtained by temperature-dependent transmission spectra, with the aid of a detailed calculation of the transmission profile. The band-tail parameter is in the range of 30-90 meV in polysilicon. A band-tail model based on the calculation of density of occupied states and the carrier-phonon interaction has been employed to analyze the temperature-dependent band-tail characteristics. It is found that the yielded structural information can be well explained by Raman measurements. We have correlated various aspects of the observed structural properties, such as the band-tail parameter, trap concentration, grain-surface charge density, and correlation length, with the conversion efficiency of the polysilicon solar cells. [ABSTRACT FROM AUTHOR]

To address the hesitancy, inconsistency and uncertainty of decision makers cognitions, linguistic interval hesitant fuzzy sets (LIHFSs) are efficient tools. This paper focuses on studying the application of LIHFSs. To do this, two correlation coefficients of LIHFSs are defined, which needn’t consider the length of elements in LIHFSs or the arrangement of their possible interval values. To address the situation where the weights of elements in a set are different and correlative, two linguistic interval hesitant fuzzy Shapley weighted correlation coefficients are defined. Considering the situation where the weight information of features/attributes is partly known, programming models to determine the optimal fuzzy measures on them are constructed, respectively. After that, an approach to pattern recognition and multi-attribute decision making with linguistic interval hesitant fuzzy information is developed, respectively. Meanwhile, illustrative examples about medical diagnosis and selecting constructors for tunnel bidding are selected to verify the application of new approaches, and comparison with a previous method is offered. [ABSTRACT FROM AUTHOR]

NiCo2S4@PPy core–shell nanotube arrays have been successfully prepared through three facile steps: solvothermal synthesis, solvothermal sulphurisation and subsequentin situelectropolymerisation of polypyrrole (PPy). Their structure and morphology were studied by XRD, FTIR, SEM and TEM. The results suggest that a thin layer of PPy with 8 nm in thickness is wrapped on the surface of NiCo2S4nanotubes. The coating PPy strong promotes pseudo-capacitance reaction of NiCo2S4nanotube arrays. NiCo2S4@PPy shows lower charge plateau and IR drop, higher discharge plateau and Coulombic efficiency. Rate performance is improved remarkably. Average specific capacitance at 24 mA cm−2is even two times that of the uncoated NiCo2S4. The galvanostatic cycling tests at 4 mA cm−2indicate NiCo2S4@PPy exhibit the highest specific capacitance of 1524 F g−1and improved capacitance retention to 78.5% after 3000 cycles. The corresponding values of the uncoated NiCo2S4nanotube arrays are only 1410 F g−1and 22%. The improved electrochemical performance is mainly attributed to unique core–shell nanotube array structure and the key assistant effect of the coating PPy which remarkably improves the conductive property of NiCo2S4long nanotubes and effectively enhances structure stability and cycling stability of NiCo2S4nanotubes. [ABSTRACT FROM PUBLISHER]

We report the microwave dielectric properties of BaTiO3 thin films fabricated via aerosol deposition, which is capable of applying functional ceramic films to Si-based semiconductor fabrication at room temperature. As the starting powder, BaTiO3 powder with an average particle size of 300 nm afforded a dense thin film with a thickness of 500 nm as well as a smooth interface with the Pt/Ti/SiO2/Si substrate. In comparison, the interface roughness of BaTiO3 thin film was degraded (>100 nm) when BaTiO3 powder with an average particle size of 450 nm was used as the starting powder, owing to the excessive impact energy during film growth. Metal-insulator–metal capacitors were realized on a Si wafer via electron beam evaporation and inductively coupled plasma etching in order to determine the relative permittivity, loss tangent, and current-voltage characteristics. The average values of the relative dielectric permittivity and loss tangent of the BaTiO3 thin film were 78 and 0.03, respectively, in the frequency range of 1–6 GHz. [ABSTRACT FROM PUBLISHER]

In this paper the model of multi-choice games on matroids is defined. The explicit expression of a Shapley function for the given multi-choice games is presented. Meantime, characterizations of the given Shapley function are discussed. Two of which are inspired by Shapley's axioms for the Shapley function in traditional case; others are enlightened by Young's characterizations for the Shapley function in classical case. When multi-choice games on matroids are convex, the relationship between the core, its subcore and the Shapley function is researched. Finally, a numerical example is given. [ABSTRACT FROM PUBLISHER]

The effect of welding speed and the response to post-weld aging treatment of Fe-Cr-Ni-Mo-Ti-Cu stainless maraging steel laser weldments have been investigated. Laser welding was carried out at a welding speed range of 1.0 to 3.0 m/min, and then post-weld aging was performed at a temperature range of 420 to 580°C. The welding speed ranging from 2.0 m/min to 3.0 m/min was suitable for laser welding of the studied maraging steel sheet. Hardness survey across the aged weldments revealed that hardness peaks in different zones after aging treatments occurred at different temperatures: 420°C for parent metal zone (PMZ), 460°C for the heat affected zone (HAZ) and 500°C for fusion zone (FZ). Hardness became higher in HAZ and FZ than in PMZ above 420°C and so the tensile failure location occurred in PMZ above aging temperature of 420°C. Among the applied aging treatments, aging at 460°C achieved the highest tensile strength of laser weldments. [ABSTRACT FROM AUTHOR]

China's electricity generation is mainly dependent on fossil fuel. Promoting electricity conservation in different sectors and regions plays a vital role in reducing China's energy-related CO2 emissions and other pollutants. This paper contributes to identify the sectors and economic regions with larger electricity-saving potential and make policy recommendations for promoting electricity conservation. Two indicators, namely TEC (technical elasticity coefficient) and PSC (price sensitivity coefficient), are constructed within an input-output analysis framework to measure the electricity-saving potential. The proposed indicators are applied to analyze the electricity-saving potentials of 20 sectors and 30 provinces in China. We also use EFC (electricity forward correlation coefficient) to examine the relationship between power consumption and electricity-saving potential. Our empirical results show that Mechanical industry, Construction industry and Chemical industry have the largest electricity-saving potential. Meanwhile, the east region of China also shows greater electricity-saving potential. It is suggested that Chinese government adopt pricing regulation and technology innovation policies jointly to promote China's energy conservation. Some important policy implications according to our empirical study are also proposed. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulation is performed to study the interaction between deformation twin and annealing twin in iron crystal. Two samples are simulated in this paper. The annealing twin in each sample is considered pre-existing automatically and the deformation twin is formed in the process of mode-I type loading and emitted from the crack tip. The distances between the twin boundary of the annealing twin and the crack tip in two samples are different. The applied stress is imposed to the top and the bottom of each sample. When the stress intensity is KI = 0·94 MPa m1/2, the partial dislocation is emitted from the crack tip of each sample, but the sample with larger annealing twin grain size will move a greater distance. As KI is increased to 2 MPa m1/2, the larger the annealing twin grain size is, the faster it will grow and the smaller the size of the deformation twin from the crack tip. That is to say, the size of the annealing twin will hinder the formation of the deformation twin and then affect the mechanical property of the material. [ABSTRACT FROM AUTHOR]

In this paper, a detached zero index metamaterial lens (ZIML) consisting of metal strips and modified split ring resonators (MSRRs) is proposed for antenna gain enhancement. The effective permittivity and permeability of the detached ZIML are designed to synchronously approach zero, which leads the ZIML to having an effective wave impedance matching with air and near-zero index simultaneously. As a result, neither does the detached ZIML need to be embedded in horns aperture nor depends on auxiliary reflectors in enhancing antenna gain, which is quite different from conventional ZIMLs. Moreover, the distance between antenna and the detached ZIML slightly affect the gain enhancement, which further confirms that the ZIML can be detached from antennas. Simulated results show that the effective refractive index of the detached ZIML is near zero in a broad frequency range where the effective relative wave impedance is close to 1. The detached ZIML is fabricated and tested by placing it in front of an H-plane horn antenna. One finds that evident gain enhancement is obtained from 8.9 GHz to 10.8 GHz and the greatest gain enhancement reaches up to 4.02dB. In addition, the detached ZIML can also work well at other frequencies by adjusting its geometric parameters to scale, which is demonstrated by designing and simulating two detached ZIMLs with center frequencies of 2.4 GHz and 5.8 GHz, respectively. [ABSTRACT FROM AUTHOR]

In this paper, the analogue of electromagnetically induced transparency is achieved in a magnetic metamaterial consisting of coupled “radiative” square closed loop (SCL) and “dark” square spiral resonator (SSR). Full-wave numerical simulations are carried out to validate the EIT-like effect of the magnetic metamaterial. Transmission spectrums and surface current distributions for the metamaterial are presented. It is shown that placing the SSR close to the SCL causes the electromagnetic field energy to be coupled back and forth between them. This leads to destructive interference and the transparency window in the transmission stop-band of the metamaterial. In addition, it is numerically demonstrated that the magnetic metamaterial can be employed as a refractive-index based sensor with a sensitivity of 41.3 mm/RIU, which means that the resonance wavelength of the sensor shifts 41.3 mm per unit change of refractive-index of the surrounding medium. [ABSTRACT FROM PUBLISHER]

In this paper, a low-loss magnetic metamaterial configuration consisting of coupled radiative and dark resonators is proposed based on analog of electromagnetically induced transparency. Full-wave numerical simulations are carried out to validate the metamaterial. Absorptions curves, transmission spectrums, surface current distributions, and effective constitutive parameters for the metamaterial are presented. These results, showing a low-loss transparency window and strong dispersion in the effective permeability with negative values, are in a good agreement with each other. [ABSTRACT FROM AUTHOR]

A type of near-perfect magnetic cloak with radical and tangential diagonal components of the permittivity and permeability tensors as constants is proposed. Only z-component of the constitutive tensor is spatial variant, and all the diagonal components of the permittivity and permeability tensors are nonsingular, which make it possible to construct this kind of cloak with 2-D metamaterials. The effects of loss and perturbations of parameters on the performance of the cloak are also investigated. This study provides a feasible way for 2-D cloak design. [ABSTRACT FROM AUTHOR]

Electromagnetic characteristics of the dielectric cylinder covered by the cylindrical cloak are investigated in detail. Analytical expressions of electric field are derived and validated. Furthermore, effects of different kinds of loss on the performance of the cloak are studied. It is shown that if loss does not follow the same property as the constitutive tensor of the anisotropic and inhomogeneous cloak, electric fields could transmit into the inner dielectric cylinder. The authors believe that the results are helpful for practical applications. [ABSTRACT FROM AUTHOR]

In this paper, a small omnidirectional microstrip antenna (MSA) is proposed based on a compact double negative (DNG) metamaterial, which is constructed by modified split ring resonators (MSRRs) and metal strips. First, the backward wave property of the DNG slab is investigated and illustrated by full-wave simulations. It is shown that the slab can exhibit double negative parameters and support backward wave in a broadband of 8.45 GHz∼11.05 GHz, so the existence of the DNG band is proven. Then the DNG unit cells are stacked and embedded into a host substrate to construct a phase-compensating substrate for the small MSA. By using the modified transmission line model (MTLM) and 3D full-wave simulation, a small MSA is modeled and characterized. Results show that the presence of the DNG fillings can indeed greatly reduce the physical dimensions from 0.5λ to 0.17λ, while its farfield pattern is significantly different from that of a conventional half-wave-length MSA. Lastly, the E-field distributions of the small MSA and a conventional half-wave-length MSA are contrasted and discussed to explain the functional mechanism of the small omnidirectional SMA. [ABSTRACT FROM AUTHOR]

In this paper, we present a new approach for separating the bulk lifetime and surface recombination velocities via a single laser microwave photoconductance. When a pulsed laser pumps on the probed sample, with the illumination of first the front surface and then the back surface with the same light wavelength, the bulk lifetime and the surface recombination velocities are obtained. Detailed theoretical analysis and preliminary experimental results are shown to demonstrate the applicability of the method. [ABSTRACT FROM AUTHOR]

Diamond films were grown on steel substrates by a hot filament chemical vapor deposition method without any special substrate pretreatment. When the deposition time was extended from 15 to 83 hrs and above, non-graphitic interfacial layers were formed below diamond films. The interracial layers were solid and mediated good adherence of diamond films on steel substrates. The interfacial layers were found to be iron and chromium carbides with traces of oxygen as determined by chemical analysis using a scanning Auger microscopy (SAM). The carbide interracial layers probably resulted from graphitic conversion processes. It is assumed that the graphitic conversion was established on chemical reaction pathways driven by thermal diffusion processes between the earlier formed graphitic layers and atomic constituents of the steel substrates. [ABSTRACT FROM AUTHOR]

Composite films of ∼10 nm nanodiamond particles embedded in an amorphous carbon matrix were formed using a double bias assisted hot filament chemical vapor deposition system with a feeding gas mixture of 1% CH[sub 4]:99% H[sub 2]. The structure was obtained via the equilibrium of a multistage process including: (1) bias enhanced nucleation of diamond in an amorphous carbon matrix, (2) growth of both amorphous carbon and diamond, (3) suppression of the diamond growth by the surrounding amorphous carbon matrix, and (4) bias enhanced renucleation of diamond on the new amorphous carbon boundaries. The work adds insight to the diamond nucleation and growth processes. [ABSTRACT FROM AUTHOR]

Field emission from multihead silicon (Si) cones was substantially improved by cesium (Cs) coating. Increasing the Cs coating lowered the emission turn-on field (for 10 μA/cm[sup 2]) from 25 V/μm to a saturated value of 13 V/μm, while the threshold field (for 10 mA/cm[sup 2]) decreased by 30%, dropping from 27 V/μm for Si cones coated with 1.8 monolayers (ML) of Cs to a saturated value of 19 V/μm with 4.1 ML of Cs. The Cs-treated Si cones could give an emission current density that was three to ten times that delivered by bare Si cones. The work function reduced by a factor of 1.43 for Si cones coated with 4.9 ML of Cs with reference to the untreated Si cones. From the slope of Fowler–Nordheim plot, the field enhancement factor β was found to increase by a factor of 2.02 for Si cones coated with 2.5 ML of Cs and then reduce to 1.57 after the 4.9 ML of Cs deposition. Reduction of the factor β might occur because of a thick Cs layer, which could flatten the sharp cone features. Stability test showed that no current decay was observed at a current density of 0.8 mA/cm[sup 2] under a constant applied field of 16 V/μm during the 10 h investigation. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]