A modified simplified coherent potential approximation model of band gap energy of III-V ternary alloys

Based on the modification of the simplified coherent potential approximation （SCPA）, a model is developed to calculate the composition dependence of the band gap energy of Ⅲ-V ternary alloys with the same anion. The derived equation is used to fit the experimental band gap energy of InxAl1-xN, InxGa1-xN and A1xGal xN with x from 0 to 1. It is found that the fitting results are better than those done by using SCPA. The fitting results are also better than those obtained by using the formula with a small bowing coefficient, especially for InxAl1-xN. In addition, our model can also be used to describe the composition de- pendence of band gap energy of other Ⅲ-V ternary alloys.

Effect of band gap energy on the electrical conductivity in doped ZnO thin film

The transparent conductive pure and doped zinc oxide thin films with aluminum, cobalt and indium were deposited by ultrasonic spray technique on glass substrate at 350 ℃. This paper is to present a new approach to the description of correlation between electrical conductivity and optical gap energy with dopants＇ concentration of A1, Co and In. The correlation between the electrical and optical properties with doping level suggests that the electrical conductivity of the films is predominantly estimated by the band gap energy and the concentrations of A1, Co and In. The measurement in the electrical conductivity of doped films with correlation is equal to the experimental value, the error of this correlation is smaller than 13%. The minimum error value was estimated in the cobalt-doped ZnO thin films. This result indicates that such Co-doped ZnO thin films are chemically purer and have far fewer defects and less disorder owing to an almost complete chemical decomposition.

The calculation of band gap energy in zinc oxide films

We investigated the optical properties of undoped zinc oxide thin films as the n-type semiconductor;the thin films were deposited at different precursor molarities by ultrasonic spray and spray pyrolysis techniques.The thin films were deposited at different substrate temperatures ranging between 200 and 500℃. In this paper, we present a new approach to control the optical gap energy of ZnO thin films by concentration of the ZnO solution and substrate temperatures from experimental data, which were published in international journals. The model proposed to calculate the band gap energy with the Urbach energy was investigated. The relation between the experimental data and theoretical calculation suggests that the band gap energies are predominantly estimated by the Urbach energies, film transparency, and concentration of the ZnO solution and substrate temperatures. The measurements by these proposal models are in qualitative agreements with the experimental data; the correlation coefficient values were varied in the range 0.96–0.99999, indicating high quality representation of data based on Equation（2）, so that the relative errors of all calculation are smaller than 4%. Thus, one can suppose that the undoped ZnO thin films are chemically purer and have many fewer defects and less disorder owing to an almost complete chemical decomposition and contained higher optical band gap energy.

Electrode Erosion of a High Energy Impulse Spark Gap Switch

Based on the principle of thermal conduction, three metal alloys （stainless steel, copper-tungsten and graphite） were chosen as the material of the high impulse current discharging switch. Experimental results indicate that the mass loss and surface erosion morphology of the electrode are related with the electrode material （conductivity σ, melting point Tin, density p and thermal capacity c） and the impulse transferred charge （or energy） per impulse for the same total impulse transferred charge. The experimental results indicate that the mass loss of stainless steel, copper-tungsten and graphite are 380.10 μg/C, 118.10 μg/C and 81.90 μg/C respectively under the condition of a total impulse transferred charge of 525 C and a transferred charge per impulse of 10.5 C. Under the same impulse transferred charge, the mass loss of copper-tungsten（118.10 μg/C） with the transferred charge per impulse at 10.5 C is far larger than the mass loss （38.61μg/C） at a 1.48 C transferred charge per impulse. The electrode erosion mechanism under high energy impulse arcs is analyzed briefly and it is suggested that by selecting high conductive metal or metal alloy as the electrode material of a high energy impulse spark gap switch and setting high erosion resistance material at the top of the electrode, the mass loss of the electrode can be reduced and the life of the switch prolonged.

Energy gap suppression and excess current in TI2Ba2CaCu208 intrinsic Josephson junctions

Intrinsic Josephson junctions in misaligned T12Ba2CaCu208 thin film were fabricated on LaA103 substrate. The temperature dependence of the critical current is investigated around liquid nitrogen temperature. In the current voltage characteristic, large voltage jump and lack of resistive branch are observed, which shows good consistency with the intrinsic Josephson junctions. By analyzing the large gap voltage in the curve, great suppression of the energy gap is found. Through discussing the temperature dependence of the gap voltage in liquid nitrogen temperature, it is shown that this phenomenon can be caused by the non-equilibrium quasiparticle injection. The temperature influence on the excess current also confirms the non-equilibrium effect.

Pseudo-invariant Eigen-operator for Deriving Energy-Level Gap for Jaynes-Cummings Model

We extend the concept of invariant eigen-operator to pseudo-invariant eigen-operator case through analyzing the standard Jaynes-Cummings model. We find the pseudo-invariant eigen-operator in terms of supersymmetric generators of this model, which diretly leads to the energy-level gap for Jaynes Cummings Hamiltonian.

The Energy Efficiency Gap in Maritime Transport

There is evidence that the shipping industry could achieve energy efficiency gains through the implementation of new technologies, with considerable reductions of fuel costs and emissions to air in the sector. Although the cost reducing effects of some new technologies are well established, companies appear reluctant to innovate despite the financial and societal benefits, as a result of what is referred to as the energy efficiency gap. The global emission impacts of the shipping industry, most notably of greenhouse gases, sulphur and nitrogen oxides are increasingly attracting the attention of regulators, non-governmental organisations and the media, and shipping companies are under pressure to find new ways to reduce their emission footprint. Understanding the determinants of the energy efficiency gap in shipping is then critical in improving the environmental profile of the industry. This paper presents the results of a survey among Norwegian shipping companies aimed at gaining a better understanding of the barriers to implementation of new cost saving technologies. The paper assesses the technical barriers that have traditionally been indicated as the main cause of the energy efficiency gap in shipping. The paper results indicate that next to technical factors, important barriers are constituted also by managerial practices and legal constraints.

Evidence for Multiple Underlying Fermi Surface and Isotropic Energy Gap in the Cuprate Parent Compound Ca2CuO2Cl2

The parent compounds of the high-temperature cuprate superconductors are Mott insulators.It has been generally agreed that understanding the physics of the doped Mott insulators is essential to understanding the mechanism of high temperature superconductivity.A natural starting point is to elucidate the basic electronic structure of the parent compound.Here we report comprehensive high resolution angle-resolved photoemission measurements on Ca_2CuO_2Cl_2,a Mott insulator and a prototypical parent compound of the cuprates.Multiple underl.ying Fermi surface sheets are revealed for the first time.The high energy waterfall-like band dispersions exhibit different behaviors near the nodal and antinodal regions.Two distinct energy scales are identified：a d-wave-like low energy peak dispersion and a nearly isotropic lower Hubbard band gap.These observations provide new information of the electronic structure of the cuprate parent compound,which is important for understanding the anomalous physical properties and superconductivity mechanism of the high temperature cuprate superconductors.

Tip-Pressure-Induced Incoherent Energy Gap in CaFe_2As_2

In CaFe2 As2, superconductivity can be achieved by applying a modest c-axis pressure of several kbar. Here we use scanning tunneling microscopy/spectroscopy （STM/S） to explore the STM tip pressure effect on single crystals of CaFe2 As2. When performing STM/S measurements, the tip-sample interaction can be controlled to act repulsive with reduction of the junction resistance, thus to apply a tip pressure on the sample. We find that an incoherent energy gap emerges at the Fermi level in the differential conductance spectrum when the tip pressure is increased. This energy gap is of the similar order of magnitude as the superconducting gap in the chemical doped compound Cao.4Nao.6Fe2As2 and disappears at the temperature well below that of the bulk magnetic ordering. Moreover, we also observe the rhombic distortion of the As lattice, which agrees with the orthorhombic distortion of the underlying Fe lattice. These findings suggest that the STM tip pressure can induce the local Cooper pairing in the orthorhombic phase of CaFe2As2.

Nitrogen-tailored quasiparticle energy gaps of polyynes

Polyyne,an sp~1-hybridized linear allotrope of carbon,has a tunable quasiparticle energy gap,which depends on the terminated chemical ending groups as well as the chain length.Previously,nitrogen doping was utilized to tailor the properties of different kinds of allotrope of carbon.However,how the nitrogen doping tailors the properties of the polyyne remains unexplored.Here,we applied the GW method to study the quasiparticle energy gaps of the N-doped polyynes with different lengths.When a C atom is substituted by an N atom in a polyyne,the quasiparticle energy gap varies with the substituted position in the polyyne.The modification is particularly pronounced when the second-nearest-neighboring carbon atom of a hydrogen atom is substituted.In addition,the nitrogen doping makes the Fermi level closer to the lowest unoccupied molecular orbital,resulting in an n-type semiconductor.Our results suggest another route to tailor the electronic properties of polyyne in addition to the length of polyyne and the terminated chemical ending groups.

Energy Gap for Some Hamiltonian Systems Describing Polariton Systems Obtained via Invariant Eigen-operator Method

Based on the invariant eigen-operator method （lEO） [Phys. Left. A 321 （2004） 75] we derive the exact energy gap for some Hamiltonians, which describe some polariton systems. The result shows that in some cases the IEO method, stemming from the Heisenberg approach, is more direct and convenient for deriving the energy-level gap formula than via the approach of solving the Schrodinger equation.

Magnon energy gap in a four-layer ferromagnetic superlattice

The magnon energy band in a four-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green＇s function technique. It is found that three modulated energy gaps exist in the magnon energy band along Kx direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the three energy gaps. The magnon energy gaps of the four-layer ferromagnetic superlattice are different from those of the three-layer one. For the four-layer ferromagnetic superlattice, the disappearance of the magnon energy gaps △ω12, △ω23 and △ω34 all correlates with the symmetry of this system. The zero energy gap △ω23 correlates with the symmetry of interlayer exchange couplings, while the vanishing of the magnon energy gaps △ω12 and △ω34 corresponds to a translational symmetry of x-direction in the lattice. When the parameters of the system deviate from these symmetries, the three energy gaps will increase.

Deriving Energy-Gap of Some Nonlinear Hamiltonians by Invariant Eigen-operator Method

By virtue of the invariant eigen-operator method we search for the invariant eigen-operators for someHamiltonians describing nonlinear processes in particle physics.In this way the energy-gap of the Hamiltonians can benaturally obtained.The characteristic polynomial theory has been fully employed in our derivation.

Critical Behavior of the Energy Gap and Its Relation with the Berry Phase Close to the Excited State Quantum Phase Transition in the Lipkin Model

In our previous work [Phys. Rev. A 85 （2012） 044102], we studied the Berry phase of the ground state and exited states in the Lipkin model. In this work, using the Hellmann-Feynman theorem, we derive the relation between the energy gap and the Berry phase closed to the excited state quantum phase transition （ESQPT） in the Lipkin model. It is found that the energy gap is approximately linearly dependent on the Berry phase being closed to the ESQPT for large N. As a result, the critical behavior of the energy gap is similar to that of the Berry phase. In addition, we also perform a semiclassical qualitative analysis about the critical behavior of the energy gap.

Crystal Sizes and Energy Gaps of Cerium Oxide Using Co-Precipitation Method

Co-precipitation was used to prepare cerium oxide nano-particles. The effects of aging temperature and concentration of cobalt ion on the optical property, morphology, and particle size were investigated. The cerium oxide was prepared by adding ammonia solution into a mixed solution of cerium nitrate with cobalt nitrate solutions to obtain a large amount of precipitates and then aged further. Subsequently, the precipitates were kept in an oven for calcination keeping the temperature at 400?C for lasting 24 h. The average size of cerium oxide particles was obtained from the (111) peak in the X-ray diffraction pattern using the Scherrer equation. The crystal sizes obtained were found to be in the range of 11.82 - 13.47 nm. The results showed that the particle size decreased with an increase in the Co ion concentration and decreased with an increase in temperature. The SEM pictures show that the morphology for cerium oxide is granular and/or columnar. It can be seen from UV/Vis absorption spectrum that the maximum absorption peaks were in the range of 334 - 390 nm, depending on the operating conditions. The corresponding energy gaps were observed in the range of 3.18 - 3.71 eV. Subsequently, the Brus equation for the energy gap was discussed. Finally, particle size was correlated with the aging temperature and Co ion concentration.

Energy gap suppression and excess current in Tl_2Ba_2CaCu_2O_8 intrinsic Josephson junctions

Intrinsic Josephson junctions in misaligned Tl2Ba2CaCu2O8 thin film were fabricated on LaAlO3 substrate. The temperature dependence of the critical current is investigated around liquid nitrogen temperature. In the current voltage characteristic, large voltage jump and lack of resistive branch are observed, which shows good consistency with the intrinsic Josephson junctions. By analyzing the large gap voltage in the curve, great suppression of the energy gap is found. Through discussing the temperature dependence of the gap voltage in liquid nitrogen temperature, it is shown that this phenomenon can be caused by the non-equilibrium quasiparticle injection. The temperature influence on the excess current also confirms the non-equilibrium effect.

Achieving highly efficient long-wavelength phosphorescence emission of large singlet-triplet energy gap materials by host-guest doping

High-efficiency long-wavelength phosphorescence emissions of large singlet-triplet energy gap(ΔE_(ST))materials are essential for applications in biology and display.However,few long-wavelength phosphorescence emissions of largeΔE_(ST)materials have been reported due to the weak spin-orbit coupling(SOC)and strong non-radiative transitions.Herein,we develop a strategy to achieve highly efficient long-wavelength room temperature phosphorescence(RTP)emission of largeΔE_(ST)materials,which display bright red RTP emission with above 400μs lifetime and 6.5%phosphorescent quantum efficiency.Our experiments and theoretical calculations reveal that the fishbone-like packing and the zig-zag interactions provide favorable conditions for suppressing the non-radiative transitions of triplet state excitons,and heavy atoms effectively promote the intersystem crossing(ISC)process for highly efficient long-wavelength phosphorescence emission.The universality of the method for highly efficient long-wavelength RTP emission of largeΔE_(ST)materials was further investigated in various guests.Moreover,these materials with largeΔE_(ST)manifest the advantages of large color contrast on the display and utilization potentiality in information encryption.This strategy paves the way for the high contrast display and development of information encryption with RTP emission.

Tradeoffbetween Narrowing Optical Band Gap and Enhancing Electrical Conductivity of the Metal Nanoparticles-Modified Titanium Oxide Films

The n-type semiconducting titanium oxide thin films are well-known as electron transporting interlayer in photovoltaic cells. The favorable characteristics of interlayers in photovoltaics are high optical transmittance （T%）, wide band gap energy （Eg） and high electrical conductivity （σ）. Modifying titanium oxide films with metal nanoparticles would increase electrical conductivity but reduce optical band gap energy. We developed the sol-gel derived titanium suboxide （TiOx） films modified with silver （Ag） or gold （Au） or copper （Cu） nanoparticles （NPs）. This study explores a tradeoff between narrowing optical band gap and enhancing electrical conductivity of nanostructured TiOx films by controlling the Au- or Ag- or Cu-NPs loading concentrations （mol%） in titania. The Au- and Cu-NPs loading concentration of 4 mol% should meet a tradeoff which yields the higher T%, wider Eg and higher compared to those of pure TiOx films. In addition, since the pure Cu is not thermodynamically stable in ambience as compared to Au and Ag, the stability of as-obtained colloidal CuNPs is also examined. A careful examination of the time evolution of surface plasmon resonance （SPR） bands of CuNPs indicates that their stability is only up to 4 h.

Cost Minimization of Wireless Sensor Networks with Unlimited-lifetime Energy for Monitoring Oil Pipelines

Cyber-physical-system (CPS) has been widely used in both civil and military applications. Wireless sensor network (WSN) as the part and parcel of CPS faces energy problem because sensors are battery powered, which results in limited lifetime of the network. To address this energy problem, we take advantage of energy harvesting device (EHD) and study how to indefinitely prolong oil pipeline monitoring network lifetime by reasonable selecting EHD. Firstly, we propose a general strategy worst case-energy balance strategy (WC-EBS), which defines worst case energy consumption (WCEC) as the maximum energy sensor node could expend for oil pipeline monitoring WSN. When the energy collected by EHD is equal or greater than WCEC, network can have an unlimited lifetime. However, energy harvesting rate is proportional to the price of EHD, WC-EBS will cause high network cost. To reduce network cost, we present two optimization strategies, optimization workloadenergy balance strategy (OW-EBS ) and optimization first nodeenergy balance strategy (OF-EBS). The main idea of OW-EBS is to cut down WCEC by reducing critical node transmission workload; OF-EBS confirms critical node by optimizing each sensor node transmission range, then we get the optimal energy harvesting rate in OF-EBS. The experimental results demonstrate that OF-EBS can indefinitely extend network lifetime with lower cost than WC-EBS and OW-EBS, and energy harvesting rate P in each strategy satisfies POF-EBS ≤POW-EBS ≤PWC-EBS. © 2014 Chinese Association of Automation.

Frequency in Middle of Magnon Band Gap in a Layered Ferromagnetic Superlattice

The frequency in middle of magnon energy band in a five-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green＇s function technique. It is found that four energy gaps and corresponding four frequencie in middle of energy gaps exist in the magnon band along Kx direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the four frequencies in middle of the energy gaps. When all interlayer exchange couplings are same, the effect of spin quantum numbers on the frequency wg1 in middle of the energy gap Δw12 is complicated, and the frequency wg1 depends on the match of spin quantum numbers in each layer. Meanwhile, the frequencies wg2, wg3, and wg4 in middle of other energy gaps increase monotonously with increasing spin quantum numbers. When the spin quantum numbers in each layer are same, the frequencies wg1, wg2, wg3, and wg4 all increase monotonously with increasing interlayer exchange couplings.