To analyze the security of two-step quantum direct communication protocol (QDCP) by using Einstein–Podolsky–Rosen pair proposed by Deng et al. [Phys. Rev. A 68 (2003) 042317] in collective-rotation noise channel, an excellent model of noise analysis is proposed. In the security analysis, the method of the entropy theory is introduced, and is compared with QDCP, an error rate point Q₀(M:(Q₀,1.0)) is given. In different noise levels, if Eve wants to obtain the same amount of information, the error rate Q is distinguishable. The larger the noise level ε is, the larger the error rate Q is. When the noise level ε is lower than 11%, the high error rate is 0.153 without eavesdropping. Lastly, the security of the proposed protocol is discussed. It turns out that the quantum channel will be safe when Q<0.153. Similarly, if error rate Q>0.153=Q₀, eavesdropping information I>1, which means that there exist eavesdroppers in the quantum channel, and the quantum channel will not be safe anymore.

How to estimate the randomness of the measurement outcomes generated by a given device is an important issue in quantum information theory. Recently, Brunner et al. [Phys. Rev. Lett. 112 (2014) 140407] proposed a prepare-and-measure quantum random number generation scenario with device-independent assumption, which indicates a method to test the randomness of bit strings according to the generation process rather than the results. Based on this protocol, we implement a quantum random number generator with an intrinsic stable phase-encoded quantum key distribution system. The system has been continuously running for more than 200 h, a stable witness W with the average value of 0.9752 and a standard deviation of 0.0024 are obtained. More than 1 G random bits are generated and the results pass all items of NIST test suite.

The 'plug & play' quantum key distribution system is the most stable and the earliest commercial system in the quantum communication field. Jones matrix and Jones calculus are widely used in the analysis of this system and the improved version, which is called the auto-compensating quantum key distribution system. Unfortunately, existing analysis has two drawbacks: only the auto-compensating process is analyzed and existing systems do not fully consider laser phase affected by a Faraday mirror (FM). In this work, we present a detailed analysis of the output of light pulse transmitting in a plug & play quantum key distribution system that contains only an FM, by Jones calculus. A similar analysis is made to a home-made auto-compensating system which contains two FMs to compensate for environmental effects. More importantly, we show that theoretical and experimental results are different in the plug & play interferometric setup due to the fact that a conventional Jones matrix of FM neglected an additional phase π on alternative polarization direction. To resolve the above problem, we give a new Jones matrix of an FM according to the coordinate rotation. This new Jones matrix not only resolves the above contradiction in the plug & play interferometric setup, but also is suitable for the previous analyses about auto-compensating quantum key distribution.

The quantum interference pattern in the double-slit experiment is qualitatively reproduced by using the entangled trajectory molecular dynamics method and compared with previous works. We compare entangled trajectory and classical trajectory with the same initial state in the phase space to show quantum effect in the evolution of trajectories. It is involved with breakdown in the statistical independence of the trajectories. Although our result does not agree well with exact quantum calculation in quantitatively with loss of part of interference pattern peaks, we can offer a reasonable explanation by analyzing quantum interference of two Gaussian wave packets in the phase space.

We numerically study the effect of the quantum coins on the two-particle quantum walks on an infinite line. Both non-interacting and interacting particles are considered. The joint probability as well as the bunching or anti-bunching behavior are greatly affected by the phase factors in the coin operation. Further, the spatial correlation can be maximized by choosing appropriate coin parameters. The entanglement between the two particles can be adjusted in the same manner.

We propose a novel strategy named basis-splitting scheme to split the intercepted quanta into several portions based on different bases, for eavesdropping in the process of quantum cryptography. Compared with intercept-resend strategy, our simulation results of the basis-splitting scheme under the non-ideal condition show a greater performance, especially with the increase of the length of shifted bits. Consequently our scheme can aid eavesdropper to gather much more useful information.

We analyze the geodesic motion in Schwarzschild spacetime with the weak-field limit. We investigate all geodesic types of the test particle by solving the geodesic equation and analyzing the behavior of effective potential. At the same time, all kinds of orbits, which are allowed according to the energy level corresponding to the effective potential, are numerically simulated in detail. Then we discuss the effect of different parameters on the effective potential energy. We also find that the test particle falls rapidly along the fall-into orbit and the radius of stable (unstable) circular orbits become larger in the Schwarzschild spacetime with the weak-field limit than those in the Schwarzschild case.

It is shown that the introduction of thermal effect, zero-point vibration, and phonon anharmonicity to a high quality and first-principle-based force field (atomic potential) results in a significant improvement in predicting the densities for the α phase crystalline hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and derivation of its high-fidelity Hugoniot locus and Mie-Grüneisen equation of state covering a very wide range of pressures and temperatures. This work can be used to efficiently and accurately predict the thermophysical properties of solid explosives over the pressures and temperatures to which they are subjected, which is a long-standing issue in the field of energetic materials.

We develop an improved design of thin gap chamber (TGC) simulation signal source. To further simulate the feature of TGC detector, a novel thought is proposed. The TGC source has 256 channels. Every channel can randomly output the signal in 25 ns. The design is based on true random number generator (TRNG). Considering the electrical connection between the TGC source and the developing trigger electronics, the GFZ connector is used. The experimental results show that the improved TGC simulation signal source can uniformly output the random signal in every channel. The output noise is less than 3 mV_rms.

We discuss the chiral phase transition of quantum chromodynamics (QCD) with a chiral chemical potential μ₅ as an additional scale. Within the framework of Dyson–Schwinger equations, we focus particularly on the behavior of the widely accepted as well as interesting critical end point (CEP), using a separable gluon propagator and a Gaussian gluon propagator. We find that there may be no CEP₅ in the T–μ₅ plane, and the phase transition in the T–μ₅ plane might be totally crossover. Our results have apparent consistency with the Lattice QCD calculation. On the other hand, our study may also provide some useful hints to some other studies related to μ₅.

Taking into account the effects of shadowing and jet quenching, the large transverse momentum distribution of K⁺, π⁺ and K⁺/π⁺ ratios at √s=200 GeV originating from resolved photoproduction processes is calculated based on perturbative quantum chromodynamics. It is found that the contribution of K⁺ and π⁺ produced by photoproduction processes is evident. The K⁺/π⁺ ratios in Au–Au collisions show an obvious enhancement compared with p–p collisions. The numerical results indicate that the photoproduction processes are good modification for kaon and pion production.

Accurate calculations are performed for the static dipole polarizabilities of HD⁺ in the rovibrational states with both of the vibrational and angular momentum quantum numbers ν and L from 0 to 5, by using variationally generated wavefunctions in Hylleraas coordinates. Comparison is made with recently published results. Significant improvements are achieved for the angular momentum quantum number L>0 excited states by including another independent block to optimize meticulously the intermediate states of unnatural parity.

The product rotational polarizations of reaction Li+HF→LiF+H at different collision energies, as well as at the different vibrational states and rotational states, are calculated by using the quasi-classical trajectory method based on a new potential energy surface constructed by Aguado et al. [J. Chem. Phys. 119 (2003) 10088]. We investigate the alignment and the orientation of the product molecule by calculating the P(θ_r,φ_r) distributions describing polar angle distribution, the P(θ_r) distributions describing the k–j' correlation and the P(φ_r) distributions describing the k–k'–j' correlation. We also explore the dependence of reaction probabilities and cross sections on the rotational and vibrational quantum number of the title reaction. It is concluded that the vibrational state has more important impact on the angular distribution, reaction probability and cross section.

The experimental scheme of 633 nm and 1359 nm good-bad cavity dual-wavelength active optical frequency standard is proposed, where He-Ne 633 nm and Cs 1359 nm stimulated emissions are working at good-cavity and bad-cavity regimes, respectively. The cavity length is stabilized by locking the 633 nm output frequency to a super-cavity with the Pound–Drever–Hall (PDH) technique. The frequency stability of 1359 nm bad-cavity stimulated emission output is then expected to be further improved by at least 1 order of magnitude than the 633 nm PDH system due to the suppressed cavity pulling effect of active optical clock, and the quantum limited linewidth of 1359 nm output is estimated to be 72.5 mHz.

Second-order Born calculations are performed to investigate the triple differential cross sections of coplanar asymmetric laser-assisted (e, 2e) collisions for hydrogen and helium targets. The incident electron is considered to be dressed by the laser field in a nonperturbative manner by choosing the Volkov solutions in both the initial and final channels. Detailed calculations of the scattering amplitudes are performed using the Sturmian basis expansion. The state of the ejected electron is described by a Coulomb–Volkov wave function. Two geometries are investigated in which the laser polarization vector is either parallel to the incident momentum of the projectile or parallel to the momentum transfer. Our numerical results show that, in the low energy range, these two laser polarization orientations give the same shape and the same order of magnitude of laser-assisted ionization cross sections of helium and hydrogen targets.

The injection of charge carriers from the electron/hole injection or transport layers in polymer light-emitting diodes potentially increases the device efficiency not by changing of charge intensity but by lattice distortion variation and quasi-particle interactions. From the low-dimensional condensed matter physics perspective, a valid mechanism is proposed to bring a type of novel channels that, under a proper external electric field, transition-forbidden triplet excitons are transformed and partially charged by charge carriers (polarons/bipolarons), thus are able to emit light and to enhance fluorescence greatly.

The ⁷Li⁺ ion is one of the most important candidates for verifying QED theory and obtaining the precise value of the fine-structure constant α. However, direct laser cooling of trapped Li⁺ ions will lead to strong background fluorescence which will influence the spectrum detection. The sympathetic cooling technique is a good choice to solve the problem. In this work, we report sympathetic cooling of ⁷Li⁺ ions to few mK using ⁴⁰Ca⁺ ions in a linear Paul trap. A mixed ion crystal of ⁴⁰Ca⁺ ions and ⁷Li⁺ ions are obtained. We also analyze the motion frequency spectra of pure ⁴⁰Ca⁺ ions and mixed ions.

We report the generation of passively tunable high peak signal-to-noise ratio harmonic mode-locked (HML) all-normal-dispersion Yb-doped fiber laser with a single birefringent filter in a ring cavity configuration. The highest fourth harmonic of the fundamental mode-locked frequency at a repetition rate of 88 MHz is obtained. The pulses are compressed to 627 fs by using an external grating-pair compressor. For the fourth HML output, the peak signal-to-noise ratio of the rf is 73 dB and the average power is as high as 110 mW with the pump power of 500 mW. Soliton bunches which contain multipulses are also observed in the weak mode-locked regime of the HML, and the separation between interpulses in a dissipative soliton bunch can be controlled by adjustment of the waveplates and spectral filter in the cavity.

The quaternion approach to solve the coupled nonlinear Schr?dinger equations (CNSEs) in fibers is proposed, converting the CNSEs to a single variable equation by using a conception of eigen-quaternion of coupled quaternion. The crosstalk of quarter-phase-shift-key signals caused by fiber nonlinearity in polarization multiplexing systems with 100 Gbps bit-rate is investigated and simulated. The results demonstrate that the crosstalk is like a rotated ghosting of input constellation. For the 50 km conventional fiber link, when the total power is less than 4 mW, the crosstalk effect can be neglected; when the power is larger than 20 mW, the crosstalk is very obvious. In addition, the crosstalk can not be detected according to the output eye diagram and state of polarization in Poincaré sphere in the trunk fiber, making it difficult for the monitoring of optical trunk link.

We report the simulation and experimental results of 1.3-μm InGaAsP/InP multiple quantum well (MQW) electro-absorption modulators (EAMs). In this work, the quantum confined Stark effect of the EAM is systematically analyzed through the finite element method. An optimized structure of the 1.3-μm InGaAsP/InP QW EAM is proposed for applications in 100 G ethernet. Then 1.3-μm InGaAsP/InP EAMs with f_{?3 dB} bandwidth of over 20 GHz and extinction ratio over 20 dB at 3 V bias voltage are demonstrated.

We demonstrate a mid-IR ZnGeP₂ (ZGP) optical parametric oscillator (OPO) pumped by a dual-end-pumped actively acousto-optic Q-switched Ho:YAG ceramic laser. The maximum average output power of 35 W is obtained at a pulse repetition frequency of 20 kHz from the Ho:YAG ceramic laser. Under the maximum incident pump power of Ho:YAG ceramic laser, the maximum output power of 14 W is obtained from the ZGP OPO, corresponding to the slope efficiency of 49.6% with respect to the incident pump power. The wavelength can be tuned from 3.5 μm to 4.2 μm (signal), corresponding to 5.2–4.1 μm (idler). The beam quality M² is less than 2.3 from the ZGP OPO.

Output performance of a continuous-wave Tm:YAP laser pumped passively Q-switched Ho:YLF laser is demonstrated with a polycrystalline Cr²⁺:ZnS as the saturable absorber. We compare the experimental results at the three different distances L of the polycrystalline Cr²⁺:ZnS saturable absorber to the output coupler. The pulse width almost remains constant for different L, when the incident pump power is changed in the range of 7.9–27.1 W. The shortest pulse duration of 33.3 ns for L=105 mm and the highest average output power of 6.8 W for L=5 mm are obtained at the incident pump power of 27.1 W. The output wavelength of the passively Q-switched laser shifts to 2045.2 nm from 2064.7 nm in the cw operation. The beam quality factor of M² is 1.2.

We present a theoretical investigation of the scattering of high frequency S0 Lamb mode from a circular blind hole defect in a plate based on the 3D theory. The S0 wave is incident at the frequency above the A1 mode cut-off frequency, in which the popular approximate plate theories are inapplicable. Due to the non-symmetric blind hole defect, the scattered fields will contain higher order converted modes in addition to the fundamental S0 and A0 modes. The far-field scattering amplitudes of various propagating Lamb modes for different hole sizes are inspected. The results are compared with those of lower frequencies and some different phenomena are found. Two-dimensional Fourier transform (2DFT) results of transient scattered Lamb and SH wave signals agree well with the analytical dispersion curves, which check the validity of the solutions from another point of view.

The coupled motion of two flexible bodies with different lengths immersed in moving fluid is studied numerically. The flapping frequency, flapping amplitude and average drag coefficient of each body are calculated and the influences of the arranging manner and separation distance are analyzed. In our simulation, when placed in the flow individually, the flexible body with a longer length will flap in period and the shorter one will maintain still straightly in the flow direction. The numerical results show that, two different flexible structures near placed in moving flow would strongly interact. When they are placed side by side, the existence of the stable shorter flexible body will restrain the flapping of the longer one while the existence of the longer flexible body may also induce the shorter one to flap synchronously. When placed in tandem with the shorter flexible body in upstream, the flapping of the longer one in downstream will be obviously enhanced. In the situation for the longer flexible body placed in upstream of the shorter one, the coupled flapping amplitude and average drag coefficients increase and decrease periodically with increasing the arranging space, and peak values appear as a result of the mediate of the tail wakes.

A new method for generating metal plasma via radio frequency (rf) glow discharge during electron beam evaporation is proposed. A probe array and an emission spectrometric analysis are employed to identify the metal plasma during rf glow discharge. Spectral results reveal that the Ti metal vapor is ionized and forms a metal plasma via rf glow discharge. The dependence of the emission intensities of Ti⁺ and Ti atoms on rf glow discharge parameters is investigated. The results show that, as rf power increases, the emission intensities of Ti⁺ are enhanced while the emission intensities of Ti atoms are suppressed due to a constant Ti atom flux and an increasing Ti⁺ flux. Furthermore, the emission intensities of Ti⁺ and Ti atoms increase with the electron-beam current. The influence of rf glow discharge parameters on the ion-beam current density is also studied. The results show that the ion-beam current density rises with increasing the rf power and the electron-beam current. The ion-beam current density at 4-cm radial distance doubles from 8×10⁹/cm³ up to 1.7×10¹⁰/cm³ with increasing the rf power from 90 to 240 W and it increases almost five-fold in the electron-beam current range of 170–230 mA at 10-cm radial distance. Additionally, the increasing ratio of the ion-beam current density at the large radial distance is greater than that in the central region resulting from the driving force which is brought about by a pressure difference and the discharging action.

The density profile of fast ions arising from a tangentially injected diffuse neutral beam in tokamak plasma is calculated. The effects of mean free paths and beam tangency radius on the density profile are discussed under typical HL-2A plasmas parameters. The results show that the profile of fast ions is strongly peaked at the center of the plasma when the mean free path at the maximum deuteron density is larger than the minor radius, while the peak value decreases when the mean free path at the maximum deuteron density is larger than twice that of the minor radius due to the beam transmission loss. Moreover, the bootstrap current of fast ions for various mean free paths at the maximum deuteron density is calculated and its density is proved to be closely related to the deposition of the neutral beam. With the electron return current considered, the net current density obviously decreases. Meanwhile, the peak central fast ion density increases when the beam tangency radius approaches the major radius, and the net bootstrap current increases rapidly with the increasing beam tangency radius.

A theoretical investigation on the propagation of positron-acoustic shock waves (PASWs) in an unmagnetized, collisionless, dense plasma (containing non-relativistic inertial cold positrons, non-relativistic or ultra-relativistic degenerate electron and hot positron fluids and nondegenerate positively charged immobile ions) is carried out by employing the reductive perturbation method. The Burgers equation and its stationary shock wave solution are derived and numerically analyzed. It is observed that the relativistic effect (i.e., the presence of non/ultra-relativistic electrons and positrons) and the plasma particle number densities play vital roles in the propagation of PASWs. The implications of our results in space and interstellar compact objects including non-rotating white dwarfs, neutron stars, etc. are briefly discussed.

We report a molecular dynamics study of structural and transport properties of liquid nickel under high pressures. Pressure dependencies of pair distribution function and pair correlation entropy along the melting line indicate that the configuration change along melting lines decreases with increasing pressure. The calculated diffusion coefficients and viscosity by using entropy-scaling laws with modified parameters and ideal parameters are compared with those extracted from mean-square displacement or the Stokes–Einstein relation. The results suggest that the entropy-scaling laws hold well for liquid nickel under high-pressure conditions, and the diffusion coefficients and viscosity increase moderately with pressure along melting lines.

Thermal conductances between Cu and graphene covered carbon nanotubes (gCNTs) are calculated by molecular dynamics simulations. The results show that the thermal conductance is about ten times larger than that of Cu-CNT interface. The enhanced thermal conductance is due to the larger contact area introduced by the graphene layer and the stronger thermal transfer ability of the Cu-gCNT interface. From the linear increasing thermal conductance with the increasing total contact area, an effective contact area of such an interface can be defined.

ZnO films on R-sapphire substrates are prepared and characterized by x-ray diffraction and scanning electron microscopy, which indicate that the thin films are well crystallized with (1120) texture. Love wave and Rayleigh wave are used for fabrications of humidity sensors, which are excited in [1100] and [0001] directions of the (1120) ZnO piezoelectric films, respectively. The experimental results show that both kinds of sensors have good humidity response and repeatability, and the performances of the Love wave sensors are better than those of the Rayleigh wave sensors at room temperature. Moreover, the theoretical calculations of the mass sensitivity of the sensors are also carried out and the calculated results are in good agreement with the experimental measurements.

Single crystals of RSeTe₂ (R = La, Ce, Pr, Nd) are synthesized using LiCl/RbCl flux. Transport and magnetic properties in the directions parallel and perpendicular to the a–c plane are investigated. We find that the resistivity anisotropy ρ_⊥/ρ_|| lies in the range 486–615 for different compounds at 2 K, indicating the highly two-dimensional character. In both the orientations, the charge-density-wave transitions start near T_CDW=284(3) K, 316(3) K, 359(3) K for NdSeTe₂, PrSeTe₂, CeSeTe₂, respectively, with a considerable increase in dc resistivity. While for LaSeTe₂, no obvious resistivity anomaly is observed up to 380 K. The value of T_CDW increases monotonically with the increasing lattice parameters. Below T_CDW, slight anomalies can be observed in NdSeTe₂, PrSeTe₂ and CeSeTe₂ with onset temperature at 193(3) K, 161(3) K, 108(3) K, respectively, decreasing as lattice parameters increase. Magnetic susceptibility measurements show that the valence state of rare earth ions are trivalence in these compounds. Antiferromagnetic-type magnetic order is formed in CeSeTe₂ at 2.1 K, while no magnetic transition is observed in PrSeTe₂ and NdSeTe₂ down to 1.8 K.

Ti/Al based Ohmic contacts to as-grown N-polar GaN are investigated by cross-section transmission electron microscopy and energy dispersive x-ray spectroscopy. Due to the higher oxygen background doping in the N-polar GaN, the Al metal in Ohmic stacks is found to react with background oxygen more easily, resulting in more AlO_x. In addition, the formation of AlO_x is affected by the Al layer thickness greatly. The AlO_x combined with the presence of AlN is detrimental to the Ohmic contacts for N-polar GaN compared with Ga-polar GaN. With the reduction of the Al layer thickness to some extent, less AlO_x and AlN are formed, and lower Ohmic contact resistance is obtained. The lowest contact resistivity ρ of 1.97×10^?6 Ω?cm² is achieved with the Al layer thickness of 80 nm.

Structural, electronic and mechanical properties of the nH-SiC (n=2, 4, 6, 8 and 10) polytypes are calculated by using the first-principles calculations based on the density-functional theory approach. The optimized lattice parameters of nH-SiC are in good agreement with the experimental data. The mechanical properties, including elastic constants, bulk modulus, Young's modulus, shear modulus and Poisson's ratio, are calculated. The analysis of elastic properties indicates that the effects of n on the mechanical properties of the five nH-SiC structures have no difference. The indirect band gap relationship for the five polytypes is E_bg2H>E_bg4H>E_bg6H>E_bg10H>E_bg8H.

We investigate the thermal characteristics of standard organic light-emitting diodes (OLEDs) using a simple and clear 1D thermal model based on the basic heat transfer theory. The thermal model can accurately estimate the device temperature, which is linearly with electrical input power. The simulation results show that there is almost no temperature gradient within the OLED device working under steady state conditions. Furthermore, thermal analysis simulation results show that the surface properties (convective heat transfer coefficient and surface emissivity) of the substrate or cathode can significantly affect the temperature distribution of the OLED.

High-quality superconducting FeSe_0.5Te_0.5 films are epitaxially grown on different substrates by using the pulsed laser deposition method. By measuring the transport properties and surface morphology of films grown on single-crystal substrates of Al₂O₃ (0001), SrTiO₃ (001), and MgO (001), as well as monitoring the real-time growth process on MgO substrates with reflection high energy electron diffraction, we find the appropriate parameters for epitaxial growth of high-quality FeSe_0.5Te_0.5 thin films suitable for angle-resolved photoemission spectroscopy measurements. We further report the angle-resolved photoemission spectroscopy characterization of the superconducting films. The clearly resolved Fermi surfaces and the band structure suggest a sample quality that is as good as that of high-quality single-crystals, demonstrating that the pulsed laser deposition method can serve as a promising technique for in situ preparation and manipulation of iron-based superconducting thin films, which may bring new prosperity to angle-resolved photoemission spectroscopy research on iron-based superconductors.

The γ'-Fe₄N films on Cu underlayers are deposited on the glass and Si substrates by dc magnetron reactive sputtering. The effects of Cu underlayer on the structure, morphology and magnetic properties of the γ'-Fe₄N films are studied. The single-phase γ'-Fe₄N films with Cu underlayers on the glass substrate are obtained, while the mixture of Fe and γ'-Fe₄N is observed on the Si substrate. In comparison with the films without Cu underlayers, the grains of the films with Cu underlayers exhibit a non-uniform size distribution and give rise to a rougher surface. The magnetic measurements indicate that the γ'-Fe₄N films show a good soft ferromagnetic behavior. The enhanced coercivity in the films with Cu underlayers is observed due to the deterioration of the crystallographic structure as well as the rougher surface.

We investigate the dynamic behavior of the magnetic domain wall under perpendicular magnetic field pulses in flat ferromagnetic nanowires using micromagnetic simulations. It is found that the perpendicular magnetic field pulse can trigger the magnetic domain wall motion, where all the field torques are kept on the plane of nanowire strip. The speed of magnetic domain walls faster than several hundreds of meters per second is predicted without the Walker breakdown for the perpendicular magnetic driving field stronger than 200 mT. Interestingly, the dynamic behavior of the moving magnetic domain wall driven by perpendicular magnetic field pulses is explained by charging- and discharging-like behaviors of an electrical RC-circuit model, where the charging and the discharging of magnetic charges on the nanowire planes are considered. The concept of the RC-model-like dynamic characteristic of the magnetic domain wall might be promising for the applications in spintronic functional devices based on the magnetic domain wall motion.

Ferroelectric and magnetic properties of Fe_1?xMn_xV₂O₄ (0≤x≤0.5) spinels are investigated on the basis of dielectric, polarization, and susceptibility measurements. Ferroelectric polarization is discovered in collinear ferrimagnetic and Yafet–Kittel magnetic phases for 0.1≤x≤0.4, which can be tuned by a magnetic field. As orbital-active Fe²⁺ is substituted with Mn²⁺, ferroelectric polarization decreases for 0≤x≤0.4 and disappears for x=0.5. We propose that the two polar components in ferroelectric polarization originate from the exchange striction mechanism and the spin-current model, respectively.

Physical properties of strongly correlated manganites are known to depend sensitively on lattice parameters. We show that in thin film form, the magnetic and transport properties of manganites can be tuned in a wide range using epitaxial strain. Specifically, by systematically varying the strain from negative to positive, we have observed 65%, ?33%, 650%, and ?17% changes for the saturation magnetization field H_s, saturation magnetization M_s, resistivity, and metal-insulator transition temperature. We explain these results with density functional theory calculations.

The growth of GaAs epilayers on silicon substrates with a thin amorphous silicon (a-Si) buffer layer by metalorganic chemical vapor deposition is investigated in detail. Combining with the two-step growth method, the growth conditions of the a-Si buffer layer are optimized for growth of high-quality GaAs/Si epilayers. The a-Si buffer layer exhibits the best effect with thickness of 1.8 nm and growth temperature of 620°C. It is found that the introduction of this a-Si layer on Si substrates effectively reduces the dislocation density in GaAs/Si films. As compared with the dislocation density of 5×10⁷ cm^?2 in the GaAs/Si sample without the a-Si layer, a density of 3×10⁵ cm^?2 is achieved in the sample with the a-Si layer, and the defect reduction mechanism is discussed in detail.

A novel method for preparing Ta-doped TiO₂ via using Ta₂O₅ as the doping source is proposed. The preparation process combines the hydrothermal fluorination of Ta₂O₅ and the subsequent formation of Ta-doped TiO₂ sol. The results show that the doped sample annealed at 393 K generates an unstable intermediate NH₄TiOF₃, which converts into anatase TiO₂ with the increase of temperature. After annealing at ≥673 K, the Ta-doped TiO₂ nanocrystals with the grain size <20 nm are obtained. Both the XRD and TG-DSC results confirm that Ta doping prevents the anatase-rutile crystal transition of TiO₂. The band gap values of the doped samples, as obtained by UV-vis diffuse reflectance spectra, are smaller than that of pure anatase TiO₂. The first-principle pseudopotential method calculations indicate that Ta⁵⁺ lies in the TiO₂ lattice at the interstitial position.

Hydride vapor phase epitaxy (HVPE) is utilized to grow nonpolar a-plane GaN layers on r-plane sapphire templates prepared by metal organic vapor phase epitaxy (MOVPE). The surface morphology and microstructures of the samples are characterized by atomic force microscopy. The full width at half maximum (FWHM) of the HVPE sample shows a W-shape and that of the MOVPE sample shows an M-shape plane with the degree of φ in the high-resolution x-ray diffraction (HRXRD) results. The surface morphology attributes to this significant anisotropic. HRXRD reveals that there is a significant reduction in the FWHM, both on-axis and off-axis for HVPE GaN are compared with the MOVPE template. The decrease of the FWHM of E₂ (high) Raman scattering spectra further indicates the improvement of crystal quality after HVPE. By comparing the results of secondary-ion-mass spectroscope and photoluminescence spectrum of the samples grown by HVPE and MOVPE, we propose that C-involved defects are originally responsible for the yellow luminescence.

Radio-frequency inductively coupled plasma jet is utilized to grow diamond films to combine the advantages of clean deposition environment and large deposition area. Before diamond growth, the simulation of deposition environment is studied to understand the flow field and the properties of the plasma. The optical emission spectra (OES) are also applied to diagnose the rf plasma. The plasma density n_e and the electron temperature T_e deduced from the data measured by OES are about 1.0×10¹⁴ l/cm³ and 1.4 eV, which are in good agreement with the data calculated in the simulation. Based on the data from both simulation and measurement, the optimized growth parameters are determined to grow diamond films. Nano-crystalline diamond with cauliflower-like morphology is obtained. The crystalline feature and impurity of as-grown films are also studied.

Effects of abrasive concentration on material removal rate (MRR) and surface quality in the chemical mechanical polishing (CMP) of light-emitting diode sapphire substrates are investigated. Experimental results show that the MRR increases linearly with the abrasive concentration, while the rms roughness decreases with the increasing abrasive concentration. In addition, the in situ coefficient of friction (COF) is also conducted during the sapphire polishing process. The results present that COF increases sharply with the abrasive concentration up to 20 wt% and then shows a slight decrease from 20 wt% to 40 wt%. Temperature is a product of the friction force that is proportional to COF, which is an indicator for the mechanism of the sapphire CMP.

We report on fabrication and photovoltaic characteristics of In_xGa_1?xN/GaN multiple quantum well solar cells with different indium compositions and barrier thicknesses. The as-grown samples are characterized by high-resolution x-ray diffraction and reciprocal space mapping. The results show that the sample with a thick barrier thickness (10.0 nm) and high indium composition (0.23) has better crystalline quality. In addition, the dark current density-voltage (J–V) measurement of this device shows a significant decrease of leakage current, which leads to high open-circuit voltage V_oc. Through the J–V characteristics under an Air Mass 1.5 Global (AM 1.5 G) illumination, this device exhibits a V_oc of 1.89 V, a short-circuit current density J_sc of 3.92 mA/cm² and a fill factor of 50.96%. As a result, the conversion efficiency (η) is enhanced to be 3.77% in comparison with other devices.

Impact of band-engineering to the performance of charge trapping memory with HfO₂/Ta₂O₅/HfO₂ (HTH) as the charge trapping layer is investigated. Compared with devices with the same total HfO₂ thickness, structures with Ta₂O₅ closer to substrates show larger program/erase window, because the 2nd HfO₂ (next to blocking oxide) serving as part of blocking oxide reduces the current tunneling out of/in the charge trapping layer during program and erase. Moreover, trapped charge centroid is modulated and contributed more to the flat-band voltage shift. Further experiments prove that devices with a thicker 2nd HfO₂ layer exhibit larger saturate flat-band shift in both program and erase operation. The optimized device achieves a 7 V memory window and good reliability characteristics.

The dependencies of hot-carrier-induced degradations on the effective channel length L_{ch, eff} are investigated for n-type metal-oxide-semiconductor field effect transistor (MOSFETs). Our experiments find that, with decreasing L_{ch, eff}, the saturation drain current (I_dsat) degradation is unexpectedly alleviated. The further study demonstrates that the anomalous L_{ch, eff} dependence of I_dsat degradation is induced by the increasing influence of the substrate current degradation on the I_dsat degradation with L_{ch, eff} reducing.

In many critical civil and emerging military applications, low-level UV detection, sometimes at single photon level, is highly desired. In this work, a mesa-type 4H-SiC UV avalanche photodiode (APD) is designed and fabricated, which exhibits low leakage current and high avalanche gain. When studied by using a passive quenching circuit, the APD exhibits self-quenching characteristics due to its high differential resistance in the avalanche region. The single photon detection efficiency and dark count rate of the APD are evaluated as functions of discrimination voltage and over-drive voltage. The optimized operation conditions of the single photon counting APD are discussed.

We report fabrication and characterization of organic heterojunction UV detectors based on N,N'?bis(naphthalen?1-yl)-N,N'-bis (phenyl) benzidine (NPB) and fullerene C₆₀. The effects of different thicknesses of NPB and C₆₀ layers are studied and compared. Notably, the optimal thicknesses of electron acceptor C₆₀ and electron donor NPB are 40 nm and 80 nm, respectively. The J–V characteristic curves of the device demonstrate a three-order-of-magnitude difference when illuminated under a 350 nm UV light and in the dark at -0.5 V. The device exhibits high sensitivity in the region of 320–380 nm with the peak located around 350 nm. Especially, it shows excellent photo-response characteristic with a responsivity as high as 315 mA/W under the illumination of 192 μW?cm^?2 350 nm UV light at -5 V. These results indicate that the NPB/C₆₀ heterojunction structure device might be used as low-cost low-voltage UV photodetectors.

We present a study on the single event transient (SET) induced by a pulsed laser in different silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) with the structure of local oxidation of silicon (LOCOS) and deep trench isolation (DTI). The experimental results are discussed in detail and it is demonstrated that a SiGe HBT with the structure of LOCOS is more sensitive than the DTI SiGe HBT in the SET. Because of the limitation of the DTI structure, the charge collection of diffusion in the DTI SiGe HBT is less than that of the LOCOS SiGe HBT. The SET sensitive area of the LOCOS SiGe HBT is located in the collector-substrate (C/S) junction, while the sensitive area of the DTI SiGe HBT is located near to the collector electrodes.

The I–V characteristics and low frequency noises for indium zinc oxide thin film transistor are measured between 250 K and 430 K. The experimental results show that drain currents are thermally activated following the Meyer–Neldel rule, which can be explained by the multiple-trapping process. Moreover, the field effect electron mobility firstly increases, and then decreases with the increase of temperature, while the threshold voltage decreases with increasing the temperature. The activation energy and the density of localized gap states are extracted. A noticeable increase in the density of localized states is observed at the higher temperatures.

We investigate the dynamics of entanglement in the excitation transfer through a model consisting of three interacting molecules coupled to environments. It is shown that the entanglement can be further enhanced if the distance between the molecules is oscillating. Our results demonstrate that the motional effect plays a constructive role on quantum entanglement in the dynamics of excitation transfer. This mechanism might provide a useful guideline for designing artificial systems to battle against decoherence.

The effect of the valence band tail width on the open circuit voltage of P3HT:PCBM bulk heterojunction solar cell is investigated by using the AMPS-1D computer program. An effective medium model with exponential valence and conduction band tail states is used to simulate the photovoltaic cell. The simulation result shows that the open circuit voltage depends linearly on the logarithm of the generation rate and the slope depends on the width of the valence band tail. The open circuit voltage decreases with the increasing width of the band tail. The dark and light ideality factors increase with the width of the valence band tail.

By means of the series method, we obtain the exact analytical solution of clustering coefficient in random Apollonian networks [Phys. Rev. E 71 (2005) 046141]. Our exact analytical result is identical with the simulation, whereas in the original work, there is a deviation of about 4% between their approximate analytical result and the simulation.