Vol. 59, No. 5 (2010)
2010, 59 (5): 3244-3248. doi: 10.7498/aps.59.3244
We demonstrate a femtosecond Ti: sapphire oscillator with ultralow repetition rate and ultrahigh peak power by inserting a specially designed Herriott telescope to increase the length of the cavity.By analyzing the intra-cavity dispersion and optimizing the extra-cavity compressor, stable pulses with repetition rate of 11 MHz and single pulse energy higher than 72nJ was obtained under 532 nm pump laser with average power of 8.2 W.The peak power of the pulses from the novel cavity is much higher than that from the original oscillators.
2010, 59 (5): 3357-3361. doi: 10.7498/aps.59.3357
Using high temperature scanning tunneling microscopy (STM) and XPS, we investigated the dynamic process of SrO/Si(100) changing to Sr/Si(100) reconstructed surface, which plays a critical role in the growth of crystalline oxide on silicon substrate. During this process we find some interesting phenomenan: there appears crystalline SrO on Si(100) substrate at low annealing temperature of 500 ℃; at higher annealing temperature of 550—590 ℃, the oxygen in the SrO/Si(100) interface will react with silicon and form volatile SiO, leading the surface with a large quantity of line vacancies. In the later case, there appears abnormal metallic property of this surface, which results from dangling bonds of silicon atoms in the surface.
Simulation of the structure and motion of grain boundary in pure substances by phase field crystal model
2010, 59 (5): 3595-3600. doi: 10.7498/aps.59.3595
The phase field crystal model was used to simulate the structure of the small angle and the large angle grain boundary (GB), the grain rotation and the GB migration during deformation. Simulated results show that the dislocation glide and climb are the main mechanisms for the small angle GB migration. While for the large angle GB, GB migration occurs by the atoms jumping over the grain boundary and the motion of dislocations and other defects.
2010, 59 (5): 2915-2918. doi: 10.7498/aps.59.2915
The problem of solving a class of disturbed Burgers equation is considered. Using the homotopic mapping method and theory ,the approximate solution with arbitrary degree of accuracy for the solitary wave is obtained.
Approximate analytic solution of solitary wave for a class of nonlinear disturbed Nizhnik-Novikov-Veselov system
2010, 59 (5): 2919-2923. doi: 10.7498/aps.59.2919
The approximate analytic solution for a class of nonlinear disturbed Nizhnik-Novikov-Veselov system is considered by a simple and valid technique. We first introduce the approximate solution of a corresponding typical differential system. And then the approximate analytic solution for the original nonlinear disturbed Nizhnik-Novikov-Veselov system is obtained using the homotopic mapping method.
2010, 59 (5): 2924-2931. doi: 10.7498/aps.59.2924
With the aid of symbolic computation system Maple, several new kinds of generalized exact solutions for the compound KdV system and extended KdV-Burgers system with nonlinear terms of any order are obtained by using a new generalize Riccati equation rational expansion method. This approach can also be applied to other nonlinear evolution equations with nonlinear terms of any order.
2010, 59 (5): 2932-2934. doi: 10.7498/aps.59.2932
Manifold stability of equilibrium state of autonomous generalized Birkhoff system is studied. The perturbation equation and equilibrium equation of autonomous generalized Birkhoff system is established. The corresponding criteria for manifold stability of autonomous generalized Birkhoff system is given by the Liapunov stability theory. Finally, an example is presented to illustrate these results.
2010, 59 (5): 2935-2938. doi: 10.7498/aps.59.2935
The unified symmetry and conserved quantities of Nielsen equation for a holonomic mechanical system are studied. On the base of the Nielsen equation, we first give the Noether symmetry, the Lie symmetry and the Mei symmetry for the equation and the conserved quantities deduced from them, then the definition and the criterion for unified symmetry of Nielsen equation are presented, lastly, the Mei conserved quantity, as well as the Noether conserved quantity and the Hojman conserved quantity deduced from the unified symmetry are obtained. An example is given to illustrate the application of the result.
2010, 59 (5): 2939-2941. doi: 10.7498/aps.59.2939
Type Ⅲ structural equation and Mei conserved quantity of Mei symmetry for a Lagrangian system are studied. Under the infinitesimal transformation of groups, type Ⅲ structural equation and Mei conserved quantity of Mei symmetry for a Lagrangian system are obtained from the definition and the criterion of Mei symmetry for a Lagrangian system. Finally, an example is given to illustrate the application of the results.
The homotopy analysis method for solving nonlinear wave propagation model in inhomogeneous cylindrical shells
2010, 59 (5): 2942-2947. doi: 10.7498/aps.59.2942
The investigation of nonlinear wave propagation in cylindrical shells is of theoretical and realistic significance. In this work, using homotopy analysis method, we study a new model of nonlinear wave propagation in inhomogeneous cylindrical shells, and obtain approximate solitary wave solution and periodic wave solution with high accuracy. It shows that homotopy analysis method is one of the most effective methods for research into the problems of nonlinear wave propagation.
2010, 59 (5): 2948-2951. doi: 10.7498/aps.59.2948
For the problem of harmonic generation caused by power high frequency pulse during transmission, based on the transmission line theory, cable distributed parameter model under the high frequency was established and negative effects caused by long cable transmission were analyzed. Be tied of the states of three-phase AC-DC-AC PWM inverter with motor, not only the article discussed the transmission and reflectance processions of impulse wave over the cable in detail, but also researched the production principle of motor over voltage. In addition, it analyzed the reasons of premature failure of the stator winding insulations and why the supply generated harmonic. The theory of this method has been verified by the experiment.
2010, 59 (5): 2952-2961. doi: 10.7498/aps.59.2952
The tunneling dynamics and periodic modulation effect of a two-component Bose-Einstein condensate in an one-dimensional optical lattice are investigated. By using the two-mode approximation, we study the influence of the interaction between two-component BECs on the tunnelling dynamics of the system numerically. The dynamic behavior of the system is investigated by adding a periodic modulation on the interaction between two-component atoms. We get the region for the onset of the tunneling, unstability and the self-trapping of the system with the changing modulation amplitude and frequency. We find that for the intermediate- and the low- frequency modulations, the dynamic behaviors of the system are dramatically different.
2010, 59 (5): 2962-2970. doi: 10.7498/aps.59.2962
In this paper, firstly according to the basic characteristics of chaos theory, we establish the nonlinear enlarge model about tent map, especially the initial-value sensitive dependence and one-to-one correspondence between chaotic orbit and the initial value. Secondly, we study the concrete characteristics with which the tent mapping system can realize nonlinear amplification. And the binary relationship between input and output is analyzed. Then we make numerical and circuit simulations of nonlinear amplification of the sine signal and the sine signal with noise. We compare the results of linear amplification and nonlinear amplification by tent mapping. At last, the advantages and disadvantages of the realized situations are discussed. The simulation results proved the superiority of the weak signal nonlinear amplification method.
2010, 59 (5): 2971-2975. doi: 10.7498/aps.59.2971
We derive the master equation of a double quantum dot charge qubit by taking into account the dissipative effects of the phonon-bath environment, and study the current noise spectrum of the double quantum dot charge qubit in terms of full counting statistics. It is found that the current is asymmetric about the current peak. The Fano factor displays an asymmetric double-peak structure, the asymmetry is due to the dissipations induced by the phonon bath. With increasing temperature T of the phonon bath, the current resonance broadens, the Fano factor peaks become smaller, and the super-Poissonian behavior vanishes.
2010, 59 (5): 2976-2981. doi: 10.7498/aps.59.2976
A linear optical experimental scheme for generation of spatial entangled qudits is proposed, which is based on the post-selection technique and is realized with some certain probability. In order to do it deterministically, the scheme based on the C-path gate which works with weak cross-Kerr nonlinearity is proposed. This new scheme is suitable for the generation of spatial entangled qudits with any photons and any dimensions. Since the generation is deterministic without post-selection technique, the entangled qudits can be used in the quantum information process without any limits. In addition, this scheme is feasible for current experimental technology.
Taking into consideration the radiation particle retroaction with the total energy, angular momentum and charge of spacetime conservation, using the Damour-Ruffini method, the Hawking radiation of particle from Kerr-Newman black hole are re-investigated. It is found that the Hawking radiation is not exactly pure thermal. Our conclusion not only contains the impact for the energy of the radiation particle, but also contains the impact for the angular momentum of particle to the angular momentum of black hole. The result is consistent with the works of Parikh and Wilczek, and satisfies the unitary theory of quantum mechanics.
Using brick wall method and thin film brick wall method to calculate the statistical-mechanical entropy of scalar field in Gibbons-Maeda spacetime
2010, 59 (5): 2987-2990. doi: 10.7498/aps.59.2987
The statistical-mechanical entropy of scalar field is calculated by using brick wall method and thin film brick-wall method in Gibbons-Maeda black hole spacetime. The entropy obtained from brick-wall method has two terms. One term is proportional to the event horizon area, and the proportional coefficient is 1/4 when the cutoff factor satisfies a suitable condition. The other term is logarithmic-divergent. The entropy obtained from thin film brick-wall method has only one term which is proportional to the event horizon area, and the logarithmic divergence vanishes.
2010, 59 (5): 2991-3000. doi: 10.7498/aps.59.2991
Another family of complex network—— the generalized Farey organized network pyramid (GFONP) is introduced. Three typical determinate constructional algorithms are shown, and corresponding topological characteristics are studied by theoretical and numerical analysis. The results show that the three determinate GFOPN networks have similar characteristics, i.e. their degree distributions follow exponential distribution in form, the clustering coefficient of the network decreases to a constant value with the step t increasing, the resulting network evolves from one with disassortative to one with assortative coefficient with increasing t, and the degree-degree correlation coefficient tends to a positive constant. This may lead to potential applications of the network of pyramidal structure.
Experimental research of weak signal detection based on the stochastic resonance of nonlinear system
2010, 59 (5): 3001-3006. doi: 10.7498/aps.59.3001
Noise can be used by the nonlinear stochastic resonance system to enhance the ability of weak signal detection, which creates a new method of weak signal detection under heavy background noise. A hardware circuit system, designed based on the basic principle of stochastic resonance, is used to detect single-frequency and multi-frequency weak signals. When the signal with noise that simulates actual engineering situation is introduced into the system, the spectrum of samples of the output signal shows that single-frequency and multi-frequency weak signals under heavy background noise can be detected by the technology based on stochastic resonance effectively. The application field of weak signal detection technology based on stochastic resonance is entended by the effective detection of mutil-frequency weak signal, and the degradation of signal recognition by low-frequency noise is eliminated by digital filtering effectively. The weak signal detection technology based on stochastic resonance has potential applications in the information recognition and information processing.
2010, 59 (5): 3007-3016. doi: 10.7498/aps.59.3007
A novel approach to Chua’s circuit based on current conveyers is proposed which overcomes the difficulties of the signal frequency being too low and the current waves and the corresponding phase diagrams not easy to test for this kind of circuit. Active simulated inductor and piece-wise nonlinear resistor in the circuit are all realized by current conveyers, so that the circuit is more stable and can work in higher frequency than does the usual Chua’s circuit. The circuit also has the advantages in that the current waves and the corresponding phase diagrams can be tested easily. The circuit has been designed, simulated, realized in hardware and tested. The experimental results are in good agreement with simulation results,which confirms the validity of the design. The circuit is suitable for secure communications.
Wireless chaotic speech communication via digital signal processor ——system design and hardware implementation
2010, 59 (5): 3017-3026. doi: 10.7498/aps.59.3017
In this paper, a novel approach for system design and hardware realization of wireless chaotic digital speech communication via digital signal processor (DSP) is proposed. According to Runge-Kutta algorithm and variable ratio expansion transformation, taking multi-scroll generalized Jerk as an example, the continuous chaotic system is converted to the discrete chaotic one so as to generate chaotic digital sequences, which are used for speech data encryption and decryption. Based on the DSP technical platform with TMS320VC5509APGE chip, by utilizing nRF2401 wireless transmitter and receiver, wireless chaotic digital speech communication is successfully implemented. The results of technical design and hardware realization are also given, which confirms the feasibility of the scheme.
2010, 59 (5): 3027-3034. doi: 10.7498/aps.59.3027
In this paper, we study a class of weighted complex networks with multi-links and nonlinear coupling. Based on a method of network split, network synchronization criteria are deduced by using Lyapunov stability theory. Numerical simulation verify the validity of the conclusions.
Adjustment and stability control for wide range input voltage Boost converter with small sinusoidal perturbation
2010, 59 (5): 3035-3042. doi: 10.7498/aps.59.3035
The Boost converter with wide range input voltage, operating at both stable section and unstable section, the chaos phenomenon makes the system work unsteadily. Based on continuous current conduction mode, the adjustment and stability control with small sinusoidal parameter perturbation for Boost converter are discussed. The transition process between stable state and unstable state for different perturbation amplitudes are analyzed in detail, the critical transition conditions between stable state and unstable state are deduced, and the stability conditions are also determined. It is shown by digital simulation that sinusoidal parameter perturbation can not only suppress the chaos phenomenon, but also cause the converter originally in steady state to turn into unsteady chaos state. The consistent and appropriate perturbation amplitude range can be selected for the wide range input voltage, so as to ensure the Boost converter to start, be adjusted and operate steadily and reliably.
2010, 59 (5): 3043-3048. doi: 10.7498/aps.59.3043
A new method based on least square support vector machines (LS-SVM) is proposed for chaos control of fractional order system. Based on the stability theory of fractional order linear system, the system is decomposed into stable linear parts and the corresponding nonlinear parts. The active controller is designed to compensate the nonlinear parts by using the excellent nonlinearity approximation ability and better generalization capacity of LS-SVM. Thus fractional order chaotic system is suppressed to the equilibrium point. Fractional order Liu system and fractional order Chen system are illustrated respectively. The simulation results verify the effectiveness and feasibility of the proposed method.
According to deterministic character and geometric property of chaotic system, the predictive method of neighborhood selection and the approach of neighborhood selection based on Delaunay triangulation were presented, and a new orthogonal local projective algorithm was derived by improvement of local projective method for noise reduction in chaotic time series, and rules of selection of optimal parameters were suggested. The method was successfully applied to extract weak signals in Lorenz chaos， that provided signal to noise ratio not lower than -80 dB. Computer simulation shows that this projective filtering method has great stability and reliability, and is effective for extracting weak signals in chaos.
2010, 59 (5): 3057-3065. doi: 10.7498/aps.59.3057
For a fourth-order autonomous nonlinear electric circuit, we present two evolution patterns to complexity associated with the three coexisting equilibrium points. In the first pattern, stable periodic movement with symmetric structure can be observed by Hopf bifurcation from the unstable equilibrium point, which may lead to chaos via cascading of period-doubling bifurcations. All the attractors, including the chaos, keep the symmetric property. While in the second evolution pattern, two limit cycles symmetric to each other may occur via Hopf bifurcations from the other two stable equilibrium points, which may also lead to two chaotic attractors, respectively. Comparing with the two evolution procedures associated with the two stable equilibrium points, not only the bifurcations keep the same pace, but also the attractors including the two final chaotic attractors are still symmetric to each other. With further variation of the parameters, the two chaotic attractors may interact with each other to form another enlarged chaotic attractor, which is qualitatively equivalent to the chaos in the first evolution pattern.
Polarization bistability characteristics of vertical-cavity surface-emitting lasers with negative optoelectronic feedback subject to time-varying current
2010, 59 (5): 3066-3069. doi: 10.7498/aps.59.3066
Polarization bistability characteristics of vertical-cavity surface-emiffing lasers with negative optoelectronic feedback subject to time-varying current
Suppressing spiral waves and spatiotemporal chaos in cardiac tissue by using calcium channel agonist
2010, 59 (5): 3070-3076. doi: 10.7498/aps.59.3070
Suppression of spiral waves and spatiotemporal chaos in cardiac tissue has been considered based on the LuoRudy 91 model. To suppress spiral waves and spatiotemporal chaos, the control strategy which employs calcium channel agonist to enhance the maximum conductivity of the slow inward calcium current is proposed. The numerical results show that the method can effectively suppress the spiral wave and spatiotemporal chaos in cardiac tissue even if the distribution of the time-dependent potassium current is non-uniform. The control mechanism has been analyzed.
2010, 59 (5): 3077-3087. doi: 10.7498/aps.59.3077
The article analyzes the chaotic dynamic characteristic of geomagnetic variation field mainly in two aspects: (1) analyzing the chaotic dynamic characteristic of the geomagnetic variation field data observed at the same period (both low geomagnetic disturbance period and high geomagnetic disturbance period) from a series of geomagnetic stations using multiple approaches, in order to get a sufficient proof to validate whether there is chaotic dynamic characteristic in geomagnetic variation field; (2) analyzing the chaotic dynamic characteristic of the geomagnetic variation field data observed at different periods from the same geomagnetic station, aiming at finding out whether there is a parameter-varying chaotic characteristic in the geomagnetic variation field. The results indicate: (1) There is definitely chaotic dynamic characteristic in the geomagnetic variation field time series. (2) In view of chaotic time series phase space reconstruction, the number of independent variables to simulate the geomagnetic variation field dynamical system is about 6. (3) Geomagnetic variation field time series shows not only chaotic dynamic characteristic but also parameter-varying dynamical chaotic characteristic.
2010, 59 (5): 3088-3092. doi: 10.7498/aps.59.3088
A theoretical model of transverse vibration of highline cable of alongside replenishment system was established, which considers the influence of the concentrated loading. The partial differential equation was asymptotically analysed by Galerkin method and muti-scale method. The bifurcation equation of system with higher order nonlinear terms was obtained by the solvability condition of eliminating the secular terms. Local bifurcation behavior of highline cable was studied with the software Mathematica. Bifurcation models and transition sets of system were obtained. The result shows that there are many kinds of bifurcation behaviors in highline cable of alongside replenishment system.
2010, 59 (5): 3093-3098. doi: 10.7498/aps.59.3093
Clustering of bus flow easily occurs due to the influence of bus stop. A new cell automaton model which considers the length and distribution of bus stations is proposed in this paper. Numerical simulation shows that the model can explicitly depict the space-time trajectories of bus movement along a bus line, reproduce the clustering phenomenon of bus flow, and quantitatively evaluate the impact of bus station distribution on bus average speed. The study provides insight on formation mechanism of clustering and may contribute to the optimization of locating bus stations.
On detection wavelength and electron-hole wave function overlap of type Ⅱ InAs/InxGa1－xSb superlattice infrared photodetector
2010, 59 (5): 3099-3106. doi: 10.7498/aps.59.3099
In this paper, the detection wavelength and the electron-hole wave function overlap of InAs/InxGa1-xSb type Ⅱ superlattice photodetectors are numerically calculated by using the envelope function and the transfer matrix methods. The band offset is dealt with by employing the model solid theory, which already takes into account the lattice mismatch between InAs and InxGa1-xSb layers. Firstly, the detection wavelength and the wave function overlap are investigated in dependence on the InAs and InxGa1-xSb layer thicknesses, the In mole fraction, and the periodic number. The results indicate that the detection wavelength increases with increasing In mole fraction, InAs and InxGa1-xSb layer thicknesses, respectively. When increasing the periodic number, the detection wavelength first increases distinctly for small periodic numbers then increases very slightly for large period numbers. Secondly, the wave function overlap diminishes with increasing InAs and InxGa1-xSb layer thicknesses, while it enhances with increasing In mole fraction. The dependence of the wave function overlap on the periodic number shows the same trend as that of the detection wavelength on the periodic number. Moreover, for a constant detection wavelength, the wave function overlap becomes greater when the thickness ratio of the InAs over InxGa1-xSb is larger.
2010, 59 (5): 3107-3115. doi: 10.7498/aps.59.3107
In the present study, we investigated the major factors and mechanisms of the pressure generation efficiency of the two-stage multianvils high pressure apparatus, which was recently designed and assembled in our laboratory. A simplified mechanical model of the pressure cell assembly was also proposed to interprete the experimental data. The results with the 10/4 (with octahedral edge-length of 10 mm, and WC cube truncation edge-length of 4 mm) cell assembly indicate that the pressure efficiency is very sensitive to the gaskets size and can be improved with the increased initial density of MgO pressure transmitting medium when cell pressure is about 12 GPa. Above 15 GPa, the pressure efficiency is mainly limited by the yield strength of the second stage WC cubes, as well as the composition and size of gaskets.
Effect of high magnetic fields on the migration of second phases during the solidification of metals
2010, 59 (5): 3116-3122. doi: 10.7498/aps.59.3116
Theoretical analysis shows that the migration behavior of a second phase during solidification processes in a high magnetic field (HMF) can be described by the migration velocity, which is a function of properties of melt matrix and the second phase, magnetic intensity and its gradient, as well as the geometry and size of the second phase. Lorentz force tends to make the second phase distribute homogenously, although its efficiency decreases with the increase of magnetic intensity beyond a certain value. When a gradient HMF is imposed, magnetization force becomes the dominant factor for the migration behavior of second phase. The effect of magnetization force increases with magnetic gradient, while it is difficult to control the migration of a second phase due to the constraint of Lorentz force when magnetic gradient is small. The theory has been experimentally verified by controlling the migration of in situ prepared particles in Al-Si and Al-Ni alloys under HMF conditions.
Research on the mode of obtaining interferograms based on the temporally and spatially mixed modulated polarization interference imaging spectrometer
2010, 59 (5): 3123-3129. doi: 10.7498/aps.59.3123
Based on the temporally and spatially mixed modulated polarization interference imaging spectrometer (TSMPIIS) developed by us, a novel mode for obtaining interferogram and spectrum is proposed. The interference data arrays acquired with this mode are analyzed, and the method for combining a series of interferograms at different moments is explained in detail. Furthermore, the interferograms of monochromatic light and polychromatic light obtained by TSMPIIS are processed. The satisfactory interferogram and reconstructed spectra show the superiority of this detection mode, such as wide field of view, high detection sensitivity and high throughput, etc.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2010, 59 (5): 3130-3135. doi: 10.7498/aps.59.3130
Based on the SU(2)L×SU(2)R×U(1) model with an U(1) family symmetry, we obtain the lepton flavor mixing matrix and research on the neutrino masses. In the model we consider, the Lagragian density which yields the Dirac masses for the leptons is U(1) family invariant, so both the mass matrix for the charge leptons and the Dirac mass matrix for the neutrinos are of the Fritzsch-type. But, generally speaking, neutrinos may have also Majorana masses. In that situation, the effective mass matrix for the light neutrinos is no longer of the Fritzsch type. We make some assumptions on the phases of the neutrino Majorana mass matrix to avoid diagonalizing the non-hermitian matrix. Then, we obtain the lepton flavor mixing matrix. The numerical calculation which is based on the lepton flavor mixing matrix shows that the model we consider may not fit the present result of the neutrino mixing experiment.
Nuclear shape phase transition SU(3)→U(5)→SU(3) of the yrast-band structure in 182Os from nucleonic order
2010, 59 (5): 3136-3141. doi: 10.7498/aps.59.3136
That quantum phase transition (QPT) that occurs at the same nucleus causing the change of the basic state by rotation can be understood as an evolution from a higher-ordered and high-excitation model to another lower-ordered and high-excitation one, which implies a nucleus populated at high-momentum state decoupling firstly to the yrast-band with some E2-trasitions mode, then to the coexist region (or critical point), wherein the structure-energy is released. The change of the nucleon coupling intensity is caused, finally the basic state of the lower-ordered excitation model is reconstructed, the evolution of basic states structure is accomplished. This description of nuclear QPTs has endowed them with some similar to Landau’s classical quantum thermal phase transition in terminology and physical significance. This standpoint is generalized into the phase transitions that occur at the same nucleus one after an other. As an example, for the 182Os nucleus, the problem is discussed carefully, and the enhanced sensitivity of nuclear binging energy to collective structure is demonstrated.
2010, 59 (5): 3142-3146. doi: 10.7498/aps.59.3142
By systematically analyzing the single particle level, the single particle occupation probability near the Fermi surface, paring energy effect and the rule of nuclear particle number fluctuation of even-even nuclei of oxygen isotopes within the relativistic mean-field model with BCS theory, we compare the neutron closed shell effect of 14O,22O and 24O nuclei, and finally predict theoretically that the proton-rich 14O nucleus has stronger neutron closed shell effect than 22O and 24O nuclei.
2010, 59 (5): 3147-3153. doi: 10.7498/aps.59.3147
Calibration of solid state nuclear track detector CR-39 was carried out with monoenergetic protons from 2×1.7 MV Tandem accelerator and 400 kV Cockcroft Walton accelerator in Beijing Normal University. To ensure the protons to have monoenergetic energy and reduce the track density to 106 cm-2, two different methods were adopted. On the tandem accelerator a slit plus rotating target plate were used to achieve the required low density irradiation while a high voltage pulse generator with pulse duration of 100 ns was used on the Cockcroft Walton accelerator. The calibration shows that the registration threshold energy of protons in CR-39 is about or a little lower than 20 keV. The response curve of track diameter vs. etching time and proton energy for protons with energy from 20 keV to 1020 keV can be used to determine the number , energy and angular distribution of the protons produced by nuclear reaction and laser plasma acceleration. Etching dynamics of high energy protons (320—1020 keV) was studied. The theoretical curve is consistent with experimental data. This method of controling the proton intensity employed in this paper could also be used in similar accelerator calibration.
ATOMIC AND MOLECULAR PHYSICS
2010, 59 (5): 3154-3161. doi: 10.7498/aps.59.3154
In this paper, spectra of odd-parity states of Sm atom are systematically studied with two-photon ionization detection method. The Sm atom is excited by a pulsed dye laser and scanned from 585 nm to 663 nm, so that it is populated in different odd-parity states with 4f66s6p and 4f55d6s2 electronic configurations from one of the 4f66s27FJ(J=0—6) states. Then the Sm atom is further excited and ionized by a two-photon transition with a second laser which has a much higher intensity and a fixed wavelength. The Sm ions emerging from the above processes were detected by an MCP detector. Some of the transitions are reported for the first time together with their resonance wavelengths and relative strengths, while the rest of them which have been reported previously in the litcrature are confirmed by the present work with supplementary information on their relative strengths.
2010, 59 (5): 3162-3167. doi: 10.7498/aps.59.3162
We theoretically investigate the high-order harmonic generation (HHG) power spectra from a one-dimensional argon model atom irradiated by an infrared two-color laser beam, which are composed of 9.7 fs/800 nm laser pulses and 9.7 fs/1600 nm laser pulses. It is found that, when the relative phase equals π, the harmonic cutoff is dramatically widened from 58 eV to 316 eV compared with the case with the single color laser beam. It is also demonstrated that an ultrabroad soft-X-ray harmonic supercontinuum with a bandwidth of 93 eV can be obtained by adopting the soft-core potential and the Pschl-Tell potential calculations. In terms of the time-frequency analysis and the semiclassical three-step model, we also demonstrate that the ultrabroad harmonic supercontinuum is mainly generated from the short path. By superposing a series of properly selected harmonics, an isolated attosecond pulse with duration of 46 as is obtained. Compared with other schemes of generating single as pulses by quantum path control in two-color laser pulse, the10 fs/800 nm pulse used in our scheme enables easier manipulations in practical experimental implementations.
2010, 59 (5): 3168-3172. doi: 10.7498/aps.59.3168
We have measured the UV-visible absorption and Raman spectra of β-carotene which contains 9 CC conjugated double bond polyenes biological molecules in 9 kinds of solvents.The results showed that the Raman scattering cross-section for C—C and CC stretching vibration bands of β-carotene increases linearly with the increase of solvent density.The mechanism is that β-carotene in high density solvent is less affected by perturbation,has higher structure order, more extended π electron delocalization，and stronger coherent weakly damping C—C bond vibration,which results in a large Raman scattering cross section.Studies on the influence of solvent density to molecular Raman cross section have not been reported.This paper is promising as on experimental hint on theoretical study of light scattering,and provides a reference for research of polyenes chain molecules and the development of optoelectronic devices.
CLASSICAL AREA OF PHENOMENOLOGY
2010, 59 (5): 3173-3178. doi: 10.7498/aps.59.3173
Metamaterial ground plane is introduced to planar inverted-F antenna (PIFA) design to explore the potential improvement in radiation.Through replacing the conventional capacitance by a metamaterial resonance circuit,the modified PIFA transmission line model physically interprets its novel properties.As is shown,such metamaterial PIFA exhibits a -10 dB return loss for more than 100% of bandwidth with resonance covering all wireless local area network applications and broadband wireless access form 2 GHz to 6 GHz.Nearly omnidirectional radiation pattern is achieved at 2.4/2.5 GHz,but mainly backward radiation is obtained at 3.8 GHz and 5.1—5.8GHz.
Investigation of electromagnetic scattering interaction between the buried target and the rough surface in different types of soil
2010, 59 (5): 3179-3186. doi: 10.7498/aps.59.3179
The problem of the composite electromagnetic scattering from 2-D buried target at the 1-D randomly rough surface with lossy media,which is different in different types of soil, is solved by the method of moments,while the tapered incident wave is chosen to reduce the truncation error.The relative dielectric constant of the soil could be calculated according to the frequency of the incident wave,the soil components,the soil moisture and soil temperature based on a cartain model.The Monte-Carlo procedure is employed to calculate the bistatic scattering cross section,which is dependent on the soil components,the soil moisture,the frequency of the incident wave,as well as the rms height of the randomly rough surface in details.The numerical results provide a guide in the application of ground penetrating radar in military,civil,as well as industrial fields.
2010, 59 (5): 3187-3191. doi: 10.7498/aps.59.3187
We present a metamaterial absorber (MA) composed of double layers of metal dendritic cells,dielectric substrate and metal film.With three different sizes of dendritic cells arranging in hexagonal array,it is able to find three discrete absorption peaks.Our experiments confirm that,if the frequencies of the three absorption peaks go closer,a combined broadband absorption peak could be achieved.Compared with the metamaterial absorber with only one singer layer of metal dendritic cells,the double-layered metal dendritic cells adopted in our MA greatly improve the absorption efficiency.The experimental result shows an absorption band of 1.93 GHz width with the absorptivity higher than 90% in the frequency range between 9.79 and 11.72 GHz.The proposed MA has a series of advantages such as high absorptivity,simple structure,small thickness,2D isotropy and wide absorption band.
2010, 59 (5): 3192-3198. doi: 10.7498/aps.59.3192
A recursive algorithm for electromagnetic fields propagating in micro-nano optical elements is proposed in this paper.This method is based on Maxwells equations and the continuity of tangential components of the electric and magnetic field vectors,and gives an exact complete solution.Taking the propagation of Gaussian beams in the sub-wavelength rectangle relief grating as an example; we analyze the propagation of beams with non-uniform amplitude in micro-nano optical elements in detail.
Realization of the broad angular spectrum of multilayer dielectric gratings based on the leaky mode resonance
2010, 59 (5): 3199-3204. doi: 10.7498/aps.59.3199
Based on the leaky mode resonance theory,the physical mechanism of producing the broad angular spectrum of Multilayer Dielectric Grating (MDG) in the -1 st order reflection diffraction direction is presented in this paper.It is found that the thin match layer would improve the bandwidth of angular spectrum effectively.A good result of ±11 degree near Littrow angle 37.9 over 90% diffraction efficiency centered at 1040nm is obtained,and the parameters of the result have excellent fabrication tolerance.The Fourier modal method is employed for calculating the diffraction efficiency.
Light intensity distribution in laser interference crystallization and the fabrication of two-dimensional periodic nanocrystalline silicon array
2010, 59 (5): 3205-3209. doi: 10.7498/aps.59.3205
Based on the general form of Fresnel diffraction,light intensity distribution in laser interference crystallization with a phase shifting grating mask (PSGM) was calculated.Two-dimensional (2D) periodic nanocrystalline silicon (nc-Si) array was fabricated by laser interference crystallization combined with 2D-PSGM.The light intensity irradiated on the surface of a-Si:H samples can be modulated by the PSGM with the periodicity of 400 nm.Experimental results demonstrate that the periodicity of 2D nc-Si array is the same as that of the PSGM,the crystalline regions of nc-Si array are consistant with the simulated results.
Combined despeckling algorithm of synthetic aperture radar images based on region classification, adaptive windowing and structure detection
2010, 59 (5): 3210-3220. doi: 10.7498/aps.59.3210
In order to overcome the shortcomings of the conventional local statistical speckle filters for synthetic aperture radar (SAR) images,a combined despeckling algorithm is proposed based on region classification,adaptive windowing,and structure detection.Firstly,the combined despeckling algorithm classifies the local region and directly preserves the strong edges and structures as well as the point targets.Then,the homogeneous region and the weak edge and structure region grow adaptively to obtain appropriate filtering windows.Lastly,the new filtering windows are classified.For the homogeneous region,the averaged filter is directly used.For the edge and structure region,the structure information is detected and the homogeneous sub-window is selected as the final filtering region.Despeckling experiments demonstrate that,the combined despeckling algorithm effectively suppresses the speckles in homogeneous region and edge region,and well preserves the strong edge and structure information as well as the point targets.
An exact solution of evolution of the field entropy in a system of three-level cascade type atom interacting with single-mode coherent field
2010, 59 (5): 3221-3226. doi: 10.7498/aps.59.3221
In this paper,the evolution of field entropy in the system of single-mode coherent light field interacting with a three-level cascade type atom is calculated exactly in the frame of complete quantum theory and without rotating wave approximation.The numerical results indicate that with the increases of the initial mean photon number n and the atom-field coupling strengths u and v the mean value of the field entropy increases at first and then decreases.Therefore,the degrees of entanglement also increase at first and then decrease.The mean value of the entropy of the field decreases with the enlarging of the detuning Δ, which leads to the decrease of the degrees of entanglement.
Preparation and control of optimal entropy squeezing states for the moving atom entangment with the field under the intensity dependent coupling
2010, 59 (5): 3227-3235. doi: 10.7498/aps.59.3227
From a quantum information point of view, preparation and control of the atomic optimal entropy squeezing state(AOEST) are researched for the system of a moving two-level atom entanglement with the field under the intensity-dependent coupling. Its results with those of atomic squeezing based on the Hesienbeg uncertainty relation is compared; sufficient and necessary conditions of preparation of the AOEST is analyzed and numerical verification of the AOEST is done. The influence of the field-mode structure parameter on the AOEST is examined. It is shown that information entropy squeezing is a remarkable precision measure for the atomic squeezing. The AOEST can be prepared by controlling the time of the atom interacting with the field, cutting the entanglement bewteen the atom and field, choosing coherence of the atom and modulating relative phase of the systems. A lasting AOEST can be obtained by controlling the field-mode structure parameter.
The dark lines in the spontaneous emission spectrum of a double V-type four-level atom in double-band photonic crystal
2010, 59 (5): 3236-3243. doi: 10.7498/aps.59.3236
The spontaneous emission spectrum of a double V-type four-level atom in a double-band photonic crystal is investigated.The double V-type atom is respectively coupled by the free vacuum modes and the photonic band gap modes.There are three types of dark lines in the spectrum: the first type originates from the quantum interference,the second type originates from the singularities of the density of states at the isotropic photonic band edges,and the third type originates from the quantum interference in the vacuum modes and zero density of states in the band-gap of photonic crystal.The causes leading to these three types of dark lines are investigated by varying the detuning of the atomic transitions from the band edge,by introducing smoothing parameter to eliminate the singularity of the density of states at the isotropic photonic band edges,and by introducing defect modes in the band gap of the photonic crystal.
The study of narrow-band terahertz-wave generation by difference frequency mixing in periodical-inverted GaAs crystal with ps pump pulses
2010, 59 (5): 3249-3254. doi: 10.7498/aps.59.3249
In this paper, the tuning of walk-off length and the optimal period of periodical-inverted GaAs crystal in narrow-band terahertz-wave generation by difference frequency mixing was numerical simulated and analyzed in the condition of different wavelengths and durations of pump pulse.The influence of the number of domains of periodically-inverted GaAs crystal on the THz-wave spectrum was also studied.The temperature tuning properties in periodical-inverted GaAs crystal were calculated and analyzed with the temperature dependent Sellmeier function of GaAs crystal; the influence of temperature tuning on the THz-wave spectrum was also studied.The simulation showed a new way to generate the wide-tunable narrow-band THz wave with temperature tuning.These theoretical calculations served for the subsequent experiment as theoretical basis and reference.
2010, 59 (5): 3255-3259. doi: 10.7498/aps.59.3255
Four kinds of microstructured polymer optical fibers based on Topas cyclic olefin copolymer(COC) are designed.The effective index of the fundamental mode,the mode area and the numerical aperture are calculated by using the finite element method.Effects of structure parameters upon the mode field distribution,single mode property and dispersion property are discussed.Structure parameters corresponding to very large or very small effective mode area,endless single mode operation and flattened-near-zero dispersion are obtained.These fibers have larger numerical apertures compared with silica or PMMA based ones,and display flattened-near-zero dispersion.
2010, 59 (5): 3260-3263. doi: 10.7498/aps.59.3260
Variable optical delays have wide application in scientific research and optical communications.In this paper two different schemes to realize a variable optical delay are proposed,one based on polarization and the other on interference.A phase modulator is employed to restrict the signal pulse within an optical loop,and to release it when required.The delay time can be varied by adjusting the length of the loop and the number of cycles the pulse travels around it.Both types of delays are suitable for fiber systems,and can be made into a small package by means of integrated optics technology.The polarization scheme is also convenient for optical delays in free space.
Investigation on characteristics of a new kind of polymer material with sine-phase waveguide grating
2010, 59 (5): 3264-3272. doi: 10.7498/aps.59.3264
Sine-phase waveguide grating is engraued on a new kind of polymer material through double-beams interference,which realizes grating coupled optical wave-guide.Conductive characteristical of optical wave-guide on different polarization incidence beam are investigated.Formation of grating is analyzed in theory as well,and propagation constant of optical wave-guide is calculated numerically in this article.The control of the wave-guide grating on guided-wave in modulation of light intensity and direction is discussed,the application of which in integrated optics is also noted.Finally,grating equation of arbitrary incident angle is analyzed.
2010, 59 (5): 3273-3277. doi: 10.7498/aps.59.3273
The finite element method is used to investigate the propagation and nonlinearity of octagonal photonic crystal fibers of total internal reflection type.We changed the structural parameters of the fibers and obtained the curves of relations about the propagation and nonlinearity. At last, we found another structure of photonic crystal fiber.It is demonstrated that it is possible to design a low-loss dispersion-flattened PCF at 1.55 micrometer wavelength.
2010, 59 (5): 3278-3285. doi: 10.7498/aps.59.3278
Photonic crystal fibers（PCFs）with rectangle core and elliptical core have been designed.Their fundamental characteristics are studied by electromagnetic scattering theory of multipole method.It is found that the fiber birefringence,dispersion and nonlinear characteristics can be flexibly adjusted by changing the radius of the air holes in the core.The PCFs have the following characteristics: With the increase of radius r1 of air holes in the core,the birefringence increases and the wavelength corresponding to the maximum birefringence shifts towards the longer wavelength region,the number of zero-dispersion-wavelengths increases from one to three and nonlinear coefficient of the short-wave band decreases while it increases in the longer wavelength region.The three zero-dispersion-wavelengths of elliptical core PCFs with r1 = 0.4 μm are located in visible,near-infrared and mid-infrared band,respectively.For similar structural parameters,elliptical core PCFs can achieve high birefringence and high nonlinearity more readily than rectangular core PCFs.
We analyze theory of the spatiotemporal coupling in the electric field of a femtosecond pulse. The complete spatiotemporal characterization of femtosecnd pulse is realized by use of spatially and spectrally resolved intensity and phase evaluation device. The apparatus combines the spatially and spectrally resolved interferometry. The unknown and reference pulses pass through a 2D diffraction grating, generating a tilted 2D array of holograms. A tilted bandpass filter separates the beam pairs so that each hologram contains a single, unique frequency. A single camera frame records all of the holograms, from which the complete spatiotemporal field of the unknown pulse can be reconstructed.
2010, 59 (5): 3290-3293. doi: 10.7498/aps.59.3290
Radiation impedance is an important parameter for evaluation of acoustic conversion efficiency of a sound and vibration system. The high power flexural vibration circular plate with stepped thickness has impartant applications in fluid, especially in air due to its large radiation area. The classical theory has difficulty in calculating the radiation impedance of the stepped circular plate due to the fact that the radiation surface is not coplanar, so the domain of integration is difficult to choose. From the point of view of radiation acoustic power, and based on superposition principle, a method is proposed to calculate the radiation impedance of a stepped circular plate in this work. As an example, calculation of the radiation impedance of a circular plate with one step is given.
The performance of matched-field localization with a horizontal line array at different depths in shallow water
2010, 59 (5): 3294-3301. doi: 10.7498/aps.59.3294
The performance of matched-field localization with a horizontal line array (HLA) at different depths in shallow water is investigated by normal mode modeling and computer simulation. It is observed that the matched-field localization performance of a bottom-mounted HLA is better than that of a HLA at other depths in shallow water. The normal mode modeling is used to explain this result. According to the normal mode theory, the mode shape is a function of water depth. The absolute values of the modes at different depths are compared. It is shown that the number of modes whose absolute values close to zero is smaller at the bottom than at other depths. It means that the HLA deployed at the bottom can sample more modes，obtain more information of the source and achieve better localization performance.
2010, 59 (5): 3302-3308. doi: 10.7498/aps.59.3302
Using a repeating deoxidization method, we prepared Au nanoparticles with different mean sizes of 11 nm, 35 nm and 58 nm. Then the Au nanoparticles were dispersed in mineral oil to form Au nanofluids by the surfactant-assisted phase transition technique. Under electric field, the optical properties of the Au nanofluids were measured. It was found that the Au nanofluids exhibit significant electric field-induced birefringence and the birefringence index can be adjusted by changing the external electric field strength. Furthermore, the birefringence index is influenced by the Au concentration and particle size. Within the suitable particle concentration range, the index decreases with the increase of Au concentration and particle size. Finally, we further discuss the electric field-induced birefringence phenomena of the Au nanofluids according to the structure transformation mechanism of electrorheological fluids under electric field.
2010, 59 (5): 3309-3314. doi: 10.7498/aps.59.3309
For the stratified fluids, based on the quasi-geostrophic potential vorticity equation, an inhomogeneous modified Korteweg-de Vried (mKdV) equation including topographic forcing is derived by employing the perturbation method and stretching transforms of time and space. With inspection of the evolution of the amplitude of Rossby waves, it is found that Coridis effect, topography effect and Vaisala-Brunt frequency are the important factors, that induce the solitary Rossby wave, and it is induced even though the basic stream function has not a shear. Assuming that there is a balance between nonlinear and topographic effects, an inhomogeneous mKdV equation is derived, the results show that the topography and Rossby waves interact in the stratified flows. The inhomogeneous mKdV equation describing the evolution of the amplitude of solitary Rossby waves as a function of the change of Rossby parameter β(y) with latitude y, topographic forcing and the Vaisala-Brunt frequency is obtained.
2010, 59 (5): 3315-3323. doi: 10.7498/aps.59.3315
The effects of salinity and other factors on flocculation settling are investigated in this paper. The many-body hydrodynamic interactions and XDLVO potential between sediment particles are taken into consideration. The effects of salinity, sediment concentration, Hamaker constant and hydration on settling speed are analyzed. The obtained fitting formula for flocculation settling speed accords with computational and experimental results and is of referential importance.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2010, 59 (5): 3324-3330. doi: 10.7498/aps.59.3324
Atmospheric pressure plasma jets based on dielectric barrier discharge have found many applications, yet its basic behavior and its formation mechanism are poorly understood. We carried out some basic experimental studies on this problem. Unlike the other similar studies based on ICCD, two MPTs with aligned slits, digital camera, and electrical measurements were mainly used to investigate the plasma jet’s behavior under different discharge conditions. Despite the materials employed in our experiment are quit simple, by comparing the measuremental results, a new charge-overflow phenomenon is obsewed, and the plasma jet mechanism (e.g. how the plasma jet is formed, how is it transported, what are the main parameters that determines the jet length, etc.) are discussed based on the experimental results.
Influence of the initial ablated-particle density on distribution of density and velocity of ablated-particles
2010, 59 (5): 3331-3335. doi: 10.7498/aps.59.3331
The influence of the density of initial ablated-particle on the spatial density distribution of the particles (Si and He) and the velocity distribution of the Si-particles was investigated via Monte Carlo simulation. With the increase of the initial ablated-particle density, both the maximum distance and the minimum distance after rebound of the mixed region from the target are decreased, and the width of the velocity distribution is increased. The splitting of the velocity was observed when the initial ablated-particle density was greater than 8.3×1025 m-3. These results give a good reference for further study of the Si nanoparticle nucleation.
2010, 59 (5): 3336-3343. doi: 10.7498/aps.59.3336
Simulation of the neutral beam emission spectroscopy (BES) is very important for the development of spectroscopic diagnostics based on neutral beam injection in the HL-2A tokamak. The effective beam emission coefficient and the effective stopping coefficient are calculated by utilizing the ADAS database (Atomic Data and Analysis Structure, 1998). Dependence of the beam emission intensity on plasma and neutral beam parameters are analyzed, and the intensity profiles of the beam emission spectra are obtained under different neutral beam energies, plasma densities and temperature profiles. About 50% of the neutral beam particles can penetrate through the plasma core when the plasma density and temperature are of 2×1013 cm-3 and 1 keV, respectively. The 2-D BES intensity profiles across the beam line are obtained and it peaks around r/a=0.6.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2010, 59 (5): 3344-3349. doi: 10.7498/aps.59.3344
The rare-earth doped phosphors Y2O3：Eu3+0.01and Y2O3：Eu3+0.01, Dy3+0.01 were synthesized by a high temperature solid-state reaction method. The phase structures of the phosphors were characterized by X-ray diffraction. The Eu3+and Dy3+doping does not change the crystal sructure of Y2O3, the Eu3+and Dy3+ ions enter into the host crystal lattice . The emission spectra due to 5D0→7FJof Eu3+show that Eu3+is the only luminescence center. There is no glow peak from Dy3+. The decay characteristics of phosphors Y2O3：Eu3+0.01, Dy3+0.01 follows the Double exponential distribution. The measurement of thermoluminescence reveals that the trap is generated by Eu3+. The Dy3+doping doesn’t change the trap depth, and helps the electrons escape from the trap, which induces long-afterglow luminescence.
2010, 59 (5): 3350-3356. doi: 10.7498/aps.59.3350
Series of Ga-doped Sc2-xGaxW3O12 samples (x=0, 0.05, 0.1, 0.2, 0.3, 0.5, 0.8) were synthesized by solid state reaction at 1100 ℃. Rietveld refinement of the X-ray powder diffraction patterns show that Ga substituted Sc in Sc2-xGaxW3O12 structure successfully. The client component Ga2W3O12 cannot be obtained in this work. The lattice parameters obtained by Rietveld refinement showed that all samples have negative thermal expansion between 25—1000 ℃. Lattice parameters a, c and cell volume of the Sc2-xGaxW3O12 decrease with the increases of Gallium content, but accompanied with the expansion of lattice parameter b. The average volume expansion coefficient also decreases with the increase of the Gallium content. As the temperature increases, the absolute value of the volume expansion coefficients decrease dramatically between room temperature and 300 ℃, but remain almost unchanged between 300 and 800 ℃, and decrease further at the temperature higher than 800 ℃, tending to zero and turning into positive expansion.
2010, 59 (5): 3362-3369. doi: 10.7498/aps.59.3362
In this paper the complex rheological behaviors of rod-like polymer solutions in plane Couette flow are studied using micro-macro simulation. The micro-macro model is described by Doi theory with local inhomogeneous fluid. The finite volume method is used to solve the conservation equation on the macroscopic level and the Smoluchowski equation on the microscopic level in the numerical simulation. The numerical results predict several plane flow modes including some typical plane modes and two new complicated modes. Furthermore, simulation results show that the rheological phase diagrams for solutions of rigid rod molecules are mainly dependent on the Deborah number, the concentration of solutions and molecular scale, and the varying Deborah number have great influence on some micro-properties of tumbling period and orientation angle of flow-aligning.
Comparative study of the first-principles and empirical potential simulation of vacancies in silicon
2010, 59 (5): 3370-3376. doi: 10.7498/aps.59.3370
Structural properties and formation energies of monovacancy (V1), divacancy (V2) and hexavacancy (V6) in silicon have been comparatively studied with density functional theory (DFT), Stillinger-Weber (SW), EDIP and Tersoff methods. The validity and shortcomings of the three classical potentials are discussed in detail. It is found that the DFT method may provide accurate description of atomic structures and energies of vacancies. As to the empirical potentials, they cannot be used to investigate quantum mechanical effects such as Jahn-Teller distortion ocurring in the DFT relaxations. Moreover, EDIP and T3 give an outward relaxation in all cases, which is contrary to the DFT and SW directions. Therefore, they are unsuitable to the structural property calculations. Based on the results calculated mainly for structure properties and formation energies, it can be concluded that SW should be the best potential to describe V1, V2 and V6.
2010, 59 (5): 3377-3383. doi: 10.7498/aps.59.3377
Based on density functional first principles method, the defect properties in tetragonal BaTiO3 have been studied. The results showed that the formation energies of neutral Ti vacancy and partial Schottky defect 2V3-Ti+3V2+Oare the lowest under oxygen-rich condition; while under reducing condition oxygen vacancy becomes the primary defect. The calculated full Schottky formation energy is higher than that obtained in the cubic phase, which may be the result of the strong hybridization between the Ti-O bonds. The hybridization is also responsible for the Frenkel formation energy of Ti. The defect-interactions are important when dealing with Schottky defects.
2010, 59 (5): 3384-3393. doi: 10.7498/aps.59.3384
A universal equation of state for solids is proposed. The equation exactly accounts for the cohesive energy; no physically incorrect oscillations exists, and its action is correct in both high pressure and expanded regions. The new equation and several typical equations in literature are applied to 15 alkali halide solids, and one alkaline earth oxide. The results show that the new equation can well fit experimental data, and can give correct cohesive energy. The parameters determined from the Vinet and Morse equations are sensitive to the data range, whereas the new equation is not . This implies that the applicability of new equation is better than the Vinet and Morse equations.
2010, 59 (5): 3394-3401. doi: 10.7498/aps.59.3394
A two-dimensional (2D) lattice Boltzmann method (LBM) model was developed to simulate liquid-liquid phase separation of monotectic alloys, which is controlled by the diffusive growth, the collisions and coagulations, and the Ostwald ripening of the minority liquid droplets. The present model combines the features of the multiphase flow model proposed by Shan-Chen and the mesoscopic interparticle potentials developed by Oin. In addition, a source term is introduced in the LB evolution equations to account for the phase transformation. The proposed LBM model was applied to simulate single droplet growth, coagulation of two droplets and multi-droplet growth during the liquid-liquid phase separation process of a monotectic alloy. The simulation shows that the single droplet growth in the two-liquid phase is controlled by diffusion and that the initial nonequilibrium composition approaches to equilibrium. The coagulation velocity of two droplets is influenced by surface tension, which is in accordance with the trend of the analytical prediction. It is found that the liquid-liquid phase separation process is obviously impacted by the collisions and coagulations and the Ostwald ripening of the droplets.
2010, 59 (5): 3402-3407. doi: 10.7498/aps.59.3402
The Sr4Al14O25: Eu2+,Sr4Al14O25: Eu2+， Dy3+ and Sr4Al14O25: Eu2+， Nd3+samples were synthesized by the conventional solid state reaction method. The influence of doping of Dy3+ or Nd3+ on trap levels of Sr4Al14O25: Eu2+ were studied. The results indicated that there are two trap levels with different depths， as shown in the thermoluminescence spetra of Sr4Al14O25: Eu2+， and the shallow trap level is suitable for electrons to escape at room temperature.The dopant Dy3+ enhances the concentration of electrons trapped by the shallow trap levels， leading to the notable increase of afterglow of Sr4Al14O25: Eu2+.The concentration of electrons trapped by deep trap levels were is by doping with Nd3+.Since the deep trap level is not appropriate for electron to escape at room temperature， the dopant of Nd3+does not improve the room temperature afterglow .
2010, 59 (5): 3408-3413. doi: 10.7498/aps.59.3408
The relaxation properties of single layer and multilayer graphene sheets were investigated using molecular dynamics simulation with REBO and AIREBO bond-order interatomic potential, respectively. The dynamic evolution of graphene sheets during relaxation was analyzed. The simulation shows that the sheets are not perfectly flat after relaxation，but show microscopic wavy corrugations at the sheets edges，but not in other areas. In addition，the waviness at the edges of multilayer graphene sheets is a little less than that of the single layer sheets.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2010, 59 (5): 3414-3417. doi: 10.7498/aps.59.3414
By means of first-principles calculations, we have investigated the band structrue, density of states (DOS) and electron density difference of the compound YFe2B2. For the exchange correction energy, we employ GGA in the form of PBE. The interactions between valence electrons and ionic core are represented by the ultrasoft pseudo potential.The results show that the compound YFe2B2 is paramagnetic. The 5s and 5p states of Y atoms are in a strong local state. The Fe and B atoms form nearest-neighbor bonds associated with Fe—B bonding. The Fe 3d-like bands with low E(k) dispersion participate in metallic-like Fe-Fe bonds. The Fe 3d states have an admixture of anti-bonding Y 4d states. In a word, YFe2B2 in the ground state is a paramagnetic ternary alloy.
2010, 59 (5): 3418-3425. doi: 10.7498/aps.59.3418
In order to investigate the properties of the p-type doping and reveal the mechanism of the hole concentration increasing after Cd：O codoping of wurtizite AlN，we have carried out first-principles calculations based on density-functional theory (DFT) for wurtizite AlN system. By calculating the binding energy of the Cdn-O（n=1，2，3，4）complex codoped AlN we found that Cd：O can be stabilized and the solubility of Cd can be increased in the system. We analysed the activation energies of the Cd and Cd2-O doped AlN and found that the activation energy of Cd2-O was decreased by 0.21 eV from that of Cd，which showed that the hole concentration of Cd2-O doped system was raised 103 times as that of Cd. We compared the band structures and densities of states，and found that the electrons of Cd atom on the 4d orbit moving to 2p orbit of N atom results in that the impurity levels which appeared near the Fermi level always occupy the highest valence band. Increasing the number of Cd atoms，the holes can occupy more states. In order to reduce the combining probability of Cd and O，hence，to enhance the Cd-N covalent characteristics and improve the hole concentration，it is important to control properly the concentrations of Cd and O.
2010, 59 (5): 3426-3431. doi: 10.7498/aps.59.3426
The electronic structure，optical and lattice dynamical properties of CeO2 are studied using first-principles density functional theory taking into account the on-site Coulomb interaction within the LDA+U scheme. Results of the charge density and electron localization function distribution indicate that CeO2 is an insulator with covalent bonding between Ce and O atoms. Calculated dielectric constants，Born effective charge tensors，phonon dispersion curves reproduce the experimental data reasonably.
2010, 59 (5): 3432-3437. doi: 10.7498/aps.59.3432
The crystal structure，electronic structure and magnetism of the double perovskite Sr2FeWO6 and SrKFeWO6 have been investigated under the framework of density functional theory (DFT) with the generalized gradient approximation taking into account the on-site Coulomb energy (GGA+U) using the projected augmented wave (PAW) method. Structure relaxation results show that K doping of Sr2FeWO6 stabilizes FeO6，WO6 octahedra and makes the Fe—O—W angles close to 180°，indicating the enhancement of superexchange interaction. From the electronic structure calculation，it was found that the contribution to the total density of states (DOS) from K itself is small. Due to the K doping，the valence and magnetic moment of B-site cation Fe are enhanced and the hybridization between Fe and O becomes stronger，as well as the band gap is enlarged. Nevertheless，it does not cause considerable change in B’-site cation W. The process of transfer of electrons is dominated by Fe-Fe in SrKFeWO6 compared with Fe-W charge transfer in Sr2FeWO6 before doping.
2010, 59 (5): 3438-3444. doi: 10.7498/aps.59.3438
The diffusion character of metal atoms in the interconnects of metal strips/solder bump was observed by series solder bumps on flip chip which were stressed by high density electric current under high temperature. Assumed that the diffusion of atoms was controlled by electrical stress and chemical potential gradient，the diffusion behavior of all metal atoms in interconnects was investigated. The Ni atoms in the Ni(V) finishes directionally diffuse along the electron flow and accelerate the interface reaction of Ni and Sn by electromigration. Thus the Ni(V) finishes lose the action of the diffusion barrier layer in turn that resulted in the direct connection of Al and the solder. The Al atoms migrate in the electron flow by the electron wind force induced the Al atoms content in solder near the passivation via increases with the stressed time. The vacancies move in the opposite direction with the Al atom flux，and collect in the Al strips. Then the voids appear after the supersaturation of vacancies. The Sn and Pb atoms in the solder diffuse along the concentration gradient because of the non-leading action of electromigration. The atoms in the solder driven by the chemical potential gradient and compression stress form the upward fluxes. The upward diffusion of solder erodes the Al strips，which made the Al strips failure due to the voids and corrosion. The Al and Sn/Pb atoms were driven by their respective dominant force，and result in durative mutual diffusion until the interconnects take place the open circuit because of the difference of mass flux.
2010, 59 (5): 3445-3449. doi: 10.7498/aps.59.3445
Theoretically predicting probabilities of the various isomers in the cluster growth is important because of the difficulty in characterizing structure of clusters. Considering that relative abundance of each isomer formed at high temperature could be obtained through molecular dynamics，what the problem comes down to is how these isomers transform from one to another at room temperature. We developed a statistical mechanics model，and obtained the analytic relationship between the temperature and the transformation time from one isomer to another. Taking cluster C12 as an example，it is shown that the time for the most probable isomer formed at 2500 K turning into the isomer with the lowest potential energy at room temperature is longer than.
2010, 59 (5): 3450-3454. doi: 10.7498/aps.59.3450
By diagonalizing the complete energy matrix for d3 configuration ion in a trigonal ligand-field based on ligand-field theory，optical and EPR spectra of Cr3+：Be3Al2(SiO3)6 system are studied，the results of which are in good agreement with experimental facts. By analyzing optical and EPR spectra of (CrO6)9- cluster，the local polarization of oxygen ligands in (CrO6)9- cluster are studied. Results show that oxygen ligands in (CrO6)9- cluster exhibit remarkable polarization effect due to the effect of surrounding environment.
2010, 59 (5): 3455-3460. doi: 10.7498/aps.59.3455
Perovskite La0.9Sr0.1FeO3 ceramics have been synthesized at 1250℃，1300℃ and 1350℃ by the conventional solid-state reaction technique. From their crystal structures determined by powder X-ray diffraction，we found that the lattice volume decreases with increasing sintering temperature. The scanning electronic microscope (SEM) images of surface microstructures of the samples show that the average grain size increases with increasing sintering temperature. The electrical resistivity and Seebeck coefficient have been measured between room temperature and 800℃. At low temperatures，the electrical resistivity shows a semiconductivity-like behavior. With further increasing of temperature，the electrical resistivity slightly increases. An adiabatic hopping conduction mechanism of small-polarons is suggested from the temperature dependence of the electrical resistivity，which has different activation energies at low and high temperatures. The Seebeck coefficient rapidly decreases with increasing temperature，and reaches a saturation value about 600℃. With further increasing of temperature，the Seebeck coefficient slightly increases. With the increase of sintering temperature，the electrical resistivity decreases，while the Seebeck coefficient increases. Therefore，the power factor increases with increasing sintering temperature. The highest power factor of 90 μW/K2m was obtained at 727℃ for sample sintered at 1350℃.
2010, 59 (5): 3461-3465. doi: 10.7498/aps.59.3461
Based on the Su-Schrieffer-Heeger (SSH) model extended to include the square term of the electron-lattice interaction，the dynamic characteristics of polarons are investigated. With increasing of the coefficient of the square term (β)，the energy gap between the valance band and the conduction band increases. but the total width of the energy band does not change. At the same time，it is found that the dimerization amplitude and the localization of polarons are strengthened by the nonlinear electron-lattice interaction. Furthermore，the results show that the polaron velocity is suppressed by the nonlinear electron-lattice interaction，and the critical electric field strength to dissociate the polaron increases with β increasing.
2010, 59 (5): 3466-3472. doi: 10.7498/aps.59.3466
In this paper，combinatorial method was introduced for the first time to disclose the effect of Ni thickness on the Ni/SiC contact properties. Sixteen contacts with the same Ni thickness showed similar Schottky contact properties.The current voltage curves (I-V) were different for the Schottky contacts with different Ni thickness from 10 nm to 160 nm. The effect of the Ni thickness to the ideality factor n and the effective barrier height ФB was found to be the origin of the different Schottky contact properties. After rapid annealed at 1000℃，all the contacts showed good linear I-V curves，which indicated the formation of ohmic contacts. Ni2Si was the main reaction product. Comparing the slopes of the IV curves，the contacts with 30—70 nm Ni showed good ohmic contact properties. The results confirmed our previous conclusion about the key role of appropriate carbon-enriched layer (CEL) for the formation of ohmic contacts on SiC.
The structure，optical and electrical properties of Li-N dual-acceptor doped p-type ZnO thin films prepared by sol-gel method
2010, 59 (5): 3473-3480. doi: 10.7498/aps.59.3473
Li-N dual-doped ZnO thin films were deposited on n-type Si(100) substrates with Sol-gel method. Then the deposited films were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the films have polycrystalline wurtzite-structure and high c-axis preferred orientation. The analysis of the results of the deposited thin films tested in the Hall measurement at room temperature shows that these thin films have p-type electrical conductivity. The optimized results obtained at 15.0at% Li-N dual-doped concentration are 0.34 Ω·cm for the electrical resistivity，16.43 cm2/V·s for the Hall mobility and 2.79×1019 cm-3 for the hole concentration，respectively. The photoluminescence (PL) spectra show that the thin films have strong emission of near-ultraviolet (UV) and violet light. However，the defect-related deep level emission is weak in visible regions. The effects of Li-N dual-doping concentration and annealing temperature on the structural，optical and electrical properties are also discussed in this paper.
Simulations of impedance matching and phase locking of Josephson junction arrays embedded in a Fabry-Perot resonator
2010, 59 (5): 3481-3487. doi: 10.7498/aps.59.3481
We proposed a method for implementing impedance matching and phase locking of Josephson junction arrays based on Hes previous report on the coupling mechanism of a millimeter wave radiation to bicrystal Josephson junction arrays embedded in a Fabry-Perot resonator，and relevant electromagnetic simulations and numerical calculations were performed. A bicrystal Josephson junction array was fabricated on a YSZ bicrystal substrate，and embedded in a Fabry-Perot resonator. Impedance matching was implemented by integrating an optimized half-wavelength dipole array fed in series with the junction array，and numerical calculations showed that the radiation efficiency of a single junction reached 94%. Through making good use of the radiation characteristics of the antenna array and optimizing the model，the FP resonator and the substrate can be driven to resonate in proper modes respectively，which benefits the high frequency electromagnetic coupling between the junction array and the resonators. The numerical simulations proved that this method is effective for realizing self-voltage locking and mutual-phase locking of junction arrays. The method proposed in this paper and calculation results are valuable for guiding the applications of Josephson junction arrays in THz signal generators and voltage standards.
2010, 59 (5): 3488-3493. doi: 10.7498/aps.59.3488
The critical current density (Jc) and flux-pinning mechanism of MgB2 doped with citric acid (C6H8O7) from 0 to 30wt% have been investigated in detail by magnetic and resistive measurements. The temperature dependence of critical current density，Jc(T)，at particular field within the single vortex regime was analyzed. δTc pinning mechanism was found to be the only important pinning mechanism in pure MgB2 samples，while δl pinning is dominant with little effect of δTc pinning for citric acid doped samples. It was observed that the contribution of δl pinning enhances with the increasing doping level of critic acid，and it was also found that MgB2 doped with 15wt% critic acid shows the best performance in Jc-B behavior.
2010, 59 (5): 3494-3498. doi: 10.7498/aps.59.3494
According to the latest experiments about the temperature effect of organic magnetoresistance，we employed a drift-diffusion equation and take into account the temperature influence on mobility and spin relaxation to investigate spin polarization and magnetoresistance of the organic semiconductor device. We found that the magnetoresistance in low temperature region decreases faster than that in high temperature region. The change of magnetoresistance with temperature is mainly dependent on spin relaxation time of organic layer. Finally，the theoretical calculation was compared with experimental data and consistency between them was obtained.
2010, 59 (5): 3499-3503. doi: 10.7498/aps.59.3499
The N doped SiO2 thin films were prepared by radio frequency magnetron reaction sputtering technique. It is found that the N doped SiO2 thin films have ferromagnetism. Magnetic order is easy to form in the system in which silicon nitride particles with relatively small sizes are distributed uniformly in silicon oxide matrix. When the substrate temperature of the film was 400℃，the N doped SiO2 thin film possesses the largest saturation magnetization and coercivity，being 35 emu/cm3 and 75 Oe，respectively. The magnetism of the film may originate from the interfaces between silicon nitride and silicon oxide. Calculations based on the first principles show that net spins exist in the N doped SiO2 film. The orbit magnetic moments caused by the charge transfer through the interface between silicon nitride and silicon oxide also contribute to the ferromagnetism of the film.
2010, 59 (5): 3504-3508. doi: 10.7498/aps.59.3504
The LLS equation is analyzed by Melnikov disturbing method when non-constant spin torque is considered. Computing codes are programmed by combining VC and MATLAB. The results reveal that the magnetization trace vibrates round the non-disturbing trace at first，and then surges when close to the reversal point，and the time of reversal is shorter compared with the trace with constant spin torque.
2010, 59 (5): 3509-3515. doi: 10.7498/aps.59.3509
A series of (Na1/2Bi1/2)Cu3Ti4O12 (NBCTO) ceramics were prepared by solid-state reaction at different sintering temperatures. The crystal structure，microstructures，dielectric properties and complex impedance and the corresponding temperature dependences were investigated. It has been revealed that the NBCTO ceramics has quite similar electrical properties with those previously found in CaCu3Ti4O12ceramics. The NBCTO ceramics prepared at sintering temperatures between 990℃ and 1060℃ exhibit low-frequency ε′ larger than 10000 at room temperature. With the increasing of sintering temperature，both ε′ and the grain size in microstructure first increase and then decrease. Although large difference is observed in their dielectric properties and complex impedance for the various NBCTO ceramics，there exist some common features. Whereas only one dielectric relaxation is seen at room temperature or lower temperatures，two are seen in the dielectric spectra within the measured frequency range of 40 Hz—10 MHz at higher temperatures.
2010, 59 (5): 3516-3522. doi: 10.7498/aps.59.3516
Pure colossal dielectric constant oxide CaCu3Ti4O12 (CCTO) compound was prepared by traditional ceramic processing. Dielectric dispersion and complex impedances spectra were investigated using a impedance analyzer within a temperature range of 10—420 K. The data were simulated by “ZVIEW” software. The result indicates that there are two obvious relaxations in the dielectric dispersion spectra when the temperature is higher than room temperature and the dielectric constant increases remarkably with increasing temperatures at a low frequency, which indicates a thermal ionic polarization. However, the frequency spectra becomes similar to Debye-type relaxation when the temperature is lower than room temperature and the low-and high-frequency relaxation step almost keeps unchanged with temperature, which reveals a feature of interface polarization and considerable temperature stability for CCTO. The relaxation revealed in the frequency spectra corresponds to the three different semicircles revealed by the impedance spectra, which indicated there are three inhomogeneous regions or polarization processes in CCTO ceramics and the colossal dielectric constant mainly comes from the extrinsic polarization of these inhomogenities. The activation energies are found to be respectively 0.05 eV, 0.58 eV and 0.49eV for the three different polarization processes by simulating the impedance semicircles using an equivalent circuit.
2010, 59 (5): 3523-3530. doi: 10.7498/aps.59.3523
Investigations on the interaction of short pulsed laser with optical films usually terminate at the ejection of film material. The plasma bursting process will happen, because the superhot ejection will absorb the remainder of laser energy. A two-steps numerical method has been used to deal with this process. In every computation time-step, two phases are used: the first one is the adiabatic expansion and cracking phase; the second one is the phase of absorbing laser energy. By this method, the energy absorption process and the bursting process are effectively coupled. For the thermodynamic parameters of the plasma micro-droplet, such as the radius, expansion speed and acceleration cracking speed and acceleration, densities and temperatures of electronic and ionic systems have been investigated. The results revealed that: the ejection will be atomized to micro-droplets in the early stage, and expansion dominates the latter part. The cracking velocity is cyclic, and the expansion velocity increases all the while. In specific cases, the expansion process may keep a dynamic stable state after the atomization. But it is difficult for this dynamic stable state to form.
2010, 59 (5): 3531-3537. doi: 10.7498/aps.59.3531
Since traditional Prony analysis of low frequency oscillations has strict requirements to the input signal and is sensitive to the noise of data, this paper proposes a empirical mode decomposition filtering and Prony analysis combined method for low frequency analysis. In this method, empirical mode decomposition is used to adaptively filter the noise of the input signals before improved Prony analysis is carried out. The order of improved Prony analysis is determined by the normalized singular value method. This method is applied to analyze the test signal and the IEEE 4-machine system oscillation signals, and compared with the Prony analysis based on low pass filter. The simulation shows the effectiveness of this method which indicates that the result of the analysis is good even in highly noisy environment.
Study on near-infrared broadband emission spectroscopic properties of Bi-doped α-BaB2O4 single crystal induced by γ-irradiation
2010, 59 (5): 3538-3541. doi: 10.7498/aps.59.3538
The bismuth-doped α-BBO single crystals were prepared by traditional Czochralski method in ambient atmosphere, and the obtained samples were irradiated by γ-ray . The absorption, emission and fluorescence decay curves were measured at room temperature. Near-infrared super-broadband emission (FWHM ~113 nm) of Bi:α-BBO single crystal subjected to γ-irradiation was observed to be center-peaked at ~1139 nm upon 808 nm excitation. The effect of irradiation and annealing treatment on the emission was discussed, and the mechanism for the wide emission band was investigated preliminarily.
2010, 59 (5): 3542-3546. doi: 10.7498/aps.59.3542
The effects of high temperature annealing on the stability of the intrinsic defects in unintentionally doped epitaxial 4H-SiC prepared by low pressure chemical vapor deposition (LPCVD) are studied by electron spin resonance (ESR) and low-temperature photoluminescence (PL). The results showed that the concentration of intrinsic defects increases with increasing annealing temperature and reaches its maximum at 1573 K, then decreases with the gradually increasing annealing temperature when annealing time is 10 min or 30 min. The annealing temperature has an important effect on the concentration of intrinsic defects in epitaxial semi-insulating 4H-SiC prepared by LPCVD, whics is attributed to the process of intrinsic defects being stabilized and the strong interaction between the intrinsic defects during annealing.
2010, 59 (5): 3547-3553. doi: 10.7498/aps.59.3547
A series of chalcogenide glasses based on Ge-Ga-S-CsI system doped with different Dy3+ ions were synthesized by melt-quenching technique. The refractive indices, Raman spectra, absorption spectra, near- and mid-infrared fluorescence of glass samples were measured. The intensity parameters (Ωi, i=2,4,6), transition probabilities (A), branching ratios (β) and radiation lifetimes (τrad) have been predicted for Dy3+ ions in the samples by using the Judd-Ofelt theory. The mid-infrared fluorescence properties were investigated for different Dy3+ ion concentrations under 810 nm laser excitation. The multiphonon relaxation rates (Wmp) of Dy3+:6H13/2→6H15/2(2.86 μm) and6H11/2→6H13/2(4.38 μm), and the constant related to the e-p coupling strength (α) of Ge-Ga-S-CsI glasses were evaluated.
2010, 59 (5): 3554-3557. doi: 10.7498/aps.59.3554
The Er2SiO5 films with strong room-temperature photoluminescence have been fabricated by using the sol-gel spin coating method. The effects of sintering temperature and time on phase structure and phase transformation of ErSiO films have been investigated. A mixture of Er2O3 crystal and amorphous SiO2 was obtained below 1000 ℃, and the Er2SiO5 phase with high (100), (200), and (300) preferred orientation was detected when the temperature increased to higher than 1200 ℃. The phase structure has an evident influence on the photoluminescence properties for ErSiO films. For the phase structure of Er2O3 crystal with amorphous SiO2, the weak PL spectra with a main peak at λ=1.535 μm were observed. The strongest main PL peak moved to λ=1.528 μm, and the intensity was increased about 10—20 times when the phase structure changed to Er2SiO5. The Er2SiO5 films with strong room temperature photoluminescence are promising candidates for application in Si-based light source and amplifier.
2010, 59 (5): 3558-3563. doi: 10.7498/aps.59.3558
A series of phosphors of Zn1.92-xMgxSiO4:0.08Mn（0≤x≤0.12）were successfully synthesized at various heating atmosphere via sol-gel method. The structure and luminescent properties of the samples were characterized by X-ray diffractometer (XRD) and the FLS920T Spectrophotometer, respectively. The results indicated that in the Zn1.92SiO4:0.08Mn system, the Mg2+ doped could substitute for the Zn2+ site and result in the decrease of lattice parameters. The absorption band of the MgO4 cluster was located at about 154 nm in vacuum ultraviolet region. Mg2+ ion doping has favorable influence on the photoluminescence properties of Zn2SiO4:Mn2+, the optimum concentration of Mg2+ being 0.06 mol under 147 nm excitation. The emission intensity of Zn1.92-xMgx SiO4:0.08Mn2+ phosphors calcined in the mixture of nitrogen and hydrogen were stronger than those of the phosphors calcined in other heating atmospheres, and the emission intensity of Zn1.86Mg0.06SiO4:0.08Mn2+ calcined in the mixture of N2 and H2 was 113% of that of Zn1.92SiO4:0.08Mn2+, being 5% higher than that of commercial phosphor. After Mg2+ doping the decay time of phosphor was much shortened and the decay time of Zn1.86Mg0.06SiO4:0.08Mn2+ was 3.89 ms, which was shorter by 1.33 ms than that of commercial product.
2010, 59 (5): 3564-3570. doi: 10.7498/aps.59.3564
Organic semiconductor (OSC) devices based on manipulation of electron spin have attracted considerable attention since the discovery of long spin relaxation time and large transport distance in OSCs. For organic light-emitting devices (OLEDs), controlling the singlet to triplet ratio by spin-polarized electrodes is one of the effective ways to realize high luminescent efficiency. Based on the drift-diffusion equation, continuous equation and Langevin recombination theory, the spin injection, transportation and recombination properties of carriers in OLEDs are modeled in this paper. The density of polarized electrons and holes in OSCs are calculated, the singlet to triplet ratio is analyzed, and the influences of the electrical field, spin-related interfacial conductance, bulk conductivity and polarization of electrodes are accounted for. It is showed that opposite spin polarization of electrons and holes are in favor of increasing singlet to triplet ratio, and the higher spin polarization of injected carrier density is, the larger singlet to triplet ratio will be. Large spin-related interfacial resistance, large polarization of electrodes, matched bulk conductivity and high electrical field under forward bias favor spin polarization of carries density in OSCs. We can obtain obviously improved density polarization by optimizing the related parameters on the basis of essential injection efficiency. The optimized polarization ensures sufficient space for manipulating singlet to triplet ratio, hence the quantum efficiency of OLEDs.
The role of magnetic fields on organic light-emitting devices based on aluminum tris(8-hydroxyquinoline) (Alq3) at room temperature
2010, 59 (5): 3571-3576. doi: 10.7498/aps.59.3571
We report the magnetic-field effect (MFE) in Alq3 based organic light-emitting device (OLED) with the structure of ITO/NPB/LiF/Alq3/LiF/Al.When an external magnetic field of 50 mT and insertion of LiF thickness of 0.8 nm is applied, the current efficiency and the brightness of the device increase to 12.4% and 17%, respectively.The origin of the improvements could be attributed to the Zeeman effect,which reduces the hyperfine interactions of electrons and holes, inhibiting energy transfer from the singlet polaron pairs to triplet polaron pairs and increasing the population of singlets.Similar MFE was observed in phosphorescent organic light-emitting diodes(PhOLEDs).The current efficiency of ITO/NPB/LiF(0.8 nm)/CBP:6 wt% Ir(ppy)3/BCP/Alq3/LiF/Al increases to 12.1% at 50 mT.Magnetic-field-induced increase of singlet excitons in the CBP matrix reflects increase of triplet excitons in the dispersed Ir(ppy)3 molecules in the CBP+Ir(ppy)3 blend.
2010, 59 (5): 3577-3582. doi: 10.7498/aps.59.3577
Aiming at determining the quantum efficiency of fully activated negative electron affinity(NEA) GaN photocathodes, we have investigated the spectral response of NEA GaN photocathodes by using a dedicated ultraviolet spectral response measurement instrument. The quantum efficiency curve of reflection-mode NEA GaN photocathode has been obtained in the band region from 230nm to 400nm. The experimental results show that the quantum efficiency of reflection-mode NEA GaN photocathode reaches up to 37.4% at 230 nm, and at 365 nm, which is the threshold of GaN photocathode, the quantum efficiency remains 3.75%. A sharp cutoff characteristic with over two orders of magnitude degradation from 230 nm to 400 nm has been observed. Based on the former research results, the factors influencing quantum efficiency were also comprehensively analyzed in the paper.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2010, 59 (5): 3583-3588. doi: 10.7498/aps.59.3583
N-doped carbon nanotubes with different nitrogen contents were synthesized by CVD with pyridine as nitrogen source and acetylene as carbon source. The samples’ morphology and bonding properties were characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). TEM images showed that with the increasing nitrogen content, the average bamboo segment distance of the carbon nonotubes decreased from 120 nm to 40 nm and more flexural tubes with coarse surface was obtained. XPS results revealed that there are pyridinic, pyrrolic and graphitic types of C-N bonds in the N-doped carbon nanotubes. The effect of nitrogen content on the bonding property was analyzed. And the chenge in morphology with increasing nitrogen content was explained by the difference in bonding forms.
2010, 59 (5): 3589-3594. doi: 10.7498/aps.59.3589
AlFe alloy single crystal film was prepared at 573 K by pulsed laser deposition (PLD) in this work. X-ray diffraction (XRD) and transmission electron diffraction (TED) showed that the space group of the alloy is PM-3M, lattice parameter is a=0.297 nm (just a little greater than that of bcc-Fe, aFe=0.293nm). Crystal lattice of AlFe was the lattice of bcc-Fe with the center Fe atom replaced by the Al atom. First-principles and quasi-harmonic Debye model were employed to study the chemical potential and thermodynamic properties of AlFe alloy. Calculations indicated that the chemical potential (μ) of AlFe is much lower than those of fcc-Al and bcc-Fe, which indicates that AlFe is the only phase formed in the process of film growth. At the same time, AlFe greatly excels the elementary substance of Al and Fe in thermodynamic properties. In the range of 150 K to 1000 K, heat capacity at constant pressure (Cp) of AlFe is much higher than that of Al or Fe, and thermal expansion coefficient (α) of AlFe is lower and more stable.
2010, 59 (5): 3601-3606. doi: 10.7498/aps.59.3601
Cu/TiOx composite films have been deposited by RF magnetron sputtering at room temperature. The chemical components and structures of the Cu/TiOx composite films have been characterized by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy and water contact angel measurement. It is found that the titanium presents in the form of Ti3+ before and after annealing. The results of UV-vis spectroscopy show the visible light absorption features of Cu/TiOx composite films with the absorption edge at about 600 nm. Contact angle results indicate that the Cu/TiOx films are hydrophilic, which is attributed to the added Cu.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2010, 59 (5): 3607-3610. doi: 10.7498/aps.59.3607
In this paper, the whitecap coverage is retrieved from the ERS-1 data and the KHCC03 scattering model which takes into account the effect of wave breaking, and a new whitecap coverage formula is obtained based on the retrieval results. The results calculated from this new formula of whitecap coverage have better agreement with the measured whitecap coverage than those obtained by some famous previous formula in the range of wind speed at 10 m height from 7 m/s to 16 m/s. This shows that it is feasible to retrieve whitecap coverage from scatterometer data and the scattering model including the effect of wave breaking. Moreover, this approach is different from those methods usually used in passive remote sensing.
Cooperative spectrum sensing for cognitive radios based on a modified shuffled frog leaping algorithm
2010, 59 (5): 3611-3617. doi: 10.7498/aps.59.3611
A modified shuffled frog leaping algorithm (SFLA) and cooperative spectrum sensing for cognitive radios based on the modified SFLA are proposed. Simulations are performed to compare the performance of the modified SFLA and traditional SFLA. The performance of the proposed cooperative spectrum sensing method based on the modified SFLA and that of the cooperative spectrum sensing method using modified deflection coefficient (MDC) are also compared. Results show that the proposed SFLA outperforms the traditional SFLA, and the proposed cooperative spectrum sensing method based on the modified SFLA gives higher detection probability than the MDC-based method, which validates the effectiveness of the modified SFLA-based cooperative sensing method.
2010, 59 (5): 3618-3626. doi: 10.7498/aps.59.3618
The spectral variation, the correlation of multi-waveband flux and the property of polarization of BL Lac objects give us important information for studying their intrinsic correlation of radiation components. The present paper analyzes the properties of RBLs and XBLs. It is indicated by statistics that the redshift of RBLs are greater than that of XBLs and the black hole mass of RBLs are smaller than that of XBLs. The paper also studies the possible correlations between the redshift and the flux densities for different wavebands in low state, and the possible correlations of flux densities for different wavebands (radio, near-infrared, optical and X-ray) in low state. The results support that the systematic difference between RBLs and XBLs is not caused by the choice effect only.