Vol. 60, No. 3 (2011)
Lie symmetry and Hojman conserved quantity of Nielsen equation in a dynamical system of the relative motion
2011, 60 (3): 030201. doi: 10.7498/aps.60.030201
Lie symmetry and Hojman conserved quantity for Nielsen equations in a dynamical system of the relative motion are investigated. The definition and the criterion of Lie symmetry of Nielsen equations in a dynamical system of the relative motion under the infinitesimal transformations of groups are given. The expressions of the determining equation of Lie symmetry of Nielsen equations and Hojman conserved quantity deduced directly from Lie symmetry in a dynamical system of the relative motion are obtained. An example is given to illustrate the application of the results.
2011, 60 (3): 030202. doi: 10.7498/aps.60.030202
Coupled consensus problem of multiple autonomous agents with communication delay and input delay is investigated. Based on the frequency-domain analysis,sufficient conditions for the first-order and second-order agents are obtained respectively. The conditions are dependent on the input delay,the communication delay and the control parameters. Simulations illustrate the correctness of the results.
2011, 60 (3): 030203. doi: 10.7498/aps.60.030203
A class of nonlinear solitary waves in dusty plasma is considered. Firstly, a variational iteration is constructed. Then the initial approximate solution is determined. Finally, using the method of the variational iteration, each degree approximation for corresponding model is found.
2011, 60 (3): 030204. doi: 10.7498/aps.60.030204
A class of delayed oscillator of El Nio-Southern Oscillation (ENSO) coupling systems is considered. Using the delayed theory, perturbation and other methods, the asymptotic expansion of the solution for ENSO model is obtained and the asymptotic behavior of solution for the corresponding problem is studied.
2011, 60 (3): 030205. doi: 10.7498/aps.60.030205
Using Mawhin's continuation theorem, the existence of periodic solutions for a class of nonlinear problem are first discussed, and then by using it, the problem of periodic solutions for a delayed sea-air oscillator coupling model for the ENSO is investigated. A new result on the existence of periodic solutions to the model is obtained.
A heterogeneous computing algorithm for two-dimensional unstable manifolds of time-continuous systems
2011, 60 (3): 030206. doi: 10.7498/aps.60.030206
Two-dimensional manifolds usually contain many nonlinear behaviors in complicate structures, which implies that much numerical calculation must be done during computing. Therefore, how to accomplish the work efficiently is a key problem. Since today’s computers tend to heterogeneous platforms including multi-core CPUs and general purpose GPUs, this paper proposes a fast manifold computing algorithm, which is not only of high precision and versatility, but also very suited to the new generation of computers. The algorithm contains two kinds of computation: extending trajectories and generating triangles. The former is large and simple, which is suitable for GPU; the later is small and complicate, which is suitable for CPU. The computation for the stable manifold of the Lorenz system at the origin shows that this algorithm ensures the best performance of heterogeneous platforms and improve the computing speed greatly.
2011, 60 (3): 030207. doi: 10.7498/aps.60.030207
In this paper, approximate solution of the Sinh-Gordon equation is obtained via the homotopy analysis method. The obtained solution contains an auxiliary parameter which provides a convenient way to control the convergence region and rate of the series solutions.
2011, 60 (3): 030301. doi: 10.7498/aps.60.030301
In this paper the model of trapping force on microsphere near focus in single optical tweezers is built by three dimensional finite-difference time-domain (FDTD) and Maxwell stress tensor methods. Fifth order Gaussian beam based on spherical vector wave function (VSWF) is adopted as simulation light source; the correct light field transmission is obtained. The influences of the wavelength, waist and polarization of light sources, the radius and refractive index of the microsphere on the optical trapping force are discussed. The influence of nearby microsphere and beam polarization on the trapping force of the trapped microsphere in single optical tweezers is analyzed. The effect of beam polarization working on the trapping force of the trapped microsphere is specially analyzed. As results of simulation, the trapping force acting on the microsphere by the circularly polarized beam is larger than that by the linearly polarized beam. The stability of the trapped microsphere in single optical tweezers will be disturbed by the nearby microsphere and lose its balance. Varying the beam polarization will lead to the change of the trapping force of the trapped microsphere.
2011, 60 (3): 030302. doi: 10.7498/aps.60.030302
We constructed a new three-mode entangled state representation in the three-mode Fock space, which is complete and can make up a new quantum representation. This state can be generated experimentally by combining beamsplitter with polarizer. The entanglement properties are analyzed by obtaining its Schmidt decomposition. As an important application of this state, we consider a single-mode state teleportation by using this new state as a quantum channel, and present the corresponding teleportation scheme.
2011, 60 (3): 030303. doi: 10.7498/aps.60.030303
The effects of Dzyaloshinskii-Moriya (DM) interaction on the thermal entanglement of mixed-spin XY chain (1/2,3/2) and spin 1 XY chain are investigated through negativity. By calculating the entanglement between two particles, it was found that the DM interaction can not only increase the entanglement, but also make the entanglement of the particles reach a stationary value. The higher the temperature, the greater the DM interaction is required to make the thermal entanglement arrive at this stationary value. Under the same condition, the entanglement between two spin 1 particles is less than that between mixed-spin. The exchange-coupling interactions between the spins are helpful to strengthen the thermal entanglement, hence the exchange-coupling can be used to modulate the entanglement along with the DM interaction. When the exchange-coupling interaction is small, one can enlarge the DM interaction to increase the entanglement, whereas, when the DM interaction is small, one can increase the thermal entanglement through increasing the exchange-coupling interaction.
2011, 60 (3): 030304. doi: 10.7498/aps.60.030304
Since the single photon is easy to attenuate and be disturbed, its key generation rate and transmission distance in quantum communication systems are generally limited. In contrast, weak coherent pulse (WCP) and heralded single photon source (HSPS) exhibit higher feasibility than the single photon source in quantum key distributions (QKD). We compare the performances of QKD using these two kinds of photon sources and decoy state method, incorporating data-postprocessing methods including the Lütkenhaus scheme and Gottesman-Lo-Lütkenhaus- Preskill (GLLP) scheme. Simulation results indicate that QKD using HSPS can transmit longer distance than using WCP with lower overall quantum bit error rate (QBER) at the same transmission distance, albeit with relatively low key generation rate.
2011, 60 (3): 030305. doi: 10.7498/aps.60.030305
Secure two-party comparing problem is used to compare two private integer without further leaking of information. But in case of the quantum computer the currently available solutions become useless. A secure two-party quantum comparing protocol in semi-honest model is presented based on the a quantum implicit module n+1 addition. The security of the protocol is analyzed.
2011, 60 (3): 030306. doi: 10.7498/aps.60.030306
In this paper, a feedback sum-product decoding algorithm of sparse quantum codes for X-Z Pauli channels is developed. Compared with the previous decoding algorithm, our feedback strategy exploits not just the syndrome but also the values of the frustrated checks on individual qubits of the code and the character of the channel model with the portion of each error to adjust the probability distribution of information nodes. Due to the smart adjustment, our decoding algorithm, on one hand, can break the symmetric degeneracy, and on the other hand, can feed back more useful information to the SPA decoder to help the decoder determine a valid output, thereby significantly improving the decoding ability of the decoder. Moreover, our algorithm, which is based on GF(4), overcomes the limitation caused by decoding in GF(2). Finally, we want to point out that, our method does not increase the measurement overhead in comparison wioth the previous methods, as the extra information comes for free from the requisite stabilizer measurement.
2011, 60 (3): 030307. doi: 10.7498/aps.60.030307
Based on Bose-Einstein condensation in minimized momentum state, the optimization criterion of potential is studied for trapped weakly interacting Bose gas according to Thomas-Fermi approximation. A criterion for the validity of potential and the limited atom number loaded in a power law attractive potential well for ultra-cold weakly interacting Bose atom gas is derived. The criterion gives the required potential field strength when the loaded atom number is fixed, or the limited atom number when the potential field strength is given, and then, the best ranges of potential field strength are obtained, for attractive interaction and repulsive interaction, respectively.
2011, 60 (3): 030308. doi: 10.7498/aps.60.030308
Analytical expressions of periodic solutions in rf-biased resistively-capacitively-shunted Josephson junction were derived by incremental harmonic balance method, and the stability of the periodic solutions was investigated using Floquet theory. We fownd that while the system is in stable periodic states, plentiful unstable periodic orbits still exist in the system. Critical parameter values for which the stable periodic solutions of the system lose their stability are obtained and the type of bifurcation is determined by computing the Floquet multipliers. We have also theoretically confirmed the period-doubling-route to chaos with increasing amplitude of driving current, which acts as the control parameter in the system. The results from analytical analysis coincide with that from numerical simulation.
The numerical study on the effect of the earlyafterdepolarization on spiral wavesin discrete excitable media
2011, 60 (3): 030501. doi: 10.7498/aps.60.030501
The early afterdepolarization (EAP) behavior is introduced into the Greeberg-Hasting model of discrete excitable medium through considering that some of the refractory states can be excited. The effect of the EAP on spiral wave is studied. The numerical results show that the EAP has significant influences on spiral waves when the related parameters are suitably chosen. These influences include that the EAP causes spiral wave drifting and meandering,and spiral breakup. The pattern of spiral wave is distorted. The spiral wave varies alternately between those with thick and thin arms. The period of spiral wave alters alternately between two values. The EAP induces the transition from stable spiral wave to breathing spiral wave or antispiral wave. When the excitation threshold of refractory states is very high,the EAP has no affect on the spiral wave. The EAP induced phenomena are briefly discussed.
A Logistic-Unified hybrid chaotic system is generated. In this system, following the random changing of the state variable values of the Logistic map, the parameter values of the Unified system can be modulated randomly, and the Logistic-Unified hybrid chaotic system can be switched between the generalized Lorenz system, Lü system and generalized Chen system randomly. The extremely complicated chaotic signal is generated via the Logistic-Unified hybrid chaotic system. The Logistic-Unified hybrid chaotic system is realized based on digital signal processing (DSP). Hardware experiments and software simulation are completely consistent, and the results demonstrate the validily of the theoretical analysis.
2011, 60 (3): 030503. doi: 10.7498/aps.60.030503
Based on the study of Chua’s circuit, a novel chaotic system is reported. Basic dynamical properties of the new system are further investigated via theoretical analysis and numerical simulation, including Lyapunov exponent, Lyapunov dimension, portrait diagrams, Lyapunov exponent spectrum, bifurcation diagrams, Poincaré mapping and power spectrum. Finally, an electronic circuit is designed by the Orcad-PSpice softeware to implement the new system. The investigation results show that the new chaotic system has broad parameter regions, an maximum Lyapunov exponent approaching one, and is not topologically equivalent to Chua’s circuit. It also shows a good agreement between numerical simulation and circuit experimental simulation, which proves the existence and physical realizability of the new chaotic system.
Anti-synchronization of different hyperchaotic systems based on adaptive active control and fractional sliding mode control
2011, 60 (3): 030504. doi: 10.7498/aps.60.030504
Taking hyperchaotic Chen system and hyperchaotic Lorenz system as examples, we study the anti-synchronization of hyperchaotic systems with slow time-varying parameters. Firstly, taking advantage of active control concept, the non-linear parts of hyperchaotic systems are eliminated, and then based on Lyapunov stability theory, a kind of parameter adaptive control law is selected reasonably to achieve anti-synchronization of two hyperchaotic systems, which is a good solution to the time-varying parameters perturbation problem. Furthermore, hyperchaotic systems of different parameters with fractional order are studied via sliding mode control,which is proved to be valid theoretically. Numerical simulation experiments verify the effectiveness and feasibility of the proposed method.
2011, 60 (3): 030505. doi: 10.7498/aps.60.030505
Combining the observer and adaptive method, chaos synchronization is realized for a class of the perturbed chaotic systems with unknown parameters. Lyapunov stability theory and Barbalat lemma are adopted to design observer for achieving chaos synchronization. This method has fewer constraints and can be applied to many chaotic systems. Numerical simulations of representative chaotic systems further verify the validity of the proposed method.
2011, 60 (3): 030506. doi: 10.7498/aps.60.030506
A method is introduced to realize spatiotemporal chaos projective synchronization for a weighted network. The coupling function between connected nodes of the weighted network is derived and the range of the linear coefficient matrix of separated configuration in state equation of the node is obtained through constructing an appropriate Lyapunov function. Each node of the weight network is a laser spatiotemporal chaos model in which Bragg acousto-optical bistable system and unilateral coupled map lattices are taken as the local function and the spatial extended system, respectively. The projective synchronization effect of the weighted network is checked by numerical emulation. The results show that projective synchronization can be realized even if the coupling strength between the nodes are given arbitrary weight values.
Many polyalcohols will change from one crystal structure to another at certain temperatures. A lot of works had reported their phase change enthalpy, phase change temperature and phase diagram. It is taken that their phase change enthalpy must be related to their hydrogen bond. This article investigated quantitatively the relation between phase change enthalpy and hydrogen bond of NPG (neopentylglycol), PG (pentaglycerino) and PE (pentaerythritol) on the basis of infrared spectrum experimental data and calorimetric results. It was shown that before phase change, all the —OH are associated and as a result NPG, PG and PE form layer structure. After phase change, NPG, PG and PE move along the layer and as a result some hadrogen bonds break. Therefore the phase change enthalpy equals the energy used to break hydrogen plus the energy used to increase the vibration frequency of other still associated —OH.
ADRC and CMAC combined optimization and control for a class of discrete-time uncertain chaotic systems
2011, 60 (3): 030701. doi: 10.7498/aps.60.030701
Immune dynamic particle swarm optimization (IDPSO) strategy integrated with active disturbance rejection control (ADRC) and cerebellar model articulation controller (CMAC) combined control is designed for uncertain nonlinear discrete-time chaotic systems. The ADRC-CMAC is comprised of a cerebellar model articulation controller (CMAC) and an ADRC controller. The ADRC controller is designed to guarantee the stability of the system and restrict the disturbance. The CMAC is used to guarantee the control precision and response speed. Immune binary-state particle swarm algorithm is used to tune online the parameters of the ADRC-CMAC. Simulation results of uncertain nonlinear discrete-time systems demonstrate that performance with favorable response speed and restrained disturbance can be achieved by using the proposed control system.
2011, 60 (3): 030702. doi: 10.7498/aps.60.030702
A 0.14 THz high-power terahertz pulse detector based on hot electron effect in semiconductors is designed in this paper. First, the working principle of the detector is analyzed and its relative sensitivity is derived according to the structural characteristics of the detector. Then a three-dimensional finite-difference time-domain method is used to simulate the voltage standing wave ratio (VSWR) and relative sensitivity in a linear region. With optimized structural parameters, the VSWR of the designed detector is less than 1.3 while the relative sensitivity is about 0.6 kW-1, fluctuating no more than 10% in a frequency range of 0.13—0.16 THz. Subsequently discussed are the effect of Joule heat on the detector, and the relation between variation ratio of the output voltage and terahertz pulse duration. Finally the detecting simulations of the detector and its analysis results show that the detector with response time of picosecond-leval can handle a maximum power of about 2.2 kW, while the maximum power of its linear working region reaches tens of watts, so it can accomplish the direct measuring of 0.14 THz high-power terahertz pulses with nanosecond-level durations, increasing the accuracy of power measurement.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2011, 60 (3): 031101. doi: 10.7498/aps.60.031101
Based on the Heisenberg model, the anti-ferromagnet following the interaction suddenly switched-on at t=0 is considered in this paper. In the limit of low temperature, the time evolution of observables is analytically studied by utilizing the flow equation method. According to the unique feature of the system, the way to obtain the evolution of observables is shown and applied to the system we focused on. Further, special emphasis is laid on the application of the flow equation method to non-equilibrium magnetic systems so that the validity of the method applied to this kind of systems is traced. By means of this method, the evolution of magnetization of the ground state is traced in detail. It is found that the magnetization oscillates with time rather than converges,which is different from that of non-equilibrium Luttinger liquids.
2011, 60 (3): 032801. doi: 10.7498/aps.60.032801
It is a key aspect to study security of radioactivity gas in reactor circulation. It is necessary to study the transport process of radioactivity inert gases krypton in plutonium aerosol environment after fission occurrence. The experimental data of Kr87 and Kr88 were analyzed. According to the physical propertics of the two different sources,Kr87/Kr88 ratio variety law was analyzed at different sampling times. The physiced picture and model of transport process in plutonium aerosol environment were established by comparing with experimental data.
2011, 60 (3): 032802. doi: 10.7498/aps.60.032802
In this paper, we used molecular dynamics to simulate dynamic properties and micro-structure of the water-hydrazine particle system under various conditions:chamber condition of 1 atm, 298 K; pressurized water reactor (PWR) environment of 155 atm, 626 K; with number of water molecules of 256, numbers of hydrazine (N2H4) molecules of 0, 25, 50 and 75. And we have also explored the impact on the dissolved oxygen in water when hydrazine molecule is added to the system. The simulation results show that in the chamber ambient, when the number of molecules of hydrazine varies from 0 to 25, 50 and 75, the mean square displacement (MSD) in the particle system will increase with the number of particles of the hydrazine. The MSD for hydrazine molecule of number 0 will be ten less than that of 25, 50 and 75. Under the PWR environment, with hydrazine molecule number of 50, the MSD is about 4 times higher than that in chamber ambient. At the same time, under such condition, the MSD of particle system does not increase with the number of hydrazine molecules. The MSD with hydrazine molecule of 50 is higher than its counterpart with the number of molecules of 25 or 75. In addition, the micro-structure of particle systems, from the perspective of the radial distribution functions (RDF), will increase with the increase of concentration of hydrazine in chamber ambient. This conclusion goes along with the fact that hydrazine is easy to react with water to generate hydrazine hydrate. While in the pressurized water reactor environment, the radial distributions of the water with the number of hydrazine molecules of 25, 50 and 0 will have no big change. But the radial distributions with the number of hydrazine molecules of 75 increase significantly. It can be seen from simulation data that hydrazine added to PWR significantly inhibits the dissolved oxygen in water, but the inhibition does not increase in proportion to the increase of the concentration of hydrazine. This phenomenon and its causes are revealed comprehensively in this paper.
Response function and relative efficiency measurementsof the BC501A scintillator by usinga 252Cf fast fission chamber
2011, 60 (3): 032901. doi: 10.7498/aps.60.032901
The response function and relative efficiency of a Φ50.8 mm×50.8 mm BC501A scintillator has been measured by using a252Cf fast fission chamber. In this method,a multi-parameter data acquisition system is employed to take the time-of-flight (TOF),pulse shape discrimination (PSD) and recoil energy (RE. note: fission neutron induces recoil proton while the prompt gamma ray induces Compton recoil electron) of the fission neutron and prompt gamma ray in an event-by-event mode with a TOF gate. The off-line data analysis method for separating the prompt gamma ray from the fission neutron as well as its contribution to the TOF spectrum and RE spectrum to obtain the relative efficiency and response function is discussed in detail. An accurate calibration of the effective neutron detection threshold is carried out by a linear extrapolation of the section around the point of inflexion in the relative efficiency plots using neutron energy directly. The relative efficiency with 0.51 MeV effective neutron detection threshold agrees with the Monte Carlo calculation result of NEFF. The response function from 0.5 MeV to 5 MeV generally agrees with the published experimental result of the NE213 scintillator of the same size.
ATOMIC AND MOLECULAR PHYSICS
Density functional theory study on the structure and electronicproperties of Aun Sc3 (n =1—7) clusters
2011, 60 (3): 033101. doi: 10.7498/aps.60.033101
Geometric structures of Aun Sc3 (n=1—7) clusters are optimized by using the generalized gradient approximation (GGA) density functional theory. Energy, vibrational frequency and electronic properties have been calculated. The 3D structure of AunSc appears earlier than that of Aun. The triangle bipyramid structure of Au2Sc3 is a building block for larger AunSc3 of n≤7. Furthermore, the investigation on the second-order difference shows that the clusters with even Au atoms have enhanced stabilities, which may be due to the electron shell effects.
2011, 60 (3): 033201. doi: 10.7498/aps.60.033201
Direct write atom lithography is a new technique in which resonant light is used to pattern an atomic beam and the nanostructures are formed when the atoms deposit on the substrate. The motion of sodium atoms in standing wave filed is discussed. Based on the semi-classical model, this paper analyses the motion equation of sodium atom in the laser standing wave field, and then gets the trajectory of the atoms in the standing wave field by analytical simulation for different longitudinal and transverse velocities. The simulative results show that the FWHM width of stripes was 2.78 nm and the contrast was 38.5 ∶1 for the optimal longitudinal velocity, while that of the stripes was 29.1 nm and the contrast was 15 ∶1 for non-optimal longitudinal velocities. At the same time, the results show that the FWHM width of stripes was 4.2 nm and the contrast was 20 ∶1 when the divergence of atomic beam was 0.15 mrad. Whereas, the stripes presented Multi-peaked configuration and the quality deteriorated with the divergence of atomic beam increased to 1.5 mrad.
2011, 60 (3): 033202. doi: 10.7498/aps.60.033202
A scheme to efficiently generate a broadband short attosecond pulse is presented by using intense multi-cycle 800 nm laser in combination with its 27th harmonic (H27) laser pulse. It is shown that the electronic dynamics can be efficiently controlled by the 1 fs H27 laser. Setting the H27 laser to the multi-cycle 800 nm laser at a proper time, we can control most of the ionizations to occur at half the optical cycle, and the short quantum path can be picked out, thus the harmonic plateau is heightened four orders of magnitude compared with the case of using the fundamental laser alone. Furthermore, a harmonic supercontinuum spectrum with a bandwidth of 108 eV is produced. By superposing the 140th-210th harmonics in the continuous region, an intense isolated pulse with the duration of 39 as is straightforwardly obtained. Using this method, the bandwidth of the continuum spectrum is 2 times wider, the intensity of the attosecond pulse is greater, and the duration of the attosecond pulse is shorter, in contrast to the scheme proposed in Ref. , which added the ultraviolet attosecond pulse to a few-cycle 800 nm laser.
The wavelength dependence of high-order harmonic generationand attosecond pulses from atom in infrared laser field
2011, 60 (3): 033203. doi: 10.7498/aps.60.033203
Basing on the strong-field approximation, we study high harmonic generation of hydrogen atom exposed to the long wavelength infrared laser field, and analyze the wavelength dependence of conversion efficiency of high-order harmonic generation near the cut-off position. It is found that high-order harmonic yield is much lower near cut-off than in the beginning of the plateau of the harmonic generation, but the width of the attosecond pulse is narrowed with increasing wavelength.
Surface enhanced Raman scattering of pyridazine molecule:absorption configuration and enhancementmechanism via bond polarizabilities
2011, 60 (3): 033301. doi: 10.7498/aps.60.033301
The temporal molecular bond polarizabilities of pyridazine molecule absorbed on Ag electrode were explored from its surface enhanced Raman intensities, showing that the two nitrogen atoms are the absorption sites and the enhancement is dominated by the charge transfer mechanism. The behaviors of the charges on the skeletal bonds were demonstrated under various applied voltages, which shows the conjugation effect. This algorithm is universal for the surface systems as long as their Raman spectra are available.
2011, 60 (3): 033401. doi: 10.7498/aps.60.033401
The thermophysical properties of pure helium-4, neon, argon, krypton and xenon are calculated using ab initio potentials of kinetic theory over the temperature range from 50 to 5000 K at zero-density, including the second virial coefficient, thermal diffusion coefficient and thermal diffusion factor. Comparing with results obtained by empirical potentials, the results of present work are in better agreement with experimental data and recommended values of REFPROP 8.0.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2011, 60 (3): 034101. doi: 10.7498/aps.60.034101
A new 2D left-handed material structural unit is proposed by setting two reversely symmetrical Z metal strips on each side of the dielectric substrate respectively. The structure can present left-handed properties in X waveband, with electromagnetic waves incident either perpendicularly or parallel to the plane of the substrate. By means of numerical simulation, extracting the effective permittivity and permeability from S parameters and building the equivalent magnetic resonance circuits of the structure, the left-handed property is further analyzed and verified. And by comparing the double Z-shape unit with the traditional H-shape unit, it is shown that they have similar responses of presenting left-handed pass band when electromagnetic waves are incident perpendicularly to the substrate, but only the double Z-shape unit can achieve left-handed features when electromagnetic waves are incident parallel to the substrate. The results indicate that the double Z-shape left-handed structural unit is superior to the traditional H-shape structure, namely, the double Z-shape can redound to design left-handed structural unit for double dimension incidence of electromagnetic waves.
2011, 60 (3): 034102. doi: 10.7498/aps.60.034102
Based on the Desantos spectral formalism, using the hybrid method that combines the numerical and approximate algorithms, the reconstruction problem for the one-dimensional rough surface is investigated. For the direct problem, the scattering data is obtained by the numerical algorithm—the method of moments (MOM). For the inverse problem, the profile of rough surface with different roughness is reconstructed by two approximate algorithms—the small perturbation approximation (SPA) and the Kirchhoff approximation (KA) combined with the method of moments. Taking the Gaussian rough surface for example, the numerical results of reconstructed rough surface with different roughness are presented for the hybrid method, and the data are compared and analyzed.
Determination of the optical constants of the magnetron sputtered aluminum oxide films from the transmission spectra
2011, 60 (3): 034201. doi: 10.7498/aps.60.034201
By combining Swanepoel's theory and the Wemple-DiDomenico dispersion model, a simple method was established to determine the optical contants of the magnetron sputtered aluminum oxide films directly from the corresponding transmission spectra. The results showed that the magnetron sputtered aluminum oxide films exhibit the optical characteristics of high refractive index of 1.5661.76 (at 550 nm), negligible absorption in spectral region of 4001100 nm, as well as the direct band gap of about 3.914.2 eV. And the specific values of the optical constants strongly depend on the annealing temperature , which is one of the important technological parameters for the magnetron sputtered aluminum oxide films. Moreover, in the weak and medium absorption spectral regions, the calculated values of refractive indices are in satisfactory agreement with the results derived from the high-resolution Tek3000 film-characterization system, indicating the reliability and feasibility of the method in determining the optical constants of Al2O3films.
2011, 60 (3): 034202. doi: 10.7498/aps.60.034202
The algorithm for three-dimensional information encryption based on the phase extraction is proposed. The three-dimensional information with the pure amplitude and pure phase are constructed as the encryption target. First, the complex amplitude of the three-dimensional information is calculated under the scalar diffraction theory. Then its phase distribution is extracted independently and it is encrypted with the double random phase encoding. The decryption algorithm is just the inverse process as the above. Computer simulations demonstrate the feasibility, the robustness and the security of the algorithm. Further, it is revealed the potential of applying the algorithm for the three-dimensional information encryption with much larger information quantity.
Sequence images hiding technique of three-dimensional object based on principal component analysis in wavelet domain
2011, 60 (3): 034203. doi: 10.7498/aps.60.034203
In order to hide sequence images of 3D object in a carrying image, eigenimages are obtained by using principal component analysis method. Wavelet coefficients of eigenimages are embedded into the wavelet domain of the carrying image. Based on the relationship of extracted eigenimages and coefficients, a series of images are reconstructed. The proposed method does not store the object images directly, but store the eigenimages which contain information of the 3D object. The experimental results show that the features of 3D object are effectively embedded into the carrying image, and the proposed algorithm has a high capacity.
2011, 60 (3): 034204. doi: 10.7498/aps.60.034204
In the study of color digital holography, using the spherical wave as the reconstruction wave, the wave-front reconstruction with the angular spectrum diffraction formula is an effective approach. However, this method is usually accompanied by intense zero-order diffraction interruption. In this paper, based on the theoretical analysis, an important modification of the wave-front reconstruction process has been made. The color digital holography experiment result demonstrated that the quality of reconstructed color image has been improved remarkably with this modified method.
The use of dynamic cavity environment to achieve controlling of the process of spontaneous emission of an atom
2011, 60 (3): 034205. doi: 10.7498/aps.60.034205
In the paper, we theoretically discuss the use of dynamic cavity environment to realize controlling of the evolution of spontaneous emission from an excited two-level atom. It is found that cyclical changes in cavity environment leads to the interaction betwcen the electromagnetic modes, resulting in the redistribution of the electromagnetic modes density; both the frequency of energy exchange and the energy dissipation rate between atom and environment are affected. When the frequency of environment change is relatively accordant with the process of energy exchange between the atom and environment, the decay rate is obviously inhibited and a stable coherence evolution can be obtained. Thus the evolution of coherent states can be modulated by using dynamic environment changes.
Micro-nano-optical machine system tunable wavelength vertical cavity surface emitting lasers with wide tunable range
2011, 60 (3): 034206. doi: 10.7498/aps.60.034206
The stucture of tunable vertical cavity surface emitting laser is obtained based on the micro-nano-mechanical technology. The DBR reflector with Al0.8Ga0.2As sacrificial layer consisted the micro-nano reflector systerm, which combines with the multi-well active region coupled structure. In addition, the structure of micro-nano-optical machine system is not only the DBR reflector, but also serves to tune the wavelength of lasing by the electrostatic force. Good laser characteristics are obtained with continuous tuning ranges over 18.8 nm near 968.8 to 950 nm for 0—7 V tuning bias.
2011, 60 (3): 034207. doi: 10.7498/aps.60.034207
The resolution of adaptive optics confocal scanning laser ophthalmoscope is constrained by human eye’s aberration, numberical aperture and pinhole size. A super resolved adaptive optics confocal scanning laser ophthalmoscope is presented. By using adaptive optics to detect and compensate human eye’s aberration, and using optical superresolution to improve resolution which is degraded by large pinhole size, the system can achieve high resolution, real-time human retina image in vivo .
Optimization of medium and control characteristics of stimulated Brillouin scattering based on mixed media
2011, 60 (3): 034208. doi: 10.7498/aps.60.034208
In this paper, the optimization of medium and control characteristics of stimulated Brillouin scattering (SBS) based on mixed media is investigated. The excellent intersolubility of perfluorocarbon liquid media is analyzed and the dependence of gain coefficient, phonon lifetime and Brillouin frequency shift of HT-230/FC-72 mixed media on mixing-ratio is numerically simulated. In Countinuum’s Nd: YAG seed-injected laser system, we measured absorption coefficient, optical breakdown threshold, energy reflectivity and Stokes pulses waveform of HT-230/FC-72 mixture under different mixing-ratio. The results indicate that the mixed media not only can optimize the medium, but also can control the characteristics of SBS within a certain range.
2011, 60 (3): 034209. doi: 10.7498/aps.60.034209
The triangular Au nanoparticle array of size 37 nm was fabricated on a quartz substrate using nanosphere lithography. By performing the Z-scan method with femtosecond laser (800 nm, 50 fs), the optical nonlinearity of the Au nanoparticle array was determined. The results showed an intensity-related two-photon absorption saturation processes. As the excitation intensity increases, the nonlinear absorption changes from two-photon absorption to saturated absorption, while the nonlinear refraction exhibits self-defocusing effect. The one- and two-photon figures of merit, W=7.5 and T=0.12, were obtained, validating a high efficiency nonlinear material for all-optical switching.
2011, 60 (3): 034210. doi: 10.7498/aps.60.034210
A novel mechanism of cascaded difference frequency generation (DFG) is advanced in this article to solve the problem of low-efficiency in terahertz (THz) DFG. The cascaded DFG process is theoretically analyzed using ZnTe crystal as an example. The optimal pumping condition and crystal length is obtained, and the effects of crystal absorption, wave number mis-match and pumping intensity are investigated by solving the coupling wave equations of cascaded DFG. It is obviously seen from the calculation results that the terahertz conversion efficiency can be greatly enhanced in cascaded DFG, in which the photon conversion efficiency can even break through the Manley-Rowe limit.
2011, 60 (3): 034211. doi: 10.7498/aps.60.034211
Basing on the accurate Gaussian analytical solution of a pair of (1+2)D optical spatial solitons with symmetrical oblique incidence,we investigated the short-range interactions in the strongly nonlocal nonlinear media.Two solitons in close proximity can be intertraped via the strong nonlocality ,and propagate together in a stable spiral and the trajectory of mass center of solitons will deflect because of the phase difference and the ratio of the power of two solitons under the condition of momentum conservation. It is possible to find its application in planar all-optical interconnection in bulk media.We analyszed the evolution of the Poynting vector as they propagate through the strongly nonlocal media.
2011, 60 (3): 034212. doi: 10.7498/aps.60.034212
This paper presents calculations based on the idea of photorefractive polymer spatial solitons, namely, screening solitons being formed in a biased series photorefractive polymer circuit consisting of two photorefractive polymer connected electronically by electrode leads in a chain with a voltage source. A system of two coupled equations is derived under appropriate conditions for two-beam propagation in the series photorefractive polymer circuit. The existence of dark-dark, bright-dark and bright-bright photorefractive polymer soliton pairs in such a circuit is proved. In the limit in which the optical wave has a spatial extent much less than the width of the photorefractive polymer, the two solitons in dark-dark soliton pairs can affect each other’s spatial profiles and the dynamical evolution by the light-induced current. For a bright-dark soliton pair, the dark soliton can affect the other soliton by light-induced current, but the bright soliton cannot. The two solitons in bright-bright soliton pairs cannot affect each other.
2011, 60 (3): 034213. doi: 10.7498/aps.60.034213
Forbidden gaps of one-dimensional compound photonic crystals consisting of cholesteric liquid crystals sandwiched by periodic isotropic layers are investigated. The common forbidden gaps appear for both incident left and right polarization light which is different from the cholesteric liquid crystals. The forbidden gaps for incident left polarization light will disappear and the forbidden gaps for incident right polarization light will merge and become wider with the increasing of thickness ratio of cholesteric liquid crystals to periodic isotropic layers. The effect of forbidden gaps for incident left and right polarization light becomes obvious with the increasing of refractive index of periodic isotropic layers. The corresponding forbidden gaps for two colors of red, green and blue will appear by tuning thickness ratio of cholesteric liquid crystals to periodic isotropic layers and the refractive index of periodic isotropic layers, which can be used to fabricate reflective color filters for liquid display.
2011, 60 (3): 034214. doi: 10.7498/aps.60.034214
The grating fabrication technology with heat method in photonic crystal fiber based on its structural change is researched. The principle of photonic crystal fiber grating is analyzed theor etically. Heat transfer theory and finite element method are both used to analyze the thermal field distribution in the fiber, as well as the influence of air hole structure in the cladding, and the parameters of laser beam in the process of grating fabrication are discussed. The research results show that the grating can be formed by the periodic air hole collapse in the cladding of photonic crystal fiber. Under double-point heating, the energy will be uniformly distributed in the radial direction and approximated by the Gaussian distribution in the axial direction. The collapsed air holes in the cladding accelerate the process of forming grating. In the same size of luminous spot, as the layers and the radii of air holes increase, the laser power for collapsing fiber decreases. Moreover, the relationship between laser power and air filling rate is obtained by stimulating the grating fabrication process in photonic crystal fiber with 1 to 7 layers of air holes. This kind of photonic crystal fiber grating can improve the thermal and long-term stability of conventional grating, and so it will have great potential applications in the relevant fields of optical fiber sensors.
2011, 60 (3): 034215. doi: 10.7498/aps.60.034215
The zigzag grating is one of the newly proposed optical dispersive elements which has an excellent diffraction characteristics and has important applications in the spectrum measurement and analysis. The simulation results of the diffraction pattern of the zigzag grating for X ray are presented using a new numerical method based on the convolution theorem, and comparison of its diffraction pattern with those of the traditional grating and sinusoidal grating are studied. It is seen from the results that all higher order diffractions of the zigzag grating are suppressed below the level of four orders of magnitude compared with the first order diffraction, which is superior to the traditional grating, being consistent with the theoretical expectations. Moreover, the impact caused by the absorber is analyzed, which eventually confirms that the zigzag grating has perfect practical application feasibility. The conclusions provide a potential alternative for the physical design of the zigzag gating, which is expected to replace the traditional transmission grating in applications to the soft X-ray spectrum measurement.
Experimental calibration of transmission grating and theoretical calculation of diffraction efficiency
2011, 60 (3): 034216. doi: 10.7498/aps.60.034216
Transmission grating is widely used in measurement of soft X rays. In order to measure the diffraction efficiencies of the transmission grating which is used in laser fusion, the transmission grating was calibrated on Beijing Synchrotron Radiation Facility in the energy region from 200eV to 1600eV, and the experimental results have been obtained. The model for grating efficiency simulation has been developed and calculations using a new so called 7-side quasi-trapezoidal cross section model were carried out. The results from the new model are in good agreement with the experimental data. The exact grating wire cross section is described.
Analysis of coupling characteristics of midinfrared high polarization chalcogenide glass dual-core photonic crystal fiber
2011, 60 (3): 034217. doi: 10.7498/aps.60.034217
A kind of chalcogenide glass midinfrared dual-core photonic crystal fiber has been proposed in this paper. The coupling characteristic of this fiber has been studied by multipole method using the basic theory of coupling. It is found that the birefringence of dual-core PCF with pitch 5.4 μm, air-hole radius 1.35 μm and air-filling fraction 0.5 is 0.551×10-2 at normalized frequency λ/Λ = 2.04 μm. At normalized frequency λ/Λ = 0.93 μm, coupling lengths are 145.32 μm and 154.68 μm for x-polarized mode and y-polarized mode, respectively. The band extended to midinfrared. This dual-core photonic crystal fiber with coupling length and high polarization is useful for manufacturing midinfrared band optical fiber coupler.
2011, 60 (3): 034218. doi: 10.7498/aps.60.034218
Novel conformal window can enhance the aerodynamic performance of aircraft obviously. Due to the surface complexity of these conformal windows, the measuring of conformal windows is infeasible by using the conventional optical measurement technique. In this paper, we describe a new sub-aperture stitching method for conformal measurement, and introduce the design of this technology. Based on the theory of compensation method, a compensator is designed for a 70mm aperture conformal window, of which the final residual wavefront error(RMS) is 0.0515λ(λ=632.8nm).
2011, 60 (3): 034301. doi: 10.7498/aps.60.034301
Transmission characteristics of elastic wave in solid-solid cylindrical phononic crystal are obtained under condition of restrictied transrerse elastic wave, and the characteristics of mode is studied. Transmission characteristics of elastic wave versus mode quantum number and cylinder radius are calculated by the transfer matrix method. The new characteristics of elastic wave in solid-solid cylindrical phononic crystal are obtained. Transmission characteristics of elastic wave are determined by the mode quantum number and cylinder radius.
2011, 60 (3): 034302. doi: 10.7498/aps.60.034302
In this paper, we present a metamaterial beam consisting of a uniform isotropic beam with many small mass-spring systems serving as mechanical wave absorbers. Based on the analysis of two different mass-spring systems, negative effective mass and negative effective stiffness are explained theoretically. The governing equations of a unit cell of a metamaterial beam are derived using the Hamilton’s principle. The mechanical wave absorbabilities of the following two different finite metamaterial beams are analyzed by numerical simulation:one is the bean in which mass-spring systems with linearly varying elastic coefficients are uniformly distributed, and the other is the bean in which four identical absorber subgroups composed of spring-damper subsystems with linearly varying natural frequenciesare uniformly distributed. The results reveal that the mechanical wave transmitted in the metamaterial beam is absorbed by resonating with spring-mass absorbers, which verifies the effectivity of the proposed metamaterial beam on mechanical wave absorption.
2011, 60 (3): 034501. doi: 10.7498/aps.60.034501
A special Chaplygin system is studied numerically by using the symplectic geometric algorithm and compared with the classical R-K method. By comparing the results of the two methods, the advantage of symplectic geometric algorithm used on this special Chaplygin mechanical system is demonstrated.
2011, 60 (3): 034502. doi: 10.7498/aps.60.034502
Granular matter is a large assemblage of dense packed particles. A granular skeleton frame is linked by grain-to-grain contacts. An external loading is usually transmitted through selective pathways from the skeleton frame, and heterogeneous force chain architecture is formed. The formation and evolution of shear band have importarit bearing to the stability of a granular assembly. In this work, the mechanical properties of granular matter under biaxial test are studied by using DEM simulations. Evolutions of stress, volumetric strain, coordination number, distribution of particle rotation and solid fractions are analyzed. The results show that within shear zone the solid fraction is smaller and the coordination number fluctuates violently, which indicates that they are unjammed, while beyond the shear band the particles are jammed. Therefore, we could say that the shear band actually corresponds to the complicated jamming transition. Three types of force chain configurations are observed under different axial strains: circle-shaped, column-shaped, both column and vortex-shaped. Such structures would be dominant to the mechanical properties of macro-mechanical properties and granular system, and pending further studies.
Centreline statistics of the small-scale turbulence of a circular jet and their dependence on high frequency noise
2011, 60 (3): 034701. doi: 10.7498/aps.60.034701
This study systematically investigates the statistics of the centreline small-scale turbulence of a circular jet issuing from a smooth contraction nozzle. Detailed velocity measurements were performed for the exit Reynolds number of Re=20100, where Re≡Ujd /ν with Uj being the exit mean velocity, d the nozzle diameter and ν the kinematic viscosity. After effectively filtering out high frequency noises, statistical properties of the small-scale turbulence were obtained appropriately; those properties include turbulence energy dissipation rate, Kolmogorov length scale, Taylor scale, turbulence Reynolds number, skewness and flatness of the velocity derivative. It is observed that these properties satisfy their self-preserving relations in the far field. It is also revealed that the small-scale turbulence reaches the self-preserving state earlier than does the large-scale motion. Besides, the smallest-scale turbulence depends least on the initial and boundary conditions and therefore behaves most universally across different flows.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2011, 60 (3): 035201. doi: 10.7498/aps.60.035201
The relevant facts to phase of relativistic klystron amplifier (RKA) are analyzed in this paper. The output microwave phase of RKA relevant to voltage, current, size, rising time and delay time of electron beams is simulated by PIC. It is found that the phase shift of RKA is changed with the voltage, current and size of electron beams. On the contrast, the leading magnetic field, rising time and delay time of electron beams do not change the phase shift of RKA obviously. The phase of RKA is investigated in experiment too. The phase sensitivity of RKA is about 2.6 degrees; the phase shaking of RKA is less than 20 degrees. The experimental results are content well with the simulations.
Generation of attosecond X-ray pulse in the interaction between the pulses and the relativistic electrons
2011, 60 (3): 035202. doi: 10.7498/aps.60.035202
The attosecond X-ray pulse which is produced by the interaction between the laser pulse and the relativistic electrons is studied in this paper. The attosecond X-ray pulse is generated by Thomson backscattering from the relativistic electrons. It also discusses the effect of the plasma parameters on the attosecond X-ray. The wavelength of attosecond X-ray pulse becomes shorter when the frequency of the laser or the velocity of the relativistic electrons increases. We obtained the "water window" X-ray by selecting the appropriate laser and plasma parameters. This paper also discusses the effect of relativistic electrons density and density grad on the translation efficiency.
2011, 60 (3): 035203. doi: 10.7498/aps.60.035203
The arc temperature field, electric field and size of conducting zone of gliding arc plasma are important parameters to determine the temperature and density of the electrons, the chemical reaction rates and energy efficiency. Electrical parameters of a 50 Hz ac gliding arc discharge were measured under conditions of two gas flow rates, 1.43 L/min and 6.42 L/min. An instantaneous model which was used to describe the energy transfer of gliding arc discharge was simplified by using an approximate expression for the electrical conductivity and diffusivity of plasma, which ravelled out the moving boundary in the gliding arc simulation resulting from variation of arc structure. The current density, electric field, dynamic temperature field and the structure of ac gliding arc was calculated. The electric field strength from the simulation result of the model was in agreement with the experimental data. According to the calculational result, the temperature on the axis of arc reached as high as 5700—6700 K. It showed the gas flow directly affected the arc structure and current density, thus further affected the electric field strength and temperature distribution. The electric field strength increased firstly and then decreased during a discharge period.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
The evolution of crystalline structure in the preparationof PAN-based carbon fibers studiedby whole powder pattern fitting
2011, 60 (3): 036101. doi: 10.7498/aps.60.036101
Based on the Rietveld theory and Maud software, the evolution of crystalline structure of PAN-based carbon fibers was studied by investigating the different stages in the preparation of carbon fibers. The microstructure parameters of PAN fibers, oxidative fibers, and carbon fibers, including cell parameters, apparent crystal grain sizes, textural structure and micro-strain, were obtained from the named whole powder pattern fitting method for XRD result. Based on rigorus theory of crystallography, the whole powder pattern fitting treats the whole XRD powder diffraction pattern rather than individual diffraction peaks, resulting in higher credibility and precision. The results indicated that polymer chains were arranged along the axis of PAN fiber and the apparent crystallite size was about 6.4 nm. After pre-oxidation, the originally ordered structure in PAN fiber was damaged and new less-ordered cyclic ladder structure was formed in the pre-oxidized PAN fibers, while the apparent crystallite size of fiber decreased obviously. With the carbonization process, the cyclic ladder structure of per-oxidized fibers transferred into layer structure similar to that of graphite. The layers were oriented along the axis of carbonized fiber that contributed to the X-ray diffraction, which comprised the apparent crystallite grains. As the carbonization temperature increased, size of the layer structure in the direction perpendicular to fiber axis increased clearly, the preferential orientation was enhanced and the layer structure became much more ordered.
2011, 60 (3): 036102. doi: 10.7498/aps.60.036102
Two kinds of poly(methyl methacrylate)/gallium (PMMA/Ga) nanocomposites with different Ga contents (11.3% and 13.5%) were prepared by free radical polymerization. The relaxation dynamics of PMMA/Ga nanocomposite above the glass transition temperature has been investigated by mechanical spectroscopy. It was found that the peak temperatures of α relaxation of the nanocomposites increase with the increasing Ga content, but the peak heights of α relaxation decrease. Besides, the composition-dependent dynamics of the α' relaxation in PMMA/Ga nanocomposites was also studied.
2011, 60 (3): 036103. doi: 10.7498/aps.60.036103
InAs/GaAs and InAs/In xGa1-xAs/GaAs nanowire heterostructures are grown by metal organic chemical vapor deposition via Au-assistant vapor-liquid-solid mechanism. We find that the InAs nanowires grow directly on GaAs nanowires in a random way, or they grow along the sidewall of the GaAs nanowires, and thet InAs nanowires grow vertically on GaAs nanowires by using an In x Ga1-xAs (0≤x≤1) buffer segment. It can be concluded that the influences of crystal lattice mismatch and difference in interfacial energy can be eliminated by inserting a ternary compound semiconductor buffer segment, thereby improving the crystal quality and the capability to control the growth of nanowire heterostructure.
First principles calculations of interaction between an armchair-edge graphene nanoribbon and its graphite substrate
2011, 60 (3): 036104. doi: 10.7498/aps.60.036104
Based on the density functional theory, first principles calculations have been performed to study interaction of armchair-edge graphene nanoribbons and their graphite substrates. As a result, it has been found that the interaction gives rise to deformation of the graphene nanoribbons and the graphite substrates, and the deformed graphene nanoribbons have the energy band structures with band gaps smaller than those of the isolatedones.
Characterization of the transparent n-type ZnO ceramic with lowresistivity prepared under high pressure
2011, 60 (3): 036105. doi: 10.7498/aps.60.036105
In this paper,the preparetion of transparent ZnO ceramic with with low resistivity by high pressure sintering was reported,and the problem of high resistivity and opaqueness for ZnO under atmospheric pressure sintering was solved. The ZnO ceramic of optimal photoelectronic performance with high transparency and low resistivity under the pressure of 5 GPa and at the temperature of 800℃ was obtained. The transmissivily is about 49%, the electronic resistivity is 0.57 Ω ·cm, the width of band gap is 3.31 eV, the carrier concentration is 8.36×1017 cm-3 and the mobility is 23 cm2 ·V-1 ·s-1. The excellent n-type electrical conductivity is attributed to the contribution of Zni and VO donor defect. The results of this work have important significance for ZnO ceramic application as photoelectronic components for ultraviolet emission.
Research on the total-dose irradiation damage effect for static random access memory-based field programmable gate array
2011, 60 (3): 036106. doi: 10.7498/aps.60.036106
In order to investigate the total-dose irradiation effects of Altera static random access memory (SRAM)-based FPGA (field programmable gate array), the irradiation response of basic cell of FPGA, i.e. the CMOS, is studied, and the relationship of the output waveform as a function of total dose has been obtained. It indicates that the output waveforms become aberrated and the peak-peak value turns to about 1/10 of the initial value as the total dose increased, resulting from the degradation of leakage current both from field oxygen and the structure; but there are relatively high and low levels left in the output waveforms. Meanwhile, the high level cant keep the already existing state and changes to the low level, and the conversion speed is accelerated with the increase of the total dose. The low level becomes larger than the initial value. As the gate-oxygen is quite thin, the rise time, fall time, and delay of the output waveforms change little with the total dose.
Effect of vacuum thermal-annealing temperatures on the microstructure and optical properties of single-phased Ag2O film
2011, 60 (3): 036107. doi: 10.7498/aps.60.036107
A single-phased Ag2O film was deposited on glass substrate by direct-current reactive magnetron sputtering, and was then vacuum thermally annealed at different annealing temperatures (T A) for 1 hour. Effect of the TAon the films microstructure and optical properties was investigated by X-ray diffractometry, scanning electron microscopy and spectrophotometry. The results indicate that Ag nano-scaled particles begin to appear in the annealed Ag2O film at TA= 300 ℃. The Ag content obviously increases with increasing TA, and in particular, Ag2O phase is completely transformed into Ag at T A = 475 ℃. The evolution of the films surface morphology from dense to loose indicates that the diffusion and escape of O atoms from film surface accompanied the thermal decomposition reaction of Ag2O to Ag particles during the vacuum thermal annealing. The changes of the films transmissivity, reflectivity and absorptivity with T A are attributed to the thermal decomposition of Ag2O and the films structure evolution during annealing.
2011, 60 (3): 036301. doi: 10.7498/aps.60.036301
Based on density functional theory of the first-principle, the electronic structures of LiFexPO4 (x=0.0, 0.75, 1.0) are calculated. The calculated results show that Fe3d states restrained by crystalline field cannot contribute to free electrons even though Fe3d states cross the Fermi level. Meanwhile, Fe—O bond is beneficial to stabilize the alloy structure due to the p-d hybrid orbital. With lithium ion extraction, the enhanced covalent bonds appear. In LixFePO4 system, the strength of covalent bond is in the order of P—O>Fe—O>Li—O. LixFePO4 system displays brittleness of material characteristic, and the LixFePO4(x=1.0, 0.75) with lithium intercalation have stronger average bonding strength than that of FePO4.
2011, 60 (3): 036401. doi: 10.7498/aps.60.036401
Based on the analysis of ferromagnetic mechanism of diluted magnetic semiconductors (DMSs), an Ising model with multi-exchange interactions is established. The reason of the shape of ferromagnetic order is simulated by Monte Carlo (MC) simulation with the Metropolis algorithm. The result reveals that the lower concentrations of Mn doping (x) are helpful for forming the ferromagnetic order. However, with the lower concentrations of Mn doping the magnetization of the system will be smaller and the Courier temperature will be lower. The modifying efect of carrier on the formation of ferromagnetism is enhanced with the increase of x and the decrease of the anisotropy constant (K). This work predicts that the increase of K will heighten the ferromagnetism and the Courier temperature.
2011, 60 (3): 036402. doi: 10.7498/aps.60.036402
The metastable phase separation and rapid solidification of ternary Co-Cu-Pb monotectic alloys have been investigated under free fall condition. With the decrease of droplet diameter, the microstructures of Co51Cu47Pb2 and Co47Cu44Pb9 alloys display a "dendrite→core-shell→dendrite" transformation and a morphology transition from core-shell to homogeneous microstructure, respectively. X-ray diffraction analysis indicates that the solidified microstructures are composed of α(Co), (Cu) and (Pb) phases. α(Co) and (Cu) phases grow mainly in dendritic manner, and (Pb) phase is distributed interdendritically among (Cu) phase. Both experimental results and theoretical calculations reveal that the interfacial energy between (Co)/(Pb) liquid phases is larger than thoses of (Co)/(Cu) and (Cu)/(Pb) phases. The weak wetting ability between (Co) and (Pb) liquids results in the distribution of (Pb) phase inside the Cu-rich zone instead of Co-rich zone. Three possible solidification routes are deduced according to the solidification microstructure, in which the solidification process consists of phase separation L→L1(Cu)+L2(Co), peritectic transformation α(Co)+L→(Cu) and monotectic transformation L(Cu)→S(Cu)+L(Pb).
Computer simulation of the string relaxation modes of the molecule-string model for glass transition
2011, 60 (3): 036403. doi: 10.7498/aps.60.036403
Monte Carlo protocols to simulate the string relaxation modes are proposed according to the Hamiltonian of the molecule-string model for glass transition. The simulated relaxation times of the 1st and 2nd modes are consistent with the predictions of the string relaxation equation of the model,thus matually verifying each other. The results show the reasonableness of not only the string relaxation equation, at least the theoretical predictions of the 1st and 2nd relaxation modes, but also the proposed simulation method, and further clarify the pictures of the molecule random energy fluctuations and jumps of the molceules in the strings, as well as provide gist and clews to the study of the multi-state molecule string relaxation dynamics and the further simulation of the complex interactions between the molecule strings.
2011, 60 (3): 036501. doi: 10.7498/aps.60.036501
Using trans-2-butene and hydrogen as the precursor, the glow discharge polymer films was successfully coated on KBr discs by glow discharge polymerization at different powers. The chemical structure, thermal stability of the GDP films and the deposition rate of GDP films were characterized by the FT-IR, TG and surface profiler technology. The Results show that the deposition rate, the olefinic structure, the ratio of C/H, and the content of C C in GDP films increase with the RF power increasing. The thermal stability of GDP films fabricated at higher RF power is better.
2011, 60 (3): 036601. doi: 10.7498/aps.60.036601
In order to effectively analyze the statistical power consumption of RC interconnect tree with process fluctuation, a method of constructing interconnect parasitic parameters and driving point admittance moments is first presented in this paper. Then, the expressions of mean and standard deviations of interconnect power consumption are obtained. The calculation results indicate that the errors of mean and standard deviations are less than 4.36 % and 6.68 % respectively compared with those calculated by the widely used Monte Carlo method. Results show that the proposed method has a good accuracy and high efficiency.
2011, 60 (3): 036801. doi: 10.7498/aps.60.036801
SrTiO3 ultra-thin film was deposited on the Sr/Si(001) surface using pulsed laser deposition (PLD) at room temperature and studied using scanning tunneling microscopy (STM). After annealing at 660 ℃ for about 60 minutes in ultrahigh vacuum (UHV), nanosize islands were formed on the Sr/Si(001) surface. High resolution STM images and dI/dV mapping of islands on Sr/Si(001) were obtained. The islands can be attributed to TiSi2 islands with C49 and C54 structures. The existence of Sr on Si is not sufficient to prevent the reaction between Si and Ti in preparation of ultra-thin SrTiO3 films.
The type identification of dislocation loops by TEM and the loop formation in pure Fe implanted with H+*
2011, 60 (3): 036802. doi: 10.7498/aps.60.036802
This paper is divided into two parts: the first part is to identify the type of dislocation loops in materials by using TEM. The inside-outside method to identify V-loops or I-loops is described in detail. The second part discusses the dislocation loops in pure Fe implanted with H+ in a accelerator and followed by aging at 673—773 K.
2011, 60 (3): 036803. doi: 10.7498/aps.60.036803
TiO2 thin films were prepared by direct current magnetron sputtering on glass substrates, then were implanted by cobalt ions, and finally annealed at 500 ℃ for 50 min. Specimens for transmission electron microscopy were prepared by peeling-scattering technology, and were observed in situ by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and high resolution transmission electron microscopy (HRTEM). The films were identified as anatase structure. The Co ions exist mainly in a thin layer beneath the surface of the films. The implanted Co ions damage the TiO2 crystals and some of them exist as CoO. The annealing treatment could repair the TiO2 grains and make the Co ions diffuse into the TiO2 lattice. The vibrating sample magnetometer (VSM) measurements show that the Co ion implanted TiO2 films are ferromagnetic at room temperature and the annealing treatment in vacuum could enhance the ferromagnetism, which could be explained within the scope of the BMP theory.
Influence of oxygen partial pressure on the crystal quality and optical properties of Mg-doped ZnO films
2011, 60 (3): 036804. doi: 10.7498/aps.60.036804
Zn1-xMgxO films have been deposited on Al2O3(0001) substrates at different oxygen pressures by using pulsed laser deposition method. The influence of oxygen pressure on the crystal quality and optical properties of the films is studied with X-ray diffraction (XRD), transmittance spectra, and photoluminescence (PL). It is found that the crystal quality of the films lowers with increasing of oxygen pressure from 10-4Pa to 10 Pa. At the pressure of 10-4 Pa, the epitaxial relationship between the film and sapphire substrate is determined to be ZnMgO (0001)// Al2O3(0001),ZnMgO 1010]//Al2O3 1120]. In the oxygen rich environment, however, another epitaxial relationship, ZnMgO (0001)//Al2O3(0001) and ZnMgO 1010]//Al2O3 1010], is also present in the films, which is suggested to be responsible for the decline of the crystal quality. Compared with pure ZnO films, the UV peak of Zn1-xMgxO alloys shows red-shift from 3.374 to 3.332 eV with increasing oxygen working pressure increasing from 10-4 Pa up to 10 Pa. The difference in red-shifts can be attributed to the decrease of Mg content in the films resulting from the variation of oxygen pressure. A broad UV PL spectrum was observed at 10 K in the films deposited under different pressures and can be decomposed into two recombination processes of excitons, corresponding to the bound and the localized exciton luminescence, respectively. The binding energy of bound excitons in the ZnMgO films is larger than that in pure ZnO and has an increasing trend with increasing oxygen pressure.
2011, 60 (3): 036805. doi: 10.7498/aps.60.036805
Erbium oxide coatings were fabricated by midfrequency pulsed reactive magnetron sputtering by varying the deposition conditions with respect to the sputtering power from 78 W to 124 W and substrate temperature from room temperature to 677 ℃. Atomic force microscopy, nanoindentation, X-ray diffraction and grazing incidence X-ray diffraction were used to investigate the coatings’ surface morphology, mechanical properties and crystallization behaviors. Electrical properties of the coatings were also measured. Erbium oxide coatings fabricated by pulsed magnetron sputtering have high deposition rate, varying from 28 nm/min to 68nm/min. A monoclinic Er2O3 phase is obtained in the coatings. The crystalline quality of the coatings decreases with the increasing of the sputtering power. The diffraction intensity of monoclinic phase decreases as the substrate temperature was increased from room temperature to 500 ℃ and 677 ℃. It is believed that the high deposition rate and low substrate temperature could lead to the formation of the monoclinic Er2O3 coatings. The hardness and elastic modulus of the coatings deposited at substrate temperatures from room temperature to 677 ℃ vary from 11.9 GPa to 15.7 GPa and from 179 GPa to 225 GPa, respectively. The coatings deposited from room temperature to 677℃ all have high resistivity, varying from 1.5×1012 Ω ·cm to 3.1×1012 Ω ·cm, meeting the requirements of the insulating coatings in application to fusion reactor.
Ballistic phonon transport and thermal conductance in multi-channel quantum structure at low temperatures
2011, 60 (3): 036806. doi: 10.7498/aps.60.036806
By using the elastic approximation model and scattering matrix method, we investigated the acoustic phonons transport and thermal conductance in a H-branch four-channel nanostructure. The calculated results show that, for the incident acoustic phonons of low frequency, as long as the transverse width of each channel is equal, the transmission coefficient of mode 0 in each channel almost equals 0.25 and receives no influence from the changes of the other structure parameters. But for the incident acoustic phonons of high frequency, the transmission coefficient of mode 0 in each channel is very sensitive to the structure parameters and there is bigger difference corresponding to the transmission coefficients of different channels. When the temperature is very low, the thermal conductance in each channel is about 1 4 π2k2BT/(3h). With the increase of temperature, the thermal conductance of each channel changes to different degrees. By changing the length of scattering region or the transverse width of each channel, we can control the separating degree of modes and the thermal conductance of each channel efficiently and realize acoustic phonon selective transport and thermal conduction.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2011, 60 (3): 037101. doi: 10.7498/aps.60.037101
The VASP (Vienna Ab-initio Simulation Package) based on the density-functional theory (DFT) method combined with projector augmented wave (PAW) method is used to calculate the lattice parameters, band gap, density of states (DOS), and formation enthalpy of ZnCdO alloy by considering all the doping configurations. The calculation results indicate that the average parameters of wurtzite (wz) Zn1-xCdxO alloy, a and c, increase linearly, but the ratio of c/a does not change obviously with the increase of Cd content. With increasing Cd content, the band gap is reduced and the variation of band gap can be fitted by Eg(x)=3.28-5.04x+4.60x2, which is consistent with the experimental results. At a given Cd content, different doping configurations result in different Eg values, being one of the reasons of widening of the photoluminescence spectra of ZnCdO alloy. The DOS of wz-ZnCdO alloy in conduction band is shifted towards the lower energy side after Cd doping, causing the reduction of band gap. The reduction of band gap can be attributed to the contribution of 5s states of Cd. By comparing the formation enthalpy of wz-ZnCdO with those of zinc blende and rocksalt ZnCdO alloys, we find that the wurtzite phase of ZnCdO can coexist with zinc blende phase in the range of Cd content from 0.25 to 0.75 and will transit to the rocksalt phase at the Cd content of about 0.80.
2011, 60 (3): 037102. doi: 10.7498/aps.60.037102
The electronic structures of ZnO and (Zn,Al)O are investigated by using the first-principles pseudopotential plane wave method in the generalized gradient approximation. The effects of Al doping on the bonding of ZnO and the interaction between electrons are analyzed from atomic population, bond population, energy band and electronic density of states based on the molecular orbital theory. Carrier concentration of (Zn,Al)O is calculated from the first-principles calculations, furthermore the change in ZnO conductivity is analyzed. The carrier concentration and the conductivity of ZnO are increased significantly by Al doped ZnO compared with the experimental results.
2011, 60 (3): 037103. doi: 10.7498/aps.60.037103
By using the first-principles ultra-soft pseudo-potential (USP) approach of the plane-wave based upon density functional theory (DFT), the energy band structure, electron density of states, difference in charge density and optical properties of the intrinsic β-Ga2O3 and Si-doped β-Ga2O3 were calculated under generalized gradient approximation (GGA). The intrinsic β-Ga2O3 and Si-doped β-Ga2O3 films were deposited on sapphire (0001) substrates by pulsed laser deposition (PLD), the optical absorption spectra and reflectance spectra were measured. The results showed that the whole energy band moved to the low energy side, the conductivity was n-type, the optical band gap increased, the absorption edge shifted to short wavelength, and the reflectivity decreased. The calculation results are consistent with experimental data.
2011, 60 (3): 037104. doi: 10.7498/aps.60.037104
Based on density functional theory with spin-orbit corrections included, the electronic structures of diadochic compounds Bi2Te3-xSex(x≤3) have been calculated by first-principles full-potential linearized augmented plane-wave method. The calculated results indicate that spin-orbit interaction is crucial in understanding the gap structure near the Fermi energy. Bi2Te3-xSex(x≤3) are indirect-gap semiconductors, and there is a saddle point at the Γ point. The density of states near Fermi level mainly consists of p orbitals of each atom. For the chemical bonding of the various layers of atoms, the covalence bond component of X(1)—Bi is stronger than that of X(2)—Bi (X=Te, Se). With the increase of the Se mol ratio in the systems, the unit cell volume is reduced, the energy of the system is increased, and the covalence bond component of Te(1)—Bi, Se(2)—Bi, Se(1)—Bi is gradually enhanced.
Non-solvent addition induced self-organization for enhancement of performance of poly(3-hexylthiophene) organic field-effect transistors
2011, 60 (3): 037201. doi: 10.7498/aps.60.037201
In order to enhance the performance of poly(3-hexylthiophene) (RR-P3HT) organic field-effect transistors (OFET) by low temperature solution-process of non-solvent addition (acetonitrile and ethanol), the resulting self-organization of polymer semiconductor layer and performance of RR-P3HT OFET are studied in this paper. The results fshow that an appropriate non-solvent addition (acetonitrile and ethanol) promotes the formation of more microcrystalline lamellae and improves the self-organization of polymer semiconductor layer, resulting in electrical properties enhancement of polymer OFET. The results indicate that the field-effect of RR-P3HT OFET with 5% acetonitrile addition can reach 3.39×10-3 cm2/V ·s, which is higher by a factor of 8 than that with 0% acetonitrile addition. Encessive non-solvent addition (acetonitrile and ethanol) leads to more precipitates which reduce microcrystalline lamellae and lowers the quality of polymer film, resulting in performance degradation of polymer OFET.
Influence of NPB:CBP modulated hole transporting layer on yellow organic light-emitting device characteristics
2011, 60 (3): 037202. doi: 10.7498/aps.60.037202
Organic light-emitting devices (OLEDs) with the structure of indium-tin oxide (ITO)/N, N'-diphenyl-N, N'-bis(1-naphthyl-pheny1)-1, 1'-biphenyl-4, 4'-diamine (NPB):4, 4'-N, N'-dicarbazole-biphenyl (CBP)/CBP:bis iridium (acetylacetonate) /2, 9-dimethyl-4, 7-diphenyl-phenanthroline (BCP)/Mg:Ag were fabricated. A doping system consisting of NPB and CBP was employed as the modulated hole transporting layer. The electroluminescent characteristics of the OLEDs were investigated by adjusting the concentration proportions of NPB:CBP doping system. The results showed that the hole transporting capability can be adjusted and the power efficiency was remarkably affected by different doping concentration of NPB:CBP system. Optimized yellow light OLED with a maximum power efficiency of 18.1 lm/W was obtained with an optimum concentration proportion of NPB:CBP of approximately 1 ∶3. The improved OLED performance was attributed to the reduction of hole injection and low transporting capability by doping bipolar host material CBP in hole transporting layer, which significantly enhanced charge carrier balance and electron-hole recombination probability.
Influence of spin-coating rate and annealing method of water-soluble CuPc on blue organic light-emitting devices performance
2011, 60 (3): 037203. doi: 10.7498/aps.60.037203
Investigated in this work are the effects of the spin-coating rate of water-soluble copper phthalocyanine (WS-CuPc) and the annealing method of WS-CuPc films obtained at the optimal spin-coating rate on the performances of blue organic light-emitting devices (OLEDs). The OLEDs, eack with a configuration of ITO/WS-CuPc/NPB/Be(PP)2/LiF/Al, are fabricated by using WS-CuPc as hole injection layer, NPB as hole transport layer and Be(PP)2 as emission layer separately. In our experiments, a new annealing method of WS-CuPc is used first for heating the ITO glass, and then for spin-coating the WS-CuPc. The performances of the device prepared with the new annealing method are compared with those of the devices prepared with the traditional annealing method or no annealing treatment. And the effects of different annealing treatments on the surface topography are analyzed by atomic force microscope (AFM). The experimental results demonstrate that there exists an optimal spin-coating rate of WS-CuPc, about 3000 r/min. Based on the optimal spin-coating rate of WS-CuPc, the roughness of the film prepared with the new annealing method is lowest and the performances of the device are best.
2011, 60 (3): 037301. doi: 10.7498/aps.60.037301
For the investigation of the interface stability of SrTiO3/Sr/Si(100) system during high temperature annealing process, we have grown 1—2 atom layer SrTiO3 ultra-thin film on Sr/Si(100)-2×1 substrate using pulsed laser deposition technique. After annealing, we found that nano-scale islands appear in the surface. These nano-islands show metallic property by scanning tunneling microscopy, and the STM image shows bias voltage dependence of these nano-islands. Oxygen in the oxide reacts with silicon and forms volatile silicon monoxide during vacuum annealing, while Ti atoms in the oxide react with silicon, forming C-54 TiSi2 islands.
2011, 60 (3): 037302. doi: 10.7498/aps.60.037302
Using the density-functional theory and the non-equilibrium Greens function method, we investigated the electronic transport properties and rectifying performance of three different molecular devices based on different molecular configurations of the same molecule species. The results show that rotation of a mid-benzene ring (bonding bridge—πbridge) can change the delocalization of a molecular orbital and thus change their transport property and rectifying performance. This finding suggests that the variation of the bonding bridge orientation can control the rectifying performance of a molecular device effectively. It is of significance for designing a novel molecular rectifier.
Non-classical state effect on the persistent current in one-dimensional mesoscopic ring with electron-phonon interaction
2011, 60 (3): 037303. doi: 10.7498/aps.60.037303
Based on the efficacy of the phonon coherent state and with consideration of the non-classical effect of the squeezed state of phonon, the influence of the electron-magnon interaction and the electron-phonon interaction on the persistent current in one-dimensional mesoscopic ring is studied. Compared with the free ring, our study shows that in one-dimensional mesoscopic ring, the amplitude of the persistent current exponentially diminishes due to the electron-magnon interaction. For the normal state electron, the interaction of the electron-phonon causes the persistent current to weakendce to the Debye-Waller effect. However, taking the correlation between the hopping electron states and the one-phonon coherent states into the equation, the ground energy of the mesoscopic system is declined in a large scale. In result, the persistent current In is increased substantially. On the other hand, taking the behavior of the two-phonon coherent state into account, as the effect of the squeezed states of phonons maintains the phase coherence of electrons, so the Debye-Waller attenuation is weakened effectively. Especially, when the squeezed angle is larger, because of the non-adiabatic correlation between the squeezed-phonon states and the coherent states of phonon, it causes a significant decline in the ground state energy and a significant increase in the squeezed angle, thus persistent current has a even more significant increase. It should be pointed out, that the persistent current shows period oscillation as the external magnetic flux changes. Even the external magnetic flux Φem=0, still the persistent current of the intrinsic has I ~ n≠0. The system continuoues to support the equilibrium spin and charge flow, the external magnetic flux only plays the role of an adiabatic parameter.
2011, 60 (3): 037304. doi: 10.7498/aps.60.037304
The transport properties of interface between metal electrode and Nd0.7Sr0.3MnO3 bulk have been investigated under 2-wire measuring mode using permeating Ag and Ag-glue contact, respectively. The results show that, for the permeating Ag contact, the measured results are similar to that of 4-wire measurement, and an ohmic character is obtained without EPIR effect. However, a strongly nonlinear V-I curve appears and exhibits a stable EPIR effect for the Ag-glue contact. Besides, It also shows remarkable difference when loaded with alternating current for the two different kinds of contacts. For the former, the real part of impedance R' increases with increasing frequency which is attributable to the skin effect; for the latter, however, the R' is of about megohm order of magnitude and the R' peak decreases with increasing frequency. Moreover, the R' peak splits into two peaks which respectively move to high and low temperature when further increasing the frequency. In combination with the data of scanning electron microscopy, the differences of electrical transport are discussed.
Thin film transistors with zinc tin oxide as the active channel layer were fabricated on ITO glass by rf magnetron sputtering. SiO2 gate dielectric was grown using plasma-enhanced chemical vapor deposition (PECVD). These devices operate with a maximum field effect mobility of 9.1 cm2/V ·s, threshold voltage of -2 V, and current on/off ratio of 104.
2011, 60 (3): 037306. doi: 10.7498/aps.60.037306
The influence of AC current (with amplitud of Iac ＝0.2—20 mA and frequency of f＝1 kHz—1 MHz) upon the profile of gian magnetoimpedance (GMI) effect of a Fe-based nanocrystalline wire with transverse domain structure have been investigated. The experiment indicates that the GMI effect of the sample exhibits a two-peak feature. With the increasing of f, the peak field Hm increases, while Hm decreases even to H=0 when Iac increases. According to the current theoretical models, the peak field Hm should conrrespond to the transverse anisotropy field Hk, Hm=Hk. However, we found that this conclusion is correct only for the case of very small AC current. So a relationship Hm=Hk cos3θ, where θ is the angle between saturation magnetisation and the axis of wire, has been deduced by minimizing the energy in the process of magnetisation rotation. The experiments can be explained by this result.
2011, 60 (3): 037401. doi: 10.7498/aps.60.037401
Based on the top seeded infiltration and growth technique (TSIG), a novel configuration was employed to fabricate single-domain Gd-Ba-Cu-O (GdBCO) bulk superconductors. And the morphology, microstructure, and superconducting properties of the products were investigated in detail. The results indicate that, employing the novel configuration can increase the supporting ability of the liquid source pellet, and the slope or collapse of the sample during the heat treatment process can be effectively avoided, thus the stability and repeatability of the experiments are advanced. In addition, the novel configuration also contributes to the complete growth of the whole bulk.
2011, 60 (3): 037402. doi: 10.7498/aps.60.037402
Electronic Raman experiments have shown the presence of two types of gaps in hole-doped cuprate superconductors: one is the gap that increases with underdoping and survives in the pseudogap normal state and the other is the gap that traces the superconducting dome and disappears above the transition temperature. This two-gap behavior is important in that it is related to the mechanism of the pseudogap. By calculating the electronic Raman spectra we show that this behavior is consistent with the picture in which the d-wave superconducting (SC) order and d-density-wave (DDW) order compete in the phase diagram. In particular, the energy of the B1g peak is determined by both the SC and the DDW orders, increases with underdoping and survives in the DDW normal state. On the other hand, the B2g peak is shown to be sensitive to the SC order alone, and thus vanishes in the normal state (even if in the presence of the DDW order). The doping dependence and the temperature dependence of the peak energies in the two channels accord nicely with recent experimental results, which strongly supports the competing-order point of view for the superconducting and pseudogap phases.
Microscopic mechanism of the zero-field splitting parameters for 6 S(3d5) state ions at trigonal symmetry crystal filed
2011, 60 (3): 037501. doi: 10.7498/aps.60.037501
The microscopic mechanism of the zero-field splitting parameters (ZFS) including D and (a-F) for 6 S(3d5) state ion in trigonal-symmetry crystal field have been investigated using the complete diagonaliztion method (CDM) by taking into account the spin-spin (SS), the spin-other-orbit (SOO) and the orbit-orbit (OO) magnetic interactions besides the well-known spin-orbit (SO) magnetic interaction. It was found that the contribution to the ZFS parameters D and (a-F) arising from the spin-orbit (SO) magnetic interaction is the most important in most of the crystal field (CF) ranges,but the contribution to the zero-field splitting (ZFS) parameter D and (a-F) from the other three mechanisms, including the SS mechanism, SOO mechanism and OO mechanism, cant be ignored. The ZFS parameters D and (a-F) arise from the net spin quartet states as well as the combined effects of the spin doublet states and the spin quartets states, and the contribution to the ZFS parameters from the net spin doublet states are zero. Our investigation shows that the rank-2 ZFS parameter D primarily results from the net spin quartet states whereas the rank-4 ZFS parameter (a-F) primarily results from the combined effect of the spin doublet states and the spin quartet states. An illustrative evaluation is performed for the typical crystal material Fe3+: Al2O3. Good agreement between the theoretical values and the experimental finding are obtained.
The analytical investigation of the magnetic orientation and hysteresis loop in exchange-spring magnetic multilayers
2011, 60 (3): 037502. doi: 10.7498/aps.60.037502
Using the interface coupling constant Ji and the soft layer thickness Ls as the main variables, the changes of the magnetic moments with the applied field and the hysteresis loops of Nd2Fe14B/α-Fe trilayers, whose easy axes of all layers lie in the film plane, have been investigated. Analysis shows that Ji has significant influence on the magnetic orientation, the pinning field HP and the coercivity mechanism. When Ls is small, HP equals to HN, where the coercivity mechanism transforms from nucleation to pinning as Ji decreases, whereas for large Ls this trend is reversed. The critical thickness, at which the nucleation field and pinning field detaches, decreases as Ji decreases. When the reduced exchange coupling is considered, the rigid composite magnet appears only when Ls is very small. The reduced exchange coupling leads to a sudden change of angle of magnetization at the interface, which results in the change of the behavior of the trilayers from the single-phase one to the two-phase one and in the decrease of HN, whereas HP increases when Ls is larger.
2011, 60 (3): 037503. doi: 10.7498/aps.60.037503
Taking into account the amorphous alloy ribbon with the 180°magnetic domain walls and transverse bias magnetic field, and adopting multi-domain structure model, the theory of giant magneto-impedance (GMI) effect was found by minimizing the total free energy and by the solution of the Maxwell’s equations combining with Landau-Lifshitz equation. A new four-state method is proposed to calculate the average magnetic permeability of four states of the amorphous materials, which is used to replace the permeability obtained based on the single domain model. The method has an advantage in explaining the GMI effect over the theory established by single domain model.
2011, 60 (3): 037504. doi: 10.7498/aps.60.037504
The stability and magnetism in fcc single-crystal nickel nanowires with low-index axial direction are studied by first principles methods in this work. For fcc nickel nanowires, it is found that  is the most stable direction, while  is less stable and  the least stable. Nickel nanowires can be described by a simple core-shell model. The core atoms of nanowires have almost the same magnetic moment as in bulk metal. Surface atoms of nickel nanowires have larger atomic magnetic moments in varying degrees related to axial direction. In our calculated nanowires with low-index axial directions, surface atoms in  nanowires have lowest magnetic moments while those in  nanowires have the largest.
Magnetostriction-jump effect in〈110〉 oriented Tb0.3Dy0.7Fe1.95 crystal after non-coaxial field annealing
2011, 60 (3): 037505. doi: 10.7498/aps.60.037505
An〈110〉 oriented Tb0.3Dy0.7Fe1.95 rod was annealed under a field of 0.3 T, which was applied 35° away from its axis. Magnetostriction-jump effect of the magnetically annealed crystal was investigated under a series of uniaxial compressive pre-stresses ranging from 0 to 30 MPa. The magnetically annealed crystal possessed much higher saturation magnetostriction λs than the ones without applying any pre-stresses. When the compressive pre-stress was less than 20 MPa, the magnetically annealed specimen still exhibited obvious magnetostriction jump effect, possessing improved saturation magnetostriction λs and enhanced burst magnetostriction λm. A satisfactory magnetostriction as high as 2315×10-6 could be obtained in the annealed crystal with the application of a pre-stress of 20 MPa. Furthermore, under a compressive pre-stress below 5 MPa, the critical field at which the magnetostriction-jump effect occurs also decreased, which was beneficial for low field applications. Difference in the magnetization processes caused by magnetic annealing was revealed through investigating the pre-stress dependences of the burst field Hjump and the distribution width of non-180° domain wall motion. Magnetic force microscopy images showed the changes of magnetic domain configurations induced by field annealing. Effects of the induced additional anisotropy on the magnetostrictive behaviors were also discussed.
2011, 60 (3): 037701. doi: 10.7498/aps.60.037701
The CaCu3Ti4O12-xMgTiO3(x= 0, 0.25, 0.5, 1.0) ceramics have been prepared by a solid-state reaction method. The effects of MgTiO3 doping on the phase structure, microstructure and dielectric properties of CaCu3Ti4O12 ceramics have been investigated. The results indicate that MgTiO3 doping not only reduced the dielectric loss of low frequency range and raised the breakdown voltage but also significantly improved the I-V nonlinearity coefficient. The optimized properties of MgTiO3 doped CaCu3Ti4O12 can be well explained by the uniformity of the grains, the reduction of the average grain boundary thinkness and the enhancement of the grain boundary resistance. Among the CaCu3Ti4O12-MgTiO3 specimens in this work, the CaCu3Ti4O12-0.5MgTiO3 specimen has achieved the best comprehensive properties, which include a dielectric constant (εr) of 53958, dielectric loss (tanδ) of 0.06 at 1 kHz, breakdown voltage (Eb) of 295 V/mm and a large nonlinearity coefficient of 66.3.
2011, 60 (3): 037702. doi: 10.7498/aps.60.037702
Y2O3-TiO2 composite film were deposited on Si substrate at room temperature by means of radio frequency magnetron sputtering. The crystalline state and topography of the film before and after annealing were measured by XRD and AFM, and the mechanism of the film being more compact was discussed. The result revealed that the evenness and compactness of the film can be improved with increasing the sputtering power, which is due to the fact of more Y2O3 filling the pores around TiO2with raising sputtering power, which inhibited the growth of big TiO\-2 grains and improved the evenness and compactness of film. After annealing, XRD pattern indicated that the addition of Y2O3 favors the formation of rutile TiO2 film which has high-dielectric constant.
2011, 60 (3): 037801. doi: 10.7498/aps.60.037801
We report the design of a quasi-omnidirectional tabulate metamaterial absorber, which is substantiated on the double-faced absorbing, polarization-insensitive and wide-angle property of the metamaterial cell. Both theoretical and simulated results reveal that our absorber surely has a distinct absorption point with double-faced absorbing property near 6.18 GHz, which is not influenced significantly by the polarization angle and the angle of incidence. The retrieved impedance indicates the electromagnetic resonance of the metamaterial could be tuned to match approximatively the impedance of the free space to suppress the reflectance at the absorption frequency. The distributions of the power loss indicates the strong absorption is mainly due to dielectric loss of the substrates and the design of adopting two different substrates could make the coupling of the front absorber and the back absorber depressed, which effectively suppresses the transmission caused by the coupling. This metamaterial absorber may have applications in many scientific and technological areas.
2011, 60 (3): 037802. doi: 10.7498/aps.60.037802
Rutile from Shuanghe and Bixiling area in the Dabie Orogen were investigated by Micro- Fourier transform infrared spectroscopy (FTIR). The results show that all the grains exhibit a sharp band near 3280 cm-1 or 3295 cm-1. Two structures have been suggested about the position of H in rutile, namely the chanel center (CC) and basal octahedron edge (BOE) models. The lattice structure and electronic band structure of Al—H and Fe—H codoped rutile TiO2 has been calculated by first-principles method. According to O—H bond vibration frequency of FTIR and O—H…O bond distance between O—O of computational results, we deduce that modified channel center (MCC) model is more reasonable. The calculation results indicate that the t2g state of Fe overlaps with the O 2p state, which will narrow the band gap and lead to red shift in optical absorption spectra.
2011, 60 (3): 037803. doi: 10.7498/aps.60.037803
Three types of FTIR spectrometers were employed to measure the mid-infrared (4000—400 cm-1) absorption spectra of geometrically frustrated hydroxyl cobalt chloride Co2(OH)3Cl, and the intrinsic absorption peaks in the functional group region and fingerprint region were selected and assigned to corresponding vibrational modes according to its known crystal structure. In the assigning process, great emphasis was laid on analyzing the exact experimental data of hydroxyl stretching vibration mode vOH, that is, estimating the free vOH of the Co3—OH group without any hydrogen bond (H-bond), to obtain the red-shift which reflects the formation of an H-band in Co2(OH)3Cl. A 156 cm-1 red-shift is obtained theoretically which demonstrates the presence of non-negligible weak H-bonds, and eventually result in the discovery of the rarely reported trimeric H-bond in the field of crystalline materials, which consists of three independent hydroxyl donors and only one Cl- acceptor. We explained the relative weakness of this kind of hydrogen bond which may have a critical effect on the lattice symmetry and magnetic structure.
2011, 60 (3): 037804. doi: 10.7498/aps.60.037804
A new method to measure the carrier concentration of p-GaN is proposed. The main idea is as follows: the difference between p-n+ structure GaN ultraviolet photodetector’s quantum efficiency at two different wavelengths varies remarkably with increasing reversed bias, and the most characteristic change occurs at a reversed voltage under which the p-GaN layer starts to be completely depleted, consequently the carrier concentration of p-GaN can be derived basing on this effect. The simulation results prove the validity of the idea even under the condition of high surface recombination velocity and bad ohmic contact. The thickness choice of p-GaN samples during the carrier concentration test experiment using this method is investigated. It is shown that the optimized thickness of p-GaN decreases with the increase of carrier concentration of p-GaN samples.
2011, 60 (3): 037805. doi: 10.7498/aps.60.037805
The SrMoO4:Eu3+red phosphors that can be excited effectively by the ultraviolet, near ultraviolet and blue light emitting diode (LED) were prepared by chemical coprecipitation. The crystal structure and luminescent properties of the SrMoO4:Eu3+ phosphors were investigated. The X-ray diffraction patterns showed that the SrMoO4:Eu3+synthesized by the process was a pure phase with tetragonal structure. The excitation spectrum of the SrMoO4:Eu3+red phosphors consisted of a broad band peak and a series of sharp peaks, and since the strong peaks were located at 280 nm (the broad band center), 395 nm and 465 nm, respectively, the phosphor can be excited effectively by the UV LED and Blue LED. The emission spectrum excited by 395 nm showed a strong emission peak at 613 nm, originating from the 5D0→7F2transition of Eu3+ions. The Eu3+ion concentration has great influence on the crystal parameters, the crystal symmetries and the luminescent properties. The influence of different concentrations of doped Eu3+ions on the luminescent intensity of SrMoO4:Eu3+was studied and the optimal doping concentration was found to be 15%.
2011, 60 (3): 037806. doi: 10.7498/aps.60.037806
Eu3+ doped Gd2W2O9 and Gd2(WO4)3 nanophosphors with different concentrations were prepared via a co-precipitation method. The structure and morphology of the nanocrystal samples were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The emission spectra and excitation spectra of the samples were measured, the J-O parameters and the quantum efficiencies of the 5D0 level of Eu3+ of the samples were calculated, and the concentration quenching curves of Eu3+ luminescence in different hosts were given. The study results indicate that similar to the Gd2(WO4)3:Eu, the red emission of Eu3+ 5D0 → 7F2 transition in Gd2W2O9:Eu can also be effectively excited by 395 nm near-UV light and 465 nm blue light. So the Gd2W2O9:Eu red phosphors may have a potential application for white light emitting diodes.
2011, 60 (3): 037807. doi: 10.7498/aps.60.037807
The photovoltaic effect of a-C: Fe/AlOx/Si based heterostructures prepared by Pulsed Laser Deposition (PLD) and its applications for solar cells were investigated. Thin alumina layer with a thickness of ~2nm was introduced to the interface between carbon and silicon, and the photovoltatic properties, such as open circuit voltage of ~0.33 V and short current density of ~4.5 mA/cm2, were improved dramatically compared with the samples without the insulation alumina layer. This may be related to the improvement of interface quality, where there are lower recombination centers such as defects and traps, which are approved by the C-V measurement. This work may shed light on the carbon/silicon based solar cells.
2011, 60 (3): 037808. doi: 10.7498/aps.60.037808
Luminescence properties of basal plane dislocations in 4H-SiC are studied by means of cathodoluminescence(CL) and defect selective etching. It is found that basal plane screw dislocations (BTSD) and basal plane mixed dislocations (BMD) have green and blue-green luminescence properties, respectively. The spectrum peaks near 530 nm and 480 nm correspond to BTSD and BMD,respectively. It is found from measurement that the luminescence peak from BMD is blue-shifted. The atoms of BTSD near the dislocation core are affected by tensile stress along the Burger’s vector direction, leading to its band gap narrowed. In addition, the Burger’s vector of BMD has both screw and edge components. It is the edge component that is responsible for the band gap broadening. In other words, the wavelength from BMD is shorter than that from BTSD.
2011, 60 (3): 037809. doi: 10.7498/aps.60.037809
Single InAs quantum dot (QD) sample is grown by molecular-beam epitaxy (MBE), and the photoluminescence (PL) from a single QD at 5 K is measured. By means of Hanbury-Brown and Twiss (HBT) setup, we measure the photon correlation of the PL which indicates that the PL of QD is single-photon emission. This single-photon source is used to demonstrate experimentally the single-photon interference via Mach-Zehnder (MZ) interferometer. In addition, the measured interference and fringe visibility are analyzed by changing the different linear polarization of the photon between two arms of MZ interferometer.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2011, 60 (3): 038101. doi: 10.7498/aps.60.038101
Ta2O5 films were deposited at room temperature by radio frequency(RF) sputtering with the target of bulk Ta2O5, in Ar or Ar-O2 mixture atmosphere. The reflectivity spectra measured from two sides of a film are compared to evaluate the optical absorption of the film. It is found that the excess optical absorption arises from deficiency in oxygen during sputtering. These defects can be eliminated effectively by selecting adequate Ar-O2 mixture and power for sputtering, and unabsorbing Ta2O5 films with compactness and smoothness can be obtained without annealing.
2011, 60 (3): 038102. doi: 10.7498/aps.60.038102
The model of ballistic deposition (BD) with shadowing means that the tilt incidence of particles in a certain angle of distribution is taken into account based on the BD model. In this paper,in order to investigate the finite size effect and the scaling properties of the BD with shadowing,the extrapolation method is used to determine the asymptotic scaling exponents of the model in the large-size limit. The simulation results illustrate that the finite size effect on BD with shadowing is different from that on BD, and the shadowing as a nonlocal interation can significantly change the scaling properties of BD model.
2011, 60 (3): 038201. doi: 10.7498/aps.60.038201
Thermally grown silicon dioxide is commonly used in high-efficiency monocrystalline silicon solar cell designs as a diffusion mask, electroless plating mask, passivation layer and rudimentary anti-reflection coating. These high efficiency device designs also utilize upright random textured up-pyramids etched by alkalinous solution to minimize front surface reflection. The silicon solar cells passivated with thermal SiO2/plasma SiN stacks have the evident character: the dark reverse current-voltage curve presents "soft breakdown", and the shunt resistance is lower than that of silicon solar cells passivated with the plasma SiN. The study shows that the cause of monocrystalline silicon solar cell performance degradation is the dislocation induced by the thermal growth of silicon dioxide on textured wafers. The performance of thermal SiO2/plasma SiN stack passivated silicon solar cells has evident improvement when a 2-min isotropic etching was applied after surface texturing to round off the pyramids.
Preparation and characterization of positive materials LiMn1-xFexPO4(0x<1) for lithium ion batteries
2011, 60 (3): 038202. doi: 10.7498/aps.60.038202
In this study, a series of phase-pure LiMn1-xFexPO4/C (x=0.2, 0.4, 0.6) cathode materials were successfully synthesized by solid-state method. The structure, particle size, surface morphology and electrochemical properties of these cathode active materials were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical model cell and cyclic voltammograms (CV). The results indicated that the different atom ratio of Mn/Fe affected its electrochemical preformance. A lithium battery using LiMn0.6Fe0.4PO4 as the active materials of the positive electrode exhibits a high initial charge capacity and discharge capacity of 141.5 mAh g-1 and 125.7 mAh g-1, respectively, and the initial coulombic efficiency is 88.8％. After 25 cycles, it retains 99.8% of the initial discharge capacity at 0.2C rate, showing perfect cyclic property.
2011, 60 (3): 038203. doi: 10.7498/aps.60.038203
The Nb/SnO2 composite thin films were successfully synthesized by sol-gel spin-coating method on glass substrate. The structures and properties of Nb/SnO2 composite thin films were characterized by X-ray diffraction (XRD), scanning electron microscopey (SEM), ultraviolet visible near-infrared spectrophotometry and four-probe method. The effects of Nb doping on structure and optical-electrical properties of the Nb/SnO2 composite thin films were researched. The results indicate that a tetragonal rutile structure is retained when the Nb content is less than 0.99at%, and the nano-particles are distributed homogeneously in the thin films and their size can be controlled in the range of 5—7 nm. The resistivity of Nb/SnO2 composite thin films decreases and then increases when the Nb content is less than 0.99at%, and reaches a very low value of 9.49×10-2 Ω ·cm at 0.37at% Nb. In the range of 400—700 nm visible region, the transmittance of Nb/SnO2 composite thin films is up to 90% when the Nb content is less than 0.99at%, and the optical band gap of Nb/SnO2 composite thin films are in the range of 3.9—4.1 eV. The visible light transmittance of Nb/SnO2 composite thin films significantly reduce at 1.23at% Nb.
2011, 60 (3): 038401. doi: 10.7498/aps.60.038401
The solar cells based on the blend of MEH-PPV(poly(2-methoxy-5-(2'-ethylhexyloxy) -1,4-phenylene vinylene)) and PCBM (1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6)C61) as acceptor were fabricated. The thickness dependence of the performance of solar cells was studied. The results showed that the solar cells with active layer thickness of 100 nm have the best performance. Increasing device thickness resulted in an increase of charge recombination and a lowering of the fill factor, which leads to lower overall power conversion efficiency. The reasons for the S-shaped kink in the thick device were also analyzed. Influence of the cathode material on the performance of the devices was discussed. The results showed that the solar cells using LiF/Al as the negative electrode formed ohmic contacts at the cathode and anode, which favored the collecting of the charge, increased the transmission of the charge and the absorption of solar light, and improved the performance of the solar cell.
2011, 60 (3): 038501. doi: 10.7498/aps.60.038501
In this paper,the fabrication details and optimization of micro-fabrication process are presented for developing superconducting nanowire single-photon detectors (SNSPD). Besides,the device failure analysis is also introduced. With those methods,we successfully fabricated high-quality SNSPDs whose maximum system efficiencies were up to 30% for 660 nm wavelength and 4.2% for 1550 nm wavelength according to the single-photon detection experiment. At the dark count rate of 10 c/s,the detection efficiencies were 20% (660 nm) and 3% (1550 nm) with the SNSPD fabricated with above mentioned methods.
2011, 60 (3): 038502. doi: 10.7498/aps.60.038502
Time-of-flight mass spectroscopy and quartz crystal oscillator are used to analyze the evaporation properties of the reservoir oxide cathode coated nano-particle carbonates in decomposing and activating process at different temperatures. The results show that the purity of the reservoir oxide cathode is high. It can fully be decomposed and activated in the conventional technologic process with more freed Ba and lower evaporation rate, compared with the conventional reservoir oxide cathode.
2011, 60 (3): 038901. doi: 10.7498/aps.60.038901
After extensive study on the small-world and scale-free properties of networks, the research focus is shifting to detailed local structures. Empirical analysis shows that many real networks exhibit the power-law clique-degree distribution. This general regularity cannot be produced by the rich-get-richer mechanism. In this paper, we propose a common-neighborhood-dirven model in which the observed power-law clique-degree distribution con be well reproduced, indicating that the common-neighborhood-dirven mechanism is an essential factor leading to the emergence of local structures.
REVIEW OF FRONTIER AREA
Comprehensive Survey for the Frontier Disciplines Progress of negative electron affinity GaN photocathode
2011, 60 (3): 038503. doi: 10.7498/aps.60.038503
GaN is becoming a promising material in ultraviolet detection and vacuum electronic source field for its good performance. High quantum efficiencies of greater than 70% and 30% have been achieved for the opaque mode and transparent mode GaN photocathode, respectively. This paper reviews the progress of GaN photocahtode in three important fields,including structure design, surface cleaning and Cs/O activation, analyzes the key factors influencing the quantum efficiency, and evaluates the prospect for its development.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2011, 60 (3): 039401. doi: 10.7498/aps.60.039401
The physics mechanisms of radiation belt electrons loss and acceleration are important issues in space physics research. Recently, France Microsatellite DEMETER has discovered the correlation between man-made VLF signals and radiation belt electrons precipitation in the NPM(the U.S. VLF transmitter located at Lualualei) experiment. Our research focuses on the explanation of the relation among affected pitch angle distribution, kinetic energy and position of electrons. This is achieved by calculating the local diffusion coeffcient based on the theory of qusi-linear diffusion with resonant interaction. Our result has a good explanation of radiation belt electron precipitation discovered by DEMETER during NPM experiment. Furthermore, we have discussed the effciency of radiation belt remediation in an artificial way.
2011, 60 (3): 039701. doi: 10.7498/aps.60.039701
To obtain the cumulation profile of pulsar signal, the traditional method needs to identify its period first, and then fold the signal with the period. This method depends on the accuracy of the period, and it has no evaluation standard for the profile. In this paper we analyze the strong correlation between the cumulation profile and the period, and present a minimum entropy method of pulsar cumulation profile and its verification. Therefore this method is applied to the identification of pulsar cycle. The RXTE data and the simulation data are used to verify the effectiveness of the method.