Vol. 55, No. 6 (2006)
2006, 55 (6): 2669-2675. doi: 10.7498/aps.55.2669
Based on the dynamic equations of particles system in non-inertial coordinate system, the higher order differential variational principle of relative motion for mechanical system is obtained, and the energy of higher order relative velocity of the mechanical system is introduced, the different kinds of higher order dynamic equations of holonomic mechanical system in relative motion are derived, and an example is given to illustrate the application of the results.
2006, 55 (6): 2676-2681. doi: 10.7498/aps.55.2676
At first the representations of polynomial angular momentum algebra and its unitary ones are obtained appling the way to get the three-parameter Lie algebra representations.Then find the basis which can be acted on by both Lie algebra and the polynomial angular momentum algebra simultaneity,so under such basis the representations of deformed algebras can be shown by introducing the relation of two algebra.At last the deformed algebra's single boson operator realization and one differential realization under finite-dimensional spaces are deduced.
2006, 55 (6): 2682-2686. doi: 10.7498/aps.55.2682
In this paper, the four coupling Dirac equations are predigested in two coupling Dirac equations by choosing null tetrad and calculating rotation coefficients in the arbitrarily accelerating charged dynamic space time.Moreover, after change these two coupling equations into Tortoise coordinate system forms and get the classical wave equations near the event horizon of black hole,the authors educe the formulation of Howking thermal spectrum successfully and obtain the Hawking radiation temperature of Dirac particles near the event horizon.
2006, 55 (6): 2687-2693. doi: 10.7498/aps.55.2687
This paper deals with the global asymptotic synchronization problem for a class of chaotic neural networks with delay. Using the drive-response conception and linear matrix inequality technique, two sufficient conditions are derived to guarantee the global synchronization of two chaotic neural networks with identical structure and different initial conditions, which also present a procedure to construct a synchronization controller. The controller gain can be achieved by solving a linear matrix inequality, and therefore, it is easily implemented in practice. Two illustrative examples are used to demonstrate the effectiveness of the proposed method.
2006, 55 (6): 2694-2701. doi: 10.7498/aps.55.2694
Purposely generating chaos when useful becomes an increasing focus of chaos research. Direct time delay feedback is proposed for anticontrol of chaos, which generates chaos from non-chaotic systems. Compared with the indirect time delay feedback, direct time delay feedback control is simple and easy to realize. The proposed method has the same structure as the time delay feedback method proposed by Pyragas for chaos control, therefore, the proposed method can generate chaos when it is useful, and eliminate chaos, when it is harmful, which will provide the designer with maximum flexibility. Simulations with nonchaotic Chen system and Lorenz system show the effectiveness of the proposed method.
ATOMIC AND MOLECULAR PHYSICS
2006, 55 (6): 2702-2707. doi: 10.7498/aps.55.2702
The Hamiltonian operator of a system of single-mode light field interacting with Bose-Einstein condensate (BEC) of two-level atoms is discussed in terms of the lattice-liquid model. It is indicated that the contribution of the interaction between atoms to the Hamiltonian was irrationally overestimated in the literature, so the Hamiltonian operator is improved in the present paper. Based on the improved Hamiltonian, the equations of motion of the photon and atomic operators are derived analytically. The relevant parameters in the model are estimated in connection with the BEC experimental conditions. The influence of the interaction between atoms in the BEC on the squeezing of light field and the atomic lasers is studied. The results show that the dependence of squeezing factor with atom number in BEC is different from that given in literature. and the fluctuations of two quadrature components of light evolve periodically with cosine law and the fluctuations of two quadrature components of the atomic laser can be squeezed.
2006, 55 (6): 2708-2713. doi: 10.7498/aps.55.2708
The photoionization and photodissociation of C2HCl3 by vacuum ultraviolet (VUV) photons from synchrotron radiation source were investigated under the supersonic beam conditions by using a reflectron-time-of-flight mass spectrometer (TOF-MS). The photoionization mass spectrum and the photoionization efficiency (PIE) curves of the parent ion and some fragment ions were measured. The ionization energy of C2HCl3 was measured to be 9.51±0.05 eV. The potentials for the appearance of C2HCl+2, C2HCl+, and CCl+ are obtained to be 12.40±0.05, 15.88±0.05, and 18.33±0.05, respectively. The formation enthalpies of some major ions and the dissociation energy (DE) of C2HCl3 have been evaluated from these data. According to the experimental results and the theoretical calculations by G1 theory, the main possible channels of dissociative photoionization of C2HCl3 have been discussed. In the future, one can detect C2HCl3 with SPI-TOFMS technique using 118.0nm laser. Based on the mass spectrum obtained at that wavelength using synchrotron radiation source.
CLASSICAL AREA OF PHENOMENOLOGY
Photon tunneling in a frustrated-total-internal-reflection structure composed of a single negative material
2006, 55 (6): 2714-2719. doi: 10.7498/aps.55.2714
The tunneling time and lateral shift of photon tunneling in a frustrated-total-internal-reflection structure composed of single negative material is derived by employing stationary-phase approximation. It is found that the tunneling time and the lateral shift are negative when the barrier is a single negative material. On account of the Hartman effect of the tunneling time and the lateral shift, the photon tunneling shows the superluminal property. An effective approach to distinguish ε-negative material and μ-negative material is proposed based on the fact that TE- and TM-polarized incident beams experience opposite lateral shift.
2006, 55 (6): 2720-2725. doi: 10.7498/aps.55.2720
By means of negativity and concurrence, we investigate the time evolution of the entanglement of the two atoms and the entanglement between the two modes in the system of two atoms interacting with two-mode fields. We find the two entanglements can swap with each other, and they have a very good coincidence relation under certain conditions. In two -qubit system, negativity and concurrence in the same range can keep identical with each other on the standard of the existence of entanglement, but they may not always keep pace with each other for mixed states of the system.
2006, 55 (6): 2726-2729. doi: 10.7498/aps.55.2726
Transparent polycrystalline MgO and TiO2 codoped Al2O3 ceramics were fabricated by conventional solid-state pressureless processing. The absorption, emission and excitation spectra of (Mg，Ti):Al2O3 ceramics were measured. Owing to charge compensation of Mg2+, only UV absorption around 250nm was observed due to O2-→Ti4+ charge transfer transitions (CT) when Ti content was low. As a result, the emission peaks of isolated Ti4+ ion located at 280—290nm and 410—420nm were observed. Besides absorption peak of Ti4+ ion, the characteristic absorption peak of Ti3+ ion centered at 490nm was observed in (Mg，Ti):Al2O3 ceramics when Ti content was high. The emission spectra of Ti3+ ion in polycrystalline Al2O3 ceramics coincide with that of Ti:Al2O3 single crystal.
The Z-scan experiments were carried out to investigate the soluble carbon nanotubes. The thickness of sample is changed in order to study “thin” and “thick” sample respectively. The experiments are carried out using 8ns, 10Hz repetition rate laser pulses at 1064nm and 532nm. The transmittance curves of closed-aperture Z-scan show that nonlinear refraction is not the optical limiting mechanism of solubilized carbon nanotubes. The curves of opened-aperture Z-scan indicate that nonlinear absorption exists in this solution obviously, which may be the primary optical limiting mechanism of this material.
2006, 55 (6): 2735-2739. doi: 10.7498/aps.55.2735
Adopting noise initiation mode of stimulated Brillion scattering (SBS), the influence of focal length on optical limiting power and energy is numerically simulated. It shows that the characteristic of limiting power and energy are controlled by focal length. When focal length is moderate, say 15cm, the limiting energy is lowest. When focal length is short, say 5cm, the characteristic of limiting power is close to ideal. In experiment, focusing 8ns, 1064nm, 16mJ pulses into CCl4 medium, the variation of limiting power and energy versus focal length is investigated. The experimental results are in good agreement with the conclusions predicted by the simulations.
Profile comparison between the Raman-induced Kerr effect spectrum and photoacoustic Raman spectrum of methane
2006, 55 (6): 2740-2745. doi: 10.7498/aps.55.2740
Two kinds of spectrum, the Raman-Induced Kerr Effect Spectrum(RIKES)and the Photoacoustic Raman Spectrum(PARS),were measured simultaneously for the ν1 vibrational band of methane. The difference between the profiles of the two spectra obtained with linearly polarized pump and Stokes laser beams lies in that, the intensity of RIKES spectrum is stronger at the small Raman shift side, and is weaker at the large Raman shift side compared to the PARS spectrum. It was confirmed that this difference is caused by the interference between the resonant and non-resonant parts of the third order non-linear susceptibility.
Wavelength converter based on cross-gain modulation in multi-electrode single-port-coupled semiconductor optical amplifier
2006, 55 (6): 2746-2750. doi: 10.7498/aps.55.2746
A new scheme for cross-gain modulation (XGM) wavelength converter based on multi-electrode single-port-coupled semiconductor optical amplifier (SOA) is proposed, and a comprehensive broad-band dynamic model of this kind of wavelength converter is presented. By numerical simulation, the output performances of two kinds of XGM wavelength converter based on multi-electrode single-port-coupled SOA and based on single-port-coupled SOA are investigated. The result shows that the extinction ratio of XGM wavelength converter based on multi-electrode single-port-coupled SOA is greater than that of the later.
2006, 55 (6): 2751-2759. doi: 10.7498/aps.55.2751
We explore the control of the Gaussian beams propagating in the planar waveguide by use of the (1+1)-dimensional Snyder-Mitchell model and the spatial sinusoidal phase modulation.The steady symmetrical co-propagation of three,five and six beams can be obtained with proper modulation parameters. Their unique interaction has potential application in the optical switch,optical coder and the spectrometer.
2006, 55 (6): 2760-2764. doi: 10.7498/aps.55.2760
The self-collimation of two polarization statcs of electromagnetic waves in two dimensional photonic crystals is studied by using finite-difference-time-domain(FDTD) method.It is proved that self-collimation can be realized in both transverse electric (TE) field and transverse magnetic (TM) field simultaneously by modification of the appropriate photonic crystal structures.Analysis and numerical simulation were carried out.This effect may be important for creating integrated optical circuits,and for improving the efficiency of light source.
Realization of an angular filter using one-dimensional photonic crystal containing negative refractive metamaterials
2006, 55 (6): 2765-2770. doi: 10.7498/aps.55.2765
A new kind of one-dimension photonic crystal (PC) which can be used as an angular filter was studied. With the knowledge of resonance tunneling mechanism in zero average index PC, we find such PC must contain negative refractive metamaterials and its structure parameters should satisfy some special conditions. When electromagnetic wave of a given frequency incident on such PC, only those portions with incident angles identical with the special angle (or angles) can pass through such PC, while the others can not. Such filter would have wids applications in microwave and optical communications.
2006, 55 (6): 2771-2776. doi: 10.7498/aps.55.2771
The Judd-Ofelt intensity parameter Ωt of a novel Er3+ doped high silica glass was calculated. The large values of Ω2,6 (Ω2=8.15×10-20,Ω6=1.22×10-20) indicate that the local structure of Er3+ has higher asymmetry and lower covalency than other oxide glasses. McCumber theory was used to calculate the stimulated emission cross section of 4I13/2→4I15/2 transition, the result was 0.51pm2. Despite the Er3+-doped concentration in high silica glass being about ten times greater than that in silica fiber, its fluorescence lifetime and quantum efficiency were 6.0ms and 66.0%， respectively. This novel Er3+-doped glass can be used in optical amplification and microchip laser.
Properties of impurity band in one-dimensional photonic crystal coupled-resonator containing defect layers with negative refractive index
2006, 55 (6): 2777-2780. doi: 10.7498/aps.55.2777
The transmission through one-dimensional photonic crystal coupled-resonator containing defect layers with negative refractive index is studied by using transfer matrix method. It is found that when the refractive index of defects is changed, the coupling effect between the defect modes is varied, which results in the change of the impurity band. Some sharp transmission peaks and a wide pass band appear at the same time in the for bidden band when the refractive index of defects is appopriate. So the structure can be used as both a multiple channel narrow-band filter and a wide-band filter at the samc time.
Electric field intensity distribution in disordered one-dimensional photonic crystal with omnidirectional reflection band
2006, 55 (6): 2781-2784. doi: 10.7498/aps.55.2781
It is theoretically demonstrated that the omnidirectional reflection band in one-dimensional disordered photonic crystals (1D DPCs) can have a width as broad as that in one-dimensional periodic photonic crystals (1D PPCs) with the same layer number. In the band gap, the electric field intensity distributions in a 1D DPC are almost the same as in 1D PPCs. However, near the band edges, the electric field intensity distribution in the 1D PPC is symmetric, remarkably different from the asymmetric field patterns in the 1D DPCs that are designable and controllable. This characteristic in the 1D DPCs should open a new way to design photonic-crystal-based devices.
Band gap characteristics of compound structure composed of lattices with different periodic constants
2006, 55 (6): 2785-2788. doi: 10.7498/aps.55.2785
Our numerical simulation results show that if a compound structure is composed of a lattice with a larger periodic constant and a lattice with a small periodic constant, the lattice with larger periodic constant will play the role of defects. The frequencies of defect modes are dependent on the rod radius (r2) of square lattice with a larger periodic constant, and the relationship of the defect modes and r2 is almost independent of a2. The defect mode is dependent on incidence angle when a22. Furthermore, by optimizing the size of the rods (r2) of the larger periodic lattice, single defect mode, multiple defect modes with equal or different frequency spacing, including single polarization or TE and TM overlap defect mode, can be gotten respectively. The transmissivity of the defect modes are inversely proportional to a2.
2006, 55 (6): 2789-2793. doi: 10.7498/aps.55.2789
A concise method of estimating high-reflection range for layered media composed of finite periodic unit is presented. Based on the Floquet theorem, the photonic bandgap properties of periodic layered media are analyzed, and the wavelength range of high-reflection region for periodic layered media is discussed. The relation between high-reflection region of layered media and forbidden band of the periodic unit is discussed. Numerical results show that the center wavelength of high-reflection region coincides with the one of the forbiddan band of periodic unit. Furthermore, as the periodic unit number of layered media is increased, the depth and width of high-reflection region become close to those of forbidden band of the periodic unit. Finally, the variations of photonic bandgap properties of periodic layered media with respect to the incidence angle and polarization have also been discussed.
2006, 55 (6): 2794-2798. doi: 10.7498/aps.55.2794
Two structures of left handed metamaterials were proposed. Using numerical simulation, the S parameters for the two structures were calculated. Because the electromagnetic fields in conducting metamaterials can be localized to regions much smaller than the incident wavelength, it can be difficult to perform accurate numerical simulations. To obtain greater numerical accuracy， finite integration technique (FIT) was used. The results show that the wire symmetry breaking affects the resonant frequency and passband for SRR owing to the coupling between wires and SRR.
Application of dispersion compensator based on chirped fiber gratings in ultra long-haul DWDM system
2006, 55 (6): 2799-2803. doi: 10.7498/aps.55.2799
The dispersion management based on chirped fiber gratings in single channel system is studied by numerical simulation and tested in a 10Gb/s system on 1500km G.652 fiber. In this article, the suppression of the XPM effects by the random time delay between channels induced by the chirped fiber gratings is also studied. The special characteristics of the dispersion management based on chirped fiber gratings are found.
2006, 55 (6): 2804-2808. doi: 10.7498/aps.55.2804
Fiber-optic grating sensing based on Loop thin-walled ring section beam is proposed and demonstrated. The temperature and stress can be measured simultaneously using only one fiber grating. The strain of the thin-walled ring section beam is investigated theoretically and experimentally. The result shows the local strain varies as the cosine function of twice the positional angle.
2006, 55 (6): 2809-2814. doi: 10.7498/aps.55.2809
Based on Khokhlov-Zabolotkaya-Kuznetsov (KZK) equation in frequency-domain, an approach to study the three-dimensional asymmetric nonlinear ultrasonic field is developed in this paper. The ultrasonic nonlinear field distribution behind the simulated rib-like barriers is investigated by numerical simulation and compared with the measured results. In addition, the influence of the barriers on the spatial-and-time-averaged intensity is discussed, which is helpful for future study on the HIFU treatment behind the ribs.
The phase transformation of xPMnS-(1-x)PZN quaternary piezoelectric ceramics was studied and the effect of composition on phase transformation characteristics was also discussed. Results indicate that xPMnS-(1-x) PZN ceramics show disperse phase change characteristic and obvious dielectric thermal lag in the course of the phase change. The result of electronic structure investigation indicates that the disperse phase change should be attributed to the difference in strength of B—O bonds. The material has relaxation ferroelectric characteristics When x value is large (or small), and shows relatively strong disperse phase change. It has normal-relaxation ferroelectric characteristics when x value is near 0.4, and shows relatively weak disperse phase change.
2006, 55 (6): 2820-2824. doi: 10.7498/aps.55.2820
Based on nonlinear Schrdinger equation, the stimulated Raman scattering (SRS) chirp, self-steepening (SS) chirp and total chirps induced by all nonlinear effects in photonic crystal fiber (PCF) are simulated numerically. The results show that the center of SRS chirp wanders and the chirps of the leading edge and the trailing edge are asymmetrical, the central SS chirp mainly shifts to the trailing edge, and the total chirps increases. Thus, SRS leads to the shift of spectrum to the longer wavelength and the asymmetric broadening of spectrum, and SS is the most important contributor to the asymmetry spectrum broadening. Consequently, asymmetrical red-shift supercontinuum (SC) spectrum is finally resulted due to all nonlinear effects mentioned above.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
A new approach has been developed to treat large-angle and small-angle binary collisions in plasmas when the test particles' distribution function fα is an even function about the test velocity vα. In the approach, the Boltzmann collision operator is derived to be suitable for the plasma considered as weakly coupled (Coulomb logarithm ln Λ≥10) or moderately coupled (2≤lnΛ≤10). The modified collision operator has a direct and practical connection to the Rosenbluth potentials. In addition, with mαmβ(such as electron-ion collision or Lorentz-gas model) and vαvβ, the reduced electron-ion collision operator differs from the original Fokker-Planck operator for Coulomb collisions by terms of order 1/lnΛ.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
The effect of interwall coupling interaction on the field emission characteristics of commensurate double-walled carbon nanotubes
2006, 55 (6): 2830-2837. doi: 10.7498/aps.55.2830
The band structure model of commensurate double-walled carbon nanotube (DWNT) was built by using tight-binding Hamiltonian with curvature effect included. The field emission characteristics of commensurate DWNT were quantitatively investigated basing on its dependence on the band structure. The results indicate that interwall coupling interaction (ICI) can form additional electronic energy level in the band structure of DWNT so as to increase the emitting channel of electrons;and at the same time, it can also increase the energy gap of the metallic DWNT and decrease that of the semiconducting DWNT, which will result in a change in the number of electrons emitted from the valence band. At a given applied electric field, the emission current of DWNT has an obvious increase, compared with that of DWNT when ICI is turn off, and the current increment of semiconducting DWNT is larger than that of the metallic one. At an applied electric field of 5V/μm, the field emission currents of commensurate DWNTs (6,6)&(12,12), (10,0)&(20,0) and (8,2)&(16,4) have an increase of about 3%,10% and 4%, respectively, compared with those when ICI is turn off. The results reveal that ICI contributes to the transport and electron emission of DWNT, which is helpful for understanding the field emission mechanism of DWNT ,and hence that of MWNT.
2006, 55 (6): 2838-2845. doi: 10.7498/aps.55.2838
The direct products and semidirect products of quasi-crystallographic point groups, were derived from group theory. According to crystallography theory, the stereographic projection of pentagonal system, octagonal system, decagonal system and dodecagonal system, were derived and drawn. Basing upon them, all maximal subgroups of each quasi-crystallographic point group were derived and drawn. As a result, subgroups and supergroups of the three-dimensional crystallographic and quasi-crystallographic point groups (the ‘family tree' of sixty point groups) were derived and depicted in drawing. In the ‘family tree', the minimal supergroups and maximal subgroups of sixty point groups were illustrated in detail in the form of maximal subgroup chains.
2006, 55 (6): 2846-2851. doi: 10.7498/aps.55.2846
The vanadium oxide thin films are fabricated for microbolometer by radio frequency reactive sputtering at room temperature. The effects of the oxygen partial pressure on deposition rate, electrical properties and compositions of the films are discussed. Films consisting mainly of VO2 can be prepared by adjusting oxygen partial pressure. After oxidation annealing in air, the VO2 films with high temperature coefficients of resistivity (about -4%/℃) and low resistivity can be obtained. The square resistances of the films are in the range between 100 kΩ/squ to 300kΩ/squ. All films are deposited at room temperature and annealed at 400℃, which is compatible with MEMS (micro electromechanical systems) process.
2006, 55 (6): 2852-2855. doi: 10.7498/aps.55.2852
Basing on the modified SCG model, a high temperature and high pressure constitutive relation of materials is proposed. The change of shear modulus of aluminum with pressure as deduced from this model shows three stages: machining indurations, high temperature inteneration and melting, and turning to zero at the point of complete melting. In the first two stages, the difference in results of modified SCG model and our model is no greater than 4%, which is in the error range of dynamic experiments, and the shear modulus given by this model is in good agreement with experimental data at the point of 145GPa.
2006, 55 (6): 2856-2859. doi: 10.7498/aps.55.2856
By taking into account of the precipitate kinetics and the dynamic strain aging mechanism, a phenomenological model with clear physical origin is established in this paper. Three types of serrated flow in the Portevin-Le Chatelier effect is reproduced by the numerical simulations of the uniaxial tensile tests with different applied strain rates. The computational results are found in good agreement with the experimental curves, which testifies the validity of the present model.
2006, 55 (6): 2860-2864. doi: 10.7498/aps.55.2860
The 12 non-degenerate phonon vibrational modes at the center of Brillouin zone for a series of single-wall carbon nanotubes have been analysed in a previous paper.［1］ The E1 and E2 of degenerate phonon vibrational modes are further discussed in this paper and the relations between frequency-chirality and frequency-tube diameter for E1 and E2 vibrational modes are also demonstrated.
2006, 55 (6): 2865-2870. doi: 10.7498/aps.55.2865
This paper set out from Holstein model of the quantization, by means of the method of incoherent state expansion, get the non-Linear Schrdinger equation of the polaron in ground state of one-dimensional molecular crystal, and get the soliton solution of fixed state,the ground state energy, the lattice displacement.
2006, 55 (6): 2871-2876. doi: 10.7498/aps.55.2871
In a regular lattice, the active sites infect their neighboring vacant sites with a certain probability step by step. A grand canonical ensemble was finally formed by all the occupied sites. To represent the system by the partition function of the ensemble, we have substituted the infect probability for the system temperature and divided the energy levels of the sites with different steps. The percolation phase transition of this system at percolation threshold Pc was substantiated by Monte Carlo simulation. Thus a new general method is established, in which the intrinsic behavior of the lattice in the dynamic process of particle growth and other infection growth is used, to estimate the percolation threshold of any lattice. The validity of the model was experimentally verified by studying the growth process of the nanometal films on a dielectric substrate. A proper explanation of the connection between the model and the physical substance was also given.
2006, 55 (6): 2877-2881. doi: 10.7498/aps.55.2877
In order to systematically understand the mechanism of martensitic transformation of NiTi shape-memory alloy, and to study the effect of temperature and stress on the electronic structure, we have carried out first-principles calculations based on the density-functional theory (DFT). Analysis of density of states shows that martensitic transformation induces the Fermi face to shift and the density of states near the Fermi face to decrease. With the temperature decreasing and deformation increasing,the density of state of B2 phase and the degree of energy band overlaps increase，thus the stability decrease.
Numerical simulation of the influence of substitutional impurity on the interaction between low-energy Pt atoms and Pt(111) surface
2006, 55 (6): 2882-2891. doi: 10.7498/aps.55.2882
The deposition process of low-energy Pt atoms on Pt (111) surface doped with substitutional impurity Cu, Ag, Au, Ni, or Pd was studied by using molecular dynamics simulation. The atomic interaction potentials with the embedded atom method (EAM) were applied in the simulation. The effects of substitutional impurity on the adatom yield, sputtering yield, and vacancy yield have been observed and summarized. We found that substitutional impurity considerably affects the adatom yield, sputtering yield, and vacancy yield. The main reasons influencing the interaction between low-energy atoms and Pt (111) surfaces are the kinetic energy of incident atoms and the mass of substitutional impurity. The light substitutional atoms induced the preferred sputtering of substitutional impurity. A model based the binary collision theory and the atomic reflection mechanism by the substrate is suggested to describe the low-energy deposition process.
Depth-dependent elastic strain in ZnO/Zn0.9Mg0.1O/ZnO heterostructure studied by Rutherford backscattering/channeling
2006, 55 (6): 2892-2896. doi: 10.7498/aps.55.2892
ZnO/Zn0.9Mg0.1O/ZnO heterostructure was grown by radio frequency plasma-assisted molecular beam epitaxy on a sapphire (0001) substrate. By using RBS/C, the depth-dependent elastic strain was deduced. The strain changes from negative to positive from interface to surface, and the value is higher at the depth close to the interface (also at the interface between ZnO and Zn0.9Mg0.1O) and decreases towards the surface. The negative tetragonal distortion was explained by considering the lattice mismatch and thermal mismatch between ZnO and sapphire substrate, and the positive distortion is due to the tensile strain in the parallel direction of Zn0.9Mg0.1O and the gradual release of the strain.
Study on the determination of interfacial binding strength of coatings (Ⅰ): theorctical analysis of stress in thin film binding interface
2006, 55 (6): 2897-2900. doi: 10.7498/aps.55.2897
The theoretical model of stress in film binding interface is established with the help of laser scratch testing (LST) and the theory of bending stress, the distribution formulae of stress such as shear stress, normal stress and stripping stress are deduced, and the mechanism of stress forming in binding interface is analyzed. It is shown that the normal stress of interface is mainly concentrated on interface center region, it decreases quickly near the interface edge, becomes zero at the interface edge. Shear stress and stripping stress are mainly concentrated in the interface edge, they decrease quickly away from the edge. Normal stress of film is not related with film thickness, matrix thickness and Young's modulus,the shear stress and stripping stress increase with film thickness, and they are determined by thickness of film and matrix and Young's modulus.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2006, 55 (6): 2901-2907. doi: 10.7498/aps.55.2901
Using a first-principles total energy method based on density functional theory within local density approximation, we have performed a first-principles computational tensile test (FPCTT) on an Al grain boundary. The theoretical tensile strength of the Al grain boundary is calculated to be 9.5 GPa at the strain of 16%. Based on the valence charge density, bond length and atomic configuration evolution with increasing strain, we demonstrate that the fracture occurs at the grain boundary interface，characterized by breaking of the grain boundary interfacial-reconstructed bonds. We further found that, because of the reduced number of the nearest neighbor of Al atoms in the grain boundary, these interfacial-reconstructed bonds have similar features to covalent bonds, which results in rather high grain boundary strength in comparison with the Al bulk.
2006, 55 (6): 2908-2913. doi: 10.7498/aps.55.2908
The structural,electronic and optical properties of BN(5,5) nanotube under high pressures were studied by means of quantum-mechanical calculations based on the density functional theory and pseudopotential method. It was found that the geometric structure has large distortion under pressures. Differences exist between BN(5,5) nanotube and zinc blende structure BN: firstly, the band gap of BN(5,5) nanotube increases with pressure with a slope of -0.01795eV/GPa; secondly, the absorption spectrum does not “blue shift”, but stretches in the direction of infrared； yet these two structures have same electronic transfer direction. The electron density map indicated that BN(5,5) has stronger ionicity, which weakens with pressure increasing.
2006, 55 (6): 2914-2921. doi: 10.7498/aps.55.2914
The electronics structures and absorption spectra of polarized light for the PWO crystal containing VPb2- have been calculated using CASTEP code with lattice structure optimization. The optimized lattice structures around lead vacancy in the PWO have been obtained. The color center models and their corresponding absorption spectra have been proposed according to the experimental results of the lattice structures and the electronic structures around the lead vacancy. The negative divalent VPb2- should trap two holes to maintain the local neutrality. The possible way of the formation of the hole centers is one trapped hole shared by two O2- ions nearest to VPb2- and other one shared by another two O2- ions nearest to VPb2- forming ［O23--VPb2--O23-］. The different ways of O2- ions trapping the holes will form different color centers corresponding to different absorption bands. The color center models around VPb2- have been proposed.
Molecular dynamics simulation of the growth and structural properties of ultra-thin diamond-like carbon films
2006, 55 (6): 2922-2927. doi: 10.7498/aps.55.2922
Molecular dynamics simulations are performed to study the growth of diamond-like carbon (DLC) films with a thickness of 2—3nm on diamond (100) substrate. Some important structural properties characterizing the quality of the deposited films, such as sp3 hybridization fraction, film density, radial distribution function, are analyzed which turn out to be consistent with experimental results. The incident energy has significant influence on the structural properties, and hence film properties. Optimal properties are obtained when kinetic energy of the incident atoms is in the range 20—60eV. The incidence of energetic species is prerequisite for growing homogeneous, continuous and compact films. A steady-state intrinsic region is required to guarantee outstanding mechanical properties of the thin film.
2006, 55 (6): 2928-2935. doi: 10.7498/aps.55.2928
We investigate the electronic and magnetic properties of the new compound Gd2Co2Al by using a self-consistent full-potential linearized augmented plane-wave method within the local spin-density approximation (LSDA) and the LSDA+U approximation to the exchange-correlation potential of the spin-density functional theory. We have also discussed the reason of system to have low Curie temperature, and made use of the average field theory to calculate the Curie temperature in combination with the results of density functional calculation. Our calculation shows that this system is a metallic conductor. The local Gd magnetic moment provides predominately the strong ferromagnetism and the Co-site local moment is unstable. Gd2Co2Al is shown to be a ferrimagnetic phase due to the moment of Gd sublattice being aligned antiparallelly to the Co moment in the LSDA. After considering the on-site Coulomb interaction by an additional Hubbard parameter U, it is found that the ground state becomes ferromagnetic at a moderate value of U (3.0eV), with a Co ion magnetic moment of 0.024μB, which is in good agreement with experiment. The moment of Co changes much and the density of states of Gd and Co are significantly redistributed with the change of U, while the magnetic moment of Gd does not change much. The competition of 5d-3d hybridization and the on-site Coulomb interaction leads to the fluctuation of the moment of Co.
2006, 55 (6): 2936-2940. doi: 10.7498/aps.55.2936
The porous fluorine doped silica (SiO2:F) films were prepared by sol-gel method. The densities of the states (DOS) of the SiO2:F films and the effect of the dose of the F dopant were studied by space charge limited current(SCLC) techniques. Distribution of defect states N(E) in the vicinity of Fermi level in SiO2:F films was determined to be about 7×1015cm-3·eV-1. The dangling bounds on the surface of the porous film were the primary cause of the DOS.
2006, 55 (6): 2941-2948. doi: 10.7498/aps.55.2941
A magnon-phonon interaction model is built in the two-dimensional double square ferromagnetic system. By using Matsubara Green function theory, we study magnetic excitation of the system, and calculate the magnon dispersion curve on the main symmetric points and lines in the Brillouin zone. The influences of optical phonon and acoustic phonon on the magnetic excitation of the system are compared, and the influences of the parameter change on the magnon softening are also studied. It is concluded that the coupling of the optical phonon and magnon has predominant effect on the magnon softening, especially the longitudinal optical phonon has the greatest effect on the magnon softening, and the effect of nonmagnetic ion on magnon softening is stronger than that of magnetic ion.
2006, 55 (6): 2949-2954. doi: 10.7498/aps.55.2949
Based on the tight-binding model of the single electron, the 1D model of disordered binary alloy is established, where two different diagonal energies εA and εB are assigned at random to each lattice site and only the short-range hopping integrals between the lattice sites are considered. Using the negative eigenvalue theory and the infinite order perturbation theory, we calculate numerically the eigenvalues and the eigenvectors of the electronic states. The results show that the electronic wave-functions only exist in some narrow region of the system and the localization properties are expected. Using the transfer matrix method, we calculate the localization lengths and discuss how they change with the eigen-energies and the degree of disorder and discuss some characteristics of the localization length with different hopping integral ranges.
Magnetoresistance oscillation of two-dimensional electrons gas in narrow gap dilute magnetic semiconductor
2006, 55 (6): 2955-2960. doi: 10.7498/aps.55.2955
This paper study the detailed magnetoresistance oscillation in Shubnikov-de Hass (SdH) of magnetic two dimensional electron gas consisting of a modulation doped n type Hg0.82Cd0.16Mn0.02Te/Hg0.3Cd0.7Te first type quantum well by changing temperature and the angle of the sample with aspect of applied magnetic field, by which found that the changing of temperature and tilt angle will cause the varying of beating node position, By analyzing beating patterns, the magnetic angle dependent Landau splitting can be separated from magnetic magnitude dependent Zeeman splitting.
2006, 55 (6): 2961-2965. doi: 10.7498/aps.55.2961
The dependence of electron spin relaxation on the momentum relaxation and carrier density are investigated based on the spin-orbit coupling and D'yakonov-Perel relaxation mechanism. Experimental results obtained by using femtosecond pump-probe technique in AlGaAs/GaAs multiple quantum wells at room temperature show that the spin relaxation time increases from 58 to 82ps with the carrier density increases from 1×1017 to 1×1018cm-3, consistent with the theoretical prediction. This results reveals that with the increase of the carrier density, the spin-orbit interaction reduces due to more frequent momentum scattering, sothat the spin relaxation time prolongs.
Effect of magnetic field on the transmission properties of electrons in a four-terminal quantum waveguide
2006, 55 (6): 2966-2971. doi: 10.7498/aps.55.2966
We investigate the quantum-mechanical transmission of electrons in a four-terminal quantum waveguide (FTQW) subjected to an inhomogeneous magnetic field perpendicular to the FTQW plane with the use of the mode-matching technique. An electron incident through one channel of the waveguide can travel into the other three channels in the quantum ballistic regime. The results show that in zero field the transmission coefficients in two channels perpendicular to the main wire are of similar behavior, but different from that of the channel parallel to the main wire. However, in an applied magnetic field, the transmission coefficients in two channels perpendicular to the main wire exhibit quite difference from each other and depend sensitively on geometric parameters. When different magnetic configurations are applied in the structure, the transmission exhibits various patterns such as step drop, wide valley, sharp peak, and so on. Our results show that one may control the transmission property of the FTQW to match practical requirements in devices by adjusting magnetic configurations or structural parameters.
High-order harmonic generation of hydrogen molecule irradiated by ultra-strong femto-second laser pulse——a simulation via TDDFT
2006, 55 (6): 2972-2976. doi: 10.7498/aps.55.2972
The high order harmonic generation (HHG) of hydrogen molecule irradiated by ultra-strong femto-second laser pulse is simulated by the TTDFT method with the classical and quantum combination technique. The results indicate that the HHG spectra of H2 have a “decrease-plateau-cutoff” structure. A kind of “odd allowed, even forbidden” selective phenomenon of the order number of HHG is observed. Change in polarization direction of laser beam may change the cut-off order and spectrum intensity of HHG simultaneously.
Characterization of crystal lattice constant and strain of GaN epilayers with different AlxGa1－xN and AlN buffer layers grown on Si(111)
2006, 55 (6): 2977-2981. doi: 10.7498/aps.55.2977
Hexagonal GaN epilayers with different AlxGa1-xN and AlN buffer layers were grown on Si(111) by metal-organic vapor phase epitaxy (MOVPE). Under the same growth conditions, the sample with four AlxGa1-xN buffer layers and one AlN buffer layer were grown on Si(111). According to the results of Rutherford backscattering (RBS)/channeling along axis, the conventional θ—2θ scans normal to GaN(0002) and (1122) plane at 0° and 180° azimuthal angles, and the reciprocal-space X-ray mapping (RSM) on GaN(1015) plane, we obtained that the crystal quality of the GaN epilayer is perfect with χmin＝1.54%. The crystal lattice constant of AlN, AlxGa1-xN and GaN epilayer has been calculated accurately, the lattice constant of GaN epilayer is almost equal to the theoretic data (aepi=0.31903nm, cepi=0.51837nm). The tetragonal distortion along the depth can got clearly from elastic strains of each layer in the normal and parallel directions, and the tetragonal distortion of GaN epilayer is nearly fully relaxed(eT=0).
High-quality multiple quantum wells selectively grown on taper-patterned substrates by ultra-low-pressure MOCVD
2006, 55 (6): 2982-2985. doi: 10.7498/aps.55.2982
High quality InGaAsP/InGaAsP multiple quantum wells (MQWs) have been selectively grown by ultra-low-pressure (22 mbar) metal-organic chemical vapor deposition. A large bandgap energy shift of 46 nm and photoluminescence with FWHM less than 30 meV were obtained with a rather small mask width variation (15—30 μm). In order to study the uniformity of the MQWs grown in the selective area, novel tapered masks were employed, and the transition effect of the tapered region was also studied. The energy detuning of the tapered region was observed to be saturated at larger ratios of the mask width to the tapered region length.
The first-principles calcultion of the electronic structure of finite length carbon nanotubes grafted by carboxyl
2006, 55 (6): 2986-2991. doi: 10.7498/aps.55.2986
We report the first-principles calculation of the electronic distribution and the density of states (DOS) of the armchair(5,5) and zigzag (9,0) single-walled carbon nanotubes (SCNTs) grafted by carboxyl within the framework of density-functional-theory(DFT). It was found that the electronic structure of the SCNTs changes significantly due to the graft, namely, the electron density of states near Fermi level and the delocalized degree of the highly occupied molecular orbital decline greatly with increase of the number of carboxylic functional groups grafted. This suggests that the graft weakens the electronic transport properties of SCNTs.
2006, 55 (6): 2992-2996. doi: 10.7498/aps.55.2992
A theoretical and experimental study on extracting channel carrier concentration for 4H-SiC buried channel MOSFET has been carried out. The distortion of C-V curve caused by the existence of p-n junction in buried channel MOS structure would affect the extracting result, and the interface states on SiO2/SiC interface make extracting result deviate from true channel carrier concentration. In this paper, firstly, a theoretical analysis about the effects of channel depth and interface state on extracting result is made. Then the C-V curves for buried-channel MOS structure with two different channel depth are presented from which the channel carrier concentration is extracted. In the measurement of C-V curves, three different sweep velocities are used to analyze the effect of interface states. The theoretical results agree with experimental results.
2006, 55 (6): 2997-3002. doi: 10.7498/aps.55.2997
Basing on first principls, we investigate the electrical properties of a molecular junction consisting of 2-amino-5-nitro-1,4-diethyny-4’-benzenethiol-benzene molecule and gold surface. Density functional theory is employed to obtain the electronic structures of the molecule and the extended molecule. Then we determine the interaction energy between the molecule and the gold surface quantitatively. The elastic Green function method is applied to study its current-voltage properties. Numerical results show that when the external applied bias is lower than 0.9V, there is a current gap. With increasing bias, the conductance of the junction exhibits plateaus. These electrical properties are closely related to the electronic structures of the molecular junction. The extended molecular orbits have great contribution to the charge transport, while localized molecular orbits contributes but little to the current where charge transport takes place by tunneling.
2006, 55 (6): 3003-3006. doi: 10.7498/aps.55.3003
V-ramp method was used to evaluate gate oxide reliability of 0.18μm dual gate CMOS process. Charge of breakdown (Qbd) and voltage of breakdown (Vbd) of gate oxide with n-type substrate and p-type substrate were extracted. It was found that for low voltage (thin oxide) gate oxide device the Qbd of gate oxide of n-type substrate and p-type substrate are almost the same, but for high voltage (thick oxide) gate oxide device the Qbd of n-type substrate and p-type substrate have a big difference. At the same time, Qbd of gate oxide with p-substrate is bigger than that of gate oxide with n-substrate. The difference of Qbd of thin gate oxide and thick gate oxide can be attributed to lithographic damage to the interface of poly-silicon gate and thick gate oxide. There is a big difference between the Weibull slopes of charge of breakdown of thin oxide and thick oxide. For the voltage of breakdown, Similar difference between n-substrate and p-substrate gate oxide was also observed. However, there is no big difference between the Weibull slopes of voltage of breakdown of thin oxide and thick oxide.
2006, 55 (6): 3007-3012. doi: 10.7498/aps.55.3007
Avalanche ionization is a dominant damage mechanism of optical films if laser power density reaches to TW/cm2 level. In order to study avalanche ionization mechanism, it is inevitable to deal with rates of electrons absorbing and losing energy. Both of these relate to the rate of collision between electrons and phonons. So it is important to study the collision of electrons and phonons. In this paper, we discuss the effect of truncating the maximum phonon vector on collision rate, and find the relation between scattering rate and electron kinetic energy. The conclusion is consistent with that obtained from other theories and experiments. At the same time, we also modify the coupling parameter, and obtain the connection of the coupling parameter with phonon vector. After modification, the curve shape of scatter rate versus electronic energy does not change, but the overall value decreases.
2006, 55 (6): 3013-3017. doi: 10.7498/aps.55.3013
Mg contents of Zn1-xMgxO film grown on A-sapphire substrates by molecular beam epitaxy were measured by inductively coupled plasma (ICP) method. Through theoretical analysis, an expression for the difference of Mg content in Zn1-xMgxO film calculated by simple and quadratic inspection formula was given. By comparing the measured results of the ICP with electron probe microanalysis (EPMA), the consistency of ICP with simple inspection formula and EPMA was deduced when Mg content in the samples is less than 0.5, thus the correctness of the data measured by ICP was validated.
2006, 55 (6): 3018-3021. doi: 10.7498/aps.55.3018
Nd1.85Ce0.15CuO4-δsingle crystals with zero-resistance temperature Tc0≈21K were successfully grown by self-flux slow cooling method. We have measured the resistivity transition curves along the c-axis in different fields parallel or perpendicular to the sample surface, respectively, and at fixed field H=0.5T for various angles. The result shows that the field dependence of differential-resistance peak temperature Tp follows the formula H=H0(1-Tp(h)/Tp(0))2 for H//c-axis and H//ab-plane, respectively. The angular dependence of peak temperature Tp can be scaled by the effective mass model as Tp∝H1/2(cos2θ+sin2θ/γ2)1/4. The anisotropic parameter γ of the crystal is about 45.
2006, 55 (6): 3022-3025. doi: 10.7498/aps.55.3022
Light doping of Mn in Ni54Fe19Ga27 plays a significant role in enhancing the magnetic exchange interaction and the rigidity of crystal lattice, it also increases the Curie temperature and stabilizes B2 phase of the material. The oriented internal stress in the single crystals improves the reorientation of the variants due to the existence of Mn. This greatly increases the shape memory deformation and the magnetic field-controlled strain. The internal stress also has an obvious effect on the superelastic behaviors.
2006, 55 (6): 3026-3031. doi: 10.7498/aps.55.3026
Heisenberg XX open chain is very important in the study of quantum state transition. In this paper, we calculate the entanglement between the boundary qubits in the five-qubit Heisenberg XX open chain. When introducing magnetic impurity and system impurity and they satisfy linear relation, the system can be solved exactly, and there exist entanglement between the boundary qubits. Choosing the magnetic and system impurity properly, the boundary entanglement can get the maximal value 0.5.
2006, 55 (6): 3032-3037. doi: 10.7498/aps.55.3032
Using a method in which the free energy is minimized, the exchange bias for ferromagnetic(FM)/antiferromagnetic(AFM) bilayers under the stress field is studied. The thin FM film is considered as a single crystal with cubic and uniaxial magnetocrystalline anisotropies, while the AFM film has only uniaxial magnetocrystalline anisotropy. In the semi-infinite approximation for the AFM layer, the analytical expressions have been derived for effective exchange bias and pinning angle. Numerical calculations show that the effective exchange bias depends on the angle of applied magnetic field, but not on its magnitude. However, the effective exchange bias depends not only on the angle of the stress field but also on its magnitude. The reason is that both the magnitude and angle of the stress field affect the pinning angle.
2006, 55 (6): 3038-3042. doi: 10.7498/aps.55.3038
The influence of pressure on the magnetotransport properties of CrO2 samples at low temperatures has been studied in this paper. The X-ray diffraction patterns of the samples show that the relative intensity of (110) peak increases with increasing pressure, which implies that pressure has the orientation effect on the CrO2 needle-shaped nanoparticles. At low temperatures, the resistance and magnetoresistance of CrO2 samples decrease with the increase of pressure. The experimental results suggest that at low temperatures, the conductance of the sample shows the typical characteristic of intergranular tunneling. Δ decreases with increasing pressure and magnetic field; and furthermore, the range of change of Δ with the magnetic field is relatied to the compacting pressure. The higher the compacting pressure, the smaller the variation of Δ with the magnetic field. These changes can be attributed to the adjustment of pressure on the intergranular tunnel barrier.
2006, 55 (6): 3043-3048. doi: 10.7498/aps.55.3043
The nano-granular magnetic films were investigated using the micromagnetics method in this paper. The nano-granular magnetic film model studied consisted of an aggregate of 122 spherical nano-granules with an fcc structure. The computational results showed that the effect of the dipolar interaction of the system on the static magnetic structure is remarkable, while the effect of exchange interaction is indistinc. The frequency dependent permeability spectra of granular films with different volume ratio of magnetic components were simulated and the percolation phenomena of nanostructural magnetic films were extensively analyzed. Thus, the percolation threshold of the system studied was obtained according to the effective medium theory. Furthermore, the design of nano-granular magnetic films with large magnetic losses were carried out.
2006, 55 (6): 3049-3053. doi: 10.7498/aps.55.3049
Pr2Fe14B/α-Fe nanocomposite magnets were prepared by the melt-spinning technique. The magnetic properties of the magnets were measured by means of a vibrating sample magnetometer(VSM). Alloy compositions were (PrxFe94.3-xB5.7)0.99Zr1 with x=8.2, 8.6, 9.0, 9.4, 9.8, 10.2, 10.6, 11.0 and 11.4(atomic fraction,%). The effects of the wheel speed and alloy composition on the magnetic properties of melt-spun ribbons were investigated systematically. A decrease of remanence Jr with the increase of atomic fraction of Pr is observed causing an increase in coercivity Hci when changing Pr fraction from 8.2% to 11.4 % which is believed to be the cause of the decrease in maximum energy product (BH)max. Despite the low value of Hci obtained for the 8.2 % Pr alloy, (BH)max is substantially raised by the high Jr which reflects the high volume fraction of α-Fe phase. The Jr, Hci and (BH)max of the best sample quenched at a wheel speed of 25 m/s are 1.37T, 501.19kA/m and 227.93kJ/m3, respectively. The magnetic properties in the direction perpendicular to the ribbon surface are much higher than that in the direction parallel with the ribbon surface.
Theoretical description and numerical computation of the relaxation of multi-spin system in the presence of an RF field
2006, 55 (6): 3054-3059. doi: 10.7498/aps.55.3054
According to the Liouville-von Neumann equation and WBR theory, a general description of relaxation of multi-spin system in the presence of an RF field is given. The relaxation equations are deduced and the theoretical computational formulas of various relaxation rates are obtained. It is almost impossible to accessthe analytical solutions of relaxation equations, so the computer program for numerical solutions is developed. By means of the program and the Bloch equations, the steady state solutions of two-spin system under various conditions are computed and these solutions are briefly discussed.
2006, 55 (6): 3060-3066. doi: 10.7498/aps.55.3060
In this paper, a method for reducing the eddy current induced in the magnet with an eddy-current-resisting board by reducing the radius of the gradient coil is proposed. First, the method is analyzed using a theoretical model. Then a gradient coil with reduced radius is designed by using a target field method, and the gradient linear region is verified by using the Biot and Savart's law. Finally, an experiment is performed to testify the result proposed in principle.
Improved dielectric and ferroelectric characteristics of highly (111)-oriented Pb(Zr0.52Ti0.48)O3 films produced by sol-gel method
2006, 55 (6): 3067-3072. doi: 10.7498/aps.55.3067
Highly (111)-oriented Pb(Zr0.52Ti0.48)O3 (PZT) films with a variety of PZT buffer layer thickness were prepared by spin coating on Pt/Ti/SiO2/Si substrates with Sol-Gel process. The thickness of PZT buffer layer was found to play a significant role on grain size and orientation of Pb(Zr0.52Ti0.48)O3 films. With the increasing of PZT buffer layer thickness, both crystallization and orientation were improved obviously. High dielectric constant (1278, 1kHz, for 28nm buffer), low dielectric loss (0.023, 1kHz, for 28nm buffer), symmetric C-V characteristics and P-E curves were obtained. Hysteresis measurements show that the remnant polarization and coercive field of the films reach 43μC·cm-2 and 78kV·cm-1, respectively.
Effects of porosity and grain sizes on the dielectric and piezoelectric properties of porous PZT ceramics and their mechanism
2006, 55 (6): 3073-3079. doi: 10.7498/aps.55.3073
Porous lead zirconate titanate (PZT) ceramics were prepared by adding pore formers, and the effects of pore structure and grain sizes on the dielectric and piezoelectric properties of samples were investigated. The research showed that an increase in the porosity led to reduced dielectric constant as well as enhanced hydrostatic figures of merit (dh·gh). The effect of porosity on dielectric constant can be predicted by the Okazaki experiential formula and Banno model under certain conditions. An increase in grain size increases the dielectric constant, piezoelectric coefficient and hydrostatic figures of merit, which can be explained by the Okazaki space-charge theory. For the sample with 10 wt% PMMA additions sintered at 1300℃, the porosity is 34% and the longitudinal piezoelectric coefficient (d33) is very close to that of dense PZT ceramics, while the hydrostatic figures of merit (dh·gh) is about fifteen times greater than that of dense PZT ceramics. Compared with PZT-polymer composites, the dielectric constant and piezoelectric coefficient of 34% porous PZT sintered at 1300℃ is much higher and can be more efficient in resisting the interference from the ambient medium.
The phase transformation of amorphous bismuth titanate fabricated by sol-gel method was investigated by X-ray diffraction (XRD), transmissions electron microscopy (TEM) and differential thermal analysis (DTA). The experimental results show that the four-step crystallizations were present on heating. The metastable phases Bi2O3 and TiO2 were formed firstly at 433℃, and Bi2Ti4O11 phase was subsequently formed at 488℃ by the reaction between Bi2O3 and TiO2. Sequential reaction between Bi2Ti4O11 and Bi2O3 resultedin the formation of Bi4Ti3O12 phase with tetragonal structure at about 644℃, and stable Bi4Ti3O12 phase with orthorhombic structure was finally formed at about 830℃.
2006, 55 (6): 3086-3090. doi: 10.7498/aps.55.3086
High quality Sr2Bi4Ti5O18 (SBTi) ferroelectric thin films on Pt/Ti/SiO2/Si(100) substrates were successfully prepared using the sol-gel method.The microstructure, ferroelectric properties and fatigue characteristics of SBTi thin films were investigated.The results show that the films with smooth surface are of single phase of SBTi and randomly oriented. The well-saturated ferroelectric hysteresis loops and the fatigue properties were obtained by hysteresis measurements using a metal-ferroelectric-metal structure. The remnant polarization (2Pr) and coercive field (2Ec) reached to 24.0μC/cm2 and 137.8kV/cm, respectcively in the electric field of 275kV/cm. No fatigue was observed up to 4.4×1010 switching cycles.
2006, 55 (6): 3091-3094. doi: 10.7498/aps.55.3091
The exchange interaction between electrons exists in the paramagnetic media CeF3. The relation of the effective exchange field Hin to the temperature is shown to be Hin=(-0.68-0.002T)×10-6M. By means of this relation and the quantum theory, the inverses of the magnetic susceptibility and Verdet constant of CeF3 crystal as a function of temperature are calculated. The calculated V-1-T and χ-1m-T curves are in good agreement with the measured results. The results are further discussed in Terms of the concepts and rules of photo-magnetic effect.
2006, 55 (6): 3095-3099. doi: 10.7498/aps.55.3095
The magneto-optic (MO) coupled-mode equations for magnetostatic waves (MSWs) and guided optical waves (GOWs) under phase-mismatch conditions were deduced and applied to the noncollinear interaction with magnetostatic backward volume waves (MSBVWs) in obliquely magnetized yttrium-iron-garnet (YIG) film using single-element microstrip line transducer. The diffraction efficiency (DE) of the incident TE0-mode light was calculated. For the case of magnetization along the MSBVW propagation direction, the calculated results are in good agreement with the experimental data. In contrast, by using an appropriately tilted bias magnetic field the DE can be increased by 6dB and is insensitive to the phase mismatch induced by the change of magnetization direction. Thus, the optimization of the direction of the bais magnetic field is an effective method for improving the diffraction performance and increasing the MO bandwidth of the Bragg cells.
Optimum exposure intervals for light-induced optical waveguides in lithium niobate crystals by laser micromachining
2006, 55 (6): 3100-3105. doi: 10.7498/aps.55.3100
The optimal exposure intervals for optical waveguides induced by laser micromachining in LiNbO3 crystals are theoretically and experimentally investigated. When the focused laser beams scan along different directions, the optimal intervals for waveguide fabrications are numerically specified by solving the photorefractive dynamic equations. The simulations show that the index distributions of the fabricated waveguides are strongly dependent on the optimal exposure interval, and the optimal exposure interval is not dependent on the scanning directions of the writing beam. When the writing beam scans the crystal along the c axis for sandwich illumination, optical waveguides cannot be fabricated efficiently. However, in this case, symmetric refractive index changes can be obtained. Experimental demonstrations are performed by scanning LiNbO3:Fe crystal with a focused green laser beam. The light-induced index changes are measured by digital holography. The experimental results conform to the theoretical analyses. Additionally, a Y-branche waveguide is experimentally formed and the results of the guiding tests are showed in this paper.
Effects of GeO2 on the thermal stability and optical properties of Er3+-doped germanate-tellurite glasses
2006, 55 (6): 3106-3111. doi: 10.7498/aps.55.3106
Germanate-tellurite glasses with the molar compositions of x GeO2-(70-x) TeO2-5K2O-5Na2O-10Nb2O5-10ZnO-0.2Er2O3 (x=0,10, 25, 50, 70) have been investigated for developing 1.5μm fiber and planar amplifiers. Effects of GeO2 on the thermal stability and optical properties of Er3+-doped germanate-tellurite glasses have been discussed. It is noted that the thermal stability of the glasses are improved and the maximum phonon energy are increased by increasing GeO2. Adding GeO2 increases the Judd-Ofelt parameters Ω2, Ω6 but decreases the stimulated emission cross sections σe. According to the McCumber theory, the maximum peak of σe is 9.92×10-21cm2 at 1.53μm in germanate-tellurite glasses. The maximum FWHM of Er3+4I13/2→4I15/2 emission spectrum is 52 nm. In addition, the intensity of upconversion luminescence of the Er3+-doped germanate-tellurite glasses decreases rapidly with increasing GeO2 content.
2006, 55 (6): 3112-3118. doi: 10.7498/aps.55.3112
In recent years, thulium-doped fluorozirconate (ZBLANP) glass has become one of the promising materials in the field of the laser cooling of solids. However, up to date, the theoretical studies on the laser cooling of the Tm3+:ZBLANP fiber and their experimental results have not been reported. In this paper, we have developed a simple theoretical model to discuss some basic problems in the laser cooling of solids. The influences of the fluorescent quantum efficiency, the pump power, the change of fluorescence wavelength and the black-body radiation on the laser cooling effect for the Tm3+:ZBLANP fiber are discussed in some detail, and some interesting and important results are obtained. These results will provide the reliable theoretical basis for further experimental study on the laser cooling of the Tm3+:ZBLANP fiber.
2006, 55 (6): 3119-3123. doi: 10.7498/aps.55.3119
In this paper, ZnO microflowers were synthesized on silicon substrates by the thermal oxidation of pure Zn powder(99.99%). The X-ray diffraction spectrum (XRD) showed that ZnO microflowers have a hexagonal wurtzite structure. The field-emission scanning electron microscope (FE-SEM) image indicated that as-synthesized ZnO microflowers consisted of lots of long and straight microrods, which possessed hexagonal prism morphology. The length of microrods ranges from 30 to 50μm. The resonant Raman spectrum showed multiphonon scattering process the 5th-order longitudinal optical phonon (A1(LO)) mode in the backscattering geometry, indicating that the sample is of high quality. In the temperature-dependent photoluminescence (PL) spectra, “ negative thermal quenching” phenomenon of neutral acceptor bound exciton (A0X) was observed, and its origin was discussed.
2006, 55 (6): 3124-3127. doi: 10.7498/aps.55.3124
Zirconium oxide (ZrO2) coatings for 632.8nm center wavelength were deposited on the Ag layer by electron beam evaporation, optical thickness of which varied in the range of 80—480nm. Surface roughness and scattering characteristics of ZrO2 coatings with different thickness were investigated. It was found that with the gradually increase of the thickness, both roughness and total integrated scattering (TIS) of the samples decreased firstly and then increased. These results indicated that TIS of the samples mainly depended on the surface roughness. According to the uncorrelated surface roughness scattering model, scattering properties of the samples were analyzed theoretically. The calculated TIS values based on this model agreed well with that obtained by TIS measurements.
2006, 55 (6): 3128-3131. doi: 10.7498/aps.55.3128
92%Pb(Mg1/3Nb2/3)O3-8%PbTiO3 (PMNT) thin films have been prepared on Pt/Ti/SiO2/Si substrate with a LaNiO3 (LNO) buffer layer and on sapphire substrate by chemical solution deposition, respectively. X-ray diffraction analysis shows that the PMNT thin films on Pt/Ti/SiO2/Si substrate are almost pure perovskite phase with (110)-preferential orientation. The optical constants (n, k) of the PMNT thin films in the wavelength range of 2.5—12.6μm were obtained by infrared spectroscopic ellipsometry measurement. By fitting the optical transmission spectra of the PMNT thin films on sapphire substrate in the wavelength range of 200—1100nm, the optical constant (n and k) and absorption coefficient (α) were obtained. And that the bandgap energy of the PMNT thin films on sapphire substrate was found to be about 4.03eV.
2006, 55 (6): 3132-3135. doi: 10.7498/aps.55.3132
Mn-doped ZnO thin films were prepared on SiO2 substrate using pulsed laser deposition (PLD) technique in order to investigate the structure and optical properties of the films. XRD, AFM, EDX analysis and UV-VIS spectrophotometry were employed to characterize the Mn-doped ZnO films. The results showed that the shape of the XRD spectrum was remarkably similar to that of the un-doped ZnO film, indicating that the structure of the films was not disturbed by Mn-doping and the film also had mainly (103) peaks. The contents of (Zn, Mn)O thin films prepared by PLD were consistent with the targets, thus realizing the thin films deposition with same constitutuents as the target. The films had rather flat surfaces with the peak-to-tail roughness of about 80nm and an average grain diameter of about 25nm. Mn-doping changed the band gap of the films, which increased with the increase of the Mn content. Moreover, when the Mn content increased from 6% to 12%，the absorbence in strong UV absorption band increased too.
Phase behavior and thermal dynamic properties of free volume on SMMA/SMA copolymer blend studied by PALS method
2006, 55 (6): 3136-3140. doi: 10.7498/aps.55.3136
The temperature dependence of the free volume in SMMA/SMA (30/70) blend was investigated by the positron annihilation life spectroscopy (PALS) at different heating rates according to the free volume theory, and the thermodynamics characteristics of the phase behavior of the polymer blends was also explored. At temperatures above Tg, we found from the positron annihilation life spectra that when the structural relaxation time is comparable with the retention time, the temperature dependence of the free volume parameters obviously departs from the linear relation. Based upon the change tendency of the free volume concentration I3 with temperature, it is postulated that there is a growing stage of the phase separation in the same temperature range.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2006, 55 (6): 3141-3146. doi: 10.7498/aps.55.3141
Yb3+-doped KY(WO4)2 (Yb:KYW) laser crystal was grown by top seeded solution growth (TSSG) method. The solute and solvent calcined at 920℃ and 600℃ respectively for 8h formed a single phase as shown by XRD analysis, which suppressed the volatilization in the growth process. The as-grown crystal was identified as β-Yb:KYW by XRD, and the cell parameters of Yb:KYW were calculated to be a=1.063nm, b=1.034nm, c=0.755nm and β=130.75°. Absorption spectrum of samples with different thickness (E//c) were obtained, in which two intensive peaks at 933nm and 981nm were observed, and the absorption cross section is 5.34×10-20cm2 at the main peak of 981nm. Fluorescence spectrum of the sample was measured and there exist three intensive emission peaks at 990, 1010 and 1030nm. It was calculated that the peak emission cross section is 3.1×10-20cm2 at 1030nm and the lifetime is 0.56ms which is closed to the measured value. The pumping parameter (β), saturated pump intensity (Isat) and minimum pump intensity (Imin) were calculated, and the parameter Imin (24kW/cm2) of Yb:KYW is very low compared to other Yb3+ doped crystals.
2006, 55 (6): 3147-3151. doi: 10.7498/aps.55.3147
Several methods are introduced to calculate the percolation threshold of nanoparticle cermet films made of ceramic matrix with embedded metal nanoparticles. For Ag-MgF2 nanoparticle cermet films, the percolation threshold of 0.14, which reasonably agrees with the experimental results, is calculated by using Priou's percolation threshold theory. The factors that affect cermet film percolation threshold are also discussed.
2006, 55 (6): 3152-3156. doi: 10.7498/aps.55.3152
Bi3.25La0.75Ti3O12 thin films were prepared on p-Si substrates by Sol-Gel technology. The effect of annealing temperature on microstructure, morphology, dielectric and ferroelectric properties of Bi3.25La0.75Ti3O12 films was investigated. Bi3.25La0.75Ti3O12 films annealed at 500℃ were not very uniform, they consisted of small grains and coarse grains with poor dielectric and ferroelectric properties. When the annealing temperature was over 550℃, Bi3.25La0.75Ti3O12 films were uniform and crack free as well as exhibiting no preferred orientation with good dielectric and ferroelectric properties. The leakage current density of Bi3.25La0.75Ti3O12 thin films is 2×10-8A/cm2 at 4V. A noticeable improvement of ferroelectric properties have been obtained when the annealing temperature was increased. Bi3.25La0.75Ti3O12 films annealed at 600℃ showed excellent dielectric and ferroelectric properties with a dielectric constant of 288, a dielectric loss of 1.57%, a remanent polarization of 17.5μC/cm2 and a coercive field of 102kV/cm.
2006, 55 (6): 3157-3164. doi: 10.7498/aps.55.3157
The oxygen adsorption on Au (111) surface has been studied systematically using density function theory (DFT). The adsorption energies, adsorption structures, work functions, density of electrons and projected density of states have been calculated in wide ranges of coverage. It is found that the fcc-hollow site is the energetically favorable site for all the coverage range considered. The repulsive interaction has been identified, and the adsorption energy decreases with the coverage θ, while work function increases linearly with the coverage. It has been found that the O-Au interaction is very weak due to the fully occupied anti-bonding states from O 2p and Au 5d hybridization.
2006, 55 (6): 3165-3169. doi: 10.7498/aps.55.3165
With the method of differential optical absorption spectroscopy (DOAS), aerosolalong the light path is monitored and its size distribution is measured with double optical path method. By using double optical path method, the absolute intensity of the source can be determined and the influence of source variation is reduced greatly. Aerosol extinction coefficient from 250nm to 650nm and size distribution from 0.1μm to 1.75μm were obtained. By comparison with optical particle counting, good correlations are found between the DOAS and optical particle counting resulcs.
2006, 55 (6): 3170-3174. doi: 10.7498/aps.55.3170
Based on a tight-binding disordered model describing a single electron band, we establish a one-dimensional disordered binary DNA model, and calculate the density of electronic states，the localization property of electronic wave-function and the localization length of a DNA sequence with 2×104 nucleotide base pairs. We also investigate the effect of composition of nucleotide base pairs, the degree of disorder of the energy base pairs on the localization length. The results indicate that the electronic states of DNA sequence are localized due to the compositional disorder of nucleotide base pairs and the energy disorder of the lattices, and the localization length is dependent on the composition of nucleotide base pairs and the disorder degree of lattices energy.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2006, 55 (6): 3175-3179. doi: 10.7498/aps.55.3175
We have investigated the dynamics of the Lorenz system under quasiperiodic driving. When the forcing amplitude is increased to certain critical value，the dynamics changes fundamentally. Therefore a new mechanism for the creation of the strange nonchaotic attractor is advanced in this paper. When the forcing amplitude is increased, the strange attractor is replaced by a strange nonchaotic attractor, eventually the phase space is suppressed into an invariant quasiperiodic torus. Numerical results show that the critical amplitude of the force is roughly proportional to the Rayleigh parameter, but slightly influenced by its frequency.
2006, 55 (6): 3180-3187. doi: 10.7498/aps.55.3180
For a long time in the past, researches of time series were often based on their external characters and used linear and statistical methods. However, most actual systems are nonlinear, nonstationary and complicated, which increased the diffculties in treating them. The research of abrupt change is one of most important research aspects of nonlinear time series, for which the traditional method based on the external characters of data and using linear process lacks enough physical foundation, and has obvious limitations. How to find out the essence of complicated systems from time series, in other words, to check the abrupt change in dynamical structure of actual data series is a really important problem pending solution. In the present paper, we present a new method——the dynamical correlation exponent segmentation algorithm for checking dynamical abrupt change based on the dynamical lag correlation exponent. The validity of this method is verified by constructing an ideal time series and put it to test. It was found that a few noise spikes have little influence, but continuously distributed white noise has some influence to this new method. Comparison with conventional t-test and Yamamoto method was made to show the relative merits of the methods.
The correction of short-range Mie scattering laser lidar returns based on the Gaussian character of laser beam
2006, 55 (6): 3188-3192. doi: 10.7498/aps.55.3188
A new method for correcting Mie scattering laser lidar short-range returns by virtue of Gaussian emission was described. Firstly, basing on the Gaussian character of laser beam, the lidar returns were corrected. Secondly, on the assumptionof an almost homogenous atmosphere, the corrected logarithmic range-adjusted power curve S(r) was fitted with conic section, then the corresponding influences of overlapping area were corrected. Some examples show that the corrected results are much closer to the real atmospheric conditions.
2006, 55 (6): 3193-3196. doi: 10.7498/aps.55.3193
Cr-doped and Mg,Cr-codoped Al2O3 crystals were grown by Czochralski method. The latter has a broad absorption peak in 900—1600nm region. We investigated the change of the absorption band with annealing under different atmospheres or temperatures. Through establishing a structure defect model, we successfully interpreted all the experiment results and confirmed that the extremely broad infrared absorption band belonged to Cr4+, which should occupy the octahedral sites in Al2O3.
2006, 55 (6): 3197-3201. doi: 10.7498/aps.55.3197
The effect of electron screening on prompt explosion energy of supernova is discussed in regard to progenitor model WS15M⊙. The average heavy nuclei model is used for calculating the electron capture rates. The simulation results show that electron capture rate is decreased and the collapsing time-scale is prolonged by the electron screening, and the total energy of neutrino leakage increases. Acordingly, by the energy of the shock wave also decreases appreciably. The effect of electron screening on other supernova simulations is estimated.