Vol. 55, No. 3 (2006)
2006-02-05
GENERAL
2006, 55 (3): 999-1004.
doi: 10.7498/aps.55.999
Abstract +
In this paper, a new particle filter based on sequential importance sampling (SIS) is proposed for the on-line estimation of non-Gaussian nonlinear systems. In this filtering method, state parameters separation and an annealing parameter are used to produce importance function. Since the distribution function makes full use of the prior, likelihood, and statistical characteristics of noise and the newest observation data, it is much closer to posterior distributions. Theoretical analysis and simulation show that the performance of proposed particle filter outperforms the standard particle filter and the extended Kalman filter.
2006, 55 (3): 1005-1010.
doi: 10.7498/aps.55.1005
Abstract +
With the development of micro chemical and medical analysis in MEMS, micro-fluid-control chip becomes more and more popular. Based on discrete droplet control system, chemical and medical analysis is applied in the micro chip lab. The change of voltage between the dielectric layer of the electrode controls the wettability of a droplet on a dielectric solid surface and then makes it possible to create,transport,merge and cut the micro droplets. This paper presents a numerical method to simulate the droplet motion by electrowetting on dielectric (EWOD). The second-order projection method is carried out to solve N-S equations and level set function. The interface is captured as zero level set. Dynamic contact angle for fluid contacting a solid surface by the electric potential is used to evaluate the wettability of fluid by EWOD. The numerical scheme is based on staggered MAC grid. Numerical simulations are used to capture the interface between two kinds of fluids in micro channels, the shapes of micro droplets resting on the horizontal solid surface under different electric potential and the transportation of a micro droplet in a parallel-plate channel when electrodes are activated.
2006, 55 (3): 1011-1015.
doi: 10.7498/aps.55.1011
Abstract +
Multi-linear variable separation approach based on the corresponding Bcklund transformation (BT-MLVSA) is a useful method to solve nonlinear systems. General multi-linear variable separation approach (GMLVSA) is its extension and there are four ways to realize it. The first one is to expand the nonlinear systems according to multi-arbitrary functions, the second one is to expand the variable separation ansatz. The third one is the MLVSA based on the Darboux transformation (DT-MLVSA) and the last one is the derivative-dependent functional variable separation method. By using the first kind of GMLVSA, the solutions can be obtained for the (2+1)-dimensional mNNV system and sine-Gordon system. In this paper, the first kind of GMLVSA is extended to solve some two-dimensional nonlinear systems which are derived from the (2+1)-dimensional sine-Gordon system by using symmetry reduction method. Namely, the applicability of the method is retained from high dimensional systems to low dimensional systems in the symmery reduction sense. This also provide a way of deducing low dimensional systems which can be solved by GMLVSA from high dimensional systems.
2006, 55 (3): 1016-1022.
doi: 10.7498/aps.55.1016
Abstract +
In this paper, variable separation solution and soliton excitations of the (1+1)-dimensional generalised shallow water wave equation are obtained. This equation includes two special cases which are completely integrable (IST integrable): the AKNS equation and the Hirota-Satsuma equation. Firstly, the variable separation (BT-VS) method based on the Bcklund transformation is extended to this eqaution for deriving VS solutions which include some low dimensional arbitrary functions. In the integrable cases, a space arbitrary function and a time arbitrary function are included. But in the other cases only a time arbitrary function is included and the space function needs to satisfy a specific condition. In addition, for the (1+1)-dimensional universal formula, abundant soliton excitations can be constructed, such as one-soliton, bell-anti-bell soltion, soliton expansion, breather-like, instaton-like. Finally, some discusions are made about the VT-VS method.
2006, 55 (3): 1023-1028.
doi: 10.7498/aps.55.1023
Abstract +
Based on a new finite-difference scheme and Runge-Kutta method together with transparent boundary conditions(TBCs), a novel beam propagation method to model step-index waveguides with tilt interfaces is presented. The modified scheme provides an precies description of the tilt interface of the nonrectangular waveguide structure, showing a much better efficiency and accuracy comparing with the previously presented formulas.
2006, 55 (3): 1029-1034.
doi: 10.7498/aps.55.1029
Abstract +
With the help of Maple procedure, the Zakharov equation, which takes the quantum effect into account, is solved by means of extended tanh-function method and bifunction method. Several solitary wave solutions are obtained, including bright soliton, W-shaped soliton, M-shaped soliton and singular solutions.
2006, 55 (3): 1035-1039.
doi: 10.7498/aps.55.1035
Abstract +
The Sprott-B and Sprott-C are topologically equivalent but they have distinct structures. Chaos synchronization is realized between the two systems via linear coupling of systemic variable. Based on Lyapunov stability theory, the threshold value of coupling coefficients for synchronization of two systems is derived. The practical circuit is designed to realize chaos synchronization between the two systems and the experimental result verifies the conclusion. A new method for secure communication, which can increase the security of a communication system is proposed based on chaos synchronization between the above systems.
2006, 55 (3): 1040-1048.
doi: 10.7498/aps.55.1040
Abstract +
Chaotic neural networks consisting of chaotic neurons exhibit rich dynamic behaviors and are expected to be used in information processing. But the output sequence of chaotic neural networks is chaotic, so the networks do not converge to a stable pattern. In order to apply chaotic neural networks to information search or pattern recognition, etc., it is necessary to control chaos in chaotic neural networks. In this paper, we propose an improved delayed feedback control method for chaotic neural networks. By means of the control method, computer simulation shows that controlled chaotic neural networks can converge to period-2 states between one stored pattern and its reverse pattern or various multiple-period states depending on the delay time.
2006, 55 (3): 1049-1054.
doi: 10.7498/aps.55.1049
Abstract +
In this paper, the effect of random phase for Duffing systems is investigated. We show that random phase can generate chaos or suppress chaos by the average of top Lyapunov exponent, which is computed based on Khasminskii's spherical coordinate formulation for linear stochastic systems. In addition, phase portraits, Poincaré surface of section and time evolution are studied to confirm the obtained results. Both methods lead to fully consistent results.
2006, 55 (3): 1055-1060.
doi: 10.7498/aps.55.1055
Abstract +
Spectroscopic ellipsometry is widely used in measuring the refractive index and thickness of optical isotropic thin layers. A simple method using spectroscopic ellipsometry to measure uniaxial liquid crystal layer is introduced. A UVISEL spectroscopic phase modulated ellipsometer is used to measure the ordinary refractive index, extraordinary refractive index and thickness of the liquid crystal layer in a parallel-aligned liquid crystal cell. The phase retardation Δnd is measured in transmission mode. The results show that the spectroscopic ellipsometry can be used to measure the anisotropic multilayer liquid crystal cell with high precision.
2006, 55 (3): 1061-1067.
doi: 10.7498/aps.55.1061
Abstract +
We studied the effect of polarization of terahertz pulse and probe beam on terahertz detection in optically isotropic detection crystals using wave coupling theory of linear electro-optic effect. The study results show that the effect is remarkable, and the detection can get its largest sensitivity when the probe beam propagates along (110) direction which is most suitable for terahertz detection. Some of the study results are in good agreement with the previously published experimental results. So our study is helpful for the design of electro-optic detectors.
NUCLEAR PHYSICS
2006, 55 (3): 1068-1076.
doi: 10.7498/aps.55.1068
Abstract +
We studied systematically the reaction dynamics induced by neutron-halo nuclei and proton-halo nuclei within the isospin dependent quantum molecular dynamics,such as the effects of loose bound halo-nuclei on the fragmentation reaction and momentum dissipation for different colliding systems with different beam energies and different impact parameters. In order to emphasize the roles of neutron-halo nucleus 19B and proton-halo nucleus 23Al on the reaction dynamics wealso calculated the the reaction dynamics induced by the stable nuclei 19F and 23Na with equal mass under identical incident channel conditions. Based on the comparison of results of reaction dynamics induced by halo-nucleus colliding systems and stable nucleus collidinmg systems we found that the roles of loose bound halo-nucleus structure on the fragmentation multiplicity and nuclear stopping (momentum dissipation) are important for all of colliding systems with different beam energies and minor impact parameters, such as, the loose bound halo-nuclei structure increases the fragmentation multiplicity, but reduces the nuclear stopping.
2006, 55 (3): 1077-1082.
doi: 10.7498/aps.55.1077
Abstract +
The three well-known parameters of motion (magnetic momentum, energy and canonical toroidal momentum) are utilized to develop a guiding center orbit code, GCORBIT. The effect of poroidal field ripple and toroidal angle scatter is considered in the GCORBIT. It is applied to compute guiding center orbit of charged particle in axisymmetric tokamak, the loss region of velocity space and the loss fraction of fast ions.To compare achieved results, the loss region of velocity space by GCORBIT includes many effects: non-closed orbit of divertor, first orbit loss by guiding-center orbit being non-closed or intersecting with any material limiters, trapping by the poroidal field ripple in local magnetic wells, ripple random diffusion and toroidal angle scatter enabled by velocity space discontinuous confinement region. The GCORBIT is now being used to analyze the confinement of fast ions in EAST Tokamak. Our numerical calculations are focused on the loss of fast ions.
2006, 55 (3): 1083-1088.
doi: 10.7498/aps.55.1083
Abstract +
Photoionization and dissociative photoionization of HFC-152a have been studied using synchrotron radiation and a reflectron time-of-flight mass spectrometry (RTOF-MS). The ionization energy of parent molecule (11.94±0.04eV) and appearance potentials of various fragment ions have been determined by measuring their photoionization efficiency curves. Energies, symmetry point groups and ground electronic states of neutrals and cations of parent and its fragments have been calculated using GAUSSIAN-03 program with the G3 method. According to the theoretical and experimental results, some dissociation channels and their dissociation energies of CH3CHF+2 have been analyzed.
2006, 55 (3): 1089-1098.
doi: 10.7498/aps.55.1089
Abstract +
The interactions between X-ray and the sample and crystals were investigated, and the influence of small angle scattering on images was emphatically analyzed in diffraction enhanced imaging in this paper. Not only were the additional noise term caused by small angle scattering introduced, and more general DEI equation established, but also expressions of absorption contrast, extinction contrast and refraction contrast were given for the peak image and the middle slope image. With the new DEI equation, the contrasts of two kinds of resultant images (apparent absorption image and refraction image) were discussed.
2006, 55 (3): 1099-1106.
doi: 10.7498/aps.55.1099
Abstract +
Diffraction enhanced imaging is a new X-ray radiographic imaging method using monochromatic X-rays from a synchrotron source which produces high contrast and spatial resolution images of thick absorbing objects. Use of this method in medicine, material science and industrial applications in non-destructive testing is highlighted at present. The purpose of this study is to discuss diffraction enhanced imaging computer tomography which combines computer tomography (CT) and diffraction enhanced imaging (DEI) method. Comparison between DEI-CT images with conventional X-ray CT images shows that the DEI-CT imaging technique gives not only surface information but also the internal structure of organs or soft tissues with high contrast. The obtained images show the micro-structures details of DEI-CT.
ATOMIC AND MOLECULAR PHYSICS
2006, 55 (3): 1107-1112.
doi: 10.7498/aps.55.1107
Abstract +
The molecular dynamics modeling method is used to study the adsorption characteristics of 1-hydroxyethyldene-1,1-diphosphonic acid(HEDP) on the {104} surface of calcite. The simulated 3-D molecular graphs display that the oxygen atoms in the phosphonate groups of HEDP are strongly electro negative and have high affinity to cationic regions of the surface of the crystals, which results in the inhibitor molecular binding to the crystal surface to form the “multi-site stereo matching". The calculated results show that the adsorption energy of HEDP on the surface, step and kink are -5.2eV,-7.0eV and -23.5eV, respectively. It suggestes that HEDP malecules prefer to adsorb on the kinks to inhibit the development of steps on the calcite surface.
2006, 55 (3): 1113-1118.
doi: 10.7498/aps.55.1113
Abstract +
The geometric configuration, electronic structures and vibrational frequency of the AlxOy(x=1—2,y=1—3) molecules were calculated with B3LYP method at 6-311++g** level. The calculations show that the ground states of AlxOy molecules can be rapidly obtained by adding one or two O atoms to the different positions of Oy clusters with the aid of the software Gaussview 3.7, and taking into account of possible symmetries. Analysis of the geometrical parameters of ground state structure reveals that the atoms have chained or planar structure only. Analysis of the energy of ground state structure shows that Al atoms tend to bind with three other atoms. With one Al atom in the molecule the ground state structures multiplicity is two, with two Al atoms in the molecule, the ground state structures multiplicity is one except for Al2O3, of which the ground state structures multiplicity is three.
CLASSICAL AREA OF PHENOMENOLOGY
2006, 55 (3): 1119-1125.
doi: 10.7498/aps.55.1119
Abstract +
Using physical optics to calculate single scattering, and using equivalent ray tubes to calculate multiple scattering, we can get the numerical results more efficiently and accurately. Several complex perfect electric conductors and medium targets are calculated, and numerical results are in good agreement with experiments.
2006, 55 (3): 1126-1129.
doi: 10.7498/aps.55.1126
Abstract +
Based on the optimization of the optical material and internal reflection angle, we designed a model of improved Fresnel prism that is insensitive to the angle of incidence. In this device, the incident light is reflected twice at the same internal reflection angle on the interface between two kinds of glass and the air. So the changes of retardation caused by reflection can compensate each other. The calculation shows that the departure of this kind of phase retarders is less than 0.36° when the angle of incidence changes between -2° and +2°.It reserves the merits of normal incidence and normal output in archetypal Fresnel prism, and brings convenience in the operation.
2006, 55 (3): 1130-1136.
doi: 10.7498/aps.55.1130
Abstract +
In the field of optical information security, the most attractive work is the so-called double-random-phase encoding encryption scheme proposed by Javidi. However, the security of this cryptosystem has not been analyzed thoroughly from the point of view of cryptoanalysis. In this article, the weakness of Javidi's optical security system is carefully analyzed with a known-plain text attack. It is shown that the double-random-phase encoding encryption scheme is a linear symmetric block cipher cryptosystem and its linearity opens avenues of attacks. Under the known-plaintext attack, attacker can obtain the phase key(s) in the input plane using the typical phase retrieval algorithms and subsequently deduce the phase key(s) in the Fourier domain easily. In addition, an optical implementation of known-plain text attack is also proposed.
2006, 55 (3): 1137-1142.
doi: 10.7498/aps.55.1137
Abstract +
Ultra-fast dynamic process can be recorded by ultra-short pulsed digital holography with angular multiplexing technique, in which the angle between reference beam and object beam has to be restricted to within a few degrees due to the restricted pixel size of CCD in the recording. In this report, spatially angular multiplexing technique is introduced, and the its applicability has been proved through a simulation experiment of digital holography with CW laser. Besides, optical set-up based on this technique is designed. Computation result shows that a series of dynamic multi-images in nanosecond time scale of ultra-fast process can be automatically recorded on a piece of digital hologram.
2006, 55 (3): 1143-1147.
doi: 10.7498/aps.55.1143
Abstract +
Based on optical interference theory and Fourier modal theory, a new multi-layer dielectric gratings is designed for use in femtosecond laser system at wavelength 0.8μm. A multi-layer dielectric with stack of H3L(HL)^9H0.5L2.4H is used as a substrate to be etched with corrugated structure. Numerical computation indicates that the diffraction efficiency of -1 order can be more than 95% when the parameters of multi-layer dielectric grating are the following: laser is incident on the grating at 36.7° in TE mode, the duty cycle is 0.35 and the line density is 1480/mm, the groove depth is 0.2μm and the top residual HfO2 is 0.15μm.
2006, 55 (3): 1148-1152.
doi: 10.7498/aps.55.1148
Abstract +
Electron holography was successfully used to investigate the distribution of the potential of the barrier in magnetic tunnelling junctions experimentally and theoretically. We got a clear profile of the potential which shows a “well” in reconstructed phase profile. We also pointed out some artefacts in electron holographic study of magnetic tunnelling junctions and suggested some possible methods to resolve them.
2006, 55 (3): 1153-1159.
doi: 10.7498/aps.55.1153
Abstract +
We consider that an ultracold two-level atom passes through multi spatially separated single-mode cavity fields and investigate the influence of the center-of-mass motion of the atom, the length of the cavity and the separation between two cavities on the transmission and photon emission probabilities of the atom. We find that both the transmission and photon emission probabilities as functions of the cavity length have multi-resonance peaks when the separation between two cavities is equal to an integer multiple of half the de Broglie wavelength of the atomic center-of-mass motion. The present work shows that the wave function of the atomic center-of-mass motion may be modulated in a macroscopic level by arranging the cavities.
2006, 55 (3): 1160-1164.
doi: 10.7498/aps.55.1160
Abstract +
Based the energy transfer between energy levels and the transition between ions of diode-end-pumped Tm,Ho:YLF laser, with consideration of energy transfer up-conversion, the rate equations of Tm,Ho:YLF Q-switched laser are given, and the analytical formulas of single pulse energy is deduced from the rate-equations. It is shown theoretically that the energy transfer up-conversion reduces not only the single pulse energy but also the upper level lifetime of Tm,Ho:YLF Q-switched laser. An experiment is carefully designed to verify these conclusions.
2006, 55 (3): 1165-1170.
doi: 10.7498/aps.55.1165
Abstract +
A six-temperature multifrequency dynamical model of pulsed CO2 lasers is presented, taking account of the collision-dependent overlap of rotational lines, the effect of hot bands and sequence bands on the gain spectrum, and non-Lorentzian line overlap effect in a wide range of pressures from 20 torr to 20 atm. Theoretical calculations of pulse shape and laser spectrum have good agreement with experimental results. This model should be useful in the understanding of pulsed CO2 laser dynamics, in the evaluation of alternative pump schemes, and in the investigation of tunable characteristics. Thus it can provide theoretical support for the design of pulsed CO2 lasers.
2006, 55 (3): 1171-1175.
doi: 10.7498/aps.55.1171
Abstract +
A high-average-power and high-beam-quality diode-side-pumped solid-state Q-switched laser was developed by use of low concentration Nd:YAG crystals with thermally near-unstable resonator design and two-rod birefringence compensation technology. Two orthogonal acousto-optic Q-switches were used to sustain fully holding of the pump gain. The 1064 nm quasi-continuous-wave average output power of 258 W at pump power of 1116 W was achieved with the beam quality factor M2～15.5 at a repetition rate of 10 kHz and a pulse width of 64 ns, corresponding to a peek power of 0.4GW and an optical-to-optical conversion efficiency of 23.1%.
2006, 55 (3): 1176-1180.
doi: 10.7498/aps.55.1176
Abstract +
Using a three-dimensional test particle simulation code, we study the pondermotive scattering of an ultrashort electron beam subject to a focused ultraintense femtosecond laser pulse. The dependence of the spatial distribution of electron beam and electron energy spectrum on the time delay between laser pulse and electron pulse is discussed in detail. Through the measurement of the spatial distribution of electron beam or electron spectrum, we present a method to measure the duration of an ultrashort electron pulse.
2006, 55 (3): 1181-1185.
doi: 10.7498/aps.55.1181
Abstract +
A code series for transient collisional excitation (TCE ) was newly developed based on the previous code series for QSS scheme, the TCE Ne-like Ge 19.6nm X-ray laser experiment done by RAL in 2000 was modeled to test our code series, a relatively good fit is obtained which provides convenience for our study of TCE scheme.
2006, 55 (3): 1186-1190.
doi: 10.7498/aps.55.1186
Abstract +
We study the three-photon resonant six-wave mixing (SWM) with phase-conjugation geometry in Doppler system. The theoretical calculation indicates that the signal spectrum is Doppler-free when the laser line width is narrow. This technique provides a new spectroscopic tool for studying the highly excited atomic or molecular states with high resolution. It has advantages of uncritical phase matching condition, excellent spatial signal resolution and simple optical alignment.
2006, 55 (3): 1191-1195.
doi: 10.7498/aps.55.1191
Abstract +
Theory of the self-starting passive mode-locked Yb3+-doped fiber ring laser generating short pulses is presented. The ultrashort pulse Yb3+-doped fiber ring laser with all-fiber structure has been designed and turned out. Two 976nm LD pumped lasers are used as the pump sources and high concentration Yb3+-doped fiber is adopted as gain medium. Using the nonlinear polarization rotation (NPR) effect of the fiber, self-starting stable mode-locked pulse is obtained. The mode-locked threshold power of the laser is 260mW and the output power is 25mW. The center wavelength of the mode-locked pulse is 1056nm with 3dB bandwidth of 11.7nm at repetition rate of 20MHz. Comparing with the other structures of the fiber lasers, the structure we adopted is more efficient and has better stability.
2006, 55 (3): 1196-1200.
doi: 10.7498/aps.55.1196
Abstract +
Internal factors (thermal lens,cavity lengths,enabled aperture etc) restricting the output of the LD end-pumped Nd:YVO4 solid-state laser with flat-flat cavity is studied. A reasonable explaination is given and a way of improving the output is pointed out through the graphic analysis of the transmitting and transforming circle.
Experimental research of laser-induced damage mechanism of the sol-gel SiO2 and IBSD SiO2 thin films
2006, 55 (3): 1201-1206.
doi: 10.7498/aps.55.1201
Abstract +
This paper investigates the high-power laser-induced damage of two types of single-layer SiO2 thin films on K9 substrate, which are respectively deposited by IBSD technique and sol-gel technique, and have the same substrate parameters and the same film thickness. They were tested by surface thermal lensing technique to obtain the thermal absorbance and the dynamic response. The results show that the laser-initiated damage threshold of Sol-Gel SiO2 thin film is far higher than that of IBSD SiO2 thin film. And combined with threshold measurement and the microscopic observation, this paper well explains in detail the threshold difference between Sol-Gel SiO2 and IBSD SiO2 thin films.
2006, 55 (3): 1207-1210.
doi: 10.7498/aps.55.1207
Abstract +
It was first reported the spectral properties of a low-temperature sintered transparent Yb:Y2-2xLa2xO3 laser ceramics. Yb:Y2-2xLa2xO3 laser ceramics have broad absorption band and large absorption cross-section of 4.0×10-20cm2 at wavelengths 977nm of the highest absorption peak. Its fluorescence lifetime is 1.1ms, and the emission cross-sections are 1.0×10-20cm2 and 0.7×10-20cm2 at wavelengths 1033nm and 1077nm, respectively. All the optical properties are similar to those of single crystals.
2006, 55 (3): 1211-1217.
doi: 10.7498/aps.55.1211
Abstract +
Using Gaussian decomposition (GD) method, we studied the theory of Z-scan with large nonlinear phase shift induced by a pulsed laser. It has been verified that the GD method is still valid to deal with analysis of Z-scan measurements with large nonlinear phase shift. By comparing the peak-valley configuration of the Z-scan curves for large nonlinear phase shift induced by pulsed and CW laser, we found that some new peak-valley features of the Z-scan curves appear as the aperture size or light intensity increases in the case of large nonlinear phase shift. Meanwhile, we carried out the Z-scan experiments of pure CS2 to confirm the results of numerical simulation in the case of large nonlinear phase shift induced by a picosecond pulsed laser. The experimental results agree well with the theoretical. Our results have some significance to the measurement of Z-scan with large nonlinear phase shift induced by a pulsed laser.
2006, 55 (3): 1218-1223.
doi: 10.7498/aps.55.1218
Abstract +
We investigate numerically the interaction between incoherent spatial solitons in a nonlinear medium with logarithmic saturable nonlinearity base on the coherent density approach. Numerical simulations show that both the intensity and the spatial coherence can be greatly enhanced through soliton interaction. At the same time, we show that the soliton interaction can be controlled by the total partial incoherence, which can not only suppress the coherent soliton interaction such as attractive, repulsive or exchange energy, but also induce weak attractive due to incoherent superposition of two incoherent solitons.
2006, 55 (3): 1224-1230.
doi: 10.7498/aps.55.1224
Abstract +
Stimulated Brillouin scattering (SBS) reflectivity as a function of pump power density, pressure of medium and focal length for broadband KrF laser pump was investigated experimentally. SBS reflectivity increases nonlinearly, approaches to saturation and decreases with the pump power density increasing. The pressure in the medium makes the SBS reflectivity to increase. SBS saturation has a peak value with the focal length from 10cm to 100cm. Broadband multimode SBS model has been built theoretically. Experimental results agree well with the model.
2006, 55 (3): 1231-1236.
doi: 10.7498/aps.55.1231
Abstract +
This paper systemically presents a theoretical analysis on pump source angle tuning in quasi-phase matched (QPM) optical parametric oscillator (OPO) in periodically poled crystal. The precise formula and the formula in paraxial approximation, both of which describe the relationship between rotation angle of pump source and wavelengths of pump, signal and idler wave in QPM OPO, are presented. It is found that the idler wave and the pump wave for signal-resonated OPO propagate along the same side of the crystal x-axis to exit, as propagate the signal wave and the pump wave for idler-resonated OPO. In addition, the separation angle between the signal wave and the idler wave for signal-resonated OPO is greater than that for idler-resonated OPO. More importantly, the tuning rate for signal-resonated OPO is also greater than that for idler-resonated OPO.
2006, 55 (3): 1237-1243.
doi: 10.7498/aps.55.1237
Abstract +
We investigate the propagation of the elliptical Gussian beam in strongly nonlocal nonlinear media with an elliptically symmetric response.We derive analytical formulas for the evolution of the beam parameters and conditions for the formation of nonlocal elliptical spatial optical soliton.
2006, 55 (3): 1244-1247.
doi: 10.7498/aps.55.1244
Abstract +
In the present paper, a new kind of honeycomb photonic crystal heterostructure(PCH) is proposed. The band gap structure of this photonic crystal heterostructure is investigated with supercell technique based on the plane-wave expansion method. The configuration of heterostructure and the corresponding band structures are obtained and the guide modes are analyzed. Furthermore, the influences of longitudinal sideslipping and transverse displacement of lattices on the band gap structures are discussed. It may provide a new configuration to generate guide modes. The achieved results show that the guide modes can exist in this heterostructure without any shift of lattices, and guide modes are highly sensitive to transverse shift, while sideslipping affects guide modes only slightly.
2006, 55 (3): 1248-1252.
doi: 10.7498/aps.55.1248
Abstract +
Two-dimensional photonic crystals in near infrared region were fabricated by using the focused ion beam (FIB) method and the method of electron-beam lithography (EBL) combined with dry etching. Both methods can fabricate perfect crystals, the method of FIB is simple,the other is more complicated. It is shown that the material with the photonic crystal fabricated by FIB has no fluorescence,on the other hand, the small-lattice photonic crystal made by EBL combined with dry etching can enhance the extraction efficiency two folds, though the photonic crystal has some disorder. The mechanisms of the enhanced-emission and the absence of emission are also discussed.
2006, 55 (3): 1253-1258.
doi: 10.7498/aps.55.1253
Abstract +
We present a design of diffractive optical element to produce 3D optical chain along optical axis near the focus of a high numerical aperture (NA) lens by spatially modulating the phase of incoming vector beam. This optical chain can trap multiple individual particles in three dimensions at different planes near the focus. For flexibly controlling this special optical trapping system, we systematically analize the factors affecting the characteristics of the optical chain, such as different incoming vector polarization of light, the NA of the lens, and the structure of the DOE.
2006, 55 (3): 1259-1263.
doi: 10.7498/aps.55.1259
Abstract +
In this work, a novel light source of strained InGaAsP/InGaAsP MQW EAM monolithically integrated with DFB laser is fabricated by ultra-low-pressure (22×102Pa) selective area growth (SAG) MOCVD technique. Superior device performances have been obtained, such as low threshold current of 19 mA, output light power of about 7 mW, and over 16 dB extinction ratio at 5 V applied voltage when coupled into a single mode fiber. Over 10 GHz 3 dB bandwidth in EAM part is developed with a driving voltage of 3 V. After the chip is packaged into a 7-pin butterfly compact module, 10-Gb/s NRZ transmission experiments are successfully performed in standard fiber. A clearly-open eye diagram is achieved in the module output with over 8.3 dB dynamic extinction ratio. Power penalty less than 1.5 dB has been obtained after transmission through 53.3 km of standard fiber, which demonstrates that high-speed, low chirp EAM/DFB integrated light source can be obtained by ultra-low-pressure (22×10\+2Pa) SAG method.
2006, 55 (3): 1264-1270.
doi: 10.7498/aps.55.1264
Abstract +
The general nerar-field acoustic holography (NAH) cannot reconstruct the surface acoustic information of each coherent acoustic source in coherent acoustic field,which has more than one acoustic sources with the same frequency, and they cannot realize holographic reconstruction and prediction of the independent acoustic field generated by one coherent acoustic source too.So the holographic reconstruction and prediction of coherent acoustic field has become the foremost problem to be resolved in the application of NAH. On the basis of the proposed combined wave superposition approach, an experiment is carried out to realize the holographic reconstruction and prediction of a coherent acoustic filed generated by two sound boxes.By this experiment,the feasibility and accuracy of combined wave superposition approach are demonstrated,the shortcoming of general wave superposition approach in holographic construction and prediction of coherent acoustic field are also demonstrated.The Tikhonov regularization method is proposed to control the ill-posedness of inverse acoustic problem, and the principle of filter coefficient selection is also studied.The experiment indicates that Tikhonov regularization method with appropriate filter coefficient can improve the precision of the holographic reconstruction and prediction.
2006, 55 (3): 1271-1275.
doi: 10.7498/aps.55.1271
Abstract +
Drawing temperature is an important factor affecting the structure of microstructure fibers (MSF) during MSF drawing. According to the Fourier equation of time-dependent heat conduction with, original conditions and boundary conditions of MSF preform, the temperature distribution equation of MSF preform is derived in cylindrical coordinates. It is shown the feeding speed of MSF preform is optimal when the temperature distribution of MSF preform is close to the steady-state heat conduction in high temperature furnace, then the temperature of high temperature furnace can be lowered to the intenerate temperature of MSF preform. In addition, the optimal speed will be increased if the air-filling fraction of MSF preform is high.
2006, 55 (3): 1276-1282.
doi: 10.7498/aps.55.1276
Abstract +
Based on the information preservation(IP) method, a simple effective temperature model is presented. The IP method with new temperature model can simulate the flow which has temperature variation. Moreover, studies show that when the local density gradient of the simulated flow is large, it will cause numerical divergence if the second order central difference scheme of the mass conservation equation is used to update the information density. So the first order upwind scheme is recommended to update the information density for the flow with large density gradient.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2006, 55 (3): 1283-1288.
doi: 10.7498/aps.55.1283
Abstract +
Magnetized plasma photonic crystals are artificial periodic structures composed of magnetized plasmas and dielectric structures (or vacuum).In this paper,the piecewise linear current density recursive convolution (PLCDRC) finite-difference time-domain (FDTD) method for magnetized plasmas is applied to study the magnetized plasma photonic crystals.The effect of parameters of magnetized plasma on electromagnetic band gap is presented.In time-domain,the electromagnetic propagation process and reflection/transmission electric field of Gaussian pulses through magnetized plasma photonic crystals are investigated.In frequency-domain,the reflection and transmission coefficients through magnetized plasma photonic crystals are computed.The results are discussed.
2006, 55 (3): 1289-1294.
doi: 10.7498/aps.55.1289
Abstract +
A ROSS-FILTER-PIN spectrometer in the spectral range of 0.28keV —1.56keV was developed to study the soft X-ray radiation emitted from gas-puff Z-pinch plasma. It is composed of five channels covering the energy interval of interest without gaps. Soft X-ray spectral energy cuts were determined by the L absorption edges of selected filter elements (K absorption edges being used for light filter elements), and the optimum thickness of filter material was designed using computer code. To minimize the residual sensitivity outside the sensitivity range of each channel, element of the first filter was added into the second filter of all the Ross pair. To diminish the area of each filter, PIN detector with small sensitive area of 1 mm2 was adopted for the spectrometer. A filter with small area is easy to fabricate and would be helpful to withstand the Z-pinch discharge shock wave. With this ROSS-FILTER-PIN spectrometer, the energy spectra of soft X-ray from a small gas-puff Z-pinch were investigated, and the correlation between the soft X-ray yield and the plasma implosion state was also studied.
2006, 55 (3): 1295-1300.
doi: 10.7498/aps.55.1295
Abstract +
Electromagnetic performances of multilayer plane delamination media with an ITO (indium tin oxide) transparent conductive film have been researched theoretically and the calculated curve well agrees with the measured curve.The research shows that the electromagnetic performances of the multilayer media are related to ITO (with sheet resistance 8Ω) film's interface location,the layer number of the plane delamination media and the thickness of the plane delamination media,and so on.An optimized system of four-layer plane delamination mediums with a thickness of only 7.35mm and very large electromagnetic reflectance within the rauge of 8—18GHz has been designed.The sheet resistance of the ITO film in the multilayer plane delamination media should be less than 30Ω,and the smaller the sheet resistance,the langer the electromagnetic reflectance of the multilayer plane delamination media.
2006, 55 (3): 1301-1306.
doi: 10.7498/aps.55.1301
Abstract +
A uniform nonlinear resonant condition for interaction between electrostatic wave and charged particles in a uniform magnetic field is given by multi-scale expansion.It is verified by numerical simulation.It is shown that resonant heating can be produced by electrostatic wave with sub-harmonic frequency of the cyclotron.Moreover,it is shown that the heating efficiency does not increase with the amplitude of driving wave even if for the same frequency,which means there is an optimum combination of frequency and amplitude to get efficient heating.
2006, 55 (3): 1307-1314.
doi: 10.7498/aps.55.1307
Abstract +
With a given density profile of plasma,the temperature profiles of the plasma operating in the negative central magnetic shear mode,the H-mode and L-mode of conventional magnetic shear,are calculated respectively by applying the energy equation of electrons and ions,according to the thermal conductivity in different operational regimes.And then the electron cyclotron current drive and wave power deposition in the above modes are investigated with the relativistic Fokker-Planck equation incorporated into a ray tracing code.The result shows that in the mode of negative central magnetic shear,the current drive efficiency is the highest,meanwhile the zones of power deposition and current profile are wide.In the H-mode of conventional magnetic shear,the current drive efficiency is low,and the zones of power deposition and current profile are narrow.In the L-mode of conventional magnetic shear,the current drive efficiency is the lowest,the zones of power deposition and current profile are very narrow.
2006, 55 (3): 1315-1319.
doi: 10.7498/aps.55.1315
Abstract +
During the plasma discharge in HL-2A, the magnetic field at the plasma boundary is computed using currents filaments code. The Shafranov integrals S1，S2 and S3 are deduced; the poloidal beta, internal inductance, the horizontal position of the magnetic axis Rm and the plasma energy Wdia are calculated; the current center of plasma (Rc,Zc)is computed with the current moments. The real time determination of these quantities is of significance for understanding and adjusting the HL-2A discharge in time, and for improving plasma performance.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Molecular dynamics simulation of the correlation between the viscosity and structure of liquid metal
2006, 55 (3): 1320-1324.
doi: 10.7498/aps.55.1320
Abstract +
The non-equilibrium molecular dynamics simulation (NEMD) has been performed based on the embeded atom potential to obtain the pair correlation function and the viscosity of liquid Al.The pair correlation function by the simulation agrees well with Waseda's X\|ray diffraction measurement.The temperature dependence of viscosity meets the Arrhenius formula:η=Aexp(E/RT) and the activation energy E calculated is 15968.27J/mol.The expression between the viscosity, pair correlation function and the inter-atomic potential has been obtained by application of the simulated viscosity value and the activation energy to meet L-J potential.The two fitted curves of viscosity agree well with that obtained by the NEMD method,showing the fitting program we compiled is excellent and the fitting to the L-J potential is achieved.This present work provides a new method to explore inter-atomic potential.
2006, 55 (3): 1325-1335.
doi: 10.7498/aps.55.1325
Abstract +
The least square method and corresponding computing programs for separating twofold broadening effects due to the crystallite-microstress, crystallite-stacking faults, microstress-stacking faults and three-fold effect of crystallite-stress-faults have been proposed and established. The least square method can be applied to closed packing hexagonal (cph), face-centered cubic (fcc) and body-centered cubic (bcc) structures. A few examples are presented and discussed.
2006, 55 (3): 1336-1340.
doi: 10.7498/aps.55.1336
Abstract +
The sine-squared potential is introduce to describe the interaction between particles and the crystal.The motion equation of the planar channelling particles is reduced to the pendulum equatione by this interaction potential.The solution of the equation and the period of the particle motion are expressed exactly by means of Jacobian elliptic function and elliptic integral.The radiation intensity and properties of the radiation spectrum are discussed.It is point out that it is possible to take channeling radiation as a new γ-Laser.
2006, 55 (3): 1341-1345.
doi: 10.7498/aps.55.1341
Abstract +
A phase-field model for multicomponent alloys based on the binary phase-field model has been developed. The isothermal dendritic growth of Al-Si-Mg alloys is presented as a numerical example, accordingly, the dendrite growing morphology of multicomponent alloys solidification could be simulated realistically using the phase-field model. As the result, the intricate figures such as secondary and tertiary dendrite arms are revealed. The decrease of solute Mg can trigger the growth of the secondary arms and increase the solute microsegregation rate, the tip speed and radius of dendrite. The variation of the speed and the radius in the dendrite tip agrees well with theoretical and experimental results in succinonitrile-acetone system. In addition, the spines of the primary arms have lowest concentration, and the mushy regions between the dendrite secondary arms have the highest concentration; the solute gradients are higher in the vicinity of the S/L interface regions, and highest in the tip.
2006, 55 (3): 1346-1350.
doi: 10.7498/aps.55.1346
Abstract +
A high dielectric constant of 2500 near room temperature was observed in (Ba０.５Sr０.５)TiO３ (BSTO) film prepared by pulsed-laser deposition (PLD) on Pt/Ti/SiO２/Si (100) substrate at 550℃ in N2 atmosphere. The dielectric constant is weakly temperature dependent above 200 K. The dielectric behavior of this film is different from the BSTO film deposited in the O2 atmosphere, but very similar to that reported for the so-called “colossal” dielectric constant materials, such as CaCu3Ti4O12. The film prepared in O2 atmosphere at 650℃ shows normal ferroelectric phase transition, which are fitted with Curie-Weiss law. However, for the film prepared in N2 atmosphere at 550℃, the temperature dependence of dielectric relaxation can be characterized by a thermally excited relaxation process. Such anomalous dielectric response of the BST films is ascribed to the formation of the Schottky barrier between the metallic electrode and the film surface.
2006, 55 (3): 1351-1357.
doi: 10.7498/aps.55.1351
Abstract +
Low energy sputtering of Pt (111) surface by noble metal atoms with the incident energy in the range of 0.1 — 200 eV has been studied by molecular dynamics sim ulation. The atomic interaction potential with embedded atom method (EAM) was us ed in the simulation. It was found that the sputtering threshold energy is indep endent of the mass of the incident atom in the case of normal impact on the Pt ( 111) surface. When the incident energy is lower than the threshold energy, the b ehavior of incident atom can be regarded as deposition process. When the inciden t energy is higher than the threshold energy, however, the sputtering yield incr eases with the increase of the incident energy. For the incident energy of 200 e V, the sputtering yield induced by various incident atoms approaches 1 or even h igher. The results mean that the atom with incident energy higher than 200 eV ma inly plays the role of sputtering. The probability of angular distribution of th e sputtered atoms and the sputtering pattern are similar to the sputtering resul ts with higher incident energy. We found that the sputtering yield is a function of the reduced energy of incident atom and the mass ratio of incident atom to t arget atom when the incident energy is higher than the threshold energy, which i s different from the linear cascade theory based on the binary collision model. We suggest a new physical mechanism for low energy sputtering, where the reflect ion of incident atom by target atom dominates the sputtering process of surface atoms.
2006, 55 (3): 1358-1362.
doi: 10.7498/aps.55.1358
Abstract +
Transparent zinc oxide (ZnO) films were prepared on ZnWO4 crystal by sol-gel technique. Surface morphology of ZnO films were observed with optical mi croscope. The results of show that ZnO films are formed in three different stage s from nucleation on surface, grain growth to island formation. Because ZnO crys tal nucleus were grown under non_equilibrium condition, it is inevitable that de ndrite growth, fractal growth and spinodal decomposition phenomenon are involved in the growing process.
2006, 55 (3): 1363-1368.
doi: 10.7498/aps.55.1363
Abstract +
Hydrogen-free silicon nitride films were deposited at room temperature by microw ave electron cyclotron resonance (ECR) plasma source enhanced unbalanced magnetr on sputtering system. Fourier-transform infrared spectroscopy and X-ray photoele ctron spectroscopy were used to study the bond type, the change of bond structur es, and the stoichiometry of the silicon nitride films. Atomic-force microscopy and nano-indentation were used to study the morphological features and mechanica l characteristics of the films. The results indicate that the structure and char acteristics of the films deposited by this technique depend strongly on the dens ity of sputtered Si in plasma and the films deposited at 4 sccm N2 fl ow show excellent stoichiometry and properties.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2006, 55 (3): 1369-1373.
doi: 10.7498/aps.55.1369
Abstract +
A model of Σ5〈001〉/(210) high angle grain boundary (GB) in austenite phase in steel was set up with computer programming. The environment-sensitive embedding energies (ESE) of C, N and microalloying elements in grains or in GB core are c alculated by recursion method, respectively. The segregation and interaction of C, N and microalloying elements in the GB core were discussed. Calculation resul ts show that: discrete light impurities C and N tend to segregate in the GB area , forming atomic clusters; microalloying elements are liable to distribute in pe rfect austenite grains. Ti, V, Nb occupy the top sites of the trigonal prism for med by iron in the GB core, and Ti, V, Nb can also form atomic clusters in GB co re like C or N. When the temperature is decreased and the concentration of C, N and microalloying elements reach to the limit of solubility, the C, N compounds of microalloying elements precipitate from the matrix in GB core of austenite in steel. These compounds can act as heterogeneous nuclei of austenite phase in th e course of recrystallization and retard the growth of austenite grains, leading to the refinement of austenite grains. Nb is the most efficient refiner of micr oalloying elements Nb, Ti, V.
2006, 55 (3): 1374-1378.
doi: 10.7498/aps.55.1374
Abstract +
The geometries and the electronic structures of t-HfO2 and its (001) surface have been studied by first-principle calculations using the density func tional theory (DFT). The optimized results show that the t-HfO2 (001) surface has no surface reconstruction. Compared with the bulk electronic struct ure, the density of states (DOS) of t-HfO2 (001) surface is higher th an that of the bulk. In addition, the DOS of t-HfO2 (001) surface is closer to the Fermi level. The valence band has the tendency to move toward the lower energy, resulting in the formation of a new surface state. The band gap of t-HfO2 (001) surface is much smaller than that of bulk band gap. The existence of a new surface state and the reduction of band gap are due to the r eduction of the Hf and O surface coordination which are different from the bulk atoms.
2006, 55 (3): 1379-1383.
doi: 10.7498/aps.55.1379
Abstract +
We obtained the high mobility of μ2K=1.78×106 cm2/V·s in Si-doped GaAs/AlGaAs two-dimensional electron gas (2DEG) structures . After the sample was illuminated by a light-emitting diode in magnetic fields up to 6 T at T=2K, we did observe the persistent photoconductivity effect and th e electron density increased obviously. The electronic properties of 2DEG have b een studied by Quantum-Hall-effect and Shubnikov-de Haas (SdH) oscillation measu rements. We found that the electron concentrations of two subbands increase simu ltaneity with the increasing total electron concentration, and the electron mobi lity also increases obviously after being illuminated. At the same time, we also found that the electronic quantum lifetime becomes shorter, and a theoretical e xplunation is given through the widths of integral quantum Hall plateaus.
2006, 55 (3): 1384-1389.
doi: 10.7498/aps.55.1384
Abstract +
Through the research of the internal structure of Light Emitting Diode (LED), we discovered that the interface trap density and diffusion current ratio are key factors determining the performance of LED, and they are also closely related to the reliability of LED. Among the many kinds of internal noises in LED, low-fre quency 1/f noise describes the interfoce trap density and diffuse current ratio effectively. Based on the mechanism of carrier number fluctuation and carrier mo bility fluctuation of 1/f noise, we put forward the electrical model and 1/f noi se model of LED. We also measured the electrical noise of the device over a wide range of current. Experimental results agree well with the proposed model. Usin g the experimental data, the relationship between noise and the performance and reliability of LED is established. It is proved that the larger the noise magnit ude, the nearer the current exponent is to 2, leading to the degradation of devi ce reliability and significant rise in device invalidation rate.
2006, 55 (3): 1390-1397.
doi: 10.7498/aps.55.1390
Abstract +
Using reactive radio-frequency magnetron sputtering, ZnO films with strong c-axi s orientation have been deposited on Si (100) substrates at temperatures ranging from room temperature (RT) to 750℃. We have studied the influence of growth te mperature on the structural characteristics of the as-deposited films in morphol ogy, grain size, microstructure, and residual stress by using atomic force micro scopy, transmission electron microscopy, X-ray diffraction, and Raman spectrosco py. With the measurement of the transmission spectra and photoluminescence (PL) properties, the relationship between the crystallinity and optical properties of ZnO films have been discussed. It is found that the grain size increases with t emperature up to 500℃, and then decreases at 750℃. ZnO grains have an epitaxia l relationship with Si (100) substrate for the films deposited at the temperatur es ranging from RT to 750℃. The films deposited below 500℃ are in the states o f compressive strain while the film deposited at 750℃ is in tensile. The differ ence in growth temperature results in the variation of refractive index, extinct ion coefficient, optical energy gap, and PL properties of the films. It is concl uded that growth temperature dominates the PL behavior of ZnO films. We also dis cuss the physical mechanism affecting the PL behavior.
2006, 55 (3): 1398-1401.
doi: 10.7498/aps.55.1398
Abstract +
A novel approach using low-cost and simple-equipment was successfully demonstrat ed on the growth of ZnO microrod array films. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) has characterized the microstructure of the samples . The results indicate that ZnO microrod array films are hexagonal, highly orien ted crystalline array films, grown along c-axis of ZnO on (0001) sapphire substr ates. The FWHM is about 1.8° for the (0004) rocking curve of the ZnO films. The photoluminescence spectra of ZnO array films show a strong and narrow peak at 395nm.
2006, 55 (3): 1402-1406.
doi: 10.7498/aps.55.1402
Abstract +
The barrier strain in Al0.22Ga0.78N/GaN heterostructure, w ith and without Si3N4 passivation layer, was investigated at temperatures from room temperature to 813K by using high resolution X-ray dif fraction. The strain relaxation occurs when the temperature exceeds 523K for the unpassivated Al0.22Ga0.78N layers. After passivation, an initial increase of the strain with increasing temperature is observed in Al0.22Ga0.78N layers, and at the higher temperatures the strain only decreases slightly in the 100-nm-thick Al0.22Ga０.78N layer, but a pronounced strain relaxation occurs in the 50-nm-thick one due to the fact that the thickness of the A10.22Ga0.78N layer is close to the critical thickness, and hence the increase of tensile strain induce d by passivation will result in partial strain relaxation via the formation of c racks or the gliding motion and multiplication of dislocations.
2006, 55 (3): 1407-1412.
doi: 10.7498/aps.55.1407
Abstract +
Deep level transient spectroscopy measurements were used to characterize the ele ctrical properties of metal organic chemical vapor deposition grown undoped, Er- implanted and Pr-implanted GaN films. Only one deep level located at 0.270 eV be low the conduction band was found in the as-grown GaN films. But four defect le vels located at 0.300 eV, 0.188 eV, 0.600 eV and 0.410 eV below the conduction b and were found in the Er-implanted GaN films after annealing at 900 ℃ for 30 mi n, and four defect levels located at 0.280 eV, 0.190 eV, 0.610 eV and 0.390 eV b elow the conduction band were found in the Pr-implanted GaN films after annealin g at 1050 ℃ for 30min. The origins of the deep defect levels are discussed. Aft er annealing at 900℃ for 30min in a nitrogen flow, Er-related 1538nm luminescen ce peaks could be observed for the Er-implanted GaN sample. The energy-transfer and luminescence mechanism of the Er-implanted GaN film are described.
2006, 55 (3): 1413-1418.
doi: 10.7498/aps.55.1413
Abstract +
We theoretically studied the properties of the ground state of the parallel-coup led double quantum dot embedded in a mesoscopic ring in the Kondo regime by mean s of the two-impurity Anderson Hamiltonian. The Hamiltonian is solved by means o f the slave-boson mean-field theory. Our results show that when the system goes into the strong coupling regime, two parallel dots can be coupled coherently, wh ich leads to an enhanced Kondo effect and a giant persistent current emerging in this system. This double quantum dot device can be a candidate for future devic e applications.
2006, 55 (3): 1419-1423.
doi: 10.7498/aps.55.1419
Abstract +
The negative-bias temperature instability (NBTI) characteristics of HfN/HfO 2 gated p-MOSFET with equivalent oxide thickness (EOT) of 1.3nm and low pre-existi ng traps are studied. Due to the low pre-existing trap density of HfN/HfO2 ga te stack, the observed NBTI characteristics are intrinsic, rather induced by the fabricating process. The observed characteristics can be compared with those re ported in SiO2 based gate stack and can be explained with the general ized reac tion-diffusion (R-D) model: under negative bias and temperature stressing, holes injected from the Si substrate could cause the Si-H bond breaking at the Si sub strate interface. The H atoms diffuse away into the bulk layer and the Si+ spe cies are left at the interface. The diffusing H atoms and the left Si+ species cause the NBTI characteristics.
2006, 55 (3): 1424-1429.
doi: 10.7498/aps.55.1424
Abstract +
The p-type GaN(p-GaN) samples grown at low temperature 870—980℃ on sapphire su bstrate were prepared by the metal organic chemical vapor deposition technique(M OCVD), and their electrical properties were investigated. The p-GaN samples grow n below 900℃ show high-resistivity, and samples grown at above 900℃ have good conductivity. In addition, the electrical properties are also related with the d oping level and the growth condition of p-GaN. The low N-Ga mole ratio leads to poor conductivity, the high ratio leads to rough morphology. At last, we use the optimized p-GaN to fabricate the green-light emitting diodes.We found that when the growth temperature is lower, the luminescence intensity and reverse voltage is higher but the forward voltage increases slightly.
2006, 55 (3): 1430-1434.
doi: 10.7498/aps.55.1430
Abstract +
Self-assembled alkanethiol monolayers (SAMs) were prepared on the Au(111) substr ate. The behavior of the transport properties of SAMs under external load was in vestigated by the conduction atomic force microscopy. The current of SAM was fou nd to increase with the external load, and this property can be well characteriz ed by the Hertz model. It was also found that the conductance of SAM decreases e xponentially with the chain length of the alkanethiol molecules. The correspondi ng current decay constant β is demonstrated to decrease with the external load at first, and then becomes independent of the external load. Furthermore, the cu rrent of SAM with long chain molecules increases more apparently than that with short ones. These features all originate from the tunneling effect via nearby mo lecular chains for the charges.
2006, 55 (3): 1435-1440.
doi: 10.7498/aps.55.1435
Abstract +
The LSMO (x=0.17) film on the Si (111) substrate was fabricated by the sol-gel m ethod.The R-T curves, the infrared spectra and XRD results of the block and the film with different thickness show that the crystals of the LSMO films are orth ogonal, and the film orientation has some relation with the film thickness. Whe n the film thickness lies between the 450nm to 680 nm, the orientation is 〈200 〉, but when the film thickness equals to 900 nm, the orientation is 〈020〉. Ac cording to the reactive energy and the harmonic oscillator model, the relational expressions, between the infrared absorption and the Mn-O-Mn bond length and bo nd angel were studied. The infrared absorption near 600cm-1 relates t o the different lattice constant b, and the metal-insulator transformation tempe ratures (TMI) of the block material and the films differ much, those of the films being much lower than that of the block material and, at the same time, has something to do with the film thickness. The paper indicates that the stress in the LSMO films inducing the lattice constant change and then arousing the change of bond angel and JT effect is the main reason for the change of the transformation temperature.
2006, 55 (3): 1441-1446.
doi: 10.7498/aps.55.1441
Abstract +
The oxide La1-xPrxMnO3 (x=0.1, 0.2) thin film s howing colossal magnetoresistance has been epitaxially grown on (100) SrTiO 3 single-crystal substrate by pulsed-laser deposition. The films have a pe rovskite structure and perform the colossal magnetoresistance effect with the ma ximum magnetoresistance ratio of 95% under the magnetic field of 5 T. The valenc e of Pr is confirmed as +4 through XPS. Therefore the epitaxial film is most lik ely an electron-doped colossal magnetoresistance fihn.
2006, 55 (3): 1447-1452.
doi: 10.7498/aps.55.1447
Abstract +
The structural and magnetic properties have been investigated by means of X-ray diffraction and magnetization measurements. The Dy2AlFe16-xMnx compounds have a hexagonal Th2Ni17-type st ructure. The thermal expansion of Dy2AlFe16-xMnx (x=1 and 2) compounds have been investigated by X-ray dilatometry in the tempe rature range 104—647K. The results show that there is a thermal expansion anoma ly at low temperature and a negative thermal expansion near the Curie temperatur e. There exists a strong and anisotropic spontaneous magnetostriction in the mag netic state of Dy2AlFe16-xMnx compounds. The sp ontaneous volume magnetostrictive deformation at low temperature decreases with increasing x. The result of magnetization measurement shows that the Curie tempe rature and the spontaneous magnetization of Dy2AlFe16-xMnx compounds at 5K decrease rapidly with increasing x.
2006, 55 (3): 1453-1457.
doi: 10.7498/aps.55.1453
Abstract +
Paramagnetic (Co3O4)x/3(TiO2)1- x(03O4 and TiO2 from 700 ℃ to 1000 ℃ in air. X-ray diffraction (XRD) re sults showed that perovskite CoTiO3 existed in all samples. Anatase p hase was also detected in samples sintered at 700 ℃ and when sintering the mixt ure at above 900 ℃, rutile phase formed with anatase phase disappearing. All sa mples exhibited room-temperature ferromagnetism (RTFM) after being hydrogenated in 10％ H2/Ar mixed atmosphere for 1 hour at 500 ℃. X-ray photoelect ron spectroscopy (XPS) showed that Co existed in the +2 formal oxidation state, and no Co clusters were detected. XRD showed that CoTiO3 disappeared and a new phase CoxTi1-xO2-δ formed after hyd rogenation. It is suggested that hydrogenation causes the phase transformation f rom CoTiO3 to CoxTi1-xO2-δ. RTFM of the sample originates from the intrinsic ferromagnetism of CoxTi1-xO2-δ. The exchange interaction between Co2+ occ urring with the phase transformation may be the essential reason for RTFM.
2006, 55 (3): 1458-1463.
doi: 10.7498/aps.55.1458
Abstract +
Diamond-like carbon (DLC) films were deposited by dielectric barrier discharge ( DBD) from CH4 or CH4 +Ar at pressure of several hundred Pa . The dependence of the film hardness on the product of p and d (p is the gas pr essure and the d is the discharge space) and Ar volume concentration (RAr) was investigated experimentally. The kinetic energies of CH+4 and Ar+ ions were analyzed theoretically based on the two-t emperature model for high reduced field E/n (the ratio of electric field strengt h to the gas number density), in which ions were assigned a temperature much hig her than the gas temperature, on the Langevin equation in other gas and on the B lanc law in mixed gases. The results showed that, 1) for CH4 DBD, whe n decreasing pd from 1.862×103Pa mm to 2.66×102Pa mm, th e kinetic energy of CH+4 increases from 5.4 to 163eV, whil e the hardness of deposited DLC films increases from 2.1 to 17.6 GPa. 2) For CH+4Ar DBD, when increasing Ar volume concentration from 20% to 83%, the kinetic energy of CH+4 increases from 69 to 92 eV, whereas the kinetic energy of Ar+ decreases from 93 to 72eV. The increase of film hardness with increasing Ar volume concentration up to 67% can be attributed to the increase of CH+4 kinetic energy. Howe ver, the impinging of energetic Ar+ on the film surface reduces the f ilm hardness owing to graphitization. For verification of the theoretical model on ion energy analysis, the kinetic energy of ions in H2 DBD were mea sured and compared with that from theoretical analysis.
2006, 55 (3): 1464-1471.
doi: 10.7498/aps.55.1464
Abstract +
The stable strontium bismuth titanate (SBTi) precursor solution were prepared us ing strontium chloride, bismuth nitrate, tetrabulyl titranate as raw materials, with citric acid as complex agent, ethylene glycol as cross linker, and ethanol absolute, water, hydrochloric acid as solvents of tetrabulyl titranate, strontiu m chloride, bismuth nitrate, respectively. SBTi thin films with enhanced a-axis orientation were prepared on Pt/Ti/Si02/Si substrates by the Sol-Gel method. Wit h the aid of ESEM and XRD, the effects of annealing time and the number of coati ngs on microstructure crystallization and growth behavior of SBTi thin films wer e investigated. The results indicate that the pyrochlore phase was restrained su ccessfully by layer-by-layer rapid thermal annealing method. The crystallization of the film was enhanced with the increase of coating number. Because of the an isotropic growth of SBTi crystals and the suppressed growth in (119) direction b y the thickness of single-annealed layer, the intensity of (200) and (119) peaks increase with the increase of layers, and the former increase more quickly.Howe ver, the intensity of (00l) peak decreased with the increase of layers, so the r elative intensity of (200) ［I(200)/I(119)，I(200)/I(0010)］ and (119) ［I(119)/ I(0010)］ increases with the increase of layers.
2006, 55 (3): 1472-1478.
doi: 10.7498/aps.55.1472
Abstract +
The c-axis oriented Bi3.15Nd0.75Ti3O12(BNT) ferroelectric thin films were grown on Si(100) substrates by pulsed lase r deposition with La0.5Sr0.5CoO3/CeO2/Y0.18Zr0.91O2.01 multi-heterostructure as buf fer layer. X-ray diffraction and scanning electron microscopy were used to deter mine the microstructure, orientation and morphology of the multi-layer films. Th e influence of deposition temperatures and the partial oxygen pressure on the mi crostructure, orientation and morphology of the BNT films were investigated and the optimal deposition parameters were determined. The BNT multi-layer thin film s deposited under optimal condition have good electric properties. The C-V patte rn of the BNT multilayer thin films deposited under optimal deposition condition s has the typical butterfly-like shape, suggesting that the films have good pola rization-reversion storage properties. The correlation between the ferroelectric properties and the orientations of the BNT films is discussed.
2006, 55 (3): 1479-1485.
doi: 10.7498/aps.55.1479
Abstract +
The absorption spectra, fluorescence spectra and the lifetimes of 4I13/2 level of Er3+-doped phosphate and tellurite glasses ha ve been measured for sample with different concentrations and thickness. The abs orption cross-section (σa), emission cross-section(σe), spontaneous emission probability(Arad), radiative lifetime(τrad ) and quantum efficiency(η) of fluorescence around 1.53 μm of Er3+-doped phosphate and tellurite glasses were determined. The effect of radia tion trapping on the spectral properties and parameters of Er3+-doped tellurite and phosphate glasses has been investigated. It was found that radiat ion trapping exists generally in erbium-doped glass hosts, even at low Er3+ -doping concentration (0.1 mol% Er2O3). Due to radia tion trapping, the values of the τrad of the Er3+∶4 I13/2 level in tellurite glasses increased about 11%—37％ with the sample thickness and erbium doping concentration, while in phosphate glasse s τrad increased by 6%—17%. The full-width at half maximum (FWHM)of fluorescence in tellurite glasses increased about 15%—64%, with 11%—55% for p hosphate glasses. It caused a high overestimation on the figure of merits (FOM) for amplifier bandwidth (σe×FWHM). The spectral overlap between the emission and absorption spectra in 1.53 μm band is relatively larger in tellur ite than in phosphate glasses, and values of the emission cross-section in tellu rite glasses are larger than that in phosphate glasses. Consequently, the radiat ion trapping in tellurite glasses is more severel than that in phosphate glasses .
2006, 55 (3): 1486-1490.
doi: 10.7498/aps.55.1486
Abstract +
The absorption and upconversion spectra of Er3+-doped fluoride (halid e) phosphate tellurite glasses were investigated for the first time, and the upc onversion mechanisms were studied. Strong red and green upconversion luminescenc e were observed under 975nm laser diode excitation at room temperature. When PbF 2 is partially replaced by PbCl2 gradually, the intensity of red emission decreases, while the green emission intensity changes only sligh tly. When ZnF2 is replaced by 5mol% ZnCl2, both red and gr een emissions intensity are enhanced obviously.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2006, 55 (3): 1491-1496.
doi: 10.7498/aps.55.1491
Abstract +
Bicrystalline ZnO nanocombs have been prepared by zinc powder evaporation proces s at 650℃. The structure of bicrystalline ZnO nanocombs was characterized by XR D, HTEM, SAD, etc., which indicate that the as-synthesized sample are composed of two crystals that form a twin structure parallel to the (1 1 3) plane with th e growth direction of the branching nanowires and the main stems closely paralle l to〈0 0 0 1〉 and〈0 1 1 0〉，respectively. Due to the unique twin structures, both sides of the main stems could be Zn-terminated ZnO (0 0 0 1) polar surface s, which are chemically active. Therefore the aligned branching nanowires can be grown from both sides of the main stems, which is consistent with the structure of the bicrystalline nanomaterials we have obtained. The growth of bicrystallin e ZnO nanocombs bears direct evidence to the polar-surface dominated growth mech anism of the ZnO nanomaterials.
2006, 55 (3): 1497-1501.
doi: 10.7498/aps.55.1497
Abstract +
Hydrogenated microcrystalline silicon (μc-Si:H) materials was prepared by plasm a enhanced chemical vapor deposition (PECVD) at silane concentration 6% and 7% w ith changing excitation frequency (40—70MHz). Relationship between excitation f requency and electrical, structural characteristics and deposition rate of the m aterials was studied. The results indicate that the crystalline volume fraction (Xc) decrease firstly and then increase with the increase of excitati on frequency. But the photosensitivity and the deposition rate be have adversely with the change of excitation frequency. The reason of change of structure and deposition rate of thin films with excitation frequency was studied by optical e mission spectroscopy.
2006, 55 (3): 1502-1507.
doi: 10.7498/aps.55.1502
Abstract +
The dependence of denderitic patterns and solute segregation on solid diffusivit y Ds is studied using a phase-field model which incorporates concentr ation field for Ni-Cu binary alloy dendritic growth. The computed results indica te that with the decrease of solid diffusivity Ds, the smaller become s the thickness of the solute diffusion layer ahead of the interface, which is a dvantageous to the growth of the sidebranching, and the more developed the side- branches. The smaller the solid diffusivity Ds, the more acutely the solute concentration in solid phase fluctuates. With the increment of solid diff usivity Ds, the fluctuations of solute concentration in solid phase a re reduced accordingly. An increased level of solid diffusivity Ds re duces the severity of microsegregation.
2006, 55 (3): 1508-1511.
doi: 10.7498/aps.55.1508
Abstract +
Phase depth profile in TiNi shape memory alloy films is studied by the combinati on of grazing-incidence X-ray diffraction and X-ray reflectivity measurement. Th e film is made from sputter-deposited Ni/Ti multilayers. At room temperature, bo th the phase depth profile and element depth profile are not uniform, and both h ave multilayer structure. There is a three-phase mixture region consisting of Ti 3Ni4 precipitates, martensite and a little of austenite ne ar the free surface. A uniform martensite phase is formed near the substrate. Di ffusion and reaction take place between film and substrate. The simulation resul t of X-ray reflectivity shows that the results of film microstructure analysis a re reasonable. It is the kinetic factors that mainly cause the ununiformity of p hase depth profile in the film.
2006, 55 (3): 1512-1516.
doi: 10.7498/aps.55.1512
Abstract +
Metal-ferroelectric-semiconductor field-effect-transistors (FFETs) with Ag/Bi4Ti3O12/p-Si gate were fabricated using the high q uality Bi4Ti3O12 on p-Si substrates prepared by Sol-Gel technique. The phase structure characteristics of Bi4Ti 3O12 films, the interface characteristics of ferroelectric/Si a nd the memory characteristics of the FFETs were investigated. Bi4Ti 3O12 films with high preferred c-axis-orientation are obta ined at appropriate annealing temperature which helps to improve the interface c haracteristics of ferroelectric/Si. The C-V hysteresis curves with clockwise loo ps prove that the FFETs could realize a memory effect due to the ferroelectric p olarization of Bi4Ti3O12 films, and the capacit ance decay of 11% in 16 hours indicates that the FFETs have good polarization ch arge retention. The counter-clockwise Ids-VG hysterisis cu rve of the FFETs demonstrates that the channel current is modulated by the ferro electric polarization of Bi4Ti3O12 films.
2006, 55 (3): 1517-1522.
doi: 10.7498/aps.55.1517
Abstract +
Porous anodic aluminum oxide (AAO) membranes were sputtered by 500eV argon ion ( Ar+) beam. Scanning electron microscopy and atomic force microscopy i mages show that not only the barrier layer of AAO can be easily removed by Ar+ beam sputtering, but also several categories of surface morphologies w ere got by changing the incidence parameters. For instance, off-normal incidence bombardment results in ripple formation on the surface of AAO and off-normal in cidence during smple stage rotation leads to AAO surface smoothing. Theory of ri pple formation and evolution on amorphous substrate under ion beam irradiation d eveloped by Bradley and Harper is used to interpret the characteristics of rippl es on AAO surface.
2006, 55 (3): 1523-1528.
doi: 10.7498/aps.55.1523
Abstract +
The influence of a weak magnetic field on the microstructure of the Zn electrode posits prepared in a thin concentric electrode cell is investigated. Mechanism o f the effect of the magnetohydrodynamic (MHD) flow on the morphological transiti on is proposed through experimental evidences. 1) In the early growth phase of a crystallite, the unbalanced force caused by the MHD flow on the crystallite, wh ich suspends in the electrolyte close to the previous branch, rotates its prefer ential growth orientation towards the downstream of the MHD flow; 2) A stable co ncentration profile is formed in the vicinity of the electrodeposits by the MHD flow. After the crystallite grows large enough to stick on its previous branch, and the concentration of the electrolyte is high enough for both the primary bra nch and its secondary branches, the single-crystalline dendrites will grow strai ght. But if the concentration of the electrolyte is small, the secondary branche s crowd to the side facing the upstream of the MHD flow and the primary branch i s forced to bend towards the downstream of the MHD flow. A spiral structure in t he branched electrodeposits grown in a magnetic field is formed by this mechanis m.
2006, 55 (3): 1529-1533.
doi: 10.7498/aps.55.1529
Abstract +
Differential optical absorption spectroscopy (DOAS) is a spectroscopic technique which can be used to monitor many kinds of air pollutants simultaneously. In th is paper, in situ measurement of nitrous acid and retrieval of aerosol parameter s in a fixed wavelength range (307 nm—380 nm) were performed with DOAS system d eveloped by our laboratory. The measurements of HONO concentration were more acc urate using the NO2 standard absorption cross section measured by our selves a nd aerosol parameters were retrieved successfully in a shorter wavelength range.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2006, 55 (3): 1534-1538.
doi: 10.7498/aps.55.1534
Abstract +
With consideration of the effects of atomic process, a simple code modeling the correction to poloidal charge-exchange recombination spectroscopy (CXRS) measure ment is developed. The simulation results show that the measured poloidal veloci ty shift is overestimated in the ion diamagnetic drift direction and the apparen t ion temperature is underestimated because of the effects of energy-dependent e mission rate and finite lifetime of excited ions. This deviation will be more ob vious with the increase of temperature or magnetic field. The contributions from gradients of density and temperature are negligible compared to that from the a tomic process.
