Vol. 54, No. 4 (2005)
2005-02-20
GENERAL
2005, 54 (4): 1457-1459.
doi: 10.7498/aps.54.1457
Abstract +
In this paper, the differential kinematic equation of onedimensional relativistic harmonic oscillator containing a quadratic velocity drag force term is obtained by using Taylor series expansion. The expressions of Lagrangian function and conserved quantity are obtained based on the differential kinematic equation and the characteristic of the conserved quantity.
2005, 54 (4): 1460-1463.
doi: 10.7498/aps.54.1460
Abstract +
The differential equations of motion of a classical particle in the field of noncentral force are expressed in Ermakov formalism, and the Ermakov invariant is obtained. By rescaling the time, the parametric orbit equations of the classical particle can be expressed in terms of energy H and Ermakov invariant. The Noether symmetry, Lie symmetry and the form invariance of the transformations of two conserved quantities are studied in this paper. The result indicates that the transformations of the two conserved quantities not only possess Noether symmetry but also possess Lie symmetry and form invariance.
2005, 54 (4): 1464-1467.
doi: 10.7498/aps.54.1464
Abstract +
This paper studies the Mei symmetry and conservation law of the relativistic mechanical system. The definition and criterion of Mei symmetry for the relativistic mechanical system are established, which are based upon the invariance of dynamical functions under infinitesimal transformations. A new conservation law is deduced directly from the Mei symmetry of the system, and the condition under which a Mei symmetry can lead to a new conservation law is obtained and the form ofthe conservation law is presented. An example is given to illustrate the application of the results.
2005, 54 (4): 1468-1475.
doi: 10.7498/aps.54.1468
Abstract +
In this work, starting from a Painlev-Bcklund transformation and a multil inear variable separation approach, a general variable separation excitation of the three-dimensional Boiti-Leon-Pempinelli system is derived first. Then based on the derived excitation, we can construct many localized structures like pe akons and compactons etc. Meanwhile, two new types of solitary waves, i.e., a b ell-like loop soliton and a peak-like loop soliton are constructed and their e volution properties of the novel localized structures are briefly discussed.
2005, 54 (4): 1476-1480.
doi: 10.7498/aps.54.1476
Abstract +
With the aid of the symbolic computation softwares Maple, we solve the (2 +1)-dimensional Boussinesq equation by doing proper unknown functions ansatz of the seed solutions of the equation and performing mathematical calculations to obtain a series of exact solutions，which contain soliton-like solutions and ra tional solutions. Some exact solutions include arbitrary functions, when these a rbitrary functions are taken as some special functions, these solutions possess abundant structures.
2005, 54 (4): 1481-1484.
doi: 10.7498/aps.54.1481
Abstract +
Using the travelling wave transformation instead of the more general function tr ansformation, the modified Jacobi elliptic function expansion method is improved . Some new periodic solutions of nolinear Klein-Gordon equation are obtained usi ng this method. When modulus m→1 or m→0, these periodic solutions dege nerate to the corresponding solitary wave solutions, trigonometric function solu tions or irregular travelling wave solutions. For some nonlinear equations, the general transformation would degenerate to the travelling wave reduction under certain conditions.
2005, 54 (4): 1485-1489.
doi: 10.7498/aps.54.1485
Abstract +
With the help of Lax operator, the monodromy matrix is constructed, and the Hamiltonian is obtained. By using algebraic Bethe ansatz method, it has been shown t hat the monodromy matrix satisfies the Yang-Baxter equation on both a finite in terval and an infinite interval. So the integrability of this model is proved.
2005, 54 (4): 1490-1494.
doi: 10.7498/aps.54.1490
Abstract +
Based on the algorithm of Kolmogorov entropy presented by Grassberger and Procac cia, as the time series data of silicon content in molten iron of No.1 BF at Laiwu and No.6 BF at Linfen Iron and Steel Group Cos. to be as samples, their Kolmo gorov entropy are computed to be (01453±00151)nats·h-1-1 an d (01553±00140)nats·h-1-1, and the time scales of forecasti ng in both BFs are estimated to be about 688 and 644h respectively. Since the value of Kolmogorov entropy is finite and positive, there is chaos in both b last furnace ironmaking processes, and the idea that Kolmogorov entropy may be u sed to judge the condition of BF is presented.
2005, 54 (4): 1495-1499.
doi: 10.7498/aps.54.1495
Abstract +
Proportional-integral-derivative (PID) control of unified chaotic system (UCS) was researched. For optimization of PID controller's structure and parameners, a parallel genetic algorithm (PGA) was proposed. In GA evolution process, hybri d decimal system and binary system matrix encoding technique was adopted. Simula tion study results of optimal PID control for UCS show that: 1) UCS can be cont rolled to unstable zero equilibrium point by using only one PI controller. 2) U CS can be controlled to any unstable non-zero equilibrium point by using three PI controllers. 3) The proposed PGA owns global optimization ability, it can av oid premature problem of simple GA. 4) The control system obtained good regulat ing performance and strong robustness.
2005, 54 (4): 1500-1509.
doi: 10.7498/aps.54.1500
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This paper proposes a new approach for generating three_dimensional (3_D) multi_scroll chaotic attractors via triangular wave series. The chaotic dynamic char acteristic of multi_scroll system constructed by triangular wave series is furth er investigated. The hardware experimental circuit is designed and the interrela ted circuit implementation is realized. A blocking circuit diagram, including in tegrator N11, triangular wave series generators N22, N33 and N44, switch linkage K, is designed for the hardware imp lementations. The triangular wave series developed here can adjust the swings, w idths, equilibrium points, breakpoints, and slopes so as to generate a large num ber of scrolls with adjustable sizes and shapes. Moreover, the number of scrolls can be controlled via switching of the switch linkage K. The experimental resul t demonstrates that this method can be a new approach for generating 3_D multi_s croll chaotic attractors with up to 21_scrolls in practical circuit by construct ing a family of triangular wave series with adjustable parameters.
2005, 54 (4): 1510-1512.
doi: 10.7498/aps.54.1510
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In this paper, we consider two FitzHugh_Nagumo (FHN) systems with delayed coupling. Firstly, dynamics of two_points with delayed coupling is analyzed. We give parameter regions about the stability of the stationary point. Spiral wave synch ronization, common_stationary states and two different patterns in two systems can be observed. There are more kinds of patterns appearing in transitional reg ions. We also discuss the dynamics of two_points and two FHN reaction_diffusion system with delayed coupling. Quantitative interpretations are given.
2005, 54 (4): 1513-1527.
doi: 10.7498/aps.54.1513
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In this paper, we report the local work function measurements on the Cu(111)-Au, and Cu(111)-Pd surfaces with scanning tunneling microscopy (STM). We successfully observed the local work function difference between the Au/Pd overlayer and the Cu substrate, the decreased work function at the step edges. We also found that the work function of the Pd film is larger than that of the bulk Pd(111). T he lower work function at step edges can be explained by the dipole moment forma tion. It is demonstrated that the local work function measurement by STM is a po werful way to identify different elements with nanometer resolution.
NUCLEAR PHYSICS
2005, 54 (4): 1528-1537.
doi: 10.7498/aps.54.1528
Abstract +
A new decomposition of the Dirac Brückner-Hartree-Fock (DBHF) G matrix is used to study the isospin-dependent relativistic microscopic optical potential (RMOP). The optical potential of finite nuclei can be obtained in the local den sity approximation. The energy dependence of proton-nucleus scattering for the optical potentials of finite nuclei is discussed. The differential cross section s and the resolution power in the p+4040Ca and p+208208Pb at Epp less than 200MeV are also calculated using the above RMOP. I t is found that the calculated results agree with the experimental results. It should be e mphasized that the ROMP obtained from DBHF G matrix without any free parameter s could well describe the proton elastic scattering. This RMOP can also be used for unstable nuclei. From the results of the Ca isotopes, it is found that the i sospin dependence is more important for the exotic nuclei.
2005, 54 (4): 1538-1542.
doi: 10.7498/aps.54.1538
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The isospin effects of Coulomb interaction on the momentum dissipation in the heavy ion collissions at an intermediate energy has been studied carefully within the isospin dependent quantum molecular dynamics model. The results show that Co ulomb interaction induces the reduction of momentum dissipation because it leads the shrinking of the mechanical and chemical instability domains, and the degre e of reduction depends sensitively on the form and strength of symmetry potentia l. However, the property that the momentum dissipation depends sensitively on th e isospin dependences of in-medium nucleon_nucleon cross section and insensitiv ely on the symmetry potential, is true for the cases with and without the Coulom b interaction.
2005, 54 (4): 1543-1551.
doi: 10.7498/aps.54.1543
Abstract +
One-dimensional ion extraction and collection is studied by parallel electrode method using particle in cell_Monte Carlo collision (PIC-MCC) simulation. The e nergy and angle distribution of extracted ions is recorded and the sputtering lo ss is calculated. The results show that the extraction time and collision loss a re decreased by increasing extraction voltage, but the sputtering loss increases and collection ratio decreases. The extraction time is decreased and the collec tion ratio is increased by increasing electron temperature, while the extraction time is increased and the collection ratio is decreased by increasing initializ ed plasma density;and the collision loss is decreased and the collection ratio i s increased, if the target isotope concentration is higher. Improving the parall el electrode method leads to decreasing sputtering loss and increasing collectio n ratio greatly.
ATOMIC AND MOLECULAR PHYSICS
2005, 54 (4): 1552-1556.
doi: 10.7498/aps.54.1552
Abstract +
The ionization energy spectra and the spherically averaged momentum distributions of inner valence orbitals for diacetyl have been investigated by using a high resolution (ΔE=115eV, Δp≈01a.u.) electron momentum spectrometer. The impact energy was 1200eV plus binding energy (i.e. 1201—1240eV) and a symmetric non-coplanar kinematics was employed. The experimental ionization energy spectra have been compared with the published photoelectron spectra. The momentum profiles of inner valence orbitals 4agg+4buu have been compar ed with the theoretical calculations obtained using Hartree-Fock method and den sity functional theory．The measured momentum distribution is consistent with th e theoretical calculations.
2005, 54 (4): 1557-1563.
doi: 10.7498/aps.54.1557
Abstract +
A simulation model for diffusion and aggregation of atomic clusters with repulsi ve interactions on nonlattice substrates is established, and the aggregation pro cess of the silver atoms on charged silicone oil surfaces has been studied. It w as found that after the stable atomic clusters form, due to the repulsive intera ction among the clusters, the number density of the atomic clusters decays with time exponentially and the time constant is Oaa; statistically, the relative speed V between two clusters increases linearly with their distance L according to V=HL, where the constant H≈Oaa after deposition and then approaches zero with time. With the increase of the viscosity coefficient o f liquid substrates, the friction force increases and H decreases. A linear relation between the friction force and H is found with the slope k≈0 10±001 We show that the critical radius r11 of the clusters, abo ve which the atomic clusters start to carry charges, is related nearly to the at omic affinity, i.e., the energy needed for the cluster to carry an extra electro n. It is found that H and Oaa increase slowly with r11 and their slopes are 12±03s-1-1μm-1-1 and 16±06s-1-1μm-1-1, respectively. Our simulation results are in agreement w ith the previous experimental findings.
CLASSICAL AREA OF PHENOMENOLOGY
2005, 54 (4): 1564-1571.
doi: 10.7498/aps.54.1564
Abstract +
The motion of electrons is affected by microwave in RF cavity. Meanwhile electrons can also generate radiation and have influence on microwave in the cavity. Ac cording to Maxwell theory, RF field in the RF cavity can be expressed by modes. So equations about such actions are established according to Maxwell theory and Lorentz force acting on electrons in the cavity. These equations are also called self-consistent equations for action between microwave and electron beam in RF cavity. Based on the equations, the single-gap RF cavity is investigated one- dimensionally (including how microwave increases and saturates in the cavity) an d the factors influencing the output power are also studied. It is concluded tha t nonlinear action is very important, and that output power is not only determin ed by cavity structure but also by the beam modulation.
2005, 54 (4): 1572-1577.
doi: 10.7498/aps.54.1572
Abstract +
Based on the nonparaxial vectorial moment theory of light beam propagation, the propagation characteristics of nonparaxial vector Gaussian beam have been system ically investigated. The results reveal that both the second_order_moment transv ersal beam widths follow a simple hyperbolic law for propagation. The analytical expression of the beam propagation factor is presented. The concise formulae ha ve been further given for highly nonparaxial case. And the maximum transverse di vergences are 90° as the dimension of light source tends to zero. When extendin g to the paraxial case, the obtained results are slightly different from the for merly paraxial formulae. Moreover, the beam propagation factor will always be gr eater than unity. Finally, comparison between the propagation of nonparaxial vec tor Gaussian beam and that of nonparaxial scalar Gaussian beam indicates that th e divergence angles show prodigious discrepancy for Gaussian light source within two times of wavelength scales.
2005, 54 (4): 1578-1582.
doi: 10.7498/aps.54.1578
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In this paper, the design of kinoforms in double-random_phase encryption method is optimized by the memory-based simulated annealing technique, which is appl ied to the simulation experiment of a binary image and an image with gray levels . The results of the experiments show that, without increasing the abundance of design, the errors caused by the quantization of phases of kinoform and key is d ecreased, and almost the same image quality as the original one is obtained as a decoded image by the proposed method.
2005, 54 (4): 1583-1586.
doi: 10.7498/aps.54.1583
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In this letter the propagation of electromagnetic wave in a round cavity of photonic crystals is analysed both theoretically and experimentally. Frequency sele cted propagation has been realized by changing the parameters of the photonic cr ystal. We have computed theoretically the transmission spectrum. In the experiment, we have also measured the transmission spectrum.
2005, 54 (4): 1587-1592.
doi: 10.7498/aps.54.1587
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The theoretical solution of the pump light absorption of a laser medium is presented. It is shown that the absorption of pump light with respect to the depth in the solid medium is not a simply exponential function. When the pump photon den sity is high enough, the variation of the absorption becomes nonexponential. The se theoretical results have been verified by experiment with the medium of ruby.
2005, 54 (4): 1593-1598.
doi: 10.7498/aps.54.1593
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In this paper, nonlinear frequency conversion of second harmonic and third harmonic of femtosecond Ti:sapphire laser is theoretically and experimentally studied. Noncolinear type Ⅰ phase matching process is chosen to generate third harmoni c of femtosecond Ti:sapphire laser, and we have obtained conversion efficiency o f 62% at 260nm output. The pulse duration is about 169fs. This work will s erve as femtosecond ultraviolet source for time_resolved electron microscopy.
2005, 54 (4): 1599-1606.
doi: 10.7498/aps.54.1599
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For the first time to our knowledge, it is put forward that GNSE can be resolved by adaptive split-step Fourier method (ASSFM) basing on split-step Fourier method (SSFM) in this paper. It is found that ASSFM must be used to resolve GNSE f or ensuring precision when the frequency shift corresponding to soliton peak val ue is remarkable and microstructure fibers' parameters change along with frequen cy remarkably. It is found that the influence of dispersion on laser pulses evol ution and supercontinuum generation in microstructure fiber is remarkably. Mech anism and scope of expanded spectrum are different in fiber different dispersion regions. The precision of numerical simulation by ASSFM is higher than SSFM in the process of laser pulses propagating in microstructure fibers by reason that the variation of wavelength corresponding to pulse peak power can be considered adequately.
2005, 54 (4): 1607-1612.
doi: 10.7498/aps.54.1607
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We have investigated the defect effect in three_dimensional (3_D) left_handed metamaterials, consisting of an array of repeated unit cells of copper wires and hexagon split ring resonators (SRRs) on strips of standard circuit board materi al. By measuring the X_band transmission through this metamaterial with differen t point_ and linear_defected SRRs, we find that the resonance frequency, its val ue and passband of transmission peaks, changes markedly. It is suggested that su ch tunable left_handed properties may arise from the symmetry breaking of SRRs i n the metamaterials.
2005, 54 (4): 1613-1618.
doi: 10.7498/aps.54.1613
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The model of the pulse front tilted by a folded reflecting telescope used as a beam expander in the chirped pulse amplification system is developed, and the relationship between the pulse front aberrance and the parameters of the telesco pe is discussed. It is found that the effect of pulse front aberrance on the bea m is too strong to be ignored when the pulse duration is less than 100fs. An e ffective method is presented to overcome this problem.
2005, 54 (4): 1619-1623.
doi: 10.7498/aps.54.1619
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In this paper, a theoretical and numerical analysis of the factors that affect mode_locked pump threshold was made. The key effect of cavity mode in Kerr_lens mode_locking was illustrated. At the same time, a soliton model showed the rela tion between the pump threshold and dispersion in the cavity. Based on the gene ral analysis, a self_starting femtosecond Ti:sapphire laser with mode_locking th reshold as low as 390 mW was demonstrated.
Numerical simulation of erbium non-uniformly doped waveguide amplifier in the pr opagation direction
2005, 54 (4): 1624-1629.
doi: 10.7498/aps.54.1624
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Design of the waveguide amplifier nonuniformly doped with Er along the propagating direction is presented. The model of waveguide amplifier is constructed by using the finite element method, including cooperative upconversion, cross rela xation and excited state absorption. The gain performances at a given length and at maximum are improved to be 1027% and 565%, respectively. Calculation res ults agree qualitatively with the experimental data of cascaded Er_doped glass s amples.
2005, 54 (4): 1630-1635.
doi: 10.7498/aps.54.1630
Abstract +
By optimizing the fabrication process of the chirped optical fiber Bragg grating (FBG), some key problems of FBG are solved, such as the temperature stabili ty, time delay ripple coefficient, bandwidth, compensation of polarization mod e dispersion (PMD), and so on. The FBG we fabricated can attain the temperature coefficient less than 00005 nm/℃, its bandwidth is bigger than 14nm, tim e delay ripple is less than 50 ps, and the dispersion is higher than -1000ps/n m. The average PMD of the FBG dispersion compensator is measured by the Jones ma trix eigenvalue method, and is compensated. Its PMD is improved from 91406 ps to 01521 ps. With dispersion compensation by two wide_band FBGs we fabricated, we have implemented a 40 Gb/s 122 km conventional single_mode optical fiber (G6 52) systems, with a power penalty being only 14 dB.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2005, 54 (4): 1636-1640.
doi: 10.7498/aps.54.1636
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A pulsed voltage of magnetically insulated diode and pulsed ion beam and temperature evolution of the target including phase transition models have been built by combining Monte Carlo method and thermodynamical method. The melting and e vaporating threshold of the target can be calculated, and the temperature of the target and the ablation plasma can also be determined.
2005, 54 (4): 1641-1647.
doi: 10.7498/aps.54.1641
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Kinetic shear Alfvn modes in tokamak plasmas (with or without temperature grad ient) in the full gyrokinetic limit are numerically investigated by using the integral eigenvalue equations. A new integration transformation is introduced in this work. This allows the growing and damping modes to be investigated. It is shown that, in the presence of ion temperature gradient (ITG), the threshold value of plasma pressure gradient for the shear Alfvn modes is well below that for ideal magnetohydrodynamic ballooning instability. It is also demonstrated in a m ore general sense that, without ITG, the former is identical with the latter. Th e electromagnetic instability is also found to exist in the second stable region of the ideal modes when a finite ITG is present. The results are compared with previous results of similar analyses for kinetic collisionless ballooning modes.
2005, 54 (4): 1648-1652.
doi: 10.7498/aps.54.1648
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Five BF33 long counters are arranged in all around the HL_1M tokama k to mea sure the flux and dose of neutron radiation under the situations: the emission o f D_D fusion neutron being in deuterium plasma or the emission of photo_neutron being in hydrogen plasma. The results of measurement are compared with those of calculation, both agree roughly with each other. The dose equivalent of neutron radiation is very low, the measured value is far below the national and ministry issued standards of permissible dose equivalent.
2005, 54 (4): 1653-1658.
doi: 10.7498/aps.54.1653
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In this paper, actinometric optical emission spectroscopy (AOES) is used to inve stigate the discharge of CF44 and CH44 mixtures. Relat ive concentratio ns of radicals in an inductively_coupled plasma are determined as functions of rf input power, pressure and the gas flow ratio R (R=［CH44］/{［CH 44］+［CF44］}). It is found that CF，CF22 ，CH，H and F radicals exis t in the CF44/CH44 plasma as well as C22 radical. The relative co ncentration of C22 increases with increasing power, and shows a rev erse “U” shape tendency with increasing pressure. As R increases, the variati on of the relative concentration of C22 is not monotonical. It reac hes a ma ximum value when Ｒ＝75%, then decreases followed by almost no change with the further increase of R. Based on these results, it is concluded that gas_pha se reaction from the reaction of CF and CH （ＣＦ＋ＣＨ→Ｃ２2＋ＨＦ ） contribu tes to the production of C22 radical. At the same time, activation reaction model of radical collision is suggested. Result of simulation agrees well with that of experiment.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2005, 54 (4): 1659-1664.
doi: 10.7498/aps.54.1659
Abstract +
Single_phase iron pyrite (FeS22) crystalpowder was prepared by so l_gel hydrothermal method, which was characterized via x_ray diffraction, Fourier transform infrared and scanning electron microscope. A simplified mathematic model was established to analyze the crystal growth process. Results indicate that phase transformation and diffusion mechanism control the process, which fits the secon d_order kinetic equation with an exponent 3215 for time t. This is a decel erated process that can be divided into three steps: during the first period, ma rcasite and pyrite phases are produced, and then with inducting of sulfur into t he reaction, the process is dominated by the merging of marcasite into pyrite. U ltimately, with the fuse of small grains and the growing of larger ones, single_ phase iron pyrite crystals grow up through diffusion mechanism.
2005, 54 (4): 1665-1670.
doi: 10.7498/aps.54.1665
Abstract +
Three processes which combined equal_channel angular pressing (ECAP) with heat t reatment were applied to fabricate super_high strength fine 7050 Al alloy. Varia tions of microstructure parameters of precipitates in 7050 Al alloys were analyz ed by using small angle x_ray scattering technique. The variations of mechanical properties and mechanism of strengthening in 7050 Al alloys were explained in the paper. Experiments discovered that “pre_ECAP solid solution treatment and post_ECAP aging treatment" was a proper process, with which the ultimate tensile strength was increased to 677MPa, and elongation to failure was improved to b e 15% or so.
2005, 54 (4): 1671-1678.
doi: 10.7498/aps.54.1671
Abstract +
Rapid growth of Cu_10%Pb hypermonotectics and Cu_374%Pb monotectics ha ve been achieved under containerless condition in drop tube. With the increase o f droplet undercooling, the primary(Cu) phase in hypermonotectios shows a morpho logy transition of “coarse dendrite→fragmental dentrite→equiaxed dentrite”. The momotectic microstructure transfers from multiple monotectic cell to single monotectic cell. Corresponding to the droplet diameter changing from 1000 to 100 μm, the calculated maximum undercooling for hypermonotectics and monotectics a re 269 K(02 TLL) and 245 K (02 TMM) respectively. The maximum grow th velocity of (Cu) dendrite is 24 m/s in Cu_10%Pb hypermonotectics. The growt h of primary (Cu) phase is always controlled by solute diffusion. The effect of Marangoni migration is more significant than that of Stokes motion, and the Mara ngoni migration velocity decreases when droplet diameter becomes small.
2005, 54 (4): 1679-1682.
doi: 10.7498/aps.54.1679
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The structure relaxation of Zr5555Cu3030Al1010Ni55 bulk amorphous alloy annealed at 340℃ for different times have been investigated by synchrotron radiation small angle x-ray scattering and differential scanning calorimetr y. Annealing time dependence of electronic density fluctuation in the amorphous alloy and apparent activation energies for the enthalpy relaxation were presente d and discussed. The experimental results show that electronic density fluctuati ons increase first and then decrease with increasing annealing time, while the a pparent activation energy for the enthalpy relaxation exhibits an opposite chang e, i.e., decreases first and then increases. Both indicate the transformatio n from the liquid-like region to the solid-like region in amorphous alloy duri ng annealing.
2005, 54 (4): 1683-1686.
doi: 10.7498/aps.54.1683
Abstract +
The nanocrystalline silicon films were prepared by pulsed laser ablation at the ambient pressures from 1 to 500 Pa of pure Ar gas. The x-ray diffraction spectrum indicates that the films are nanocrystalline, i.e. they are composed of Si nanoparticles. Scanning electron microscopy shows that with increasing gas pressur e, the average size of Si nanoparticles first increases and reaches its maximum (20nm) at 100Pa, and then decreases. The dynamics are analysed theoretically to explain the phenomenon. Furthermore, our result is compared with that in He gas.
2005, 54 (4): 1687-1692.
doi: 10.7498/aps.54.1687
Abstract +
Copper nitride(Cu33N) thin films with nano-crystalline were deposite d on glass substrates at a temperature of 100℃ by DC magnetron sputtering with a columnar target. The structure of the Cu33N thin films was characterized by x-ray diffraction, x-ray photoelectron spectroscopy and atomic force microsco py. The results indicate that Cu33N thin films are composed of nanome ter grains with a cu bic crystal structure of anti-ReO33 type. The films have a uniform s mooth surf ace with only a roughness(Raa) of 17nm. The binding energy peaks of Cu2 p3/23/2, Cu2p1/21/2 and N1s were at 9327, 9527 and 3999eV respecti vely, and spin-orbit coupling energy gap of Cu2p was 20eV. The film thickness was determined by a profile step scanner, and its resistivity was measured usin g the four-probe method. The deposition rate and resistivity were found to chan ge with the nitrogen content.
2005, 54 (4): 1693-1696.
doi: 10.7498/aps.54.1693
Abstract +
Large numbers of highly ordered Ni8080Fe2020 nanow ire arrays have be en fabricated by using electrochemical deposition technique with anodic aluminiu m oxide templates. The density of Ni8080Fe2020 nan owire is as high a s 101212—101313/cm22. The Ni8080Fe2020 nanowires were grown in a preferred direction of (111) with a high aspect ratio. Compared with the bulk sample, Ni8080Fe2020 nanowire arrays have enh anced coercivity and larger remanence magnetization.
2005, 54 (4): 1697-1701.
doi: 10.7498/aps.54.1697
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The variation of electrical parameters during microarc oxidation(MAO) of aluminium alloys at constant voltage has been studied by means of a laboratory-made data acquisition system. Experimental results show that the variations of the cath odic and anodic current amplitude and effective working current in an electrical loop with the duration of treatment show obviously five stages, and the variati ons of dynamic positive resistance and the rate of change of resistance in coati ngs also show different stages, while the variations of dynamic negative resista nce and the rate of change of resistance with oxidation time are not evident. Du ring the MAO process, the dynamic positive resistance is always not equal to the negative resistance, and the former is generally greater than the latter in gen eral. Scanning electron microscopy analysis shows that the surface morphology of MAO coatings is macro-porous and its variations with treatment time are in ste ps.
2005, 54 (4): 1702-1706.
doi: 10.7498/aps.54.1702
Abstract +
The ab initio method is used to model the colour centers and self-trapped excit ons in KMgF33. The geometry optimization of the defect cluster， incl uding the F center， shows that the relaxation of the lattice around the F center is very small. The calculated Mulliken populations for F center in its ground state and excite state show that the ground state wavefunction of F center is well localized, but the excited state wavefunction of it is more diffuse. Furthermore, our results show that the VKK center moves toward the nearby interstitia l site , but keeping the molecular axis along the［110］ direction. The relaxation of the self-trapped excitons consists of an axial translation superimposed wit h a rotation. The calculated excitation energies of F center, VKK ce nter a nd the emission energy of self-trapped exciton are compared with their experim ental values.
2005, 54 (4): 1707-1710.
doi: 10.7498/aps.54.1707
Abstract +
To describe the damage process of polymer in the energetic heavy-ion tracks by thermal spike model, polycarbonate foil (PC，Makrofol KG) stacks were irradiated with various swift heavy ions (1158GeVFe5656, 1755GeVXe13 6136 and 2636GeVU238238) in a very wide range of ele ctronic stopping power (from 19 to 171keV/nm) and the range of fluence fro m 1×101010 to 3×101212ions/cm22. The amorphization processes in the irradiated PC were studied by x-ray diffraction. By using the saturated track model (the damaging process only occur in the cyli ndrical track of area σ), the mean damage radii of tracks of the amorphization were calculated for Fe, Xe and U ion irradiation. The results obtained by using the thermal spike model, proved to be reasonable.
2005, 54 (4): 1711-1718.
doi: 10.7498/aps.54.1711
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Both shock wave crystallization and annealing crystallization of amorphous alloys FeSiB, FeMoSiB and FeCuNbSiB were studied by x-ray diffraction, transmission electron microscopy,and differential scanning calorimetry techniques. A series of novel physical effects of shock wave crystallization have be found according to the experimental results. These physical effects are very difficult to explain by the diffusion theory of solid-state phase transition, but using the theory of fluid diffusion change for shock wave crystallization is feasible.
2005, 54 (4): 1719-1721.
doi: 10.7498/aps.54.1719
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Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) have been used to probe the martensitic transformation behaviors of Ni-Fe-Ga magnetic shape memory alloys. A complete intermartensitic transformation was observed in polycrystallineNi56556.5Fe19019.0Ga2452 4.5和Ni56356.3Fe17017.0Ga2672 6.7 alloys, which is stimulated by the change of temperature and include s an intermartensitic transformation and the corresponding retransformation. The intermartensitic transformation and the martensitic transformation are both the rmoelastic and the martensitic phases existing at room temperature are character ized as a monoclinic 14M structure.
2005, 54 (4): 1722-1725.
doi: 10.7498/aps.54.1722
Abstract +
A large strain of 14% during the martensitic transformation has been observed in the textured Ni50550.5Mn2424Ga25525 .5 polycrystal prepared by vertical zone melting unidirectional solidification. This martensitic transformation strain decreases to 08% at the ninth and tenth thermal cycles. Expansion and shrinkage phenomenon during the martensitic transformation has been obtained, indicating the existence of a preferential orientation of martensitic variants.
2005, 54 (4): 1726-1730.
doi: 10.7498/aps.54.1726
Abstract +
The morphology of InP self-organized islands grown on GaInP buffer layer was calculated by employing the combination of the elastic energy Err cause d by the stress of the buffer layer and the excessive surface energy of the island Ess. The result shows that the island morphology is affected by the mi smatch between GaxxIn1-x1-xP buffer layer and InP island. With Ga content in creasing in GaInP layer, the island elongates itself with mismatch increasing. T he island metamorphosis was elongated also with volume increasing of the island. The parameters of the buffer layer determine the volume of the island which is at the minimized state. The morphology of different InP/GaxxIn1-x1-x P systems, grown on GaAs substrate by metal organic chemical vapor deposition me thod, was consistent with our calculations.
2005, 54 (4): 1731-1735.
doi: 10.7498/aps.54.1731
Abstract +
SnO22:Sb films have been prepared on glass substrates by rf magnetron sputtering method. The prepared samples are polycrystalline thin films with rutile structure of pure SnO22 and have orientation of ［110］ direction. The phot oluminescence of the samples was measured at room temperature. An ultraviolet-violet luminescence peak near 392nm was observed. The effect of different oxygen partia l pressures on the structure and luminescence was investigated, and the luminesc ent mechanism was also tentatively investigated.
2005, 54 (4): 1736-1741.
doi: 10.7498/aps.54.1736
Abstract +
Transparent and conductive oxides CdIn22O44 thin films wer e prepared by radio-frequency reactive sputtering from a Cd-In alloy target in Ar+O22 atmosphere. The structure and constitution of the films were obtained by x-ray diffraction. All films prepared contained the polycrystalline CdIn22O44 while a secondar y crystalline phase of CdO was also present. Theoretically, it is proposed that three types of point defects play the most important role in affecting the carri er concentration and the scattering of conduction electrons, namely, oxygen vaca ncies, impure point defects and dissolved surplus oxygen trap centers. By the me asurement and computing for Hall and themopower, we could get carrier concentrat ion, Hall mobility, effective mass and relaxation time. At the same time, this p aper formulated the effect on optical band-gap due to band-gap narrowing and B urstein-Moss (B-M) shift, and a proper substrate temperature, namely Tss≈280℃, was used in sputtering for getting higher transmittance of light. Analy sis indicated that better thin films were prepared at oxygen density of 8%. By p ost-deposition heat treatment, a charge-carrier mobility of 31×10-4-4m2/V·s and resistivity of 189×10-5Ω·m were obtained, and the thin films also retain high visible transmittance.
2005, 54 (4): 1742-1748.
doi: 10.7498/aps.54.1742
Abstract +
Superhard and oxide-composed multilayers are promising coatings for tools working under extreme conditions. In this paper, TiN/SiO22 nanomultilayers with vari ous individual SiO22 and TiN layer thicknesses have been prepared by multi-tar gets magnetron sputtering method. The growth structure and mechanical properties of the films have been studied by x-ray diffraction, energy dispersive x-ray spectrometry, high-resolution transmission electron microscope and nanoindenter. It reveals that although SiO22 and TiN monolithic films form amorp hous and nanocrystalline structures, respectively, the TiN/SiO22 multilayers exhibit coherent epitaxial growth due to the mutual growth-promoting effect. At small Si O22 layer thickness (～1nm) S iO22 layers transform into amorphous structure and block the coherent growth of multilayers, and then the hardness and elastic modulus of the multilayers decre ase gradually with increasing SiO22 layer thickness. On the other han d, the cha nging of TiN layer thickness shows a relatively small effect on the growth struc ture and mechanical properties of the nanomultilayers.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2005, 54 (4): 1749-1755.
doi: 10.7498/aps.54.1749
Abstract +
A systematic study based on ab initio calculation within local spin density appr oximation is carried out for material design of Ⅱ-Ⅳ-Ⅴ22 chal copyrite semiconductor (CdGeP22 and ZnGeP22) doped with 3d-TM (TM= V, Cr, Mn, Fe, Co and Ni). It is found that the ferromagnetic (FM) state will be realized in V and Cr doped CdGeP22 and ZnGeP22; for Mn, Fe and Co doped ones, the antiferromagnetic (AFM) states are more stable than FM states; whereas dope d with Ni, the dilute magnetic semiconductor (DMS) shows unstable ferromagnetism . It is suggested that Ⅰ-Ⅳ-Ⅴ22 chalcopyrite semiconductor doped with Cr is a candidate for high Curie temperature (TCC) DMS. When th e t2g2g states of TM are partially occupied, the DMS doped with TMs shows a stable FM state, whereas when the t2g2g states of TMs are fully occupied or empty, the DMS with the TM shows AFM state. In order to elucid ate the underlying mechanism of the ferromagnetism in DMS, the magnetism in (C d,Mn)GeP22 and (Cd,Mn)GeP22 under the carrier (elect ron or hole) doping treatment is investigated. It is found that it is crucial to realize the carrier-induced ferromagnetism, indopendent of whethe r the doped carrier has itinerant TM-3d character or not.
2005, 54 (4): 1756-1761.
doi: 10.7498/aps.54.1756
Abstract +
Using the density-functional theory within the full-potential linear augmented plane wave method, we have calculated the influence of the mercury vacancy on the bonding mechanism and the relaxation effects in the Hg050.5Cd 050.5Te (MCT) alloy. The bonding charge density and charge transf er gave the explanation for the relaxation results. The results of density of st ates revealed that the re-coupling of the dangling bond of the nearest neighbor (NN) of the vacancy make the NN Te 5s state energy level shift up. The reasons for the energy level shift were discussed with the Te s-state bonding charge density. The results of the partial density of state at the band edge reveal that the mercury vacancy will narrow the band gap of the MCT materials.
2005, 54 (4): 1762-1770.
doi: 10.7498/aps.54.1762
Abstract +
Dipole moments, polarizabilities and first hyperpolarizabilities of a series of transition metal complexes have been studied by employing various exchange-correlated potentials within the density functional theory (DFT). Taking into consideration the basis set and frequency-dispersion effects, the efficiencies of these potentials have been calibrated by comparing with the ab initio results of MP2, HF and experimental measurements. The effect of different portion of exchanged-correlated functional of hybrid-DFT on dipole moment, polarizability and first hyperpolarizability has been discussed as well.
2005, 54 (4): 1771-1776.
doi: 10.7498/aps.54.1771
Abstract +
The models of interphase boundaries of austenite/ferrite(γ/α) in the undeformde austenite and deformed austenite, and the model of 12[1 1 0] edge dislocation in austenite matrix were set up with computer programming. The interfacial energ y of γ/α interphase boundaries in the undeformde austenite and deformed austen ite, the environment sensitive embedding energies (EESEESE) of C, N a nd microalloying elements Nb, Ti or V (in the form of air mass) in the area of e dge dislocation in austenite were calculated by using recursion method. The refineme nt mechanism of steels in the deformation process was discussed. Interfacial ene rgy calculation results show that the most preferred ferrite nucleation sites ar e the area of high density dislocations such as deformation bands, the austenite grain boundaries and subbounaries, which leads to a considerable increase in th e nucleation rate. This is why ferrite grains formed in the deformed austenite a re far more smaller than those in undeformed austenite. The EESEESE calcu lation results show that C,N microalloying elements (Nb, Ti or V) in form of the air mass, C,N together with microalloying elements (Nb or Ti) in the form air m ass are all easy to aggregate to the area of edge dialocations, which results in the carbonitride precipitation in there (deformation band, grain boundary or gr ain subboundary). The growth of ferrite grains is considerably suppressed by def ormation due to impingement with carbonitride particles and other ferrite grains , which leads to the further refinement of ferrite grains.
2005, 54 (4): 1777-1782.
doi: 10.7498/aps.54.1777
Abstract +
We report the low-temperature resistance under a magnetic field (μ０0H=0, 5 and 10T) within the temperature range from 18 to 300K and low temp erature (T=19 and 15K) magneto_resistance (μ00H=0—10T) of hea vy electron compounds CeCu6-x6-xCdxx(x=010，015 ，020，0 30，050). The experiments show that the Tmaxmax（correspondin g to the max imal resistance）of all samples are not observed over 18K under zero magneti c field. When a magnetic field is applied, the Tmaxmax increases with inc reasing magnetic field and doping content x. Meanwhile, the magneto_resista nces are all negative at 19K and the positive magneto_resistance of part of samples is observed at 15K. This phenomenon can be explained by Kondo scatteri ng and coherent scattering.
2005, 54 (4): 1783-1787.
doi: 10.7498/aps.54.1783
Abstract +
Variations of the irradiated defects, resistivity, carrier mobility ratio and ca rrier concentration in high-dose neutron-irradiated n-type Czochralski silico n have been investigated by means of Fourier transform infrared spectrometer, po sitron annihilation spectroscopy and Hall effect. After irradiated with fast neu tron, the sample transformed from n to p-type. Two types of acceptor centers th at contribute to the V22O22, V22O, VO22, V-O-V and V 44-type defects will appear after annealing at temperature of 450 a nd 600 ℃, respectively. After annealing at temperatures above 650℃, with the elimin ation of acceptors, the carrier mobility ratio and the carrier-type began to re cover and a type of donor related to the irradiated defects will appear. The eff ective annealing temperature is 750℃ at which the donor is formed, and anneal ing above 900℃ for 1h will eliminate the donor.
Theoretical study on the absorption and dispersion in asymmetrically coupled qua ntum well structure
2005, 54 (4): 1788-1793.
doi: 10.7498/aps.54.1788
Abstract +
The absorption and dispersion behaviors of an asymmetrically coupled quantum well (ACQW) structure are studied based on V-type system. We show that the quantum-confined Stark shift due to an electric field applied along the growth direction of ACQW leads to the detuning absorption, and the corresponding linear refraction is dramatically decreased in a smaller negative-bias voltage region. This means that refraction quenching induced by an external electric field can occur in an ACQW structure. However, the absorption and the dispersion behaviors become the same as those of the lowest excitonic state in a single quantum well structure as the negative-bias voltage further increases due to the disappearance of quantum-confined Stark effect. This means that the ACQW structure has controllable dispersion by using an external field.
2005, 54 (4): 1794-1798.
doi: 10.7498/aps.54.1794
Abstract +
We have studied the exciton states in vertically stacked self-assembled quantum disks within the effective mass approximation. The energy spectrum of the elect ron and hole is calculated using the transfer matrix formalism in the adiabatic approximation. The Coulomb interaction between the electron and the hole is trea ted accurately by the direct diagonalization of the Hamiltonian matrix. The effe ct of the vertical alignment of the disks on the ground energy of heavy- and li ght-hole exciton is presented and discussed. The binding energy is discussed in terms of the probability of the ground wave function. The ground energy of heav y- and light-hole excitons as a function of the magnetic field is presented an d the effect of the disk size (the radius of disks) on the exciton energy is dis cussed.
2005, 54 (4): 1799-1803.
doi: 10.7498/aps.54.1799
Abstract +
Based on the fact that the charge is discreteness in the mesoscopic circuit, taking 3-rings for example, the effect of quantum current magnification in a mesoscopic multi-ring coupling system has been investigated. The results show that the effect of quantum current magnification not only can be observed in a dual-ring coupling system, but also in the metallic multi-ring coupling circuit.
Realization and output characteristics analysis of the multiple islands single- electron transistors
2005, 54 (4): 1804-1808.
doi: 10.7498/aps.54.1804
Abstract +
In this paper, a new kind of multiple islands single-electron transistor is prepared successfully with indium quantum dots deposited among nanometer-gap electrodes. The output characteristics are tested and the Coulomb blockade effects are observed. As a result, the harmful co-tunneling effects occurring usually in the single island single-electron transistors are weakened significantly, and a big threshold voltage is got. At the end of the paper, the different transport states from source to drain are discussed.
2005, 54 (4): 1809-1813.
doi: 10.7498/aps.54.1809
Abstract +
Thin CaCu33Ti44O1212 ceramic films have been successfully fabricated by a magnetron sputtering method and the surface morphology, microstructure and dielectric property of the samples have been measured by using atom force microscope, x-ray diffractometer (XRD) and LCR meter. XRD patterns show that the lattice constant of the films is less than that of the bulk materials, while the distort ion of the lattice in the films is comparatively larger. LCR results show that t he relative dielectric constant of the films is lower than that of the bulck mat erials at fixed temperature, and the temperature at which the dielectric constan t transits abruptly is higher and the activation energy of the films is larger. Further analysis shows that the lower crystallinity and more defects in the samp les result in the rapid decrease of the barrier layer capacity and film density, which should be responsible for the lower relative dielectric constant. The inc rease of the activation energy in the samples depends mainly on the factors such as internal stress, microstructure, defect and domain etc. The rapid increase o f the dielectric constant in lower frequency range implies that there exists int erface polarized phenomenon in the samples, which is related to the defects and dangling bonds on the interface.
2005, 54 (4): 1814-1820.
doi: 10.7498/aps.54.1814
Abstract +
The electronic density of states, spin-splittings and atomic magnetic moment of RE-TM compound SmCo55 have been studied by spin-polarized MS-Xα method. The results show that a few of electrons are transferred to Sm(5d00) o rbital because of orbital hybridization between Sm and Co atoms in the compound. The exchange interactions between 3d and 5d electrons lead to the magnetic coupling betwee n Sm and Co, and therefore, result in the long-range ferromagnetic order inside the compound SmCo55 There are some negative exchange couplings occ urring at six levels, which make the Curie temperature of SmCo55 decrease disti nctly, com pared with pure Co. The spin moment and orbital moment of 2c and 3g site s have been also studied in this paper. We found that the spin moment, orbital m oment and its quenched part of Co(2c) are greater than that of Co(3g).Th erefore, the strength of L-S coupling of the former is a little greater tha n that of the latter, which implies the contribution to magneto-anisotropy of 2c site is greater than that of 3g site. But the unquenched orbital mome nt in 2c site is slightly smaller than that in 3g site. So, the differen ce of contribution to the anisotropy between the two Co-sites is not very disti nct. Considering the localization of 4f electrons and the few 5d electrons, the magnetic moment of Sm atom will be 129μBB in SmCo55, wh ich is in agreem ent with the experiments of Sm3+3+ ion-moment (132—163μBB) and the Sm atom-moment (174μBB) in metal.
2005, 54 (4): 1821-1825.
doi: 10.7498/aps.54.1821
Abstract +
The giant magneto-impedance (GMI) effect has been observed at room temperature in soft magnetic alloy films of FeZrBCu prepared by radio frequency (RF) sputtering. The dependence of the soft magnetic properties and the GMI effect on the RF sputtering power has been studied. The results measured by electron probe micro-analysis show that the as-deposited films sputtered at 240W possess 29at% Cu and 8732at% Fe. This sample possesses excellent soft magnetic properties and a maximum value of GMI effect, the coercive force is about 68A/m, the saturation magnetization is about 111×1055A/m, and the maximum GMI r atios are 17% and 11% in longitudinal and transverse fields at frequency of 13MHz, respectively. In addition, the dependence of resistance R, inductance X and effective permeability μee on the frequency has been investigated, and the results show that the GMI effect is mainly a magneto-inductive effect at low frequencies.
2005, 54 (4): 1826-1830.
doi: 10.7498/aps.54.1826
Abstract +
SrFe12-x12-xCrxxO1919 (x=0—10) hexaferri te nanoparticles have been fabricated using a sol-gel technique for perpendicular magnetic recording. Experimental results have shown that the values of specific saturation mag netization, σss, increase for x≤04 as the Cr doping content incre ases, and reach maximum at x=02, while the coercivity, Hcc, decreas es for x＜05 This feature is favorable to magnetic recording. It is also fou nd that the α-Fe22O33 non-magnetic phase appears after x=06 and remai ns to be a hexagonal magnetoplumbite phase for x=0—04 Magnetic measurem ents have revealed that Cr substitution can decrease the magnetization and incre ase the peak-widening for Hopkinson peak when doped with Cr3+3+.
2005, 54 (4): 1831-1835.
doi: 10.7498/aps.54.1831
Abstract +
We report the effect of Ru(seed-layer) on the interlayer antiferromagnetic coupling field Hexex, and coercivity Hcc in the Cr/Ru(se ed-layer)/PtCo(thermal stabilizing layer)/Ru(spacer layer)/PtCo(recording layer)/Ru(protective layer) films. Both Hexex and Hcc increase with t he increase o f the thickness of the seed-layer Ru. It arises probably from the appearance of hcp structure in the seed-layer Ru. Hexex and Hcc sh ow a peak value at Ru(seed-layer) layer with a thickness of ～08nm.
2005, 54 (4): 1836-1840.
doi: 10.7498/aps.54.1836
Abstract +
Fe/Pt multilayers and FePt thin films were prepared by DC magnetron sputtering. The as-prepared samples were subjected to vacuum annealing at temperatures in t he range of 300—550℃. The multilayered structure is an effective approach fo r reducing the ordering temperature of FePt. The ordering parameter S is evaluated to be 06, and correspondingly the coercivity is evaluated to be 501kA/m in ［Fe(15nm)/Pt(15nm)］1313 multilayers annealed at 350℃ for 20min. Relatively low ordering temperature for the multilayer is due to the e xtra driving force of ordering process caused by the vanishing of the multilayer interface at annealing.
2005, 54 (4): 1841-1846.
doi: 10.7498/aps.54.1841
Abstract +
The ［Co8585Cr1515/Pt］2020 multilayers w ith Pt underlayers were prepared by magnetron sputtering and the effects of sputtering Ar gas pressure on m icrostructure and magnetic properties of ［Co8585Cr1515 /Pt］2020 mul tilayers were studied. The results show that sputtering Ar gas pressure has a gr eat effect on the microstructure, perpendicular magnetic anisotropy and the coer civity of ［Co8585Cr1515/Pt］2020 mul tilayers. For all samples, we have the effective magnetic anisotropy constant K effeff＞0, and all s amples showed perpendicular magnetic anisotropy. With increasing sputtering Ar g as pressure, the perpendicular and in-plane coercivity of the samples increase, but the effective magnetic anisotropy constant decreases. The coercivity of Pt( 20nm)/［(Co8585Cr1515(05nm)/Pt(15nm)］2020 multilayers spu tter-depositied at 16Pa Ar gas pressures is increased to 130kA/m. The Pt( 20nm)/［(Co8585Cr1515(05nm)/Pt(15nm)］ 2020 multilayers display perpendicular magnetic anisotropy and can be used as perpendicular magn etic recording media. The images of atomic force microscopy show that both avera ge grain size and the surface roughness increase with increasing sputtering Ar p ressure, which leads to the enhancement of perpendicular coercivity and the decr ease of effective magnetic anisotropy constant.
2005, 54 (4): 1847-1853.
doi: 10.7498/aps.54.1847
Abstract +
Compared with massive magneto-optical (MO) crystals, the one-dimensional MO photonic crystals, which are composed of magneto-optical and dielectric films per iodically or quasi-periodically, have a notable enhancement in MO effects, so t hey are very useful for fabricating micro-size MO isolators with only tens of m icrons in thickness. Our theoretical calculations are based on a transfer matri x method that is suitable to solve the problems of the propagation of polarized light in anisotropic media at an oblique incident angle. Using this method, we h ave discussed the working stability of two particular types of “sandwiched" ref lection-mode MO multilayer film isolators with the change of incident angle and film thickness at λ=1053μm. It is revealed that the structure with a thicker central MO medium has the advantages of better working stability and les s necessary layers.
2005, 54 (4): 1854-1858.
doi: 10.7498/aps.54.1854
Abstract +
A series of new glasses of 70TeO22-(20-x) ZnO-xPbO-5La22O33-25K22O-25Na22O (x=0,5,10,15, 20mol %) doped with Yb22O33 is presented. Thermal stability, spectra and laser properties of Yb3+3+ ions have been measured. It has been found that the glass with x=15 has a good thermal s tability ((Txx-Tgg)>195℃), high stimulated emission cross -section of 125pm22 for the 22F5/25/2 →22F7/27/2 transition and a long fluorescence lifetime of 094ms and a broad fluorescence effective linewidth of 72nm. From the viewpoint of good potential laser parameters, it is desirab le to have high-average power and short pulse tunable laser, which can be achie ved by doping with Yb22O33.
2005, 54 (4): 1859-1862.
doi: 10.7498/aps.54.1859
Abstract +
The urea has been used as a precipitant agent to react with soluble Zn2+2+ salt and Eu3+3+ salt for preparing ZnO:Eu3+3+ nanocrystals. The particle size, the crystal structure and morphology of the nan ocrystalline ZnO:Eu3+3+ were characterized by x-ray diffractio n and transmission electron micrograph. Narrow-sized, finely dispersed nanocrys talline ZnO:Eu3+3+ with a small size about 8nm has been obtained by homogeneous precipitation method. By using different preparation methods, obtai ning different dimensions of crystals with different doping concentrations, the luminescence characteristics of nanocrystalline ZnO:Eu3+3+ were stu died. The results indicate that the homogeneous precipitation method is a kind o f superior preparation technique for nano-size doped materials, and also demons trate the feasibility of nanocrystalline ZnO:Eu3+3+ for luminescent applications.
2005, 54 (4): 1863-1867.
doi: 10.7498/aps.54.1863
Abstract +
Quantum interference control photocurrent in bulk semiconductors is analyzed using the Fermi golden rule and Kane six-band model. The initial momentum distributions of photoexcited carriers in different polarized light fields are calculat ed. The polarization dependence of the coherent currents is shown explicitly in a microscopic level. For the case of parallel linear polarizations, the current direction is along the direction of the light polarization; while for the case of perpendicular polarizations the current direction is along the polarization o f the harmonic frequency light. It is also shown that when the one-photon trans ition and the two-photon transition is balanced, the maximum current injection efficiency is achieved.
2005, 54 (4): 1868-1873.
doi: 10.7498/aps.54.1868
Abstract +
Positron lifetime parameters have been measured by position annihilation technique in binary Ni7777Al2323 and Ni7474 Al2626 alloys with different Al contents and Ni33Al alloy doped with different amounts of Zr. The density o f free electrons in bulk materials and grain boundaries was calculated in this p aper. The results show that the density of free electrons in bulk materials and grain boundaries in Ni7474Al2626 alloy is lower t han that in Ni7777Al2323 alloy. The open volume in grain boundary is larger in Ni7474Al2626 alloy, and the cohesion of grain boundaries is weaker. When an amount of Zr atoms is added into the Ni33Al alloy, they increase the density of f ree electr ons in the bulk and thus increase the bonding cohesion in the bulk. The other Z r atoms will segregate at grain boundaries and increase their free electron dens ity; this will strengthen the bonding cohesion in grain boundaries. Alloying ele ment Zr is found to be beneficial to reduce the brittleness of Ni33Al alloy with different Al contents.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2005, 54 (4): 1874-1878.
doi: 10.7498/aps.54.1874
Abstract +
ZnS films are prepared on glass and quartz substrates by sulfidation of the ZnO films which are deposited via reactive magnetron sputtering and annealed under v arious conditions. The sulfurized films are characterized by using x_ray diffrac tion, scanning electron microscope and UV—VIS spectrometer. The results show t hat the crystalline structure and optical properties of the sulfurized films dep end on the annealing conditions. ZnO films annealed in vacuum and pure O2 2 at mosphere, respectively, are converted partially to the hexagonal ZnS, while the annealed ZnO films in air and pure N22, respectively, are converted t otally to ZnS. Also the ZnS films produced by sulfurizing the annealed ZnO films in air an d pure N22, respectively, have a high optical transmittance of about 80% at the wavelength of 400—800nm, with the band-gap energies of 366 and 361eV, respectively.
2005, 54 (4): 1879-1884.
doi: 10.7498/aps.54.1879
Abstract +
The structural, optical and electrical properties of CdSxxTe1-x1-x thin films prepared by co_evaporation of powders of CdS and CdTe ha ve been studie d by x_ray diffraction, atomic force microscopy and optical transmittance spectr a measurements. Results show that the as_deposited CdSxxTe1-x1 -x thi n films are homogeneous, adherent and compact on the glass slides substrates wit hout pinhole and that their conductivity is n_type for x≥05 and p_type fo r xxTe1-x1-x thin f ilms are pol ycrystalline and show highly preferential orientation. The predominant direct op tical transitions were observed and the variation of the optical energy gap E gg is nonlinear with x. Given the values of lattice parameter and opt ical energy gap, the exact composition of the phase change at x=025 has been determined. The films are of a cubic phase for x025. After annealing there is no change in the structure of the films with a slight decrease in optical energy gap. Finally, a new structure of CdS/CdTe/Z nTe/ZnTe:Cu/Au solar cells with a CdSxxTe1-x1-x buffer l ayer has been proposed.
2005, 54 (4): 1885-1889.
doi: 10.7498/aps.54.1885
Abstract +
Diamond-like carbon (DLC) films were deposited on Si substrates by a dual direct current and radio frequency plasma-enhanced chemical vapor deposition (DC-RF-PECVD) technique. The effect of RF power on the surface morphology, micros tructure, hardness and Young's modulus of DLC films was investigated by atomic f orce microscopy, Raman spectroscopy, x-ray photoelectron spectrometry, infrared spectroscopy and nano-indentation. The films produced by DC-RF-PECVD have typical hydrogenated diamond-like characteristics, and the surface of the film s was smooth and compact.With the increase of RF power the bonded hydrogen conte nt in the films decreased while the sp33 content, hardness and Youn g's modulus of the DLC films reached the maxima at an RF power of 100W and then they decr eased with further increase of the RF power.
2005, 54 (4): 1890-1894.
doi: 10.7498/aps.54.1890
Abstract +
Microcrystalline silicon thin films at different growth stages were prepared by hot wire chemical vapor deposition. Atomic force microscopy has been applied to investigate the evolution of surface topography of these films. According to the fractal analysis, it was found that, the growth of Si film deposited on glass substrate is the zero_diffused stochastic deposition; while for the film on Si substrate, it is the finite diffused deposition on the initial growth stage, and transforms to the zero_diffused stochastic deposition when the film thickness reaches a certain value. The film thickness dependence of island density shows that a maximum of island density appears at the critical film thickness for both substrates. The data of Raman spectra approve that, on the glass substrate, the a_Si:H/μc_Si:H transition is related to the critical film thickness. Different substrate materials directly affect the surface diffusion ability of radicals, resu lting in the difference of growth modes on the earlier growth stage.
2005, 54 (4): 1895-1898.
doi: 10.7498/aps.54.1895
Abstract +
Oxygen contamination of samples fabricated by very high_frequency plasma_enhanced chemical vapor deposition with the variation of silane concentration and disc harge power was studied by secondary ion mass spectroscopy. The results showed t hat oxygen content in the samples depended strongly on the silane concentration and discharge power. Microcrystalline silicon thin films with higher crystallin e volume fraction has relatively higher oxygen content. Oxygen contamination of samples was also related with the background vacuum, especially for microcrystal line silicon thin films. Therefore, higher background vacuum is extremely necess ary in the fabrication of high-quality microcrystalline silicon thin films.
2005, 54 (4): 1899-1903.
doi: 10.7498/aps.54.1899
Abstract +
Microcrystalline silicon solar cells with the variation of silane concentration (SC) and discharge power were fabricated by very high frequency plasma_enhanced chemical vapor deposition. The results of J_V measurements showed that open circuit voltage (Vococ) of solar cells decreases with the decr ease of silane concentration and the increase of power in the range of experiments. I nfluence of SC on short_circuit current density (Jscsc) is more evi dent than power. As for microcrystalline silicon solar cells, the optimum choice for N layer is amorphous, because it can decrease the lateral collection effect of current on the one hand and increase the fill factor on the other hand.
2005, 54 (4): 1904-1908.
doi: 10.7498/aps.54.1904
Abstract +
Micro-distribution of C acceptor defect in semi-insulating gallium arsenide (SI-GaAs) wafer has been investigated by means of chemical etching, microscopic observation, transmission electron microscope, eelectron probe x-ray microanalyz er.Experimental results show that there is a corresponding relationship between the distribution of C impurity and dislocation density in a wafer. In relatively high dislocation density areas, dislocations form relatively small cells with few isolated dislocation within each cell. Here the profile of C distribution in the area of a cell is “U”-shaped. The cell diameter increases as the dislocation density decreases, and the dislocations form relatively large cells with a few isolated dislocations within each cell. The profiles of C distributio n in the area of a cell is “W”-shaped.
2005, 54 (4): 1909-1913.
doi: 10.7498/aps.54.1909
Abstract +
At the composition of Ti4040Zr4040Ni2020 , a single_phase cylindr ical quasicrystalline alloy, 3mm in diameter and 15mm in length, can be fabr icated by a copper-mold casting method. Its quasicrystalline nature and structu ral homogeneity were confirmed by x_ray diffraction and transmission electron mi croscopy. According to compression and indentation tests at room_temperature, th e as_cast Ti4040Zr4040Ni2020 quasicry stalline rod has a hardness of 55GPa and a fracture strength of 542MPa. In particular, the Young's modulus (～43GPa) of Ti404Zr4040 Ni2020 quasicrystals is consid erably low while they possess a high Poisson's ratio (～048). Under monax ial compression, the Ti4040Zr4040Ni2020 quasicrystalline alloy e xhibits a highly elastic deformation capability of 125%. The cleavage fracture morphologies indicate a brittle fracture mechanism.
2005, 54 (4): 1914-1918.
doi: 10.7498/aps.54.1914
Abstract +
Nanosized TiO２2 particles are prepared by sol-gel method, the avera ge size of which varies from 15 to 23nm. These nanoporous TiO２2 films are ap plied to d ye-sensitized solar cell modules. The x-ray diffraction patterns are used to d etermine the phase and average nanocrystalline size of TiO２2. The sh ape and pa rticles size of the crystal TiO２2 are shown by transmission electron microscop e. The conditions of nanoporous films microstructure in solar cells are measured by testing the BET surface and the microscopy of titania films. The photovoltai c performance of dye-sensitized solar cell modules with the size of 15cm×20 cm (the active area is 187.2cm２2) is discussed, at the same ti me, the eff ect of nanoporous TiO２2 films microstructure and average particles s ize of nan ocrystalline TiO２2 on dye-sensitized nanosized films solar cells is investigated in this paper.
2005, 54 (4): 1919-1926.
doi: 10.7498/aps.54.1919
Abstract +
The key technologies in dye-sensitized solar cell, including nanoporous TiO２2 film, dye-sensitizer, electrolyte, platinum catalysis, and TCO glass, have bee n investigated, and we also optimized the different technologies with assemblyin g the small area dye-sensitized solar cells. About 9% photo-electric conversion efficiency has been demostrated in our lab under AM1.5 solar simulator. Our results show that there would be a possibility for commercial production based on our technologies.
2005, 54 (4): 1927-1930.
doi: 10.7498/aps.54.1927
Abstract +
Tunable diode laser absorption spectroscopy (TDLAS) is a new trace gas detective method developed with the combination of a diode laser source and a long absorption path. It has the significant advantage not only in sensitivity but also in rapidity of response. The concentration of the ambient methane has been measured using a TDLAS system developed in the laboratory. The system has some advantage s, such as sensitivity, low detective limit (below 0.087mg/m33) an d rapidity of response, and also it is easy to be integrated to a portable apparatus to mon itor the methane concentration in the atmosphere.
2005, 54 (4): 1931-1936.
doi: 10.7498/aps.54.1931
Abstract +
An adaptive training and pruning algorithm for variable bit rate(VBR) video traffic prediction is proposed in this paper. By simulation and comparison, the adaptive neural network model proposed in this paper is shown to be promising and practically feasible in obtaining the best adaptive prediction of real-time VBR video traffic.
2005, 54 (4): 1937-1942.
doi: 10.7498/aps.54.1937
Abstract +
This paper presents the implementation about adaptive noise cancellation by prov iding several kinds of algorithms with the objective of removing the 50Hz noi se from magnetocardiogram(MCG) based on SQUID. The computer simulation results o f the algorithms are given for comparison. The result shows that 50Hz power li ne noise in MCG taken by SQUID has been fairly well eliminated by an adaptive no ise canceller.
2005, 54 (4): 1943-1949.
doi: 10.7498/aps.54.1943
Abstract +
How to extract the magnetocardiographic (MCG) signals from the noisy background is the key of MCG signal processing. In this paper, wavelet transformation is adopted to recover the MCG signals, acquired by using the high Tcc dc -SQUI D magnetometer developed at our institute. The results of this work show that t his method is much more effective than other methods used before and can be implemented in the MCG system for routing operation. This method can also be used in noise cancellation of other non-stationary signals.
2005, 54 (4): 1950-1957.
doi: 10.7498/aps.54.1950
Abstract +
A general analytical solution is derived for an electric potential produced by a direct current point source located at any position in a multilayered spher ical volume conductor. Starting from Poisson's equation, the electric potential whose coefficients are rapidly got in the form of matrix expressions is obtained according to the boundary conditions. Simulation for a four-layered spherical volume conductor denoting the scalp, skull, cerebrospinal fluid and brain tissue proves that electric potential in this paper converges more rapidly in the whol e region than that expressed only in spherical harmonics expansion form, and ite rative times decrease. Electric potential contour and current streamline figur es show that it is important to consider the effect of the low conductivity of s kull on electric potential and current flow. The distribution of electric potent ial on the surface of sphere is discussed, which will be useful in electroenceph alography inverse problems, and also in analyzing and interpreting the electric potential measurement.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
A study on the soil heat flux along the Qinghai-Tibet railway based on the mult i-timescale analysis
2005, 54 (4): 1958-1964.
doi: 10.7498/aps.54.1958
Abstract +
By using soil temperature data from ANDUO, TTH and NODA station along the Qinghai-Tibet railway, the soil heat fluxes at 3 different depths in these 3 stat ions from September 1997 to August 1998 are calculated by use of integral method. Based on the multi-time scale analysis method, the time series of the soil heat fluxes is analyzed, and some important characters on the variation of soil he at fluxes against time and depth on different time scales are concluded.
