Vol. 50, No. 8 (2001)
2001-04-20
GENERAL
2001, 50 (8): 1405-1408.
doi: 10.7498/aps.50.1405
Abstract +
We built up a nuclear warhead verification system based on an Intranet platform. The hardware of the system consists of an Intranet server, two personnel computers and a portable high purity gerinanium gamma-ray spectrometer. The software, Blanking-out, is made of two modules designed for the inspecting and inspected parties respectively. Both modules are interactive and communicate through the Intranet. When the system operates, any sensitive information carried by the high resolution gamma-ray spectrum collected by the detector will be meddled by the inspected module before the package of spectral data is sent to the inspecting module to prevent a disclosure of sensitive information. After receiving the spectral data, the inspecting module will display on the screen of the inspecting PC terminal the verification results in a form of blankouted spectrum (spectral blanking-out form) or a form of a piece of phrase (phrase form). The guideline to the spectral blanking-out is that: for those ranges of energy obligated to be inspected, the inspected module should ensure that the inspecting module can display truly their objective spectrum; and for the other ranges of energy, the inspected module can blankout certain parts of the spectra based on the knowledge of sensitive information. Phrase form is rather straightforward, answering the question whether the inspected warhead is a “uranium-type”, “plutonium-type” or “non-nuclear type.” We conducted a demonstration on some surrogates for nuclear warheads to see whether the nuclear warhead verification system possesses the capability of identifying the type of a warhead and blanking-out sensitive spectral information. The demonstration was carried out successfully. Phrase form is especially recommendable due to its stronger capability to prevent sensitive information from disclosure and its higher verification credibility. The demonstration also disclosed some deficiencies of the system, such as too much disintegrated hardware components lower the integration of the system, the interactive operation of the inspected module and the spectral blanking-out form decrease the verification credibility and so on.
2001, 50 (8): 1409-1414.
doi: 10.7498/aps.50.1409
Abstract +
The matrix eigenvalues method is used to analyze the laser cavity in which the traditional spherical mirror is replaced by the phase type diffraction optical elements. The authors analyze the characteristics of the modes under the conditions of different Frenesl number. The results show that this laser cavity can enhance the discrimination between spatial modes effectively and can be used to design the output laser beam.
2001, 50 (8): 1415-1420.
doi: 10.7498/aps.50.1415
Abstract +
This paper is devoted to the simulation of acoustic wave propagation in complex media, applying the finite difference scheme and the orthonormal compactly supported wavelet transform approximation,to the time and the space dimension of the wave equation, respectively. A new method, which is a fast adaptive arithmetic, named Multiresolution Finite Difference (MRFD) is first proposed to solve the problem of the wave propagation in multi-layered medium with nonperiodic boundary condition. Thus the problem is solved in the wavelet domain rather than in the traditional Euclidian space. Due to adaptive and vanishing-moment property of the wavelet basis, the difference operator and solution vector have sparseness in the wavelet domain. MRFD is a promising method because of some advantages such as lighter computational burden, efficiency of convergence and robustness. Numerical results in geophysics exploration show the effectiveness and potential of the method.
2001, 50 (8): 1421-1424.
doi: 10.7498/aps.50.1421
Abstract +
By means of canonical transformation,a direct quantization scheme is found for a harmonic oscillator whose damping coefficient is time-dependent.By adopting the Gaussian-type propagator and Feynman's path integral method,the exact wave function is derived.Some discussions made.
2001, 50 (8): 1425-1428.
doi: 10.7498/aps.50.1425
Abstract +
The general formula of probability current operator is obtained by generalizing the concept of probability current and the theorem of probability conservation.With the help of this new formula,we derive a probability current operator for the tight-binding models of single electron system and interacting-multi-electron system,and then prove,in a very simple way,the normalization condition of reflection-transmission currents.
2001, 50 (8): 1429-1433.
doi: 10.7498/aps.50.1429
Abstract +
A 1.1km long all-fiber quantum key distribution experimental setup has been realized for the first time at 850nm. The system employs the BB84 protocol to establish a secret key between two parties, the security of which is guaranteed by Heisenberg's uncertainty relationship and the quantum noncloning principle. Phase modulated single photons are used to carry the key. The effective transmission rate is 3 bit/s, with a bit error rate of 9%.
2001, 50 (8): 1434-1439.
doi: 10.7498/aps.50.1434
Abstract +
A new type of one-dimensional periodic ally driven Hamiltonian system (an harmonic) has been proposed and its characteristics discussed. Chaotic dynamics in the driven oscillator is controlled using an adjustable, passive limiter (a weight for the oscillator). The chaotic trajectories of the conservative system can be controlled to some of the low periodic (or low energy) orbits. The results demonstrate that chaos control can be accomplished using controllers that are very simple relative to the system being controlled.
2001, 50 (8): 1440-1446.
doi: 10.7498/aps.50.1440
Abstract +
A simpl wavelet control function is presented on the basis of the realization in control of beam halo-chaos for high intensity ion beam in period-focusing channel by wavelet function, and the feedback control method of multi-periodical intervals is studied .The beam with the K-V distribution is taken as a typical example. The simulation results demonstrate that beam halo-chaos can be controlled well by selecting the parameters of control function and the number of control multi-periodical intervals,and the beam halo and its regeneration can also be eliminated perfectly .The research offers a valuable reference for the application in the control of beam halo-chaos in high intensity accelerators.
2001, 50 (8): 1447-1450.
doi: 10.7498/aps.50.1447
Abstract +
Based on X-ray photoelectron spectrum intensity measurements of thin film by ARXPS, a method of determination of the thickness of PtSi ultra-thin films through calculations of electrom mean free path, is described in this article.The result of calculation is in agreement with that of the TEM crystal lattice images analysis.It shows that the method is convenient and can be used to determine the thickness of other ultra-thin films.
2001, 50 (8): 1451-1455.
doi: 10.7498/aps.50.1451
Abstract +
The laser induced voltage effect had been found in HTSC YBCO thin film grown on vicinal cut SrTiO3 substrate. The relationship between the decay time constant of response signal and the thickness of YBCO thin film was studied. It was found that the relationship between the decay time constant and the film thickness can be fitted by a fitting curve. The film thickness can be obtained from the fitting. We discussed the error induced to the fitting.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2001, 50 (8): 1456-1462.
doi: 10.7498/aps.50.1456
Abstract +
A rigorous solution of Bargmann-Wigner equation for spin-5/2 in coordinate representation is given in this paper. A relativistic equation and the representative function of momentum for the spin-5/2 are deduced.
ATOMIC AND MOLECULAR PHYSICS
2001, 50 (8): 1463-1466.
doi: 10.7498/aps.50.1463
Abstract +
The effect of pressure broadening on the line shape of velocity modulation laser spectroscopy is considered here, which is induced by the collisions of the gas molecules. The old theory on velocity modulation spectroscopy is revised and new theory is setup to get the precise simulation of our experimental spectrum. It has been shown that the new theory agrees with experiments perfectly, and has potential applications in the investigation of the dynamics of the collisions of molecular ions and obtaining more precisely resolved spectrum.
2001, 50 (8): 1467-1474.
doi: 10.7498/aps.50.1467
Abstract +
The thermodynamic behavior of single molecule-photon cryocooler(SMPC)was described by the study of participating frequency of phonons in light transitions, heat-light converting efficiency and cooling efficiency. The times of heat distribution were taken as a time scale in the investigation of cooling efficiency. The cooling efficiency curve obtained from our theory has the same shape of experiment curves obtained by other researchers. The reason of a bending of cooling efficiency curve appearing in the cooling region was given. The greatest cooling efficiency of SMPC was investigated, and it is obtained that the best wavelength, which results in the greatest cooling efficiency,is located at the point of one fourth exciting band width from the red edge. As a main conclusion, crystal-line materials are the sole kind of promising materials for obtaining the greatest cooling efficiency.
2001, 50 (8): 1475-1480.
doi: 10.7498/aps.50.1475
Abstract +
By using a distorted-wave Born exchange ( DWBE ) approximation method including the relativistic correction, we calculated the direct ionization and excitation autoionization cross sections of eight Na-like ions. Based on the calculated results, we present two empirical formulas with high accuracy for calculating direct ionization and excitation autoionization cross sections. Our results are in good agreement with the experiment data and other theoretical values.
CLASSICAL AREA OF PHENOMENOLOGY
2001, 50 (8): 1481-1485.
doi: 10.7498/aps.50.1481
Abstract +
Characterization of the structure of spatial inhomogeneities embedded in a highly scattering medium is required in many fields. In this paper, a model of a stratified medium embedded with an inhomogeneous ball is considered. With an assumption that the ball is small enough, a perturbation solution to diffusion equation is obtained with some boundary treatments. According to the characteristics of this solution in the two-dimensional Fourier space, a new weighted Fourier transform is used to process the surface data. After this process, a singularity appears at the center of the ball. Combining with the symmetry of the surface data, the information of three-dimensional position of the ball is determined.
2001, 50 (8): 1486-1491.
doi: 10.7498/aps.50.1486
Abstract +
In opto-electronic imaging systems, aliasing will occur when sampling a scene containing spatial frequencies exceeding one half of the sampling frequency. A novel superresolution technique, micro zooming, is proposed, which can reduce aliasing and improve the resolution of the imaging systems through a series of aliased frames with different optical magnifications. Both computer simulations and experimental results are presented to verify the effectiveness and simplicity of micro-zooming technique for obtaining superresolution.
2001, 50 (8): 1492-1495.
doi: 10.7498/aps.50.1492
Abstract +
A quasi- phase-matched optical parametric oscillator(QPM OPO)consisting of a periodically poled LiNbO3(PPLN) crystal is pumped by an all-solid state single frequency Nd:YVO4 laser. The triple resonance of the pump mode and two subharmonic modes with near- degenerate frequencies are experimentally demonstrated by means of precision temperature control of the crystal. The threshold pump power is only 1.2mW. The quadrature phase noise squeezing of the pump field reflected from the OPO up to 1.1dB is observed at the pump power of 2.8 times of the oscillation threshold. The numerically calculated result is in good agreement with the experimentally measured data.
2001, 50 (8): 1496-1500.
doi: 10.7498/aps.50.1496
Abstract +
The cavity field spectra of a two level atom interacting with two mode field through Raman process are investigated. It is shown that the basic features of the spectra is unchanged whether the atom is in the high or low level state initially. Symmetrical two peak structure appears in the spectrum for each mode when the initial fields are both in the pure number states or both in the coherent states. The split of the two peaks is proportional to the field intensity of the other mode.
2001, 50 (8): 1501-1506.
doi: 10.7498/aps.50.1501
Abstract +
Reversible thermochromic properties were observed in Bi2O3-Li2O system glasses. The temperature coefficient of optical absorption edge increases with increasing Bi2O3 content, implying that Bi2O3 is the main reason of thermochromism. The thermochromic mechanism is explained in terms of the temperature dependence of the optical energy gap Eg, caused mainly by the electron-phonon interaction. The low phonon energy and high electron density of Bi—O bond are important factors contributing to the electron-phonon interaction in these glasses.
2001, 50 (8): 1507-1511.
doi: 10.7498/aps.50.1507
Abstract +
Obtaining true beautiful data from any photon correlation experiment demands on serious attention to improve the signal-to-noise ratio. Single-mode optical fibers provide the ideal receiver optics for photon correlation spectroscopy measurements. The analysis shows that a single-mode fiber can achieve a high collection efficiency and improve the signal-to-noise ratio effectively in photon correlation experiments. All these features are also demonstrated in experiments.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2001, 50 (8): 1512-1516.
doi: 10.7498/aps.50.1512
Abstract +
Under low vacuum condition (5Pa), Q-switched YAG laser ablates plane aluminum target and plasma are produced. Optical emission spectroscopy is used to carry out time-resolved analysis of atomic particles. Using the resonance transition of AlI 396.1 nm(3p2P—4s2S), the velocity distribution of AlI in space has been determined at laser power densities of 1.91×1010, 5.10×1010 and 7.64×1010W/cm2, respectively, when the ablating size is about 200 μm. The velocity is of the order of 106 cm/s and the time decays nearly agree with the exponential law as the radial distance from the target surface increases. At a fixed position, the velocity shows some decrease as the laser power density being increased, but when the distance is above 15 mm, the velocity converges to unification one. Shockwave model is used and gives a good agreement with the experimental results. From the model, it is deduced that the shockwave front has cylindrical symmetry.
2001, 50 (8): 1517-1520.
doi: 10.7498/aps.50.1517
Abstract +
A numerical simulation study was done on effects of an ambient radiation field on the processes of excitation and ionization in a plasma, using a non-LTE ionised material package NIMP. It has potential importance in the future experimental design to study the effects of the radiation field on the physical processes in the astrophysical reseach.
2001, 50 (8): 1521-1527.
doi: 10.7498/aps.50.1521
Abstract +
The radial profiles of the electron temperature Te,the electron density ne,the plasma potential φp,the toroidal Mach number Mp and their electrostatic fluctuations in the plasma boundary region of the HT-7 superconducting tokamak have been measured with a multiarray of Langmuir probes and a set of Mach probes,under the conditions of both ohmic discharge and a lower hybrid current drive.The experimental results show that,under ohmic discharge condition,there is a poloidal velocity shear layer located in the vicinity of the limiter radius,which has a suppression effect on the fluctuations and results in the increase of the radial gradients of Te and ne LHCD intensifies the shear.In the same radial position of the poloidal shear layer,there is also a radial shear with the toroidal velocity,which could be the drive source of the mean poloidal flow needed by the formation for radial electric field.
2001, 50 (8): 1528-1533.
doi: 10.7498/aps.50.1528
Abstract +
The characteristics of DC hollow cathode discharge and cathode sputtering was investigated by means of a two dimensional hybrid model, combing Monte Carlo simulation of the motion of fast electrons and a fluid description of slow electrons and positive ions. The results demonstrate the existence of the hollow cathode effect in the discharge and show that the spatial shape of the normalized ionization source is dependent more on the gas pressure than on the discharge voltage. The factors related to the cathode sputtering were analyzed. Investigations have demonstrated that the non uniform sputtering on the cathode surfaces in a sputter-type ion laser is due to the non-uniform distribution of electric field, flux and density of ions bombarding the cathodes.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2001, 50 (8): 1534-1539.
doi: 10.7498/aps.50.1534
Abstract +
Based on a study of the phase relation in the Fe- and Co-rich region of the equi-gadolinium content section with the Gd content corresponding to the chemical formula Gd3(Fe,Co,Cr)29 in the Gd-Fe-Co-Cr quaternary system, formation, structure and magnetic properties of the 3∶29-type Gd3(Fe1-xCox)29-yCry compounds have been investigated. It has been found that the composition range of formation of the single phase Gd3(Fe1-xCox)29-yCry Compounds is 0≤x≤0.7 for y=5.0, 0.7≤x≤0.8 for y=5.5, and 0.8≤x≤1.0 for y=6.0. A pure Co-based Gd3Co29-xCrx compound series have been synthesized. The solubility limit of the Cr atoms in the Gd3Co29-xCrx compounds was found to be from x=6.5 to x=7.3. The results indicate that all the synthesized Gd3(Fe1-xCox)29-yCry compounds crystallize in Nd3(Fe,Ti)29 type structure of the monoclinic system and the space group A2/m.The solubility limit of Co atoms in the Gd3(Fe1-xCox)29-yCry compounds increases with increasing the stabilizing element Cr. It is noteworthy that substitution of Co for Fe leads to a remarkable change of the magnetocrystalline anisotropy of the Gd3(Fe1-xCox)29-yCry compounds. When x≥0.4 the anisotropy changes from the easy plane type to the uniaxial type, which is important for permanent magnet application.
2001, 50 (8): 1540-1544.
doi: 10.7498/aps.50.1540
Abstract +
We have grown clean N-salicylideneaniline (SA) single crystals large enough in size by physical vapour depositaion. The photochromism of the SA single is studied by probe light at different optical polarizations At different temperatures and different polarizations,we measured the time dependence of the change of optical density in the colored crystal in the forward and backward reactions.The activation energies of the single crystal are obtained in different optical polarizations.Based on theoretical calculations,the structure configurations of the SA molecules in the colored keto form are analyzed.When an ultraviolet (UV) light is irradiated on the sample at 200 K,about 60% of the ketone form molecules are found to be in the trans-configuration and about 40% of them in the cis-configuration.
2001, 50 (8): 1545-1548.
doi: 10.7498/aps.50.1545
Abstract +
A multiple parallel plate aluminum ionization chamber has been designed for the study of dose distribution at and near the interface of different materials.The measurement of dose gradient distribution at and near the interface of Kovar/Au/Al,Pb/Al,Ta/Al has been done for 30—100 keV X rays from the synchrotron radiation source, and the dose enhancement factor(DEF) are also provided. DEF for interface of different materials is calculated by Monte-Carlo simulation of particle transportation, and the results are consistent with the measured dose-enhancement factor. A reliable evaluation approach of theoritival and experimental method is proposed for studying X-ray dose enhancement.
2001, 50 (8): 1549-1554.
doi: 10.7498/aps.50.1549
Abstract +
The diamond-like carbon (DLC) films were deposited under different deposition parameters by using arc technology. The detailed relationship of sp3 structure with the D peak of the DLC films' Raman spectra is discussed. In aid of the discussion, X-ray photoelectron spectroscopy was used to determine the DLC films' C1s binding energy. By comparing the binding energy with the Raman shift of the films, it can be found that the intensity of D peak decomposed from the Raman shift can be increased not only by the graphite cluster, but also by higher content of sp3 bonds. Higher sp3 content of DLC films can be obtained by using 90 degree magnetic filter. The study shows that the C1s binding energy of DLC films, whose Raman spectra have higher intensity of D peak, can be 284.15 or 285.50 eV, which reveals that the DLC films may have higher graphite-like or diamond-like structure, respectively.
2001, 50 (8): 1555-1559.
doi: 10.7498/aps.50.1555
Abstract +
The atomic processes of nucleation and initial growth of thin films on metal surfaces are simulated by Monte Carlo method,using realistic growth model-Fe on Fe (001) surface and physical parameters.By taking into account the physical processes involved in film growth,such as deposition,diffusion,nucleation,growth,evaporation,edge diffusion and coalescence,the morphology and quantitative characteristies of thin film growth are obtained.The details of thin film growth at high substrate temperatures,such as the change of island density and growth rate with temperature and coverage,are obtained by making statistical counting during the growth processes,which are difficult to access directly in real experiments.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2001, 50 (8): 1560-1566.
doi: 10.7498/aps.50.1560
Abstract +
Effects of Ba filling fraction and Fe content on thermoelectric properties of Ba2+-filled p-type skutterudite compounds BayFexCo4-xSb12(x=1.0—1.6,y=0—0.63) were investigated.Effects of oxidation valence of filling atoms on electrical transport properties of filled skutterudeite compounds were also discussed.The greatest ZT value of 0.9 was obtained for Co-rich Ba0.27FeCo3Sb12.
2001, 50 (8): 1567-1573.
doi: 10.7498/aps.50.1567
Abstract +
We develop the physical model based on the real space charge transfer mechanism and derive the dynamic equations of GaAs/AlGaAs heterostructures. Complex bifurcations are studied in detail for the forced and unforced cases. It is shown that both periodic attractors and fixed points attractors can coexist under a right dc bias. The hysteresis phenomena are also investigated in theory. For the forced GaAs/AlGaAs, numerical simulation shows that the occurance of frequency-locking, quasiperiodicity, and chaos depends on the frequency and amplitude of the externally applied microwave field, as expected.
2001, 50 (8): 1574-1579.
doi: 10.7498/aps.50.1574
Abstract +
InP/SiO2 composite thin films have been deposited on hot substrates of slice of silica glass and polished silicon by a radio frequency magnetron co-sputtering technique, and annealing under several conditions. Detailed analysis of the composition of the films by X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy shows that the InP and SiO2 exist in normal stoichiometry as a whole. X-ray diffraction patterns and Raman spectra of the films conform the presence of InP nanocrystals in the composite films. Very small amounts of extra indium and In2O3 have been removed and pure InP/SiO2 nanocomposite films have been obtained by annealing at high temperature (520℃) in over-pressure of phosphorous vapor. Blue shifts of optical absorption spectra and great enhancement of optical nonlinearity of the films at room temperature have been observed.
2001, 50 (8): 1580-1584.
doi: 10.7498/aps.50.1580
Abstract +
Si-containing silicon oxide (SSO) films and Ge-containing silicon oxide (GSO) films were deposited on p-type Si substrates using the RF magnetron sputtering technique with a Si-SiO2 and a Ge-SiO2 composite target, respectively. These films were annealed in a N2 ambient at temperatures from 300 to 1100℃. Using high resolution transmission electron microscopy,nanometer Si particles and nanometer Ge particles were observed in the SSO and GSO films,respectively,after annealing at 900 or 1100℃. All the PL spectra from the two types of films annealed at various temperatures have similar shapes with peak positions around 580nm (～2.1eV). It is indicated that light emission originates from luminescence centers in Si oxide films. The experimental results have been explained reasonably.
2001, 50 (8): 1585-1589.
doi: 10.7498/aps.50.1585
Abstract +
High electric field annealing effect in thin gate oxide of MOS structure is studied in depth, and the detrapping mechanisms of trapped charge in the gate oxide are investigated. Comparison between the growth mechanism and the detrapping mechanism of trapped charge in gate oxide is made by experiments and simulations. A satisfactory physical description is presented for explaining this effect. Comparison between annealing under negative and positive gate voltages shows that the former is more effective .
2001, 50 (8): 1590-1595.
doi: 10.7498/aps.50.1590
Abstract +
We carried out magnetization loop measurements on melt-textured YBa2CuO7-δ sample at various temperatures with the magnetic sweep method by using a vibrating sample magnetometer(VSM). We derived the curves of, J(T,B),lnE-lnJ and thermal excited potential U0(T,B), and analyzed the magnetic response of this sample, especially the influence of field sweep rates to the second peak. The peak effect of the sample, as well as the factors affecting the magnitude and position of the second peak, is discussed.
2001, 50 (8): 1596-1559.
doi: 10.7498/aps.50.1596
Abstract +
One-dimensional steady state and evolutionary Ginzburg-Landau equations for superconductivity is disussed. Instability of constant steady state solutions and the existence of limit sets of infinite-dimensional dynamic system are proved. Using the author's definition of chaos for finite-and infinite-dimensional dynamic systems, we conclude that superconductors governed by G-L equations possess chaotic phenomena. Therefore strange phenomena may occur in conducting. The theoretical results indicate that it is advisable to improve the design of experiments or try to find new structures of superconductors in future research to suppress the chaotic behavior.
2001, 50 (8): 1600-1604.
doi: 10.7498/aps.50.1600
Abstract +
Effect of the Ga content substituting the Fe on the crystal structure and magnetic properties of the Nd2(Fe,Co)14B/(Fe,Co)3B+(little)α-Fe permanent magnetic materials is studied. The change mechanism of magnetic properties of the dual-phase nanocrystalline magnets is discussed.The results show that the crystal size was markedly decreased by adding Ga. With the increase of x, the dependence of the Br and the (BH)max on annealing time undergoes a chang from two-peak curves to one-peak curves in the Ga content range of xj Hc decreases at first to a minimum and then increases slowly. The best value of the magnetic properties is obtained at x=0.2.
2001, 50 (8): 1605-1609.
doi: 10.7498/aps.50.1605
Abstract +
Systematic study on magnetic properties of Fe-nanowires fabricated by electrochemical deposition is performed by micromagnetic simulation,which reveals that all nanowires show magnetic anisotropy,and the coercivity dependents on the diameter with a relationship of inverse square ratio.With fixed diameter,it increases as the length increases,stopping at a platform.The hysteresiss loop,static magnetic configuration and reversal mechanism all vary with changing diameter and length of the wires.Explicit explanation is presented based on the details of the magnetization process.Nanowires with diameter of 5nm,which have not been successfully acquired by experiments all show uniform reverse mechanism in the simulation.Even more intriguing magnetic behaviors emerge when the shape of the wires becomes more particle-like.
2001, 50 (8): 1610-1615.
doi: 10.7498/aps.50.1610
Abstract +
Based on the electromagnetic model of ferromagnetic/non-ferromagnetic/ferromagnetic layered films proposed in references [17] and [18] the enhanced giant magneto-impedance (GMI) effects and the GMI ratio dependence on the thickness of the constituent thin films are analyzed numerically in detail.It is showsn that larger difference of resistivity between the ferromagnetic and non-ferromagnetic layers as well as an optimum thickness of the layered thin films are beneficial to the improvement of the GMI effects.
2001, 50 (8): 1616-1622.
doi: 10.7498/aps.50.1616
Abstract +
The heteroepitaxial diamond films were grown on the p-type Si (100) substrate by microwave plasma chemical vapor deposition (CVD). The diamond films were patterned to strip types with the oxygen plasma etching technology. The magnetoresistance measurements have been carried out in a magnetic field ranging from 0 to 5 T, using the four-probe method. It was shown that the heteroepitaxial diamond films may produce fairly big magnetoresistance. Based on the Fuchs and Sondheimer thin film theory, mixed scattering by lattice vibration,ionized impurities and surfaces is considered. Taking the parallel connection resistance model, a theoretical description of the magnetoresistive effect in heteroepitaxial diamond films is presented by solving the Boltzmann transport equation in the relaxation time approximation. A relationship between the magnetoresistance and the film thickness, magnetic field, mobility and hole density is developed. The influence of valence deformation and surface scattering to the magnetoresistance of heteroepitaxial diamond films is discussed. A possible cause is proposed to explain the fairly big magnetoresistance of the films.
2001, 50 (8): 1623-1626.
doi: 10.7498/aps.50.1623
Abstract +
This Letter describes the photoluminescence properties of ZnO nanoparticles enclosed in BN capsules (ZnO/BN core/shell structure). PL enhancement of over one thousand times of ZnO/BN compared to pure ZnO nanoparticles was observed, which is attributed to the dielectric environment effects of the capsule on the interfacial structures and defect amounts of ZnO quantum dots.
2001, 50 (8): 1627-1631.
doi: 10.7498/aps.50.1627
Abstract +
The influence of Gd3+ and Y3+ doping on the low temperature thermoluminescence (TL) of PbWO4(PWO) is investigated. In the case of polycrystal powder, the TL above 180K is eliminated by doping Y3+ or Gd3+ ions. Meanwhile, a new TL peak at lower temperature appeare. For the PWO single crystal there are two TL peaks at about 130 and 253K, but only one single peak at about 130K for PWO:Y crystals. The common effect of doping trivalent ions is to decrease or eliminate the TL above 180K and create a new TL peak at lower temperature. It indicates that the traps responsible for TL above 180K are due to the intrinsic defects which probably are Pb3+ and O-. During the preparation of PWO, the evaporation of the PbO component is easier than that of WO3, which will lead to the deficiency of PbO. The deficiency of O ions can be compensated by annealing in air while the deficiency of Pb is permanent. Therefore in the volume surrounding the Pb vacancy, there is a lack of positive charge. So the charge deficiency in the Pb-sublattic can be most easily balanced by an increase of concentration of Pb3+ and O- Doping Gd3+ or Y3+ can decrease the concentration of Pb3+ and O-. Gd3+ or Y3+ can also play a role of electron traps, which create new TL peaks at 150 and 125K, respectively. The trap depth of Gd3+ and Y3+ are 0.32 and 0.29eV, respectively. The difference between doping Gd3+ and Y3+ can be explained by the difference between their coulomb potentials.
2001, 50 (8): 1632-1636.
doi: 10.7498/aps.50.1632
Abstract +
CeCu6 is one of heavy fermion materials. The effect of the partly substitution of Cu by Au, Ag, Pd and Pt on the low temperature properties has been intensively studied. In this paper, we study the temperature dependence of resistance of CeCu6-xNix(x=0.00, 0.05, 0.10, 0.15, 0.20) at temperatures below 1K. Experimental result shows that the temperature dependence of resistance changes with increase of doping content x. Below 500mK, the resistance of sample with x≈0.1 has a linear temperature dependence, showing a typical non-Fermi liquid behavior, while other samples behave as Fermi liquid. This means x≈0.1 is the critical doping for this system. In the case of Au substitution of Cu, the critical doping of which is also x=0.1, the ground state of the system is changed from Fermi-liquid to non-fermi liquid and antiferromagnetic ordering by volume expansion. But in the present case, the ground state of Ni doping systems changes from FL to NFL due to the magnetism of Ni.
