Vol. 54, No. 1 (2005)
2005, 54 (1): 1-5. doi: 10.7498/aps.54.1
The first-order and second-order effects of perturbation on Landau-Ginzburg-Higgs Soliton have been derived,namely,both the slow time-dependence of the soliton parameters and the first-order and second-order correction has been obtained.
2005, 54 (1): 6-11. doi: 10.7498/aps.54.6
The fields in 3-dimensional tapered waveguides are unstable compared with the fields in the straight waveguides. In the case of waveguide-to-fiber coupling and fiber-to-waveguide coupling, a sequence of short straight waveguides has been modeled to approximate the 3-dimensional tapered waveguide; and the unstable incident and reflected fields, as well as their derivatives, were determined by the beam propagation method(BPM). Then free space radiation mode(FSRM) was employed to calculate the reflected and transmitted powers. Analysis results of the coupling of fiber with silicon-on-insulator(SOI) tapered rib waveguides showed the feasibility of the method.
The eigenfunction of hydrogen atom is expressed in a unified way with four boson operators and Bogoliubov transformation, and the corresponding relations with t he wave function expressed in spherical coordinates is given as well. The proble m of operator expressions of hydrogen atoms is solved completely.
The study of static and stable gravitational fields by using the gravitational field theory including the energy-momentum tensor of the pure gravitational field part of matter
2005, 54 (1): 18-23. doi: 10.7498/aps.54.18
In this paper, a general gravitational field theory containing the effect of cosmic constant and the energy_momentum tensor of the pure gravitational field part of matter is proposed. The equation of the grovitational field is Rμν -gμνR/2+λgμν=8πG(T(Ⅰ)μν+T(Ⅱ)μν )/c4， where λ is Einstein’s cosmic constant， Ｔ（Ⅰ） μν and Ｔ（Ⅱ）μν are energy_ momentum tensor of the p ure matter part and pure gravitational field part, respectively. Ｔ（Ⅱ） μν can be expressed by T(Ⅱ)μν=(DμρＤρ ν-gμνＤαβＤαβ/4)/4πG， where Ｄμν＝ωμ／xν-ων／xμ， and the vector is defined as: ωμ≡-c2gμ0/g00. The several static and stable gravit ational fields, such as the external static metric tensor of an isolated globula r symmetric pure matter which contain Einstein's cosmic constant or that with charge, the external stable metric tensor of a rotation isolated globular symm etric pure matter or that with charge, and the internal static gravitational equ ilibrium in a globular symmetric pure ideal fluid star matter are studied and di scussed respectively by the general gravitational field theory which contains the energy-momentum tensor of pure gravitational field part of matter.
2005, 54 (1): 24-29. doi: 10.7498/aps.54.24
Based on the equation of state of the ideal quantum gas, regenerative characteristics of the quantum Stirling refrigeration cycle is analyzed. The general expression for the coefficient of performance is derived. Under the condition of strong and weak gas degeneracy, the special expressions for the coefficient of performance are discussed. These results will be significant for the research of a Stirling refrigerator in the low temperature range.
2005, 54 (1): 30-34. doi: 10.7498/aps.54.30
A new approach to control chaotic systems is presented. This control approach is based on least squares support vector machines (LS_SVMs) modeling. Compared wit h the feed_forward neural networks, the LS_SVM possesses prominent advantages: o ver fitting is unlikely to occur by employing structural risk minimization crite rion, the global optimal solution can be uniquely obtained owing to the fact tha t its training is performed through the solution of a set of linear equations. A lso, the LS_SVM need not determine its topology in advance, which can be automat ically obtained when the training process ends. Thus the effectiveness and feasi bility of this method are found to be better than those of the feed_forward neur al networks. The method does not needs an analytic model, and it is still effect ive when there are measurement noises. The chaotic systems with one_and two_ dim ensional nonlinear maps are used as examples for demonstration.
2005, 54 (1): 35-42. doi: 10.7498/aps.54.35
In this paper, we adopt the Particle_in_Cell(PIC) program to study the transverse movement of particles in high_intensity beam. It is found that the transverse movement of halo particles in not always in halo region. The movement is restricted in a narrow region after the beam is controlled. Changes of root_mean_squared radius are nearly periodic. According to the regulation and variation of root_mean_squared radius, a new self_adaptive controller method is put forward. This research demonstrates that the halo can be completely controlled by the controller quickly. There is no need to precisely calculate the coefficient of controller, and the controller can work well even if the system parameters are changed.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2005, 54 (1): 43-46. doi: 10.7498/aps.54.43
The property of fractional spin of the O(3) nonlinear sigma model with Hopf and Maxwell_Chern_Simons (MCS) terms is studied. According to the rule of path integral quantization for a constrained Hamilton system in Faddeev_Senjanovic sc heme，the system is quantized. Based on the quantal Noether theorem，we get the quantal conserved angular momentum, and the fractional spin at the quantum level of this system is presented.
2005, 54 (1): 47-52. doi: 10.7498/aps.54.47
There exists a dual symmetry between the equations of motion and Maurrer_Cartan equations of the type IIB superstring on AdS5S5. We generalize the finite dual transformation to the infinitesimal dual transformation by the twisted dual. We also obtain the Lax connexion and the compatibility condition for this integrable system.
2005, 54 (1): 53-57. doi: 10.7498/aps.54.53
This paper discusses the possibility of using nanocrystalline ZnO films as photo_electrode in dye_sensitized solar cells (DSCs). The performances and mechanism of DSCs based on ZnO nanoporous film are observed by using IR, UV_vis spectra and LSV method, and compared with dye_sensitized solar cells based on nanocrystalline TiO2 films. It is found that the low efficiency of DSCs based on ZnO is due to the poor binding force between the surface of nanocrystalline ZnO films and the RuL2(NCS)2(L=2,2′_bipydyl_4,4′_dicarboxylate) dye.
2005, 54 (1): 58-63. doi: 10.7498/aps.54.58
Diffraction_enhanced imaging by using two crystals has been recently developed i n x_ray topogrphy station in Beijing Synchrotron Radiation Facility. In this art icle the analysis for the influence of the thermal expansion of the first crysta l on the diffraction enhanced imaging is presented. The conclusion is that the i nfluence of the thermal expansion of the first crystal can be avoided and much b etter images can be obtained when the axes of crystals are placed vertically to the polarization plane of the synchrotron radiation. The experimental results co nfirmed this analysis.
2005, 54 (1): 64-69. doi: 10.7498/aps.54.64
The optically stimulated luminescence (OSL) of SrSO4:Eu (01mol%) powder samples was studied. The continuous wave OSL and linearly modulated OSL curves measured after irradiation by beta rays of 90Sr in the dose range of 0116—116kGy, illustrate that there are four components in OSL signal and the OSL dose response is linear-sublinear. Thermal stability of OSL signal was also measured, and the results showed that OSL from SrSO4:Eu is quite stable a t temperatures up to ～200℃. Meanwhile, the intensity of OSL signal is stronges t when the read temperature is about 180℃. The thermal luminescence(TL) three-d imensional spectra were measured after gamma rays irradiation (absorbed dose is 100Gy) of 60Co source. The emission wavelength at about 375nm indicate s that the luminescence comes from the transitions between energy levels of Eu 2+.
ATOMIC AND MOLECULAR PHYSICS
2005, 54 (1): 70-77. doi: 10.7498/aps.54.70
A traditional average-atom model (AAM) is improved in several aspects. 1. A dynamic criterion for free electrons is adopted. 2. The free electrons are classifie d in three types, each of which is treated by the partial wave method and Fermi- Dirac statistics. 3. An exchange potential in mixed type is obtained to replace the Slater potential by applying the variation principle. 4. A parameter α in t he atomic structure is calibrated by the constants of material under normal cond itions. As examples electron pressures of Iron, Nickel and Copper at zero temper ature are calculated and compared with the results obtained by other theories an d in experiments.
2005, 54 (1): 78-84. doi: 10.7498/aps.54.78
Analytic local potential energy surfaces for S2O in the ground state and the excited states were calculated at MRCISD and MRPT2 levels. Further, the data points selected were fitted to a polynomial force field and the calculations for the interaction of vibration configuration were carried out. Then, the analyses of normal vibration modes and vibration energy levels were performed. The local potential energy surfaces were improved by adjusting a few force constants. The mean-square roots of the deviation between computed and available experimental vibration spectra for the ground state and the excited state are 3852cm-1 and 644cm-1, respectively.
The x-ray spectra of hollow atoms in the interaction of highly charged argon ions with beryllium solid surface are reported. The interaction ions, provided by t he electron cyclotron resonance (ECR) ion source in the National Laboratory of t he Heavy Ion Research Facility in Lanzhou(HIRFL), include bare argon ions, which are produced by the ion source for the first time, and hydrogen-like, helium-li ke and lithium-like argon ions. We found that the K-shell x-ray yield of single particles in the interaction of hydrogen-like argon ions is 36×10-3, wh ich is 5 orders more than that of helium-like argon ions, and the K-shell x-ray cannot be measured in the interaction of lithium-like argon ions with beryllium surface.
Molecular dynamics study on the energy characteristic of copper nanoclusters at room temperature and during heating
2005, 54 (1): 89-95. doi: 10.7498/aps.54.89
Molecular dynamic method and Finnis Sinclair potential are used to study the e nergy characteristic of copper nanoclusters at room temperature and its changes during heating, by which we get the surface thickness and surface energy in diff erent cluster sizes at room temperature and get the probability density of energ y distribution of the copper nanoclusters at different temperatures. The differe nce of the energy characteristic during heating between the inner atoms and the surface atoms is given in detail.
CLASSICAL AREA OF PHENOMENOLOGY
Study on the electromagnetic scattering and Doppler spectra from two-scale time-varying fractal rough sea surface
2005, 54 (1): 96-101. doi: 10.7498/aps.54.96
In this paper, the two-scale model method, which is much applicable to the comp utation of the electromagnetic scattering field from the rough sea surface, is used to calculate the backscattering cross-section of the one-dimensional time-varying fractal rough sea surface, the related results are also compared with those calculated by small perturbation method. The fractal characteristic of the Doppler spectra of the backscattering signal from the sea surface is studied, th e dependances of the the backscattering cross-section and the width of Doppler s pectra on the incident angle and fractal dimension are also analyed. Finally, th e relationship between the central frequency of the Doppler spectra and the Brag g resonant frequency is discussed in detail.
Analysis on the principle of multilevel optical data recording and the study on the processing of the front signals of a multilevel read-write system
2005, 54 (1): 102-106. doi: 10.7498/aps.54.102
This paper utilized the calculation methods in vector diffraction theory, such as the wave_coupled method and the finite difference time domain method, to a nalyze two multilevel optical recording methods in principle. Meanwhile the prin ciple to achieve multilevel optical recording by modulating the amplitude of pha se_change media is also discussed. According to these analysis, the multilevel d ata recording utilizes the mutual action between laser and recording media. Lase r beam has some special effects on the media; simultaneously the media will modu late some characteristics of the light. Generally, the diversities of these cha racteristics are more than two states, so the multilevel data recording can be a chieved by recording these different states. Besides, the design and development of the front signals processing system is also presented. It is an important pa rt of the experimental system for multilevel recording. It can output some servo and error signals such as TE, FE and RF etc, which will be fed back to the appr opriative chip for multilevel recording. Additionally the processing system not only can control the laser power and the writing time of the optical pickup, but it also can make the pickup realize focusing and tracking automatically.
Eigenenergies and wave functions of the Tavis-Cummings system driven by an external classical coherent field
2005, 54 (1): 107-112. doi: 10.7498/aps.54.107
We study the interaction of the atoms in the two-atom Tavis-Cummings (T-C) model under an external classical driving field. The eigenenergies - quasienergies and eigenstates of the T-C system driven by the external field are calculated i n the interaction picture. We also give the general wave function of the system in the Schrdinger picture. We show that the driving field does not change the energy levels of the T-C model, but makes the Fock states displaced. A stationar y state with a definite frequency in the normal two-atom T-C model is transform ed into the Fock states with infinite frequencies by the driving field.
2005, 54 (1): 113-116. doi: 10.7498/aps.54.113
Using a theoretical model for generation of the third_order harmonic in a gas_fi lled capillary driven by fs laser pulses, the signal_pressure curves of the thir d_order harmonic generation in a gas_filled capillary driven by fs laser pulses are discussed. It is found that when the parameters of the capillary and laser pulse are given, the generation efficiency of the third harmonic is influenced b y the waveguide modes of the third harmonic, the pressure, the walk_off and the phase modulation, and that the theoretical value of the generation efficiency of the third harmonic, which is given in this paper, approaches the experimental one.
2005, 54 (1): 117-122. doi: 10.7498/aps.54.117
Based on the energy transfer between ions and the transition between energy leve ls of diode_end_pumped Tm,Ho:YLF laser, under the consideration of energy transf er up_conversion, the threshold rate equations are given, and the analytical for mulas of laser threshold are deduced from rate_equations. The relations between laser threshold and laser designing parameters are derived. The dependence of en ergy transfer up_conversion on the laser designing parameters is analyzed in det ail. Experiments on Tm,Ho:YLF crystals are performed to validate the present mod el.
2005, 54 (1): 123-128. doi: 10.7498/aps.54.123
A simple method is provided for the performance comparison of the Raman-amplifie d optical-fiber transmission systems. The results show that, compared with conve ntional hybrid-Raman-amplification systems, the maximum transmission distance ca n be increased by about 10% and 30% separately, and the input signal power can b e decreased by about 6 dB for bidirectional-pumping all-Raman-amplification syst ems based on uniform or dispersion-managed transmission fibers.
2005, 54 (1): 129-133. doi: 10.7498/aps.54.129
Two independent femtosecond Ti:sapphire lasers are passively synchronized by an enhanced cross-phase-modulation technique. The synchronization operation is ma intained over 24 h with a timing jitter of 078 fs.
2005, 54 (1): 134-138. doi: 10.7498/aps.54.134
The new wave coupling theory of linear electrooptic effect is used to study the thermal property of an electrooptic modulator made from biaxial crystal KTP. We find one direction, along which the output intensity of the modulator is not sensitive to temperature within an angle range of azimuth φ. Furthermore, we achieve an optimal design of the modulator by adjusting the length of the crystal and the direction of the external electric field.
2005, 54 (1): 139-143. doi: 10.7498/aps.54.139
We have investigated, by using Z-scan technique with ns pulses at 532nm, the nonlinear absorptions of Au-nanoparticles-precipitated glasses obtained by irradiation of focused femtosecond pulses with the help of heat treatment. We observed the saturable absorption behavior in Au-nanoparticles-precipitated glasses.We obtain, by fitting to the experimental results, in the light of the local field effect near the surface plasmon resonance,Imχ(3)m=57×10-7 esu for the imaginary parts of the third-order susceptibilities for Au nanoparticles. The nonlinear response of Au nanoparticles in the glass samples arises mainly from the hot electron contribution.
Study on the influence on the characteristic of the second-order nonlinear optics by using aggregation of silver nanoparticles
2005, 54 (1): 144-148. doi: 10.7498/aps.54.144
The hyper-Rayleigh scattering(HRS) technique has been employed to determine the second-order nonlinear optical response of a highly monodisperse silver colloid and its aggregation which is induced in the presence of KNO3. Through the size distribution and TEM measurements, the silver nanoparticle aggregates have been observed as a chain-like aggregation. The experimental result reveals that HRS signal increases 15 times when the aggregation average size is up to 120nm.
2005, 54 (1): 149-154. doi: 10.7498/aps.54.149
We study the quantum interference in two-photon resonant nondegenerate four-wave mixing (NFWM) in a dressed cascade four-level system in which the two upper levels are coupled by a strong laser field. We find that in the presence of a strong coupling field, two-photon resonant NFWM spectrum exhibits Autler-Townes splitting, which reflects the levels of the dressed states. It also leads to either suppression or enhancement of the NFWM signal. This scheme involves the resonant three-photon excitation, therefore, provides a new spectroscopic tool for studying highly excited atomic states with high sensitivity.
2005, 54 (1): 155-158. doi: 10.7498/aps.54.155
It has been an increasing interest in the measurement and control of the carrier-envelope-phase offset (CEO) of femtosecond laser, which leads to an unprecedented progress in both fields of ultrafast laser techniques and frequency metrology. Based on the supercontinuum with a bandwidth of exceeding one octave, we measured and optimized the beat frequency signal by the self-reference technique. A frequency offset of 23 MHz was observed for the Ti:sapphire laser with a power of 500mW and pulse width of 18fs; it corresponds to the CEO of 053π. This work is a significant step toward coherent control of the femtosecond laser.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2005, 54 (1): 159-163. doi: 10.7498/aps.54.159
The noise caused by ion relaxation oscillation becomes a research focus in the field of microwave tubes recently because of the improvement of radars and communications requirements. In this paper, electron beam is described by beam envelope equation, and ions generated from ionization of the background gas in microwave tubes are treated as discrete macro-particles. One dimensional Particle-in-Cell(PIC) simulation code was developed, and time series of ion relaxation oscillation are obtained by using the presented method. The ion relaxation oscillation is treated as the response of a complex nonlinear dynamical system, and the time series is analyzed by the power spectrum; the phase diagram and Lyapunov exponent are restructured. From the analysis results we find that the ion relaxation oscillation has a chaotic character. The reason of chaos was attributed to the dissipative Structure of the system. This would be useful for depressing relaxation oscillation and processing signals with relaxation oscillation noise.
2005, 54 (1): 164-172. doi: 10.7498/aps.54.164
A theoretical method of getting rid of the dust grains in a plasma cylindrical reactor is designed. The motion of ions, elections and the dust grains under the control of a modulated magnetic field has been investigated by our fluid mechanics computational simulation subsequently. The dust grains have two kinds of motion: the pulse motion and the contrary cylinder center motion.Our method depends on the second condition.
2005, 54 (1): 173-179. doi: 10.7498/aps.54.173
In this paper, experimental results of plasma characteristics in several discharges have been measured in the plasma boundary region of the HL-1M tokamak using a multiarray of Mach/Langmuir 6 probes, electrostatic 4 probes and 20 group of 3 probes. In the experiments of Ohmic discharge, lower hybrid current drive, supersonic molecular beam injection, multi-shot pellet injection and neutral beam injection, etc., the correlation between the Reynolds stress and poloidal flow in the edge plasma is obtaimed. The experimental results suggest that the confinement improvement is related to the increasing rotation velocity and to the decreasing edge fluctuation. The results indicate that the sheared poloidal flow can be generated in tokamak plasma due to the radially varying Reynolds stress. The particle confinement with low-density discharge can increase 1—2 times in LHCD. The particle confinement time and poloidal rotation velocity can at least be doubled after MPI, and that the particle confinement time can increase one order of magnitude and can obtain high performance plasma during the experiment of SMBI.
A Fokker-Planck study is carried out for tokamak lower hybrid current drive (LHCD)by considering the wave absorption in the presence of trapping effect situation. This Fokker-Planck code is developed based on FASTFP, and is suitable for various auxiliary heating and current drive situations. The energy loss mechanism through anomalous transport is modeled by using a suitable loss term. In the h eating phase, the electron distribution deviates clearly from the Maxwellian, an d this results in nonlinear absorption characteristics. As an electrostatic forc e, the lower hybrid wave makes the trapped electrons untrapped, and the wave los ses its energy,which cuts down the LHCD efficiency 30%.
Experimental study on energy distribution of the hot electrons generated by femtosecond laser interacting with solid targets
2005, 54 (1): 186-191. doi: 10.7498/aps.54.186
This paper reports the results of the experiment of hot electron energy distribution during the femtosecond laser-solid target interaction. The hot electrons formed an anisotropic energy distribution. In the direction of the target normal, the energy spectrum of the hot electron was a Maxwellian-like distribution with an effective temperature of 206keV, which was due to the resonance absorption. In the direction of the specular reflection of laser, there appeared a local plateau of hot electron energy spectrum at the beginning and then it was decreased gradually, which maybe produced by several acceleration mechanisms. The effective temperature and the yield of hot electrons in the direction of the target normal is larger than those in the direction of the specular reflection of laser, which proves that the resonance absorption mechanism is more effective than others.
2005, 54 (1): 192-196. doi: 10.7498/aps.54.192
During the interaction of laser with solid targets, the counteracting force is generated by the plasma, which can be used as a new type source of propulsion. Compared with the chemical propulsion, laser plasma has unique advantages such as high specific impulse and large load ratio. In this paper, the momentum generated by the laser plasma is measured during the interaction of nanosecond laser pulses with aluminum, graphite, lead and CH targets. The relation of target momentum with laser focal area in atmosphere and vacuum ambient pressure is obtained,and the comparison is performed between the experimental and analytical results. It is shown that the target momentum in vacuum is different from that in atmosphere. In vacuum, the target momentum shows a dependence on the target property. These results are different from those generated by long width pulses.
2005, 54 (1): 197-201. doi: 10.7498/aps.54.197
We have successfully developed the two-dimensional quasi-static particle simulation code MLPIC2D, which is an effective numerical tool to be used to describe the long-time plasma behavior under the action of an ultra high intensity short pulse laser. Simple physical modeling, numerical realization and code framework are discussed in detail. Three nonlinear phenomena of laser-plasma interaction:1) production of laser wake-fields, 2)relativistic focusing for short laser pulses, 3)quasi-static magnetic fields, are correctly simulated and analysed.
2005, 54 (1): 202-205. doi: 10.7498/aps.54.202
The interferometry with an x-ray laser as probe is an important tool of diagnosing the electron density of a high temperature and dense plasma. A successful experiment of diagnosing the density of a CH plasma was demonstrated by using a Ni-like Ag x-ray laser as a probe and a Mach-Zehnder interferometer as instrument under the ShenguangII laser facility. The legible interferogram indicating the information of electron density was obtained.
2005, 54 (1): 206-210. doi: 10.7498/aps.54.206
The reason of the emergence of longitudinal modes in the single-mode slow-wave structure(SWS) is analyzed in terms of the transmission line theory, which proves that the occurrence of the longitudinal modes can be attributed to the unmatchi ng between the impedance of the SWS and that of its input and output ends. With the method of S-parameter, the features, such as frequency, field distributi on and the Q-factor of the longitudinal modes of TM01 mode in the over moded SWS are investigated, and the influence of the period-number of the SWS on the number, the frequency interval and the Q-factor of longitudinal modes a re analyzed. It is proposed that the introduction of a well designed resonant ca vity to O-type HPM devices can help to achieve the longitudinal mode selection a nd reduce the period-number of the SWS, which not only can make the devices more compact, but also can avoid the destructive competition between various longitu dinal modes, therefore can enhance the efficiency and stabilize the frequency.
2005, 54 (1): 211-216. doi: 10.7498/aps.54.211
Based on the collisionless, Maxewellian Thomson theory, a program is developed for carefully analyzing the influence of experimental set-up and plasma gradients and electron drifts on Thomson scattering spectrum. Calculations show that spectra resolution, collection angle, drift velocity and plasma gradient only have minor effects on diagnostics, so we can conveniently ignore these in fitting the spectrum. An important result is that signal-to-noise ratio can be enhanced by increasing the collection angle of the experimental system. The uncertainty of the scattering parameter can strongly affect the inferred plasma parameters when it is less than 3 This problem could be solved by choosing a smaller scattering angle or by accurately measuring the plasmas density.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2005, 54 (1): 217-220. doi: 10.7498/aps.54.217
SrTiO3 surface was monitored in-situ by reflection high-energy electron diffraction(RHEED) during annealing and homoepitaxial growth in laser molecular beam epitaxy(LMBE). By analyzing RHEED pattern, we show the oscillation behavior of in-plane lattice constant and full-width at half maximum (FWHM) of diffraction streaks; the former is due to the interface between the annealed reconstruction surface and the growing film, and the origin of the latter is related to the relaxation of 2D islands by their edges. In addition, the phase shift of RHEED intensity oscillation was observed, due to plasma influence on the incident electron beam.
2005, 54 (1): 221-227. doi: 10.7498/aps.54.221
Analysis of the structure of most irregular porous materials has recently been developed on the basis of the concepts of fractal geometry. The geometry enables general statements about so-called irregular structures to be made in terms of a few well-defined mathematical ideas, e.g. self-similarity and scaling, and a few mathematical parameters, e.g. fractal dimension. Gas adsorption is an ideal tool for characterization of the pore structure of xerogels and other porous materials. In this short paper, a simple and effective method to determine the fractal dimension of xerogels is presented. Instead of carrying out a series of gas adsorption/desorption experiments with various gases, only one gas adsorption/desorption experiment using a kind of gas is needed here. By studying the relations between the scaling and the data of pore size distribution and specific surface area, both surface fractal dimension and pore distribution fractal dimension can be easily derived. The reliability of the results is realized by performing error analysis and correction. The effectivity of the method is tested by experimental N2 adsorption/desorption data of silica xerogels prepared with sol-gel routine.
Resistivity of polyaniline nanotubes doped with naphthalene sulfonic acid: dependence on moisture and ethanol
2005, 54 (1): 228-232. doi: 10.7498/aps.54.228
The moisture and ethanol dependences of electrical properties of polyaniline (PANI) nanotubes doped with naphthalene sulfonic acid (NSA) are reported. The experiments were carried out in a temperature range from 80 to 300K. On the basis of analyzing the characteristics of the samples, we suggest that the resistance of the samples is dominated by the contact resistance between the PANI nanotubes, and the observed lnR(T)∝T-1/2 relation is explained in terms of the charge-energy-limited tunneling (CELT) model. The presence of water or ethanol molecules increases the conductivity, which is ascribed to the enhancement of charge carrier transfer and contact interface between the nanotubes upon exposure to water and ethanol. However, the extent of change during exposure to water and ethanol can be attributed to the differences in their chemical structures as well as their physicochemical properties.
2005, 54 (1): 233-236. doi: 10.7498/aps.54.233
The characteristics of quantum transmission through a four-terminal nano-molecular bridge are investigated theoretically by using tight-binding approach, based on the Green's function with only a π orbital per carbon atom at the site. The transmission probabilities of the electrons transported through the molecular bridge to every terminal are obtained. The electronic current distributions inside the molecular bridge are calculated and shown in graphical analogy by the current density method and Fisher-Lee formulism at the energy points E=±12 and E=±149 where transmission probabilities show peaks, the maximum bond currents are also presented. It is found that the loop currents in molecules are induced by the phase difference of the molecular orbitals.
2005, 54 (1): 237-241. doi: 10.7498/aps.54.237
Interface-energies of Ag(111)//Ni(001) and Ag(001)//Ni(111) twist boundaries have been calculated with the modified afom-embeded analysis method(MAEAM). The results show that, for Ag(111)//Ni(001) twist boundary, the lowest energy is corresponding to the twist angle θ=0° (or 30°), this preferable twist angle orientation is consistent with the experimental results reported in the literature. For Ag(001)//Ni(111) twist boundary, similarly, the lowest energy is corresponding to θ=0° (or 30°). From interface energy minimization, the preferable twist angle is 0° (or 30°) for Ag(001)//Ni(111) twist boundary too.
2005, 54 (1): 242-245. doi: 10.7498/aps.54.242
Silver nanoparticles with homogeneous size and density were deposited on the surface of a cellulose triacetate film through chemical dipping and photoreduction. UV-VIS absorption spectra and high resolution transmission electron microscopy (HRTEM) show that spherical silver nanoparticles with 2—5nm diameter were formed effectively at room temperature by properly modulating the concentration. By contact copying technique, holographic gratings were constructed with metallic nanoparticles embedded in the polymer film.
2005, 54 (1): 246-250. doi: 10.7498/aps.54.246
This article put forward a method to calculate the temperature coefficient for shear modulus(G′T) by means of theoreticial calculation and dynamic experiments. Firstly,introduce a calculation data G(PS), then combine with dynamic experimental data G(PH) to obtain G′T. Taking tungsten alloy as an example, the results show that G′T varies with pressure and temperature at the beginning, but at high pressure and high temperature, it is almost a constant of -004Gpa/℃ for tungsten alloy. This also verifies the assumption in Steinberg constitutive model that G′ T should be a constant. When we applied this constant to calculate the corrected shear modulus under shock compression, the calculated results are in accordance with the experimental data.
2005, 54 (1): 251-255. doi: 10.7498/aps.54.251
The effect of Al content on the Zener relaxation peak in annealed Fe-Al alloys has been investigated using a computer-controlled automatic inverted torsion pendulum through free-decay and forced vibration method. It has been shown that alloys with medium Al contents show strong relaxation while lower or higher Al content leads to relatively weak Zener relaxation peak. The relaxation in Fe-Al alloys originates from the next-nearest-neighbor atom-pairs and their interaction instead of the nearest-neighbor atom-pairs. The latter may not produce the Zener relaxation because of the ordered-structure formed, which suppresses Zener relaxation.
2005, 54 (1): 256-262. doi: 10.7498/aps.54.256
A new phase-field model is developed based on the Ginzberg-Landau theory, which is consistent with WBM model and KKS model. The dendritic growth process during the solidification in a Al-65%Cu binary alloy was simulated using the phase-field model. Solute diffusion equation was solved simultaneously. The effects of undercooling on the dendritic growth and solute profile in isothermal solidification of binary alloy were investigated. The results indicate that the dendritic has well-developed secondary arms with the increase of undercooling. Correspondently, the solute Peclet number and the tip speed increases, the tip radius decreases, and the solute segregation in solid-liquid interface increases. The results agree well with Ivantsov theory.
2005, 54 (1): 263-268. doi: 10.7498/aps.54.263
The characteristics of premartensitic transition on nearly stoichiometric Ni 505Mn245Ga25 single crystals have been investigated systematic ally by various methods, such as the ac magnetic susceptibility, resistance, mag netostriction, premartensitic transition strain and magnetization measurement. T he premartensitic transition strain in free samples was reported, and the enhanc ed premartensitic transition strain with an external magnetic field applied alon g the different directions was investigated. A large magnetostriction up to 505ppm in the  direction of the parent phase is obtained in a pulse magnetic field of about 80kA/m applied along the  direction at the premartensitic t ransition point, which is over five times larger than that in the parent phase. Based on the soft mode condensation and characteristic of the crystal growth, th e mechanism of the premartensitic transition strain was analyzed. The effect of magnetic field intervened premartensitic transition strain is attributed to the competition between the crystal lattice deformation induced by the enhancing mag netoelastic coupling and the intrinsic deformation originated from the soft-mode condensation. We found that the premartensitic transition further generated the anisotropy between two crystallographic directions of  and , which is proved by the magnetization measurement. Furthermore, the resulting strain prop erties, such as the largest magnetostriction, the saturated premartensitic trans ition strain and saturated field, have been discussed in detail.
Aluminum-induced crystallization during deposition of silicon films by inductively coupled plasma CVD
2005, 54 (1): 269-273. doi: 10.7498/aps.54.269
Silicon thin films were deposited on Al-coated glass substrates by inductively coupled plasma chemical vapor deposition(ICP-CVD) in SiH4/H2 mixtures at a low temperature of 350℃. The structure of the films was characterized by x-ray diffraction, x-ray photoelectron spectrum, atomic force microscopy and spectroscopic ellipsometry. It has been shown that the films are of a highly ordered structure with a strong (111) orientation. Grain size is larger than 300 nm. There is no residual Al in the films. Considering the high electron density in inductively coupled plasma, a preliminary interpretation is given for the mechanism of Al-induced crystallization during low-temperature deposition of Si films.
Impact of stress on the thermodynamic properties of ferroelectric films within the transverse Ising model
2005, 54 (1): 274-279. doi: 10.7498/aps.54.274
The thermodynamic properties of ferroelectric thin films are investigated within the framework of the transverse Ising model. A two-dimensional in-plane stress is introduced into the Hamiltonian of the system, and is supposed exponentially decreasing from the interface between the substrate and the film to the surface of the film. It is demonstrated that the compressive stress is benefitial to the polarization and shifts the Curie temperature to higher temperatures, but the tensile stress has the inverse influence on the Curie temperature and polarization. Besides, it is also shown that the diffusive length greatly affects the thermodynamic properties of the film.
2005, 54 (1): 280-283. doi: 10.7498/aps.54.280
The thermodynamic properties in one-dimensional S=1 Heisenberg antiferromagnet with single-ion anisotropy in the presence of a transverse magnetic field is obtained on the basis of the Schwinger boson mean-field theory. The anomalies of the specific heat at low temperatures, which might be an indicative of a field-induced transition from a Luttinger liquid phase to an ordered phase, are explicitly uncovered under the transverse field. A schematic phase diagram is proposed. The little effect of the single-ion anisotropy on specific heat is also observed, the result is very different from that obtained under a longitudinal field. All results above are expected to be helpful for the experimental investigation.
2005, 54 (1): 284-290. doi: 10.7498/aps.54.284
The behavior of tetradecane and octadecanol adsorbed on graphite in solid-gas interface is investigated at room temperature by STM. The studies reveal that tetradecane and octadecanol on graphite are self-assembled into a high degree of two-dimensional order, and the lamellar structure, which is similar to that of STM observation in solid-liquid interface, is obtained. But the high-resolution images give striking differences in molecular arrangement, lattice constant and orientation of molecules in one lamella, and we attribute these differences to the solvent effect suggested in previous neutron diffraction studies.
Fabrication and characterization of La2/3Ca1/3MnO3/Eu2CuO4/ La2/3Ca1/3MnO3 magnetic tunneling junctions
2005, 54 (1): 291-294. doi: 10.7498/aps.54.291
Magnetic tunneling junctions of La2/3Ca1/3MnO3/Eu2CuO4/ La2/3Ca1/3MnO3 have been fabricated by RF-magnetron sputtering, photolithography and ion beam etching. Tunneling effect was observed in these junctions by measuring their I-V curves. Interestingly, a discontinuity was observed in the I-V curves below the metal-insulator transition temperature (Tp) of La2/3Ca1/3MnO3 By changing temperatures, the discontinuity in I-V curves happens at the same voltage of 209mV, but starts at different currents. The discontinuity starting current (Ic) decreases with increasing temperature. There is a hysteresis near the discontinuity when the current increases and decreases. The discontinuity in I-V curves could indicate a novel switching process. This switching phenomenon occurs only in the ferromagnetic metal state and strongly suggesting a magnetic related effect. The physics of the switching process has not been understood yet, but it could be of interest for potential applications in spintronic devices.
2005, 54 (1): 295-301. doi: 10.7498/aps.54.295
A practical modeling for inhomogeneous coatings, which are prepared by double-source co-evaporation, is proposed in this paper, and then, the relationship between the deposition rate of inhomogeneous coatings and that of double-sources co-vaporation is discussed. The deposition rate of inhomogeneous coatings is close to the sum of the evaporation of the two materials when their bulks are close to or the amount of small molecules is far more than big ones. When the bulks of molecules of the two materials is different, the deposition rate of inhomogeneous coatings will vary with the ratio of their bulks and their deposition rates. Some deposition rates of inhomogeneous coatings in different situations are also detailed in this paper.
2005, 54 (1): 302-306. doi: 10.7498/aps.54.302
An optical microscopy study of ordered structures and self-organized phenomena in a continuous gold film system deposited on silicone oil surface is presented. Band-shaped ordered patterns, namely bands, are formed after deposition under certain condition. The bands are composed of a large number of parallel key-shaped domains with different width but nearly uniform length. Further experiments show that the ordered patterns result from compressive stress in films. We also study the formation mechanism of internal stress in nearly free sustained films.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2005, 54 (1): 307-312. doi: 10.7498/aps.54.307
We have investigated the ground-state phase diagram of the one-dimensional Hubbard model with alternating chemical potentials at half-filling by bosonization technique and the Gaussian wave functional method. We calculate variations of the charge density wave (CDW) and the spin density wave (SDW) gaps, ad well as their classical trajectory c,s with increasing on-site Coulomb repoulsion potential. For the fixed potential, it is found that the transition from the band insulator (BI) to the spontaneously dimerized insulator (SDI) is of the Ising type, at which charge gap vanishes, while the transition from SDI to the Mott insulator (MI) is of the KT type.
2005, 54 (1): 313-316. doi: 10.7498/aps.54.313
Electronic structures of Li(Co, Al)O2 and Mg-doped Li(Co, Al)O2 were studied theoretically via ab initio calculation based on density-functional theory. Studies of band structures and density of states show that hole states appear in the valence bands of the Mg-doped material as well as an increase in bandwidth, which are in charge of the increase in the observed electronic conductivity. It was found by analysis of Co3d density of states that the divalence Mg doping induces a higher cobalt valence state between Co3+ and Co4+ in Li(Co, Al, Mg)O2, which is in good agreement with experimental results. Using the band theory, we have calculated the average valence states of Co and O.
2005, 54 (1): 317-322. doi: 10.7498/aps.54.317
We have calculated the atomic and electronic structures of the non-polar surface of GaN(1010) by employing the full potential augmented plan wave and local orbital method (APW+lo). The calculated lattice constant and bulk modulus of zinc-blend GaN crystal are in excellent agreement with the experimental dat a. Using the slab and supercell model, we find that the surfae is characterized by a top-layer bond-lenth-contracting rotation relaxation. The surface Ga atom moves inward with 0014nm and form a planar sp2-like bonding with its three N neighbors. While the surface N atom moves outward with 0013nm and tends to a taper p3-like bonding with its three Ga neighbors. The surface layer rotation angle is 85°. From the calculated results of the desity of states of GaN (1010) surface we find that the surface relaxation induces the transformation from s emi-metallic to semi- conducting characteristic. Furthermore, it is also shown t hat the surface charges have a large transfer, and the surface bonds have a rehy bridization, which makes the ionicity reduce and the covalence increase, we beli eve that it causes the surface bond shortening and rotating.
Anatase TiO2 and red-shift introduced by doping with Fe:pseudopotential calculations and ultraviolet spectroscropy
2005, 54 (1): 323-327. doi: 10.7498/aps.54.323
The crystal structure and electronic band structure of undoped and Fe-doped anatase TiO2 have been investigated by using the plane-wave ultrasoft pseudopotential method in the generalized gradient approximation (GGA). The calculation shows that Fe-doping introduces a localized level and narrowing of band gap in TiO2. The t2g state of the dopant plays a significant role in red-shift of spectrum. The previous prediction is confirmed by our experiment.
2005, 54 (1): 328-332. doi: 10.7498/aps.54.328
In this paper, by using the linearized augmented plane wave based on the density functional theory of the first principles, the parameters of a unit cell were o ptimized for CoSi firstly. The steady state energy of a many-particle system was -134684297Ry. The corresponding volume and lattice parameter of the unit cell in the steady state were 5899360a.u.3 and 04438nm respectively. Secondly, the calculations of the electronic structures for CoSi and CoSi075A l025 were performed. At the same time, the characteristics of electronic structures of CoSi and CoSi075Al025 were analyzed. The shape of density of states of CoSi in this paper is almost the same as that of the exist ing calculations except for some differences. The Fermi level of CoSi075 Al025 shifted slightly, compared with that of CoSi. Finally, the int rinsic relations between the electronic structures of CoSi and CoSi075Al 025 and their respective thermoelectric properties were discussed in det ail. The increase of material factor B of CoSi075Al025 w as attributed to the doping with Al. Therefore, doping was a practicable means t o improve the thermoelectric property of CoSi.
2005, 54 (1): 333-337. doi: 10.7498/aps.54.333
Based on the tight-binding model, we develop a transfer-matrix method to study the electronic conductance of single-walled carbon nanotubes. It is found that there exists a narrow conductance gap in metallic zigzag nanotubes corresponding to the curvature-induced energy gap. In addition, the conductance near the Fermi level depends on both the diameter and the length of the carbon nanotube. Moreover, ballistic, diffused or classical transport may be found in carbon nanotubes with variation of energy.
Symmetrical invariant transformation of localization length in one-dimensional randomly-perturbed periodic structure
2005, 54 (1): 338-342. doi: 10.7498/aps.54.338
Based on the spectral symmetry of the one-dimensional periodic structure, a new invariant transformation, named symmetrical invariant transformation, of localization length is presented for the one-dimensional randomly-perturbed periodic structure. The validity of the transformation is confirmed by numerical stimulations performed by means of transfer-matrix method. Since the symmetrical invariant transformation explores an equivalent relation of localization length at different frequencies between different structures, it is expected to provide a new tool for further investigation of the light localization in disordered structures.
2005, 54 (1): 343-347. doi: 10.7498/aps.54.343
The wave transportation in nonlinear Kronig-Penney model is investigated by a two-dimensional real map.The maps for different nonlinear parameters under the condition of fixed wave vector are calculated, and the corresponding evolution of the square of wave displacement along the nonlinear superlattice is also numerically calculated. The nonlinear parameter of the nonlinear Kronig-Penny superlattice has a distinctive modulation effect on the Bloch wave vector of the wave function in the superlattice. In response to the increase of the nonlinear parameter, the map evolutes from a finite number of dots to a closed orbit or an attractor, which corresponds to a periodic function, quasiperiodic function or chaos.
Effects of the technology of implanting nitrogen into buried oxide layer on the characteristics of partially depleted SOI nMOSFET
2005, 54 (1): 348-353. doi: 10.7498/aps.54.348
The effects, caused by the process of the implantation of nitrogen in the buried oxide layer of SIMOX wafer, on the characteristics of partially depleted silicon_on_insulator nMOSFET have been studied. The experimental results show that the channel electron mobilities of the devices fabricated on the SIMON (separation by implanted oxygen and nitrogen) wafers are lower than those of the devices made on the SIMOX (separation by implanted oxygen) wafers. The devices corresponding to the lowest implantation dose have the lowest mobility within the range of the implantation dose given in this paper. The value of the channel electron mobility rises slightly and tends to a limit when the implantation dose becomes greater. This is explained in terms of the rough Si/SiO2 interface due to the process of implantation of nitrogen. The increasing negative shifts of the thre shold voltages for the devices fabricated on the SIMON wafers are also observed with the increase of implanting dose of nitrogen. However, for the devices fabri cated on the SIMON wafers with the lowest dose of implanted nitrogen in this pap er, their threshold voltages are slightly larger on the average than those prepa red on the SIMOX wafers. The shifts are considered to be due to the increment of the fixed oxide charge in SiO2 layer and the change of the density of the int erface-trapped charge with the value and distribution included. In particular, t he devices fabricated on the SIMON wafers show a weakened kink effect, compared to the ones made on the SIMOX wafers.
2005, 54 (1): 354-358. doi: 10.7498/aps.54.354
ACu3Ti4O12 (A=Ca, Y or La) ceramic materials have been successively fabricated by using the solid-state reaction method. In the temperature range of 50—300 K, the dielectric characteristics of the samples are measured and the relationship among the AC conductivity, external frequency and temperature is analyzed. It has been found that if the relative content of Ca in the CaCu 3Ti4O12 crystals with identical components is greater than or equal to 0 776, the dielectric constant of the samples can reach the value of 104 For the ceramic compounds with a 3+ covalence in the `A' site such as La2/3 Cu3Ti4O12 and Y2/3Cu3Ti4O12, however, the dielec tric constant is only of the order of 103 Further analysis shows that the di electric constant of the ACu3Ti4O12 materials is mainly related to the number density of the barrier capacity in the samples. The relationship amo ng the conductivity, frequency and temperature depends on the combination of act ion of electrons, phonons and external field.
Contributions of the surface resistance of high-temperature superconducting films to the insertion loss of the microwave filters
2005, 54 (1): 359-363. doi: 10.7498/aps.54.359
In this paper it is shown that the influence of the surface resistance of the high_temperature superconductors (HTS) on the insertion losses of the microwave filters with various poles and central frequencies was analyzed using simulat ion software for the electrical circuits. It is shown that HTS thick films or HT S thin films with relatively high surface resistance can be used to construct lo w insertion loss microwave filter with a few poles or with low central frequency . But high_quality epitaxial thin films must be used to construct low loss microwave filter with many poles (more than 8-poles) or with high central frequency (higher than 6GHz).
2005, 54 (1): 364-368. doi: 10.7498/aps.54.364
We have discussed the conditions under which a double_junction π ring magnetize spontaneously and provided the theoretical derivation. The condition is not onl y related with the parameter of induction, but also related to the ratio of the critical currents of the two junctions. Analyzing the free energy illustrates th at the spontaneous magnetization results in a stable state.
2005, 54 (1): 369-372. doi: 10.7498/aps.54.369
Co-doped TiO2 ferromagnetic semiconductor flms were prepared by rf co-sputteri ng method and then annealed in vacuum at 300℃ for 2 h. Superconducting quantum interference device (SQUID) measurements indicate that the samples are ferromagn etic and the Curie temperature is above 300K. The saturation magnetization, coer civity, and saturation field are 55emu/cm3, 400×80A/m and 1500×80A/m at room temperature, respectively. And the magnetic moment was observed to be 0679 μB/Co. No pure Co metal grains were found by x-ray diffraction and x-ray p hotoemission spectroscopy measurements.
Fine structure and hyperfine structure of Mn2+ in LiNbO3 are analyzed with electron spin resonance (ESR) at room temperature. It is concluded that the zero-field splitting of energy levels of electron spin angular moment between ±12〉 and ±32〉 is Δε1=-587×10-4cm-1, and that between ±32〉 and ±52〉 is Δε2=-2633×10-4cm-1. The anisotropic La nde factors are g∥=21810，and g⊥=20937 The fine structure co nstant is D=-536×10-4cm-1, and hyperfine structure constants ar e A∥=8836cm-1 and A⊥=8120×10-4cm-1. The interaction action of the fine structure is larger than that of the hyperfine structure. In addition, it is worth paying special attention to the fact that two forbidden transitions -32〉12〉 and -12〉52〉 are found.
2005, 54 (1): 379-383. doi: 10.7498/aps.54.379
The colossal magnetoresistance (CMR) effect and the low-field magnetoresistance (LFMR) of the electron-doped manganites La1-xTexMnO3 (x=0 04, 01) have been observed. The experimental results showed that LFMR of the samples varied with the increase of temperature from 5 to 300 K as follows: app earing-disappearing-appearing again. Furthermore, the samples exhibited large CM R in the temperature regime where the LFMR disappear. These related results have been analyzed.
2005, 54 (1): 384-388. doi: 10.7498/aps.54.384
Structure and morphology of single-crystalline hcp Co nanowires fabricated by electrodeposition were investigated in detail by various x_ray diffraction method s. The results confirm that the Co nanowires can be deposited in single crystall ine with the same crystal orientation of ［100］ along the longitudinal axes. The arrays were composed from those nanowires preferentially in ［100］ direction with very high parallelity, but the ［001］ axis of the nanowires randomly lies in the array plane. By slightly higher depositing voltage, some twisted deformat ion could happen in the nanowires with chiral behavior. A twisted model has been brought forward to explain the experimental results. Magnetization properties m easured by superconducting quantum interference device magnetometer at 300K indi cated that the twisted lattices in the wire significantly affected the anisotrop y of the nanowires due to the magnetoelastic effect, and consequently, the magne tic easy axis can be tuned to the longitudinal direction effectively.
2005, 54 (1): 389-392. doi: 10.7498/aps.54.389
Three different_structured Fe nanowires, including preferred orientations of , and morphology nanowires,were electrodeposited by a method of changing the pH value of the aqueous bath.And the _preferred Fe nanowire was reported for the first time so far as we know.Magnetic properties of the three kinds of nanowires were measured by superconducting quantum interference devics(SQ UID) magnetometer.Compared with the  preferred nanowire array,the  preferred one has a high aspect ratio with improved anisotropy and coercivity.It is first time that the magnetization of Fe nanowire arrays with the crystal anis otropy and shape anisotropy in the same direction has been reported.
Formation of L10-FePt nanoparticles with the precursor of [(Fe/Pt/Fe)/Ag]n multilayer at lowered annealing temperature
2005, 54 (1): 393-396. doi: 10.7498/aps.54.393
Microstructure and magnetic properties of [(Fe/Pt/Fe)/Ag]n multilayer films after ex situ annealing at various temperatures have been investigated. The results indicate that, the multilayer starts to transform to isolated L10-FePt nanoparticles embedded in Ag matrix after annealing at temperatures above 400℃ . The formation of the face_center tetragondal (fct) phase at relatively low tem peratures seems to relate with the rapid diffusion at the interface of "Fe/Pt/Fe " and the defects caused by Ag, and the high migration speed as well as the much smaller surface free energy of Ag leads to the separation of FePt nanoparticles , which is evidenced by the result of ΔM measurements.
The measurement of piezoelectric coefficient for PP cellular electret and the improvement of its piezoelectricity
2005, 54 (1): 397-401. doi: 10.7498/aps.54.397
In this paper, mechanical and dielectric parameters of virgin PP cellular film(t ype PQ50) were analyzed by dielectric resonance spectroscopy, and piezoelectric d33 coefficient of 18pC/N was measured. Up to 367pC/N of piezoelectric d33 coefficient for PP cellular electret was performed by means of pr essure-expansion techniques under the reasonable treatment conditions, which is about 20 times higher than that of famous ferroelectric polymer β-PVDF and whic h is higher than that of piezoelectric ceramic PZT. Based on scanning electron m icrograph and according to the piezoelectric theory model for PP cellular film t he structural and physical sources for high piezoelectric coefficient of these k inds of nonpolar porous film electret with space charge were discussed.
2005, 54 (1): 402-406. doi: 10.7498/aps.54.402
The piezoelectricity of commercially available PP cellular (EUH75 and SHD50) has been studied. Their piezoelectric d33 coefficients up to 219 pC/N and 196 pC/N were achieved after heat expansion, which are about two orders of magn itude larger than the corresponding coefficients of the samples without heat exp ansion and over one order of magnitude larger than that of the well_known ferroe lectric polymer PVDF. Definitely different influence of corona charging with high voltage up to 60kV in dielectric gas SF6 on the piezoelectric d33 coefficient for EUH75 and SHD50 samples was observed. The structural origin o f this phenomenon was discussed.
2005, 54 (1): 407-410. doi: 10.7498/aps.54.407
By using the single particle model, the diamagnetic Faraday rotation (FR)spectra of Pr3+ ion in Pr:YIG crystal is presented based on the quantum theory. The linear dependence of λF-1/2θ on λ2 is calculated at 300 and 77K in the 105—13 micron wavelength range. It is found that the diamagn etic FR is 64% of paramagnetic FR at 77K and the two types of FR can be of more or less equal importance. The diamagnetic FR depends on the temperature and the exchange field for the ions with orbit single ground states derived from the cr ystal field.
2005, 54 (1): 411-415. doi: 10.7498/aps.54.411
Two_dimensional macroporous photonic crystal with mid_infrared band gap was fabr icated by electrochemical etching method in this work. The sample structure is o f square lattice with structure parameters: lattice constant a=4μm and the length of the square lattice structure l=2μm. The reflection spectrum of th e sample was measured using the microscopic infrared spectrometer and showed the photonie crystal characteristics.
The microstructure and characteristics of luminescent porous silicon film prepared by the physicochemical sonic-vacating method
2005, 54 (1): 416-421. doi: 10.7498/aps.54.416
The special physicochemical environment caused by sonic_vacating provides an important outlet for the preparation of highly efficient luminescent porous silicon films.Experimental results show that sonic_chemical treatment is an effective t echnology for the improvement of the microstructure of porous silicon,and the luminescent efficiency and stability thereof.Luminescent porous silicon films,prep ared by ultrasonic-enhanced anode electrochemical etching,display better qualiti es than the samples prepared by conventionai methods widely used at present.This ultrasonic_chemical effect roots in sonic_vacating,i.e. the generation,formatio n and rapid collapse of bubbles in the etching solution.In the process of the po rous silicon being etched,the escape rate and caving_in of hydrogen bubbles in t he pores is increased as a result of the work of the ultrasonic waves,which is h elpful to the vertical etching of the pores.
2005, 54 (1): 422-428. doi: 10.7498/aps.54.422
We report on fluorescence and upconversion emissions of Er3+-doped TeO2-ZnO-PbCl2 tellurite-based oxyhalide glasses under 977nm laser diode excitation. A strong 153μm emission from 4I13/2→4I15/2 transition with a full width at half maximum of ～69 nm, and three intense infrared -to-visible upconversion emissions at 524, 546 and 668 nm, corresponding to 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F11/2→4I15/2 transitions of Er3+ ions, respectivel y, have been observed under 977 nm excitation and the mechanisms involved have b een explained. The intensity parameters Ωt (t=2,4,6) of Er3+-doped TeO2-ZnO-PbCl2 oxyhalide glasses have been calculated according to the Judd- Ofelt theory, and the results are Ω2=59×10-20cm2，Ω4=2 1×10-20cm2，and Ω6=12×10-20cm2，respectively. The e mission cross_section has also been calculated from the absorption cross-section and the emission spectrum by using the McCumber theory. The maximum emission cr oss_section is 875×10-21cm2 at 153μm. Our results indicate that Te O2_ZnO_PbCl2 oxyhalide glasses are promising candidates for optical amplifie rs and upconversion lasers in comparison with the glasses such as silicate, phos phate, and fluoride glasses.
2005, 54 (1): 429-433. doi: 10.7498/aps.54.429
The abnormal IR effects(AIREs) of the adsorption of CO on electrodes made of Pt nanostructured thin films generated in square wave potential treatment were obs erved. Based on the experimental results, the AIREs were analysed and simulated by taking into consideration of the interparticle interaction and the electron- hole damping. The results illustrate that the islanded nanostructured Pt surface s give rise to the interactions between CO molecules as well as between CO molec ules and nanostructured Pt surface. The energy transfer due to electron_hole dam ping and the enhancement of interparticle interaction are the important cause of the changes of IR absorption spectra.
Exciton transfer and the optical properties of two types of quantum islands (dots) in ultrathin CdSe/ZnSe layers
2005, 54 (1): 434-438. doi: 10.7498/aps.54.434
We have investigated the temperature_dependent photoluminescence of two types of quantum islands in ultrathin CdSe/ZnSe layers. At low temperatures, excitons in these two types of quantum islands can transfer by tunneling. The hopping process of the localized excitons gradually becomes the dominant mechanism with increasing temperature. We found that the small islands are nano_scale clusters with quasi_zero_dimensional properties, which are different from those of the large islands. Experiments indicated that these two types of islands are optically correlated although their excitonic properties are different.
2005, 54 (1): 439-444. doi: 10.7498/aps.54.439
A simple method was established based on the envelope curves of the optical transmission spectrum over the wavelength range of 200 to 2500 nm at normal inc idence, which was used for the accurate determination of the optical constants o f the anodic aluminum oxide(AAO) films. The results showed that the AAO films exhibited the optical features of a semiconductor with direct band gap of about 45 eV, and the optical constants of the AAO films depended strongly on the ano dic oxidation voltage, an important technologic parameter for preparation of AAO films. With the increase of the anodic oxidation voltage, the optical constants including the refractive index, thickness and optical band gap of AAO films inc reased, and the extinction coefficient decreased. Meanwhile, the fact that the c alculated values of the thickness of AAO films were in satisfactory agreement wi th the values of measurement illuminated that the results were well self_consist ent with the experiment.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
A study of Raman and optical emission spectroscopy on microcrystalline silicon films deposited by VHF-PECVD
2005, 54 (1): 445-449. doi: 10.7498/aps.54.445
Structural properties of microcrystalline silicon films deposited by very high f requency plasma_enhanced chemical vapor deposition(VHF_PECVD) and on-line monit or were studied using Raman and optical emission spectroscopy. The results obta ined showed that the discharge power has a modulation function on crystalline volume fraction (χc) of materials. A larger silane concentration means a stronger modulation function. The intensity of SiH* peak can characterize the deposition rate in a certain range, however the higher power indicates the lower deposition rate, and the ratio of intensity Hα* to SiH* peak value reflects the extent of crystallinity which is consistent with the result obtained from Raman measurement. In addition, the ratio of I［Hβ *］／ I［Hα*］ indicates the decrease of electronic temperatur e in hydrogen plasma with the increase of discharge power.
Al3O3N nanowires were successfully synthesized by dc arc_discharge in H2+Ar with a little amount of N2+O2 Composition, morphologies, microstructures were characterized using x_ray diffraction, scanning electron microscopy, Trans mission electron microscopy(TEM),and high resolution TEM. The synthesized Al3O 3N nanowires had the diameters ranging from 25 to 110 nm and the lengths up t o 55 μm. Al3O3N nanowires is of a spinel type structure. Besides, the growth mechanism of Al3O3N has also been studied.
2005, 54 (1): 454-459. doi: 10.7498/aps.54.454
Some computational results on directional solidification of a binary alloy obtained by using the phase field model are reported. Frozen temperature approximatio n is adopted to simplify the modeling. The onset of morphological instability, t he pattern evolution and the solute redistribution are shown. The cell to planar interface transition is modeled near the high velocity absolute stability condi tion. The cell spacings, tip temperatures and solute partitioning coefficients a t different velocities are calculated. The solute trapping is also observed.
The structure and electronic state of the ordered thin film of perylene and tetracene on Ag(110) surface
2005, 54 (1): 460-466. doi: 10.7498/aps.54.460
The growth of perylene and tetracene on Ag (110) has been studied by the ultraviolet photoemission spectroscopy (UPS) and low-energy electron diffraction (LEED). The LEED results illustrate that an ordered C(6×2) structure can be observed when the thickness of perylene is about one monolayer (thickness of 03n m), and an ordered C (4×2) structure for tetracene with a thickness of one monolayer. From the measurements of UPS, four emission features of perylene are located at 35, 48, 64 and 85eV below the Fermi level respectively, and f our characteristic peaks, for tetracene, are located at 34, 49, 59 and 9 4 eV below the Fermi level. The angle_resolved ultraviolet photoemission spectro scopy measurements show that both perylene and tetracene near the interface are parallel to the substrate, the tetracene molecule is along ［110］ direction.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2005, 54 (1): 467-470. doi: 10.7498/aps.54.467
In this paper, 1991 March 24 CME's structure is analyzed by determining the moment of sudden change in galactic cosmic ray intensites using wavelet method based on the sudden change in galactic cosmic ray intensities when a CME just arrives at the magnetosphere. The results show that the thickness of the CME_driven sho ck is about 02228AU,while the space scale from the front side of the CME to th e most intense magnetic structure is about 0325AU.
2005, 54 (1): 471-474. doi: 10.7498/aps.54.471
Selecting the advanced Eddington coordinates, and adopting the statistical method ,the instantaneous radiant exitance of non_static black hole is calculated. It is found that the instantaneous radiant emittance of non_static black hole is not only related to the radiant exitance by supposing it is in the state of thermal equilibrium, but also related to the rate of change and the temperature of its event horizon, and the absorption coefficient and the radiation coefficient of the black hole. In the situation of the spherically symmetric non_static black hole, the instantaneous radiant exitance of the black hole is always proportional to quartic power of temperature of the event horizon of black holes at anytime.
2005, 54 (1): 475-480. doi: 10.7498/aps.54.475
Considering the Klein_Gordon equation near the event horizon, Hawking temperature is calculated under a new Tortoise coordinate transformation. In the meantime , the cut-off parameter in thin membrane model is also simplified to the same as that in the static and stationary cases.
Problems in the paper “A link between chaos dynamics and the onset of turbulence in a transitional boundary layer”
2005, 54 (1): 481-482. doi: 10.7498/aps.54.481
Further investigation on the calculation of the fractal dimensions of the attractors reveals that some problems about the data processing existed in the paper “A link between chaos dynamics and the onset of turbulence in a transitional boundary layer”.Here,they are improved or revised.