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Vol. 52, No. 3 (2003)

2003-02-05
Topics
GENERAL
A new beam propagation method based on least-squares expansion approximating
Xia Jin-Song, Yu Jin-Zhong
2003, 52 (3): 515-521. doi: 10.7498/aps.52.515
Abstract +
A new finite difference wide-angle beam propagation method is developed by introducing the least-squares expansion approximant in the propagator expansion- In this new method it is not necessary to select the reference index point because of the whole region approaching the lease-square expansion- This method avoids the problems induced by error selection of the reference index in the old methods based on Taylor or Padè expansion- Several typical structures are simulated by the new method and the results prove the validity of it-
The quasi-wavelet solutions of MKdV equations
Tang Jia-Shi, Liu Zhu-Yong, Li Xue-Ping
2003, 52 (3): 522-525. doi: 10.7498/aps.52.522
Abstract +
The quasi-wavelet method is used for obtaining the numerical solution of the MKdV equation- The quasi-wavelet discrete scheme is adopted to make the spatial derivatives discrete, while the fourth-order Runge-Kutta method is adopted to make the temporal derivative discrete- One of the MKdV equation ut+6u2ux+uxxx=0, which has an analytical solution, is solved numerically- The numerical results are well consistent with the analytical solutions, even at t=10000s-
Chaos-based weak sinusoidal signal detection approach under colored noise background
Yang Bao-Jun, Li Yue, Shi Yao-Wu
2003, 52 (3): 526-530. doi: 10.7498/aps.52.526
Abstract +
In this paper we consider a new weak signal detection scheme which uses the sensitivity of chaos to the parameters under a certain status to realize weak signal detection- This scheme can effectively extract the weak sinusoidal signal from the strong colored noise background- We present a chaos-based signal detection approach, analyze the influence of noise to the system status in the chaos detection process- Simulation experiments show that the chaos detection system is very sensitive to weak signal and have strong constraint to any colored noise with zero mean value-
Control of chaos solely based on RBF neural network without an analytical model
Liu Ding, Ren Hai-Peng, Kong Zhi-Qiang
2003, 52 (3): 531-535. doi: 10.7498/aps.52.531
Abstract +
An intelligent control method based on RBF neural network is proposed for chaos control- The control objective can be either periodic orbits or continuous variable functions without the need of an analytic model- The method is still effective when there are parameter perturbation and measurement noise- The influence of the RBF model error upon control precision is studied, and related theorem is developed and testified- Simulation results with a Logistic mapping and Henon attractor show the effectiveness and feasibility of this method-
A method for synchronizing chaos and hyperchaos by single driving varlable
Zhang Ru-Yuan, Cheng Li, Peng Jian-Hua
2003, 52 (3): 536-541. doi: 10.7498/aps.52.536
Abstract +
In order to reduce the number of signals in the process of chaotic and hyperchaotic synchronization and to improve the synchronization efficiency, we propose a method of recombining system by a linear reversible transform- After the transform, the system which could not synchronize before, achieves the synchronization with a single signal, and the efficiency of synchronization has been improved distinctly-
ATOMIC AND MOLECULAR PHYSICS
Average-bond-energy method in Schottky barrier height calculation
Li Shu-Ping, Wang Ren-Zhi
2003, 52 (3): 542-546. doi: 10.7498/aps.52.542
Abstract +
Ten barrier heights of metal-semiconductor contacts are calculated by taking the average-bond-energy as the reference level- The coincidence degree of the calculational values and the experimental values is as good as that of Tersoff's charge-neutrality point method in theoretical calculation of metal-semiconductor contacts- The calculational results are much better than that of Harrison's tight-binding method and Cardona's dielectric midgap energy method-
Ultra-narrow electromagnetically induced transparency and inversionless gain in a ladder-four-level system
Li Yong-Fang, Sun Jian-Feng
2003, 52 (3): 547-555. doi: 10.7498/aps.52.547
Abstract +
In this paper, we study the effects of Rabi frequencies and multi-path radiation on the electromagnetically induced transparency (EIT) and the inversionless gain in a ladder- four-level system driven by two-coherent fields- The Rabi frequencies of the field-driven transition from the upper level to middle levels play an important role for the realization of the ultra-narrow EIT and inversionless gain- Different excitation mechanism can change the position of the EIT- The action of the spontaneous alignment of the dipole moment is investigated- The explanation for the numerical results is presented using the theory of dressed state
Spectral characterization of double-driven x-ray laser plasmas
Wang Rui-Rong, Wang Wei, Wang Chen, Dong Jia-Qin, Sun Jin-Ren, Wan Bing-Gen
2003, 52 (3): 556-560. doi: 10.7498/aps.52.556
Abstract +
A soft x-ray spectra of double-driven laser-produced Ta plasmas is measured by a time-integrated space-resolved keV crystal spectrometer from 045 to 075nm- Some resonant transition of the Ni-like, Co-like and Fe-like ions and some intrashell transition of the Ni-like ions are identified- The experimental results have been processed, the spectroscopic line intensity of the higher ionization stages is obtained- The effect of the double-laser driven time difference on the plasma condition is inferred through the spectroscopic line ratio diagnostics- The results obtained can, at least in part, give a good explanation of the upper lasing level population and the ionization properties of the plasmas-
Influence of relaxation and correlation effects on probabilities of the 2s22p3s 3P1—2s22p21D2 and 2s22p3s 1P1—2s22p23P0,1,2 intercombination transitions in NII
Xie Lu-You, Dong Chen-Zhong, Yuan Ping, Liu Xin-Sheng, Zhang Yi-Jun
2003, 52 (3): 561-565. doi: 10.7498/aps.52.561
Abstract +
The transition probabilities for the intercombination lines of 2s22p3s 3P1—2s22p21D2 and 2s22p3s 1P1—2s22p23P0,1,2 in NII have been calculated by using a large-scale multi-configuration Dirac-Fock method- In the calculation the most important effects of relativity, correlation, and relaxation are considered- The strong influence of correlation and relaxation effects on the transition probabilities have been confirmed by a compared calculation- When taking into account these effects in calculations, a remarkable improvement is found- From the results, the intensity of the 2s22p3s 3P1—2s22p21D2 line is supposed to be smaller than the previous theoretical prediction-
Measurement of hyperfine structure spectrum in 56908 nm line of 141Pr+
Ma Hong-Liang, Lu Jiang, Wang Chun-Tao
2003, 52 (3): 566-569. doi: 10.7498/aps.52.566
Abstract +
Hyperfine structure spectrum in 56908nm line of 141Pr+ was measured by the collinear fast-ion-beam laser spectroscopy- All the spectral lines were resolved- The magnetic dipole and electric quadruple coupling constants, and hyperfine splitting of the metastable levels and excited levels were determined- Our results were in agreement with the published data within experiment uncertainty- The accuracy of the magnetic dipole coupling constants was improved by one order of magnitude compared with the published data-
CONTENT
Numerical study of tie spatially induced group velocity dispersion
Hu Wei, Lu Guang-Shan, Yang Zhen-Jun, Guo Hong, Liu Cheng-Yi
2003, 52 (3): 570-574. doi: 10.7498/aps.52.570
Abstract +
We have studied, by numerical simulations, the spatially-induced group velocity dispersion in the propagation of ultrashort-pulsed Bessel beams in free space- The simulation results have confirmed the existence of the spatially-induced dispersions in the propagation of a truncated Bessel beam which can be constructed in practice- It is shown that the spatially-induced dispersion is observed when the diffraction length of truncated Bessel beams is longer than the dispersion length of spatially-induced group velocity dispersion-
Nonlinear optical properties of insulator inclusions/liquid host composite media
Hong Gang, Gao Lei
2003, 52 (3): 575-580. doi: 10.7498/aps.52.575
Abstract +
The effective optical properties have been investigated in granular insulator/liquid host composite media- In the weak nonlinearity limit, we calculate numerically the effective linear dielectric function (ε0e) and optical nonlinearity (χe) as functions of the volume fraction of insulator inclusions (f)-The results show that χe can be achieved at a resonant frequency ω≈32- In the general nonlinear case, we study how the intensity of incident light affects the effective dielectric function- Furthermore, the total effective refectances of s-and p-polarized light are investigated-
Optimization of chirped-pulse amplification systems using Martinez stretcher
Song Yan-Rong, Zhang Zhi-Gang, Wang Qing-Yue
2003, 52 (3): 581-586. doi: 10.7498/aps.52.581
Abstract +
This paper presents an analytical formula for calculating the phase of a Martinez stretcher in which a‘phase correction term' is added- From this phase expression, the group delay and higher-order dispersions are easily extracted- The calculated group delay evaluated the contribution of the Martinez stretcher to the system dispersion, and the formula is used to optimize the complete chirped-pulse amplification systems-
Numerical studies of characteristics and the design of 1PW optical parametric chirped pulse amplifier for the “Shenguang-Ⅱ” facility
Qian Lie-Jia, Zhu Peng-Fei, Xue Shao-Lin, Lin Zun-Qi
2003, 52 (3): 587-594. doi: 10.7498/aps.52.587
Abstract +
In this paper, the characteristics of optical parametric chirped pulse amplification(OPCPA) are numerically studied by a computer- The infection of the group velocity mismatch, the phase-velocity mismatch, and the cubic nonlinearity in the process of amplification has been discussed respectively- The comparison between the OPCPA and the chirped-pulse amplification(CPA) is made, such as of the mechanism of amplification, the synchronization, the red-shift phenomenon, the gain-narrowing effect, and so on- To realize the fast ignition of inertial confinement fusion, we have designed an OPCPA system for the “Shenguang-Ⅱ” facility, which can generate pulse with a duration as short as 50fs and a power of multi-petawatt-
The condition for forming a polychromatic light photovoltaic spatial soliton and its application
Wang Xiao-Sheng, She Wei-Long
2003, 52 (3): 595-599. doi: 10.7498/aps.52.595
Abstract +
We discuss the conditions under which some polychromatic light photovoltaic spatial solitons can be formed in a photorefractive crystal with a positive perturbation refractive index- Generally, under these conditions we can form bright-bright,dark-dark and bright-dark polychromatic light photovoltaic spatial solitons in the crystal- In the case of bright-bright solitons, if we launch a monochromatic beam(ray2,its effective Glass constant is less than that of the background), bright soliton cannot be obtained- But if we add another monochromatic beam(ray1, its effective Glass constant is larger than that of the background beam), both ray1 and ray2 can form bright solitons under some condition- This gives a new way to control ray2 with ray1- It is shown that the width of bright-bright solitons can be modified by the peak intensity of ray1-
Implementation of complete two-dimensional bandgap in photonic crystals of square Bravais lattice using complex unit cell
Qiu Gao-Xin, Lin Fang-Lei, Li Yong-Ping
2003, 52 (3): 600-603. doi: 10.7498/aps.52.600
Abstract +
In two-dimensional photonic crystals of square Bravais lattice, complex unit cell was considered to achieve a complete bandgap- By adding an optimal algorithm in our calculation, the structure parameters of photonic crystals with the largest complete two-dimensional bandgap were obtained-
Optical transmission enhancement of two-dimensional subwavelength hole arrays in metallic films
Shan Hong, Yi Yong-Xiang, Wang Guo-Ping, Long Yong-Bing
2003, 52 (3): 604-608. doi: 10.7498/aps.52.604
Abstract +
Numerical simulation has been performed on the optical transmission enhancement of a metallic film with a two-dimensional subwavelength hole array- The results show that the ideal conducting film of the same array structure also presents a transmission enhancement, but the enhancement is not higher than that of the real one- Further analysis reveals that a complicated waveguide coupling effect is responsible for the enhanced transmission- The excitation of surface current on metallic surface transfers the light energy of incidence from metallic surfaces to the holes and then adjusts the optical transmission- We believe that the resonant excitation of surface plasmon is not necessary for the enhancement effect-
Experimental and theoretical study on the compound dual-period fibre grating
Wang Mu-Guang, Wei Huai, Jian Shui-Sheng
2003, 52 (3): 609-614. doi: 10.7498/aps.52.609
Abstract +
In this paper we design a novel compound dual-period fibre grating structure, and analyze its spectrum response using the coupled mode theory- The simulation result is compared with the experiment,and it is shown that the model is correct- We also apply it in a temperature and strain sensor system-
Research on the 4×10Gb/s 400km dispersion compensation by chirped optical fibre grating
Pei Li, Jian Shui-Sheng, Yan Feng-Ping, Ning Ti-Gang, Jian Wei, Li Tang-Jun
2003, 52 (3): 615-619. doi: 10.7498/aps.52.615
Abstract +
In this paper, we introduce the successful dispersion compensation of 4×10Gb/s 400km G-652 fibre by chirped optical fibre Bragg grating- When BER is 10-10, the power penalty of transmission in each channel is less than 2dB, and the best result is negative-
Effects of vapour on the stability of single-bubble sonoluminescence
Liu Hai-Jun, An Yu
2003, 52 (3): 620-625. doi: 10.7498/aps.52.620
Abstract +
We have derived a dynamical equation of shape instability for a spherical bubble,where water vapor evaporation and condensation at a sonoluminescencing bubble wall are considered- Using the derived equation and the mass diffusive equilibrium condition for the bubble vibration, we investigate the bubble instability on those controlled conditions of water temperature and corresponding acoustic frequency (for 14% of argon concentration dissolved in water with the frequency of 206kHz at 217℃, for a 20kPa 1% argon in nitrogen bubble with the frequency of 319kHz at 0℃ and with the frequency of 338kHz at 20℃)- Comparing the calculated results with the published experimental data, we find that the determination of critical boundaries of the instability can be improved to some extent by considering the effect of vapor-
A new numerical method for simulating fluid flow through porous media
Xu You-Sheng
2003, 52 (3): 626-629. doi: 10.7498/aps.52.626
Abstract +
A new numerical method is developed for simulating fluid flow through the porous media based on the lattice Boltzmann method-No measure is adopted on the boundary,and no nonphysical by-product is produced at the same time-The numerical result also agrees well with the exact solution, therefore the model is considered to be reliable-
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Analysis of activated carbon from city solid waste by small angle x-ray scattering
Rong Li-Xia, Dong Bao-Zhong, Wang Jun, Xie Li-Ping, Lin Wei-Gang
2003, 52 (3): 630-634. doi: 10.7498/aps.52.630
Abstract +
The structure of activated carbon prepared from city solid wastes under different conditions was investigated by synchrotron radiation small angle x-ray scattering- Our results demonstrate that the structure of the activated carbon depends on the component of the carbonized residua, the carbonized conditions, etc-
Pore structures of methyl-modified silica xerogels by small angle x-ray scattering
Wang Jun, Dong Bao-Zhong, Xu Yao, Li Zhi-Hong, Fan Wen-Hao, Wu Dong, Sun Yu-Han
2003, 52 (3): 635-640. doi: 10.7498/aps.52.635
Abstract +
Two kinds of methyl-modified silica xerogels were prepared by mixing SiO2 colloidal suspension deriving from basic-catalyzed hydrolysis of TEOS (tetraethoxysilane) and siloxane polymer solution prepared from acid-catalyzed hydrolysis of MTES (methyltriethoxysilane) or DDS (dimethyldiethoxysilane). The xerogels were tested at the small angle x-ray scattering (SAXS) station of Beijing Synchrotron Radiation Facility. The distribution of pore size, the average size of pores DSAXS, and the thickness of interface layer E were calculated. With the aid of nitrogen adsorption measurement, the pore structure was analyzed. Some micropores were found to be produced in methyl-modified SiO2 xerogels while second-aggregates were constructed through connecting first-aggregates with siloxane polymer of MTES or of DDS. At the same time, methyl groups were attached to the bone of SiO2 clusters and become an interface layer between bone and pore. The interface layer have effects on both pore size and the adsorption of nitrogen in methyl-modified xerogels. Through transmission electron microscope we confirmed that the pore structures of the xerogels were affected strongly by the two different siloxane polymers. SAXS is a powerful technique to study pore structure of xerogel system.
Structural and magnetic properties of (Nd1-xErx)3Fe273Ti17 compounds
Yan Yu, Wang Xiang-Qun, Wang Xue-Feng, Jin Han-Min, Wang Wen-Quan
2003, 52 (3): 641-646. doi: 10.7498/aps.52.641
Abstract +
Structural and magnetic properties of (Nd1-xErx)3Fe273Ti17 compounds have been investigated by means of x-ray diffraction and magnetic measurements. All the compounds with x in the range of 00—05 crystallize in a Nd3(Fe,Ti)29-type structure. Substitution of Er for Nd leads to a contraction of unit-cell volume. Curie temperature TC of the (Nd1-xErx)3Fe273Ti17 compounds decreases monotonically with increasing Er content. Saturation magnetization Ms of the (Nd1-xErx)3Fe273Ti17 compounds decreases with increasing x. As temperature decreases from room temperature to 5K, a spin reorientation from easy plane to easy cone occurs for (Nd1-xErx)3Fe273Ti17 compounds. The anisotropy field Ba for(Nd1-xErx)3Fe273Ti17 compounds decreases with increasing Er content. Spin-phase diagrams have been constructed for (Nd1-xErx)3Fe273Ti17 compounds.
Structural and magnetic properties of Gd3 Co29-xCrx compounds
Yan Yu, Wang Xiang-Qun, Wang Xue-Feng, Su Feng, Jin Han-Min, Wang Wen-Quan
2003, 52 (3): 647-651. doi: 10.7498/aps.52.647
Abstract +
The novel Co-based Gd3Co29-xCrx compounds with a Nd3(Fe,Ti)29-type structure have been synthesized successfully for x=65 and 70 The crystal structure and magnetic properties of the Gd3Co29-xCrx compounds have been investigated by x-ray diffraction analysis and magnetic measurements. It has been found that Gd3(Co,Cr)29 with x=65 and 70 are ferrimagnetic with the Curie temperature of 412 K for x=65 and 359 K for x=70. Temperature dependence of magnetization shows a compensation point of the magnetization at a certain temperature below Curie point. The intersublattice molecular field coefficient, nRT, was derived to be 33 T f.u./μB for Gd3Co225Cr65 on the basis of the magnetization curve at the compensation temperature. It is noteworthy that the Gd3(Co,Cr)29 compounds exhibit a favourable easy-axis anisotropy in the whole temperature range below the Curie temperature.
Hard magnetic Pr55Al12Fe30Cu3 bulk metallic glass
Bai Hai-Yang, Zhao De-Qian, Pan Ming-Xiang, Wang Wei-Hua, Li Zheng, Wang Wan-Lu
2003, 52 (3): 652-655. doi: 10.7498/aps.52.652
Abstract +
In this paper we report the formation of a new Pr55Al12Fe30Cu3 bulk metallic glass. Cylindrical Pr55Al12Fe30Cu3 specimens of 5 mm in diameter and 100 mm in length were prepared by copper mold suction casting. Differential scanning calorimetry results indicated that the Pr-based bulk metallic glass system has a wide supercooled liquid region about 64K. The melting temperature of the amorphous state is about 140K higher than that of its crystalline state. Hysteresis loops were measured, and the results indicated that the Pr55Al12Fe30Cu3 bulk metallic has hard magnetic property, while the completely crystallized alloy has soft magnetic property at room temperature.
Bundle structure formation on polymer film by varying temperature AFM scanning
Shi Qin-Wei, Wang Xiao-Ping
2003, 52 (3): 656-663. doi: 10.7498/aps.52.656
Abstract +
The bump and bundle structures formed by atomic force microscopic tip scanning on 133nm thick PtBuA films were examined from room temperature to 58℃ with various scanning velocities of 1—20μm/s. It was observed that the bump structures were readily created at low temperature and high scanning velocity, while the bundles were created at high temperature and low scanning velocity. The period of bundles was about 100nm. The effects of temperature and scanning velocity could be explained by the equivalence of temperature and time of viscoelasticity of the polymer. The roughness increased with the scanning numbers at low temperatures while kept almost the same at high temperatures. All the above results indicated that the bump and bundle structure could be formed more frequently on the polymer surface at glassy state due to its larger modulus, smaller adhesion and weaker relaxation, as compared to its rubber state.
The structure and electronic properties of carbon nanotube heterojunction
Liu Hong, Chen Jiang-Wei
2003, 52 (3): 664-667. doi: 10.7498/aps.52.664
Abstract +
In this paper we study the structures of defects in carbon nanotube and the influences of defects on the electronic properties. The geometric constructions of carbon nanotube heterojunctions are investigated, and a simple way is found to connect two carbon nanotubes with different chirals.
A study of the band structure in two-dimensional phononic crystals based on plane-wave algorithm
Qi Gong-Jin, Yang Sheng-Liang, Bai Shu-Xin, Zhao Xun
2003, 52 (3): 668-671. doi: 10.7498/aps.52.668
Abstract +
In this paper, the calculating course of the plane-wave algorithm is introducedto solve the sound wave equation and the band structure of phononic crystals. The phononic crystals of two-dimensional binary liquid systems are studied. In conclusion, the CCl4/mercury system is easier to obtain the band-gap than the mercury/CCl4 system. With the increase of the filling fraction(f), the width of the band-gap becomes wider and then narrower. The widest band-gap of CCl4/mercury system appears at f=0229,where ΔΩmax=0549.While the width of the band-gap in mercury/CCl4 system increases consistently with the filling fraction, when f=0.554,ΔΩmax=0515.Under the same filling fraction, the variation of the cylinder diameter and lattice constant does not affect the band-gap width ΔΩ.
Investigation of the influence of directional internal stress on the arrangement of martensitic variants
Li Yang-Xian, Meng Fan-Bin, Liu He-Yan, Qu Jing-Ping, Wang Wen-Hong, Cui Yu-Ting, Liu Zhu-Hong, Chen Jing-Lan, Wu Guang-Heng
2003, 52 (3): 672-676. doi: 10.7498/aps.52.672
Abstract +
Microstructure and magnetic measurements were performed to reveal the distribution of the internal stress in single crystals of Ni2MnGa.It was suggested that due to the existence of the directional internal stress in the growth direction of single crystals results in the perfect arrangement of martensitic variants along the growth direction.Furthermore,the influence of such a perfect arrangement of variants on the formation of magnetic domain was studied in this paper.
Investigations of three-terminal electronic measurement on quantum dot devices
Zhu Yun, Wang Tai-Hong
2003, 52 (3): 677-682. doi: 10.7498/aps.52.677
Abstract +
Theree-terminal electronic measurements have been performed on quantum devices with a modulation-doped two-dimensional(2D) electron gas structure.The resistance with the 2D electron gas and that with the tunnel resistance through the dots can be obtained by analyzing the experimental data.Our results show that the lateral coupling between the quantum dots mainly determine the transport properties of the quantum dot devices under small biases.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Thermal conductivity of two-energy-gap superconductor MgB2
Yang Dong-Sheng, Wu Bai-Mei, Li Bo, Zheng Wei-Hua, Li Shi-Yan, Fan Rong, Chen Xian-Hui, Cao Lie-Zhao
2003, 52 (3): 683-686. doi: 10.7498/aps.52.683
Abstract +
We present in this paper the thermal conductivity of the superconductor MgB2 between 5—300 K. The temperature dependence of the thermal conductivity can be fitted with the BRT thermal conductivity method by a phenomenological two-gap model. The sizes of the two energy gaps are 16 and 51meV. The analysis about electronic thermal conductivity indicates that the σ-band impurity scattering rate is small relative to the π-band scattering rate. In contrast to the single-crystal sample, our result indicates that the scattering of phonons from the σ-band quasi-particles exist in the c-axial direction heat transport of a polycrystalline sample. This result demonstrates the anisotropic energy transport in MgB2.
Silicon nitride films prepared by helicon wave plasam-enhanced chemical vapour deposition
Yu Wei, Liu Li-Hui, Hou Hai-Hong, Ding Xue-Cheng, Han Li, Fu Guang-Sheng
2003, 52 (3): 687-691. doi: 10.7498/aps.52.687
Abstract +
Silicon nitride films(SiN) are deposited by helicon-wave plasma-enhanced chemical vapour deposition(HWP-CVD) under the condition that a gas mixture of SiH4 and N2 is required.The influence of experimental parameters on the properties of the sample films is investigated.The parameters such as bond structure,thickness and refractivity of SiN films are measured by using Fourier transform infrared(FTIR) spectroscopy,ultraviolet-visible spectroscopy and ellipsometer detection technique.Results show that SiN films with a low hydrogen content can be prepared by HWP-CVD at a higher rate and lower substrate temperature,and the main bond mode in the deposited SiN films is Si—N stretching mode.At lower reactive gas pressure,the deposition rate is promoted and the density of the sample films increases.The appropriate increase in N2/SiH4 ratio is beneficial to the decrease of the H content in SiN films.
Influences of an external pulse on the quantum state of a mesoscopic RLC circuit
Ji Ying-Hua
2003, 52 (3): 692-695. doi: 10.7498/aps.52.692
Abstract +
In this paper, the influences of an external pulse on the variation of the quantum state of a mesoscopic RLC circuit are investigated emphatically. Our research result indicates that the transition probabilities of the variation of the quantum state are adjusted by controlling the variation of the pulse parameters when the parameters of the mesoscopic circuit are constant. We point out that the quantum state of a system is stable when the width of the pulse is equal to the integral times of the minimum fixed value. The minimum fixed value is not related to the altitude of pulse but the circuit parameters. The larger the resistance, the wider the minimum fixed width of the external pulse.
Single-electron control by single-electron pump and its stability diagrams
Wu Fan, Wang Tai-Hong
2003, 52 (3): 696-702. doi: 10.7498/aps.52.696
Abstract +
Based on both Coulomb blockade and single-electron tunneling, the single-electron control by a single-electron pump is discussed.The stability diagram is obtained by considering its equivalent circuit in terms of the electrostatic energy.One of Its applications is discussed by analyzing its stability diagram.Our results show that random charges on the gate have less influence on the control of small curerent.
Effective anisotropy and coercivity in nanocomposite permanent materials
Li Wei, Guo Yong-Quan, Li Xiu-Mei, Gao Ru-Wei, Feng Wei-Cun, Wang Biao, Chen Wei, Han Guang-Bing, Zhang Peng, Liu Han-Qiang
2003, 52 (3): 703-707. doi: 10.7498/aps.52.703
Abstract +
The effects of exchange-coupling interactions between grains on the effective anisotropy and the variation in Nd2Fe14B/α-Fe nanocomposite permanent materials were investigated. The calculatied results showed that due to the exchange-coupling interactions, the effective anisotropy Keffof the nanocomposite decreases with the decrease of grain size and the increase of magnetically soft phase component. When the average grain size decreases to 4nm, Keff decreases to about 1/3—1/4 of the value of the ordinary anisotropy constant. This variation character is basically similar to that of the coercivity. The decrease of coercivity for the nanocomposite permanent materials is mainly due to the decrease of the effective anisotropy.
The study of domain-wall pinning by inhomogeneities in nanocrystalline permanent magnets
Rong Chuan-Bing, Zhang Hong-Wei, Zhang Jian, Zhang Shao-Ying, Shen Bao-Gen
2003, 52 (3): 708-712. doi: 10.7498/aps.52.708
Abstract +
The coercive force of the domain-wall pinning model can be expressed as Hc=αpink2K1/μ0Ms-NeffMs. The dependences of the microstructure parameter αpink on the exchange and anisotropy constants of inhomogeneities are discussed in this paper. The results show that there is a wide range of the αpink values. The effects of magnetic parameter and thickness of Nd2Fe14B grain boundary on the αpink are also studied. It was found that αpink reaches the maximum where A′/A=0.5,K′1/K1=0.1 and the grain-boundary thickness r0=3.32nm. αpink of nanocomposite Nd2Fe14B/α-Fe magnets reaches the maximum when the grain size r0 is 7nm.
Methods for preventing magnetic deviation saturation of high power amorphous transformer
Sun Mei-Sheng, Xu Xiao-Peng, Lu Wei, Fang Xing-Hao
2003, 52 (3): 713-717. doi: 10.7498/aps.52.713
Abstract +
This paper summarizes the basic characteristics of amorphous materials, and thoroughly analyses the reason why magnetic deviation saturation occurs in high-power amorphous transformers. And also, the incremental amplitude method, the incremental pulse width method, the current integral pulse width adjustment method and some other methods are proposed to prevent magnetic deviation saturation.
Simulation of magnetization behaviour in nanocrystalline Pr2Fe14B by micromagnetic finite element method
Zhang Hong-Wei, Rong Chuan-Bing, Zhang Jian, Zhang Shao-Ying, Shen Bao-Gen
2003, 52 (3): 718-721. doi: 10.7498/aps.52.718
Abstract +
Magnetization behaviour in the nanocrystalline Pr2Fe14B has been simulated by micromagnetic finite element method. The decrease of anisotropy in an interlayer leads to the drop of coercivity and enhancement of remanence, while the decline of intergrain exchange coupling increases the coercivity and decreases the remanence. The experimental coercivity and remanence may be simultaneously obtained by selecting proper parameters for the interlayer. Unfortunately, it is difficult to simulate the demagnetization curve of the ribbons before many efforts mustbe paid in future.
Mechanism of magnetization reversal in nanocrystalline Pr8Fe87B5
Zhang Hong-Wei, Rong Chuan-Bing, Zhang Jian, Zhang Shao-Ying, Shen Bao-Gen
2003, 52 (3): 722-725. doi: 10.7498/aps.52.722
Abstract +
Nanocomposite Pr2Fe14B/α-Fe was prepared by melt spinning. The magnetization reversal has been examined by the initial magnetization curve, recoil curve, minor hysteresis loops, applied field dependence of coercivity and remanence, and thermal activation. Inhomogeneous pinning controls mainly the coercivity in the melt-spun ribbons. Due to the intergrain exchange coupling between soft and hard phases, the magnetization reversal is different from that in traditional permanent magnets. Thermal activation is determined by the irreversible magnetization of the hard phase.
Dielectric,elastic and piezoelectric properties of La3Ga5SiO14 crystal
Wang Zeng-Mei, Yuan Duo-Rong, Li Zheng-Fa, Zhang Pei-Lin, Zhao Ming-Lei, Wang Chun-Lei, Zhong Wei-Lie
2003, 52 (3): 726-728. doi: 10.7498/aps.52.726
Abstract +
The dielectric,elastic and piezoelectric properties of the La3Ga5SiO14 crystal have been investigated. Its elastic and piezoelectric constants were measured by the resonant method through high-frequency vibration mode.
The luminescence of Er3+,Yb3+,Tm3+-codoped tellurite glass pumped at 970nm
Yang Jian-Hu, Liu Zhu-Ping, Wen Lei, Hu Li-Li, Dai Shi-Xun, Jiang Zhong-Hong
2003, 52 (3): 729-735. doi: 10.7498/aps.52.729
Abstract +
The fluorescence and up-conversion spectrum of Er3+/Yb3+, Tm3+/Yb3+, Er3+/Yb3+/Tm3+-codoped tellurite glasses pumped by a 970nm laser diode has been studied. The lifetimes of Er3+:4I11/2 and Er3+: 4I13/2 levels have been measured. It is found that the fluorescence width in the range of 1450—1700nm in Er3+/Yb3+/Tm3+-codoped tellurite glass has been broadened clearly. There is a fluorescence peak at 1630nm which is probably due to Tm3+:1G4→3F2 transitions in Er3+/Yb3+/Tm3+-codoped tellurite glass. Up-conversion phenomena exist in all the three kinds coped tellurite glasses because of its lower phonon energy of host. The addition of Tm3+ in Er3+/Yb3+-codoped tellurite glasses quenches the up-conversion efficiency of Er3+:4S3/2 green and Er3+:4F9/2 red emissions. The quenching effect is due to the energy transfer between Er3+ and Tm3+, especially the cross-relaxation process among them.
Influence of coupling between Er3+, nc-Si and nonradiative centers on photoluminescence from Er3+-doped nc-Si/SiO2 films
Wang Yong-Qian, Chen Chang-Yong, Chen Wei-De, Song Shu-Fang, Xu Zhen-Jia
2003, 52 (3): 736-739. doi: 10.7498/aps.52.736
Abstract +
Correlation between nc-Si, Er3+ and nonradiative defects in Er-doped nc-Si/SiO2 films is studied. Upon the 514.5 nm laser excitation, the samples exhibit a nanocrystal-related spectrum centered at around 750 nm and an Er3+ luminescence line at 154μm. With increasing Er3+ content in the films,the Er3+ emission becomes intense while the photoluminescence at 750 nm decreases. Hydrogen passivation of the samples is shown to result in increases of the two luminescence peaks. However, the effect of hydrogen treatment is different for the samples annealed at different temperatures. The experimental results show that the coupling between Er3+, nc-Si and nonradiative centers has a great influence on photoluminescence from nc-Si/SiO2 films.
A study on photoluminescence characterization of high-quality nanocrystalline ZnO thin films
Xiao Zhi-Yan, Zhang Wei-Li, Gao Hong, Wang Yu-Xi, Zhang Xi-Tian, Liu Yi-Chun, Zhang Ji-Ying, Xu Wu
2003, 52 (3): 740-744. doi: 10.7498/aps.52.740
Abstract +
In this paper, we report the photoluminescence from high-quality nanocrystalline ZnO thin films. The high-quality nanocrystalline ZnO thin films are prepared by thermal oxidation of ZnS films at 800℃, which are deposited by low-pressure metal-organic chemical vapor deposition technique. X-ray diffraction indicated that the nanocrystalline ZnO thin films have a polycrystalline hexagonal wurtzite structure. A strong ultraviolet emission peak at 3.26 eV was observed and the deep-level emission band was barely observable at room temperature. The strength (ΓLO) of the exciton-longitudinal-optical (LO)-phonon coupling is deduced from the temperature dependence of the full width at half maximum of the fundamental excitonic peak. ΓLO is reduced greatly due to the quantum confinement effect.
Investigation of influences of concentration of Mn and Cu dopants on the decay process of photogenerated charge carriers in the ZnS:Mn,Cu luminescence materials
Dong Guo-Yi, Li Xiao-Wei, Wei Zhi-Ren, Yang Shao-Peng, Han Li, Fu Guang-Sheng
2003, 52 (3): 745-750. doi: 10.7498/aps.52.745
Abstract +
The decay process of photogenerated charge carriers of ZnS:Mn,Cu luminescence materials after excitation with a short-pulse laser has been investingated in this paper by using the microwave absorption dielectric spectrum detection technique. It was found that the concentration of the Cu and Mn dopants has a great influence on the lifetime of electrons in the conduction band. The lifetime of electrons in the conduction band decreases obviously with increasing concentration of the Cu and Mn dopants. The effect of the concentration of Cu and Mn dopants on the luminescence intensity was also investigated.
Experimental investigation of photoluminescence spectrum of two erbium-doped glass samples in series
Song Chang-Lie, Rao Wen-Xiong, Li Shu-Feng, Li Cheng-Ren
2003, 52 (3): 751-755. doi: 10.7498/aps.52.751
Abstract +
Fabrication technology of erbium-doped glass samples is introduced. Photoluminescence(PL)characterization of one sample or two samples in series are measured.The results show that the PL intensity of two samples is higher than that of one sample,and the full width at half maximum of two samples is approximately equal to that of a high concentration Er-doped sample.In the formation of two samples in series,the PL intensity with the high-concentration sample facing the pump laser source is higher than that with the low-concentration sample facing the pump laser source .The ratio of PL intensity of two low-concentration samples to PL intensity of a single sample is bigger than the ratio of PL intensity of two high-concentration samples to PL intensity of a single sample.
The occupying activities of helium in ball-milled hydrogen-storage alloys
Yang Xun, Liu Shi, Zheng Hua, Zhao Yue, Xiong Liang-Yue, Wang Long-Bao
2003, 52 (3): 756-760. doi: 10.7498/aps.52.756
Abstract +
Through the measurements of positron lifetime and analysis of structure, the properties of helium in the ball-milled LaNi4.75Al0.25 and Zr50Co50 alloys were investigated. It was found that the amount of the injected helium increases with increasing helium pressure. It is comparatively easier for helium to enter the LaNi4.75Al0.25 alloy. The difference of the positron lifetime parameters between the above two specimens shows that the properties of the injected helium are different. For Zr50Co50, helium occupies the intersection of two or three crystallite interfaces and/or cluster of vacancies at grain boundaries or groups of vacancies firstly. With increasing pressure of the helium atmosphere, a small amount of helium enters the free volume of single vacancies, and thus vacancy-helium compounds form. For LaNi4.75Al0.25, helium enters the free volume of single vacancies and vacancy-helium compounds form.
A study on spatial light modulator of bacteriorhodopsin film
Yang Wen-Zheng, Yang Qing, Feng Xiao-Qiang, Chen Feng, Hou Xun
2003, 52 (3): 761-766. doi: 10.7498/aps.52.761
Abstract +
An optically addressed spatial light modulator (OA-SLM) is presented by using the excellent nonlinear-optical characteristics of bacteriorhodopsin films (BR films). The BR films have two dominant photoactive states (B state and M state) which have well-separated absorption bands with maxima of B state at 570nm and M state at 412nm. Using the ratio of the shift between the forward (B→M)and backward(M→B)photoreactions, the experimental study on the conversion of coherent-to-incoherent image is realized on BR films. Using the genetic manipulation of the BRD96N film as a sample, the 670nm coherent light as a writing light and the 530nm incoherent light as a readout light, the experimental results for the resolution of ~200 lines/mm and the contrast of about 2.1∶1are achieved.