Vol. 53, No. 11 (2004)

Investigation of open RF cavity by coupling theory
Li Zheng-Hong, Meng Fan-Bao, Chang An-Bi, Hu Ke-Song
2004, 53 (11): 3627-3631. doi: 10.7498/aps.53.3627
Abstract +
In the paper, an open cavity is divided into two parts: closed part and open part. The closed part means the closed cavity, and the open part is equi valent to the absorbing traveling boundary. According to Maxwell theory, there exists a coupling equation between the modes of the closed cavity and those of the open part.Utilizing the method, the X-band six-cavity transit time oscill ator is calculated; the calculated frequency and the Q value of the working mode are very close to the measured values.
p-n GaInP2/GaAs tandem solar cells*
Cui Rong-Qiang, Chen Ming-Bo, Wang Liang-Xing, Zhang Zhong-Wei, Lu Jian-Feng, Chi Wei-Ying
2004, 53 (11): 3632-3636. doi: 10.7498/aps.53.3632
Abstract +
This paper reports the study on p-n GaInP2/GaAs tandem cells. The cell samples were produced by metal-organic chemical vapor deposition at a low gas pressure. In order to optimize the device configuration, numerical modeling has been performed for the impacts of a fieldaided collection on the performances of the top cells. On the basis of modeling results, a modified configuration of top cells is introduced, using p+-p—n—n+ structure instead of p+n structure. This modification has brought about much improved photovoltaic performance of the top and tandem cells, with the conversion efficiency Eff=14.26% and 23.82% (AMO, 25℃, 2×2cm2), respectively.
Numerical simulation and analysis on the mechanical behaviors of the single-crystalline and poly-crystalline nano-Cu film
Xu Zhou, Wang Xiu-Xi, Liang Hai-Yi, Wu Heng-An
2004, 53 (11): 3637-3643. doi: 10.7498/aps.53.3637
Abstract +
Molecular dynamics simulation and analysis are performed on the mechanical properties of mono-and poly-crystalline nano-Cu film. Computational results indicate that the temperature effects are very significant on the tensile strength and the deformation mechanism of the mono-crystalline Cu-film. The strength of the sample is much higher at absolute zero temperature than at normal temperature. The plastic deformation at zero temperature is induced by the short-distantce sliding of the particles while it is caused by the long-distance propagation of dislocations at normal temperature. The strength of polycrystalline Cu-film increases with the decrease of grain size. In the process of strain accretion, grain boundary sliding dominates the plastic deformation. Dislocations originating from grain boundaries propagate toward grains. The area of the grain boundary enlarges and the grain size shrinks with the development of plastic deformation. However, the shapes of the basic grains have no remarkable change even at very large strain.
A new type of conserved quantities for Birkhoffian systems*
Ge Wei-Kuan, Zhang Yi, Fan Cun-Xin
2004, 53 (11): 3644-3647. doi: 10.7498/aps.53.3644
Abstract +
This paper gives a new type of conserved quantities for Birkhoffian systems. First, the equations of motion of the systems are established, and the definitions and criterions of Mei symmetries are given. Next, an existence theorem for the n ew type of conserved quantities of the systems is given, and the generalized Killing equations used to determine the infinitesimal generators are deduced. Finally, the inverse theorem of the conservation law is established.
The discussion on Lagrange equation containing third order derivatives
Ma Shan-Jun, Xu Xue-Xiang, Huang Pei-Tian, Hu Li-Yun
2004, 53 (11): 3648-3651. doi: 10.7498/aps.53.3648
Abstract +
In this paper, the third order Lagrange equation is obtained, by which can be obtained motion equation of a body. This equation contains third order rate of change of generalized coordinates and the rate of change of force. In addition, the third order Lagrange equation and the fraditional Lagrange equation are used to solve the same problem of the motion of a body, and their results are discussed. Finally, it is pointed out that the third order Lagrange equation provides a method of obtaining equation of motion which is different from that of the traditional Lagrange equation.
The variable separation approach and study on solving the variable-coefficient nonlinear Schr?dinger equation
Zhang Jie-Fang, Xu Chang-Zhi, He Bao-Gang
2004, 53 (11): 3652-3656. doi: 10.7498/aps.53.3652
Abstract +
In this paper, a variable separation approach is proposed and successfully extended to the (1+1)dimensional physics models. The new exact solution of two classes of variable-coefficient nonlinear Schrdinger equations are obtained. As a specific example, the envelope soliton solution for nonlinear Schr?dinger equations are a by-product, which is somewhat different in form, from the present result.
Gazeau-Klauder and Klauder-Perelomov coherert states for the anharmonic oscillator
Cheng Yan-Fu
2004, 53 (11): 3657-3662. doi: 10.7498/aps.53.3657
Abstract +
Using the Kinani-Daoud method we have constructed the Gazeau-Klauder(GK) and KlauderPerelomov(KP) coherent states for the anharmonic oscillator. It is shown that the two types of coherent states have totally different forms in their expressions. We have also discussed the resolution of unity of the two coherent states and the Hilbert space of each state. The study of Mandel Q pa rameter of the states shows that GK coherent state coincides with the sub-Poissonian and KP coherent state coincides with the super-Poissonian statistical distributions.
Exact quantum solution for the general time-dependent linear potential and related problems
Sun Yu-Jing, Liang Mai-Lin
2004, 53 (11): 3663-3667. doi: 10.7498/aps.53.3663
Abstract +
For the general time-dependent linear potential, the exact and complete solution of the Schr?dinger equation was obtained by assuming a form of wave function. Meanwhile, it was pointed out that the matrices φ(t)〉和ψ(t)〉 defined by the two wave functions 〈φ(t)xψ(t)〉和〈φ(t)pψ(t)〉 satisfy classical equations of motion. According to the ensemble theory of quantum mechanics, such classical equations describe the motion of fluid. A further research shows that similar conclusions apply to any linear system.
The uncertainty relations and squeezing effects for mixed states*
Liu Ping, Deng Wen-Ji, Xu Xiao
2004, 53 (11): 3668-3672. doi: 10.7498/aps.53.3668
Abstract +
Based upon the Heisenberger's uncertainty relations for mixed states, the minimu muncertainty and squeezing effects are studies. Although all minimum uncertainty states must be pure states, the nucertainty of one dynamical variable can be squeezed in some pure states or mixed states, even if they are not minimum uncert ainty states for the pair of dynamical variables. In addition, we present the ge neral uncertainty relation of statistics, which has the similar mathmatical stru cture of Heisenberg's indeterminacy principle, but has no relation with quantum interfernce.
Statistical entropy of Barriola-Vilenkin black hole
Li Gu-Qiang
2004, 53 (11): 3673-3675. doi: 10.7498/aps.53.3673
Abstract +
The partition functions of bosonic and fermionic field in Barriola-Vilenkin blac k hole are directly derived by using the method of quantum statistics. Then the entropy of the Barriola-Vilenkin black hole is calculated by using the improved brick-wall method in the frame of membrane model.
Application of resonant parametric perturbation to the chaos control in Boost converter and its optimization
Zhou Yu-Fei, Chen Jun-Ning, Ke Dao-Ming, Shi Long-Xing, Sun Wei-Feng, C.K.Tse
2004, 53 (11): 3676-3683. doi: 10.7498/aps.53.3676
Abstract +
The method of resonant parametric perturbation is a simple non-feedback chaos control means. It is such a suitable control method for controlling chaos in non-autonomous systems that we are inspired to study its applications for chaos control in current controlled Boost converter. Furthermore, the method of resonant parametric perturbation is optimized by selecting the best perturbation phase, so as to achieve the best chaos control results. These relative applications (with or without optimization) in Boost converter can be analyzed theoretically, and the influence induced by variable circuit parameters on the effective perturbation can also be calculated or predicted.
A nonuniform ratchet model with Gausstransition rates for Brownian motor
Guo Hong-Yong, Li Wei, Ji Qing, Zhan Yong, Zhao Tong-Jun
2004, 53 (11): 3684-3689. doi: 10.7498/aps.53.3684
Abstract +
A nonuniform ratchet model with Gauss-transition rates is proposed to discuss the directional motion of Brownian particles in an asymmetrical periodic potential. It is assumed that the particles experience several internal states in a single mechanical-chemical circle. In this model, the transition rates between diff erent states are position-dependent, which have the form of Gaussian function. For any internal states, the probability distribution as a function of time and position may be expanded near the transition points to any rank if necessary. Fin ally, the focus of our study is concentrated on a two-state model, in which we choose (M, K)=(2, 2) and calculate the average current as a function of the transition width, temperature and transition rate. It is revealed that the trans ition width influences the current greatly.
The driven-effect of external fluctuation on phase separation of binary mixtures
Feng Wen-Qiang, Zhu Yue-Jin
2004, 53 (11): 3690-3694. doi: 10.7498/aps.53.3690
Abstract +
Using the Monte Carlo method, we have investigated the effect of the external noise on the phase-separation dynamics in binary mixtures. It is found that the addition of the fluctuation has speeded up the pattern growth, and driven the system to form[1,1]oriented tilted strip formation. When the noise intensity is fixed and the noise acting probability is less thanp=0.015, the noise will erase the effect of the deep quench, and the system will avoid being frozen.With the increase of the noise acting probability, the structure factor will grow linearly. If the noise intensity is adequate, in an appropriate noise acting probability region, the system can form a high-oriented tilted strip pattern.
Average path length of Internet with power law degree distribution
Li Ying, Shan Xiu-Ming, Ren Yong
2004, 53 (11): 3695-3700. doi: 10.7498/aps.53.3695
Abstract +
The average path length of Internet with power law degree distribution is stud ied in this paper. The main work is to give a formula to compute the average pat h length . The essential of Internet or many other complex networks is to realize the least cost (the smallest total number of edges) and the best benefi t (the short average path length), which can be expressed as two optimization fa ctors to minimize the average degree and the average path length . By analyzing the main factor affecting , we find the main property of p ath length distribution P(l), and then give a formula of P(l) only inclu ding one parameter α. This work shows that P(l) and a direct relation with P(k),and α represent the effective link between nodes and the tota l number of networks on . This formula makes it possible that if we get the α of P(k)~k-α, we can calculate easily. The simulati on shows the formula is quite exact. Our method is successful. In the end, we di scuss that the parameter αis very important for Internet design.
Nonlinear dynamics and control of symmetric chaotic systems*
Xu Hai-Bo, Zhang Ming-Xuan, Yu Jin-Jiang
2004, 53 (11): 3701-3705. doi: 10.7498/aps.53.3701
Abstract +
Based on the continuous feedback control idea,a novel nonlinear dynamics of map and control method for a symmetric chaotic system is presented.Different from t he periodical orbit method,the basis to choose controlling parameters has been g iven.Only by appropriately adjusting feedback parameters,any periodical orbit can be reached.This method is applied to Logistic map,and good results have been o btained.
A method for controlling hyperchaos of Er-doped fiber laser——Nonlinear time-delay feedback modulating-parameter
Zhang Sheng-Hai, YangHua, Qian Xing-Zhong
2004, 53 (11): 3706-3709. doi: 10.7498/aps.53.3706
Abstract +
We present a method of nonlinear time-delay feedback modulating/parameter to control chaos/hyperchaos.A scheme of controlling the hyperchaotic dualring Er-doped fiber laser by using this method is proposed.Numerical simulation shows th at a hyperchaotic dual-ring Er-doped fiber laser can be successfully controlle d into different periodic states by this method only when the delay time and fee dback intensity are suitably matching.
Simulation and analysis of 6H-SiC pn junction ultraviolet photodetector
Zhou Yong-Hua, Zhang Yi-Men, Zhang Yu-Ming, Meng Xiang-Zhi
2004, 53 (11): 3710-3715. doi: 10.7498/aps.53.3710
Abstract +
The spectral responsibility of 6H-SiC pn junction ultraviolet photode tector has been simulated by 2D numerical model. The effect of different impurity concentration and different junction-depth on the responsibility is discussed in this paper. For p+n device, the responsibility can be as high as 167.2 mA/ W when the width of p+ layer is about 0.2μm, and the impurity concentrations are about 9×10.18cm-3and 1×10.6 cm-3 in p+layer and nlayer, re spectively. For n+p device, the responsibility is as high as 183.5 mA/W when the width of n+-layer is about 0.2μm, and the impurity concentrations are abo ut 9× 10.18cm-3 and 1×10.6cm-3in n+-layer and p-layer, respe ctively. It is shown that the result of simulation agrees with the experimental data very well.
Step scan time resolved spectroscopy and its application to photoconductivity of Si solar cells*
Zhu Jian-Min, Shen Wen-Zhong
2004, 53 (11): 3716-3723. doi: 10.7498/aps.53.3716
Abstract +
We report on the establishment of Fourier transform step-scan time-resolved photoconductivity spectroscopy to study the solar cell's minority carrier lifetime ,which has close relationship with its conversion efficiency.Three typical Si so lar cells are selected in our experiments,including both the monocrystalline and polycrystalline silicon samples.We find that the rise and decay curves of the t ransient photoconductivity can be well described by two simple exponential funct ions.Due to the participation of recombination centers,the recombination minorit y carrier lifetimes are generally smaller than those of generation.In order to p rove the reliability of our experimental results,we extract the bulk lifetime an d the effective diffusion length of the three samples.Furthermore,we analyze the correlation of the minority lifetime with the shortcircuit current,open volta ge and conversion efficiency,by the aid of the investigation of solar cells' dark I-V characteristics and load characteristics.In addition,we also discuss in detail other applications of the established stepscan time-resolved spect roscopy.
Nonparaxial vector Gaussian beams diffracted at a circular screen*
Liu Pu-Sheng, Lü Bai-Da
2004, 53 (11): 3724-3728. doi: 10.7498/aps.53.3724
Abstract +
By using the vector Rayleigh diffraction integrals, an analytical expression for the diffraction of nonparaxial vector Gaussian beams at a circular screen is de rived. The diffracted on-axis field and farfield expressions and free-space pro pagation equation of nonparaxial vector Gaussian beams, as well as the paraxial Fresnel and Fraunhofer diffraction formulae of Gaussian beams diffracted at a ci rcular aperture are treated in a unified way as special cases of our general res ult. Numerical comparative examples are given to illustrate the intensity distri butions and far-field behavior of nonparaxial vector Gaussian beams. It is show n that for the diffraction at the circular screen both the f-parameter and truncation parameter affect the beam nonparaxiality.
Phase probability distributions of Roy-type even and odd nonlinear coherent states
Feng Jian, Wang Ji-Suo, Sun Jin -Zuo, Liu Tang-Kun
2004, 53 (11): 3729-3732. doi: 10.7498/aps.53.3729
Abstract +
Based on our previous work, with the aid of the numerical method, the phase pro bability distributions of Roy-type even and odd nonlinear coherent states are in vestigated. It is shown that the distributions for the states are rather different, and unlike the case of ordinary even and odd coherent states the Pegg-Barnett distribution clearly reflects the different characters of quantum interference in the case of Roy-type even and odd nonlinear coherent states.
Entanglement swapping in the process of two-level atoms interacting with cavity fields of coherent states*
Lai Zhen-Jiang, Sun Zhong-Yu, Yang Zhi-Yong, Bai Jin-Tao
2004, 53 (11): 3733-3738. doi: 10.7498/aps.53.3733
Abstract +
From the viewpoint of quantum information theory, a multiatom and muticavity system was investigated. In the system the interaction between the atoms and the fi elds in the cavities is described by the intensity-dependent coupling Jaynes-Cummings model. It is found that the atomic maximal entangled state can be transformed into the maximal odd-even-like coherent entangled state, whereas the maximal odd-even-like coherent entangled state also can be transfor med into the atomic maximal entangled state.
Cavity field spectra of two different atoms interacting with a Two-mode field through Raman process
Zhang Gui-Ming, Li Yue-Ke, Gao Yun-Feng
2004, 53 (11): 3739-3743. doi: 10.7498/aps.53.3739
Abstract +
The cavity field spectra of two different atoms interacting with two-mode field s through Raman process are studied.The effects of relative coupling constant R=g2/g1 on the spectrum structure are discussed.It is found thatR pla ys a different role in the syectrum for vacuum,weak or strong initial field.Dege nerate spectrum structure appears usually forR=1 orR=0.A complicated a symmetric multipeak structure appears when R is between 0 and 1.When the f ield of upper frequency mode is vacuum,its spectrum is influenced sensitively by the field intensity of the other mode for fixed R.
Influence of the potential in n-type DBR on threshold in vertical-cavity surface-emitting lasers
Zhao Hong-Dong, Song Dian-You, Zhang Zhi-Feng, Sun Ji ng, Sun Mei, Wu Yi, Wen Xing-Rao
2004, 53 (11): 3744-3747. doi: 10.7498/aps.53.3744
Abstract +
In this paper, a simulation software with a direct coupling in quasi-three-di mensions for the gain-waveguide vertical-cavity surface-emitting lasers has b een realized. The electrical field, carrier density, optical-field and temperature distributions in the vertical-cavity surface-emitting lasers are given. The proper threshold characteristics are shown only when the potentia ls in the p-type and n-type DBR layers are studied together.
Influence of hydrogen additive and excitation circuits on the output performance of barium vapor laser
Pan Bai-Liang, Mao Bang-Ning, Chen Gang, Fang Ben-Min, Yao Zhi-Xin
2004, 53 (11): 3748-3751. doi: 10.7498/aps.53.3748
Abstract +
The output performances of barium vapor laser with and without hydrogen additive excited by pulsed discharge with Blumlein circuit were experimentally investiga ted. The result indicates that the laser output power increases two times with 1.5% hydrogen mixed into the neon buffer gas. Based on this experimental result,this paper further compares the working characteristics of barium vapor laser w ith interactive circuit and Blumlein circuit, and finds that the interactive cir cuit can greatly improve the laser output power and its efficiency. The maximum laser power of 3W and efficiency of 0.4% have been obtained at 1.5μm laser line. The dependence of laser power on working parameters is measured and discuss ed, and the mechanisms of hydrogen additive and interactive circuit for impr ovement of the laser performance are qualitatively analyzed.
Experimental studies of Ni-like Ta x-ray laser
Zhang G uo-Ping, Zhang Tan-Xin, Zheng Wu-Di, Huang Guan-Long, Lin Zun-Qi, Wang Chen, Wang Wei, Wu Jiang, Dong Jia-Qin, Sun Jin-Ren, Wang Rui-Rong, Fu Si-Zu, Gu Yuan, Wang Shi-Ji
2004, 53 (11): 3752-3755. doi: 10.7498/aps.53.3752
Abstract +
The experimental studies of Ni-like Ta x-ray laser at near “water window" on Shenguang Ⅱ laser facility were reported. By using a new scheme of united driving of fundamental- and double-frequency laser, the distinct spectrum signal of N i-like Ta x-ray laser at 4.48 nm was obtained under the total drive energy of 400J. The efficient gain-length product was about 5.5
Influence of external electric field on photorefractive two-wave coupling in SBN:Cr crystal and its applications
Zhao Jian-Lin, Li Zhen-Wei, Yang De-Xing, Ma Yang-Hua, Yang Dong-Sheng
2004, 53 (11): 3756-3760. doi: 10.7498/aps.53.3756
Abstract +
The properties and applications of the photorefractive two-wave coupling in con gruent SBN:Cr(Sr0.61Ba0.39Nb2O.6:Cr)crystal under external dc e lectric field are experimentally investigated in this paper.The variation of the intensity gain coefficient of the two-wave coupling with the external field is analyzed,and the measurement results are presented.It is found that the photore fractive two-wave coupling gain and response rapidity can be both increased,by applying appropriate external electric field to the crystal.Further study indica tes this electric response property of SBN:Cr crystal is useful to some applicat ions,such as improving the image edge-enhancement and the image edge-enhanceme nt joint-transform correlator based on the nonlinear energy transfer of photore fractive two-wave coupling in the crystal.
Nonlinear optical properties of mixed Cd0.35Hg0.65Ga2S4 crystal*
Y.Andreev, P.Geiko, G.Lanskii, V. Badikov, Ren De-Ming, Hu Xiao-Yong, Qu Yan-Chen, Huang Jin-Zhe
2004, 53 (11): 3761-3765. doi: 10.7498/aps.53.3761
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The linear and nonlinear optical properties,as well as phase-matching of mixed Cd0.35Hg0.65Ga2S4 nonlinear crystal are investigated. Da mage threshold is determined in comparison with the widely used middle IR crystal under identical experimental conditions. CO2 laser second harmonic generatio n (SHG) is realized in this crystal at a phase-matching angle in well coi ncidence with estimation.
Numerical study on damage phenomenon induced by transverse stimulated Brillouin scattering
Guo Shao-Feng, Lu Qi-Sheng, Zhou Ping, Zeng Xue-Wen, Deng Shao-Yong, Cheng Xiang-Ai
2004, 53 (11): 3766-3770. doi: 10.7498/aps.53.3766
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Based on the coupled wave equations of nonlinear optics, a two-dimensional p hysics model is established to describe transverse stimulated Brilluoin satteri ng (TSBS) in large-aperture optics of a high-power laser system. The temporal and spatial profile of the stress induced by TSBS is evaluated numerically, and the damage characteristics of optical components is presented, which agrees well with the experimental phenomenon observed at LLN laboratory. The energy loss induced by TSBS are calculated to be up to 20%, sho wing that TSBS may have strong influence on routine operation of high-power las er systems.
Induced focusing due to two optical beams counterpropagating in self-defocusing nonlinear media*
Jiang Xiu-Juan, Li Hua-Gang, Guo Qi, Hu Wei
2004, 53 (11): 3771-3776. doi: 10.7498/aps.53.3771
Abstract +
In this paper,a research work is done on two optical beams co-propagating in opp osite directions in two-dimensional self-defocusing nonlinear media.Numerical re sults show that the probe beam can be induced to focus due to cross-phase modula tion by the pump beam under certain conditions.We also discuss the effect on the focusing of the probe beam from the four parameters:the specimen length,the ini tial amplitudes of the pump beam and the probe beam,and the initial transversal distance between the centers of the two beams.We find that some of them have opt imum values,which result in the strongest focusing.
Interaction of photovotaic spatial solitons between dark and dark as well as dark and bright
Jiang De-Sheng, Ouyang Shi-Gen, She Wei-Long
2004, 53 (11): 3777-3785. doi: 10.7498/aps.53.3777
Abstract +
The parallel interaction between two photovoltaic spatial solitons of dark and dark as well as dark and bright with different wavelengths is investigated by numerical method. Our numerical study indicates that the dark solitons can both remain as quasi soliton form in certain distance while they propagate coaxially. H owever,they attract each other while closely overlapping. And they have a conver gent effect on each other at the slowly varying region of optical field while in larger separations. For the case of interaction between dark and bright, the br igh t one may experience compression, expansion or energy transfer depending on thei r mutual separation.The physical interpretation of this solitons interaction is also given in terms of the refractive index waveguide they jointly induce.
Comparative studies on annealed proton exchange waveguides inY-cut MgO:LiNbO.3 and Z-cut LiNbO.3
Xia Yu-Xing , Zhan Li, Wang Zhi-Guo, Cao Xia, He Sai-Ling
2004, 53 (11): 3786-3793. doi: 10.7498/aps.53.3786
Abstract +
Proton exchange waveguides in MgO:LiNbO.3 and LiNbO.3 crystals were fabricated , and the diffusion coefficients for the proton exchange process are obtained. The evolution characteristics of the waveguide index profile in the annealing process are studied. The structural deformation of the proton exchange waveguides in Mg O:LiNbO.3 and LiNbO.3 and the restoration effect of annealing are also studied tho roughly by the x-ray diffraction method and the OH-infrared absorption method. The optical and structural characteristics of annealed proton exchange waveguides in MgO:LiNbO.3 and LiNbO.3 are analysed and compared with eath other.
Wavelength demultiplexer using the spatial dispersion of repeated-period double-chirped structures*
Qin Xiao-Yun, Huang Bi-Qin, Chen Hai-Xing, Yang Li-Gong, Gu Pei-Fu
2004, 53 (11): 3794-3799. doi: 10.7498/aps.53.3794
Abstract +
Based on the rudimentary double-chirped stack, exploiting wavelength-dependent penetration depth, repeated-period double-chirped structures, in which each couple of Bragg layers is repeated for different times, are presented to increase the spatial linear shift and the beam shifting with different incident wavelength, thus allowing the design of compact thin-film spatial wavelength demultiplexer. We compare the improved structure repeated for n times with the directly double -chirped structure with the same layer number, finding that the former has not only more advantages in theoretical design but a higher tolerance in experiment al fabrication. Besides, we have given the qualitative analysis for the strongosc illation appearing in the spatial dispersion curves when the repeated times of improved double-chirped structure or the wavelength of incident beam are relatively large.
Growth and periodic repeating of travelingwave convection with through-flow
Li Guo-Dong, Huang Yong-Nian
2004, 53 (11): 3800-3805. doi: 10.7498/aps.53.3800
Abstract +
Growth dynamics and spatiotemporal evolutions of one-dimensional tra veling-wave pattern in a binary-fiuid-mixture Reylaigh-Benard convection with extremely weak through-flows are investigated by numerically simulating basic hydr odynamic equations. We show that the system exhibits repeated dynamics of trave lingwave convection, and their repeating periods depend sensitively on the strength of through-flow。
Study of the characteristic of D.C.arc plasma torch*
Yuan Xing-Qiu, Zhao Tai-Zhe, Wang Fei, Guo Wen-Kang, Xu Ping, Li Hui, Y u Guo-Yang
2004, 53 (11): 3806-3813. doi: 10.7498/aps.53.3806
Abstract +
The magnetohydrodynamic model,which describes the plasma flows inside the c plasma torch,is presented.By numerical simulations,the plasma flow characteris tics inside the plasma torch and the turbulence effects on the flows are studied in detail.Then the parameter studies are carried out.At last,comparisons betwee n the numerically predicated results and the experimental data are made in detail.
Diffusion theory of spin injection into organic polymers*
Ren Jun-Feng, Fu Ji-Yong, Liu De-Sheng, Xie Shi-Jie
2004, 53 (11): 3814-3817. doi: 10.7498/aps.53.3814
Abstract +
Based on the theory of electrical spin injection into semiconductors, by conside ring the car riers of spin polarons and spinless bipolarons in organic polymers, we suggested a model of spin injection into organic polymers. It was found that a high curre nt polarization can be obtained by adjusting the spin current polarization in the ferromagnetic layer or the conductivities of the ferromagnetic and organic layers. Effect of the proportion of polarons to carriers on the spin current polarization was discussed.
Low temperature fabrication of nanostructured Si-SiOx and Si-SiNx composite films and their photoluminescence features
Ji Ai-Ling, Ma Li-Bo, Liu Cheng, Wang Yong-Qian
2004, 53 (11): 3818-3822. doi: 10.7498/aps.53.3818
Abstract +
Silicon nanoparticles were fabricated in both silicon oxide and nitride matrices by using plasmaenhanced chemical vapor deposition, for which a low substrate t emperature belowo 50℃ has been found most favorable. High-density (up to 4.0 ×1012cm-2, from TEM micrograph) amorphous silicon nanoparticles with an averaged size down to 3 nm have been obtained. Strong roomtemperature photoluminescence was observed in the whole visible light range from the deposits that were postannealed at 500 ℃ for two minutes. Careful comparison shows that the Si-SiNx films provoke a significantly more effective photoluminescence than Si-SiOx films f abricated with similar processing parameters, especially in the green and blue light range. Theis low- temperature procedure for fabricationg light-emitting silicon structures opens up the possibility of manufacturing silicon-based tunable high-efficiency light-e mitting devices.
Wear resistance of Ti-implanted H13 steel using covering implantation technology
Zhang Tong-He, Yang Jian-Hua
2004, 53 (11): 3823-3828. doi: 10.7498/aps.53.3823
Abstract +
Ti and C ions extracted from a metal vapor vacuum arc ion source were implanted into H13 steel, with an implantation dose of 3×1017cm-2,an extractio n acceleration 48kV,and an average ion beam flux between 20 and 47μAcm-2. Rutherf ord backscattering (RBS) spectrum was used to measure the Ti concentration depth profile in H13 steel after Ti ion implantation. The surface microstructure observation was carried out using glancing xray diffraction analysis(GXRD). Wear test results showed that the wear rate of the implanted layer dropped by about 40% for Ti ,C dual implantation. In addition, the Ti implantation was found to significant ly reduce the friction coefficient of steel H13. The wear mechanisms of the impl anted layer were discussed by results of RBS and GXRD.
The two internal friction peaks in rapidly cooled Fe71Al29 alloy*
Wang Qiang, Zhou Zheng-Cun, Han Fu-Sheng
2004, 53 (11): 3829-3833. doi: 10.7498/aps.53.3829
Abstract +
Three internal friction peaks were found around 180℃ (termed as P1),340℃ (termed as P2) and 510℃(termed as P3) in rapidly cooled Fe71Al29 alloy,while only the P3 peak can be observed in slowly cooled sp ecimens.Only the P1 and P2 peaks were investigated using a computer- controlled inverted torsion pendulum in the present study.The P1 and P2 peaks in air-cooled specimens disappear during cooling or after long term ag eing at 350℃.They decline even disappear with increasing ageing time.Both the P1 and P2 peaks have relaxation features and their activation energy values are H1=1.03±0.08eVfor the P1 peak and H2=1.64±0.05eV for the P2 peak.It is suggested that P1 peak originates from the nearestneighbor jumps of Al atoms within tetrahedral lattices and P2 peak from the next-nearest-neighbor jumps of Al atoms within tetrahedral lattices in quenched alloys.
Phase separation in La2NiO4+δ studied by lowfrequency internal friction technique
Zhang Hua-Li, Liu Wei, Li Dong-Cai, Wu Xiu-Sheng, Chen Chu-Sheng
2004, 53 (11): 3834-3838. doi: 10.7498/aps.53.3834
Abstract +
There exists a low-frequency relaxation internal friction peak in La2NiO4+δwithδ=0.071, 0.110, 0.135 and 0.140, the peak position shifting to higher temperatu re, when more excess oxygen is incorporated. At δ=0.087 two peaks were obse rved which may be attributed to the jump of the interstitial oxygen atoms in the diff erent kind of the one-dimensional ordering phase formed by phase separation. At δ=0.038 two peaks were also observed which may be attributed to the jump of the i nterstitial oxygen atoms in the low-temperature tetragonal phase and the one-dimensional ordering phase formed by phase separation.
Glass transition kinetic property of novel bulk Zr-Al-Ni-Cu (Nb,Ti) amorphous alloy*
Chen Zhi-Hao, Liu Lan-Jun, Zhang Bo, Xi Yun, Wang Qiang, Zu Fang-Qiu
2004, 53 (11): 3839-3844. doi: 10.7498/aps.53.3839
Abstract +
The kinetic property during the glass transition process of Zr_Al_Ni_Cu (Nb,Ti) amorphous alloys was systematically investigated by differential scanning calorimetry method. The activation energy (ΔE) at the glass transition temperature was much smaller than tradition amorphous alloys and have different magnitude compared to ΔEvalue at Tx. These reveal that the bulk amorphous alloys show special structure characteristics and that is the reason of its big glass_forming ability. The Vogel_Fulcher_Tammann fits to the experimenta l data are given by the full curves and the fragility parameter mvalue was calculated to be about 30, reflecting its “strong" liquid property in deep_unde rcooled region. The B value of Lasocka function,atom activation energy and glass fragility parameter reveal a close relationship between kinetic behavior at glass transition and the glass_forming ability. So it could be used as an impor tant judgment for glass_forming ability.
Diffusion of Co in Zr_46.75Ti_8.25Cu_7.5Ni_10Be_27.5 bulk metallic glass in supercooled liquid region under high pressure
Wang Xiu-Ying, Wang Wen-Kui, Liu Ri-Ping, Sun Li-Ling, Yao Yu-Shu , Zhang Jun
2004, 53 (11): 3845-3848. doi: 10.7498/aps.53.3845
Abstract +
Diffusion of Co in Zr_46.75Ti_8.25Cu_7.5Ni_10Be_27.5 bulk metallic glass under high pressure is investigated in supercooled liquid regio n by ion implantation combined with secondary ion mass spectroscopy.Before impla ntation of Co atoms,the amorphous samples were annealed and relaxed in supercool ed liquid region.Diffusion coefficients of Co at 603K in the relaxed samples are found to increase with increasing pressure.And the activation volume for diffus ion is obtained to be -1.236Ω,where Ω is the mean atomic volume of the alloy.The result shows that diffusion of Co in this case is in an interstitial way.
Studies on the transport behavior of Ag/TCNQ thin films*
Xie Heng-Bo, Jiang Yi-Ming, Guo Feng, Liu Ping, Li Jin
2004, 53 (11): 3849-3852. doi: 10.7498/aps.53.3849
Abstract +
Ag/TCNQ bi-layer films with different thickness were prepared on glass substrates by alternating vacuum deposition of Ag and TCNQ. The transport behavior in the film was studied using transmission spectrum to monitor the process. An ab normal accelerated transport phenomenon was observed when the film was ultra thin and a tunneling model was proposed to explain this phenomenon.
Anomalous thermal conductivity in Nd_1.67Sr0.33NiO_4
Gao Hui-Ping, Li Bo, Yu Yong, Ruan Ke-Qing, Wu Bai-Mei
2004, 53 (11): 3853-3857. doi: 10.7498/aps.53.3853
Abstract +
The temperature dependence of thermal conductivity (K),resistivity (ρ) and low field ac susceptibility (χ) of perovskite nick elates Nd_2-xSr_xNiO_4(x =0.33,1.35) have been measured at temperatures from 77 to 300 K. The thermal conductivity an omalies associated with charge_order (CO) and spin_order (SO) are observed simultaneously in Nd_1.67Sr0.33NiO_4 for the firs t time so far as we know. The thermal conductivity is enhanced belowT_CO , but is suppressed near T_SO. There is also response to CO and S O in the χ-Τ curve. Only CO is observed in the ρ-Τ curve. In contrast, th ere are no anomalies in K-Τ, ρ-Τ andχ-Τ of Nd_1.67Sr0.33NiO_4. The anomalous phonon thermal conductivi ty in Nd_1.67Sr0.33NiO_4 indicates that there are strong charg e_phonon interaction and the spin_phonon interaction in this compound.
Theoretical study on the atomic structure, electronic states, and STM image of c(2×2) Cu(001)/O surface
Tao Xiang-Ming, Tan Ming-Qiu, Xu Xiao-Jun, Cai Jian-Qiu, Chen Wen-Bin, Zhao Xin-Xin
2004, 53 (11): 3858-3862. doi: 10.7498/aps.53.3858
Abstract +
Abstract In this article we have studied the surface structure, rel axation, and oxygen absorbed c(2×2) Cu(001) surface by using ab initio projector augmented wave and Car-Parinello method. It i s concluded that the bond length between oxygen and surface Cu atom is 0.194nm which yields a perpendicular distance of 0.069nm from O to Cu(S). The absor ption of oxygen produces a hybridized band and yields the well localized surface states a t 6.7 eV below E_F. The calculated work function for this absorbed sur face is 5.29 eV. We also calculate the scanning tunneling microscope images in the Tersoff-Hamann approach and make comparison with available experimental observ ations.
Thermal analysis and structure transformation of Mn12-Ac magnetic molecular crystals
Zhang Li-Juan, Ge Pei-Wen, Su Shao-Kui, Wang Yun-Ping, Liu Ying
2004, 53 (11): 4015-4020. doi: 10.7498/aps.53.4015
Abstract +
The thermal stability of Mn12-Ac[Mn12(CH3COO)16(H2O)4O12]52CH3COOH54H2O magnetic molecular crystals was investigated by TG-DTA from room temperature to 270℃. According to the results of XRD and TG,we found that Mn12-Ac lost the crystal water and the acetic acid molecules of solvation which were located between the adjacent molecules in the temperature range from 25℃ to 1 10℃. At the same time, 4H2O which were linked with 4 Mn3+ were lost. The crystalline structure of Mn12-Ac single crystal was destroyed during this course. However, the core structure in the molecule was well preserved. From 180℃ to 230℃, a further transformatio n took place, Mn12-Ac lost all the CH3COO- ions and turned intoγ-Mn2O3, with a little amount of Mn3O4.
Oxide overlayer effect on the measurement of the parameters of interband critical point: A fractional-dimensional space approach*
Tao Ke-Yu, Zhang Yue-Li, Mo Dang
2004, 53 (11): 3863-3867. doi: 10.7498/aps.53.3863
Abstract +
The fractional-dimensional space approach and analysis of spectroscopic ellipsometry are used to study an oxide overlayer effect on the measurement of the parameters of interband critical point (CP) of Si by a Si-SiO_2 model. There sults of the calculation show that the oxide overlayer effect can influence the calculated CP parameters derived from an optical spectrum by decreasing t he ampl itude and dimensionality, and increasing the lifetime broadening. Moreover, the effect is enhanced with increasing thickness of the overlayer. However, this eff ect on threshold energy is shown to be very small and can be ignored.
Ab initiocalculation of the voltage profile curve of Li insertions in InSb
Liu Hui-Ying, Yang Yong, Hou Zhu-Feng, Zhu Zi-Zhong, Huang Mei-Chun
2004, 53 (11): 3868-3872. doi: 10.7498/aps.53.3868
Abstract +
InSb is an important non-carbon-bearing anode material for lithium (ion) batteri es. An ab initiomethod with first-principles pseudopotentials based on the density functional theory has been used to calculate the total energies, formation energies and equi librium volumes of Li intercalations in InSb in 125 possible cases. Comp aring with the experimental voltage profile curve, we have picked out the possib le reaction routes of Li insertions in InSb and a theoretical voltage pr ofile curve is reached. Our results show that, from bulk InSb to bulk Li_3Sb, the re are no possible reaction routes undergoing five or more intermediate ph ases. The most favored route for undergoing only one intermediate phase is Li+In_4Sb_4→Li_1In_4Sb_4,11Li+Li_1In_4Sb_4→Li_12Sb_4+4In;whereas there exists only one reaction route for undergoing four intermediate phases, that is, Li+In_4Sb_4→Li_1In_4Sb_4,2Li+Li_1In_4Sb_4→ Li_3In_4Sb_4,4Li+Li_3In_4Sb_4→Li_7In_3Sb_4+In,3Li+Li_7In_3Sb_4→Li_10In_2Sb_4+In,2Li+Li_10In_2Sb_4→Li_12Sb_4+2In..
First-principles investigation of charge disproportionation in HoNiO_3 perovskite
Meng Xing, Xu Xiao-Guang, Liu Wei, Sun Yuan, Chen Gang
2004, 53 (11): 3873-3876. doi: 10.7498/aps.53.3873
Abstract +
We have investigated the electronic structure of HoNiO_3 perovskit e using first principles based on the density_functional theory. A comparison of elec tron_density map between orthorhombic and monoclinic structures indicated that there is only one type of Ni^3+state in the orthorhombic_metallic phase (space group Pbnm), and there are two types of Ni^(3-δ)+ and Ni^(3+δ) + states in the monoclinic_insulating phase ( space group P2_1/n). The characteristic parameter of charge di sproportionation δis concerned with the non_bonding t_2g band of partial density of states of Ni3d electron. δis calculated to be 0. 34±0.01, based on the changes of t_2gband from orthorhombic to monoclinic phase.
The variable metric algorithm for ground state energy of ionized-donor-bound excitons in semiconductors
Yan Hai-Qing, Tang Chen, Zhang Hao, Liu Ming, Zhang Gui-Min
2004, 53 (11): 3877-3881. doi: 10.7498/aps.53.3877
Abstract +
We present an optimization method, called the variable metric algorithm, to calc ulate the ground-state energies of excitons. The ground-state energ ies of two-dimensional ionized-donor-bound excitons(D^+,X)have been calcu lated variationally for all values of effective electron-to-hole mass ratioб. They are compared with those obtained by the variational method. The results show that the proposed method is simple in software programming, acc urate, and has more advantages than the traditional variational method for the g round-state energies. The method is especially fitted for complex systems.
Quantum lattice dynamical effects on the low-energy excitations in spin-Peierls systems
Wang Zhi-Guo, Chen Yu-Guang, Chen Hong, Shi Yun-Long, Xu Jing
2004, 53 (11): 3882-3887. doi: 10.7498/aps.53.3882
Abstract +
Using the bosonization technique and Gaussian wave functional method, we investi gate the low-energy excitations of a spin-Peierls chain where the spins interact with quantum phonons. The results show that the energy gap of the one- and two- particle excitation states decrease gradually when spin-phonon coupling constant decreases or the phonon frequency increases. A quantum phase transition from a gapless spin-fluid phase to a gapped dimerized phase occurs at a nonzero critica l value of the spin-phonon coupling. Our results indicate that the two-particle excitation spectrum is much more sensitive to spin-phonon coupling constant than the one-particle excitation spectrum.
Study of interface trap states of AlN-Si(111) heterostructure*
Zhang Rong, Zhou Chun-Hong, Zheng You-Dou, Deng Yong-Zhen, Kong Yue-Chan, Chen Peng, Xi Dong-Juan, Gu Shu-Lin, Shen Bo, Jiang Ruo-Lian, Han Ping, Shi Yi
2004, 53 (11): 3888-3894. doi: 10.7498/aps.53.3888
Abstract +
The charge trap states of AlN_Si(111) grown by metal_organic chemical, vapor dep osition are studied by the c apacitance spectroscopy of Al_AlN_Si MIS structure. The interface charge trap st ates of AlN_Si heterostructure and discrete trap center in AlN films are studied . The discrete trap center 2.55eV about E_v in AlN film is found. The dist ribution of interface states is continuous in the energy range of Si. The lowest state density N_ss is 8×10^11eV^-1cm^-2in the middle of the band gap. The corresponding time constantτ is 8×10^-4s and the cap ture cross section σnis 1.58×10^-14cm^2. T here are three kinds of trap states in the boundary layer of AlN film which caus es the frequency dispersion in the accumulation region of Al_AlN_Si MIS structure.
Microfabrication of magnetic tunnel junctions on 4-inch Si/SiO_2 substrate*
Wang Tian-Xing, Wei Hong-Xiang, Li Fei-Fei, Zhang Ai-Guo, Zeng Zh ong-Ming, Zhan Wen-Shan, Han Xiu-Feng
2004, 53 (11): 3895-3901. doi: 10.7498/aps.53.3895
Abstract +
Magnetic tunnel junctions (MTJs) with different sizes from 5μm×5μm to 15μm×60μm were fabricated on 4_inch Si/SiO_2 substrates. Their mag netoelectronic properties were investigated using the four_probe measuring system. The typical values of junction resistance_area product and tunneling mag netoresistance (TMR) ratio of the MTJs are 16 kΩμm^2and 18% respectively. The absolut eerrors of junction resistance_area product and TMR ratio are within 10% and 7% respectively for all the MTJs. All of the MTJs fabricated and measured show a good uniformity. Our experimental results show that such MTJs can be used to fabrica te the prototype demonstration devices for magnetoresistive random access memory .
Effects of proximity coupling and substitutions for Ba-sites on the transition temperature and ARPES of high-T_c superconductors
Luo Da-Feng, Yang Zhi-Hong, Shi Da-Ning
2004, 53 (11): 3902-3908. doi: 10.7498/aps.53.3902
Abstract +
Abstract Taking into account the proximity effects of the CuO chain on the hig h-T_c superconductivity, we introduce an S-N (superconducting-normal) model with d-wave Cooper pairing in the S layer. The hopping interaction between the S and N layers shows the suppression effect on the transition temperature T_c from the Green's function obtained in the Nambu space. Based on this model, we investigat e the negative effects of the substitution for Ba-site on the transition tempera ture T_c in the Y-Ba-Cu-O system. Experimental observations are qualita tively con sistent with our theoretical results. Finally, the hump/dip/peak structure in th e line shapes of the angle-resolved photoemission of the high-T_c supercond uctors has also been discussed in the framework of the S-N model.
Thickness and strain effects on electronic transport and Curie temperature in La_0.67Ca0.33MnO_3 films
Xiong Chang-Min, Sun Ji-Rong, Wang Deng-Jing, Shen Bao-Gen
2004, 53 (11): 3909-3915. doi: 10.7498/aps.53.3909
Abstract +
La_0.67Ca_0.33Mn_O.3 films with thickness between 25 and 400nm were fabricated on (001)SrTiO_3 and (001)LaAlO_3 substrates, using pulsed laser deposition. The magnetization and resistivity ρ of the fil ms were studied as functions of thickness. The reduction of t causes the decrease of the Curie temperature T_C in addition to the increase of ρ of the films. Com pared with the compressive strain in the La_0.67Ca_0.33Mn_O.3/La AlO_3 films, the tensile strain in the La_0.67Ca_0.33Mn_O.3/SrTiO_3 films causes a faster reduction of T_C with t, and a larger value of ρ_0. The low_temperature ρ is found to follow well ρ=ρ_0+Bω_s/sin h^2(ω_s/2/k_BT)+CT^n, with ρ_0 being the residual resistivity. The second term arises fro m the scattering by a soft optical phonon mode, and the third term denotes the other possible transp ort mechanisms. B, ω_s(the frequency of a soft optical mode) and C are fitting parameters. At temperatures higher than T_C, ρ of all the films show activated conduction with ρ=DT×exp(E_a/k_BT). Here, E_a is the activation energy. Based on the investigation of ρ_0, ω_s and E_a, the thickness and strain effect s in the films are discussed, separately. Further study shows that the variation of T_C is mai nly associated with E_a and ω_s, confirming the crucial role of the electron_phonon coupling in the strain effects on T_C.
Effectivity of Hamiltonian terms of "forbidden" 3-magnon interaction
Shi Qing-Fan, Li Liang-Sheng, Zhang Mei
2004, 53 (11): 3916-3919. doi: 10.7498/aps.53.3916
Abstract +
Analyzing the effectivity of "forbidden" 3-magnon processes locally excitated in magneto-ordered crystals, we successfully constructed the corresponding effe ctive 4-magnon interaction terms by the unitary transformations.
The antiferromagnetic coupling and interface diffusion in Fe/Si multilayers
Yan Shi- Shen, Mei Liang-Mo, Zhu Shi-Fu, Cai Jian-Wang, Zhao Jian-Gao, Ni Jing
2004, 53 (11): 3920-3923. doi: 10.7498/aps.53.3920
Abstract +
The antiferromagnetic coupling in Fe/Si multilayers was investigated with spa cers varying from pure Si to heavy-doped n-type and p-type Si. It was found that interlayer diffusion between Fe and Si occurred even though the multilayers sho wed well-defined layer structure, and the diffusion dominated the hea vy-doped Si, which made no difference at all for the antiferromagnetic coupl ing with different type of Si. Furthermore, the antiferromagnetic coupling in Fe/Si multi lay ers still goes on while the diffusion between Fe and Si layers enhanced and the layer structure was degraded to some extent after annealing.
Characteristics of the ZnxMg1-xO fil ms grown by electrophoresis method
Wang Zhuang-Bing, Xu Xiao-Liang, Chen Ying-Ying, Zhou Shi-Ming, Kong Ning, Guo Jia, Liu Hong-Tu, Shi Chao-Shu
2004, 53 (11): 3924-3928. doi: 10.7498/aps.53.3924
Abstract +
A series of ZnxMg1-xO films are prepared with electro phoresis deposition. The x-ray diffraction of the film is consistent with that of the multicrystal ZnO, it shows the structure of the ZnxMg1-xO film agree with the polycrystal of ZnO. The photoluminescence study of the ZnxMg1-xO film shows that there are two promine nt peaks in the ultraviolet region of the emission spectra, corresponding to the light emission of free and bound excitons, respectively. The intensity of the emi ssion spectra is invariable in the visible region, and no new peaks including the green band exist. This phenomenon indicates that the oxygen in the film keeps a fine stoichiometry with other elements, and restrains the emission of the green band based on the oxygen vacancies. On the other hand, the blue shift of the UV peaks in the photoluminescence spectra is found to be associated with increasing Mg content in ZnxMg1-xO films, and the intensity of peaks is also reinforced significantly with increasing annealing temperature.
Study on Raman spectra of Bi_4-xLa_xTi_3O_12-SrBi_4-yLayTi_4O_15 intergrowth ferroelectrics
Zhu Jun, Mao Xiang-Yu, Chen Xiao-Bing
2004, 53 (11): 3929-3933. doi: 10.7498/aps.53.3929
Abstract +
The Raman spectra of lanthanum-doped intergrowt h ferroelectric ceramics Bi_4-xLa_xTi_3O_12-SrBi_4-yLayTi_4O_15[BLT-SBLT(x+y),x+y= 0.00, 0.25,0.50,0.75,1.00,1.25,1.50]achieved at room temperature were inve stiga ted. The results show that La was substituted the Bi ions in the pseudo-perovski te blocks when La content is lower than 0.50 When La content is higher than 0.50, so me of La ions are incorporated into the (Bi_2O_2)^2+ blocks. The inco rporation of La ions into the (Bi_2O_2)^2+ layers would change th e structure of (Bi_2O_2)^2+ and destroy its functions as the insu lating layers and the space charge storage, which leads to the decrease of the remnant polarization. The relaxation characteristics observed in BLT-SBLT(1.50) are consistent with the softening of the mode lower than 30 cm^-1. This in dicates that La-doping may bring about the structural phase transition.
Luminescence properties and energy transfer in the mixed thin film of Alq3 and PVK
Sun Shi-Ju, Teng Feng, Xu Zheng, Zhang Yan-Fen, Hou Yan-Bing
2004, 53 (11): 3934-3939. doi: 10.7498/aps.53.3934
Abstract +
In this paper, the properties of fluorescence were studied of the thin films with different component ratios of polyvinyl carbazole(PVK)and Alq3. The energy transfer between PVK and Alq3 was studied through analysis of absorption spectra, excitated spectra, emission spectra of the thin films. When the content of Alq3 was high enough,the peak of Alq3 was quite evident in the abs orption spectra and excitated spectra, at the same time the emission spectra was the characteristic emission band of Alq3.When the content of PVK was high enough, the peak value of PVK is much greater than that of Alq3. At this time the extraordinary strong characteristic emission band of Alq3 and the feeble charac teristic emission band of PVK was observed. It is proved that the energy can transfer from PVK to Alq3 in a wide concentration range and it is most efficient at the concentration of 1∶7. A model Hamitonian based on single chain model including the dopant was put forward to simulate the experiment .This model can explain the experimental results very well.
Study on 3D thermoluminescence spectra in sapphire:Mn
Lin Li-Bin, Zhang Chun-Xiang, Tang Qiang, Luo Da-Ling
2004, 53 (11): 3940-3944. doi: 10.7498/aps.53.3940
Abstract +
The 3D thermoluminescence(TL) spectra were used to study the defect structure and luminescence mechanism produced by neutron irradiation in sapphire:Mn. The TL spectra of sapphire:Mn irradiated with 1000 Gy60Co γ-rays before n eutron irradiation show a broad wavelength band around 680nm at about 350℃ which may be related to the Mn2+ ions emission, and there is the 695 nm line spectrum which superposes to 680 nm broad band that is emitted from Cr3+ ions. Comparison between the spectra of undopedα-Al2O3 crystal and that of sapphire:Mn shows that the emission spectra of undopedα-Al2O3 at 416nm at about 207℃ related to the relaxation of an electron from the excited 3P state to the ground state 1S of the F center, is seriously suppressed. After neutron irradiation with fluence 1017cm-2, new glow peaks occur at about 150℃,at wavelengths 416 nm, 680 nm and 695 nm. The intensity of the glow peak at 150℃, 695 nm is greatly enhanced compared to that before neutron irradiation. The glow peaks at wavelength 520 nm at about 150℃, 190℃ and 250℃ emitted probably from Mn2+ ions are observed after 1018cm-2 fluence neutron irradiation. This indicates that neutron irradiation produces a quite amount shallow traps and F centers, and that 3D spectra are useful for studying the trap structures and luminescence mechanism.
Judd-Ofelt parameters determined experimentally for nanoparticles Gd2O3:Eu3+
Liu Chun-Xu, Zhang Jia-Hua, Lü Shao-Zhe, Liu Jun-Ye
2004, 53 (11): 3945-3949. doi: 10.7498/aps.53.3945
Abstract +
The spectral properties of nanoparticles Gd2O3:Eu3+ have been investigated by using Judd Ofelt theory at 77K. Intensity parameters Ωλ(λ=2,4) were calculated using the experimental data of 5D0→7F2 and 5D0→7F4 transitions by taking the magnetic dipole transition 5D0→7F1 as reference. The intensity of the transition is almost completely unaffected by the local environment. It is indicated that intensity parameter Ωλ changes with the variation of diameter of nanoparticles Gd2O3:Eu3+,dramatically different from that of the bulk material.With decreasing diameter of the nanoparticles Gd2O3:Eu3+ from 135 to 15nm,the quantum efficiency of the emitting level 5D0 reduces from 23.6% to 4.6%. The smaller the diameter of nanoparticles Gd2O3:Eu3+, the bigger the ratio of surface to volume and the more the surface defect.It is the enhancing of the non radiation channels that results in the decrease of the quantum efficiency. The other two non radiation channels, charge (Eu3+-O2-) transfer state and multiphonon nonradiative re excitaton, were also studied.
Control of grain size during low-temperature growth of polycrystalline silicon films
Huang Wen-Yong, Yao Ruo-He, Huang Rui, Lin Xuan-Ying, Yu Yun-Peng, Lin Kui-Xun, Wei Jun-Hong, Wang Zhao-Kui, Yu Chu-Ying
2004, 53 (11): 3950-3955. doi: 10.7498/aps.53.3950
Abstract +
Polycrystalline silicon thin films were prepared at high-speed by plasma-enhanced chemical vapor deposition technique at low temperatures using SiCl4 and H2 as source gases. It was found that the grain growth is strongly affected by the relative concentration of different active radicals in the gas-phase space. On the other hand, the relative concentration depends on the deposition conditions. With the decrease of the rf power and the H2/ SiCl4 flow ratio, and the increase in the reaction pressure, the grain size increases. By changing the deposition conditions, variations of the relative concentration were analyzed. It is suggested that the “gas-phase crystalline" is of crucial importance to the grain growth.
Distribution and spectrum properties of uranium in U:CaF2 crystal
Su Liang-Bi, Yang Wei-Qiao, Dong Yong-Jun, Xu Jun, Zhou Guo-Qing
2004, 53 (11): 3956-3960. doi: 10.7498/aps.53.3956
Abstract +
Transparent and integral U:CaF2 single crystals with diameter of 75mm were successfully grown by temperature gradient technique. The distribution coefficient of uranium in Ca F2 is equal to 0.53, which was calculated using the formula, K0=Cs/Cl.The calculated concentrations of uranium in CaF2 according to general distribution equation, Cs=K0C0(1-g)K0-1, are consistent with the measured values, indicating that the process of crystal growth was nearly in equilibrium. Unit cell paramenters and optical absorption spectra of U:CaF2 crystals grown under different conditions have been analyzed. Results indicate that the growth atmospheres determine the valences of uranium ions and the mechanism of charge compensation: the uranium ion is U4+ with green color in the absence of Pb F2; uranium is apt to form U3+with radius most close to that of Ca2+ in the presence of Pb F2 as a scavenger. From the beginning part to the end of U3+:Ca F2 crystal, only optical densities of all absorption bands gradually increase with the concentration of uranium. With increasing concentration of doped uranium, the color of the as grown U:Ca F2 crystals change from pink to brownish. The 5mm thickness periphery of the U3+:Ca F2 crystal with a yellow color was confirmed to contain mixed valences of U2+ and U3+, as a result of the reduction effect of graphite crucible.


Large scale synthesis of single-walled carbon nanotubes by an arc-discharge method at controlled temperatures
Zhao Ting-Kai, Liu Yong-Ning
2004, 53 (11): 3961-3965. doi: 10.7498/aps.53.3961
Abstract +
Large amounts of single-wall carbon nanotubes(SWNTs) deposited on all the wall of the chamber have been obtained in helium and nitrogen mixed atmosphere using Co-Ni alloy catalyst with a modified arc furnace which can control the temperature during arcing process. Additionally, there are many weblike deposition products located between the cathode and anode. By twostep purification:the as-grown SWNT was heated in air at 500℃ for 30min, then soaked in 37% hydrochloric acid for 72h and filtered with deionized water. Microanalysis was carried out by Transmission electron microscopy(TEM), high-resolution TEM and Raman spectroscopy. The results obtained indicate that the purified SWNTs have high purity (higher than 95%) and uniform diameter (from 1.24 to 1.38nm).This experiment indicates that the temperature strongly affects the production of SWNT; the production and purity of SWNT increase with temperature. When the temperature is 600℃, the purity is about 70% and the production of SWNT is 12g/h.
The investigation on the nucleation mechanism of Au-containing glass in an electric field
Wang Guo-Liang, Liang Kai-Ming, Liu Wei, Zhou Feng
2004, 53 (11): 3966-3970. doi: 10.7498/aps.53.3966
Abstract +
The investigation on the nucleation mechanism of Au-containing glass in an electric field By means of x-ray diffraction, scanning electron microscopy and absorption spec troscopy, we have studied Au-containing glass which is heat-treated under a n a pplied electric field. The experimental results are consistent with the conclusi ons obtained from a new thermodynamic model, which is proposed based on the static electromagnetic theory and thermodynamic theory in order to describe the nucl eation process of glass doped with metals. As a key factor in the model, the ele ctric energy change is calculated by two methods in this study. One is based on some approximation treatment, and the other the finite element method. The resul ts obtained by the two methods are similar and can explain the experimental results fairly well.
Time-dependent interface stability during directional solidification of a single phase alloy(Ⅰ) Theoritical
Lin Xin, Li Tao, Wang Lin-Lin, Su Yun-Peng, Huang Wei-Dong
2004, 53 (11): 3971-3977. doi: 10.7498/aps.53.3971
Abstract +
The initial transient solute redistribution during directional solidification is systematically investigated by carefully comparing the current theoreltical models with experimental results. It is shown that at the transient front solute redistribution generally meets an exponential profile no matter whether there exi sts liquid convection or pure diffusion in front of the liquid/solid interface.The profile can be described by a unified formula. Based on this, a general time-dependent linear dynamic analysis of the morphological instability of a solidifying planar interface during directional solidification is carried out. It is found that the timedependent instability solution has the same form as the steadystate solution described by Mullins and Sekerka, but the timedependent concentration gradient GtC, interface velocity Vi and diffusion length l should replace the corresponding steadystate concentration gradi ent GC,interface velocity V,diffusion length DL/V in Mulli ns and Sekerka solution.
A time-dependent interface stability during directional solidification of a single phase alloy(Ⅱ)Comparison with experimental results
Y. Inatomi, Huang Wei-Dong, Lin Xin, Li Tao, Wang Lin-Lin
2004, 53 (11): 3978-3983. doi: 10.7498/aps.53.3978
Abstract +
In situ observation on the interface instability and the solute transport boundary layer in front of the solid/liquid interface is carried out during the di rectional solidification of SCN-1.5at%Salol. Based on this, and in combination with the experimental results of SCN-1.1 wt%Eth, SCN-0.43wt%C152 alloys, the morp hological instability of a solidifying planar interface is systematically invest igated during directional solidification with and without the convection. It is found that the interface stability analysis in our previous paper describes corr ectly the time-dependent evolution of interface instability. Both the incubation time ti for instability and the incubation time tb for breakdown of the planar interface can be determined from the time-dependent instability so lution, and the convection obviously shortens the incubation time ti for i nstability and the incubation time tb for breakdown of the planar interface. The steady-state instability solution overestimates the unit amplitude devel oping rate by an order of magnitude, as compared to the experimental value, while the time-dependent solution underestimates the experimental result.
Self-assembly under gravity sedimentation of large size silica particles
Zhou Qian, Dong Peng, Cheng Bing-Ying
2004, 53 (11): 3984-3989. doi: 10.7498/aps.53.3984
Abstract +
Highly monodispersed colloidal silica particles in sizes ranging from 700 to 1300 nm were synthesized by a two-step method. The transmission electron microscope images showed that the mean standard deviation of these particles is less than 5%. Silica particle size range for self-assembly in the gravitational sedimentation was broadened through adjusting the viscosity of media in silica suspensions. The synthetic opals with particle diameters ranging from 700 to 1300 nm were obtained,and their optical characteristics were examined. Scanning electron microscope images showed that the synthetic opals have a face-centered-cubic structure and have partial photonic band-gaps. This provides the foundation for the study of complete photonic crystals with wavelengths within near-infrared and infrared regions and for the fabrication of other macroporous materials.
Simulation of pulse shortening phenomena in high power microwave tube using PIC method
Gong Yu-Bin, Zhang Zhang, Wei Yan-Yu, Wang Wen-Xiang, Meng Fan-Bao, Fan Zhi-Kai
2004, 53 (11): 3990-3995. doi: 10.7498/aps.53.3990
Abstract +
Pulse shortening is an universal phenomenon in highpower microwave tubes, which hinders the improvement of microwave output energy. So far, it is also an unres olved problem in the field of high-power microwave devices. In this paper, the relativistic backward wave tube (RBWO) is treated as an example to study the pul se shortening phenomena. The influences of explosive emission in the inner surface of RBWO and fluctuation of the relativistic electron beam on the pulse width and output power are investigated by means of the particle in cell(PIC) method .Through the simulation results, some useful conclusions have been drawn. The explosive emission in the surface of the slow wave structure due to intense elec tric field is one of the most important factors causing pulse shortening in high-power microwave tube. The fluctuation of the electron beam can also lead to pulse shortening. Some methods to overcome pulse shortening are given in this paper.
Effect of atmospheric turbulence on the propagation properties of spatially partially coherent polychromatic light
Lü Bai-Da, Xiao Xi, Ji Xiao-Ling
2004, 53 (11): 3996-4001. doi: 10.7498/aps.53.3996
Abstract +
Based on the propagation law of partially coherent light, the longdistance pro pagation of the spatially partially coherent polychromatic light through the atm osphere is studied. It is shown that the atmospheric turbulence gives rise to sp ectral shift and to beam spreading of spatially partially coherent polychromatic-light whether the scaling law is satisfied or not. The influence of turbulence on beam spreading of the spatially partially coherent polychromatic light is sma ller than that of spatially fully coherent polychromatic light. However, the inf luence of bandwidth on the intensity distribution is relatively small.
Improvement and extension of the thin film brick wall model without cut-off
Sun Xue-Feng, Liu Wen-Biao, Jing Ling
2004, 53 (11): 4002-4006. doi: 10.7498/aps.53.4002
Abstract +
Applying the generalized uncertainty relation to the thin film brick wall model, the method of calculating black hole entropy without cutoff was first proposed in 2002. However, it was then only determined that the upper bound of entropy is proportional to the event horizon. Since the method is studied more deeply, the entropy itself is found proportional to the horizon too. The relation between the ratio coefficient and the second-order uncertainty parameter is also discusse d. Moreover, the non-spherical Rindler horizon is studied, and the expected res ult is given. It is apparent that the cut-off in the brick wall model is something related to the quantum theory of gravity.
Discussion on the characteristics of the quantumradiation of unstationary and slowly-changing Reissner-Nordstr?m black hole
Yang Shu-Zheng
2004, 53 (11): 4007-4014. doi: 10.7498/aps.53.4007
Abstract +
Taking into account the case that the mass M and charge Q of Reissner-Nordstr?m black hole varying slowly with time t, the discussion on the quant um radiation characteristics of the black hole shows that the thermal radiation spectrum of charged Dirac particles is connected with the black hole's evaporati on rate together with the factors M(t), Q(t) etc. changing with time, and that the maximum energy of the quantum nonthermal radiation of nonstationary and slowly-changing Reissner-Nordstr?m black hole is equal to the chemical potential in the quantum thermal radiation spectrum.