Vol. 56, No. 3 (2007)

Designing the microstructure of the coated radar absorbent
Shi Yun-Long, Huang Chang-Geng, Lian Chang-Chun, Zhang Shuan-Qin
2007, 56 (3): 1231-1237. doi: 10.7498/aps.56.1231
Abstract +
The model for the effective electromagnetic coefficients is established. The influence of the volume ratio of the outer layer and the inner on the absorption and the characteristic impedance is discussed. The microstructure of the coated absorbent is designed. Sol-gel method is used to prepare the coated radar absorbent. It is shown by the theoretical and experimental results that the absorbing ability of the coated magnetic absorbent has be improved greatly, and the absorbing band below -8 dB is about 9 GHz.
Equilibrium distribution boundary condition in lattice Boltzmann model and numerical simulation of Darcy-Forcheimer drag for fluid flow across a square cylinder array
Dong Ping, Feng Shi-De, Zhong Lin-Hao, Gao Shou-Ting
2007, 56 (3): 1238-1244. doi: 10.7498/aps.56.1238
Abstract +
This article presents a boundary condition for the equilibrium distribution suitable for a variety of non-slip flow Llattice Boltzmann simulations. The boundary condition is based on the Bounce-back method and satisfies mass and momentum conservation principles.The computational results show that the new boundary condition for the equilibrium distribution overcame the erroneous slip velocities resulted from the conventional bounce-back method. The porous flow field around prism-shaped particles which is governed by Darcy-Forcheimer formula is calculated and compared with Lee and Yang's (1997) the predictions are found to be sufficiently reliable.
Influence of noise on self-trapping of Bose-Einstein condensates in double-well trap
Liu Ze-Zhuan, Yang Zhi-An
2007, 56 (3): 1245-1252. doi: 10.7498/aps.56.1245
Abstract +
In this paper we study self-trapping of Bose-Einstein condensates in a symmetric double-well potential with uniform noise or Gaussian noise existing respectively. We find that both uniform noise and Gaussian noise destroy the critical behavior of self-trapping with the interaction increasing and create a transition zone between Josephson oscillation and self-trapping, between which exists a critical point originally. Furthermore, the stronger the noise becomes, the wider the transition zone is. Meanwhile, we find that the phase space falls into complete confusion when we increase noise intensity to a certain extent with interaction fixed, and the trajectories reappear after we increase the interaction without increasing the noise intensity. In the full-quantum situation, when noise exists there is a transition zone instead of a critical value, and stronger noise creates wider transition zone, which is the same as in mean field treatment. What is different is that in full-quantum situation noise creates self-trapping, and the stronger the noise, the more obvious the self-trapping becomes.
A new Young tableau method of obtaining equivalent-electron Young basis
Hu Kun-Ming, Wang Jian-Bo
2007, 56 (3): 1253-1259. doi: 10.7498/aps.56.1253
Abstract +
In this paper, the projection function of regular Young tableau of equivalent-electrons is proved to be a Slauer function, and the operation rules of Young's permutation operators operating on the Slater function are given. The Young operators can be distinguished as elimination operator and effective permutation operator by the normalization of Young basis, then the constructive rules of permutation operators of the orthogonal normalization of Young basis is given. By this method, the number of Young's permutation operators is reduced and the new Young tableau method of obtaining equivalent-electron Young basis is represented.
The q-boson hopping model with integrable open boundary condition
Li Bo, Wang Yan-Shen
2007, 56 (3): 1260-1265. doi: 10.7498/aps.56.1260
Abstract +
Utilizing the algebraic Bethe Ansatz method, the Hamiltonian of q-boson hopping model and its eigenvalue equation are calculated under the integrable open boundary condition. Our result may serve as a theoretical basis for studying strongly correlated boson systems of still smaller scales.
Further discussion on the entropy of Dirac field in spherically symmetric non-static black hole
Zheng Yuan-Qiang
2007, 56 (3): 1266-1270. doi: 10.7498/aps.56.1266
Abstract +
A new general tortoise coordinate transformation is used with the thin film brick-wall model.We further discuss the Hawking temperature and the entropy of Dirac field in spherically symmetric non-static black hole.The cut-off parameter does not vary for different time-space structure,and it is reduced to that of the stationary cases.
Eigenaction of metric operator on Gaussian weave state and spin-geometry
H.Noda, Shao Chang-Gui, Shao Dan, Shao Liang
2007, 56 (3): 1271-1291. doi: 10.7498/aps.56.1271
Abstract +
In the recouping theorem and the graph calculation for loop quantum gravity, it is proved that the action of metric matrix operator on Gaussian weave state is an eigenaction, and the representation matrix elements of the metric operator and their expectation values are calculated. The values of the length of tangent vectors with 4 edges (P=1) adjacent to the vertex of Gaussian weave state ψp, as well as the angles between them, are also obtained in the cases of k=0 and k=2.
Effect of Nb addition on the glass transition and crystallization kinetics of bulk Cu-Zr metallic glasses
Fang Qi, Wang Qing, Zhao Zhe-Long, Dong Yuan-Da
2007, 56 (3): 1292-1296. doi: 10.7498/aps.56.1292
Abstract +
In the present work, bulk Cu50.3Zr49.7-xNbx(x=0,2) amorphous alloys 2 mm in diameter were produced by copper mold suction casting. The effect of Nb addition on the glass transition as well as crystallization kinetics of the binary Cu based amorphous alloy has been investigated by using differential scanning calorimetry (DSC). It is found that the alloy containing 2%Nb has a lower fragility parameter m and higher crystallization activation energy Ec, which suggests that the thermal stability and hence the glass forming ability of the surpercooled metallic liquid for the Cu based alloy are enhanced by the addition of very small amounts of Nb element.
A TCML-based spatiotemporal chaotic one-way Hash function with changeable-parameter
Liu Jian-Dong, Yu You-Ming
2007, 56 (3): 1297-1304. doi: 10.7498/aps.56.1297
Abstract +
A TCML-based spatiotemporal chaotic one-way Hash function with changeable parameter was constructed based on the analysis of sensitivity to initial value and parameters of one-way and two-way coupled map Lattice(TCML) systems.The approach is implemented by employing part of the initial values of coupled map system as the secret key, and the parameters of two-way coupled map system in each iteration is dynamically determined by the value of the last iteration and the corresponding message bit in different positions,and then making message with multigrid embedded in spatiotemporal chaos track in parallel. Choosing some suitable spatial items of the result of the final iteration, the Hash value was obtained by means of linear transform limited with 128 bits.Iteration process has very strong irreversibility and sensitivity to initial values and parameters. Each bit of Hash value has very sensitive, complex and strongly nonlinear coupling relation with the corresponding message and secret key because of the bidirectional diffusion and confusion characteristics. Simulation and analysis demonstrate that the algorithm satisfies all the performance requirements of Hash function and is reliable,secure and efficient.
Regular and chaotic motions of a single trapped ion interacting with a flashing ratchet potential
Hai Wen-Hua, Li Hui, Chen Wen-Qin, Ma Zhi-Ying
2007, 56 (3): 1305-1312. doi: 10.7498/aps.56.1305
Abstract +
Under the pseudopotential approximation, for a single Paul trapped ion which interacts with a flashing ratchet potential formed by two laser standing waves, we apply the method of integral-equation to construct the exact solution of the classical equation, and use the numerical technique to plot the orbits in phase space and calculate the current defined by the average velocity. By combining the analytical results with numerical ones,we investigate the regular and chaotic motions of the system. Compared to the case of the flashing lattice potential, two important ratchet effects are found here: First, the flashing ratchet potential changes the chaotic region in the parameter space such that we can make the regular motion of ion chaotic or vice versa by adjusting the parameters of the second laser. Secondly, by analyzing the evolutions of the average current versus the laser parameters, we find that the presence of the flashing ratchet potential can lead the trapped ion to be transported in averagy along a single direction. When the potential strength is increased to the chaotic region, the current decreases evidently and its direction varies, indicating the onset of chaotic motion.
An investigation on local area control of virus spreading in complex networks
Xu Dan, Li Xiang, Wang Xiao-Fan
2007, 56 (3): 1313-1317. doi: 10.7498/aps.56.1313
Abstract +
The local area control of virus spreading is studied in the light of the path length in complex networks, and the efficiency of local area control for complex networks with different topologies is analyzed. The research suggests that local area control method is effective in the WS small world networks, the BA scare-free networks, and the ER random networks; but the optimal radii d=3 of the local control area for zero infection applies only to the WS small world networks. In the Kleinberg small world networks, when the distance bias of long-range links increases, the epidemic threshold increases, and the effect of local area control strengthens.
Self-consistent variational calculation of the dense fluid helium plasma in the region of partial ionization
Lu Tie-Cheng, Chen Qi-Feng, Gu Yun-Jun, Cai Ling-Cang, Zhang Ying
2007, 56 (3): 1318-1324. doi: 10.7498/aps.56.1318
Abstract +
The dense fluid helium will be ionized under high pressures and temperatures. The ionization energy of helium will be lowered as the result of interactions between all particles of He, He+, He2+, and e. In this paper, the thermodynamic parameters are obtained from nonideal ionization equilibrium, taking into account the correlation contributions to the chemical potential which is determined self-consistently by the free energy function. The theoretical equation of state (EOS) is verified by shock compression experiments and other theoretical calculations. The EOS of dense helium plasma are predicted and the contributrions of interactions are discussed for the density and temperature range of 10-3—100.3 g/cm3 and 4—7 eV, respectively. The calculations show that the pressure ionization is caused by the reduced ionization energy induced by the nonideal interactions, and the ionization energy should be corrected at high temperatures and densities.
Discussion on the stratified merit of graded index coatings
Shao Jian-Da, Fan Zheng-Xiu, Shen Zi-Cai, Shen Jian, Liu Shi-Jie, Kong Wei-Jin
2007, 56 (3): 1325-1328. doi: 10.7498/aps.56.1325
Abstract +
Optical property analysis and preparation of graded index coatings can be approximated by subdividing it into a stack of many homogeneous layers. In this paper, layered medium theory is introduced firstly, which clarifies how to subdivide graded index coatings into homogeneous layers. Then a stratification merit method to get optimal layered number is put forward. At last, linear graded index coatings is taken as an example to illustrate how to obtain the optimal layer number of graded index coatings. Our discussion shows that the optimal layer number of graded index coatings depends on the coating thickness and changing speed of refractive index. When refractive index changes in given range, the layer number of graded index coatings decreases firstly and then increases with the increasing coating thickness.
A possible route of nuclear quantum phase transition induced by rotation
Tong Hong, Zhao Xing-Zhi, Ni Shao-Yong, Shi Zhu-Yi, Shi Zhu-Ya, Zhang Chun-Mei
2007, 56 (3): 1329-1333. doi: 10.7498/aps.56.1329
Abstract +
Based on the microscopic IBM-theory, a possible route of boson quantum phase transition induced by rotation is put forward. Once the nucleus is in a high-energy excited or high-speed rotating state, the nucleus would occupy the coexist-phase of collective superfluid phase with single-particle phase, if the energy is enough to realize the boson's breaking up and aligning in the nucleus, characterized by a more dense spectrum. If the energy is not enough, either of following two cases will happen. When the rotating state of nucleus arrives at critical rotating-frequency ωc, one case is that a higher-momentum boson may be decoupled from the `collective state' as a quantum `free boson', the other case is that the transition from a higher-momentum boson to a lower-momentum boson takes place, and the nucleus remaius in a collective state.Both cases are acompanied by the light-emission from the transition from higher excited-state to lower excited-state, and the total superfluous band energy of nuclear system is released by means of excited element, and an energy level appears in the ground-state band, which signifies a quantum phase transition. Just owing to these boson quantum phase transition, nuclear quantum phase transition could happen. Descriptions of boson phase transitions on breaking up and aligning as well as on decoupled and released photons have been united in this physical picture. As an example, this model has been expounded with the mechanism of producing 14+1, 14+2, and 14+3 states on the 100Pd nucleus.
Symmetry energy and isospin effects of threshold energy of radial flow in heavy ion collisions
Bian Bao-An, Zhou Hong-Yu, Zhang Feng-Shou
2007, 56 (3): 1334-1338. doi: 10.7498/aps.56.1334
Abstract +
The threshold energies of radial flow in reactions of 124Sn+124Sn and 124Ba+124Ba in central collisions are investigated within an isospin dependent quantum molecular dynamics model by using three different forms of symmetry energy. It is found that the neutron-rich system has smaller threshold energy of radial flow and its value depends strongly on the form of symmetry energy. It indicates that the threshold energy of radial flow may provide a new method to determine the symmetry energy of nuclear matter.
Isospin effect in the nuclear reaction induced by neutron-halo nuclei
Liu Jian-Ye, Xing Yong-Zhong, Zuo Wei, Lee Xi-Guo
2007, 56 (3): 1339-1346. doi: 10.7498/aps.56.1339
Abstract +
We study the average property of the isospin effect of reaction induced by halo-neutron nuclei 8He and 10He in the intermediate energy heavy ion collisions using the isospin-dependent quantum molecular dynamics model (IQMD). This study is based on the extended neutron density distribution for the halo-neutron nuclei, which includes the average property of the isospin effect of reaction mechanism and loose inner structure. The extended neutron density distribution brings an important isospin effect into the average property of reaction mechanism because the interaction potential and nucleon-nucleon(N-N)cross section in IQMD model depend sensitively on the density distribution of colliding system. In order to see clearly the average properties of reaction mechanism induced by halo-neutron nuclei we also compare the results for the neutron-halo colliding systems with those for the corresponding stable colliding systems under the same incident channel condition. We found that the extended density distribution for the neutron-halo projectile brings an important isospin effect to the reaction mechanism, which leads to the decrease of nuclear stopping R, yet induces obvious increase of the neutron-proton ratio of nucleon emissions and isospin fractionation ratio for all beam energies studied in this work, compared to the corresponding stable colliding system. In this case, nuclear stopping, the neutron-proton ratio of nucleon emissions and isospin fractionation ratio induced by halo-neutron nuclei can be used as possible probes for studying the average property of the isospin effect of reaction mechanism and extracting the information of symmetry potential and in-medium N-N cross section by the neutron-halo nuclei in heavy ion collisions.
Study of mass distributions of quasifission products based on dinuclear system
W.Scheid, Xu Hu-Shan, Zhang Hong-Bin, Li Jun-Qing, Jia Fei, Huang Tian-Heng, Yuan Xiao-Hua
2007, 56 (3): 1347-1352. doi: 10.7498/aps.56.1347
Abstract +
In the concept of dinuclear system, the quasifission rate from Kramers formula has been incorporated in the master equation in order to study the competition between fusion and qusifission. Mass yields of quasifission products of the three reactions 48Ca+244Pu, 48Ca+238U and 58Fe+232Th have been calculated, and the experimental data are reproduced very well, which is a critical test for the existing fusion model. Also we have shown the time evolution of the mass distributions of quasifission products, which provides valuable information of the process of competition between fusion and quasifission.
φ60,1000 μm Si-PIN Detectors for pulsed γ flux measurement
Ho Yu-Kun, Ouyang Xiao-Ping, Li Zhen-Fu, Song Xian-Cai
2007, 56 (3): 1353-1357. doi: 10.7498/aps.56.1353
Abstract +
Using high-resistivity (10000—20000 Ω·cm) n-type Si wafers,we have developed φ60 PIN semiconductor detector with depletion thickness ~1000 microns for low-intensity pulsed γ-ray flux measurement.For determination of thickness of the depletion depths, a recoil proton chamber with 20° scattering angle has been constructed.The detector's performance have been measured and analyzed,which indicates that the developed detector satisfactorily meets the expected specifications.Compared with the existing detectors with depletion depths of 200—300 microns,the detector has much greater γ detecting sensitivity and suited for measuring pulsed γ-ray flux in low-intensity mixed γ/n fields.
Calculation of dielectronic recombination rate coefficients of Kα- and Kβ-type decays of Ni27+
Mu Zhi-Dong, Wei Qi-Ying
2007, 56 (3): 1358-1364. doi: 10.7498/aps.56.1358
Abstract +
The dielectronic recombination(DR) rate coefficients are investigated for low-density hydrogen-like Ni27+ at plasma temperatures 0.1—10 keV by the wavefunction from Hartree-Fock with relativistic Corrections(HFR) method. Based on the KLn and KMn resonance excitation, the partial DR rate coefficients of the DR processes are calculated by taking into account the important radiative decay tunnel including the Kα- and Kβ-type decays. It was found that the Kα- and Kβ-type radiative decays are important in the DR processes of hydrogen-like Ni27+. The partial DR rate coefficient of Kα processes is much larger than that of Kβ.
The preliminary result of laser- focused Cr atomic deposition for fabricating nanostructure
Ma Yan, Zhang Bao-Wu, Zheng Cun-Lan, Ma Shan-Shan, Li Fo-Sheng, Wang Zhan-Shan, Li Tong-Bao
2007, 56 (3): 1365-1369. doi: 10.7498/aps.56.1365
Abstract +
The technology of laser-focused atomic deposition can be used to develop the nanostrucrure transfer standard of length. When the frequency of laser standing wave is higher than the resonant frequency of atoms, the atoms will be focused on the wave node of the standing wave. The collimated Cr atoms are focused by a standing-wave laser field as they are deposited on a silicon substrate. Atomic force microscopy measurements shows a spacing of 215nm.
THz spectra study of MgF2 crystals
Hou Bi-Hui, Shao Meng, Wang Ji-You, Fan Zhi-Da, Xu Xin-Long, Wang Li
2007, 56 (3): 1370-1374. doi: 10.7498/aps.56.1370
Abstract +
THz (terahertz) properties of MgF2 crystal (sample 1) and MgF2: Co crystal (sample 2) is measured using transmission THz time domain spectroscopy in the frequency range between 0.5 and 2.5 THz. The absorption coefficients α(ν) of sample 1 increases and has a maximum 24cm-1 with increasing frequency ν from 0.5 THz to 2.5 THz. The absorption coefficient of sample 2 is much larger than that of the sample 1, and its absorption band edge of the crystal lattice shifts to lower frequency side because of the dopant Co. Moreover, there is an absorption peak at 1.9THz and the absorption coefficient is greater than 70 cm-1, the force constant K of F-—Co2+ ionic chemical bond stretch vibration calculated from this peak is 3.40×10-2 N/cm. The THz spectroscopy can be an important technique for research of chemical bond in crystal. Real dielectric functions between 0.5 and 2.5 THz of the two samples are calculated by relations between optical constants. The ε1(ν) of sample 1 varies from 4.67 to 4.73 and ε1(ν) of sample 2 varies from 4.62 to 5.01.
1 kHz-0.1 TW high efficiency Ti: sapphire laser amplifier
Liu Jun, Li Xiao-Fang, Chen Xiao-Wei, Jiang Yong-Liang, Li Ru-Xin, Xu Zhi-Zhan
2007, 56 (3): 1375-1378. doi: 10.7498/aps.56.1375
Abstract +
A Ti:sapphire multipass amplifier with high efficiency at the repitation of 1 kHz is described. The incident 0.66 W pulses are amplified to 7.2 W when the pump power is 23 W. The energy extraction efficiency is about 30%. After compressed in the compressor, we obtained 4.5mJ, 38fs pulses with peak power greater than 0.1 TW.
Guassian soliton in biased photorefractive crystal
Shi Shun-Xiang, Chen Shou-Man, Dong Hong-Zhou
2007, 56 (3): 1379-1384. doi: 10.7498/aps.56.1379
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Using a variational approach, the low intensity photorefractive nonlinear Schr dinger equation is solved. The evolution properties of Guassian beam propagating in photorefractive crystal biased with positive electric field are obtained. The dynamic variation of the beam width spread or compression is investigated by analyzing the potential function description for the variation of beam width. Solutions of the low intensity Guassian beam propagating in the positively biased photorefractive crystal are obtained for the beam width, beam amplitude, and the curvature of wave front. The results show that the amplitude and width of Guassian beam will exhibit a periodical oscillatory or deconcentration behavior when propagating in the positively biased photorefractive crystal. Under certain condition, the Guassian beam can steadily propagate with invariant shape, forming a Guassian soliton. These properties have a high practical value in engineering.
Study on two-cell stimulated Brillouin scattering system with new media
Hasi Wu-Li-Ji, Lü Zhi-Wei, Li Qiang, Ba De-Xin, He Wei-Ming
2007, 56 (3): 1385-1389. doi: 10.7498/aps.56.1385
Abstract +
According to the relationships between the chemical structure of the medium and the absorption coefficient, a series of new media with small absorption coefficients has been found, which are suited for use as the amplifier media. The stimulated Brillouin scattering (SBS) parameters of these media have been calculated or measured when the pump wavelength is 1.064 μm. Choosing C2Cl4 and C4Cl6 as amplifier medium and C2H5OH as generator medium, we investigated the performances of two-cell SBS system pumped by Nd:YAG Q-switched laser. The C2H5OH has a high optical breakdown threshold and the Brillouin frequency shift of C2H5OH is close to those of C2Cl4 and C4Cl6. The results indicate that the system has the characteristics of high power-load ability, high phase-conjugation fidelity and high energy reflectivity stability.
Study of tunable terahertz-wave generation via difference frequency mixing in isotropic semiconductor crystals
Sun Bo, Yao Jian-Quan, Wang Zhuo, Wang Peng
2007, 56 (3): 1390-1396. doi: 10.7498/aps.56.1390
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The tunable, coherent terahertz wave generation in a variety of isotropic semiconductor nonlinear crystals, such as Ⅲ-Ⅴ and Ⅱ-Ⅳ compounds, by difference frequency mixing is studied theoretically based on the theory of the cross-Reststrahlen band dispersion compensation phase-matching. An angle-tuned, dual-wavelength KTP-OPO operating near the degenerate point is used as the pump source for THz wave generation. The theoretical analysis of phase-matching conditions and coherence length for different materials mentioned above is presented according to their optical dispersion properties, and their gain characteristic and nonlinear figure of merit are also described and calculated. Through the theoretical analyses and calculations, it is shown that ZnTe is a promising DFG crystal for THz wave generation under the collinear phase-matching condition, while InP is the one under the noncollinear phase-matching condition.
Theoretical investigation of propagation of nonlocal spatial soliton in nematic liquid crystals
Lan Sheng, Long Xue-Wen, Hu Wei, Zhang Tao, Guo Qi, Gao Xi-Cun
2007, 56 (3): 1397-1403. doi: 10.7498/aps.56.1397
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In this paper, we investigate the propagation of the nonlocal optical spatial soliton in undoped nematic liquid crystals. On the basis of Schrdinger-type nonlinear equation and reorientation equation, we not only obtained the analytical expression of spatial soliton but also got the expression of breather in the vicinity of the critical power by use of Guassian trial solution. By comparisons of analytical and numerical simulations, we found that our expressions are more precise than those of C.Conti and G.Assanto. Furthermore,we thoroughly compare the nonlocal model in nematic liquid crystals with the linear model suggested by Snyder and Mitchell.
Antireflection coating for two-dimensional air hole-type photonic crystal negative refraction slab lens
Zhang Bo, Wang Zhi
2007, 56 (3): 1404-1408. doi: 10.7498/aps.56.1404
Abstract +
We propose and optimize the antireflection coating composed of a row of tapered dielectric waveguides for two-dimensional air hole-type photonic crystal negative refraction slab lens. The image quality of the lens with the antireflection coating is improved. The simulation result using finite difference time domain method shows, at the working frequency leading to the effective index neff=-1, the reflection rate of the surface of photonic crystal with anti-reflection coating is reduced to below 1% in the range of incident angle less than 23 degrees.
Experimental and theoretical study of displacement measurement based on frequency modulation optical feedback in a birefringence dual frequency laser
Mao Wei, Zhang Shu-Lian
2007, 56 (3): 1409-1414. doi: 10.7498/aps.56.1409
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Acoustic-phonon transmission in multilayer heterojunctions
He Meng-Dong, Gong Zhi-Qiang
2007, 56 (3): 1415-1421. doi: 10.7498/aps.56.1415
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Using a transfer matrix method, we investigate the transmission property of the acoustic-phonon modes in symmetrical multilayer heterojunctions consisting of many different heterojunctions (GaAs/AlxiGa1-xiAs) within elastic continuum approximation. Our results show that the oscillation amplitude and frequency are different between transmission curve in such structure and transmission curve in the superlattice (GaAs/AlAs) with the same thicknesses of constituent layers. The features of transmission spectrum are influenced by the distribution of the concentration xi(i denotes the i th AlxiGa1-xiAs slab on both sides of the symmetrical axis) . When the concentration xi in AlxiGa1-xiAs slab decreases with the increase of i, the curve in transmission spectrum is flat except in the vicinity of the main valley. When the concentration xi increases with the increase of i, the oscillation amplitude of the curve increases and the main valley is split. Our results also show that the transmission coefficient is sensitive to the thicknesses of constituent layers, especially the thickness of AlxiGa1-xiAs. In addition, it is found that the number of heterojunctions influences the transmission of acoustic phonon.
Generalized parametric constitutive law for van der Waals force simulation and its applications in computation of nanotubes
Zhang Hong-Wu, Wang Jin-Bao, Ye Hong-Fei, Wang Lei
2007, 56 (3): 1422-1428. doi: 10.7498/aps.56.1422
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In this paper, a parametric variational principle for van der Waals force simulation between any two non-bonded atoms is established together with the corresponding improved quadratic programming method for numerical simulation of mechanical behaviours of carbon nanotubes. Carbon-carbon covalent bond interaction in carbon nanotubes is modeled and computed based on molecular structural mechanics model. Van der Waals force is simulated by the network of bars with a special nonlinear mechanical constitutive law in the finite element analysis. In comparison with conventional numerical methods, the suggested method does not depend on displacement and stress iteration, but on the base exchanges in the solution of a standard quadratic programming problem. Thus, the model and method developed exhibit very good convergence behavior in computation and provide accurate predictions of the mechanical behaviours and displacement distributions in the nanotubes. Numerical results demonstrate the validity and the efficiency of the proposed method.
Experimental study of propagation time of electromagnetic pulse through laboratory plasma
Wang Liang, Cao Jin-Xiang, Wang Yan, Niu Tian-Ye, Wang Ge, Zhu Ying
2007, 56 (3): 1429-1433. doi: 10.7498/aps.56.1429
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The propagation time of electromagnetic pulse(EMP) through nonmagnetic stationary laboratory Xe plasma was investigated by using network analyzer, with EMP frequency of 9—11 GHz. The research indicates that the propagation time of EMP through plasma will be less than that through the same distance in vacuum when the plasma density is in the range of 0.65—1.43×1011 cm-3,and the time delay will be a minimum at ne1.10×1011 cm-3. In this range of plasma density, the dispersion relation of electromagnetic wave in Xe plasma without magnetic field will be invalid.
Effects of temporal chirp on laser filamentation in air
Zhao Gang, Hao Zuo-Qiang, Zhang Zhe, Lu Xin, Jin Zhan, Liu Yun-Quan, Wei Zhi-Yi, Zhang Jie, Wang Zhao-Hua, Zhong Jia-Yong
2007, 56 (3): 1434-1438. doi: 10.7498/aps.56.1434
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Effect of the laser chirp on the laser filamentation is investigated. It is found that the chirp plays a crucial role in the formation of filamentation and its evolution. An initial negative chirp is favorable for long-distance propagation of filaments in air. As the chirp increases, the distance between the compressor and the position of the onset of filaments becomes larger. We also investigate the influence of initial chirp on the focusing laser pulses by a lens. It is found that there are the same tendency of filaments formed by lens and those in free propagation.
Polarization dependence of third-harmonics and spectral modulation properties of supercontinuum radiation from plasmas channels generated by femtosecond laser pulses propagation in air
Li Kun, Xu Miao-Hua, Jin Zhan, Liu Yun-Quan, Wang Zhao-Hua, Ling Wei-Jun, Zhang Jie
2007, 56 (3): 1439-1442. doi: 10.7498/aps.56.1439
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We carried out spectroscopic studies on the supercontinuum radiation from the plasma channels generated by femtosecond laser pulses propagating in air, which confirmed the polarization dependence of third harmonics and the spectral modulation of supercontinuum radiated from filaments. The new phenomenon of spectral modulation is also explored.
SO-FDTD analysis of anisotropic magnetized plasma
Chen Ru-Shan, Yang Yang, Yuan Hong, Yang Hong-Wei
2007, 56 (3): 1443-1446. doi: 10.7498/aps.56.1443
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A novel finite-difference time-domain (FDTD) method, called shift operator FDTD (SO-FDTD) method is developed for anisotropic magnetized dispersive media. The recursive relation between operators is used. In this paper, some expressions containing the dielectric constants of magnetized dispersive media are written as rational polynomial function. The SO-FDTD formulation for anisotropic magnetized plasma is derived. The high efficiency and effectiveness of the method are confirmed by computing the reflection and transmission through a magnetized plasma layer, with the direction of the propagation parallel to the direction of the biasing field. A comparison with frequency domain analytic results is included. The CPU time was several times shorter than that of the JEC method.
A time-resolved three-channel soft X-ray spectrometer
Zhang Jing-He, Zhang Hua-Quan, Hu Xin, Jiang Shao-En, Cui Yan-Li, Huang Yi-Xiang, Ding Yong-Kun, Liu Zhong-Li, Yi Rong-Qing, Li Chao-Guang
2007, 56 (3): 1447-1451. doi: 10.7498/aps.56.1447
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Developing of a time-resolved three-channel soft X-ray spectrometer is reported,and the operating principle and the parameters of spectrometer designed in three energy bands of 210eV,420eV and 900eV are presented specially. On the ShenGuang-Ⅱ high power laser facility,the spectrometer was applied in experiments with good results. This work is the first attempt in China to construct a spectrometer which couples planar mirrors and filters to X-ray streaked camera,and which is capable of measuring X-ray signal with spatial- and temporal-resolution in three sub-Kev energy channels simultaneously. Experimental results show that by combining X-ray reflector and filter,the spectrometer has achieved enery resolution of 5 and temporal resolution ability of 10 ps.
Investigation of gas puff imaging on HL-2A tokamak
Zheng Yin-Jia, Huang Yuan, Feng Zhen, Shi Le, Cui Cheng-He, Wang Ming-Xu, Xu Hong-Bing
2007, 56 (3): 1452-1460. doi: 10.7498/aps.56.1452
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GPI (gas puff imaging) is one of the important diagnostics method for investigation of the radiation in the edge region of plasma. In this paper, atomic and molecular processes during GP (gas puff) passage are analyzed. The main radiation emitting from the gas is identified as the Hα line, appearing on the plasma edge region, and the expressions of its intensity and location are given. As viewed from imaging angle, space radiation photograph of hydrogen gas during the GP was obtained experimentally. Improvements of the imaging system and GP experiment arrangement on the HL-2A tokamak are introduced. The observation results confirm the above analysis. In the beginning stage of plasma, the GP hydrogen atoms can pass through the region where the plasma column is to be set up and the bright strip region is formed. In the general GP fuelling, CCD photos are in accordance with the control signals, and other diagnostic results. The strong Hα emissions in both the HFS and LFS sides of plasma are observed.
Axial property of the inner surface of a metal tube processed by GEPSII
Wang Jiu-Li, Chen Guang-Liang, Feng Wen-Ran, Gu Wei-Chao, Niu Er-Wu, Fan Song-Hua, Liu Chi-Zi, Yang Si-Ze, Zhang Gu-Ling
2007, 56 (3): 1461-1466. doi: 10.7498/aps.56.1461
Abstract +
As a novel inner surface processing method, grid enhanced plasma source ion implantation (GEPSII) method can realize uniform inner surface ion implantation of a metal tube and metal binary compound can be produced. In the experiment, three 0.45% carbon steel (45-steel) work pieces were axially put on the inner surface of the tube, and golden titanium nitride (TiN) films were produced on the work pieces by GPSII. Structure analysis shows that the TiN films have the preferred crystal faces (111) and (200), and the depth of the films is about 20 nm with partial embedding in the substrate. Analysis on the electrochemistry corrosion, hardness and friction of the work pieces indicates that the surface property of the 45-steel has been greatly improved by the protective TiN film, and very good axial uniformity has been obtained.
Study on the properties of the square pattern in Air/Ar dielectric barrier discharge
Fan Wei-Li, Dong Li-Fang, Li Xue-Chen, Yin Zeng-Qian, He Ya-Feng, Liu Shu-Hua
2007, 56 (3): 1467-1470. doi: 10.7498/aps.56.1467
Abstract +
The properties of the square pattern as a function of the relative air content is studied in Air/Ar dielectric barrier discharge system at one atmosphere pressure. The dependence of the spatial wavelength and the traveling velocity of the square pattern on the relative air content is obtained. It is found that the spatial wavelength of the square pattern is decreased with the increased relative air content at different gas gap distances. The traveling velocity of the square pattern is also closely related to the value of the relative air content, which reaches its maximum 14mm/s when the air relative component is 10%.
Study on the interaction of microdischarge channels in dielectric barrier discharge pattern
Dong Li-Fang, Gao Rui-Ling, He Ya-Feng, Fan Wei-Li, Li Xue-Chen, Liu Shu-Hua, Liu Wei-Li
2007, 56 (3): 1471-1475. doi: 10.7498/aps.56.1471
Abstract +
The spatial wavelength of the hexagon pattern are studied for different discharge parameters in dielectric barrier discharge system near the atmospheric pressure. The generating process and the movement of the microdischarge channels are observed. It is found that the wavelength of the hexagon decreases as the applied voltage increases. It is also dependent upon the gas gap and the gas pressure. The new filaments appear near the discharge boundary when the applied voltage increases slowly. The filaments at the outmost vertexes of hexagon move along the radial axis. The filaments on the side of hexagon move along axis parallel to the C2 axis, which has the least distance to those filaments. The discharge spots change into discharge stripes and finally into the spiral or target pattern when the applied voltage is increased further. Based on the experimental results and the force analysis, the confined potential, which exists in two dimensional coulomb crystals, is proposed to exist in the discharge domain.
Generation and suppression of deep level defects in InP
Zhao You-Wen, Dong Zhi-Yuan
2007, 56 (3): 1476-1479. doi: 10.7498/aps.56.1476
Abstract +
Deep level defects in as-grown and annealed n-type and semi-insulating InP have been studied. After annealing in phosphorus ambient, a large quantity of deep level defects were generated in both n-type and semi-insulating InP materials. In contrast, few deep level defects exist in InP after annealing in iron phosphide ambient. The generation of deep level defects has direct relation with in-diffusion of iron and phosphorus in the annealing process. The in-diffused phosphorus and iron atoms occupy indium sites in the lattice, resulting in the formation of P anti-site defects and iron deep acceptors, respectively. The results indicate that iron atoms fully occupy indium sites and suppress the formation of indium vacancy and P anti-site, etc., whereas indium vacancies and P anti-site defects are formed after annealing in phosphorus ambient. The nature of the deep level defects in InP has been studied based on the results.
Enhancement factor formulation of doped nematic liquid crystals in the presence of photoisomerization
Deng Luo-Gen, Luo Li-Yuan
2007, 56 (3): 1480-1488. doi: 10.7498/aps.56.1480
Abstract +
The mechanism of the orientational optical nonlinearity enhancement in the azo-dye doped liquid crystals is studied. The expressions of the enhancement factors based on the multiple-level transition model of azo-compound are derived. Our results show that, the simpler the model, the fewer the number of items contained in the expression of the enhancement factor. Using the enhancement factor expression obtained by the four-level model to describe the influences of the photoisomerization of azo-dyes on the enhancement of orientational optical nonlinearity is better than using that acquired by the three-level model. Besides, the expression of the enhancement factors in the case that the cis molecules do not absorb light is also obtained from the enhancement factor expression obtained by the four-level model. Except for a minor difference, the enhancement factor expression obtained in this case is the same as what was obtained for the anthraquinone-dye doped liquid crystals by Marrucci et al in 1997. This result also shows that under a given simplified condition, our theory is consistent with the last theory.
Molecular dynamics simulation of deformation-induced crystallization mechanism in amorphous Ti3Al alloy
Wang Hai-Long, Wang Xiu-Xi, Wang Yu, Liang Hai-Yi
2007, 56 (3): 1489-1493. doi: 10.7498/aps.56.1489
Abstract +
The crystallization of Ti3Al amorphous alloy during tensile deformation was studied with molecular dynamics. The simulation results show that the crystallization of amorphous alloy is induced by the local plastic deformation. The microstructure evolution was analyzed in the tension process. It is found that the nucleation and growth are induced by the shear localization and the final crystal phase has fcc structure. It is also found that the crystallization process is accompanied by strengthening of the material. The nanocrystal grains embedded in the amorphous phase can enhance the rigidity of the sample.
Study of rare-gas atom injection into defective carbon nanotube by molecular dynamics simulation
Jin Nian-Qing, Teng Yu-Yong, Gu Bin, Zeng Xiang-Hua
2007, 56 (3): 1494-1498. doi: 10.7498/aps.56.1494
Abstract +
Based on the classical molecular dynamics method and using TLHT potential, the dynamic processes of rare-gas atom (He, Ne, Ar, Kr, Xe) injection into defective single-wall carbon nanotube (SWCNT) are investigated. The threshold energies of rare-gas atoms injected into a defective wall and absorbed on an open end of SWCNT are obtained and compared with the case of perfect SWCNT. It shows that the threshold energy Ek0 decreases with increasing of the defect size. When the defect radius is less than 4.5 ?,the rare-gas atoms with proper threshold energies can be encapsulated in SWCNT. But when the defect radius is over 4.5 ?,the rare-gas atoms can not be encapsulated in SWCNT, and the transport properties of Ar, Kr and Xe will change greatly.
Freezing of Ni nanowires investigated by molecular dynamics simulation
Zhou Guo-Rong, Gao Qiu-Ming
2007, 56 (3): 1499-1505. doi: 10.7498/aps.56.1499
Abstract +
The freezing of Ni nanowires at different cooling rates was studied by classical molecular dynamics simulation via embedded atom potential method. The structure evolution of Ni nanowires in the freezing region was also presented. In order to distinguishing the local clusters in the cooling process of Ni nanowires formed at different cooling rates the bond, pair analysis is employed. The simulation results indicate that the freezing of the nanowires starts from the surface and the structure of the nanowires changes from amorphous to fcc crystal via helical multi-shelled structure along with the decrease of cooling rate. The helical multi-shelled structure possesses not only the short-range order and long-range disorder of amorphous structure but also a definite crystallization temperature.
Influence of van der Waals force on the buckling of double-walled carbon nanotubes
Wang Lei, Zhang Hong-Wu, Wang Jin-Bao
2007, 56 (3): 1506-1513. doi: 10.7498/aps.56.1506
Abstract +
Several novel double-walled carbon nanotubes (DWCNT) composed of different internal and external nanotubes with different diameters are presented and studied by molecular dynamics simulation (MD). Initial equilibrium configurations and characteristics during free relaxation are examined. Buckling of these DWCNTs under axial compression are simulated to examine the influence of van der Waals force on mechanical properties of DWCNTs. The interaction of atoms in each wall and the van der Waals force between inner and outer walls are described by Tersoff-Brenner potential and Lennard-Jones potential respectively. Results show that new stable DWCNTs exist whose interlayer distances are not necessarily 0.34 nm. And these new DWCNTs show different mechanical behaviors as compared with the normal DWCNT.
Effect of foreign particles on the dendritic growth in phase-field theory
Li Jun-Jie, Wang Jin-Cheng, Xu Quan, Yang Gen-Cang
2007, 56 (3): 1514-1519. doi: 10.7498/aps.56.1514
Abstract +
The presence of foreign particles in the undercooled melt can influence the evolution of solidification structure and change the dendritic morphology. In this work, according to the KKS model, a hybrid phase field model for binary alloys, which takes into account the random crystallographic orientation, is developed to analyze the effect of misorientation between foreign particles and crystal grains on the dendritic growth. The simulation results show that the influence of foreign particles depends on the particle size, position, numbers and the degree of misorientation. The foreign particles which do not match the initial orientation of the crystal cause the dendrite trunks to deflect and split, leading to the formation of irregular dendritic morphology.
The dual-species model study of co-enrichment of trace elements and Ni at Ni3Al grain boundary
Li Dou-Xing, Xu Zi-Jian, Zhu Zhi-Yuan, Zheng Li-Ping
2007, 56 (3): 1520-1525. doi: 10.7498/aps.56.1520
Abstract +
The dual-species model is based on the Monte Carlo simulation conjoined with the embedded atom method (EAM) potentials. The model suggests that during relaxation of Ni3Al grain boundary,the trace element atoms can be seen not only as segregating species but also as inducing species. As segregating species the trace element atoms segregate (or enrich) to the grain boundary, but as inducing species they induce Ni atoms to segregate (or enrich) to the grain boundary. Evidently, the model can explain why the trace element atoms and Ni atoms co-segregate (or co-enrich) to the grain boundary. According to combination of positive (as inducing species) and negative (as segregating species) effects, the model explains the most obvious Ni-enrichment phenomenon at Ni3Al grain boundaries.
Molecular dynamics study of deformation mechanism of γ-TiAl intermetallics
Zhou Zong-Rong, Wang Yu, Xia Yuan-Ming
2007, 56 (3): 1526-1531. doi: 10.7498/aps.56.1526
Abstract +
The generalized planar fault (GPF) energies of various slip systems in γ-TiAl intermetallics are studied by using molecular dynamics (MD) method. The unrelaxed and relaxed GPF curves of various slip systems are compared. It was show that the γ-TiAl has fewer mobile slip systems than the fcc crystal. It is also found that the γ-TiAl intermetallics would exhibit brittle behavior at ambient temperature. The relaxed generalized stacking and twinning fault energy curves of (1/6)〈112〉{111} twinning system are obtained. By analyzing the unstable stacking fault energy γusf, the stable stacking fault energy γsf, and the unstable twinning fault energy γutf, it can be predicted that the major deformation mechanisms are twinning (1/6)〈112〉{111} and ordinary dislocation slip (1/2)〈110〉{111}, as well as superdislocation slip (1/2)〈011〉{111}.
Calculating elastic constants of Fe-based cubic magnetic material using first principles
Zheng Lei, Jiang Cheng-Bao, Shang Jia-Xiang, Zhu Xiao-Xi, Xu Hui-Bin
2007, 56 (3): 1532-1537. doi: 10.7498/aps.56.1532
Abstract +
Using the first principles full potential linearized augmented plane wave (FLAPW) method and the pseudopotential plane wave (CASTEP) method, the elastic constants of Fe-based magnetic cubic phases are investigated. The key point is confirmed to be the lattice constants when calculating elastic constants, and the basis sets also affect the precision of calculation. More precise results were got by FLAPW. The elastic constants C11, C12, C44 of bcc-Fe are 283 GPa, 158 GPa and 112 GPa, respectively,which approximately consist with the intrinsic ones. The elastic constants C11, C12, C44 of Fe-Ga magnetostrictive material are calculated to be 207 GPa, 166 GPa and 108 GPa, respectively.
Theoritical analysis of quasi-isentropic compression via flier-plate with grade wave impadence
Shen Qiang, Luo Guo-Qiang, Zhang Lian-Meng, Huang Hai-Jun
2007, 56 (3): 1538-1542. doi: 10.7498/aps.56.1538
Abstract +
The process of shock waves propagation in the target material is analyzed theoretically when hitted by a flier-plate with graded wave impedance. Under the impact, the compression curve of target consists of small Hugoniot curves originating from different original states, which are located between the Hugoniot and the isentropic curves. Thus any state between Hugoniot and isentropic curves can be obtained by controlling the number of flier-plate's layers. It provides a theoretical basis for experimental study of off-Hugoniot equation of state. The validity and reliability of the theoretical analysis are supported by the consistency of experimentally measured and calculated interface velocity values.
A new model for calculating critical cooling rates of alloy systems based on viscosity calculation
Wang Zhen-Yu, Yang Yuan-Sheng, Tong Wen-Hui, Li Hui-Qiang, Hu Zhuang-Qi
2007, 56 (3): 1543-1548. doi: 10.7498/aps.56.1543
Abstract +
Based on the model for calculating the critical cooling rate of bulk metallic glasses under non-isothermal condition, a new model for calculating the critical cooling rate of alloy systems based on viscosity calculation is put forward in this paper. The critical cooling rates of Zr-Ni-Al-Cu quaternary alloys were calculated and the glass forming range in Zr66.67(NixAlyCuz)33.33 quaternary alloy system is predicted. The results are in good agreement with the experimental values. The calculation results show that there is high glass forming ability in Zr66.67(NixAlyCuz)33.33 quaternary alloy system. The glass forming range is near eutectic point in which critical cooling rates are less than 100 K/s. There is not crystallization in the temperature range higher than 1000K, the fraction of crystals increases rapidly in the temperature range from 980 K to 870 K, and it is not changed in the temperature range below 870 K. In addition, the effects of Al,Cu,Ni mole fraction on the critical cooling rate are analyzed in this paper.
Approximate analytical solutions for a class of nonlinear differential equations
Zhang Xin-Xin, Zheng Lian-Cun, Feng Zhi-Feng
2007, 56 (3): 1549-1554. doi: 10.7498/aps.56.1549
Abstract +
This paper presents a theoretical analysis for a class of generalized diffusion equations. An effective analytical decomposition and numerical technique is given by similarity transformations and the analytical decomposition technique. The approximate analytical solution may be expressed in terms of a rapid convergent power series with elegantly computable terms. The reliability and efficiency of approximate solutions are illustrated by good agreement with numerical results.
Analysis of adhesion process between material surfaces
Qing Tao, Shao Tian-Min, Wen Shi-Zhu
2007, 56 (3): 1555-1562. doi: 10.7498/aps.56.1555
Abstract +
In this paper, adhesion process of two material surfaces was analyzed. Formulas for calculating jumping distance were deduced. The results of analysis showed that the jumping distance was retated to the radius of spheres, elastic modulus of the spring and the relative humidity. Effect of relative humidity was also discussed. Basing on single asperity model and the constructive equations for power-law fluid, the formulas for describing the relationship between pull-off force and the rest time were improved. Jump-to-contact force and pull-off-force were measured by a self-built adhesion apparatus.
Effect of substrate temperature on the ZnO thin films as TCO in solar cells grown by MOCVD technique
Chen Xin-Liang, Xue Jun-Ming, Zhang De-Kun, Sun Jian, Ren Hui-Zhi, Zhao Ying, Geng Xin-Hua
2007, 56 (3): 1563-1567. doi: 10.7498/aps.56.1563
Abstract +
Geng Xin-HuaMicrostructural,optical and electrical properties of updoped-ZnO films grown by metal organic chemical vapor deposition at different substrate temperature were investigated. XRD spectra and SEM photos indicate that the substrate temperature plays an important role on the microstructure of ZnO films. Morphological transition takes place obviously at around 175℃. The morphology of the ZnO films shows sphere-like structure at low temperature (177℃). The grain size of ZnO films grows up with the increase of substrate temperature. The high mobility (17.96 cm2/Vs) and low resistivity (3.28×10-2Ω·cm) at 177℃ have been obtained for undoped-ZnO film deposited on glass substrate. By further optimizing the structure and B-doping, ZnO film as front electrode will be applied in solar cell soon.
Microstructure and mechanical properties of VN/SiO2 nanomultilayers synthesized by reactive sputtering
Yue Jian-Ling, Kong Ming, Zhao Wen-Ji, Li Ge-Yang
2007, 56 (3): 1568-1573. doi: 10.7498/aps.56.1568
Abstract +
VN/SiO2 nanomultilayers with different individual SiO2 and VN layer thicknensses were prepared with V and SiO2 targets by reactive sputtering. The microstructure and mechanical properties of the films have been studied by X-ray diffraction, energy dispersive X-ray spectrometry, high-resolution transmission electron microscopy and nanoindentation. The results reveal that the SiO2 film synthesized by radio frequency reactive sputtering in Ar-N2 gas mixture contains no N element, normally amorphous SiO2 is forced to crystallize at very low layer thickness (2 layer gradually forms an amorphous structure and blocks the coherent growth of nanomultilayers, and the hardness of nanomultilayers gradually decreases. On the other hand, the changing of VN layer thickness has relatively small effects on the microstructure and mechanical properties of nanomultilayers.
Effect of SiO2 crystallization on AlN/SiO2 nano-multilayers with superhardness effect
Zhao Wen-Ji, Kong Ming, Huang Bi-Long, Li Ge-Yang
2007, 56 (3): 1574-1580. doi: 10.7498/aps.56.1574
Abstract +
A series of AlN/SiO2 nano-multilayers with different SiO2 thickness were prepared by reactively magnetic sputtering. The microstructure of the nano-multilayers was characterized with X-ray diffraction and high-resolution transmission electron microscopy, and a nanoindentor was used to measure their mechanical properties. The phenomenon of crystallization of SiO2 in the multilayers and its effects on multilayer growth and mechanical properties were studied. Results show that SiO2, normally amorphous under sputtering condition, was crystallized when thickness was below 0.6 nm due to the effect of hcp crystal structure of AlN. And SiO2 formed a pseudocrystal structure just the same as AlN and grew epitaxially with AlN on the crystal plane of (0001). Because of the lattice mismatch between two layers, there existed an alternate stress field in the multilayer, which counted for a large portion of the hardness enhancement of the multilayer. Further increasing SiO2 layers thickness, the coherent interfaces of the multilayers were damaged and SiO2 become amorphous, accompanying by the decline in the hardness of the films.
Electronic theory studies of aluminum matrix composite reinforced by carbon nanotube
Zhang Guo-Ying, Zhang Hui, Wei Dan, He Jun-Qi
2007, 56 (3): 1581-1584. doi: 10.7498/aps.56.1581
Abstract +
The models of the high angle grain boundaries with different Σ(5,9,11) of pure aluminum and the interface between carbon nanotube and pure aluminum were constructed by the self-developed computer software. The electronic structures (structure energies of aluminum grain boundaries,the interfaces between carbon nanotube and pure aluminum,carbon nanotubes and fermi levels of different systems, etc.) of the carbon nanotube reinforced aluminum matrix composites were calculated with Recursion method. The calculated results show that the structure energy of the aluminum high angle grain boundary with Σ=5 is the lowest, it is t
First-principles study the optical properties of anatase TiO2 by N-doping
Peng Li-Ping, Yin Jian-Wu, Xu Ling
2007, 56 (3): 1585-1589. doi: 10.7498/aps.56.1585
Abstract +
We have calculated the optical properties of anatase TiO2 and anatase TiO2 by N-doping by plane-wave pseudo-potential method (PWP), namely the imaginary part of dielectric function ε2(ω),the optical absorption coefficient I(ω) and the reflectivity R(ω). We have given an explanation in terms of band structures why the optical spectrum has three main peaks around 2.93 eV,3.56 eV and 3.97 eV after N-doping. Our studies of the optical spectra show that the Red-shift will happen after N-doping, and experimental phenomena also approve the result.
Full-mode analysis of a two-dimensional photonic crystal waveguide
Yin Hai-Rong, Gong Yu-Bin, Wei Yan-Yu, Lu Zhi-Gang, Gong Hua-Rong, Yue Ling-Na, Huang Min-Zhi, Wang Wen-Xiang
2007, 56 (3): 1590-1597. doi: 10.7498/aps.56.1590
Abstract +
To determine the guide operating band, we derived the eigenvalue equations for a two dimensional photonic crystal rectangular waveguide, and found that the E(y), TEy, H(y) and TMy modes can exist in the photonic crystal rectangular waveguide. The calculation explains that this kind of waveguide can operate in single mode, if the height of the waveguide is low enough. And the bandwidth when the waveguide operates in single mode is determined by the cutoff frequency of the E(y)1 mode and that of the E(y)2 mode.
First-principles calculations of structures, properties and high pressures effects of Fe
Sun Bo, Liu Shao-Jun, Duan Su-Qing, Zhu Wen-Jun
2007, 56 (3): 1598-1602. doi: 10.7498/aps.56.1598
Abstract +
In this paper, we performed first-principles calculations for iron with different crystal structures based on density-function theory, employing the pseudopotentional and plane-wave method. We set the computational precision of energy to 0.01 eV/atom and made total-energy calculations. The calculated results show that: 1) The bcc iron undergoes a pressure-induced phase transform to hcp structure at about 15 GPa, which is in good-agreement with the experimental values; 2) The magnetic moment decreases with increasing pressure, which demonstrates that the high pressures will destroy the magnetism of iron; 3) The ratio of lattice parameters of hcp structure, c/a, will slowly increase with the pressure increasing. When set to a constant about 1.59, the c/a value can give the energy computation precision of 0.01 eV/atom under the pressures in the earth core.
Electron irradiation induced defects in high temperature annealed InP single crystal
Wang Bo, Deng Ai-Hong, Miao Shan-Shan, Yang Jun, Zhao You-Wen, Dong Zhi-Yuan
2007, 56 (3): 1603-1607. doi: 10.7498/aps.56.1603
Abstract +
Electron irradiation induced defects in InP material which has been formed by high temperature annealing undoped InP in different atmosphere have been studied in this paper. In addition to Fe acceptor, there is no obvious defect peak in the sample before irradiation, whereas five defect peaks with activation energies of 0.23 eV, 0.26 eV, 0.31 eV, 0.37 eV and 0.46 eV have been detected after irradiation. InP annealed in P ambient has more thermally induced defects, and the defects induced by electron irradiation have characteristics of complex defect. After irradiation, carrier concentration and mobility of the samples have suffered obvious changes. Under the same condition, electron irradiation induced defects have fast recovery behavior in the FeP2 ambient annealed InP. The nature of defects, as well as their recovery mechanism and influence on material property have been discussed from the results.
Proposal for single attosecond pulse production with a 43 fs super intense laser pulse
Cao Wei, Lan Peng-Fei, Lu Pei-Xiang
2007, 56 (3): 1608-1612. doi: 10.7498/aps.56.1608
Abstract +
High harmonics generation (HHG) from Ne atom driven by a multi-cycle 43 fs laser pulse is investigated. The numerical simulation demonstrates that when the intensity of the driving laser is over-saturated, the atom will be ionized rapidly during a few optical cycles, this will lead to a continuous multi-plateau structure in the cutoff region of the high harmonics spectrum from the neutral atom. It is also shown that the signal of high-order harmonics from the ion becomes remarkable when the driving laser is super intense. The superposition of an appropriate sub-plateau can give single attosecond soft X-ray pulse, and the effect of HHG from ion has been eliminated through the band selection.
Grating optimization and experiment on high-power distributed feedback lasers
Fu Sheng-Hui, Song Guo-Feng, Chen Liang-Hui
2007, 56 (3): 1613-1616. doi: 10.7498/aps.56.1613
Abstract +
Coupling coefficient is an important parameter for distributed feedback lasers. Modified coupled-wave equations are used to calculate the effect of grating shape on coupling coefficient of the second-order gratings. Corresponding devices demonstrate that the maximum kink-free power per facet reaches 50 mW and the sidemode suppression ratio is 36 dB.
The calculation of electronic structure in GaN/AlN quantum dots with finite element method
Liang Shuang, Lü Yan-Wu
2007, 56 (3): 1617-1620. doi: 10.7498/aps.56.1617
Abstract +
We investigate electronic structure theoretically in strained GaN/AlN quantum dots (QDs) with wurtzite (WZ) crystal structure. The QD electron energy levels are calculated using the finite element method (FEM) in the framework of effective mass approximation (EMA). We analyze the influence of strain and polarization to the electron energy levels and calculate electron energy levels with different dot sizes. It is shown that the strain dependent deformation potential and piezoelectric potential increase the electron energy levels and split the degenerate states. The electron energy levels decreases rapidly with increasing QD height, which is partly due to the confinement energy reduction. However, the piezoelectric field makes a more significant contribution.
Study on optical properties of Er/Er+O doped GaN thin films
Xu Xu-Rong, Song Shu-Fang, Chen Wei-De, Xu Zhen-Jia
2007, 56 (3): 1621-1626. doi: 10.7498/aps.56.1621
Abstract +
We extend the use of Raman spectroscopy to investigate the modes of Er-implanted and Er+O co-implanted GaN, and discuss the influence of O ions on Er3+-related infrared photoluminescence (PL). It is found that Er3+ implantation introduces new Raman peaks in Raman spectra at frequencies 300 and 670 cm-1, and one additional new peak at 360cm-1 is introduced after Er+O implantation. It is proposed that the broad structure around 300 cm-1 mode originates from disorder-activated scattering (DARS). The Raman peak at 670 cm-1 is assigned to nitrogen vacancy related defects. The 360 cm-1 peak is attributed to the O implantation induced defect complexes (vacancies, interstitial, or anti-sites in the host). The appearance of the 360 cm-1 mode results in the decrease of the Er3+-related infrared PL of GaN:Er+O.
Synthesis and thermopower measurement of LixNayCoO2
Chen Xiao-Yang, Xu Xiang-Fan, Hu Rong-Xing, Ren Zhi, Xu Zhu-An, Cao Guang-Han
2007, 56 (3): 1627-1631. doi: 10.7498/aps.56.1627
Abstract +
Polycrystalline samples of LixNayCoO2 with an intergrowth structure have been successfully synthesized by solid-state reaction. The measured thermopower of LixNayCoO2 at room temperature is about 60 μV/K higher than that of NaxCoO2. Based upon the O2p characteristic for the mobile carriers, the origin of the increment in thermopower is interpreted in terms of the occupancy entropy of the O2p holes.
Dynamic electrical characteristics of organic light-emitting diodes
Zhang Xiu-Long, Yang Sheng-Yi, Lou Zhi-Dong, Hou Yan-Bing
2007, 56 (3): 1632-1636. doi: 10.7498/aps.56.1632
Abstract +
The charge carriers conduction mechanism of single-layer device ITO/Alq3(90 nm)/Al has been studied by impedance spectroscopy. According to the frequency-dependent response and its equivalent circuit model,the device can be interpreted in terms of the equivalent circuit model of a contact resistance Rs in series with a parallel combination of a capacitance Cp and a resistance Rp, and the values of Rp, Cp and Rs can be found from experimental data. Our experimental results confirmed that the charge carriers conduction mechanism of ITO/Alq3(90 nm)/Al is trap-charge limited current with exponential distribution, and the dielectric relaxation time of the material decreases dramatically with increasing applied bias voltages.
Theoretical study on electric-pulse-induced resistance change in perovskite Pr1-xCaxMnO3 films
Li Qian, Liu Su, Liu Mei, Wang Zhi-Guo, Xing Zhong-Wen
2007, 56 (3): 1637-1642. doi: 10.7498/aps.56.1637
Abstract +
We developed a effective tunneling model to study the electric-pulse-induced resistive switching (EPIR) effect in PCMO films, and find that the tunneling probability of the charge transport at interfaces plays an important role in the EPIR effect. We also study the nonvolatile characteristics and the hysteretic current-voltage curve in the PCMO films, the calculated results consistent with the recent experimental data. This electric-pulse- induced resistive switching effect at room temperate has excellent potential of application.
The electronic states in one-dimensional disordered system with long-range correlations
Xu Hui, Deng Chao-Sheng, Liu Xiao-Liang, Ma Song-Shan, Wu Xiao-Zan
2007, 56 (3): 1643-1648. doi: 10.7498/aps.56.1643
Abstract +
We generated the long-range correlated random energy sequences with the power-law spectral density s(q)∝q-p in the one-dimensional Anderson disordered chain, and then investigated the localization length by using the transfer matrix method. The density of electronic states were also analyzed with the help of the negative eigenvalue theory. Then we made a comparison between the results and that of the system which does not have long-range correlations. Our results show that after introducing the long-range correlations in the one-dimensional Anderson disordered chain, the properties of electronic states change greatly, and when the correlation exponent p≥2.0, there exists a localization-delocalization transition at the energy band center. Accordingly, the density of electronic states changes obviously and presents six van Hove singul arities, and moreover, the energy band of the system also extends slightly, accompanying the above changes.
Spin polarized transport properties for quantum wire irradiated by THz electromagnetic wave
Zhou Guang-Hui, Xiao Xian-Bo, Li Xiao-Mao
2007, 56 (3): 1649-1654. doi: 10.7498/aps.56.1649
Abstract +
We theoretically study the spin-polarized electron transport properties of a quantum wire under irradiation of a transversely polarized external electromagnetic (EM) wave in the presence of Rashba spin-orbit interaction (SOI). Using the free-electron model and the scattering matrix approach, we show that spin polarization is independent on the EM frequency and the electron incident energy when Rashba SOI is weak, while it is strongly dependent on the EM frequency and the incident energy when Rashba SOI is comparatively strong. In addition, an unusual step-structure appears in the electronic transmission probability as the incident energy increases to a threshold value when a coherent EM field is applied. We demonstrate that the first effect comes from Rashba subband intermixing and the latter comes from inelastic scattering of electrons with lateral photons through intersubband transitions.
Performance of CdTe solar cells with different back electrodes and back contact layers
Yan Qiang, Song Hui-Jin, Zheng Jia-Gui, Feng Liang-Huan, Cai Wei, Cai Ya-Ping, Zhang Jing-Quan, Li Wei, Li Bing, Wu Li-Li, Lei Zhi
2007, 56 (3): 1655-1661. doi: 10.7498/aps.56.1655
Abstract +
In this paper, the effects of Ni and Au back electrode on the performance of CdTe solar cells and the mechanisms have been studied by experiment. Among the back electrodes of Ni, Ni/Au, Au/Ni and Au film, only when the Ni film contacts the ZnTe/ZnTe:Cu complex layers, does the conversion efficiency increase with the short current increasing. So it is probable that the conversion efficiencies of cells will be increased by 4% at least, and the cost in large scale manufacturing will be cut down. By analyzing the dark C-V/I-V cures and the XPS using different back electrode films, it has been found the concentration and depth of Ni diffusion in the ZnTe/ZnTe:Cu back contact layer are greater than that of Au. What's more, most Nix+ combine with the abundant Te ions in ZnTe/ZnTe:Cu back contact layer to form the NixTe. So the diffusion concentration is increased, which makes the characters of CdTe improved.
Characteristics of degradation under GIDL stress in ultrathin gate oxide LDD nMOSFET’s
Chen Hai-Feng, Hao Yue, Ma Xiao-Hua, Tang Yu, Meng Zhi-Qin, Cao Yan-Rong, Zhou Peng-Ju
2007, 56 (3): 1662-1667. doi: 10.7498/aps.56.1662
Abstract +
The threshold voltage (VTH) degradation have been investigated under GIDL (gate induced drain leakage) stresse in LDD nMOSFET with 1.4 nm-thick gate oxide. The trapped holes and interface states generated in the stress process at interface around LDD overlapping region result in the increase in VTH. The logarithm of VTH degradation after GIL stresses at constant VDG is proportional to the ratio of VD/VDG. The VTH degradation after GIDL stresses at constant VD increases with increasing VG in the stress, and that after GIDL stresses at constant VG increases with increasing VD in the stress In the last two cases the VTH degradation is always linear with the reciprocal of the bias which changes in the stress, and the absolute values of degradation slopes are 0.76 and 13.5, respectively. Experimental result shows that the degradation depends more strongly on VD than on VG.
Fabrication of SOI material based on smart-cut technology
Shu Bin, Zhang He-Ming, Zhu Guo-Liang, Fan Min, Xuan Rong-Xi
2007, 56 (3): 1668-1673. doi: 10.7498/aps.56.1668
Abstract +
The process of the low-temperature-direct-bonding and smart-cut technologies is optimized, and the SOI material is fabricated at 550℃ under 2.1×10-2 Pa. The bonding strength of this structure is 153.7 kg/cm2, the total thickness variation and the defect density of the top monocrystalline silicon film are 8.5 nm and 90 cm-2, respectively. This method can produce a good insulator layer between active layers in the fabrication of the three-dimensional integrated circuits (3D ICs), avoiding the unfavorable effects of the high-temperature process on the device structure, material quality and performance of the active layers. At the same time, the high quality monocrystalline silicon layer can be available for producing subsequent active layers in the fabrication of the 3D ICs.
The effect of terminal group on the electronic transport property of alkanethiol self-assembled monolayer
Hu Hai-Long, Zhang Kun, Wang Zhen-Xing, Kong Tao, Wang Xiao-Ping, Hu Ying
2007, 56 (3): 1674-1679. doi: 10.7498/aps.56.1674
Abstract +
The electronic transport properties of the alkanethiol self-assembled monolayer (SAM) with various terminal groups on Au (111) surfaces have been investigated by the conducting atomic force microscopy (CAFM). The results show that the terminal group has obvious effect on the conductance of the SAMs. Combining the X-ray photoelectron spectrum (XPS) analysis and CAFM, we have further studied the relationship between the conductance of SAM and the C1s binding energy of the terminal group of the molecule. It is found that the higher the binding energy, the lower the conductance of the SAM. We attribute this behavior to that the high binding energy would induce strong electronic localization in the terminal group of alkanethiol molecule, which results in raising the effective barrier of the electron injecting into the molecular chains and reducing the transport ability of the electrons in the molecule. In addition, we also find that different group terminated SAMs have different surface potentials, which can shift the zero point of I-V curve of SAMs.
Phase transition and vortex noise spectrum in two-dimensional Josephson-junction array
Wu Bing-Guo, Zhao Zhi-Gang, You Yu-Xin, Liu Mei
2007, 56 (3): 1680-1685. doi: 10.7498/aps.56.1680
Abstract +
Using the resistively shunted junction (RSJ) model,we calculate the temperature dependence of vorticities and fluctuations of vorticities in two-dimensional Josephson junction array (JJA). It is found that the phase transition is of the Berezinski-Kosterlitz-Thouless (KTB) type. We also study the temperature and driving current dependence of the noise power spectrum in the vicinity of phase transition. The calculated results are consistent with recent experimental reports, and the main characteristics of the noise power spectrum can be explained by the motion of vortices.
Characteristics of the Si-doped ferromagnetic shape memory alloy Co50Ni21Ga29Six
Dai Xue-Fang, Liu Zhu-Hong, Yu Shu-Yun, Chen Jing-Lan, Wu Guang-Heng, Wang Xin-Qiang, Liu Guo-Dong
2007, 56 (3): 1686-1690. doi: 10.7498/aps.56.1686
Abstract +
In order to improve the properties of Co—Ni—Ga alloys, experiments of adding Si to Co50Ni21Ga29 alloys were carried out to examine the effect of Si in quaternary Co50Ni21Ga29Six (x=1—2) alloys on their structure, martensitic transformation behavior and magnetic properties. The Co50Ni21Ga29Six (x=1,2) single crystals were successfully grown. All the samples with low Si doping show a sharp martensitic transformation with increasing temperature. The single crystal samples show a completely recoverable two-way shape memory with a strain of 2.5% upon the thermoelastic martensitic transformation. A large magnetic-field-induced strain of 110 ppm was measured at room temperature. A small quantity of Si doping can down-shift the martensitic transformation temperature, reduce the thermal hysteresis, decrease the magnetization but increase the Curie temperature. Especially, the Si doping can increase the magnetic anisotropy of Co—Ni—Ga-alloys, which is available to obtain large magnetic-field-induced strain in a low magnetic field. An electronic resistance “jump" of 4.5% upon the thermoelastic martensitic transformation was also reported.
Phase diagrams and magnetization behaviors of transverse random crystal field Ising model
Xu Ling, Yan Shi-Lei
2007, 56 (3): 1691-1696. doi: 10.7498/aps.56.1691
Abstract +
Within the framework of the effective field theory (EFT) and cutting approximation, the spin-1 transverse random crystal field Ising model is investigated for a square lattice. We discuss in detail the influence of transverse random crystal field concentration and crystal field ratio on the phase diagram and magnetization behavior. We give phase diagrams in T-Dx space and magnetization curves in m-T space. Under crystal field dilution condition, there exists the peak value of critical temperature in the direction of negative crystal field and reentrant phenomena in the direction of positive critical field. While choosing crystal field ratio α=+0.5 and α=-0.5, the range of magnetic ordered phase shrinks. In particular, we found, with decreasing of concentration, the peak value of critical temperature undergoes a crossover from negative to positive direction of transverse crystal field when the ratio α=-0.5. The magnetization behaviors have apparent difference for a given negative crystal field value when the crystal field ratio is different. We give a meaningful comparison with the results of Ising model with longitudinal dilution crystal field.
The effective magnetic anisotropy of nanocrystalline Fe39.4-xCo40Si9B9Nb2.6Cux alloys
Wang Guang-Jian, Han Xian-Tang, Wang Zhi, Ma Xiao-Hua
2007, 56 (3): 1697-1701. doi: 10.7498/aps.56.1697
Abstract +
The effective magnetic anisotropy of nanocrystalline Fe39.4-xCo40Si9B9Nb2.6Cux alloysHan Xian-Tang1) Wang Zhi1) Ma Xiao-Hua1) Wang Guang-Jian2)The effective magnetic anisotropy 〈K〉 of nanocrystalline Fe39.4-xCo40Si9B9Nb2.6Cux(x=0.5,1,1.5) alloys annealed at different temperatures was investigated based on the law of approach to saturation at room temperature. The experimental results showed that the grain size D of samples with low content of Cu (x=0.5) is larger and a hard magnetic phase precipitated from the residual amorphous matrix at lower annealing temperature which lead to a higher value of 〈K〉. And with increasing content of Cu, which effectively refined the grains and retarded the formation of borides at x≥1,a clear drop tendency of 〈K〉 was observed. The correlation between 〈K〉 and D as well as 〈K〉 and initial permeability μi was also discussed.
XRD analysis on lattice structure of La1-xTexMnO3
Chen Zheng-Hao, Tan Guo-Tai
2007, 56 (3): 1702-1706. doi: 10.7498/aps.56.1702
Abstract +
Based on X-ray powder diffraction data, the lattice structure and symmetry of La1-xTexMnO3 (0.04≤x≤0.2) have been analyzed by Rietveld refining method. the results show that all samples structure have a rhombohedral symmetry with space group R3C, and the lattice of MnO6 octahedron has a stretching distortion due to the difference in cation size. Besides, the degrec of structure distortion is closely related to Te content and can be depicted with the following three factors: the Mn—O—Mn bond angle θMn—O—Mn, the average A-site radius 〈rA〉 and the A-site sizemismatch σ2. According to the changing trend of these factors, several conjecture on physical properties are discussed, including the Curie temperature, spin-glass and phase separation etc.
Peculiar transport properties and CMR effect of La0.67Sr0.08Na0.25MnO3
Tang Yong-Gang, Yan Guo-Qing, Guo Huan-Yin, Mao Qiang, Peng Zhen-Sheng
2007, 56 (3): 1707-1712. doi: 10.7498/aps.56.1707
Abstract +
The La0.67Sr0.08Na0.25MnO3 sample was prepared by solid-state reaction. The transport properties and CMR effect of the sample were studied through M-T curves, ρ-T curves and ρ-T fitted curves. The results show that: Both the ρ-T curves and the MR-T curve exhibit the double-peak phenomenon; the high-temperature peak corresponds to the I-M transition accompanied by the PM-FM transition, and the low-temperature peak is attributed to grain boundary effect. The two insulator phases have different transport mechanisms: in the low temperature range(248 KTρ(T) accords with variable-range-hopping model of polaron, while in the high temperature range(330 KTρ(T) accords with near- neighbor- hopping model of polaron; and the two metal-like phases also have different transport mechanisms: in the low temperature range(67 KTρ(T) accords with the ρ-T2.5 relation, and the transport mechanism is the actions of spin wave scattering and electron-magneton scattering, while in the high temperature range(292 KTρ(T) accords with the ρ-T2 relation, and the transport mechanism is single magneton scattering.
A numerical study on the aging of two-dimensional spin systems
Zheng Bo, Ying He-Ping, Lei Xiao-Wei
2007, 56 (3): 1713-1718. doi: 10.7498/aps.56.1713
Abstract +
With a large-scale Monte Carlo simulation, the aging of the two-dimensional dynamic Ising and XY models is numerically studied. Starting from a disordered state, the systems are quenched to critical temperature Tc and then evolve according to dynamics of model A. By calculating the autocorrelation function A(t,t′) we observe the aging phenomenon for both spin systems. Then, relatively accurate values of the dynamic critical exponent λc and z are estimated. Especially, we confirm that for the two-dimensional XY model, there is a strong logarithmic correction to scaling in the dynamic relaxation starting from a completely disordered.
Magnetic and magneto-optical properties of perpendicularly c-axis orientated FePt thin films
Wang Shu-Hua, Zha Chao-Lin, Gao Jing, Ma Bin, Zhang Zong-Zhi, Jin Qing-Yuan
2007, 56 (3): 1719-1724. doi: 10.7498/aps.56.1719
Abstract +
A series of FePt thin films with perpendicular c-axis orientation were deposited on single crystal MgO (001) substrates by DC magnetron sputtering. With the increase of substrate temperature during deposition, FCC disordered structure transforms to FCT ordered structure (L10 phase) gradually, and the chemical ordering parameter increases simultaneously. Furthermore, the magneto-crystalline anisotropy, coercivity and squareness ratio of the hysteresis loops along perpendicular direction increase also. The magneto-optical Kerr spectra were found to be changing notablely with the chemical ordering of FePt films.
The magnetic interactions in FePt nanocomposite film
Zhan Xiao-Yuan, Zhang Yue, Qi Jun-Jie, Gu You-Song, Zheng Xiao-Lan
2007, 56 (3): 1725-1729. doi: 10.7498/aps.56.1725
Abstract +
Fe53Pt47 nanocomposite films have been deposited on naturally oxidized Si(100) substrates by magnetron sputtering. The relationship between the grain size, the magnetic interaction and the annealing temperature have been studied. The FePt films exhibit magnetically hard property with average grain size of about 20 nm after annealing at 400℃, and exchange spring behavior was found in the sample because it is composed of magnetically soft γ-FePt phase and hard γ2-FePt phase. As the annealing temperature increases, the content of the γ2-FePt phase increases, at the same time, the grain size gets large, and the exchange spring behavior in some particles was discoupled. The static magnetic interaction only occur between the FePt particles in the film annealed at 600℃.
Effect of Ti(Cr) underlayer on the magnetic properties and microstructure of CoCrTa film for perpendicular magnetic recording media
Zhen Cong-Mian, Ma Li, Zhang Jin-Juan, Liu Ying, Nie Xiang-Fu
2007, 56 (3): 1730-1734. doi: 10.7498/aps.56.1730
Abstract +
C/CoCrTa/X (X=Cr, Ti) films were fabricated with DC facing target magnetron sputtering apparatus. Their magnetic properties and microstructure were characterized by vibrating sample magnetometer (VSM), X-ray diffraction (XRD), and scan probe microscope (SPM), respectively. The experimental results indicate that the Ti underlayer can induce the c-axis orientation of Co grain in the direction perpendicular to the film surface. For samples with Ti underlayer, the grain size and the surface roughness are relatively finer, and magnetic domains can be observed obviously. These results show that the sample with Ti underlayer is more suitable for the perpendicular magnetic recording media.
Enhanced ferroelectricity of Pb(Zr0.5Ti0.5)O3 film by the introduction of La0.3Sr0.7TiO3 template layer
Wang Xiu-Zhang, Liu Hong-Ri
2007, 56 (3): 1735-1740. doi: 10.7498/aps.56.1735
Abstract +
LaNiO3(LNO) and LaNiO3/La0.3Sr0.7TiO3 (LNO/LSTO) bottom electrodes were prepared on Si(111) substrates by sol-gel process. Then Pb (Zr0.5Ti0.5)O3 (PZT) ferroelectric films were then deposited on the bottoms also by sol-gel process. XRD showed that both of the PZT films have perovskite structure. The one on LNO bottom adopts (100) preferred orientation and the one on LNO/LSTO bottom adopts random orientation. The results of ferroelectric measurement showed that the ferroelectricity of the PZT film on LNO/LSTO bottom electrode was substantially enhanced compare with the one on LNO bottom electrode. The coercive field was also enhanced. The film on LNO/LSTO bottom electrode has larger dielectric constant and leakage current.
Effect of the secondary crystal field-effect and the exchange interaction on magnetic and magneto-optic properties of PrF3
Zhang Xue-Long, Xia Tian, Zhang Guo-Ying, Xue Liu-Ping
2007, 56 (3): 1741-1745. doi: 10.7498/aps.56.1741
Abstract +
In the PrF3 crystal, the lowest crystal field state of Pr3+ ion is a single state, which has no contribution to the susceptibility and the Verdet constant of the crystal in first-order effect. The secondary crystal field-effect admixes the state with other states and makes the state have a great contribution to the magnetic properties of PrF3 crystal. In this paper, the effect of secondary crystal field-effect on the magnetic and magnetio-optic properties of PrF3 crystal is presented. Furthermore, the effective field of exchange interaction between the ions is investigated, which has the form is Hin=(1.9-0.02556 T)×10-5M. By means of the effective field, the inverses of the magnetic susceptibility and Verdet constant of PrF3 crystal as functions of temperature are calculated, and the results are in good agreement with the measured ones. The results show that the crystal field's second-order contribution and exchange interaction between ions shouldn't be ignored.
Reflected Gaussian beam splitting phenomenon in the thin-film Fabry-Perot filter
Ma Xin, Li Ming-Yu, Liu Xu, Zhang Jin-Long, Li Yi-Yu, Sun Xue-Zheng, Gu Pei-Fu
2007, 56 (3): 1746-1750. doi: 10.7498/aps.56.1746
Abstract +
A numerical method to simulate the splitting of the reflected Gaussian beam in the thin-film Febry-Perot filter is described. The splitting can be simply explained by studying the reflection curve. The thin-film Febry-Perot filter has been fabricated by coating TiO2 and SiO2 on glass. The reflected beam splitting phenomenon is observed and measured in practice. The theoretical result is in accord with the experimental result.
Spectroscopic properties of self-exited Raman scattering of the Nd3+:SrMoO4 crystal
Han Lin, Song Feng, Wan Cong-Shang, Zou Chang-Guang, Yan Li-Hua, Zhang Kang, Tian Jian-Guo
2007, 56 (3): 1751-1757. doi: 10.7498/aps.56.1751
Abstract +
The spectral performance of a self-Raman-active material (Nd:SrMoO4 crystal) was investigated. Its stimulated Raman scattering (SRS), absorption spectra, luminescence lifetime, and infrared emission under 808 nm LD excitation were measured at room temperature. All vibration modes in the SRS spectra were identified. The most intense vibration is Ag (898 cm-1) mode, which is assigned to fully symmetric extension vibrations of the (MoO2-4) group. Optical parameters were calculated from absorption spectra with Judd-Ofelt (J-O) theory. The integrated emission cross-section and spontaneous emission probability corresponding to 1068 nm emission are 0.57×10-18 cm2 and 141.06 s-1, respectively. The lifetime of the 1068 nm emission was measured to be 0.2 ms. Considering the infrared luminescence excited by 808 nm LD, the possibility of obtaining 1180 nm first-Stokes component relevant to the 1068 nm emission is demonstrated. These conclusions can be our guidance to develop high-efficiency new-wavelength self-excited Raman lasers.
Investigation of spectral properties and thermal stability of Er3+/Yb3+ co-doped TeO2-B2O3-SiO2 glasses
Zhang Xiang-Hua, Zhang Xu-Dong, Xu Tie-Feng, Nie Qiu-Hua, Dai Shi-Xun, Shen Xiang, Lu Long-Jun
2007, 56 (3): 1758-1764. doi: 10.7498/aps.56.1758
Abstract +
A series of Er3+/Yb3+ co-doped (85-x) TeO2-15B2O3-xSiO2 (TBS x=0,5,10,15,20 mol%) glasses have been prepared. The thermal stability, absorption and emission spectra, lifetime of Er3+: 4I13/2 level and infrared transmit spectra were measured and discussed. The emission spectra of Er3+:4I13/2→4I15/2 transition was analyzed using a peak-fit routine, and an equivalent four-level system was proposed to estimate the Stark splitting for the 4I15/2 and 4I13/2 levels of Er3+ ions. It was found that the thermal stability of these glasses was improved by introducing SiO2. The difference between the glass transition temperature (Tg) and the crystallization onset temperature (Tx), ΔT=Tx-Tg, have came to 178℃ when SiO2 was 20 mol%, indicating that they were suitable for fiber drawing. The fluorescence full width at half maximum (FWHM) and peak of emission cross-section (σpeake) of Er3+ ions in different glass hosts have been compared. The results indicate that these new TBS glasses are promising host material for broadband amplifiers.TeO2-B2O3-SiO2, thermal stability, G
The luminescent properties of YBO3:Eu3+ nanocrystal
Luo Wen-Xiong, Huang Shi-Hua, You Fang-Tian, Peng Hong-Shang
2007, 56 (3): 1765-1769. doi: 10.7498/aps.56.1765
Abstract +
YBO3:Eu3+ nanoparticles have been prepared by hydrothermal method. The size and morphology of the nanoparticles were controlled by the reaction conditions. The luminescence of the nanoparticles has been investigated and compared to that of the bulk YBO3:Eu3+. In nano-sized materials, a large portion of doped rare earth ions located at the sites with micro-environments are affected by the surface. Such an influence could enhance the Judd-Ofelt Ω2 parameter, and hence increase the relative intensity of the Eu3+5D0→7F2 emission and improve the chromaticity of the red phosphor.
Research on several parameters influencing on laser cooling of solids
Jia You-Hua, Yin Jian-Ping, Ji Xian-Ming
2007, 56 (3): 1770-1774. doi: 10.7498/aps.56.1770
Abstract +
Laser cooling of solids is also called anti-Stokes fluorescent cooling, it is a new optical cooling technology in recent years. We propose a two-level model to analyze the absorption and stimulated-emission processes between the Yb3+2F7/2 ground-state manifold and the 2F5/2 excited-state manifold, and discuss several parameters that influence the cooling power, and find some ways to improve the cooling power. The influences of the doped concentration, pumping power and the effective pump-spot area on cooling are particularly analyzed. At the same time, we make computer simulation about the cooling process and obtain the temperature as a function of the cooling time, which is similar to the experimental results. So this shows that our model is reasonable.
High quality SnO2 crystals grown with catalyst-assistance and study on their photoluminescent spectroscopy
Ding Cai-Rong, Wang Bing, Yang Guo-Wei, Wang He-Zhou
2007, 56 (3): 1775-1778. doi: 10.7498/aps.56.1775
Abstract +
SnO2 nanocrystals were synthesized, and their photoluminescence spectra revealed the following results. Firstly, we found that the main emission peak of the sample grown with catalyst-assistance is the emission peak of band gap (3.68 eV), and the photoluminescence efficiency of the crystal grown with catalyst-assistance is much higher than that without it. These results show that the quality of the crystal grown with catalyst-assistance is much improved. Furthermore, the emissions of twin-born crystal surfaces (101) and (101)T are demonstrated from the results of the deconvolution of photoluminescence spectra.
The optical properties of conical bubble sonoluminescence in glycol
He Shou-Jie, Zhang Zi-Sheng, Zhao Zeng-Chao, Dong Li-Fang, Wang Zhi-Jun, Ha Jing, Wang Long
2007, 56 (3): 1779-1784. doi: 10.7498/aps.56.1779
Abstract +
Using an improved conical bubble U tube, the optical properties of conical bubble sonoluminescence in glycol are measured. A strong single flash is observed and the width of light pulse reaches 150 us, which is much higher than that of the results obtained by other methods. The spectrum is a continuum ranging from ultraviolet to visible region, superposed with the spectral line of the 3P-3S transition of sodium around 589 nm. The blue satellite bands of Na-Ar has been measured on the sides of atomic spectral line; the red satellite band of Na-Ar and the 3S-4S atomic spectral line of Na are firstly measured in sonoluminescence.
As-soak dependence of interface roughness of AlSb/InAs superlattice
Li Zhi-Hua, Wang Wen-Xin, Liu Lin-Sheng, Jiang Zhong-Wei, Gao Han-Chao, Zhou Jun-Ming
2007, 56 (3): 1785-1789. doi: 10.7498/aps.56.1785
Abstract +
Different As-soak time is applied during InSb-like interfaces growth of InAs/AlSb superlattices on GaAs(100) substrates. The interface roughness is studied by grazing incidence X-ray reflectivity. The reflectivity curves are simulated by standard software and the rms roughness of the interfaces is obtained. It was hown that the sample with As-soak time of 20 seconds has the most smooth interfaces. By analyzing the microscope images of the samples, we suggest that In-rich interfaces will be formed with too short As-soak time and AlAs-like interfaces are obtained with too long As-soak time, and in hoth cases the interface will be cearsened. Grazing incidence X-ray reflectivity is also recommended as a powerful tool for assessing the structure of superlattices.
Preparation of polycrystalline V0.97W0.03O2 thin films with ultra high TCR at room temperature
Li Jin-Hua, Yuan Ning-Yi, Xie Tai-Bin, Dan Di-Di
2007, 56 (3): 1790-1795. doi: 10.7498/aps.56.1790
Abstract +
The W doped vanadium oxide film was deposited on the SiO2 substrate by modified ion beam enhanced deposition (IBED) method. The V2O5 and WO3 mixed powders, atom ratio of W/V being 3/97, were pressed as the sputtering target. After annealed in Ar or N2 the polycrystalline IBED VO2 film doped with tungsten was obtained. The annealed IBED V0.97W0.03O2 film was orientated only to [002] of VO2 structure, and the latice parameter d was larger than that of VO2 crystal powder measured by X-ray diffraction. The results of resistance-temperature test showed that the phase transition temperature was decreased from 68℃ to 28℃. The thermal coefficient of resistance (TCR) was high up to 10 %/K at 300K. With the ionic radius of tungsten larger than the radius of vanadium, W6+ ion doping would induce a tension stress into the film. As a result, the transition temperature of the W-doped VO2 films was decreased to the room temperature, and the TCR was increased greatly.
The effect of composition of the catalysts on the preparation of single-walled carbon nanotubes
Niu Zhi-Qiang, Fang Yan
2007, 56 (3): 1796-1801. doi: 10.7498/aps.56.1796
Abstract +
The Mo-Co-MgO and W-Co-MgO catalysts were first prepared by the citric acid method. The single-walled carbon nanotubes(SWCNTs) were synthesized by decomposing CH4 in Ar over the Mo-Fe-MgO,Mo-Co-MgO and W-Co-MgO catalysts at 1123 K in the fluidized bed reactor. The effects of composition of the catalysts on the synthesis of SWCNTs were studied by Raman spectroscopy and transmission electron microscopy (TEM). And the mechanism of growth of SWCNTs was discussed. The results show that the citric acid method is effective for to preparing the catalysts and the high-quality SWCNTs were synthesized over the three catalysts. At 1123 K, the growth of SWCNTs over the catalysts may be similar to the liquid micro-area model. The dependence of diameter distribution on the composition of the catalysts was weak. There were some differences in the inner structure of SWCNTs synthesized over the three different catalysts. The carbon yield rates of products were increased by the addition of W and Mo in the catalysts.
Study of FN-DLC thin films: (Ⅰ) sp structure and chemical bond analysis
Wang Huan-You, Xu Hui, Guo Ai-Min, Xiao Jian-Rong
2007, 56 (3): 1802-1808. doi: 10.7498/aps.56.1802
Abstract +
Nitrogen doping of fluorinated diamond-like carbon (FN-DLC) thin films were prepared by radio frequency plasma enhanced chemical deposition (RF-PECVD) under different radio frequency power (RF-power) with CF4, CH4 and nitrogen as source gases. The sp hybrid structure and chemical bond structure of the films were characterized by Auger electron spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared absorption spectrometry, and the sp2/sp3 hybrid ratios were analyzed by fitting multi-peaks of Gauss an form. The results show that the thin films are a type of diamond-like carbon films. The sp2/sp3 hybrid ratios in the films deposited by different RF-power lie between 2.0 to 9.0. The sp2 structure in the films increases with the increasing RF-power. The chemical bond structure in the films are C—Fx(x=1,2),C—C, C=C and C≡N. The C—C bond increases with the increasing RF-power, while the C—F bond decreases. Higher RF-power is shown to reduce the F content in the films. The degree of cross-linking in the films is enhanced and the films become more stable with increasing RF-power.
Study on FN-DLC thin films: (Ⅱ) effect of radio frequency power on the optical band gap of the thin films
Wang Huan-You, Xu Hui, Guo Ai-Min, Xiao Jian-Rong
2007, 56 (3): 1809-1814. doi: 10.7498/aps.56.1809
Abstract +
FN-DLC thin films, radio-frequency power, optical band gap
A theory of polymer solubility parameter
Ji Qing, Qiao Bao-Fu, Zhao De-Lu
2007, 56 (3): 1815-1818. doi: 10.7498/aps.56.1815
Abstract +
Recently, our group introduced Gibbs distribution into Flory—Huggins polymer solution theory. It reasonably describes the polymer cohesion energy. In the present study, we applied the said theory to calculate the polymer solubility parameter and a more accurate value has been found. It indicates that the present theory is reliable and can be used to compute polymer solution parameters.
Effect of far field flow on the spherical crystal in the undercooled melt
Wang Zi-Dong, Sun Ren-Ji, Chen Ming-Wen
2007, 56 (3): 1819-1824. doi: 10.7498/aps.56.1819
Abstract +
The influence on the growth morphology of the spherical crystal in the undercooled melt imposed by the far field flow is studied by the asymptotic method. It is shown that the far field flow leads to convection in the melt such that the front interface of a growing spherical crystal grows into the undercooled melt in the opposite direction to the flow and enhances the growth rate in the same direction, while the back interface of the growing spherical crystal decays. On the other hand, the front interface of a shrinking spherical crystal further decays, and the back interface of the shrinking spherical crystal decays slower.
Application of fiber mode mixer in differential optical absorption spectroscopy
Si Fu-Qi, Liu Jian-Guo, Xie Pin-Hua, Zhang Yu-Jun, Li Ang, Qin Min, Li Yu-Jin, Dou Ke, Li Su-Wen, Liu Wen-Qing
2007, 56 (3): 1825-1830. doi: 10.7498/aps.56.1825
Abstract +
Differential optical spectroscopy (DOAS) has become an important method for determination of tropospheric trace gases, using the photomultiplier (PMT) as detector. The use of photodiode array (PDA) detectors enhances DOAS system considerably owing to PDA's higher sensitivity and advantage in multi-channel application. When the PMT is simply replaced by PDA, a difference between lamp spectrum and atmosphere spectrum, as will as unwanted standard deviation of residual noise as much as 1.4×10-3 appears after corrected for the pixel response. A fiber mode mixer, based on fiber disturb mode principle was developed and tested. This new device reduces the standard deviation to 3.4×10-4 in field experiments.
The mechanism of self-assembly of polystyrene submicrospheres at water-air interface
Wang Xiao-Dong, Dong Peng, Chen Sheng-Li, Yi Gui-Yun
2007, 56 (3): 1831-1836. doi: 10.7498/aps.56.1831
Abstract +
The mechanism of polystyrene submicrospheres assembling in aqueous suspension was studied systemically. During the evaporation of solvent, the PS spheres were transported to the water-air inter-surface, where these spheres self-assemble into colloidal crystal through the capillary force between the particles at water-air interface. The wettability of the PS spheres at the water-air interface changes from complete wetting to partial wetting and finally to non-wetting with the evaporation of water, so that the contact angle between the PS spheres and water increases gradually. The experiment showed that only after the contact angle reached a critical value θ′critical, could the PS sphere-assembly occur. The critical value θ′critical obtained from the Wenzel equation was greater than the measured value θcritical=22° because the surface of the PS colloidal crystal was “regularly” coarse. The change of the PS spheres at water-air interface from the hydrophilic to hydrophobic is essential for the PS spheres to assemble into colloidal crystals.
The influence of different scale systems on precipitation analyzed on the basis of power-law exponent
Lian Yi, Feng Guo-Lin, Zhi Rong
2007, 56 (3): 1837-1842. doi: 10.7498/aps.56.1837
Abstract +
Based on the daily precipitation observations of 740 stations in China from 1960 to 2000, this paper expounds the power-law tail distribution characteristic of the daily precipitation ≥30mm in 7 climate characteristic regions, and the power-law exponent γ>3.0 in most part of China. It is found that the daily precipitation ≥30 mm is a non-stationary process, and it makes the long-term prediction of heavy rainfall very difficult. It is also found from further investigation using the filtering method that the power-law tail distribution characteristic is the result of the interaction of atmospheric systems of various scales, among them the one-week scale system has the most important influence on power-law tail exponent of the daily precipitation ≥30 mm.