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Acta Physica Sinica  
  Acta Physica Sinica--2005, 54 (3)   Published: 15 March 2005
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CLASSICAL AREA OF PHENOMENOLOGY

Effect of optical magnifications on the displacement measurements in optical tweezers system

Liu Chun-Xiang, Guo Hong-Lian, Jiang Yu-Qiang, Li Zhao-Lin, Cheng Bing-Ying, Zhang Dao-Zhong
Acta Physica Sinica. 2005, 54 (3): 01162 doi: 10.7498/aps.54.1162
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The effect of different optical magnifications on the amplitude and linearity of displacement signals measured by the photodiode quadrant detector in an optical tweezers system is studied both experimentally and theoretically. Based on the experimental results we find that the output signal with larger amplitude and more preferable linearity can be obtained when the magnified images of α particle have diameters of 50% to 60% of the detector diameter. Theoretical calculation confirms it.

Suppression of pulse walk-off effect during the process of pulse compression by cross-phase modulation of pulse pair

Xia Guang-Qiong, Wu Zheng-Mao, Chen Hai-Tao
Acta Physica Sinica. 2005, 54 (3): 01167 doi: 10.7498/aps.54.1167
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A new asymmetrical pulse pair method is proposed which can be used to suppress the pulse walk_off effect during the process of pulse compression by the cross phase modulation of pulse pair. By using asymmetrical pulse pair method and asynchronous coupling method, the suppressions of the walk_off effect have been investigated numerically. Results show that for an incident Gaussian pulse with peak power 10mW and full_width_at_half_maximum (FWHM) 5ps, we can obtain a compressed pulse with the compression factor 137, pedestal energy ratio 0122 and the peak power 116mW by adopting the asymmetrical pulse pair method.

Study on the inside source hologram reconstruction algorithm based on discrete Fourier transform

Wang Jun-Yue, Zhu Pei-Ping, Zheng Xin, Yuan Qing-Xi, Tian Yu-Lian, Huang Wan-Xia, Wu Zi-Yu
Acta Physica Sinica. 2005, 54 (3): 01172 doi: 10.7498/aps.54.1172
Full Text: [PDF 264 KB] Download:(1005)
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The inside source hologram reconstruction algorithm based on discrete Fourier transform was investigated in detail, and how to calculate the contribution of whole spherical hologram to the reconstructed image of atoms was demonstrated in this algorithm, which was previously regarded to be capable of calculating only half of the spherical hologram. Using the sampling theorem in this issue, we are able to examine such essential factors as the sampling rate of the hologram, domain and resolution of reconstructed image.

Entanglement for excitons in three quantum dots in a cavity coupled to a broadband squeezed vacuum

Tan Hua-Tang, Gan Zhong-Wei, Li Gao-Xiang
Acta Physica Sinica. 2005, 54 (3): 01178 doi: 10.7498/aps.54.1178
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The dynamical behavior of purity and entanglement for excitions in three quantum dots placed in a cavity driven by a broadband squeezed vacuum is studied in the low exciton density regime. It is found that the excitions in the three quantum dots can evolve into a pure entangled state only when the dissipation of the cavity and excitions is negligible. When the injected field into the cavity is a squeezed vacuum, the excitions will be in a three_mode Gaussian entangled mixed state even in the long time limit .Analytical expressions are derived showing the dependence of the purity and entanglement property of the excitions in the three quantum dots on the squeezing properties of the initial state prepared in the cavity and the strength of two_photon correlations of the squeezed vacuum injected into the cavity.

Entropy evolution of the field interacting with a quasi-Λ-type four-level atom

Zhou Qing-Chun, Zhu Shi-Ning
Acta Physica Sinica. 2005, 54 (3): 01184 doi: 10.7498/aps.54.1184
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The evolution of the field (atomic) entropy in a system of a quasi_Λ_type fourlevel atom interacting with an uncoupled two_mode coherent field is investigated. The effects of initial atomic state, the initial mean photon number and the splitting of the atomic energy levels on the entropy are discussed. The system reduces to that of a twolevel or threelevel atom interacting with a singlemode coherent field in special cases.

Transfer of quantum information via cavity QED technique

Xiang Shao-Hua, Song Ke-Hui
Acta Physica Sinica. 2005, 54 (3): 01190 doi: 10.7498/aps.54.1190
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We present a scheme for transferring quantum information, which is based on the nonresonant interaction of two two_level atoms with a single_mode cavity field. We show that quantum information can be transferred from one atom to another atom, and from cavity mode to two atoms by manipulating the interactions between cavity field and two atoms, and the information contained in the transferred atom or cavity mode is completely erased.

Measurement of femtosecond laser pulses using PG frequency-resolved optical gating

Wang Zhao-Hua, Wei Zhi-Yi, Zhang Jie
Acta Physica Sinica. 2005, 54 (3): 01194 doi: 10.7498/aps.54.1194
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A frequency_resolved optical gating (PG_FROG) with polarization gating technique is developed to diagnosis the characteristics of laser pulses generated from a 20_TW femtosecond laser amplifier. Based on the data of the correlation signal in time and frequency domains, we obtained the detail information on pulse shape, bandwidth, pulse duration and phase by using the retrieval algorithm. The measured results with different phase compensation are also presented and discussed.

Theoretical and experimental studies on large-ratio stretching of femtosecond pulse with ?ffner triplet stretcher

Tian Jin-Rong, Sun Jing-Hua, Wei Zhi-Yi, Wang Zhao-Hua, Ling Wei-Jun, Huang Xiao-Jun, Liu Lan-Ting, Wei Xiao-Feng, Zhang Jie
Acta Physica Sinica. 2005, 54 (3): 01200 doi: 10.7498/aps.54.1200
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The dispersive character of ?ffner stretcher was studied, and a concise expression of output pulse duration was presented. An ?ffner stretcher was setup experimentally, which could stretch a 19fs seed pulse to 605 ps after 4 passes in it free of aberration.

The main multi-pass amplifier with double-side pumped Ti:sapphire

Ling Wei-Jun, Wang Zhao-Hua, Wang Peng, Jia Yu-Lei, Tian Jin-Rong, Wei Zhi-Yi
Acta Physica Sinica. 2005, 54 (3): 01208 doi: 10.7498/aps.54.1208
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Based on the theory of multi_pass amplification, we analyse numerically the character of gain for amplified pulse and design a 6_pass amplifier. With two 13J, 532nm Nd:YAG lasers as the source, amplified pulse energy as high as 1J was obtained, which corresponds to a 38% conversion efficiency.

Investigation of Ti:sapphire femtosecond laser mode-locking mechanism

Zhang Xiao-Hua, Zhang Guang-Yin, Jiao Zhi-Yong, Gu Xue-Wen, Yan Cai-Fan, Wu Ding-Er, Chai Lu, Cao Shi-Ying
Acta Physica Sinica. 2005, 54 (3): 01213 doi: 10.7498/aps.54.1213
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In this paper,the luminescence dynamics of X_folded cavity Ti:sapphire femto_second laser has been measured,and the self_mode_locking mechanism and process of femto_second laser have been investigated systmatically by means of propagation_circle and transform_circle graphic method.A new mode_locking mechanism,self_pulsing Kerr_lens switching and magnifying mode_locking,has been put forward.

Two-dimensional silicon-based photonic crystal slab with partial air-bridge

Tian Jie, Han Shou-Zhen, Cheng Bing-Ying, Li Zhi-Yuan, Feng Shuai, Zhang Dao-Zhong, Jin Ai-Zi
Acta Physica Sinica. 2005, 54 (3): 01218 doi: 10.7498/aps.54.1218
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We describe the fabrication process of a two_dimensional silicon_based photonic crystal (PC) slab with partial air_bridge, which has a photonic band gap in the nearIR range .The process involves the formation of the air_bridge silicon slab by wet etching and the fabrication of periodic air holes by a focused ion beam. We successfully obtained such a sample and measured its transmission in a wide spectrum. It is found that the observed spectrum is consistent with the theoretical values calculated by the plane wave expansion method. The TM0_like modes reduce the size of the band gap, and the partial air bridge is beneficial to the fabrication of large PC slabs. Meanwhile, it is possible to draw light out from the supporting material of the air bridge.

Theoretical analysis of tunable wavelength conversion based on FWM in semiconductor fiber ring laser

Li Pei-Li, Zhang Xin-Liang, Chen Jun, Huang Li-Rong, Huang De-Xiu
Acta Physica Sinica. 2005, 54 (3): 01222 doi: 10.7498/aps.54.1222
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In this paper, a comprehensive broad_band dynamic model of tunable wavelength converter based on four_wave mixing in semiconductor fiber ring laser is presented. Critical factors, e.g., the materal gain profile, the longitudinal variation of the optical field, and the broad_band spontaneous noise emission are considered in the model. By numerical simulation, the effects of the input signal power, injection current, the coupling of the output coupler and the lasing wavelength on the performance of the wavelength converter are investigated. Numerical results are in agreement with the experimental results in the literature

Dispersion and polarization properties of near-rectangle core photonic crystal fibers

Lou Shu-Qin, Ren Guo-Bin, Yan Feng-Ping, Jian Shui-Sheng
Acta Physica Sinica. 2005, 54 (3): 01229 doi: 10.7498/aps.54.1229
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Dispersion and polarization properties of near_rectangle core photoric crystal fibers (PCFs) were analyzed with a full vector model. The numerical results show that the modal birefringence of near_rectangle core PCF is at least one order of magnitude higher than the conventional elliptical polarization_maintaining fibers (PMFs). In order to obtain higher birefringence, an efficient way is to increase the relative hole diameter. Zero walk_off point occurs at the longer wavelength than that of convention elliptical PMF. With increasing hole pitch, the walk_off curve and zero walkoff point would shift towards the longer wavelength region. The corresponding wavelength of zero walkoff point is in proportion to the size of the hole pitch. The occurrence of zero walkoff point can efficiently restrain the first_order polarization mode dispersion. Through choosing the suitable structural parameter of near_rectangle core PCF, we can get the more flexible dispersion properties. The approximate 400nm ultra_flatten dispersion was gotten near the wavelength 155μm for a nearrectangle core PCF with Λ=2μm and d/Λ=03 This fiber has a number of potential applications in polarization control, dispersion control and management.

Studies on the dispersion in photonic crystal fiber using the step effective index model

Zhang De Sheng, Dong Xiao Yi, Zhang Wei-Gang, Wang Zhi
Acta Physica Sinica. 2005, 54 (3): 01235 doi: 10.7498/aps.54.1235
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As a precondition , it was presented that the single_mode optical fiber , the dispersion_shift optical fiber and the dispersion_flatten optical fiber can be regarded as the special examples of the index_guiding photonic crystal fiber(PCF) under a determinate condition, when the new step effective index model (SEIM) was used to discuss the chromatic dispersion properties of PCF. The result compared with the experimental data reported in the literature indicated that such a SEIM can be used to uncover more interesting dispersion regimes in PCFs. In particular, the speed of calculation by using the SEIM is very quick. Finally, the dispersion characteristics of the PCF with different air hole diameter d, air hole pitch Λ and the core radius a were also discussed.

Theoretical study of polarization mode dispersion emulators

Zeng Li, Lou Cai-Yun, Zhang En-Yao
Acta Physica Sinica. 2005, 54 (3): 01241 doi: 10.7498/aps.54.1241
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The performances of the three polarization mode dispersion (PMD) emulators commonly used today are analyzed and compared among them through numerical simulation of their differential group delay (DGD) statistical characteristics and PMD vector autocorrelation function. The results demonstrate that to produce DGD that can match theoretical distribution, one DGD generator is adequate, while at least 15 sections are necessary in the emulator built by polarization maintaining fibers and rotatable connectors. And the autocorrelation function of the emulator based on polarization maintaining fibers depends on DGD of every section, while that of the emulator based on DGD generators is smooth and can be regarded as constant outside the central frequency range.

Lumped-mass approach for the calculation of band structure of two-dimensional phononic crystals with high contrast of elastic constant

Wang Gang, Wen Ji-Hong, Liu Yao-Zong, Yu Dian-Long, Wen Xi-Sen
Acta Physica Sinica. 2005, 54 (3): 01247 doi: 10.7498/aps.54.1247
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With each unit cell replaced by a system of finite freedoms of motion, two_dimensional phononic crystals can be simplified to an infinite discrete periodic system. Therefore, the elastic wave band structures of the two_dimensional phononic crystals can be calculated with a straightforward lumped_mass approach, whose computational cost is much lower than the well_known plane wave expansion(PWE) method. The numerical results of the two methods are in reasonable agreements. As the well_known Gibbs oscillations in the PWE can be eliminated with the lumped_mass method, this new approach is insensitive to the sharp variation of elastic constants on the interfaces inside the phononic crystals. Furthermore, the lumped_mass method can also be used to calculate the band structures of two_dimensional phononic crystals with arbitrary unit shapes easily.

The principle of statistically optimal planar near-field acoustical holography and the sound field separation technique

Li Wei-Bing, Chen Jian, Yu Fei, Bi Chuan-Xing, Chen Xin-Zhao
Acta Physica Sinica. 2005, 54 (3): 01253 doi: 10.7498/aps.54.1253
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Since the sound pressures are measured on the holographic plane with a finite size, there are windowing effects and wraparound errors in the planar near_field acoustical holography (NAH) based on spatial fast Fouries transform (FFT)_based planar NAH). In order to overcome the windowing effects and wraparound errors, statistically optimal planar near_field acoustical holography (SOPNAH) is used. The sound field superposition theory is used to prove the formulas for the SOPNAH. A simple and effective method for choosing the wave number vector is proposed by means of limiting the spatial wavenumber in the kx,ky directions and discretizing the wavenumber space plane demarcated by the maximum and minimum of kx,ky. To overcome the limitation, that sound field on one side of the holographic plane must be free, in the application of the normal SOPNAH, the sound field separation technique with double holographic planes is proposed. Some results of experiment and numerical simulation are presented to demonstrate the validity of the formulas.

Mechanism of broad acoustic band-gap in the three-component composite

Hua Jia, Zhang Shu, Cheng Jian-Chun
Acta Physica Sinica. 2005, 54 (3): 01261 doi: 10.7498/aps.54.1261
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Mechanism of broad acoustic band_gap in the two_dimensional three_component composite is investigated by calculating acoustic transmission spectra and acoustic fields for different inserted steel rows embedded in epoxy resin matrix with or without rubbers as the coating material. By comparing the acoustic fields inside the two_ and three_component crystal slabs, one can conclude that the broad acoustic band_gap in the three_component crystal slab is formed by the coexistence of the Bragg reflection of a periodic structure and the localized resonance in the soft rubber. The former is evidence in higher frequency and the latter is dominant in lower frequency with the wavelength longer than that of the coating layer.

A study of a kind of hyper chaotic cryptosystem security

Xie Kun, Lei Min, Feng Zheng-Jin
Acta Physica Sinica. 2005, 54 (3): 01267 doi: 10.7498/aps.54.1267
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In this note, we apply the sub_sampling idea to the design of the chaotic secure communication system and analyze the Lorenz system and a kind of hyper chaotic system. The result obtained indicates that the security of the cryptosystem is not only determined by the dimension, but also related with the sampling interval. Then, we verify these two systems using the VWK (Volterra_Wiener_Korengerg) nonlinear test and surrogate data test methods.

Phenomena of impact bifurcations in vertically vibrated granular beds

Jiang Ze-Hui, Li Bin, Zhao Hai-Fa, Wang Yun-Ying, Dai Zhi-Bin
Acta Physica Sinica. 2005, 54 (3): 01273 doi: 10.7498/aps.54.1273
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The pressure of granular mass on container bottom has been experimentally investigated in vertically vibrated granular beds. Pulse signals are found of the pressure, and the pulse strength undergoes subharmonic bifurcations controlled by the scaled vibration acceleration. Condensed state of particles is observed at the bed bottom, in which the particles are closely packed, with small free path, and move like a bulk block.

Dilute granular flow distribution near roughboundary on a two-dimensional inclined channel

Bao De-Song, Zhou Ying, Zhang Xun-Sheng, Tang Xiao-Wei
Acta Physica Sinica. 2005, 54 (3): 01279 doi: 10.7498/aps.54.1279
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The dilute granular flow distribution near the rough boundary of a two_dimensional inclined channel have been reported. It is caused by the increasing inclination and the width of the channel. Compared with the viscous fluids, the velocity profiles of the granular flow are more blunted than the parabolic form and the density profiles are nonuniform. In thie paper, we present the density of granular flux ξ near the rough boundary of a two_dimensional inclined channel. the results show that there is a critical width of channel Wc for the transition of the density of granular flux ξ=ρv, and the density of granular flux near the boundary decaying exponentially with incresaing inclination of the channel when the width of channel is less than Wc.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Phase transition in biaxial nematic liquid crystal

Liu Hong, Wang Hui
Acta Physica Sinica. 2005, 54 (3): 01306 doi: 10.7498/aps.54.1306
Full Text: [PDF 246 KB] Download:(813)
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Assuming a simple biaxial molecular interaction model in nematic liquid crystal, and using the mean field approximation, phase transitions from isotropic to uniaxial nematics, uniaxial to biaxial nematics are obtained. The result obtained shows that at certain temperatures, the biaxial phases are induced by the asymmetry of molecular shape of liquid crystal. In nuclear magnetic resonance experiment, a general relation between order parameters and spectrum frequency splitting is derived, and possible experimental measurement is discussed.

Thermodynamic functions of nanocrystals and its application to the study of phase transformations

Song Xiao-Yan, Gao Jin-Ping, Zhang Jiu-Xing
Acta Physica Sinica. 2005, 54 (3): 01313 doi: 10.7498/aps.54.1313
Full Text: [PDF 269 KB] Download:(1280)
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In the literature, a majority of studies on thermal properties of nanocrystals have taken the thermal features of interfaces as a representative of those of the whole nanocrystal. This treatment may cause big errors in predicting some important parameters such as the transition temperatures and critical sizes of phase for transformation in nanocrystalline materials, when the grain size is larger than several tens of nanometers. In the present paper, a model to calculate the thermodynamic functions of the whole nanocrystal has been developed with the consideration of the effects of both the interfaces and the crystal in the grain interior. The expressions of the enthalpy, entropy and Gibbs free energy, as a functions of the excess free volume at interfaces, temperature and grain size, are derived for single_phase nanocrystals. Using the Co nanocrystal as an example, thermal features of interfaces and the bulk nanocrystal have been compared with the conventional. Furthermore, the characteristics of β_Co→α_Co phase transformation in nanocrystalline materials are studied, the transformation temperatures at different levels of grain size, as well as the critical grain sizes at different temperatures, are predicted and compared with experimental results.

Molecular dynamics simulation of atomic configurations at γ/γ′(001)interface in Ni-based single-crystalline superalloys

Geng Cui-Yu, Wang Chong-Yu, Zhu Tao
Acta Physica Sinica. 2005, 54 (3): 01320 doi: 10.7498/aps.54.1320
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In this paper, three different atomic configurations at γ/γ′(001)interface in Ni_based single_crystalline superalloys has been studied by means of molecular dynamics. The most stable atomic configuration was obtained by energetics calculation. Among the three configurations analyzed, dynamics simulation results show that a pairs of edge misfit dislocations appeared at all the relaxed interfaces. The related calculations reveal that the system energy, the interface formation energy and the relaxed energy are determined by the stacking sequence, while the geometric character of different atomic configurations is the same. That is, different atomic configurations at γ/γ′(001)interface have the same strain relief mechanism.

Phonon dispersion relation calculations of armchair and zigzag carbon nanotubes

Zhang Bin, Wang Yu-Fang, Jin Qing-Hua, Li Bao-Hui, Ding Da-Tong
Acta Physica Sinica. 2005, 54 (3): 01325 doi: 10.7498/aps.54.1325
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When we calculate the phonon dispersion relations by using the force constant parameters for two_dimensional(2D) graphite, it is necessary to consider the problem that a 3D nanotube is formed by a rolled 2D graphene sheet. The present paper reports results on phonon dispersion relations of armchair and zigzag carbon nanotubes calculated with the considerations to the effect of curvature. Based on the results of the calculations and the symmetry analysis of the structures of single wall armchair and zigzag carbon nanotubes, the decomposition of the vibration modes at the Γ point is discussed.

Growth and characteristics of Ge on Ru(0001)

Hu Fang, Zhang Han-Jie, Lü Bin, Tao Yong-Sheng, Li Hai-Yang, Bao Shi-Ning, He Pi-Mo, X. S. Wang
Acta Physica Sinica. 2005, 54 (3): 01330 doi: 10.7498/aps.54.1330
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Scanning tunneling microscopy (STM) and x_ray photoemission spectroscopy (XPS) studies of germanium growth on Ru(0001) were carried out. STM measurements showed a typical Stranski_Krastanov growth mode of Ge on Ru(0001), i.e. first atomic wetting layer is formed in the submololayer range, and the formation of islands on top of a flat first layer occurs for subsequent layers. XPS measurements showed a weak interaction between Ge and the substrate of Ru(0001). The Ru 3d5/2 and Ru 3d3/2 corelevels of Ru(0001) are located at 2798 and 2840 eV in binding energy respectively. Upon Ge growth, up to a thickniss of about 20 atomic layers, the Ru 3d corelevels shift downward in binding energy by an amount of about 02 eV,while the Ge 3d corelevel shift upward in binding energy from the Ge low coverage limit of 289 eV to 290 eV,with a relative change of 01 eV.

Effects on the mechanism of nucleation and orientation of amorphous PZT nano thin film treated by different crystallization technics

Huang Wen, Zeng Hui-Zhong, Zhang Ying, Jiang Shu-Wen, Wei Xian-Hua, Li Yan-Rong
Acta Physica Sinica. 2005, 54 (3): 01334 doi: 10.7498/aps.54.1334
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Pb(Zr048Ti052)O3(PZT) thin films were prepared on the Pt/Ti/SiO2/Si substrates by RF_ magnetron sputtering method at room temperature. After rapid thermal annealing (RTA) and conventional furnace annealing (CFA) at different temperatures, the amorphous films were transformed into polycrystalline PZT thin films with (100) and (111) orientation, respectively. The phase formation and degree of orientation were investigated by x_ray diffraction (XRD). The surface micro_structure and ferroelectric domains formed by the spontaneous polarization in the corresponding region were observed by atom force microscopy and piezoresponse force microscopy. The distribution character of the ferroelectric domains with different preferred orientation in the films were studied. The result shows the perovskite PZT crystalline was found to hetero_nucleate epitaxially on top of the PtPb intermetallic phase at the PZT/Pt interface during RTA. The crystallizing speed along the interface is much faster than perpendicular to the film surface. While the nucleation of the films annealed by CFA dominantly homo_nucleate around the defects and impurities in the films. Different preferred orientation growth is attributed to different nucleation mechanism.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Effect of the distance between electrodes on the electronic transport properties of single molecular devices

Zou Bin, Li Zong-Liang, Wang Chuan-Kui, Xue Qi-Kun
Acta Physica Sinica. 2005, 54 (3): 01341 doi: 10.7498/aps.54.1341
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Basing on ab initio methods and the elastic scattering Green function theory, we have investigated electronic transport properties of metal_molecule_metal junctions by taking the 4_4′_dimercaptodibenzene molecule as an example. The molecular geometric structures, electronic structures, and current_voltage characteristics have been studied for varying the distance between the two electrodes. Numerical results show that the changes of the distance between electrodes give various influence on the extended molecule's geometric and electronic structures, which brings effects on the electronic transport properties of the molecular systems. The equilibrium state of the extended molecule is not the best situation for electronic transportation. The characteristics of electronic transportation can thus be improved by adjusting the distance between the two electrodes.

Calculation of the enhancement factor for the individual conductive nanowire in field emission

Wang Xin-Qing, Wang Miao, Li Zhen-Hua, Yang Bing, Wang Feng-Fei, He Pi-Mo, Xu Ya-Bo
Acta Physica Sinica. 2005, 54 (3): 01347 doi: 10.7498/aps.54.1347
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The potential and the electric field at the end of the individual nanowire under an electric field were calculated with the image charge model. With the nanowire as a field emitter, the enhancement factor was given by the expression: β0=h/ρ+35. Taking into account the influence of the anode_cathode distance, the enhancement factor at the end of the nanowire could be adjusted based on the equation: β=h/ρ+35+A(h/d)3, where h and ρ are the length and the radius of the nanowire respectively; d is the anode_cathode distance and A is a constant. From the above results, it is concluded that the aspect ratio is the most important factor for the nanowire emitter and the anode_cathode distance also slightly influence the enhancement factor of the nanowire in field emission, and the enhancement factor increases with the decrease of the anode_cathode distance.

A first principle study on the geometry and the electronic structures of VC(001) relaxed surface

Zhang Yong-Fan, Ding Kai-Ning, Lin Wei, Li Jun-Qian
Acta Physica Sinica. 2005, 54 (3): 01352 doi: 10.7498/aps.54.1352
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By using the first principle method, the geometry and electronic structures of the clean VC(001) surface are investigated. Similar to the TiC(001) surface, the relaxation of the VC(001) surface leads to the C and V atoms on the top layer move outward and inward, respectively. Results of band structure calculation show that the band structures of transition metal (001) surfaces can be well described by the rigid band model. For the VC(001) surface, the surface states are mainly located around 30eV below the Fermi level, and mainly originate from the 2pz orbital of C atom in the top layer. In addition, the surface states derived from the top layer V 3d orbitals are also observed near the Fermi level. Since these states contain significant contributions of those 3d orbitals vertical to the surface (3d2z and 3dxz/dyz), which will play important roles in the surface reactions, it could be expected that the VC(001) surface exhibits different surface reactivity compared with the TiC(001) surface.

Quantization of mesoscopic quartz piezoelectric crystal equivalent circuit

Li Hong-Qi
Acta Physica Sinica. 2005, 54 (3): 01361 doi: 10.7498/aps.54.1361
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By using the idea of damped harmonic oscillator operation,a mesoscopic quartz piezoelectric crystal equivalent circuit is quantized. By this basic theory, we studied the quantum fluctuation of the voltage and current in each branch of the mesoscopic quartz piezoelectric crystal equivalent circuit under the squeezed vacuum state and the vacuum state.

Conductance and thermopower in quantum point contact: effect of magnetic field and temperature

Li Yu-Xian, Liu Jian-Jun, Li Bo-Zang
Acta Physica Sinica. 2005, 54 (3): 01366 doi: 10.7498/aps.54.1366
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We calculate the conductance and thermopower in saddle quantum point contact under a finite temperature and different magnetic fields. The steplike conductance becomes flatter and the length between the peaks of the thermopower becomes longer with increasing magnetic field. The quantization of the conductance is destroyed and the peak structure of the thermopower disapears when the temperature becomes higher.

Fabrication and characterization of YBa2Cu3O7-δ/SrNb0.01Ti0.99O3 p-n junctions

He Meng, Lü Hui-Bin, Zhou Yue-Liang, Cheng Bo-Lin, Chen Zheng-Hao, Jin Kui-Juan, Yang Guo-Zhen
Acta Physica Sinica. 2005, 54 (3): 01370 doi: 10.7498/aps.54.1370
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A pn junction is fabricated by using the pulsed laser deposition (PLD) technique for a ptype YBa2Cu3O7-δ (YBCO) film on the ntype SrNb001Ti099O3(SNTO) single crystal substrate. The measured results reveal that the YBCO thin film is highly corientated structure and shows very good superconducting properties. The YBCO/SNTO pn junction has good rectification property and stability under variation of temperature and magneticfield.

Degradation and physical mechanism of NBT in deep submicron PMOSFET's

Liu Hong Xia, Zheng Xue Feng, Hao Yue
Acta Physica Sinica. 2005, 54 (3): 01373 doi: 10.7498/aps.54.1373
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This paper investigates the dependence of current and voltage characterizations on stress time in deep submicron PMOSFET's before and after negative bias temperature (NBT) stress, we mainly focus on the threshold voltage shift under NBT stress. It is experimentally demonstrated that the electrochemical reactions at the interface between gate oxide and substrate and the diffusion of hydrogen related species in the oxide are the major causes of the NBT in PMOSFET's. PMOSFET degradation caused by NBT depends on the balance of reactionlimited and diffusionlimited mechanisms.

The model of the magnetic mirror effect in the unbalanced magnetron sputtering ion beams

Mu Zong-Xin, Li Guo-Qing, Qin Fu-Wen, Huang Kai-Yu, Che De-Liang
Acta Physica Sinica. 2005, 54 (3): 01378 doi: 10.7498/aps.54.1378
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A conventional magnetron and a coaxial electrosolenoid were used to construct an unbalanced magnetron sputtering deposition system for investigating its properties. At 02Pa, argon gas discharging, a shielded planar ioncollecting electrode was taken to measure the saturation ion beam flux density at the different axial positions. The saturation ion flux reached about 9mA/cm2. The magnetohydrodynamics was applied to analyse the influences of the magnetic mirror effect on the discharge properties caused by the solenoid. As a result, the comparisons of the theoretical calculations with the experiments indicated that the model described correctly the plasma properties in the unbalanced magnetron sputtering system.

Mechanism of nodule growth in ion beam sputtering films

Zhang Dong-Ping, Qi Hong-Ji, Shao Jian-Da, Fan Rui-Ying, Fan Zheng-Xiu
Acta Physica Sinica. 2005, 54 (3): 01385 doi: 10.7498/aps.54.1385
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Zirconium singlelayer films were prepared by ion beam sputtering method. By using a novel designed substrate holder in preplanting seeds method, the growth process of the nodular defects in thin films was studied. With the help of high resolution optical microscopy and electron scanning microcopy, the phenomenon that the nodules nucleation exhibits fractal characters in their initial growth period was observed. By using the molecular dynamics theory and diffusion limited aggregation model of film growth, the fractal phenomenon of the nodule nucleation was well explained.

Dielectric and interface characteristics of SrTiO3 with a MIS structure

Ma Jian-Hua, Sun Jing-Lan, Meng Xiang-Jian, Lin Tie, Shi Fu-Wen, Chu Jun-Hao
Acta Physica Sinica. 2005, 54 (3): 01390 doi: 10.7498/aps.54.1390
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SrTiO3 (STO) films were deposited onto the ptype Si substrates by metalorganic decomposition (MOD) technique. The dielectric and interface characteristics of STO with a metalinsulatorsemiconductor(MIS) structure were investigated. The results showed that the dielectric constant was about 105 and the dissipation factor was lower than 001 for our STO films at a frequency of 10kHz. The excellent dielectric properties were attributed to the polycrystalline structure with good crystallinity. The fixed charge density Nf and the interfacetrap density Dit were calculated to be about 15×1012cm-2 and (14—35)×1012cm-2eV-1, respectively. Both Nf and Dit were mainly connected with an interface layer with low dielectric constant formed at the interface of Si/STO.

Study on impedance transition of PEN thin film

Guo Feng, Jiang Yi-Ming, Xie Heng-Bo, Wan Xing-Gong, Hu Jing-Ping, Li Jin
Acta Physica Sinica. 2005, 54 (3): 01396 doi: 10.7498/aps.54.1396
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PEN films were prepared by vacuum deposition. Their electrical bistable properties were studied under conditions of various circuit parameters.A decrease of time needed for impedance transition with increasing circuit current was observed. The film impedance showed a nonlinear characteristics and then data fitting was done for the nonlinearity. Furthermore, an energy effect was found during the transition, i.e. when the applied voltage exceeds a threshold, the energy consumption keeps invariable.

Synchrotron radiation photoemission study of Yb2.75C60

He Shao-Long, Li Hong-Nian, Wang Xiao-Xiong, Li Hai-Yang, Kurash I., Qian Hai-Jie, Su Run, Abbas M. I., Zhong Jun, Hong Cai-Hao
Acta Physica Sinica. 2005, 54 (3): 01400 doi: 10.7498/aps.54.1400
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The Yb275C60 thin film was prepared and studied by using the synchrotron radiation ultraviolet photoemission spectroscopy(PES) in an ultrahighvacuum system. The spectral line obtained in the range between the Fermi level and ~5 eV binding energy consists of those lines from the valence band (the molecular orbital LUMO, HOMO and HOMO1 derived energy bands of C60) and core levels(Yb 4f7/2 and 4f5/2). Taking into account the variations of the photoinization cross sections of C 2p and Yb 4f with different photon energies, we have measured the photoemission spectra under the condition of varying photon energies, and carried out simulations to deduce the component contributions. The peak positions, widths and intensities for the components are obtained quantitatively. The results reveals that the photoemission of 4f electrons has a significant intensity with the photon energies larger than ~300 eV, and that the measured spectra depart drastically from the density of states of the valence band. To observe the valence band structure, one should carry out the PES measurements by using photons with energies less than 300 eV. The photoionization crosssection oscillation is also observed in Yb275C60 with almost the same oscillation period as that for pure C60 However, the oscillation amplitude is obviously smaller than that for pure C60, which reveals that the chemical environment of C60 in compounds has nonnegligible effects on the photoionization crosssection oscillation phenomenon.

Pairing symmetry with interband interaction

Cao Tian-De, Xu Li-Na
Acta Physica Sinica. 2005, 54 (3): 01406 doi: 10.7498/aps.54.1406
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We investigate the superconductivity of highTc oxides with the dp model. It is shown that the dp pairing can dominate the superconductivity. The pairing symmetry depends on the anisotropic dp interaction in CuO2 plane. The anisotropic dp interaction can lead to dwave or swave symmetry, but the repulsive interaction in the CuO2 plane cannot lead holes to being paired. The ‘preliminary pairing' may appear in a lightly doped regime. The critical temperature cannot be found for the pairing order parameter when the pairs are localized. The delocalization of holes and evolution of pairing symmetry with increasing doping are explained.

Coexistence of ferromagnetic and antiferromagnetic phases in compound LaFe11.4Al1.6

Wang Guang-Jun, Wang Fang, Shen Bao-Gen
Acta Physica Sinica. 2005, 54 (3): 01410 doi: 10.7498/aps.54.1410
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A metastable state with coexistence of ferromagnetic and antiferromagnetic phases has been confirmed in compound LaFe11.4Al1.6 by thermomagnetic curves at different external fields. The temperature behavior of the critical field could be explained by taking into consideration the metastable state. The existence of the metastable state is attributed to the exchange interactions and lattice disorder.

Structure and magnetic properties of CoPt(FePt)-C nanocomposite films

Wang Hao, Yang Fu-Jun, Xue Shuang-Xi, Cao Xin, Wang Jun-An, Gu Hao-Shuang, Zhao Zi-Qiang
Acta Physica Sinica. 2005, 54 (3): 01415 doi: 10.7498/aps.54.1415
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CoPt(FePt)C nanocomposite thin films were prepared by a pulsed filtered vacuum arc deposition technique. Thermal annealing was performed in vacuum at various temperatures. The dependence of the magnetic properties on the carbon fraction and annealing temperature was studied. Both xray diffraction and magnetic force microscopy analyses confirmed the formation of nanocrystallites of facecenteredtetragonal phase of CoPt or FePt in the carbon matrix after annealing at a sufficiently high temperature. For the film with particular compositions of Co24Pt31C45 and Fe43Pt35C22,the coercivity and the grain size were observed to increase with increasing annealing temperature. For the Co24Pt31C45 film at an annealing temperature of 700℃, the coercivity was 2.1×105 A/m and the grain size was about 17nm. For the Fe43Pt35C22 film at an annealing temperature of 650℃, the values were 2.8×105 A/m and 105nm,respectively.

Moving and zero-velocity gap soliton in resonantly absorbing Bragg reflector of finite atomic widths

Shao Hui-Guo, Zhao Ji, Wu Jia-Wen, Zhou Jian-Ying
Acta Physica Sinica. 2005, 54 (3): 01420 doi: 10.7498/aps.54.1420
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Selfinduced moving and zerovelocity(ZV) gap solitons were studied in a resonantly absorbing Bragg reflector of finite atomic width. Numerical results showed that the existence of moving gapsoliton is in general not affected by the finite atomic width but the existence of the ZV gapsoliton is highly affected by the widths of the atomic layers. Thus the trapping of the photonic energy occurs only in very thin atomic layers arranged with Bragg periodicity.

A theoretical study on symmetrical magnetostrictive/piezoelectric laminated composite

Wan Hong, Shen Ren-Fa, Wu Xue-Zhong
Acta Physica Sinica. 2005, 54 (3): 01426 doi: 10.7498/aps.54.1426
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The magnetoelectric (ME) effect is a product property of the composite material consisting of individual piezoelectric and magnetostrictive phases. Based on the constitutive equations of the materials, the ME coupling of a symmetrical magnetostrictive/piezoelectric laminated composite is modeled using a simple static elastic method. The ME coupling is also simulated by numerical technique employing the ANSYS 80/Multiphysics finite element software. It is found that the ME voltage coefficient in the static method is quite close to that in the equivalent circuit approach and increases with the increase of the magnetostricive/piezoelectric thickness ratio. Using the numerical modeling we can calculate the ME voltage coefficient of the magnetostrictive/piezoelectric laminated composite effectively.

Combination of inversion and fitting as an effective method for the analysis of NMR relaxation data

Wang He, Li Geng-Ying
Acta Physica Sinica. 2005, 54 (3): 01431 doi: 10.7498/aps.54.1431
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A method is proposed for analyzing the NMR relaxation data. The procedure includes using the nonnegative leastsquares (NNLS) to determine roughly the relaxation time values. Then those values are used as the initial parameters of the nonlinear fitting computation. As a result, accurate relaxation time data can be conveniently obtained without any preknowledge of the sample. This method is verified and demonstrated by computer simulations and NMR experimental results.

Field-induced displacement properties of nanoscale domain structure in PZT thin film

Zeng Hua-Rong, Yu Han-Feng, Chu Rui-Qing, Li Guo-Rong, Yin Qing-Rui, Tang Xin-Gui
Acta Physica Sinica. 2005, 54 (3): 01437 doi: 10.7498/aps.54.1437
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Nanoscale characterization of fieldinduced displacement was made in compositionally graded PZT thin film according to the inverse piezoelectric effects by SFM in contact mode. The nanoscale piezoelectric displacement  electric field butterfly loop was obtained due to the combined contribution from linear piezoelectric effect and domain switching effect, which substantiate nanoscale validity of CaspariMerz theory. The nanoscale imprint phenomena were also observed in the thin film.

Luminescent properties in Er-Yb-doped oxyfluoride glass ceramics with a nanocrystal line structure

Meng Jie, Zhao Li-Juan, Yu Hua, Tang Li-Qin, Liang Qin, Yu Xuan-Yi, Tang Bai-Quan, Su Jing, Xu Jing-Jun
Acta Physica Sinica. 2005, 54 (3): 01442 doi: 10.7498/aps.54.1442
Full Text: [PDF 194 KB] Download:(735)
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Oxyfluoride glass and glass ceramics codoped with Er3+/Yb3+ ions of the same composition were prepared. Nanocrystals in the glass ceramics were formed,characterized by xray diffraction and fluorescence spectra. The measurements by using the differential thermal analysis and the crystal parameter calculation by JuddOfelt theory indicated that the rareearth ions have entered the nanocrystals. At the same time, the ratio of the nanocrystalline phases in glass and glass ceramics before and after annealing was calculated respectively.

The effect of nitrogen-implantation on the field-emission properties of CVD diamond films

Li Jun-Jie, Wu Han-Hua, Long Bei-Yu, Lü Xian-Yi, Hu Chao-Quan, Jin Zeng-Sun
Acta Physica Sinica. 2005, 54 (3): 01447 doi: 10.7498/aps.54.1447
Full Text: [PDF 197 KB] Download:(963)
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Nitrogen was implanted into the chemical vapor deposition(CVD) diamond films, and the electron fieldemission properties of the nitrogenated diamond films were investigated. Raman and xray photoelectron spectroscopy(XPS) measurement revealed that nitrogenimplantation damaged the structure of diamond film and promoted the formations of sp2 C—C and sp2 C—N bonding. By increasing the implantation dose, the threshold field of the emission of the diamond film could be lowered from 18V/μm to 4V/μm. The enhancement of field emission for nitrogenimplanted CVD diamond films was attributed to the increase of the fraction of sp2 C bonds and the formation of defect bands within the bulk diamond band gap induced by nitrogenimplantation, which could alter the work function and elevate the Feimi level. Consequently, the energy barrier on diamond surface for electron tunneling was reduced.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Self-assembling behavior and optical properties of triangular silver nanoplates

Wu Qing-Song, Zhao Yan, Zhang Cai-Bei, Li Feng
Acta Physica Sinica. 2005, 54 (3): 01452 doi: 10.7498/aps.54.1452
Full Text: [PDF 203 KB] Download:(911)
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Triangular silver nanoplates with its border size of 100±10nm and thickness of 30nm were synthesized by a chemical method. These triangular silver nanoplates were characterized by TEM, UVVis spectroscopy and xrays diffraction analysis. Results obtained showed that these triangular silver nanoplates are perfect with sharp corners and selfassembled into twodimensional ordered monolayer on the carboncovered copper grid due to the adsorption of organic molecules in between these silver nanoplates. The wellaligned silver film on Si (100) substrate showed strong surfaceenhanced Raman scattering for pyridine molecules.
GENERAL

The homotopic solving method for a class of El Ni?o sea-air oscillator mechanism

Mo Jia-Qi, Lin Wan-Tao
Acta Physica Sinica. 2005, 54 (3): 0993 doi: 10.7498/aps.54.993
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A class of coupled systems in oscillation of the El Nio-Southern Oscillation (ENSO) mechanism has been studied. Using the homotopic mapping and perturbed theory, approximate expansions of the solution for a class of ENSO model are obtained in a simple manner.

Solution of the nonlinear Schr?dinger equation using the generalized Lie group reduction method

Ruan Hang-Yu, Li Hui-Jun
Acta Physica Sinica. 2005, 54 (3): 0996 doi: 10.7498/aps.54.996
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In this paper, by using the technique of generalized Lie group reduction, the exact solutions of the nonlinear Schrdinger equation with distributed dispersion, nonlinearity, and gain (or loss) are obtained. And, the potential application of the general solitary wave solutions and the chirped solitary wave solutions in optical fibers communication and optical fibers amplifiers have also been studied thoroughly. This will provide the possibility in making new optical fibers amplifiers.

A series of new exact solutions to the (2+1)-dimensional Broer-Kau-Kupershmidt equation

Zhi Hong-Yan, Wang Qi, Zhang Hong-Qing
Acta Physica Sinica. 2005, 54 (3): 01002 doi: 10.7498/aps.54.1002
Full Text: [PDF 239 KB] Download:(763)
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With the aid of computer symbolic systems Maple, and by an improved algebraic method which is used to construct a series of more general exact solutions to nonlinear differential equation or coupled equations, we have solved the (2+1)-dimensional Broer-Kau-Kupershmidt equation, and obtained a number of new exact solutions including polynomial solutions,exponential solutions, rational solutions, triangular periodic solutions,hyperbolic solutions, and Jacobi and Weierstrass doubly periodic wave solutions.

Hojman conserved quantity for a holonomic system in the event space

Xu Xue-Jun, Mei Feng-Xiang, Qin Mao-Chang
Acta Physica Sinica. 2005, 54 (3): 01009 doi: 10.7498/aps.54.1009
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A Hojman conserved quantity constructed by using the special Lie symmetry, or the Noether symmetry, or the form invariance for a holonomic system in the event space is studied. First, the differential equations of motion of the system are established. Second, the critera of three kinds of symmetries, such as the Lie symmetry, the Noether symmetry and the form invariance, and the relation among them are obtained. Third, the conservation law theorem gained by Hojman is generalized and applied to the system, and a non-Noether conserved quantity is obtained. Two examples are finally given to illustrate the application of the results.

Mei symmetry for two-dimensional charged particle in motion

Lou Zhi-Mei
Acta Physica Sinica. 2005, 54 (3): 01015 doi: 10.7498/aps.54.1015
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The motion of a charged particle in an electromagnetic field is studied by Mei symmetry.Based on the Mei symmetry of two-dimensional particle motion, the generator and the partial differential equations for the electromagnetic field are obtained by comparing the coefficients of all the monomials. A specific example is given in this paper.

Parameters that influenece the nonlinear Thomson scattering of single electrons in high-intensity laser fields

Zheng Jun, Sheng Zheng-Ming, Zhang Jie, Wei Zhi-Yi, Yu Wei
Acta Physica Sinica. 2005, 54 (3): 01018 doi: 10.7498/aps.54.1018
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The scattering of ultrashort and ultraintensie laser pulses by single electrons has been investigated theoretically and numerically by use of the classical theory of Thomson scattering by free electrons. The results indicate that attosecond pulse trains are emitted during the interaction. The temporal and spatial characteristics of the radiation are presented for different laser parameters(including intensity, pulse duration, initial phases and polarizations) and initial states of the electron(including different initial velocities and positions). Usually, with the increase of the incident laser intensity, the radiation becomes more powerful, its central frequency becomes higher, its duration becomes shorter, and its angular distribution becomes smaller. The radiation produced by the electron under a linearly polarized laser has a higher amplitude than under a circularly polarized laser pulse with the same intensity. In both cases, the polarization state of the radiation is very complicated, which depends n the observation direction. In spite of its initial energy and moving direction, the radiation produced by relativistic energetic electrons tends to be predominantly along the moving direction of the electron.

A note on paper “a simple fast method in finding the analytical solutions to a class of nonlinear partial differential equations”

Xie Yuan-Xi, Tang Jia-Shi
Acta Physica Sinica. 2005, 54 (3): 01036 doi: 10.7498/aps.54.1036
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By using a transformation we introduced formerly, a nonlinear partial differential equation can be reduced to a nonlinear ordinary differential equation, and then solve it directly. And the exact analytical solutions to the Burgers equation can be easily derived. The results obtained in this paper is in good agreement with those given in the literature.

New exact solutions of coupled Klein-Gordon-Schr?dinger equations

Liu Cheng-Shi, Du Xing-Hua
Acta Physica Sinica. 2005, 54 (3): 01039 doi: 10.7498/aps.54.1039
Full Text: [PDF 178 KB] Download:(695)
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By using a functiontransformation method, coupled KleinGordornSchrdinger equations are reduced to the integrals that can be solved with elementary functions and elliptic functions. Its exact solutions that include discontinuous solutions, hyperbolic function type solutions and elliptic function type solutions, and a special solutions obtained in a reference, are given.

The space dent of sphere-symmetry harmonic oscillator in ground state

Long Shu-Ming, Ran Qi-Wu, Xiong Xiao-Jun
Acta Physica Sinica. 2005, 54 (3): 01044 doi: 10.7498/aps.54.1044
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A rigorous solution of Schrdinger equation of an spheresymmetry harmonic oscillator is studied by the power series method.We found that wave function ψ(r,θ,φ)|r~0 can be infinite, rψ(r,θ,φ)|r~0 must be finite; this is in accord with Born's statistical explanation. The groundstate energy of the spheresymmetry harmonic oscillator is ω/2. The space dent will appear in the ground state of the spheresymmetry harmonic oscillator.

The nonadiabatic conditional geometric phase shift in a coiled fiber system

Shen Jian-Qi, Zhuang Fei
Acta Physica Sinica. 2005, 54 (3): 01048 doi: 10.7498/aps.54.1048
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The nonadiabatic conditional geometric phase gate is required in the topological quantum computation in order to overcome the conflict between the requirement of adiabatic condition(to avoid the severe distortion from the nonadiabaticity to the results) and the removal of decoherence effects. It was demonstrated that the effective Hamiltonian that describes the propagation of photon fields inside the coiled fiber is just the WangMatsumoto type of Hamiltonian. Thus, the coiled fiber system will automatically generate the nonadiabatic conditional geometric phase shift. In addition, it was shown that the dynamical phase(resulting from the effective Hamiltonian) acquired by the polarized photons vanishes, and the conditional initial state can be easily prepared only by controlling the initial wave vector of photons. In a word, the coiled fiber system can automatically satisfy the requirements and conditions, which were proposed by Wang and Matsumoto in order to create the nonadiabatic conditional geometric phase shift in their NMR scheme.

Vector modulation instability in an arbitrary polarized direction in strong birefringence fibers

Jia Wei-Guo, Yang Xing-Yu
Acta Physica Sinica. 2005, 54 (3): 01053 doi: 10.7498/aps.54.1053
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The coherently coupled nonlinear Schrdinger equation of the propagation of a light pulse in a nonlinear birefringence fiber has been utilized.We have studied modulation instability not only in an anomalous dispersion regime but also in a normal dispersion regime when the angle between the polarized direction and the birefringence axes is arbitrary.The results show that the instability polarized region and stability polarized region exist not only in the anomalous dispersion regime but also in the normal dispersion regime. The input pulses have obviously different gain spectra when the instability polarized region and input different power are different.

Detecting the nonlinearity for time series sampled from continuous dynamic systems

Lei Min, Meng Guang, Feng Zheng-Jin
Acta Physica Sinica. 2005, 54 (3): 01059 doi: 10.7498/aps.54.1059
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This paper studies the detection of the nonlinearity of time series sampled from continuous dynamics systems by using the surrogate data method. The results show that under the different sampling conditions, the detection finds different nonlinearity of chaotic time series. Especially for the oversampling time series, there can often be some illusive results. For this, we suggest that it is best to apply nonlinear values as testing statistics for detecting nonlinearity of oversampling time series.

Hopf bifurcation from synchronous chaos and its circuit simulation in a coupled nonlinear oscillator system

Ma Wen-Qi, Yang Cheng-Hui
Acta Physica Sinica. 2005, 54 (3): 01064 doi: 10.7498/aps.54.1064
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For a coupled nonlinear oscillator system with diffusion and gradient couplings, spatial Fourier transformation is performed and the dynamic equations of various space modes are derived. By calculating the Lyapunov exponents of the transverse modes, one can determine the stable region of the synchronous chaos on the plane of coupling parameters. On the boundary of the stable region, a couple of conjugate transverse modes destabilize, and a Hopf bifurcation takes place. Numerical simulations are carried out for the coupled Lorenz oscillator system. An electronic circuit is designed for simulating the bifurcation in the system. Results from the simulations show that the frequency created by the Hopf bifurcation is equal to the oscillation frequency of the destabilized transverse modes.

A fat strange set crisis in a piecewise-continuous system

He Yue, Jiang Yu-Mei, Shen Ying, He Da-Ren
Acta Physica Sinica. 2005, 54 (3): 01071 doi: 10.7498/aps.54.1071
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This article reports a characteristic crisis observed in a kicked rotor subjected to a piecewise continuous force field. The discontinuity border in the definition range of the twodimensional mapping, which describes the system, oscillates as the discrete time develops so that the forward images of the border form a fat fractal. With a chosen group of parameters the iterations on the fat fractal display chaotic motion, and the transient iterations from the initial values in a certain region of the phase space are attracted to the fat fractal. At a threshold of a control parameter, an elliptic periodic orbit suddenly appears inside the fat strange set, inducing an escaping of the iterations to the elliptic islands around it. The fat chaotic attractor thus suddenly transfers to a fat transient set. The influence of the feature of the crisis on the dependence of the lifetime in the transient set on the control parameter has been analyzed. It is shown that the dependence follows a universal scaling law suggested by Grebogy, Ott and Yorke, and the scaling exponent can be approximated according to the variation rules of the elliptic islands and the measure of the fat fractal as control parameter changes. It is possible to compare the results of the direct numerical computation on the scaling exponent and that obtained with the approximation. They are in good agreement.

A variational iteration method for solving El Ni?o mechanism of atmospheric physics

Mo Jia-Qi, Lin Wan-Tao
Acta Physica Sinica. 2005, 54 (3): 01081 doi: 10.7498/aps.54.1081
Full Text: [PDF 113 KB] Download:(846)
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The El Nio atmospheric physics mechanism is studied. Using the variational iteration theory, the approximation of the solution for its model is obtained for shortcut calculation. And compared to the special case for the exact solution of the model, the first approximate solution from the variational iteration method is in excellent agreement with the exact solution in degree of accuracy.

Analysis of bifurcation and chaos in a class of piecewise smooth systems based on symbolic sequence

Li Ming, Ma Xi-Kui, Dai Dong, Zhang Hao
Acta Physica Sinica. 2005, 54 (3): 01084 doi: 10.7498/aps.54.1084
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Based on the sequence of circuit topologies, a symbolic sequence method is proposed for analyzing the bifurcations and chaos in a class of piecewise smooth systems like DC/DC converters. The largest subsequence(LS) is used to distinguish the type of bifurcation and detect border collision bifurcation e. g., when a perioddoubling bifurcation occurs, the LS is unchanged; when border collision bifurcation occurs, the LS is changed; and when chaos occurs,the LS does not exist.It is shown that the duty ratio is an essential variable for describing the nonlinear dynamics of a class of piecewise smooth systems like DC/DC converters, and saturating nonlinearity is the root cause of border collision bifurcation.

An adaptive chattering-free variable structure control method for uncertain time-variant chaotic systems

Yu Dong-Chuan, Meng Qing-Hao
Acta Physica Sinica. 2005, 54 (3): 01092 doi: 10.7498/aps.54.1092
Full Text: [PDF 229 KB] Download:(775)
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The conventional variable structure control(VSC) methods for controlling chaos have some drawbacks, such as high_frequency chattering and the need of a prior knowledge about the upper bound of the uncertainty. Trying to solve the drawbacks, we proposed an adaptive chatteringfree variable structure control(ACFVSC) method for controlling a class of uncertain timevariable chaotic systems towards arbitrarily desired trajectory. The ACFVSC method not only eliminates the chattering phenomenon and tracks arbitrarily desired trajectory asymptotically, but also removes the prior knowledge about the upper bound of uncertainty. Both the asymptotic tracking analysis of ACFVSC and simulation results show that the arbitrarily desired tracking accuracy can be achieved within a finite time if the parameter of ACFVSC controller is appropriately set.

Studies on chaotic multiple-quantum-well laser synchronization via controlling phase and its application in secure communication using external chaos phase shift keying modulation

Yan Sen-Lin
Acta Physica Sinica. 2005, 54 (3): 01098 doi: 10.7498/aps.54.1098
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In this paper, the control of chaotic externalinjection multiplequantumwell laser synchronization via phasecontrollers is presented and external chaos phase shift keying modulation is proposed for secure communication. Chaotic laser synchronization is numerically achieved under controlling by phasecontrollers. Lasing phase shift is controlled via continuous ON/ON chaos shift keying and chaotic laser signal is transmitted by chaos phase shift keying modulation on end. Chaotic laser demodulation is realized by setting a phase shift of the receiver phasecontrollers. ON/ON chaos phase shift keying communications at bit rates of 01 and 05Gbit/s are numerically simulated. ON/ON chaos phase shift keying communication bit rate,the synchronization characterization and the system parameter mismatch are numerically analyzed, in particular.

Solutions of path integration for nonlinear dynamical system under stochastic parametric and external excitations

Xie Wen-Xian, Xu Wei, Lei You-Ming, Cai Li
Acta Physica Sinica. 2005, 54 (3): 01105 doi: 10.7498/aps.54.1105
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The numerical path integration based on GaussLegendre scheme is extended to the case of nonlinear dynamical system under stochastic parametric and external excitations. For the purpose of comparison between the numerical solutions and the analytic solution(if the system has) or MonteCarlo simulation, we discuss the system under parametric and external Gaussian white noise excitations. The numerical method is shown to give accurate results. Via the numerical solutions of path integration, we have studied the P bifurcation of the stochastic system.

Anomalous diffusion and fractional advection-diffusion equation

Chang Fu-Xuan, Chen Jin, Huang Wei
Acta Physica Sinica. 2005, 54 (3): 01113 doi: 10.7498/aps.54.1113
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Anomalous diffusion happens often in nature and society systems. In this paper, we develop a nonlocal method with temporal and spatial correlations to introduce a fractional order advectiondiffusion equation based on the usually used local 2_nd order advectiondispersion equation. In this equation, the diffusion is a fractional order derivative of time and space. And then, we extend the classical Fick's law for standard diffusion to a general fractional Fick's law. The fractional Fick's law shows that the current is related to the concentrations all over the space, also depends on the previous history and the initial condition. The solution of this fractional order advectiondispersion equation is fractional Lévy probability distribution density. And the mean square displacement is a nonlinear function of time.

Stochastic resonance behaviors of bistable systems connected in series

Leng Yong-Gang, Wang Tai-Yong, Guo Yan, Wang Wen-Jin, Hu Shi-Guang
Acta Physica Sinica. 2005, 54 (3): 01118 doi: 10.7498/aps.54.1118
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The stochastic resonance(SR) characteristics of two bistable systems connected in series have been investigated. It is deduced that the first bistable system of the cascaded system is most important because of its converting a white noise into a color one, and the subsequent bistable systems continuously concentrate noise energy into lowfrequency area in terms of Lorentzian distribution, which weakens the highfrequency dithering of the last output waveform and outlines the basic shape of the wave. The law of the signal spectral amplitude varying with noise intensity indicates that within a limited lowfrequency band, the cascaded system is able to promote the height of the signal spectral spike by a certain amount of noise. If the former of the cascaded system does not stay in SR, the latter could not optimize the former output to become a SR state. With the increase of the number of the bistable systems in the cascaded system, the lowfrequency area where most of the noise energy is collected will be narrowed gradually, and hence the signal peak is easily reduced and submerged in noise. For this case, in spite of using the twice-sampling technique to improve the signal spectral spike, the improvement is limited. Therefore, a single bistable system is effective for signal detection.

Effect of induced magnetic field on microstructure and magnetic properties of Bi-Mn alloy

Jia Guang-Qiang, Zhang Jin-Cang, Liu Yong-Sheng, Zhang Xiao-Yong, Ren Zhong-Ming, Cao Shi-Xun, Li Xi, Deng Kang
Acta Physica Sinica. 2005, 54 (3): 01126 doi: 10.7498/aps.54.1126
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The Bi_Mn wt6% alloys were solidified from semi_solid state in a magnetic field. The microstructure and magnetic properties have been studied systematically. The results show that the samples were of a eutectic structure of double phases and have large anisotropy. It was shown that the alignment of MnBi crystals occurred along the induced field. With increasing induced magnetic field, the remanence(Mr) increased gradually, which shows that the higher the induced magnetic field, the better the alignment. The spin reorientation temperature (TSR) for MnBi alloys increases with increasing induced magnetic field. The effects of the induced field on the microstructure and the magnetic properties of Bi_Mn wt6% alloys were also discussed.

Neutron phase contrast tomographic imaging method

Chen Jian-Wen, Gao Hong-Yi, Zhu Hua-Feng, Xie Hong-Lan, Li Ru-Xin, Xu Zhi-Zhan
Acta Physica Sinica. 2005, 54 (3): 01132 doi: 10.7498/aps.54.1132
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The principle for neutron phase contrast and tomography is presented in this paper.The imaging method for neutron phase_contrast tomography is suggested.It has the merits of both neutron phase contrast and tomography.The 3D space distribution for phase objects can be reconstructed with high resolution without using interferometry.The objective space structure with near absorption coefficient can be detected and resolved.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Heavy quarkonium mass spectra in a relativistic quark model

Chen Hong, Mei Hua, Shen Peng-Nian, Jiang Huan-Qing
Acta Physica Sinica. 2005, 54 (3): 01136 doi: 10.7498/aps.54.1136
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The mass spectra of heavy quarkonia are calculated with the relativistic quark model.The effective interaction between a quark and an antiquark of the same flavor is assumed to be the sum of the one_gluon exchange with the inclusion of annihilation terms and the mixture of scalar and vector linear confining potentials with the relativisic corrections.The effects of the annihilation and the relativistic correction terms on the hyperfine splittings of quarkonium states are discussed in detail,and a good fit to the observed experimental data is obtained on the mass spectra.

ATOMIC AND MOLECULAR PHYSICS

Precise criterion for excited states of the lithiumlike systems

Chen Chao, Wang Zhi-Wen, Li Jia-Ming
Acta Physica Sinica. 2005, 54 (3): 01142 doi: 10.7498/aps.54.1142
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By using the accurate inequalities of the electron density at the nucleus and radial expectation values for atomic systems derived by Gálvez and Porras, we separately construct two sets of precise criterion of the wave function, they are another precise criterion independent of energy to test quality of the wave function. In this paper, we use the excited states of lithiumlike systems as research objects and examine the upper bound of the electron density at the nucleus and radial expectation value <r> for the lithiumlike systems 1s23s state, R6 defined by the upper bounds of the electron density at the nucleus and R4 defined by the upper bounds of radial expectation value <r> for the lithium atom 1s23s state in different calculation methods are also tested,at the same time we check up the upper bound of the electron density at the nucleus and radial expectation value <r> for double excited states of the lithium atom. Research has shown that these two sets of inequalities can be used as precise criterion for wave function of energy states of atomic systems.

A new expression for photoionization cross sections and its application in high density system

Ma Xiao-Guang, Sun Wei-Guo, Cheng Yan-Song
Acta Physica Sinica. 2005, 54 (3): 01149 doi: 10.7498/aps.54.1149
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A new expression for photoionization cross section has been proposed based on the Beer_Lambert's law and Maxwell equations for a material.And we also proposed a function varying with the number density of the system,which includes the local field effect and the higher_order dielectric correction to the famous formula for photoionization cross section of isolated atoms,proposed by Fano and Cooper in 1968The photoionization cross sections of solid xenon have been studied by using this alternative expression which couples the macroproperty and the quantum quantity of the photoionization system,and which makes it possible for one to study the influence of induced dipoles on the photoionization.The dielectric behaviors of the matter in condensed state under several physical conditions (given the complex dielectric constants or the model of electric susceptibility of the system) are considered using our new expression for photoionization cross sections.The results show that it is reasonable in physics to calculate the cross sections of atoms in a real system by using the accurate expression.Furthermore,the more correct the model of electric susceptibility for the real system,the more accurate the cross section obtained from our formula will be.

Interaction between a trapped ion with a single-mode quantized radiation field

Qu Zhao-Jun, Liu Sheng-Dian, Yang Chuan-Lu
Acta Physica Sinica. 2005, 54 (3): 01156 doi: 10.7498/aps.54.1156
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The statistical properties of the system consisting of a trapped ion and a single_mode quantized radiation field are investigated under the conditions of carrier excitation (ωL=ω0), red excitation [ωL=ω0-jν(j=1,2,3)] and blue excitation [ωL=ω0+jν(j=1,2,3)].The time_evolution of the state of the system,the photon_and phonon_state exchange conditions and the corresponding populations of the ion are discussed.The corresponding averages and variances for photon and phonon numbers,as well as the second_order correlation function for the photon and phonon fields etc,have been obtained.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Variation of the target absorptance and target temperature distribution before melting in the pulsed laser ablation process

Zhang Duan-Ming, Li Li, Li Zhi-Hua, Guan Li, Hou Si-Pu, Tan Xin-Yu
Acta Physica Sinica. 2005, 54 (3): 01283 doi: 10.7498/aps.54.1283
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We have discussed the effect of the variation of target absorptance on the temperature distribution of the target before melting. The relationship of the target absoptance with time is derived. Based on this relationship and the actual shape of incident energy density which is a Gauss distribution, the relevant heat flow equation is set up. By using the finite difference method, heat flow equation under an appropriate boundary condition is solved. We have obtained the temperature distribution as function of time and location. At the same time, we have also discussed the physical picture of a relevant process in detail. Finally, we have studied the effect of the variation of absorptance and the distribution of incident energy density on the relevant process. The result shows that during the pulsed laser process, the variation of target absorptance has an important effect on the final simulation result. If this variation is neglected, a remarkable difference can be found between theoretical results and experimental data.

Acoustic diagnostics of plasma channels in air induced by intense femtosecond laser pulses

Hao Zuo-Qiang, Yu Jin, Zhang Jie, Yuan Xiao-Hui, Zheng Zhi-Yuan, Yang Hui, Wang Zhao-Hua, Ling Wei-Jun, Wei Zhi-Yi
Acta Physica Sinica. 2005, 54 (3): 01290 doi: 10.7498/aps.54.1290
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Long plasma channels can be formed when intense femtosecond laser pulses propagate in air. In contrast to other conventional diagnostic techniques, the acoustic method to probe the plasma channel has its advantages. By measuring the sound signals along the channel, the channel length and the distribution of electron density along it can be retrieved easily.

Study on homogeneous multiple-pulse barrier discharge at atmospheric pressure

Wang Yan-Hui, Wang De-Zhen
Acta Physica Sinica. 2005, 54 (3): 01295 doi: 10.7498/aps.54.1295
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The homogeneous barrier discharge with multiple current pulses at atmospheric pressure in helium is numerically investigated on the basis of one_dimensional fluid model. The influence of the applied voltage amplitude, frequency, as well as dielectric layer characteristics on the multiple_pulse discharge is discussed and analyzed. The simulation results show that, in the case of smaller gap width, multiple current pulses can be formed in each half_cycle of the applied voltage due to the increase of surface density of the accumulation charges, leading to the enhancement of the induced electric field. Multiple pulses correspond to separate breakdowns in the same time interval. The smaller the gap width, the bigger the number of current pulses per half cycle. The applied voltage and frequency can also influence the number and the amplitude of current pulses. However, there is no obvious influence of the barrier thickness and the permittivity on the number of current pulses.

Study on the microstructure and properties of (Ti, Al)N film deposited by pulsed high energy density plasma

Liu Yuan-Fu, Han Jian-Min, Zhang Gu-Ling, Wang Jiu-Li, Chen Guang-Liang, Li Xue-Ming, Feng Wen-Ran, Fan Song-Hua, Liu Chi-Zi, Yang Si-Ze
Acta Physica Sinica. 2005, 54 (3): 01301 doi: 10.7498/aps.54.1301
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Hard and corrosion resistance (Ti, Al)N film was deposited by pulsed high energy density plasma on the substrate of 045% C carbon steel at ambient temperature. The microstructure of the film has been investigated by SEM,XRD,XPS and AES. The nanohardness of the film was tested by nanoindentation tester. The corrosion resistance of the film was tested by potentiodynamic polarization in 05 mol /L H2SO4 aqueous solution. The results indicate that the film mainly composed of (Ti, Al)N and a small amount of AlN. The nanohardness of the film approaches 26 GPa. The corrosion resistance of the film is improved by about one order of magnitude, compared with 1Cr18Ni9Ti austenitic stainless steel.
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