Table of Content

20 April 2006, Volume 15 Issue 4 Previous Issue    Next Issue

GENERAL

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Elaborate calibration procedure for cell irradiation at the CAS-LIBB single-particle microbeam Hu Zhi-Wen, Ding Ke-Jian, Yu Liang-Deng, Zhang Jun, Wu Li-Jun, Yu Zeng-Liang 2006, 15 (4):  659-664.  doi: 10.1088/1009-1963/15/4/001 Abstract ( 0 )   PDF (1148KB) ([an error occurred while processing this directive])   Single-particle microbeam is uniquely capable of precisely delivering a preset number of charged particles to individual cells or sub-cellular targets to be determined in vitro. It is crucial to find a reference point that relates the microbeam's location to the microscope's plane, and align individual targets at this reference point for cell irradiation. To choose an appropriate reference point, an approach based on analysing the intensity distribution of fluorescence in a thin scintillator excited by traversing particles is newly developed using the CAS-LIBB single-particle microbeam,which features decisive physical signification and sufficient resolution. As its bonus, this on-line analysis provides precise and fast response to the determination of beam profile and potentially optimizes the microbeam quality by further adjusting hardware setup.

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Linear superposition method for (2+1)-dimensional nonlinear wave equations Lin Ji, Wang Rui-Min, Ye Li-Jun 2006, 15 (4):  665-670.  doi: 10.1088/1009-1963/15/4/002 Abstract ( 0 )   PDF (469KB) ([an error occurred while processing this directive])   New forms of different-periodic travelling wave solutions for the (2+1)-dimensional Zakharov--Kuznetsov (ZK) equation and the Davey--Stewartson (DS) equation are obtained by the linear superposition approach of Jacobi elliptic function. A sequence of cyclic identities plays an important role in these procedures.

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Variational iteration method for solving the mechanism of the Equatorial Eastern Pacific El Ni?o--Southern Oscillation Mo Jia-Qi, Wang Hui, Lin Wan-Tao, Lin Yi-Hua 2006, 15 (4):  671-675.  doi: 10.1088/1009-1963/15/4/003 Abstract ( 0 )   PDF (215KB) ([an error occurred while processing this directive])   A class of coupled system for the El Ni\~{n}o--Southern Oscillation (ENSO) mechanism is studied. Using the method of variational iteration for perturbation theory, the asymptotic expansions of the solution for ENSO model are obtained and the asymptotic behaviour of solution for corresponding problem is considered.

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Efficient scheme for teleportation of an unknown N-atom state via a two-atom entangled state without the Bell-state measurement in cavity QED Wang Xin-Wen, Liu Xiang, Fang Mao-Fa 2006, 15 (4):  676-680.  doi: 10.1088/1009-1963/15/4/004 Abstract ( 0 )   PDF (265KB) ([an error occurred while processing this directive])   We propose a scheme for teleportation of an unknown $N$-atom state using a two-atom entangled state within a cavity QED and show the feasibility in experiment. Our scheme does not involve the Bell-state measurement and is insensitive to the cavity decay, which is important from the experimental point of view. Another feature of the scheme is that teleporting a N-atom state just requires a small amount of entanglement (i.e. a two-atom entangled state) and less classical bits (two bits).

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Quantum entanglement and quantum nonlocality for N-photon entangled states Sun Yan-Hua, Kuang Le-Man 2006, 15 (4):  681-686.  doi: 10.1088/1009-1963/15/4/005 Abstract ( 0 )   PDF (291KB) ([an error occurred while processing this directive])   Quantum entanglement and quantum nonlocality of N-photon entangled states |\psiN m\rangle =Cm[\cos\gamma|N-m\rangle1|m\rangle2 +\e{\i\θm}\sin\gamma|m\rangle1|N-m\rangle2] and their superpositions are studied. We point out that the relative phase θm affects the quantum nonlocality but not the quantum entanglement for the state |\psiN m\rangle. We show that quantum nonlocality can be controlled and manipulated by adjusting the state parameters of |\psiN m\rangle, superposition coefficients, and the azimuthal angles of the Bell operator. We also show that the violation of the Bell inequality can reach its maximal value under certain conditions. It is found that quantum superpositions based on |\psiN m\rangle can increase the amount of entanglement, and give more ways to reach the maximal violation of the Bell inequality.

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An implementation of cellular automaton model for single-line train working diagram Hua Wei, Liu Jun 2006, 15 (4):  687-691.  doi: 10.1088/1009-1963/15/4/006 Abstract ( 0 )   PDF (233KB) ([an error occurred while processing this directive])   According to the railway transportation system's characteristics, a new cellular automaton model for the single-line railway system is presented in this paper. Based on this model, several simulations were done to imitate the train operation under three working diagrams. From a different angle the results show how the organization of train operation impacts on the railway carrying capacity. By using the non-parallel train working diagram the influence of fast-train on slow-train is found to be the strongest. Many slow-trains have to wait in-between neighbouring stations to let the fast-train(s) pass through first. So the slow-train will advance like a wave propagating from the departure station to the arrival station. This also resembles the situation of a highway jammed traffic flow. Furthermore, the nonuniformity of travel times between the sections also greatly limits the railway carrying capacity. After converting the nonuniform sections into the sections with uniform travel times while the total travel time is kept unchanged, all three carrying capacities are improved greatly as shown by simulation. It also shows that the cellular automaton model is an effective and feasible way to investigate the railway transportation system.

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Study of surface cell Madelung constant and surface free energy of nanosized crystal grain Zhang Wei-Jia, Wang Tian-Min, Rong Ai-Lun, Cui Min 2006, 15 (4):  692-696.  doi: 10.1088/1009-1963/15/4/007 Abstract ( 0 )   PDF (250KB) ([an error occurred while processing this directive])   Surface cell Madelung constant is firstly defined for calculating the surface free energy of nanosized crystal grains, which explains the physical performance of small crystals and may be greatly beneficial to the analysis of surface states and the study of the dynamics of crystal nucleation and growth. A new approximative expression of the surface energy and relevant thermodynamic data are used in this calculation. New formula and computing method for calculating the Madelung constant α of any complex crystals are proposed, and the surface free energies and surface electrostatic energies of nanosized crystal grains and the Madelung constant of some complex crystals are theoretically calculated in this paper. The surface free energy of nanosized-crystal-grain TiO2 and the surface electrostatic energy(absolute value) of nanosized-crystal-grain α -Al2O3 are found to be the biggest among all the crystal grains including those of other species.

ATOMIC AND MOLECULAR PHYSICS

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Study on the interaction of intense femtosecond laser pulses with nanometre-sized hydrogen clusters Zheng Li, Wang Cheng, Li Shao-Hui, Liu Bing-Chen, Ni Guo-Quan, Li Ru-Xin, Xu Zhi-Zhan 2006, 15 (4):  697-701.  doi: 10.1088/1009-1963/15/4/008 Abstract ( 0 )   PDF (237KB) ([an error occurred while processing this directive])   The interaction of intense femtosecond laser pulses with hydrogen clusters has been experimentally studied. The hydrogen clusters were produced from expansion of high-pressure hydrogen gas (backed up to 8\tm106Pa) into vacuum through a conical nozzle cryogenically cooled by liquid nitrogen. The average size of hydrogen clusters was estimated by Rayleigh scattering measurement and the maximum proton energy of up to 4.2keV has been obtained from the Coulomb explosion of hydrogen clusters under 2×1016 W/cm2 laser irradiation. Dependence of the maximum proton energy on cluster size and laser intensity was investigated, indicating the correlation between the laser intensity and the cluster size. The maximum proton energy is found to be directly proportional to the laser intensity, which is consistent with the theoretical prediction.

CLASSICAL AREAS OF PHENOMENOLOGY

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Effects of the microstructure slab with pillars on light extraction of GaN light-emitting diode Li Yan, Zheng Rui-Sheng, Feng Yu-Chun, Liu Song-Hao, Niu Han-Ben 2006, 15 (4):  702-707.  doi: 10.1088/1009-1963/15/4/009 Abstract ( 0 )   PDF (720KB) ([an error occurred while processing this directive])   The positive z direction relative light extraction efficiency of GaN light-emitting diodes with microstructure slab is calculated by three-dimensional finite-difference time-domain method, where the microstructure slab consists of a graphite lattice of pillars. The results show that the two-dimensional graphite-arranged pillars suppress light extraction. When there is a thick pillar in the middle of the pillars, the structure can enhance light extraction of the light-emitting diodes. The tower-like pillars, which are thin on the top of the pillars and thick on the bottom of the pillars, benefit the light extraction when the angle of the tower-like pillars is proper.

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Influences of phase shift on superresolution performances of annular filters Liu Xi-Min, Liu Li-Ren, Bai Li-Hua 2006, 15 (4):  708-714.  doi: 10.1088/1009-1963/15/4/010 Abstract ( 0 )   PDF (255KB) ([an error occurred while processing this directive])   This paper investigates the influences of phase shift on superresolution performances of annular filters. Firstly, it investigates the influence of phase shift on axial superresolution. It proves theoretically that axial superresolution can not be obtained by two-zone phase filter with phase shift π, and it gets the phase shift with which axial superresolution can be brought by two-zone phase filter. Secondly, it studies the influence of phase shift on transverse superresolution. It finds that the three-zone phase filter with arbitrary phase shift has an almost equal optimal transverse gain to that of commonly used three-zone phase filter, but can produce a much higher axial superresolution gain. Thirdly, it investigates the influence of phase shift on three-dimensional superresolution. Three-dimensional superresolution capability and design margin of three-zone complex filter with arbitrary phase shift are obtained, which presents the theoretical basis for three-dimensional superresolution design. Finally, it investigates the influence of phase shift on focal shift. To obtain desired focal shifts, it designs a series of three-zone phase filters with different phase shifts. A spatial light modulator (SLM) is used to implement the designed filters. By regulating the voltage imposed on the SLM, an accurate focal shift control is obtained.

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Supercontinuum spectra generation in the single-mode optical fibre with concave dispersion profile Xu Wen-Cheng, Gao Jie-Li, Liang Zhan-Qiang, Chen Qiao-Hong, Liu Song-Hao 2006, 15 (4):  715-720.  doi: 10.1088/1009-1963/15/4/011 Abstract ( 0 )   PDF (295KB) ([an error occurred while processing this directive])   In this paper, a new method is proposed to generate broad supercontinuum (SC) spectra in the single-mode optical fibre with concave dispersion profile. We numerically simulate pulse evolutions and discuss physics mechanism in detail for SC spectrum generation in the optical fibre with concave dispersion profile. Furthermore, general criteria are presented for specifying the shape of SC spectrum by introducing normalized parameters, which are related to the fibres and the initial pump pulses. The results show that the flat and broad SC spectra are indeed generated in our proposed optical fibre.

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One- and two-photon absorption-amplification response in a four-level atomic system with vacuum-induced coherence Li Jia-Hua, Chen Ai-Xi, Liu Ji-Bing, Xie Xiao-Tao 2006, 15 (4):  721-728.  doi: 10.1088/1009-1963/15/4/012 Abstract ( 0 )   PDF (324KB) ([an error occurred while processing this directive])   This paper theoretically studies the effects of the vacuum-induced coherence on one- and two-photon absorption in a four-level atomic medium. It finds that the one- and two-photon absorption and amplification properties are quite sensitive to the vacuum-induced coherence. It is also shown that the one- and two-photon absorption spectra can be dramatically affected by modulating the relative phase of the applied fields. With the proper choice of the relative phase, the amplification without inversion for the probe field can be realized.

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Anomalous behaviour of long-time increase in diffraction efficiency of photorefractive grating in Ce:BaTiO3 in dark Zhang Jia-Wen, Zhang Ming, Xu Ying, Hong Zhi 2006, 15 (4):  729-734.  doi: 10.1088/1009-1963/15/4/013 Abstract ( 0 )   PDF (271KB) ([an error occurred while processing this directive])   Anomalous long-time increase of the diffraction efficiency is observed in dark-decay experiments of photorefractive gratings in Ce:BaTiO2. It is deduced that a phase-conjugate beam is induced by the writing beam at acute angle to the +c axis of the crystal and it interferes with the other writing beam to form a second grating which is perpendicular to the first grating formed by the interference between two writing beams. The rising behaviour of the diffraction efficiency results from the different decay rates of these two photorefractive gratings. Furthermore, a simplified model of two gratings, both induced by two deep traps, is proposed to account for this phenomenon and the fitting results agree well with the experimental results.

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Existence of the transverse relaxation time in optically excited bulk semiconductors Zhang Hai-Chao, Lin Wei-Zhu, Wang Yu-Zhu 2006, 15 (4):  735-749.  doi: 10.1088/1009-1963/15/4/014 Abstract ( 0 )   PDF (382KB) ([an error occurred while processing this directive])   Two basic types of depolarization mechanisms, carrier-carrier (CC) and carrier-phonon (CP) scattering, are investigated in optically excited bulk semiconductors (3D), in which the existence of the transverse relaxation time is proven based on the vector property of the interband transition matrix elements. The dephasing rates for both CC and CP scattering are determined to be equal to one half of the total scattering-rate-integrals weighted by the factors (1-\cos\chi), where \chi are the scattering angles. Analytical expressions of the polarization dephasing due to CC scattering are established by using an uncertainty broadening approach, and analytical ones due to both the polar optical-phonon and non-polar deformation potential scattering (including inter-valley scattering) are also presented by using the sharp spectral functions in the dephasing rate calculations. These formulas, which reveal the trivial role of the Coulomb screening effect in the depolarization processes, are used to explain the experimental results at hand and provide a clear physical picture that is difficult to extract from numerical treatments.

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Thiophene-fluorene derivatives with high three-photon absorption activities and their application to optical power limiting Ma Wen-Bo, Wu Yi-Qun, Han Jun-He, Liu Jun-Hui, Gu Dong-Hong, Gan Fu-Xi 2006, 15 (4):  750-755.  doi: 10.1088/1009-1963/15/4/015 Abstract ( 0 )   PDF (534KB) ([an error occurred while processing this directive])   The three-photon absorption (3PA) properties of two thiophene-fluorene derivatives (abbreviated as MOTFTBr and {ATFTBr}) have been determined by using a Q-switched Nd:YAG laser pumped with 38ps pulses at 1064nm in DMF. The measured 3PA cross-sections are 152\times 10-78cm6s2 and 139\times 10-78cm6s2, respectively. The optimized structures were obtained by AM1 calculations and the results indicate that these two molecules show nonplanar structures, and attaching different donors has different effects on the molecular structure. The charge density distributions during the excitation were also systematically studied by using AM1 method. In addition, an obvious optical power limiting effect induced by 3PA has been demonstrated for both derivatives.

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Second-order random wave solutions for interfacial internal waves in N-layer density-stratified fluid Chen Xiao-Gang, Song Jin-Bao 2006, 15 (4):  756-766.  doi: 10.1088/1009-1963/15/4/016 Abstract ( 0 )   PDF (286KB) ([an error occurred while processing this directive])   This paper studies the random internal wave equations describing the density interface displacements and the velocity potentials of N-layer stratified fluid contained between two rigid walls at the top and bottom. The density interface displacements and the velocity potentials were solved to the second-order by an expansion approach used by Longuet-Higgins (1963) and Dean (1979) in the study of random surface waves and by Song (2004) in the study of second-order random wave solutions for internal waves in a two-layer fluid. The obtained results indicate that the first-order solutions are a linear superposition of many wave components with different amplitudes, wave numbers and frequencies, and that the amplitudes of first-order wave components with the same wave numbers and frequencies between the adjacent density interfaces are modulated by each other. They also show that the second-order solutions consist of two parts: the first one is the first-order solutions, and the second one is the solutions of the second-order asymptotic equations, which describe the second-order nonlinear modification and the second-order wave--wave interactions not only among the wave components on same density interfaces but also among the wave components between the adjacent density interfaces. Both the first-order and second-order solutions depend on the density and depth of each layer. It is also deduced that the results of the present work include those derived by Song (2004) for second-order random wave solutions for internal waves in a two-layer fluid as a particular case.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Enhancing low-field magnetoresistance of La0.67Ca0.33MnO3 films deposited on anodized aluminium-oxide membranes Tang Wei-Hua, Li Pei-Gang, Lei Ming, Guo Yan-Feng, Chen Lei-Ming, Li Ling-Hong, Song Peng-Yun, Chen Chinping 2006, 15 (4):  767-772.  doi: 10.1088/1009-1963/15/4/017 Abstract ( 0 )   PDF (952KB) ([an error occurred while processing this directive])   In this paper we report a new method to fabricate nanostructured films. La0.67Ca0.33MnO3 (LCMO) nanostructured films have been fabricated by using pulsed electron beam deposition (PED) on anodized aluminium oxide (AAO) membranes. The magnetic and electronic transport properties are investigated by using the Quantum Design physics properties measurement system (PPMS) and magnetic properties measurement system (MPMS). The resistance peak temperature (Tp) is about 85\,K and the Curie temperature (Tc is about 250\,K for the LCMO film on an AAO membrane with a pore diameter of 20\,nm. Large magnetoresistance ratio (MR) is observed near Tp. The MR is as high as 85% under 1\,T magnetic field. The great enhancement of MR at low magnetic fields could be attributed to the lattice distortion and the grain boundary that are induced by the nanopores on the AAO membrane.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Electronic and luminescent properties of Cr-doped cadmium sulfide nanowires Tang Wei-Hua, Fu Xiu-Li, Zhang Zhi-Yong, Li Ling-Hong 2006, 15 (4):  773-777.  doi: 10.1088/1009-1963/15/4/018 Abstract ( 0 )   PDF (772KB) ([an error occurred while processing this directive])   Cr-doped CdS nanowires were synthesized in large scale through thermal co-evaporation of CdS and metal Cr powders. General morphology, detailed microstructure and optical properties were characterized using various techniques. Devices consisting of individual Cr-doped CdS nanowire were fabricated and they exhibited remarkable rectifying characteristics. I-V curves of individual Cr-doped CdS nanowire devices demonstrate that the present nanowires are n-type doped and have high conductivity (10.96 \Omega -1cm-1, indicating great potential applications in nanoscale electronic and optoelectronic devices.

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Numerical simulation of dendrite growth and microsegregation formation of binary alloys during solidification process Li Qiang, Guo Qiao-Yi, Li Rong-De 2006, 15 (4):  778-791.  doi: 10.1088/1009-1963/15/4/019 Abstract ( 0 )   PDF (6615KB) ([an error occurred while processing this directive])   The dendrite growth and solute microsegregation of Fe-C binary alloy are simulated during solidification process by using cellular automaton method. In the model the solid fraction is deduced from the relationship among the temperature, solute concentration and curvature of the solid/liquid interface unit, which can be expressed as a quadric equation, instead of assuming the interface position and calculating the solid fraction from the interface velocity. Then by using this model a dendrite with 0 and 45 degree of preferential growth direction are simulated respectively. Furthermore, a solidification microstructure and solute microsegregation are simulated by this method. Finally, different Gibbs-Thomson coefficient and liquid solute diffusing coefficient are adopted to investigate their influences on the morphology of dendrite.

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Improvement of total-dose irradiation hardness of silicon-on-insulator materials by modifying the buried oxide layer with ion implantation Zhang En-Xia, Qian Cong, Zhang Zheng-Xuan, Lin Cheng-Lu, Wang Xi, Wang Ying-Min, Wang Xiao-He, Zhao Gui-Ru, En Yun-Fei, Luo Hong-Wei, Shi Qian 2006, 15 (4):  792-797.  doi: 10.1088/1009-1963/15/4/020 Abstract ( 0 )   PDF (325KB) ([an error occurred while processing this directive])   The hardening of the buried oxide (BOX) layer of separation by implanted oxygen (SIMOX) silicon-on-insulator (SOI) wafers against total-dose irradiation was investigated by implanting ions into the BOX layers. The tolerance to total-dose irradiation of the BOX layers was characterized by the comparison of the transfer characteristics of SOI NMOS transistors before and after irradiation to a total dose of 2.7 Mrad(SiO2. The experimental results show that the implantation of silicon ions into the BOX layer can improve the tolerance of the BOX layers to total-dose irradiation. The investigation of the mechanism of the improvement suggests that the deep electron traps introduced by silicon implantation play an important role in the remarkable improvement in radiation hardness of SIMOX SOI wafers.

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Stability and electronic structure of InN nanotubes from first-principles study Chen Li-Juan 2006, 15 (4):  798-801.  doi: 10.1088/1009-1963/15/4/021 Abstract ( 0 )   PDF (218KB) ([an error occurred while processing this directive])   The stability and electronic structure of hypothetical InN nanotubes were studied by first-principles density functional theory. It was found that the strain energies of InN nanotubes are smaller than those of carbon nanotubes of the same radius. Single-wall zigzag InN nanotubes were found to be semiconductors with a direct band gap while the armchair counterparts have an indirect band gap. The band gaps of nanotubes decrease with increasing diameter, similar to the case of carbon nanotubes.

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First-principles calculations for transition phase and thermodynamic properties of GaAs Lu Lai-Yu, Chen Xiang-Rong, Yu Bai-Ru, Gou Qing-Quan 2006, 15 (4):  802-806.  doi: 10.1088/1009-1963/15/4/022 Abstract ( 0 )   PDF (252KB) ([an error occurred while processing this directive])   The transition phase of GaAs from the zincblende (ZB) structure to the rocksalt (RS) structure is investigated by ab initio plane-wave pseudopotential density functional theory method, and the thermodynamic properties of the ZB and RS structures are obtained through the quasi-harmonic Debye model. It is found that the transition from the ZB structure to the RS structure occurs at the pressure of about 16.3\,GPa, this fact is well consistent with the experimental data and other theoretical results. The dependences of the relative volume V/V0 on the pressure P, the Debye temperature \Th and specific heat CV on the pressure P, as well as the specific heat CV on the temperature T are also obtained successfully.

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Simulation of multilayer homoepitaxial growth on Cu (100) surface Wu Feng-Min, Lu Hang-Jun, Wu Zi-Qin 2006, 15 (4):  807-812.  doi: 10.1088/1009-1963/15/4/023 Abstract ( 0 )   PDF (2193KB) ([an error occurred while processing this directive])   The processes of multilayer thin Cu films grown on Cu (100) surfaces at elevated temperature (250--400\,K) are simulated by mean of kinetic Monte Carlo (KMC) method, where the realistic growth model and physical parameters are used. The effects of small island (dimer and trimer) diffusion, edge diffusion along the islands, exchange of the adatom with an atom in the existing island, as well as mass transport between interlayers are included in the simulation model. Emphasis is placed on revealing the influence of the Ehrlich--Schwoebel (ES) barrier on growth mode and morphology during multilayer thin film growth. We present numerical evidence that the ES barrier does exist for the Cu/Cu(100) system and an ES barrier $E_{\rm B} >0.125$\,eV is estimated from a comparison of the KMC simulation with the realistic experimental images. The transitions of growth modes with growth conditions and the influence of exchange barrier on growth mode are also investigated.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Semi-quantitative study on the Staebler--Wronski effect of hydrogenated amorphous silicon films prepared with HW-ECR-CVD system Ding Yi, Liu Guo-Han, Chen Guang-Hua, He De-Yan, Zhu Xiu-Hong, Zhang Wen-Li, He Bin, Zhang Xiao-Kang, Tian Ling, Ma Zhan-Jie 2006, 15 (4):  813-817.  doi: 10.1088/1009-1963/15/4/024 Abstract ( 0 )   PDF (268KB) ([an error occurred while processing this directive])   The method of numerical simulation is used to fit the relationship between the photoconductivity in films and the illumination time. The generation and process rule of kinds of different charged defect states during illumination are revealed. It is found surprisingly that the initial photoconductivity determines directly the total account of photoconductivity degradation of sample.

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Molecular dynamic simulation of lubricant spreading: effect from the substrate and endbead Li Xin, Hu Yuan-Zhong, Wang Hui, Yang Dong 2006, 15 (4):  818-821.  doi: 10.1088/1009-1963/15/4/025 Abstract ( 0 )   PDF (212KB) ([an error occurred while processing this directive])   Molecular dynamic simulations based on a coarse-grained, bead-spring model are adopted to investigate the spreading of both nonfunctional and functional perfluoropolyether (PFPE) on solid substrates. For nonfunctional PFPE, the spreading generally exhibits a smooth profile with a precursor film. The spreading profiles on different substrates are compared, which indicate that the bead-substrate interaction has a significant effect on the spreading behaviour, especially on the formation of the precursor film. For functional PFPE, the spreading generally exhibits a complicated terraced profile. The spreading profiles with different endbeads are compared, which indicate that the endbead-substrate interaction and the endbead--endbead interaction, especially the latter, have a significant effect on the spreading behaviour.

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Local density of states of dc-biased superlattices with time-dependent imperfection Yan Wei-Xian, Li Xiang-Rong 2006, 15 (4):  822-827.  doi: 10.1088/1009-1963/15/4/026 Abstract ( 0 )   PDF (281KB) ([an error occurred while processing this directive])   The single-particle Green's function for a dc-biased superlattices with single impurity potential varying harmonically with time has been obtained in the framework of U(t,t') method and Floquet--Green's function. The calculation of the local density of states shows that new states will emerge between the resonant Wannier--Stark states as a result of the intervention of time-dependent impurity potential, and the increase in electric field strength of impurity will result in the growing of the number of new states between the gaps of neighbouring Stark ladders.

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Kondo effect for electron transport through an artificial quantum dot Sun Ke-Wei, Xiong Shi-Jie 2006, 15 (4):  828-832.  doi: 10.1088/1009-1963/15/4/027 Abstract ( 0 )   PDF (268KB) ([an error occurred while processing this directive])   We have calculated the transport properties of electron through an artificial quantum dot by using the numerical renormalization group technique in this paper. We obtain the conductance for the system of a quantum dot which is embedded in a one-dimensional chain in zero and finite temperature cases. The external magnetic field gives rise to a negative magnetoconductance in the zero temperature case. It increases as the external magnetic field increases. We obtain the relation between the coupling coefficient and conductance. If the interaction is big enough to prevent conduction electrons from tunnelling through the dot, the dispersion effect is dominant in this case. In the Kondo temperature regime, we obtain the conductivity of a quantum dot system with Kondo correlation.

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The role of hydrogen in negative bias temperature instability of pMOSFET Li Zhong-He, Liu Hong-Xia, Hao Yue 2006, 15 (4):  833-838.  doi: 10.1088/1009-1963/15/4/028 Abstract ( 0 )   PDF (312KB) ([an error occurred while processing this directive])   The NBTI degradation phenomenon and the role of hydrogen during NBT stress are presented in this paper. It is found that PBT stress can recover a fraction of Vth shift induced by NBTI. However, this recovery is unstable. The original degradation reappears soon after reapplication of the NBT stress condition. Hydrogen-related species play a key role during a device's NBT degradation. Experimental results show that the diffusion species are neutral, they repassivate Si dangling bond which is independent of the gate voltage polarity. In addition to the diffusion towards gate oxide, hydrogen diffusion to Si-substrate must be taken into account for it also has important influence on device degradation during NBT stress.

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Ultraviolet photovoltaic characteristic of MgB2 thin film Zhao Song-Qing, Zhou Yue-Liang, Zhao Kun, Wang Shu-Fang, Chen Zheng-Hao, Lü Hui-Bin, Jin Kui-Juan, Cheng Bo-Lin, Yang Guo-Zhen 2006, 15 (4):  839-841.  doi: 10.1088/1009-1963/15/4/029 Abstract ( 0 )   PDF (450KB) ([an error occurred while processing this directive])   Fast photoelectric effects have been observed in MgB2 thin film fabricated by chemical vapour deposition. The rise time was $\sim $10 ns and the full width at half-maximum was \sim185\,ns for the photovoltaic pulse when the film was irradiated by a 308\,nm laser pulse of 25\,ns in duration. X-ray diffraction and the scanning electron microscope revealed that the film was polycrystalline with preferred c-axis orientation. We propose that nonequilibrium electron--hole pairs are excited in the grains and grain boundary regions for MgB2 film under ultraviolet laser and then the built-in electric field near the grain boundaries separates carriers, which lead to the appearance of an instant photovoltage.

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The study of magnetization of the spin system in the ground state Jiang Wei, Wang Xi-Kun, Zhao Qiang 2006, 15 (4):  842-844.  doi: 10.1088/1009-1963/15/4/030 Abstract ( 0 )   PDF (182KB) ([an error occurred while processing this directive])   Within the framework of the effective-field theory with self-spin correlations and the differential operator technique, the ground state magnetizations of the biaxial crystal field spin system on the honeycomb lattices have been studied. The influences of the biaxial crystal field on the magnetization in the ground state have been investigated in detail.

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Magnetic entropy change and magnetic phase transition of LaFe11.4Al1.6Cx (x=0--0.8) compounds Chen Jing, Zhang Hong-Wei, Zhang Li-Gang, Dong Qiao-Yan, Wang Ru-Wu 2006, 15 (4):  845-849.  doi: 10.1088/1009-1963/15/4/031 Abstract ( 0 )   PDF (285KB) ([an error occurred while processing this directive])   The unit cell volume and phase transition temperature of LaFe11.4Al1.6Cx compounds have been studied. The magnetic entropy change, refrigerant capacity and the type of magnetic phase transition are investigated in detail for LaFe11.4Al1.6Cx with x=0.1. All the LaFe11.4Al1.6Cx (x=0--0.8) compounds have the cubic NaZn13-type structure. The addition of carbon atoms brings about a considerable increase in the lattice parameter. The bulk expansion results in the change of phase transition temperature ($T_{\rm c})$. Tc increases from 187\,K to 269\,K with x varying from 0.1 to 0.8. Meanwhile an increase in the lattice parameter can also cause a change of the magnetic ground state from antiferromagnetic to ferromagnetic. Large magnetic entropy change \vert \Delta S\vert is found over a large temperature range around Tc and the refrigerant capacity is about 322J/kg for LaFe11.4Al1.6C0.1. The magnetic phase transition belongs in weakly first-order one for x=0.1.

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Simultaneous observation of positive and negative giant magnetoresistances in composite (La0.83Sr0.17MnO3)1－x(ITO)x Wang Miao, Zhang Ning 2006, 15 (4):  850-853.  doi: 10.1088/1009-1963/15/4/032 Abstract ( 0 )   PDF (243KB) ([an error occurred while processing this directive])   We have studied the transport property of the composites (La0.83Sr0.17 MnO3)1-x(ITO)x [ITO=(In2O3)0.95 (SnO2)0.05], which were fabricated by mechanically mixing La0.83Sr0.17 MnO3 and ITO grains. A giant positive magnetoresistance (PMR) has been observed above the Curie temperature Tc for samples with x around 0.40, in addition to the negative magnetoresistance related to spin-dependent interfacial tunnelling below Tc. For (La0.83Sr0.17MnO3)0.6(ITO)0.4, the magnetoresistive ratio for the PMR can reach 39.3% under a magnetic field H=2.24\tm105A/m. Theoretical analysis suggests that the magnetic-field-induced broadening of the p--n barrier between both kinds of grains and the density of the p--n heterostructures should be responsible for the PMR behaviour.

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Raman spectroscopic study of ceramic Sr2Bi4Ti5O18 Du Chao-Ling, Zhang Shan-Tao, Lu Ming-Hui, Gu Zheng-Bin, Cheng Guang-Xu, Wang Jia, Chen Yan-Feng 2006, 15 (4):  854-858.  doi: 10.1088/1009-1963/15/4/033 Abstract ( 0 )   PDF (261KB) ([an error occurred while processing this directive])   Raman spectra of ceramic Sr2Bi4Ti5O18 (SBTi5) are reported to consist of four different Raman bands.Temperature-dependent spectra reveal the relationship between the lattice vibration and the material's structure. There appears a relatively large change in structure of the material at about 273K.The anharmonic potential of the material has a great influence on its phonon mode full width at half maximum (FWHM), which can be expressed by a function of temperature. Theoretical fittings of the FWHMs for the two modes at around 312\,cm-1 and 464\,cm-1 indicate that the latter phonon mode is more anharmonic than the former one.

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Microstructure and optical absorption of Au--MgF2 nanoparticle cermet films Sun Zhao-Qi, Cai Qi, Song Xue-Ping 2006, 15 (4):  859-865.  doi: 10.1088/1009-1963/15/4/034 Abstract ( 0 )   PDF (1342KB) ([an error occurred while processing this directive])   The microstructure and optical absorption of Au--MgF2 nanoparticle cermet films with different Au contents are studied. The microstructural analysis shows that the films are mainly composed of the amorphous MgF2 matrix with embedded fcc Au nanoparticles with a mean size of 9.8--21.4nm. Spectral analysis suggests that the surface plasma resonance (SPR) absorption peak of Au particles appears at \lambda =492--537nm. With increasing Au content, absorption peak intensity increases, profile narrows and location redshifts. Theoretical absorption spectra are calculated based on Maxwell-Garnett theory and compared with experimental spectra.

CROSSDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Preparation of hydrogenated microcrystalline silicon films with hot-wire-assisted MWECR-CVD system He Bin, Chen Guang-Hua, Zhu Xiu-Hong, Zhang Wen-Li, Ding Yi, Ma Zhan-Jie, Gao Zhi-Hua, Song Xue-Mei, Deng Jin-Xiang 2006, 15 (4):  866-871.  doi: 10.1088/1009-1963/15/4/035 Abstract ( 0 )   PDF (301KB) ([an error occurred while processing this directive])   Intrinsic hydrogenated microcrystalline silicon (\muc-Si:H) films have been prepared by hot-wire-assisted microwave electron-cyclotron-resonance chemical vapour deposition (HW-MWECR-CVD) under different deposition conditions. Fourier-transform infrared spectra and Raman spectra were measured. Optical band gap was determined by Tauc plots, and experiments of photo-induced degradation were performed. It was observed that hydrogen dilution plays a more essential role than substrate temperature in microcrystalline transformation at low temperatures. Crystalline volume fraction and mean grain size in the films increase with the dilution ratio (R=H2/(H2+SiH4)). With the rise of crystallinity in the films, the optical band gap tends to become narrower while the hydrogen content and photo-induced degradation decrease dramatically. The samples, were identified as \mu c-Si:H films, by calculating the optical band gap. It is considered that hydrogen dilution has an effect on reducing the crystallization activation energy of the material, which promotes the heterogeneous solid-state phase transition characterized by the Johnson--Mehl--Avrami (JMA) equation. The films with the needed structure can be prepared by balancing deposition and crystallization through controlling process parameters.

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Metastable phase separation and rapid solidification of undercooled Co-Cu alloy under different conditions Cao Chong-De 2006, 15 (4):  872-877.  doi: 10.1088/1009-1963/15/4/036 Abstract ( 0 )   PDF (2128KB) ([an error occurred while processing this directive])   The metastable liquid phase separation and rapid solidification behaviours of Co61.8Cu38.2 alloy were investigated by using differential thermal analysis (DTA) in combination with glass fluxing, electromagnetic levitation (EML) and drop tube techniques. It is found that the liquid phase separation process and the solidification microstructures intensively depend on the experimental processing parameters, such as undercooling level, cooling rate, gravity level, liquid surface tension and the wetting state of crucible. Large undercooling and surface tension difference of the two liquids tend to facilitate further separation and cause severe macrosegregation. On the other hand, rapid cooling and low gravity effectively suppress the coalescence of the minority phase. Severe macrosegregation patterns are formed in the bulk samples processed by both DTA and EML. In contrast, disperse structures with fine spherical Cu-rich spheres homogeneously distributed in the matrix of Co-rich phase have been obtained in drop tube.

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Improvement in efficiency of solar cell by removing Cu2－xSe from CIGS film surface Li Wei, Sun Yun, Liu Wei, Li Feng-Yan, Zhou Lin 2006, 15 (4):  878-881.  doi: 10.1088/1009-1963/15/4/037 Abstract ( 0 )   PDF (227KB) ([an error occurred while processing this directive])   CIGS thin films are deposited by sputtering and selenization. The synthesis of semiconducting polycrystalline thin films and characteristics of devices based on the CIGS absorbing layers are investigated. Their microstructures are characterized by x-ray diffraction and Raman spectroscopy. The results reveal that there exist metallic Cu2-xSe compounds in CIGS film surfaces and the compounds are thought to be responsible for the degradation of the open circuit voltage of solar cells. The optimization of selenization temperature profile and copper content in the precursor surfaces is studied, concluding that the conversion efficiency may be improved by removing metallic Cu2-xSe compounds from the surfaces of CIGS thin films.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Analogue correction method of errors and its application to numerical weather prediction Gao Li, Ren Hong-Li, Li Jian-Ping, Chou Ji-Fan 2006, 15 (4):  882-889.  doi: 10.1088/1009-1963/15/4/038 Abstract ( 0 )   PDF (359KB) ([an error occurred while processing this directive])   In this paper, an analogue correction method of errors (ACE) based on a complicated atmospheric model is further developed and applied to numerical weather prediction (NWP). The analysis shows that the ACE can effectively reduce model errors by combining the statistical analogue method with the dynamical model together in order that the information of plenty of historical data is utilized in the current complicated NWP model. Furthermore, in the ACE, the differences of the similarities between different historical analogues and the current initial state are considered as the weights for estimating model errors. The results of daily, decad and monthly prediction experiments on a complicated T63 atmospheric model show that the performance of the ACE by correcting model errors based on the estimation of the errors of 4 historical analogue predictions is not only better than that of the scheme of only introducing the correction of the errors of every single analogue prediction, but is also better than that of the T63 model.