Vol. 52, No. 1 (2003)
2003, 52 (1): 1-4. doi: 10.7498/aps.52.1
The high-resolution γ-ray detection technology is a kind of reliable technologies to verify nuclear warhead.In this paper,the relationship that the γ-ray intensity emitting from warhead varies with the thickness of the absorber is studied by modeling calculation and experimental demarcation.A more compendious method to analyze the temper thickness and its application conditions are also discussed.
2003, 52 (1): 5-11. doi: 10.7498/aps.52.5
Starting from a subalgebra of loop algebra 1 we construct a linear isospectral problem.A type of Liouville integrable system and its bi-Hamiltonian structure are presented by the use of Tu-model again.The reductions to the integrable system give rise to the well-known Schrdinger equation and mKdV equation.Therefore,the system is called S-mKdV hierarchy.In terms of the subalgebra of A constructed,we also construct a new subalgebra G of loop algebra A with five dimensions,from which a linear isospectral form is designed.Again,using Tu-model one obtains a type of expanding integrable models of the S-mKdV hierarchy.Some expanding integrable models of hierarchies,such as BPT hierarchy,TB hierarchy etc.are also obtained by using this method.Hence,the method proposed in this paper has important applications generally.Finally as special cases,the integrable couplings of the well-known Schrdinger equation and mKdV equation are obtained.
2003, 52 (1): 12-17. doi: 10.7498/aps.52.12
In this paper,the bifurcation behaviour and chaos control are investigated for a DC-DC buck converter with load capacitor.Some valuable new results are obtained,e.g.,the periodicity adding windows are found in this circuit system and the measure of chaotic motion is found to converge to zero asymptotically increasing load capacitance.Moreover,it is found that the transform ratio of voltage for periodict motion is higher than that for the chaotic motion in the buck converter.These results have some applications for designing practical circuits.At the same time,chaotic behaviours of this circuit system can be effectively controlled by applying suitable periodic impulses to the system.
2003, 52 (1): 18-24. doi: 10.7498/aps.52.18
A two-dimensional discrete system with chaotic and hyperchaotic characteristics and the control of chaos and hyperchaos by means of time-delayed variable feedback have been realized in an electronic circuit.Both the complex behaviours in the circuit without control and the various stabilized periodic states in the controlled circuit are in good agreement with the results obtained by analyzing theoretically and simulating numerically.In addition,the experimental results confirm that it is effective to control chaos and hyperchaos by using the method of improved time-delayed variable feedback.
Simulation investigation on multi-scroll chaotic and hyperchaotic attractors for four-dimensional systems
2003, 52 (1): 25-33. doi: 10.7498/aps.52.25
On the basis of double scroll chaotic attractors,taking the modified Chua's circuit and fourth-order Chua's circuit as examples,a new method for study chaotic and hyperchaotic attractors with multi-scroll in four-dimensional systems is presented.According to this method,the recursion rules used to generate multi-scroll attractors are mathematically obtained.Only given initial values of ma,mb and x1,according to the presented recursion formulas,can the values of other breakpoints and equilibrium points of a piecewise linear characteristic in multi-scroll attractors be determined,and multi-scroll chotic and hyperchaotic attractors for 4D systems generated.This method can be applied to generating attractors having any scrolls with general regularity.Theoretic analysis,computer and circuit simulation results have proved the feasibility of this method.
The theoretical calibration coefficient in the measurement of nonlinear dielectric constant with a scanning tip microwave near-field microscopy
2003, 52 (1): 34-38. doi: 10.7498/aps.52.34
In this paper,the interactions between the tip of the scanning tip microwave near-field microscopy and the nonlinear dielectric material were analyzed.The theoretical calibration coefficient in the measurement of nonlinear dielectric constant as a function of dielectric constant was obtained.The contributions to the coefficient from different directions and the resolution limit were also discussed.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
The x rescaling parameter′ formula of the extended x rescaling model and the nuclear effect 1-A DIS process
2003, 52 (1): 39-41. doi: 10.7498/aps.52.39
In this paper we present an x rescaling paramenters' formula for partons in the extended x rescaling model,where we have established the connection between the rescaling parameter and the mean binding energy.Using x rescaling parameters obtained by the x rescaling parameters' formula,we calculate the average nucleon structure function ratio of DIS process in l-A(Al,Ca,Pb)collision to l-C collision respectively.The result is in good agreement with experimental data.
Specific heat capacity and phase transition on 148—158Sm nucleiin microscopic core plus two-quasiparticle model
2003, 52 (1): 42-47. doi: 10.7498/aps.52.42
Using microscopic core plus two-quasiparticle model, the ground-band, β-band, γ-band and partial high spins states at zero temperature in even 148—158 Sm isotopes are successfully reproduced, these values are coincident with recent experimental one. Under canonical ensemble theory, their finite temperature specific heat capacity is calculated. Seeing that the peak of specific heat capacity is the signal of phase transition, it is by means of this approach that the phase transition of model thermo-excited, one from the superfluid nuclear phase to the normal phase, and one from the deformed shape to the spherical shape taken place in nuclei may be described untidily. The aligned energy and the identity of two-quasiparticle are discussed, and then the thermal stability of nuclear shape is investigated.
2003, 52 (1): 48-52. doi: 10.7498/aps.52.48
The angular momentum projected shell model(PSM) is applied to the nucleus 84Rb. The results of theoretical calculations about the positiveparity yrast band with configuration πg9/2νg9/2 and the negativeparity yrast band with configuration π(p3/2,f5/2)νg9/2 are comparedwith experimental data;especially,the mechanism of signature inversion in the positiveparity yrast band is discussed.The interpretation within the PSM shows that this signature pattern is a signal of a substantial quadrupole shape change with increasing spin,where the nucleus evolves from a prolate shape at low spins through a triaxial shape to an oblate shape at high spins.In addition,the nuclear shape for these two bands are also specified.
2003, 52 (1): 53-57. doi: 10.7498/aps.52.53
The LET factors RＬＥＴ(RＬＥＴ≈005) of neutron response for LiF(Mg,Cu,P)TLD have been determined experimentally due to the existing LET effects of the response for LiFTLD to neutron absorbed dose.Based on the data,one experimental method to define the photon fluence in various n+γ mixed fields in the fast neutron reactor with coupled 6LiF7LiFTL detectors has been checked.The experimental results show that the ratios of the TL due to the effect of neutrons in 7LiF(Mg,Cu,P)to the total TL due to the combined effects of the γrays and neutrons are between 81% and 17.1%.In order to reduce the effect caused by the uncertainty of the neutron spectra and improve the accuracy of the measurement for the photon fluence,we propose a new LiFTLD,in which there are 50% 6LiF and 50% 7LiF.It is coupled with a 6LiFTLD to measure the photon fluence in the n+γ mixed fields.
Fitting the data of nonexotic structural nuclear total reaction cross section with a corrected Glauber model
2003, 52 (1): 58-62. doi: 10.7498/aps.52.58
In the theoretical calculation of total reaction cross section, the results can fit the experimental data very well at high energy, but they are about 10%—20% lower at intermediate energy. In this work the finite range correction has been added to the Glauber model, and a Fermidensitydistribution with two parameters has been chosen as the input density distribution of the nucleus. This shows that the results of the theoretical calculation are in agreement with the experimental one for nonexotic structural nucleus, both at high and intermediate energy regions.
ATOMIC AND MOLECULAR PHYSICS
2003, 52 (1): 63-66. doi: 10.7498/aps.52.63
On the basis of the calculated wavelengths and intensities of n=3→2 transition in Nelike,Nalike and Mglike ions of Eu,and by considering the broadening of individual lines and overlapping of a large number of lines in plasma,we have simulated the spectral structure of n=3→2 resonance transition in Nelike ions and all of the dielectronic satellites transitions of Nalike and Mglike ions of Eu.Also the contributions from highn dielectronic satellites to the resonance line is considered and calculated.Compared with a few existing experimental results,the dielectronic satellite wavelength of 3s—2p transition shows a good agreement with experimental result.
There is very little data public about the molecular structures and molecular spectroscopy for plutonium hydride. The fullelectronic structures in the molecule PuH2 are calculated with the discrete variational method (DVM) based upon the density functional theory. The optimal data of the ground level molecule PuH2 is as follows: bond angle(HH))=115.011°, bond length(PuH)=0208617nm,total orbital energy is -19838.6630 a.u., Fermi energy level is -12.571 eV. The comparisons of the results of full-electronic calculation with the frozen core calculation are given.
CLASSICAL AREA OF PHENOMENOLOGY
2003, 52 (1): 72-76. doi: 10.7498/aps.52.72
We present a set of random number generator based on a quantum mechanical source,which is the process of splitting a beam of photons on a polarizing beam splitter.The randonmess of the polarizing photon is detected by the synchronous singlephoton coincidence detection technique.The random bit data are transferred to a personal computer via a digital I/O interface.The random numbers are tested by the Pseudorandom Number Sequence Test Program(ENT) which is the most popular random number test program in the world.The result is perfect.
2003, 52 (1): 77-80. doi: 10.7498/aps.52.77
Based on physics of micro-cavity and quantum well, the spontaneous emission spectra and spontaneous emission lifetime in the vertical cavity surface emitting laser have been calculated. It is found that the minimum spontaneous emission lifetime is the main reason that the vertical cavity surface emitting laser can realize high\|modulation response after the transfer function of the semiconductor laser is studied.
2003, 52 (1): 81-86. doi: 10.7498/aps.52.81
Laser rapid solidification experiments have been performed on Cu31.4%Mn alloy to investigate the response of microstructure pattern and cellular spacing selection to the variation of growth rate.With increasing growth rate,microstructures go from light band to elongated cell,regular cell,then elongated cell and planarlike structure,and finally to absolute stability planar in turn.Experimental results show that there is a distribution range in cellular spacing under the aser rapid solidification condition,the distribution range and the average spacing decrease with the increase of the growth rate.The maximum,λmax, minimum,λmin,and average primary spacing,A,as functions of growth rate vs, can be given by λmax=682v-033s，λmin=289v-028s and =435v-031s,respectively.The experimental results are compared with the HuntLu numerical model for rapid cellular/dendritic growth,and a reasonable agreement is found.
2003, 52 (1): 87-90. doi: 10.7498/aps.52.87
The method of Power spectra density was introduced to estimate the quality of a high intensity laser beam, and the near field of the self-focusing laser beam was analyzed. We obtained a certain ΔB restriction of the laser beam.The results of numerical simulations were coincident with the experimental data very well .
2003, 52 (1): 91-95. doi: 10.7498/aps.52.91
Holographic polymer-dispersed liquid crystal (HPDLC) is a kind of switchable volume holography. It can be manufactured according to the photo-initiated polymerization-induced phase separation. HPDLC is composed of parallel, periodic polymer-rich and liquid crystal-rich planes. The diffraction efficiency can be modulated by the application of electric field. HPDLC devices are potentially useful for optical communication, information storage and display. How to increase the diffraction efficiency is the key to application. We investigated the dependence of diffraction efficiency on the refractive index of the polymer, exposure intensity, liquid crystal loading and temperature. The best conditions were found to make the diffraction properties optimized. Now the highest diffraction efficiency was 802%. The HPDLC morphologies were also observed and analyzed by scanning electron microscope (SEM).
Theoretical analysis and numerical calculation for the transmission spectrum of long-period fiber gratings with a rectangular index modulation
2003, 52 (1): 96-101. doi: 10.7498/aps.52.96
In this paper, we present a theoretical method to analyze the spectral characteristics of long-period fiber gratings (LPGs) with a rectangular index modulation. Furthermore, we numerically calculate the transmission spectrum of a long-period grating written in Corning FlexcorTM 1060 fiber. The calculation results agree with the experimental results.
A simple model of single-bubble sonoluminescence (SBSL) is proposed. The model is based on the approximation of pressure uniformity, while the mass and the temperature in the bubble remain nonuniform. The water vapor evaporation and condensation at the bubble wall and the water vapor diffusion versus the noble gas inside the bubble are also considered. The number density of electrons is estimated by the Saha equation, and in evaluating the light emission from bubbles, bremsstrahlung from electron-neutral particle and electron-ion collisions, as well as recombination radiation, are accounted for. The intensity of light emission at different water temperature is calculated. It has been found that the results obtained using the bremsstrahlung model at a water temperature of 0 ℃ agree with the experimental data. When the wtater tempreture increases, for example at 20 ℃ or above 20 ℃, the calculated results differ from the experimental data in magnitude. If chemical reactions are taken into account, the results by using bremsstrahlung model are always lower than the experimental data by 2 order of magnitude.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Plasma source ion implantation near the end of a cylindrical bore using an auxiliary electrode for finite rise time voltage pulses
2003, 52 (1): 109-114. doi: 10.7498/aps.52.109
The temporal evolution of the plasma sheath during plasma source ion implantation(PSII) is crucial because it affects the resultant surface properties and structures. In this paper two dimensional fluid model is applied to the problem in computing ion dynamics in the sheath of the end of a cylindrical bore using an auxiliary electrode for finite rise time voltage pulses. The ion density, flux, dose distributions are calculated by solving Poisson's equation and the equations of ion motion and continuity using finite difference methods. Our results indicate that there exist the differences of ion flux and dose among the inner, outer surfaces and the end surface of the bore.
Numerical simulation of liguid alloy flow field during solidification under applied pulsed magnetic fields
2003, 52 (1): 115-119. doi: 10.7498/aps.52.115
A numerical simulation of the flow field during solidification in Al-alloy was corried out by the ANSYS 55 in the present paper. The simulation results were in good agreement with the experimental data. It was found, through the simulation, that not only the melt's movement but also the mechanism of the refinement for the solidified structure and the formation of some defaults during solidification were elementally understood.
In this paper, we report the Terahertz computer tomography(Terahertz-CT). Compared with the x ray computer tomography(XCT), more information could be extracted to process the image. Theoretically, Terahertz-CT could be used to map the complex refractive index distribution in target three-dimensional space. Therefore, it is possible to employ the principle of Terahertz-CT to classify the target inside a black box. This implies potential applications is security inspection and nondestructive examination.
Generation of low frequency electromagnetic solitons in plasmas near the critical density with ultrashort intense laser pulses
2003, 52 (1): 125-134. doi: 10.7498/aps.52.125
Generation of low frequency electromagnetic solitons in plasmas near the critical density by use of an ultrashort intense laser pulse has been studied with a two-dimensional (2D) particle-in-cell simulation code. They are formed while the ultrashort laser pulse is exciting a wake field, with its trailing edge experiencing strong frequency down-shift and part of its energy trapped in the plasmas. The formed solitons are usually found to move with small velocity, which results in the formation of plasma cavities and the acceleration of ions to high energy. It is also found that the soliton formation in 2D simulation geometry depends heavily on the polarization state of the incident pulse.
2003, 52 (1): 135-139. doi: 10.7498/aps.52.135
We analyse the influence of forward Raman scattering(FRS) on the wake-field induced by ultra-intense short-pulse laser with a 25D PIC simulation model. FRS is the major unstable mechanism that draws out the length of scattering pulse, as well as steeps the tail of the laser. Therefore, the wake wave phase velocity decreases obviously and the maximum electron kinetic energy trapped is much less than the conventional theoretic value. Furthermore, the frequency spectrum profile shifts to lower freguency.
Investigation of diamond-like-carbon films deposited on glass substrate by using a pulsed high energy density plasma gun
2003, 52 (1): 140-144. doi: 10.7498/aps.52.140
Smooth, densie and uniform nano-crystalline diamond-like-carbon (DLC) film is deposited on an optical glass substrate by pulsed high energy density plasma(PHEDP) gun charging in nitrogen atmosphore. Scanning electron microscope, Raman spectra and EMSA show that, the grain size of the DLC film is less than 20nm; there are a number of nitrogen atoms and nano-crystalline diamond in the DLC film. The sheet resistance of this film is larger than 109Ω/sq. When the change voltage is lower and charge distance is longer, the deposited film is loose. Theoretic analysis show that, at higher charge voltage, the deposited grain is larger, with longer charge distance, the collision force between deposition grain and substrate is weaker. The theoretic results are in agreement with the experimental conclusion.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2003, 52 (1): 145-149. doi: 10.7498/aps.52.145
Abnormal grain growth and texture change in free-standing Ag and Cu films and those attached to the Si substrates have been investigated with transmission electron microscopy (TEM) and x-ray diffraction (XRD) analysis, after annealing the samples at 300℃ for 2 h.The as-deposited Ag and Cu films, as shown by XRD analysis, have(111) and (100) preferred orientations. After annealing, the free-standing films show a slight increase in the (111) texture, while the films attached to the silicon substrates show strong increases in the (100) and (110) textures. Two anomalous large grains with (110) orientation and four anomalous large grains with (211) orientation are observed by TEM in the attached Cu film after annealing. The results are discussed from an energy point of view.
2003, 52 (1): 150-155. doi: 10.7498/aps.52.150
Magnetic and structural properties of RCo12-xTix with R=Y and Sm compounds have been investigated by using x-ray diffraction and magnetic measurements. It was found that all compounds investigated are almost of a single phase with the ThMn12-type structure. x-ray diffraction patterns of magnetically aligned powder samples indicate that the easy magnetization directions (EMD) at room temperature are in the basal plane for SmCo12-xTix compounds while for YCo12-xTix compounds the EMDs are along the c-axis. The lattice parameters increase monotonically with increasing Ti content for all the compounds investigated. The Curie temperature Tc decreases monotonically with increasing Ti content for both YCo12-xTix and SmCo12-xTix. The saturation magnetization Ms decreases with increasing Ti content for all the systems. The anisotropy field μ0Ha of YCo12-xTix compounds decreases monotonically with increasing Ti content, while the Ti content dependence of the anisotropy fields μ0Ha for SmCo12-xTix compounds exhibits a maximum at about x=1.74, which can be understood in terms of a two-sublattice model of anisotropy.
2003, 52 (1): 156-162. doi: 10.7498/aps.52.156
In the course of a systematic search for stable silicon surfaces, we have studied four stable high-index silicon surfaces, i.e., Si(1,1,11), (1 0 8), (2 1 2), and (15,1,17), by analyzing their low-energy electron diffraction (LEED) patterns. The results show not only that all these surfaces are stable but also that Si(15,1,17) is a major stable surface,whereas the rest three are minor stable surfaces, meaning that their unit cells consist of a nanometer facet of a major stable surface along with a double height step. In view of the periodic facet-step morphology of these minor stable surfaces, we suggest that these surfaces have the potential to be used as templates for growth of periodic nanowires of some suitable materials.
2003, 52 (1): 163-168. doi: 10.7498/aps.52.163
Grand canonical Monte Carlo method is used to simulate the adsorption of linear two-centre ethane molecules in MCM-41 of different pore sizes at different temperatures and a range of pressures.Beside the amount of adsorption, the local density profiles for the mass centre and methyl groups as well as the angle distributions simulated for the ethane molecules are used to explore microscopic and orientational structures of the adsorbate inside MCM-41. The results indicate that ethane molecules near the wall of MCM-41 prefer to lie on the surface both at 180 and 300 K, while the rest molecules exhibit a trend to be perpendicular to the wall,and the increase of temperature makes the molecules placed more randomly.In addition, the distributions show that the molecules in the vicinity of the centre are basically disordered even at a low temperature of 180 K.
Infrared analysis on hydrogen content and Si-H bonding configurations of hydrogenated amorphous silicon films
2003, 52 (1): 169-174. doi: 10.7498/aps.52.169
The Fourier transform infrared (FTIR) spectrum is an effective technology for studying the hydrogen content (CH) and the silicon-hydrogen bonding configuration (Si-Hn) of hydrogenated amorphous silicon (a-Si∶H) films. In this paper, CH and Si-Hn of a-Si∶H films, fabricated at different substrate temperatures (Ts) by plasma enhanced chemical vapor deposition method, have been obtained by analyzing their FTIR spectra that are treated by baseline fitting and Gaussian function fitting. The effects of Ts on CH and Si-Hn are studied.
2003, 52 (1): 175-179. doi: 10.7498/aps.52.175
Nanotubular polyaniline (PANI) doped with protonic acids have been synthesized by a “template-free”method. The temperature dependence of resistivity (ρ) and magnetic susceptibility has been studied. The influences of different protonic acids (counterions), doping concentration and the synthesizing concentration of dopant on resistivity also have been investigated. It is obvious from experimental results that ln ρ is linear against T-1/2. With increasing acidity of protonic acids ,doping concentration and the synthesizing concentration of dopant, the resistivity of the samples decreases, and the magnetic susceptibility can be written as a sum of a temperature-independent Pauli spin susceptibility term and a Curie-law term.
2003, 52 (1): 188-191. doi: 10.7498/aps.52.188
Linear response theory was used to predict threshold-voltage shifts for CC4007-NMOS device at dose rates of 0.1, 2.3, 44 and 91rad(Si)/s. These predictions were compared with the threshold-voltage shifts obtained after 60Co irradiations actually performed at these dose rates, and the agreement is excellent. Also, we use the linear response theory to predict the response of CC4007-NMOS device during radiation and 25℃ annealling for high and low-dose-rates. According to the predictions, under the same conditions of radiation and annealling, the threshold-voltage shifts caused by high dose-rate irradiation after room temperature annealling were equal to that by low-dose-rate irradiation within the limit of error, but the total times for both were the same. Finally, the failure doses for CC4007-NMOS device at different dose rates of irradiation were predicted also using the linear response theory.
The initial angle solution for the ultra-short laser pulse induced transient twist reorientation in a plane-aligned nematic liquid crystal
2003, 52 (1): 192-196. doi: 10.7498/aps.52.192
The optical phase retardation method was employed to observe the transient twist reorientation effect of a plane-aligned nematic liquid crystal induced by ultra-short laser pulses. The experimental result indicated that, although the electric field intensity of laser pulses is much higher than that needed for twist deformation, it does not ensure the twist reorientation under the laser pulse. This is because the width of laser pulse is very short and the response time for the twist reorientation is very long. To overcome this barrier an optimum angle (45°)between the polarization of the laser pulse and the director orientation in substrates is found by analysis.Using this initial angle, we observed a plane-aligned nematic liquid crystal cell doped with a few o-(D-Thr)N-C2-(TPP) to possess memory effect after the laser pulse pump, which was important in optical data storage and memory display.
2003, 52 (1): 197-201. doi: 10.7498/aps.52.197
Pyroelectric properties in alternating DAEP/NC Langmuir-Blodgett (LB) films and effects of incorporating the barium cations on pyroelectric behaviours have been investigated.The pyroelectric coefficient measured is found to be 58μCm-2K-1 at 300K.The dielectric properties have been measured and used to determine the figures of merit in thermal devices. Relative permittivity εr and dielectric loss values tanδ of pyroelectric films (in the range of 1kHz—100kHz) are 2.34—1.96 and 0.08—0.04, respectively. The effects of different deposition and incorporated metal ions on pyroelectric properties are also discussed in this paper. It is indicated that the alternating LB films is promising in the field of pyroelectricity and pyroelectric infrared detector.
2003, 52 (1): 202-206. doi: 10.7498/aps.52.202
The favourite adsorption site of ethylene on the Ni (110) surface at high and low coverages was investigated by theoretical calculation. In the cluster calculations a partial optimization of adsorbate geometry has been carried out. At low coverage the ethylene molecule occupies approximately the midway between the short-bridge and atop sites. The C—C axes of molecules are almost parallel to the ridges and are offset in the direction, the angle of C—C axis with respect to the Ni surface plane is about 10°. The C—C bond length is 0151 nm. At a high coverage (05ML), ethylenes form a c (2×4) phase. The local adsorption sites of two ethylene molecules in a surface unit mesh are found to be quite similar to that at low coverage, but the C—C bond lengths are 0142 nm and 0142 nm, respectively.
2003, 52 (1): 207-210. doi: 10.7498/aps.52.207
Due to the very low thermal conductivity of the thick-buried oxide layer, the silicon-on-insulator(SOI) power devices have an inherent self-heating effect, which limits their operation at high current level. Adopting the new silicon-on-insulator-multilager (SOIM) structures is a good solution to reduce the self-heating effect. In this paper, the SOIM structures were successfully produced by electron beam evaporation of silicon on porous silicon and epitaxial layer transfer. The quality of the structures was investigated by XTEM and SRP. Experimental results show that the buried Si3N4 layer is amorphous and the new SOIM sample has good structural and electical properties.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2003, 52 (1): 211-216. doi: 10.7498/aps.52.211
The reverse I(V) measurement and analytic calculation of the electron transport across a Ti/6H-SiC Schottky barrier are presented. Based on the consideration of the barrier fluctuations and the barrier height shift caused by image charge and the applied voltage drop across Ti/SiC interfical layer, a comprehensive analytical model for the reverse tunneling current is developed using a WKB calculation of the tunneling probability through a reverse biased Schottky barrier. This model takes into account the main reverse conduction mechanism, such as field emission, thermionic field emission and thermionic emission. The fact that the simulated results are in good agreement with the experimental data indicates that the barrier height shift and barrier fluctuation can lead to reverse current densities orders of magnitude higher than that obtained from a simple theory. It is shown that the field and thermionic field emission processes, in which carries can tunnel through the barrier but cannot surmount it with insufficient thermal energy, dominate the reverse characteristics of a SiC Schottky contacts in a normal working condition.
2003, 52 (1): 217-224. doi: 10.7498/aps.52.217
AMPS simulator, which was developed by Pennsylvania State University, has been used to simulate photovoltaic performances of nc-Si:H/ c-Si solar cells. It is shown that interface states are essential factors prominently influencing open circuit voltages (VOC) and fill factors (FF) of these structured solar cells. Short circuit current density (JSC) or spectral response seems more sensitive to the thickness of intrinsic a-Si:H buffer layers inserted into n+-nc-Si:H layer and p-c-Si substrates. Impacts of bandgap offset on solar cell performances have also been analyzed. As ΔEC increases, degradation of VOC and FF owing to interface states are dramatically recovered. This implies that the interface state cannot merely be regarded as carrier recombination centres, and impacts of interfacial layer on devices need further investigation. Theoretical maximum efficiency of up to 3117%(AM15, 100mW/cm2, 040—11μm) has been obtained with BSF structure, idealized light-trapping effect(RF=0, RB=1) and no interface states.
2003, 52 (1): 225-228. doi: 10.7498/aps.52.225
The Hamilton's equations of motion were derived by analyzing the process of excitation for magnon pair in magneto-ordered medium placed in a microwave oscillator. The result showed that the magnon pair couples with the microwave resonator with nonlinearly oscillatory characterization.
2003, 52 (1): 229-232. doi: 10.7498/aps.52.229
Bismuth sodium titanate Bi05Na05TiO3 ceramic with about 96% of theoretical density was prepared by sol-gel processing. The saturate P-E hysteresis loop can be obtained under a 100kV/cm AC electric field for the sol-gel processed Bi05Na05TiO3 ceramic and the remanent polarization Pr and coercive field Ec are 32μC/cm2 and 61kV/cm respectively. Moreover, from the piezoelectric measurements, this material fabricated by sol-gel processing was found to have increased piezoelectric constant d33=102×10-12C/N and electromechanical coupling factor kt=58%. Therefore, sol-gel method is a potential fabrication technique for this lead-free piezoelectric ceramic.
Structure and infrared absorption characterizations of yttrium silicides formed by ion beam synthesis
2003, 52 (1): 233-236. doi: 10.7498/aps.52.233
Buried hexagonal YSi2 layers were formed using 100 keV yttrium ions to a dose of 1×1018 Y+cm-2 implanted into (111) oriented silicon wafers by a metal vapor vacuum arc ion source. The structure and infrared absorption spectra of the compound layers have been investigated by x-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) and Fourier transform infrared (FT-IR) transmittance spectrometry. It was shown that YSi2 has been directly formed during the implantation. A tendency of preferred growth was found in the following process of infrared irradiation. RBS measurements revealed that, after infrared irradiation, the average atomic density ratio of Si to Y in the buried layers decreases from 24 down to around 20, which is close to the stoichiometry of hexagonal YSi2. The characteristic vibration absorption spectra of the silicides have been obtained by FT-IR transmittance measurements.
2003, 52 (1): 237-241. doi: 10.7498/aps.52.237
CNx nanotubes have been generated by thermal decomposition of ferrocene/xylene over cobalt powder at 780℃—940℃ in an atmosphere of N2, H2 and NH3 released from NH4Cl pyrolyzing at 300℃. The high-resolution transmission electron microscope (HRTEM) images show that the tubes consist of unusual “interlinked-cone". The catalytic growth mechanism of CNx nanotubes is discussed based on the formation energy of different structures. Raman spectroscopic studies show that the ID/IG ratio represents the crystallinity of the CNx nanotubes. The shift of the Raman band to higher frequencies confirms the nitrogen incorporation.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2003, 52 (1): 242-246. doi: 10.7498/aps.52.242
By finite difference method, the evolvement of plasma generated by a pulsed laser is studied for pulsed laser deposition of KTa065Nb035O3(KTN) thin film. We have discussed the movement of particles in plasma in isothermal and adiabatic expansion stages in more detail. At the same time, we have simulated the change of figure of plasma at different time. Moreover, the physics mechanism in expansion of the plasma have been explained. The theoretical results are compared with our experiments and other author's conclusions.