Vol. 52, No. 5 (2003)
2003, 52 (5): 1048-1050. doi: 10.7498/aps.52.1048
For a generalized Hamiltonian system, a new conservation law derived by using the Lie symmetry is studies. Firstly, the differential equations of the system are given. Secondly, the Lie symmetry under special infinitesimal transformations is studied. Thirdly, the theorem of Hojman is generalized to this system. Finally, an example is given to illustrate the application of the result.
2003, 52 (5): 1039-1043. doi: 10.7498/aps.52.1039
A theory of relativistic analytical statics of rotational systems is constructed. The relativistic virtual work principle and the relativistic generalized equilibrium equations of rotational system are obtained, and an example is given to illustrate the application of the results.
2003, 52 (5): 1044-1047. doi: 10.7498/aps.52.1044
In this paper, the form invariance of nonconservative nonholonmic systems in the phase space is studied. The definition and criterion of the form invariance of nonholonmic nonconservative systems in the phase space is given.The structure equation and conservation law of form invariance is obtained.An example is given to illustrate the application of the result.
2003, 52 (5): 1051-1056. doi: 10.7498/aps.52.1051
In this paper,a form invariance of Hamilton's canonical equations of a nonholonomic mechanical system is studied.First,the definition and criterion of the form invariance in the system under infinitesimal transformations of groups are given .Next,the relation between the form invariance and the conserved quantity of the system is established.Finally,an example is given to illustrate the application of the result.
2003, 52 (5): 1057-1060. doi: 10.7498/aps.52.1057
The extended canonical Noether identities derived from an extended action in the phase space for a system with a higher-order singular Lagrangian are formulated.Based on the canonical symmetries of generalized constrained Hamiltonian systems, a counterexample to a conjecture of Dirac is given. Using the canonical first Noether theorem and canonical Noether identities and the extended canonical Noether identities, we have shown that Dirac's conjecture fails for a system with a higher-order singular Lagrangian in which there is no linearization of constraint in our treatment.
2003, 52 (5): 1061-1065. doi: 10.7498/aps.52.1061
The three Hamaker hypotheses is the theoretical basis to resolve a discrete problem by continuance method. The atomic force, which is obtained by the continuance method on the basis of the Hamaker hypotheses, does not agree with the classical Lennard-Jons potential. The conclusions, that the Hamaker homogeneous hypothesis holds true only for two micro-substances separated far away, and that the digital density and the Hamaker constant vary with the distance, are obtained, followed by the forms of the digital density and the force between the micro-substances.
2003, 52 (5): 1066-1070. doi: 10.7498/aps.52.1066
Nonlinear evolution equations are classified by introducing a concept of “rank”. A new application of the Jacobi elliptic function expansion method is given， and some exact periodic solutions of a new kind of nonlinear evolution equations are obtained.
2003, 52 (5): 1071-1074. doi: 10.7498/aps.52.1071
The s-wave bound states of Klein-Gordon equation and Dirac equation with scalar and vector reflectionless-type potentials are obtained.
2003, 52 (5): 1075-1078. doi: 10.7498/aps.52.1075
The s-wave bound states of Klein-Gordon equation and Dirac equation with scalar and vector potentials with four parameters for diatomic molecules are obtained.
2003, 52 (5): 1079-1084. doi: 10.7498/aps.52.1079
A sudden topological change of a strange repeller happened after a hole-induced crisis is reported. This change is signified by the sudden change of its fractal dimension, and induces a sudden change of the behaviour of the long chaotic transient motion after the crisis, therefore it should be of importance in both basic theory and practice.
The additivily of chaotic time series is proven theoretically. The result of our computer simulation illustrates that the new chaotic time series, praduced by combining several chaotic time series. Canbave fractal attractors, and is sensitive to the initial states, and predictable in short-term prediction. Also, two different trajectories well depart exponentially with time. Therefore,these new series are chaotic time series. We can say that chaos has characteristic of addition. The characteristic that chaotic time series can be integrated is not only important in theory, but also important in practice. It is a theoretical base to research hopping frequency codes of multi-radio-station.
The free-item extrapolated multistep method for precise integration of a nonline ar system and its application in the digital analysis of a chaotic system
2003, 52 (5): 1091-1095. doi: 10.7498/aps.52.1091
The free-item extrapolated multistep method for precise integration is proposedfor a nonlinear system, and the calculation formula for the free-item extrapolated multistep method is obtained. The accuracy of the extrapolated multistep me thod can be improved through increasing the number of extrapolated points; at th e same time, evaluations cannot be increased too much. The precise integration m ethod has been developed and perfected by the present studies. When the method i s applied to a chaotic system, the result is admirable. Numerical calculations s how that the present method is high by accurate and computationally efficient.It has more advantages than the traditional methods in the analysis of a chaotic s ystem.
Adaptive predict-filter of chaotic time series constructed Based on the neighbou rhood in the reconstructed phase space(Ⅰ)linear adaptive filter
2003, 52 (5): 1096-1101. doi: 10.7498/aps.52.1096
A kind of adaptive linear predict-filter of chaotic time series by neighbourhood in the reconstructed phase space is proposed. It can convert the time domain i nto the multi-dimensional vector domain, and predict the chaotic time series by linear filter. The result of computer simulation illustrates that the algorithm is effective in predicting some chaotic series and identifying the signal in the chaotic wave.
Adaptive predict-filter of chaotic time series constructed Based on the neighbou rhood in the reconstructed phase space(Ⅱ)nonlinear adaptive filter
2003, 52 (5): 1102-1107. doi: 10.7498/aps.52.1102
A kind of adaptive nonlinear predict-filter of chaotic time series using the neighbourhood in the reconstructed phase space,the minimum square-root-error criterion and the steepest descent principle is proposed.It can convert the time domain into the multi-dimensional vector domain, and predict chaotic time series by nonlinear filter. The result of computer simulation illustrates that the algorithm is available to predict some chaotic series and anti-noise.
2003, 52 (5): 1108-1111. doi: 10.7498/aps.52.1108
In this paper the design of observers of a class of 3D continuous chaotic systems is discussed. Only using a state variable and its (first-and second-order) time derivatives, one can construct a control law to implement the synchronization between the investigated chaotic systems and its observers.
2003, 52 (5): 1112-1120. doi: 10.7498/aps.52.1112
The experimental data of interspike intervals were recorded in a neural pacemaker,and the presence of period-adding bifurcation cascade was demonstrated.By detecting unstable periodic orbits from the chaotic interspike intervals located in between period-n bursting and period-(n+1) bursting,it is found that the unstable period-n orbit can be detected from the chaotic interspike intervals near the period-n bursting,and the unstable period-(n+1) orbit exists in the chaotic interspike intervals near period-(n+1) bursting.Moreover,the unstable period-n orbit also can be detected.For such a phenomenon the theoretical analyses are presented from the point of view of the nonlinear dynamics by way of the pancreatic β-cell model suggested by Sherman.The direct causes of emergence of the phenomenon are shown to be the intermittency of type Ⅰ and that of type Ⅲ,and they are induced by the saddle-node bifurcation and period-doubling bifurcation,respectively.Consequently,the mechanism for identification of chaotic firing interval is revealed.At the same time,the universality of the phenomenon is elucidated to a certain extent.Furthermore,a novel method is put forward for identifying the chaotic firing interval.
Local projective nonlinear noise reduction method,which is based on locally linear fits to the nonlinear dynamics,is introduced to reduce the noise in electrocorticograms of Spragure-Dawley rats.Recurrence plots are used to estimate the size of local neighbours.In this way,the noise reduction is improved markedly.In order to show that the program for noise reduction is correct,a noise reduction process is implemented for x-axial time series of Lorenz equation contaminated by 50% gaussian white noise.And then,this noise reduction scheme is applied separately to electrocorticograms of anaesthetized rats and those of the onset of epilepsy induced by penicillin in anaesthetized rats.The analyses of a nonlinear prediction demonstrate the efficiency of noise reduction.
2003, 52 (5): 1127-1131. doi: 10.7498/aps.52.1127
A cellular automata model is presented to simulate the traffic flows on a main road in city network in which there are traffic lights at the intersections.We have investigated how the traffic shock wave forms and how it spreads.It is found that the traffic flows have several peak values.When the distances between the intersections are equal,for a fixed value of cycle times of the traffic lights,the current does not depend on the density of vehicles for a range of density.For a high density,when the distance between the intersections is greater than a certain value,the traffic flow maintains constant.
2003, 52 (5): 1132-1136. doi: 10.7498/aps.52.1132
An absolute self-calibration method is proposed for determining the quantum efficiency of a single photon detector which does not require any standard referenc e or a second detector. The method is based on the time correlation of photon pa irs generated in parametric downconversion. A beam of frequency downconverted ph otons is split at a polarizing beamsplitter then recombined at a second beamspli tter, but with a time delay introduced between them so that the two photons of a n original pair enter the detector one by one. The photoelectric pulses from the detector are split into three paths; a compensating delay is introduced into tw o of the paths so that the two signals arrive simultaneously at a coincidence co unter; the third path goes directly to a photon counter. From the ratio of the r eadings of the two counters we can derive the quantum efficiency of the detector . Two methods are given, one for continuous wave lasers and another for high rep etition rate pulsed lasers.
2003, 52 (5): 1137-1142. doi: 10.7498/aps.52.1137
In this paper, a new illation of the principle of PWP (Pressure Wave Propagation) method is presented, and the results, after comparing the PWP method with the PEA (Pulsed Electro-Acoustic) method, indicate that the two methods very resemble with each other in physics. In order to testify the conclusion, the measurement of space charge distribution in XLPE by using the combined system of piezo-PWP/PEA has been corried out, and the experimental results confirm the conclusion.
ATOMIC AND MOLECULAR PHYSICS
The application of modern radio-frequency excitation theory in nonhomogeneous fi eld magnetic resonance imaging
2003, 52 (5): 1143-1150. doi: 10.7498/aps.52.1143
In the problem of nonhomogeneous field magnetic resonance imaging (MRI),echo peaks decay quickly due to traditional design of radio frequency (RF) pulse.In this article,using inverse scattering transform (IST) of the nonlinear dynamics and Shinnar-Le Roux selective excitation pulse design algorithm (SLR Algorithm),we have designed the RF pulse for the nonhomogeneous field MRI.Simulation has been made to test the signal loss induced by the excitation of different types of RF pulses.Simulation results show that the RF pulse sequence optimized by IST and SLR algorithm can improve the signal to noise ratio of MRI considerably
2003, 52 (5): 1151-1156. doi: 10.7498/aps.52.1151
Potassium tunable ultra-narrow bandwidth optical filter at 532nm was studied theoretically and experimentally (T-ESFADOF). The theoretical model of T-ESFADOF was proposed and the transmission spectrum of T-ESFADOF was calculated. The transmission spectra under different electric fields were measured. The e xperimental frequency shift of T-ESFADOF versus electric field and the comparins on with the corresponding theoretical curve have been given
CLASSICAL AREA OF PHENOMENOLOGY
2003, 52 (5): 1157-1161. doi: 10.7498/aps.52.1157
In this paper broad sense grating equation and broad sense chromatic dispersion formula that can be applied to reflection and transmission regions of phase grating in arbitrary oblique angle of incidence are discussed based on the vector diffraction theory. At the same time, the theoretical and numerical analyses for the chromatic dispersion capabilities of the phase grating are made to confirm the reciprocal restricted relation among the incident angle, the incident azimu thal angle, the incident wavelength, the grating period, the refractive index of the substrate in the diffraction area, and the order of diffraction,then the re stricted inequality of grating can be constructed. On the other hand, all possib ilities of improving the chromatic dispersion are presented.
2003, 52 (5): 1162-1167. doi: 10.7498/aps.52.1162
We investigated experimentally the coupling behaviours of the transmitting and reflected light in three c-cut doped lithium niobate crystals.We find that when the direction of the incident light is along the -c axis,the quasi-period oscillation behaviour of the reflectivity and transmissivity is caused by the energy transfer with diffusion and the photovoltaic-effect related transient energy transfer,the directions of these energy transfers are opposite to each other,but not caused by quasi-breakdown of the photovoltaic field.When the direction of the incident light is along +c axis,the directions of energy transfers caused by both mechanisms are the same,so oscillations will not appear.
2003, 52 (5): 1168-1173. doi: 10.7498/aps.52.1168
Considering the larger detuning approximation and the effect of phase damping of cavity field,we have studied the time evolution of the linear entropies for the atom-field system,the field and the atom in the system of a cascade three-level atom interacting with a two-mode field.The effects of ac Stark shifts and initial states of the cavity field on all the linear entropies are analyzed.
Stochastic resonances in the linear model of single-mode lasers driven by color noises with color cross-correlation
2003, 52 (5): 1174-1178. doi: 10.7498/aps.52.1174
We have detected the stochastic resonance(SR) phenomenon by studying the output signal-to-noise ratio (SNR) of the linear model of single-mode laser, which is driven by two color noises correlated in the form of an exponential function. Moreover, we also discuss the influence on SNR from the noise (noise intens ity, correlated strength and correlation time between noises) and signal (signal frequency and signal amplitude).
2003, 52 (5): 1179-1183. doi: 10.7498/aps.52.1179
The refractive index changes of waveguides fabricated by light irradiation in LiNbO3:Fe crystals were investigated by using ordinary and extraordinary laser beams at wavelengths of 632.8nm and 532nm. The experimental results show that the waveguide fabricated by ordinary light is better than that by extraordinary lig ht, as the ordinary light causes much less light-induced scattering. The illuminated time must be strictly controlled when the region with a positive index change, formed by a single thin laser beam, is used as waveguide structure. This is beacuse the waveguide properties may be influenced by the strong noise grati ng and the shift of the waveguide region after the LiNbO3:Fe crystal was irrad iated for a long time. For avoiding the influence of the noise grating, the symm etric waveguide structure with high quality can be fabricated by sheet beam illu mination employing the sandwich method at a relatively low exposure intensity. M oreover, waveguides with different index distributions and different dimensions can be fabricated by changing the width of the irradiating beam and the distance between twice irradiations.
2003, 52 (5): 1184-1189. doi: 10.7498/aps.52.1184
The stability of reflectivity of stimulated Brillouin scattering（SBS） for KrF laser, which is caused by the fluctuation of pump power density, depends on experimental parameters including the pump energy,pressure of the medium and focal length. The stable SBS output can be obtained when the following conditions are satisfied: the pump energy exceeds 5 times the threshold energy, the SF6 pressure is 16×105Pa and the focal length is within 15—50cm. It is also disc overed that the stability of SBS reflectivity is increased with the SBS reflecti vity. The stability of SBS reflectivity is in fact determined by GIL. The th eoretical calculation results are consistent with the experimental results.
2003, 52 (5): 1190-1195. doi: 10.7498/aps.52.1190
In this paper,a fabrication method for the bi-functional bend optical fiber probe which is the key element of atomic force/photon scanning tunnel microscope (AF/PSTM)system,is described.The heated pulling combined with dynamic/static two-s teps chemical etching method is proposed and developed.Using this method,we have made the AF/PSTM bend optical fibre probe.The bend angle of the probe is about 150 degrees;the radius of curvature at the top end is better than 100nm;the cone angle varies from 60 to 90 degrees.The bi-functional bend optical fiber probe i s used in our newly developed AF/PSTM system.The optical and topographic images are obtained simultaneously and the image separation is realized.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2003, 52 (5): 1196-1202. doi: 10.7498/aps.52.1196
A twofluid model has been used to study the influence of the existence of the directive ions and directive electrons on the Bohm criterion of sheath. The main collisions included in this study consist of the charge exchange collision, ionization collision and total energy loss collision. The operated gas is argon with a gas pressure 101325 Pa. Numerical calculation results are obtained, which show that the minimal speed at which drift ions enter into the sheath for directive ions is decreased. This is also valid for the charge exchange collision. The directive electrons make this speed increase, but the ionization collision related to directive electrons makes the speed decrease obviously.
2003, 52 (5): 1203-1206. doi: 10.7498/aps.52.1203
A temporalspatial resolution system, which is composed of a slit, infra scintillator, optical fibre array, streak camera, image intensifier, etc., is constructed for the diagnosis of the Zpinch plasma. This system can effectively shield visible light and has an advantage of gaining flat response in the interested region of xray energy. The designed parameters and experimental results of gaspuff Zpinch are presented in this paper.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2003, 52 (5): 1207-1212. doi: 10.7498/aps.52.1207
A theoretical model is proposed for the abnormal grain growth in thin films of columnar grains. In addition to the grain boundary energy usually considered for the grain growth in bulk materials, the influences of surface energy, interface energy and strain energy are also considered in the model. A reviewed analysis is given out for the anisotropy of energy. For fcc and bcc metal films, surface energy minimization generally favours (111) and (110) textures, while strain energy minimization generally favours (110) and (100) textures.
2003, 52 (5): 1213-1217. doi: 10.7498/aps.52.1213
A realspace renormalizationgroup approach is developed to calculate hopping conductivity of ThueMorse（ＴＭ） nanostructured chain. It is found that the kinds and the sizes, as well as the interface structures and lattice distortion of nanograins have a notable effect on the hopping conductivity of nanostructured systems. From the effect of the degree of random on hopping conductivity, TM chain is a system between Fibonacci and periodic sequence.
2003, 52 (5): 1218-1221. doi: 10.7498/aps.52.1218
Based on a mangbody expansion of shortrange interatomic force,the fourbody interactions in compressed solid helium are computed by ab initio HartreeFock selfconsistent field technique and the atomic cluster method. It is concluded that fourbody terms give a repulsive contribution to the binding energy. By combination of the present manybody expansions with Aziz's longrange attractive potential, the equation of state(EOS) (T=0K) is calculated and compared with available experimental data. Results emphasize the importance of the fourbody interactions in compressed solid He. If only twobody interactions are included such as in the description of the helium gas, the pressure is much overestimated. Good agreement with experiments can only be extended up to about 10 GPa when the threebody corrections are added to; however, the predicted compression curve is obviously lower than that obtained in recent experiments at above 10 GPa. Our study shows that fourbody corrections can bring the calculated EOS into a good agreement with experimental data at pressures of 10\_27GPa. Our result also implies that the higherorder manybody effects should be taken into account at higher pressures.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2003, 52 (5): 1222-1229. doi: 10.7498/aps.52.1222
Electroluminescence (EL) from Sibased organic microcavity has firstly been reported in the literature. The microcavity is made up of the central active multilayers sandwiched between a silver film and a porous silicon Bragg reflector (PSDBR), formed by electrochemical etching of p+Si substrate in the electrolyte of HF: C2H5OH:H2O. The central active multilayers consist of Al (1 nm) / LiF (05 nm) / Alq3 / Alq3: DCJTB / NPB / CuPc / ITO / SiO2． The reflectivity (relative to an Al mirror) of the PSDBR is up to 99%, and the stopband is about 160 nm wide. Resonant cavity mode appears as a tip in the reflectivity spectrum of the Sibased organic multilayer films, indicating that the Sibased organic multilayer structure is indeed a microcavity. The peak widths of the EL spetra are greatly reduced from 70 nm to 12 nm as compared with those measured from noncavity structures. Note that the EL emission from the cavity devices is singlemode, and the offresonant optical modes are highly suppressed. Moreover, an increase of a factor of about 4 of the resonant peak intensity is observed. In addition, the currentbrightnessvoltage characteristics and the effect of parameters on the lifetime of the cavity devices are also discussed. The present technique for obtaining enhanced EL emission from Sibased organic microcavity may also be another novel effective method for realizing allSibased photonic devices and optoelectronics device integration.
2003, 52 (5): 1230-1233. doi: 10.7498/aps.52.1230
Based upon the quantization of a mesoscopic lossless transmission line, analysis is made for the quantum fluctuations of the current and current gradient of the line in the vacuum state and squeezed vacuum state, especialy for the difference between the quantum fluctuations of the transmission line and LC circuit.
2003, 52 (5): 1234-1239. doi: 10.7498/aps.52.1234
A simple expression for the yield strength of a thin polycrystalline film attached to a substrate and with a passivated layer has been derived from a relationship between stress work for dislocation moving and strain energy. It is shown that, the yield strength of a polycrystalline film is determined by two affecting factors (orientation of grains and type of dislocations) and three strengthening factors (passivated layer strengthening, substrate strengthening, and grainsize strengthening). Predictions from the expression are in agreement with reported experimental results. This shows that the model is reasonable.
2003, 52 (5): 1240-1244. doi: 10.7498/aps.52.1240
The AlN film with GaN initiallayer (GaN buffer layer and epilayer)has been grown on αAl2O3 (0001)substrate by electron cyclotron resonanceplasmaenhanced metal organic chemical vapor deposition(ECRPEMOCVD) technique at low temperatures using TMAl and high pure N2 as Al and N sources, respectively. The effects of hydrogen plasma cleaning, nitridation and GaN initallayer on the quality of AlN epilayer have been investigated by RHEED(reflection highenergy electron diffraction) , TEM(transmission electron microscope) and XRD(xray diffraction). And highquality hexagonalphase AlN single crystal films whose cleavability is the same as the substrate have been grown at low temperatures. The full width at half maximum of XRD peaks is 12′.
2003, 52 (5): 1245-1249. doi: 10.7498/aps.52.1245
Singlephase polycrystalline samples of La067Pb033MnO3 were prepared by conventional solidstate reaction method. The crystal structure and magnetic and transport properties are investigated. The structure revealed by the room temperature xray powder diffraction is rhombohedral(R3C), and the Curie temperature is very close to TMI(=360K). At the Curie point, the magnetic properties show the transition from ferromagnetic to paramagnetic, and the conductivity changes from metal to semiconducting. The resistivity decreases with increasing magnetic field. Magnetoresistance reaches a maximum at the Curie point. The maximum magnetoresistance is 14\^5% at H=1\^2MA/m, and 9% at H=0\^6MA/m. The transport results show that the transport data satisfy ρ(T)=ρ0+ρT2.5 for TTMI. This phenomenon is due to the magoncarrier scattering.
2003, 52 (5): 1250-1254. doi: 10.7498/aps.52.1250
The magnetic properties and magnetic entropy change near Curie temperature TC have been investigated for the Ce2Fe16Al compound with a rhombohedral Th2Zn17type structure. The magnetic behaviour is found to obey the secondorder phase transition laws near TC which is 2758K. The critical indices β＝044±001， γ＝130±001， δ＝383±001 are obtained by calculating the field and temperaturedependences of magnetization. The critical indices satisfy the scaling law γ=β(δ-1), but these values deviate the threedimensional Heisenberg model. The maximum entropy change at TC under a field of 2T is 195J/kgK.
2003, 52 (5): 1255-1259. doi: 10.7498/aps.52.1255
The dielectric behaviour of antiferroelectric lead zirconate titanate has been studied by measuring the polarization and capacitance changes with the electric field.The results show that the differential dielectric constant εd calculated from the polarization versus electric field curve exhibits sharp peaks at the electric fields that switch an antiferroelectricsferroelectrics transition,and the maximum value of εd can reach up to 41000. The smallsignal dielectric constant εc measured will decrease rapidly during the phase transition from an antiferroelectric state to a polarized ferroelectric state by increasing the dc bias field, and εc will increase during the ferroelectric state returns to the original antiferroelectric state by reducing dc bias field. It is noticed that the extreme values of the differential dielectric constant εd are electric hysteretic to the extreme of the small signal dielectric constant εc. These phenomena are analyzed by using the electric domain evolution under an electric field.
2003, 52 (5): 1260-1263. doi: 10.7498/aps.52.1260
The photoacoustic spectra from ptype αporous silicon carbides prepared under UV photoassisted process and under darkcurrent condition have been measured，the original silicon carbides were also measured. Combined with RosencwaigGersho theory, the photoaconstic spectra are turned into the absorption spectra. It is found that the energy band gaps of the porous silicon carbide were lower than that of the original silicon carbide, and the causes were analyzed in detail. The absorptions near the absorption edge were studied as well.
2003, 52 (5): 1264-1271. doi: 10.7498/aps.52.1264
A simple model of the graded heterojunction in ALGaInP compound semiconductors was introduced to analyze the energy band profile.We analyze the energy band profiles with the different grading ways but the same grading length,under the different doping densities.We analyze the effect of the different grading lengths on the surplus of the spike potential to the potential of the n region under the different doping densities.We analyze the effect of the graded heterojunction,finding it can improve the HB-LED (high-brightness light emitting diode)performance,and proved by the experiment.A graded heterojunction should be applied to HB-LED,based on this analysis.
2003, 52 (5): 1272-1277. doi: 10.7498/aps.52.1272
A composite of polyaniline (PANI) encapsulating mutilwall carbon nanaotube(MWNT) composite nanotube with nanometer size has been synthesized by insitu emulsion polymerization. Nanotube dimensions have been measured and the nature of the association between the components have been observed using SEM and TEM techniques, the diammer of nanocomposite tube is about 6070 nm.The improvement of thermal stability and crystallinity of nanocomposites have been evaluated by using TGA and XRD. The photoconductivity of PANIMWNT composite nanotube has been enhanced markedly and discussed by taking the photoinduced charge transfer between PANI and MWNT into consideration.
Evaluation of the contribution fraction of close collision to the backward electron emission induced by He+ ion
2003, 52 (5): 1278-1281. doi: 10.7498/aps.52.1278
Electron emission for He+ incident on solid surfaces of C, Cu and Al was simulated with the MonteCarlo method.The backward electron emission yields are calculated.The contribution fraction of electrons emitted by close collision to the total backward emission yield is evaluated with this code, and contribution fraction is 0.5,0.55 and 0.42 for C, Cu and Al, respectively. The effect of highenergy (E＞100eV) δ electrons on the backward electron yield is also considered in detail, and only those δ electrons with an energy of a few hundred eV plays an important role in the backward electron emission. For C, δ electrons will affect the behaviour of electron emission yield near the maximum electronic stopping power. Results of yield obtained are compared with experimental data of other authors, and a good agreement is found.
2003, 52 (5): 1282-1286. doi: 10.7498/aps.52.1282
Influence of oxygen on the field emission of singlewalled carbon nanotubes (SWCNTs) was studied using a fieldemission microscope (FEM) and a quadrupole mass spectrometer. After heat treatment at 1000℃, the field emission of clean SWCNTs occurred. Then oxygen was introduced into the vacuum system and the curves of field emission current versus anodecathode voltage (IV curves) were acquired after oxygen adsorption and desorption, respectively. We have observed that oxygen adsorption on SWCNTs leads to a decrease in field emission current, indicating an increase in the work function. Oxidation etching occurred when the SWCNTs were annealed at about 1000℃ under a pressure of 10-4Pa, and the corresponding changes were observed in both field emission images and IV curves.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2003, 52 (5): 1287-1291. doi: 10.7498/aps.52.1287
Amorphous silicon oxygen nitride (aSiOxNy) films are prepared by microwave electron cyclotron resonance chemical vapor deposition (ECR-CVD) method using 10% SiH4 in N2/O2 mixtures. The Fourier transform infrared absorption spectroscopy shows that the main bonding configuration of the films is SiO and SiN. If O2 is input, the dominant composition of the films is SiOx, while it is SiNx at zero O2 flow rate. A blue photoluminescence (PL) band at 460nm produced by 565eV laser excitation is observed at room temperature from these films, and the emission intensity increases with decreasing O2 flow rate. The blue PL for aSiOxNy films, mainly composed of aSiOx, comes from oxygen deficient defects in the SiOx matrix. For aSiOxNy films, mainly composed of aSiNx, its blue PL is due to the electronhole radiative recombination from the defect states in the SiNx matrix.
2003, 52 (5): 1292-1296. doi: 10.7498/aps.52.1292
Dielectric behavior and optical absorption of quartz glasses before and after irradiating were investigated. Experimental results demonstrate that complex dielectric function of quartz glasses is changed by the irradiation. Its magnitude is decreased by the irradiation. In addition, the change in the dielectric function does not relate to the hydroxyl group in quartz glasses. Experiments also show that dielectric function is relating to the color centers in quartz glasses. Contribution of color center to dielectric function is dependent on its sort and amount in quartz glasses. Dielectric constant decreases with increasing the density of color center
Formation and emission spectra of C2 swan band during the reaction of laser ablating target of aluminum with CF4 beam
2003, 52 (5): 1297-1301. doi: 10.7498/aps.52.1297
The emission spectra of C2 Swan band transition has been observed in the 430nm-600nm region by Qswitch laser ablating target of Al and reacting with CF4 beam.Five vibrational band sequences (Δv=2,1,0,-1 and -2) of d3Πga3Πu are identified and the largest vibrational number of the excited state d is 6.Using a local thermal equilibrium model, the vibrational temperature of d state is about 6340K. Emission spectra from AlF have not been found. Comparing with the results of laserablated Al+O2 system and similar experiment of Cu+CF4 system, while the timeofflight profile of Al(2P1/2-2S1/2,3944nm)and(0,0)band head of C2 are analyzed, we consider that the primary reason of the producing of excited state d3Πg is the electronic energy transformation between excited states Al(2S1/2) and C2.
2003, 52 (5): 1302-1306. doi: 10.7498/aps.52.1302
Highly monodispersed colloidal silica spheres in submicrometer sizes were synthesized by a chemical method.The sizes of silica spheres measured by transmission electron microscopy range from 200 to 600 nm in diameter, and its distribution standard deviation is less than 5%.Scanning Electron Microscopy images show that using selfcrystallization of the silica spheres, we have successfully obtained artificial opals with the three dimensional closepacked, facecentered cubic (fcc) silica matrixes. Reflection spectra study reveals that artificial opals show (111) directional photonic bandgap features.
2003, 52 (5): 1307-1312. doi: 10.7498/aps.52.1307
Differential optical absorption spectroscopy (DOAS) has become a widely used method to measure trace gases in the atmosphere.Their concentrations can be retrieved by a numerical analysis of the atmospheric absorption spectra. But it has been found that DOAS could not gain continuous data under a bad weather condition.Thus it could not fully fit for the demand of the environment monitoring statute.A prediction technology has been developed, based on the stepwise regression analysis method.It is shown that the forecasting data using this method is consistent with the real data after doing a great deal of experiments. This technology has been used in practice.