Vol. 48, No. 2 (1999)
1999, 48 (2): 193-197. doi: 10.7498/aps.48.193
In this paper, the self-affine Sierpinski carpet is constructed. The viscous fingering (VF) in self-affine Sierpinski carpet, based on the assumption that bond radii are truncated Rayleigh distribution, is simulated by means of successive over-relaxation techniques. The fractal dimension of VF is calculated. The results show that the VF pattern of self-affine Sierpinski carpet in the limit viscosity ratio M→∞ is found to be similar to the DLA pattern. When M=1, the interior of the cluster of the displacing fluid is compact and the displacement process is stable for long length scales.
1999, 48 (2): 198-205. doi: 10.7498/aps.48.198
Using a very easy and very convenient method, we controlled the unstable intermediate state of the hysteresis loop in an optical bistable system governed by a delay differential equation. Simultaneously, we also stabilized and suppressed the Hopf bifurcation and double-period bifurcation by this technique. All the numerical results are obtained by simulating the experimental condition of Gibbs et al.
Based on the property that the wavelet can approximate any nonlinear continuous function in the compact supporting set,a new method is presented to control chaos.By this method the trajectories of some typical chaotic systems,such as Duffing equation,Lorenz model,etc.,are controlled to the target orbits or points.It is proved that the wavelet base control algorithm is feasible and control effect is better.
ATOMIC AND MOLECULAR PHYSICS
1999, 48 (2): 213-217. doi: 10.7498/aps.48.213
The local wave function of π electrons is constructed according to the structural property of C60 molecules, and the hopping energies are calculated. For the unequal sp3 hybridization, when the effective nuclear charge number Z=1.112 the energy gap (LUMO-HOMO), bandwidth and ionization threshold (T3g-Hu) obtained by optimizing calculation are 1.70eV,12.19eV and 8.13eV,respectively, these coincide with the experimental results. The corresponding hopping energies are:-2.299eV and -2.113eV for the nearest neighbors; 0.103eV and 0.170eV for the next nearest neighbors; -0.036eV，-0.013eV and -0.005eV for the third neighbors. On the other hand, the computed result also reveals that there are a lot of Rydberg orbitals for C60 molecules.
1999, 48 (2): 218-226. doi: 10.7498/aps.48.218
The generalized Jaynes-Cummings model describes the quantum interaction of the vibration of center-of-mass of a trapped ultracold ion and its inner degree of freedom with a quantized radiation field. By calculating the state vectors and corresponding mean values especially those evolving from the initial entangled ion states, we find that the system will present new phase-sensitive and all-quantized dynamical properties under red and blue sideband excitations.
1999, 48 (2): 227-234. doi: 10.7498/aps.48.227
This article demonstrates some important characteristics of the slow-wave spectra; the Doppler broadening varies with the geometrical parameters of slow-wave structures. Several experimental standing slow-wave spectra was given under different conditions. The influence of magnetic field on the spectra was also discussed.
THE SIMULATION OF 6a10 BAND AND THE DETERMINATION OF ROTAIONAL CONSTANTS IN THE (2+3)PRMPI SPECTRA OF B1(nπ*) STATE IN PYRIDINE
1999, 48 (2): 235-241. doi: 10.7498/aps.48.235
Through simulating the 6a10 band with a partly resolvable rovibronic contour in the (2+3)PRMPI spectra of B1(nπ*) state in pyridine, the rotational constants in B1(nπ*) state are obtained as follows: A′=0.21670cm-1, B′=0.16758cm-1, C′=0.09450cm-1, showing that the negative electricity of N itself becomes weak after one of its lone-pair electrons transits to π* orbital, and the molecular frame expands in general. Moreover, comparing the experimentally measured band with the theoretical curve of 6a10, two vibronic bands, 17a106a101210 and 11b10, which are drowned under the high intensity of 6a10 and have never been reported before, are found.
CLASSICAL AREA OF PHENOMENOLOGY
1999, 48 (2): 242-249. doi: 10.7498/aps.48.242
We have studied the asymmetric behavior of the polarization beats in a four-level system when the pump beams have either narrowband or broadband linewidth, we attribute this asymmetry to the shift of the zero time delay which is due to the dispersion of the optical components.
1999, 48 (2): 250-256. doi: 10.7498/aps.48.250
A single-axis acoustic levitator driven by a magnetostrictive ultrasonic transducer was developed, which can stably levitate metallic, semiconducting and organic materials as dense as 11.3g/cm3 in ground-based laboratory. Two types of resonant chambers were investigated by using boundary element approachin order to well understand the effect of chamber geometry on the sound field and, more importantly, on the capability and stability of acoustic levitation. The calculated results and experimental research indicate that the chamber possessing both a planar and a conical reflecting surface can produce radial positioning forces at the lowest mode. This makes its positioning capability larger than that of the chamber with only a planar reflecting surface.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
PROPERTIES OF ELECTRON CYCLOTRON RESONANCE PLASMAS AND THEIR INFLUENCE ON THE DEPOSITION OF GaN FILMS
1999, 48 (2): 257-266. doi: 10.7498/aps.48.257
Langmuir probes and Faraday cups have been used to characterize electron cyclotron resonance plasmas which have been used in the depositions of GaN films on the substrate of (0001)α-Al2O3.These plasmas were generated with microwave power(Pw) from 300W to 1100W at pressures(p) range from 0.8Pa to 0.05Pa using N2 as the plasma source.The relationship between the plasma parameter,such as ion density(Ni),electron temperature(Te),plasma potential(Vp) and ion current density(Ji),and system parameters,such as pW and p,is given.And the axial and radial distributions of Te,Ni,Vp and Ji are presented.The growth rate and the quality of the GaN film strongly depend on the growth condition.The higher the plasma density,the higher the N/Ga ratio of GaN film.When the microwave power was 850W and gas pressure was 0.22Pa,the plasma near the substrate was characterized by a Te near 1.4eV and plasma density near 2.0×1011 cm-3,and the growth rate of GaN was as high as 0.9μm/h.The full width at half maximum of double-crystal X-ray diffraction rocking curve is 16 arcmin.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1999, 48 (2): 267-272. doi: 10.7498/aps.48.267
A new method,Profile-fitting of X-ray diffraction spectroscopy (PFXDS) method,which was adopted to determine the size distribution of nanocrystalline grains,was introduced in this paper.Its theoretical model and basic hypothesis were clearly interpreted and its advantages and disadvantages were discussed in details.The PFXDS method was applied to the size distribution calculation of nano-SnO2 powder produced by sol-gel technology and the relatively ideal results were obtained.
1999, 48 (2): 273-278. doi: 10.7498/aps.48.273
The first and second-order Raman spectra were measured for single-wall carbon nanotubes (SWNTs). Eighteen first-order Raman spectral lines and seven second-order Raman spectral lines were observed. Spectral lines predicted by theory were almost fully detected. Positions of the spectral lines observed are well coincident with theoretical values. The number of Raman active phonon modes and the second-order Raman spectral lines for high-purity SWNTs observed is the biggest up to date.
1999, 48 (2): 279-283. doi: 10.7498/aps.48.279
Based on the atomic cluster theory and quantum mechanics, the isothermal curves of solid helium and solid hydrogen have been calculated. In the calculation for solid hydrogen, the spherical potential approximation suggested by Cui et al. and the effective helium atomic model of ours were adopted. Comparisons of the theoretical results with the avialable experimental data, which are all below 100GPa, were made and it was found that they are in good agreement with each other.
1999, 48 (2): 284-288. doi: 10.7498/aps.48.284
Oxygen overlayers with different coverages on Ru(0001) were prepared by dissociative adsorption of O2, and sequential dissociation of O2 and NO2. The high-resolution electron energy loss spectroscopy measurements showed a strong coverage dependence of O-Ru strectch mode. The vibrational energy of this mode shifts from 54 meV for the lower coverage limit (θO→0.0) upward to 81 meV for densely packed (1×1)-O overlayer (θO=1.0).
1999, 48 (2): 289-295. doi: 10.7498/aps.48.289
The experimental results about structures and properties of FexMn1-x alloys grown epitaxially on GaAs(001) surface have been reported.For x>0.8, the FexMn1-x alloy grows in single crystal line bcc structure,and for xxMn1-x alloy film transforms from ferromagnetic phase to antiferromagnetic one.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1999, 48 (2): 296-301. doi: 10.7498/aps.48.296
By using the Fermi-Bose transformation, the antiferromagnetic chain is mapped into the bosonic field, and the energy density of the ground state and the excite states of the model are given. The relationship between the energy density of the ground state and the strength of distortion of the model is obtained. The results show that there exists a spin-Peierls transition in the model. Finally, the numerical simulation is performed to verify the above theoretical prediction.
SPECTRAL DENSITY FOR THE TUNNELING CURRENT ZERO-FREQUENCY SHOT-NOISE IN A ONE-DIMENTIONAL MESOSCOPIC SYSTEM
1999, 48 (2): 302-313. doi: 10.7498/aps.48.302
We have derived the expression of the spectral density for the current shot-noise in terms of the nonequilibrium Green's functions(closed-path Green's functions) for a one-dimentional mesoscopic junction, and performed numerical calculations to discuss the dependence of the zero frequency spectral density for the currentshot-noise on other variables when the tunnling junction is pure or impure.
1999, 48 (2): 314-319. doi: 10.7498/aps.48.314
In terms of Miller-Abrahams' theory, a real-space renormalization group approach is developed to calculate the hopping conductivity of one-dimensional nanostructured chain.It is found that the kinds and the sizes,as well as the interface structures and lattice distortion,of nano-grains have a notable effect on the hopping conductivity of nanostructured systems.
1999, 48 (2): 320-325. doi: 10.7498/aps.48.320
The nonlinear optical properties of In2O3 nanoparticles coated by a layer of organic molecules (DBS) in toluene sol and bare In2O3 nanoparticles in hydrosol have been studied in the transparency region by the Z-scan technique.It was found that the surface modification can enhance nonlinear response of In2O3 nanoparticles.The influences of pole effect resulting from surface modification on the optical nonlinearities of In2O3 nanoparticles were also investigated.
RESEARCH OF ELECTRON RESONANT TUNNELING AND LIGHT EMISSION PROPERTIES OF DOUBLE-BARRIER TUNNER JUNCTION
1999, 48 (2): 326-331. doi: 10.7498/aps.48.326
The Cu-Al2O3-MgF2-Au double-barrier tunnel junction has been fabricated. In this structure the electron resonant tunneling occur when a bias voltage is applied because of the existence of a series of separated energy levels in the barrier.Together with the analysis of I-V characteristics of the junction, the light emission properties have been discussed in detail.It shows that the light emission efficency,light emission stability etc,have been improved greatly.The light emission spectrum shifts towards short wavelength region as compared with that of the single-barrier metal/insulator/metal junction.
1999, 48 (2): 332-341. doi: 10.7498/aps.48.332
The structural and electronic properties of eight and fourteen Na or K atoms adsorbed in the β-cage of zeolite LTA(Linde type A) have been studied by using the first-principles discrete variational method(DVM)based on the framework of local density formalism.The β-cage are used as a cluster to simulate the geometrical structures of alkali metal atoms incorporated into the zeolite cages.It isfound that after Na and K atoms are adsorbed by the β-cage of zeolite LTA,the adsorbed Na or K cations prefer to stay near the hexagonal center site of the β-cage.Since the adsorbed Na or K cations are far away from each other(＞0.4nm),the interaction between them is weak and it is hard to say that they form a cluster.The calculated average moment of adsorbed Na or K is very small.For adsorbed eight and fourteen Na,the moments are 0.01μB and 0.02μB,respectively and the total moments of the doped β-cage are 0.10μB and 0.31μB.For adsorbed eight and fourteen K,the moments are all 0.01μB and the the total moments of the doped β-cage are 0.12μB and 0.22μB.These results are in agreement with the experimental observation.
1999, 48 (2): 342-351. doi: 10.7498/aps.48.342
We study the pairing symmetry in high-temperature superconductors from the point of view of group theory analysis in the framework of Ginzburg-Landau model. By considering an orthorhombic distortion from C4v point group because of the correlation of intralayers, the two apparent transitions needed in earlier work on mixed s and d state have been removed. The structure of a single vortex is presented by solving the Ginzburg-Landau wave function equations of the mixed s±idx2-y2 state. The analysis of the magnetic field dependence of the transport behaviors including the critical current and the R-T curve expansion reveals the origin of the so-called “eigen-pinning effect” and offers a good interpretation of the experimental observations.
1999, 48 (2): 352-362. doi: 10.7498/aps.48.352
Starting from a tight binding description,the existence of mixed s-dwave pairing state is discussed. Then,within the framework of the phenomenological G-L theory, the structure of vortex lattice in a high-Tc superconductor is studied.It is shown that there is a strong correlation between the structure of a single vortex and the shape of the vortex lattice.At low temperatures,with the existence of s-wave component and its coupling to d-wave component,the d-wave order parameter and the local magnetic field show tetragonal anisotropy,and the structure of vortex lattice is oblique;however,when the temperature is close to Tc, it may become triangular.
1999, 48 (2): 363-369. doi: 10.7498/aps.48.363
The in-plane resistivity ρab(T) and the out-of-plane ρc(T) have been extensively measured for pure single crystal Bi2Sr2CaCu2O8+δ(Bi2212) annealed at different oxygen pressures.The ρc(T) and anisotropy (ρc(T)/ρab(T)) decrease rapidly with increasing carrier concentration.It is found that the out-of-plane resistivity decreases linearly with decreasing temperature down to about 120K for the overdoped sample,its resistivity anisotropy is of weak temperature dependence.The data of ρc(T) and ρc(T)/ρab(T) are well fitted by the bipolaron theory proposed by Alexandrov and Mott.
1999, 48 (2): 370-377. doi: 10.7498/aps.48.370
A series of polycrystal bulk samples of (La1-yTby)2/3Sr1/3MnO3(x=0,0.05,0.15,0.20,0.25,0.33,0.4,0.5,0.6,1.0) have been prepared. Their microstructrues, magnetization M, resistance R as well as magnetoresistance (MR) have been systemically studied in the temperature range 10K≤T≤420K. The ferromagnetic transition temperature of the samples TC decrease with the increase y. For each sample, R have peak values at a temperature close to TC. The peak values of R increase rapidly with increasing y. At the sample (y=0.40), a colossal magnetoresistance up to 900% has been observed on the temperature 170K.
1999, 48 (2): 378-384. doi: 10.7498/aps.48.378
Three photoluminescence (PL) bands at 340—370,400—430, and 740 nm were observed at room temperature in a-Si∶H∶O films fabricated by plasma enhanced chemical vapor deposition without any post-processing. The violet-blue emission is very strong and stable, and its intensity is closely related to the oxygen content in the films, which can be controlled by the applied dc biases on the sample substrates during deposition. The first two PL peaks are ascribed to oxygen-related colour centers in the a-Si∶H∶O matrix, and the last one is ascribed to the quantum size effect of the nanocrystallites embedded in a-Si∶H∶O matrix and the colour centers in the crystallites interfaces.