Vol. 55, No. 10 (2006)
2006, 55 (10): 4983-4986. doi: 10.7498/aps.55.4983
Optical properties of Al0.9Ga0.1As/AlyGa1-yAs/GaAs/AlxGa1-xAs DBR with inhomogeneous graded interfaces has been investigated by using characteristic matrix method. The refractive index model and the analytic characteristic matrix of graded interfaces are obtained. The reflectance spectrum and the reflective phase shift are calculated for GaAs/Al0.9Ga0.1As DBR and graded interfaces DBR by using characteristic matrix method. The effect of graded interfaces on the optical properties of DBR is discussed. The result shows an extra graded phase matching layer must be added in front of the graded interfaces DBR to fulfil the conditions of phase matching at central wavelength. The accurate thickness of phase matching layer is calculated by optical thickness approximation method.
First, the method presented by Hojman for finding the conserved quantity of the system of second order differential equations is generalized and applied to the system of first order differential equations, particularly to the odd-dimensional system for finding the integral in this paper. Next, it is proved that the Hojman theorem is a special case of the theorem given in this paper. Finally, an example is given to illustrate the application of the result.
2006, 55 (10): 4991-4994. doi: 10.7498/aps.55.4991
In this paper, by using Mathematica software to disclose the relationship between partial derivative and high-order derivative of different variables in the function r=r(q(t),t), the symmetry of Yang Hui Triangle of the function r=r(q(t),t) is discovered. Combining the symmetry of Yang Hui triangle with the Newtonian second law, the high-order differential equations of motion are deduced. Finally the high-order differential equations of systems under ideal constraints are discussed.
2006, 55 (10): 4995-4998. doi: 10.7498/aps.55.4995
Based on the total time derivative along the trajectory of the system, the definition and the criterion of Noether form invariance of nonholonomic controllable mechanical systems of non-Chetaev’s type are presented. A new conserved quantity, as well as the Noether conserved quantity are deduced from the Noether-form invariance. An example is given to illustrate the application of the result.
New exact solutions and complex wave excitations in (2+1)-dimensional generalized Nozhnik-Novikov-Veselov system
2006, 55 (10): 4999-5006. doi: 10.7498/aps.55.4999
Starting from an extended mapping approach and a linear variable separation method, new families of exact solutions with arbitrary functions for (2+1)-dimensional Generalized Nozhnik-Nivikov-Veselov system(GNNV) are derived. We found that some new and interesting complex wave excitations are derived from a periodic wave solution.
2006, 55 (10): 5007-5013. doi: 10.7498/aps.55.5007
By using a two-dimensional, time-dependent electromagnetic field model (EM model), the spherics and red sprite phenomenon is studied. The simulation results show that the total electric fields produced by lightning include radiation field and quasi-electrostatic field (QEF). The spherics result from the radiation field, which propagates within the earth-ionosphere waveguide. The optical emissions of the first positive band of N2 caused by the QEF form the red sprite phenomenon. By means of simulation we have found the red sprite apparently appearing in “V” shape during its evolution and a bright nucleus existing within the structure of the red sprite, while the brightness of the exterior of the red sprite, which is referred to as sprite halo, being relatively weaker.
2006, 55 (10): 5014-5017. doi: 10.7498/aps.55.5014
A family quasi-distribution function representation is defined in this article. This family quasi-distribution function representation is constructed from the family wave function of the Schrdinger equation in phase space in which the definitions of the operators are α=αp-i?q and α=(1-α)q+i?p. Two interesting relationships are found. The first one is that the family wave function of the Schrdinger equation in phase space is a “Window” Fourier transform of the function φ(λ)exp［i(1-α)qp/?］. The second one is that different choices of the window functions result in different distribution functions. When the window function g(λ) is a Gaussian function the distribution function is the Husimi-like distribution function. When the window function g(λ) is a plural function representing an ellipse, the quasi-distribution function is the Ellipse distribution function; and finally when the plural function g(λ) is supplemented with the additional condition α=0, it will result in the standard ordering, anti-standard ordering distribution function and Wigner function. In this case g(λ) is a function depieting a rectangular window with width λ and height 1/12π?.
2006, 55 (10): 5018-5022. doi: 10.7498/aps.55.5018
Quantum constraint dynamics and tracking control strategy to stabilize the coherence of a decoherent system is applied to a dissipative qubit system at a finite temperature. By using a control field dependent on the dynamical state of the qubit through the constraint equations, we show that the quantum state of the qubit can be preserved within a finite time duration by the feedback effect of the qubit system. It is also shown that the temperature plays a negative role in the control strategy.
Effect of the longitudinal and transverse stacking period of InAs/GaAs quantum dots on the distribution of strain field
2006, 55 (10): 5023-5029. doi: 10.7498/aps.55.5023
A systematic investigation is made on the influence of the longitudinal and transverse period distributions of quantum dots on the elastic strain field. The results showed that the effects of the longitudinal period and transverse period on the strain field are just opposite along the direction of center-axis of the quantum dots, and under proper conditions, both effects can be eliminated. The results demonstrate that in calculating the effect of the strain field on the electronic structure, one must take into account the quantum dots period distribution, and it is inadequate to use the isolated quantum dot model in simulating the strain field.
Experimental generation of bright green light in amplitude-squeezed state via extracavity frequency doubler
2006, 55 (10): 5030-5035. doi: 10.7498/aps.55.5030
Bright green light in the amplitude-squeezed state is experimentally generated from a frequency doubler with semi-monolithic F-P configuration consisting of an a-cut type-Ⅱ KTP crystal and a concave mirror. The amplitude-squeezing of 3.1±0.2dB at 540nm wavelength is obtained with the pump power of 50mW under the conditions of the two infrared modes in resonance and the green mode nearly in resonance.
2006, 55 (10): 5036-5040. doi: 10.7498/aps.55.5036
An analytic model of direct tunneling current of small-scale MOSFETs in depletion and inversion is developed based on analytic surface-potential model and replacing the multi-subband with a single-subband. The simulated results are in good agreement with the results of self-consistent solution and experimental data, but take much shorter computing time than the self-consistent solution method. This indicates that the model can be used for analysis of gate-leakage properties of MOS devices with not only SiO2 but also high-k materials as gate dielectric and high-k gate dielectric stack structures, and circuit simulation of MOS devices.
Selective effect to frequency and direction of gravitational waves on gaussian beam resonance system
2006, 55 (10): 5041-5047. doi: 10.7498/aps.55.5041
Gaussian beam resonance system (GBRS) opens a very important window for detection of relic stochastic high frequency gravitational waves (HFGWs) of early universe. The results of calculation show that the first-order perturbation photon flux produced by this system has no observable effect when the GWs frequency is different from that of Gaussian beam. The first-order perturbation photon flux produced by GBRS will be reduced by several orders of magnitude when the propagation direction of GWs is different from that the positive direction of the symmetrical axis of Gaussian beam, i. e., GBRS only responds to relic HFGWs that propagate along a specific direction. Therefore, GBRS have a useful selective effect with respect to the frequency and propagation direction of relic HFGWs.
The collision problem of one kind of methods for constructing one-way Hash function based on chaotic map
2006, 55 (10): 5048-5054. doi: 10.7498/aps.55.5048
Chaos would happen within certain ranges of parameters of chaotic system. The chaos sequence has good pseud random character. Now some papers have provided some methods to construct one-way hash function based on chaotic map. Through analyzing these methods, the appearance of collision is proved. So some key problems are pointed out which should be taken care of while constructing one-way function based on chaotic map.
Synchronization of Liu chaotic system based on linear feedback control and its experimental verification
2006, 55 (10): 5055-5060. doi: 10.7498/aps.55.5055
Synchronization of Liu chaotic system is studied. Based on the characteristic of the chaotic system and linear feedback control method, the range of the controller parameter for synchronization is derived, the results of simulation and experiment are provided to show the effectiveness of the proposed method.
2006, 55 (10): 5061-5069. doi: 10.7498/aps.55.5061
In this paper, the Liu chaotic system is discussed. Its basic dynamical behaviors, such as the phase portrait, Lyapunov exponents, Poincaré mapping, power spectrum are studied. The influence of system parameter on the chaotic system is discussed through Lyapunov exponents spectrum and bifurcation diagram. Various attractors are demonstrated not only by computer simulation but also by the realization of an electronic circuit.
2006, 55 (10): 5070-5076. doi: 10.7498/aps.55.5070
A method is presented here to direct two or many chaotic systems towards low-period motions by using adaptive pulse perturbation method. Many chaotic systems can be controlled to different periodic orbits simultaneously. When the same input state variable of the adaptive pulse perturbation is used, two or more chaotic systems can be controlled to different periodic synchronizations. Simulation shows that the R?ssler chaotic system can be stabilized to different periodic orbits by using the method, which verifies its effectiveness.
2006, 55 (10): 5077-5082. doi: 10.7498/aps.55.5077
This paper addresses the adaptive control and synchronization of the coupled dynamos system with unknown system parameters. Adaptive controller is developed to suppress chaos to equilibrium points and realige synchronization of two identical coupled dynamos systems with unknown system parameters. Numerical simulations are employed to show the effectiveness of the proposed method.
2006, 55 (10): 5083-5093. doi: 10.7498/aps.55.5083
This paper studies the problem of control ling the chaotic behavior of a modified coupled dynamos system. Two different methods, namely the feedback and non-feedback methods are used to control chaos in the modified coupled dynamos system. Based on the Lyapunov direct method and Routh-Hurwitz criteria, the conditions of suppressing chaos to unstable equilibrium points or unstable periodic orbits (limit cycles) are discussed, and they are proved theoretically. Numerical simulations show the effectiveness of the two different methods.
Effects of spontaneous emission noise in semiconductor lasers on chaotic optical communication systems
2006, 55 (10): 5094-5104. doi: 10.7498/aps.55.5094
A chaotic optical communication system based on external optical feedback is constructed. By introducing the Langevin noise sources, the master-slave rate equations including spontaneous emission noise characteristics are deduced. Utilizing the obtained mathematical model, two kinds of possible chaos synchronization in the system, i.e. complete chaos synchronization and generalized mode-locking chaos synchronization, are studied. The effects of the spontaneous emission noises of the two lasers on the two types of synchronization as well as the chaotic outputs of the transmitter and receiver are discucsed. Finally, for a sequence of pseudorandom digital bits at 2.5Gb/s bit rate, the encoding/decoding process basing on chaotic masking method is presented, and the effects of noise on decoding performance are examined.
Synchronizing erbium-doped fiber dual-ring lasers by using the method of feedback modulating-parameter
2006, 55 (10): 5105-5108. doi: 10.7498/aps.55.5105
A method of feedback modulating-parameter is presented to synchronize hyperchaotic systems, and is applied to the hyperchaotic erbium-doped fiber dual-ring laser systems. A circuit is designed in the laser synchronization system to avoid phase-vagueness automatically. Numerical simulation shows that two hyperchaotic erbium-doped fiber dual-ring lasers can be identically synchronized, when the feedback intensity is suitably selected.
2006, 55 (10): 5109-5114. doi: 10.7498/aps.55.5109
In this paper, a method of chaotic controlling is presented via controlling the phase in semiconductor lasers under to external optical injection. Chaos can be controlled to a periodic state or multi-periodic states by periodically modulating a phase-controller to control the injection light phase. Under the conditions of different intensities of injection light, numerical results shou thet: (1) Chaos is controlled into periodic state, dual-periodic state, triple-periodic state, four fold-periodic state and multi-periodic state respectively by a method of half-wavelength periodic modulation; (2) Chaos can be controlled into periodic state or multi-periodic state by the method of quarter-wavelength periodic modulation. Injection-locking phenomena in laser is produced under the conditions of high frequency modulation, where the frequency_locking domain is from 19GHz to 21GHz; (3) Chaos is also controlled into periodic state and multi-periodic state by a method of a wavelength periodic modulation.
2006, 55 (10): 5115-5121. doi: 10.7498/aps.55.5115
The odd multiple frequency phenomenon emerging in the stochastic resonance was studied, and some new theoretical conclusions was drawn. Based on these conclusions we found the reference frequency which must be set in the chaotic detector. Using the frequency selectivity of chaotic detector, the false frequency existing in the odd multiple frequency was filtered out.
2006, 55 (10): 5122-5128. doi: 10.7498/aps.55.5122
In this paper, the collective dynamic behaviors of N two-level atoms pumped by two-mode light field in a harmonic trap are investigated. When atoms are driven by the intense pump field, the atomic oscillating modes in the trap are continually excited by the photon recoil effect, which discretely changes the atomic detuning from the pumping field. Under proper resonant conditions the weak probe field will be greatly amplified and the atomic spatial structures will be spontaneously formed in the phase space.
2006, 55 (10): 5129-5134. doi: 10.7498/aps.55.5129
The solidified structure of solute elements is important for the quality and the properties of alloys. In the present study, the solidification behavior of aluminum alloys is studied under various high magnetic field conditions, and the influences of uniform and gradient magnetic fields with different intensities and directions on the distribution and the morphology of solute elements of Al-Cu and Al-Mg alloys are investigated. It is found that because of the difference in the electromagnetic forces acting on Cu element and Mg element which have different physical properties in the matrix, the distributions of Cu element and Mg element are the opposite both in the matrix crystallites and in grain boundaries under high static magnetic field, and not only the content but also the distributions of Cu and Mg elements are obviously different under gradient magnetic field. This paper offers a reference to control the solidification structure of solute elements whose physical properties are different in alloys under high magnetic fields.
2006, 55 (10): 5135-5139. doi: 10.7498/aps.55.5135
In this paper, the digital image correlation method for the analysis of 3-D displacement field is firstly presented. The 3-D displacement field caused by internal microstructures evolution is obtained by correlative calculation of digital images taken before and after deformation of the object. The 3-D searching window, correlation function and the fitted function of correlation coefficient are obtained. The numerical simulation results confirmed this technique. The precision of displacement measuvement is 0.02 pixel.
2006, 55 (10): 5140-5144. doi: 10.7498/aps.55.5140
Samples of Er3+/Yb3+ co-doped ZrO2-Al2O3 powders were prepared by solid-state reaction. The upconversion luminescence spectrum excited by 980 nm laser light suggests that there exit three main emission bands: one red emission band centered at 654 nm and two green emission bands centered at 545 and 525nm, corresponding to Er3+ ions transitions of 4F9/2→4I15/2, 4S3/2→4I15/2 and 2H11/2→4I15/2, respectively. The emission band centered at 654 nm is much stronger than the other two. The upconversion mechanisms are discussed and it is found that both red emission and green emissions are two-photon processes. It can be seen from the XRD spectra that zirconia (ZrO2) mainly exists as a cubic phase,while Al3+ is implanted into the ZrO2 lattice, producing the ZrO1.87. The solid solution towers the site symmetry of the lattices in ZrO2 crystals, which promotes the upconversion efficiency.
2006, 55 (10): 5145-5149. doi: 10.7498/aps.55.5145
Diamond films deposited by hot filament chemical vapor deposition (HFCVD) under different deposition conditions are characterized using spectroscopic ellipsometric measurements in infrared region of 2.5—12.5 μm. Effects of deposition conditions on infrared spectroscopic ellipsometry of diamond films are investigated. The optical properties of diamond films depend strongls on its quality. The refractive index increases and the extinction coefficient decreases monotonicly with increasing sp3 C content. High quality optical diamond films are obtained under reactor pressure of 4.0 kPa when substrate temperature and carbon concentration are 750℃ and 0.9%, respectively. Refractive index and extinction coefficient of diamond film of high transparency are 2.385 and of the order of 10-4, respectively.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2006, 55 (10): 5150-5156. doi: 10.7498/aps.55.5150
The electromagnetic field of helix TWTs in the sheath model is analyzed. The dispersion and coupling impedance equations are derived and the one-dimensional space charge reduction factor is discussed in detail. The study shows that the difference of the space charge reduction factor between the sheath model and the perfect conducting tube is small at high frequency. The difference can be interpreted as the effect of the sheath helix. The higher frequency electromagnetic field has greater ability to affect the e-beam. Therefore, the space charge reduction factor equation based on the sheath helix model is inappropriate at high frequency.
2006, 55 (10): 5157-5160. doi: 10.7498/aps.55.5157
Glancing angle deposition is a novel method for the preparation of coatings, it can be used to prepare graded index coatings. In this paper, the packing factor of the coatings prepared by glancing angle deposition is analyzed under the conditions that the flux arrival angle of coating material is α and the columnar microstructure inclination angle of coatings is β. And then the relation between the refractive index of the coatings, the flux arrival angle and the columnar inclination angle is discussed based on Drude theory.
2006, 55 (10): 5161-5165. doi: 10.7498/aps.55.5161
We have analyzed the experimental data obtained by NA50 Collaboration in Pb-Pb collisions at 158A GeV/c. By assuming the QGP phase transition in central Pb-Pb collisions and its 100% suppression to J/ψ, we correct the differential cross section of J/ψ production in high-energy heavy-ion collisions based on the theory of J/ψ absorption by nucleons and comovers. The theoretical result fits the experimental data well.
2006, 55 (10): 5166-5171. doi: 10.7498/aps.55.5166
Within the IBUU transport model, flipping of the symmetry potential in heavy-ion collisions is studied. It is found that there exist flipping of the symmetry potential in the isospin fractionation, the single neutron to proton ratio, the double neutron to proton ratio and the neutron-proton differential flow from lower to higher incident energies. The flipping of the symmetry potential results from the change of the relative magnitude of the hard and soft symmetry energies at lower and higher densities. Future observations of the flipped symmetry potential in experiment will help the study of the density-dependent symmetry energy.
2006, 55 (10): 5172-5177. doi: 10.7498/aps.55.5172
TiO2 nanoparticles capped with a layer surfactant were prepared by colloid-chemical method, and their structural phase transformation and optical absorption properties were investigated. XRD and TEM results showed that the surfactant capping effectively inhibits the grain growth during heat-treatment, and results in a different crystallization behavior in which titania nanoparticles with amorphous structure can simultaneously transform into anatase and rutile when heat-treated below 400℃. It was found from optical absorption measurement that the capped TiO2 colloidal particles in toluene sol have a large red shift of absorption band edge in contrast with that without capping, which is mainly attributed to the effects of the interface dipole and dielectric confinement. In the investigation of the relation between the absorption coefficient and photon energy, it was found that there exist two linear correspondences of (αhν)1/2 vs hν(indirect transition) and (αhν)2 vs hν (direct transition) for the titania films and colloidal-particle organic sol. The respective band gap values were obtained by extrapolation of the above linear relation.
2006, 55 (10): 5178-5185. doi: 10.7498/aps.55.5178
Diffraction enhanced imaging (DEI) with two crystals has been recently performed at the 4W1A beamline at the Beijing Synchrotron Radiation Facility (BSRF). In the first experiments, images collected with a set up where the rotation axis of the crystal was perpendieular to the orbit, show a higher quality with respect to those taken with a geometry with the rotation axis of the monochromatic crystal parallel to the orbit. When the rotation axis of the crystal is perpendicular to the orbit plane, e.g. to the polarization plane of the synchrotron radiation, the influence of both vibration and thermal expansion of the first crystal can be significantly reduced, allowing the collection of better images. In this work, a systematic comparison is male between two geometrical arrangements of crystals in DEI framework with respect to the reflectivity of crystals, spacial resolution, angular resolution and image contrast.
Improving the off-center resolution in position emission tomography using depth-of-interaction information
2006, 55 (10): 5186-5190. doi: 10.7498/aps.55.5186
It is well known that if the depth of interaction(DOI) within the crystal can be measured, the parallax error can be corrected and the resolution should be uniform throughout the field of view. We have investigated the spatial resolution of off-center sources in a positron emission tomography (PET) ring detector configuration using our proposed DOI detector. It is confirmed that the depth-encoding detector provides better spatial resolution for the oblique incidence of gamma-rays.
CLASSICAL AREA OF PHENOMENOLOGY
2006, 55 (10): 5191-5199. doi: 10.7498/aps.55.5191
In this paper, an improved 2D fractal model is present for modeling the sea surface, the fractal spectrum of which satisfies the positive or negative power law for spatial wave numbers smaller or larger than the fundamental wave number, respectively. The spatial correlation function and the spectrum of this improved model show good agreements with those given in the literature for different windspeed. Based on the Kirchhoff approximation, the scattering coefficient and the scattering intensity coefficient of this new model are derived and evaluated. The angular distributions of backscattering intensity coefficient of the improved fractal sea model are compared with those of the conventional model, the influence of the incident frequency, windspeed and wind-direction on the backscattering intensity coefficient is also discus sed in detail.
Experimental and theoretical studies on auxiliary violet light increasing the diffraction efficiency of holographic gratings in bacteriorhodopsin film
2006, 55 (10): 5200-5205. doi: 10.7498/aps.55.5200
Due to the saturation absorption characteristic of bacteriorhodopsin film, in holography, when the intensity of the recording light is higher than the saturation intensity, the distribution of the transmission of the holographic gratings deviates from the cosine shape. As a result, the steady level of diffraction efficiency is very low. Using the mutual suppression property of bacteriorhodopsin films between the violet light and the red light, the saturation intensity of the film at 633nm can be increased by adding an auxiliary irradiation of 405nm violet light, which results in the holographic recording being changed from the nonlinear region to linear region. Consequently the distribution of the transmission of the holographic gratings retrieves to the cosine shape, and the diffraction efficiency is improved to a high value. Base on this principle, a three-beam holography system is set up. The diffraction efficiency and the quality of the diffraction image are shown to be greatly improved by the auxiliary violet light.
2006, 55 (10): 5206-5210. doi: 10.7498/aps.55.5206
Electromagnetically induced transparency (EIT) resonance is obtained in a Λ three-level configuration when the coupling field and the probe field satisfy the two-photon resonance condition. When an additional microwave field drives the transition between two low levels of the Λ three-level system the EIT is observed to split into multiple EITs. In this paper we present a theoretical study of this effect. The results show that the EIT resonance can be split into triplet and the spectral positions of EIT windows is determined by the intensity and the frequency of the microwave field. Therefore, a microwave field can be used to open more than one EIT windows and the EIT frequency tuning can be realized by controlling intensity and frequency of the microwave field.
2006, 55 (10): 5211-5215. doi: 10.7498/aps.55.5211
Through the introduction of effective reflectivity, the influence of external optical feedback on the oscillating characteristics of a semiconductor laser is discussed, such as the threshold gain, laser frequency and output power, according to the self-consistency condition and the photon and carrier density ratio equation. In the experiment, the threshold current of a laser diode decreased from 420mA to 370mA with external cavity feedback and the slope efficiency increased. The output power obtained by theoretical simulation agrees well with the experiment results.
Material growth and device fabrication of highly strained InGaAs/InGaAsP long wavelength distributed feedback lasers
2006, 55 (10): 5216-5220. doi: 10.7498/aps.55.5216
1.6—1.7μm highly strained InGaAs/InGaAsP distributed feedback lasers was grown and fabricated by low pressure mentalorganic chemical vapor deposition. High quality highly strained InGaAs/InP materials were obtained by using strain buffer layer. Four pairs of highly strained quantum wells were used in the devices and carrier blocking layer was used to improve the temperature characteristics of the devices. The uncoated 1.66μm and 1.74μm lasers with ridge wave guide 3μm wide have low threshold current (14mW at 100mA). In the temperature range from 10℃ to 40℃, the characteristic temperature T0 of the 1.74μm laser is 57K, which is comparable to that of the 1.55μm-wavelength InGaAsP/InP-DFB laser.
Experimental and theoretical study on the optimization of the normalized heating parameter in the operating LD side-pumped Nd:YAG ceramic lasers
2006, 55 (10): 5221-5226. doi: 10.7498/aps.55.5221
The suppressing effect of laser extraction on the non-radiation transition process is taken into account when the heat model of gain media is developed. Based on the developed heat model, the heat generation in the operating LD side-pumped Nd:YAG ceramic lasers is quantified through using the normalized heating parameter, which can be deduced from the experimental results of the slope efficiency and the absorbed pumping power of the gain media. The main factors which influence on the heat generation are investigated by studying the normalized heating parameter, and the results show that the changes of the laser extraction efficiency, the beam overlap efficiency and the Nd3+ concentration will result in obvious variations of the normalized heating parameter. In this work, the laser extraction efficiency increases to 0.905 by the optimization of the transmission of the output coupling, and the normalized heating parameter decrease to 0.474, correspondingly.
A 3 W continuous-wave 589 nm yellow laser based on the intracavity sum frequency generation in a V-shaped cavity
2006, 55 (10): 5227-5231. doi: 10.7498/aps.55.5227
This paper reports an all-solid-state yellow laser, which is based on two Nd：YAG rods connected in series and the intracavity sum frequency generation in a KTP crystal by use of a V-shaped folding configuration, and continuous-wave 589 nm light with the output power of 3 W is obtained. In order to improve the output power of the yellow light, two means are introduced. One means is optimizing the space overlapping of two fundamental beams by optimized designing of the oscillators, and the other is optimizing the intracavity power ratio of two fundamental beams by choosing proper pump powers of the two beams.
2006, 55 (10): 5232-5236. doi: 10.7498/aps.55.5232
In this paper we show that non-maximal coherence can lead to more efficient nonlinear frequency conversion than maximal coherence does. For this purpose we exemplify with the three-level cascade system (with no maximal coherence) to calculate the intensity of nonlinear-optical signal. A comparison is made between the Ξ system and the Λ system (with maximal coherence). The generated intensity is calculated by employing a nonperturbative approach. It is shown that under the conditions of the two-photon resonance and the same parameters, the largest intensity from the Ξ system is about twice as large as that from Λ system. The difference is analyzed in terms of dressed states. It is shown that both the spontaneous emission on the coupling transition and the spontaneous emission mediated three photon process play a contrary role for the two systems. These two processes enhance the generation of nonlinear signals for Ξ system but act contrarily for the Λ systems.
Optimize the output performance by shortening the cavity length of the THz electromagnetic wave parametric oscillator
2006, 55 (10): 5237-5241. doi: 10.7498/aps.55.5237
We realized a 85mm short cavity Fabry-Perot optical parametric oscillator by using high performance reflection mirror, and the experimental results of the THz wave output with this 85mm short cavity parametric oscillator based on the MgO:LiNbO3 Crystal are reported. Compared with the conventional 160mm parametric oscillator, the threshold decreases by 22.3%, the peak energy output of THz wave increases by 170%, the frequency tuning range increases from 0.5—2.4THz to 0.8—3.0THz. The THz wave linewidth was measured by using a Fabry-Perot interferometer based on the metal mesh plate.
2006, 55 (10): 5242-5246. doi: 10.7498/aps.55.5242
T-matrix approach is generalized to study the AC response of nonlinear metal/dielectric granular composites. We have derived general expressions for effective AC response at the fundamental frequency ω and the third harmonic 3ω and the fifth harmonic 5ω. When the components possess real dielectric response, our theoretical work reduces to the one with perturbative method. We take one step forward to perform numerical calculations on the metal/dielectric composites, and the results show that the effective third-order and fifth-order nonlinear susceptibility for fundamental and third-harmonic and fifth-harmonic frequencies can achieve large enhancement near the surface plasmon resonant frequency. Moreover, the resonant frequency exhibits a red-shift with increasing volume fraction of the nonlinear component. In addition, the effect of dimensionality on the effective nonlinear responses is studied.
2006, 55 (10): 5247-5251. doi: 10.7498/aps.55.5247
Based on the numerical models of stimulated Brillouin scattering(SBS) limiting, the influence of seed pulse duration, induced time and seed power on transmitted pulse shape in SBS optical limiting process is theoretically investigated. By seeding a Stokes pulse into the SBS optical limiting system, the SBS induced by this seeded Stokes pulse can reshape the transmitted limited pulse profile. By choosing suitable physical parameters, the best limited temporal profile can be obtained. The theoretical simulation shows that limited pulse shape can be controlled. When seed pulse duration is chosen as five times the length of the pump pulse duration and the delay time is just the same as the pump pulse duration, the limited pulse shape levels off, and the higher the seed power is, the lower the limited power steps. Optical limiting of pulse-shape can be controlled by introducing a seed to a stimulated Brillouin scattering cell.
The influences of the size of suspended particles in the medium and chemical structural characteristics of the medium on the threshold of the optical breakdown are researched experimentally. The experimental results show that the optical breakdown threshold first rises slowly in accord with the size of suspended particles in the medium, while later it rises sharply (when the diameters of the particles are less than 0.22μm). By purifying the medium, the optical breakdown threshold can be increased; thus the phase-conjugation fidelity, the reflectivity of the energy and the stability of SBS increase correspondingly. Generally speaking, better protection to the inner chemical bond offered by the outer atoms, and less valence electron together with higher ionization energies of the outer atoms will lead to higher optical breakdown threshold of the media.
2006, 55 (10): 5257-5262. doi: 10.7498/aps.55.5257
We numerically investigate the impact of diffusion field in photovoltaic photorefractive crystals on the interaction between two coherent photovoltaic spatial solitons. Numerical simulations show that the in-phase interaction will result in the separation of the two solitons from each other, accompanied by the energy coupling between the beams, which is different from the case without diffusion field. And for the case of interaction out of phase, the two solitons are no longer the simply separated. Under certain conditions, they are exclusive to each other but deflect simultaneously to the same side.
2006, 55 (10): 5263-5267. doi: 10.7498/aps.55.5263
The GeO-B2O3-Na2O (GBNB)，GeO2-Al2O3-Na2O(GANB), GeO2-Al2O3-BaO(GABB)and GeO2-Al2O3-Y2O3(GAYB) glasses doped with bismuth of 1mol% concentration were prepared by melting method and measurement of their DTA curves, absorption and emission spectra and fluorescence decay curves were carried out. It was found that the absorption edges of GBNB，GANB，GAYB，GABB were red-shifted. Since the absorption edges are ascribed to the charge transfer transition from Bi3+ 6s2 to Bi5+ 6s0，we conclude that the content of Bi5+ in GBNB, GANB, GAYB, and GABB glasses increased gradually. Near infrared super-broadband emission of GANB, GABB and GAYB samples were observed to be center-peaked at ～1220nm. The fluorescence intensity, FWHM and emission lifetime of GABB，GAYB，GANB were reduced gradually. The super-broadband emissions may be due to the formation and fluorescence of Bi5+. It could be deduced from the absorption and emission spectra that the introductions of BaO and Y2O3 into GeO2-Al2O3 glass were advantageous to the formation of Bi5+ in the glass. The mechanism of BaO and Y2O3 composition affecting the formation of Bi5+ in the GeO2-Al2O3 glass is discussed.
2006, 55 (10): 5268-5276. doi: 10.7498/aps.55.5268
Compared with the photonic crystal (PC) structures composed of Si circular, the PC structrures composed of triangular lattice of air holes in a dielectric slab are more easily fabricated and integrated. The tunability of directional band gap in a two-dimensional photonic crystal of air holes in a semiconductor matrix is demonstrated numerically, using the plane wave expansion calculation. Numerical simulations show that the photonic crystal band gaps are modulated by nematic liquid crystals infiltrated in the air holes. Then the band gap can be controlled easily under the influence of the external electric field. So the results can serve as a field-sensitive polarizer. These results are in agreement with that of Liu. However, the tunable field-sensitive polarizer based on the phenylacetylene liquid crystals instead of 5CB liquid crystals has the wider frequency range. Moreover, the transmission spectrum of the photonic crystal infiltrated by liquid crystal is analyzed, using finite difference time domain (FDTD) method. Numerical simulations show that the shift of the spectrum modulated by liquid crystal can be used to design a novel switch.
2006, 55 (10): 5277-5282. doi: 10.7498/aps.55.5277
Using the aberration control and ghost image tracing theory and the idea of partial optimizing, integration and complete optimizing, the optimization of optical design of the master amplifier in a 4-pass off-axis amplification system is accomplished. The work provides guidance for the system optical design in the high power laser facility.
2006, 55 (10): 5283-5287. doi: 10.7498/aps.55.5283
The structure of silica ridge waveguides with upper-cladding is optimized by theoretical simulation. Based on this design, a Mach-Zehnder electro-optic modulator is fabricated by micro-electronics techniques, which is used for the study of electro-optic effect and nonlinear effect induced by thermal poling. The nonlinear effects in silica are improved after thermal poling, with 0.093pm/V and 8.50×10-22(m/V)2 achieved in the experiment for linear electro-optic coefficient and second-order electro-optic coefficient，respectively. The physical mechanism of the enhancement of nonlinear effects in silica by thermal poling is also analyzed theoretically.
Effects of nonideal characteristics of chirped fiber grating dispersion compensators on the system with different modulation formats
2006, 55 (10): 5288-5293. doi: 10.7498/aps.55.5288
The causes leading to the nonideal characteristic of the chirped fiber Bragg grating (CFBG ) are discussed. The impact of the group delay ripple (GDR), reflectivity ripple (RR) and bandwidth of the CFBG on the 10Gb/s transmission system where non-return-to-zero (NRZ), return-to-zero (RZ) and carrier-suppressed return-to-zero (CSRZ) formats was investigated and the CFBG employed as dispersion compensator was simulated and compared in detail. The analytical result helps to optimize the practical 1500km CFBG-based transmission and the relation between the system performance and the nonideal characteristic of the grating validated the analysis in this paper.
Dependence of spectrum broadening on inner diameter of capillary restricting the filamentation in high pressure gas
2006, 55 (10): 5294-5297. doi: 10.7498/aps.55.5294
Inner diameter of capillary has important effect on the spectrum broadening when used to restrict filamentation in high pressure gas. In this paper, the dependence of spectrum broadening on the inner diameter of the capillary was experimentally studied. The results showed that the spectrum broadening was mainly due to filamentation at low pulse energy (0.4mJ) and the guide effect of capillary at high pulse energy (1.3mJ). Between these pulse energy levels, the capillary with a smaller diameter can result in much better spectrum broadening.
2006, 55 (10): 5298-5304. doi: 10.7498/aps.55.5298
This paper presents a theoretical analysis for the flow and heat transfer induced by Marangoni convection and an efficient analytical decomposition and numerical technique is given. The approximately analytical solution may be represented in terms of a rapid convergent power series with elegantly computable terms. The results are compared with the numerical ones in references and the associated transfer behavior is analyzed.
Molecular dynamics simulations are carried out to investigate the velocity slip phenomenom of liquid flow in nanochannels. The liquid is argon, and the wall is taken to be platinum or its model solids. The effect of the surface wettability on the velocity slip is obtained through varying the potential interaction strength between the liquid and the wall. The simulation results show that the liquid adjacent to a hydrophilic surface is solid-like and has high density and orderliness. However, the liquid near a hydrophobic surface forms a gap of low density. The velocity slip of the liquid flow over solids decreases with the increasing interaction strength between the liquid and the channel surface. The slip, the no-slip and the negative slip are all possible to take place for different liquid-surface wettabilities. We find that the apparent slip of the liquid flow over solids is affected by the integrated factors of boundary slip, liquid sticking and liquid-internal slip.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2006, 55 (10): 5311-5317. doi: 10.7498/aps.55.5311
Based on a transformer model for inductively cowpled plasmas (ICPs), the dependence of power coupling efficiency on Q value, plasma electron density and effective electron-atom collision frequency is analyzed. The effect of coil configuration on power coupling efficiency is studied using four types of coils (one-turn, two-turn, three-turn and four-turn planar concentric coils) experimentally. The results indicate that the inductive discharge depends on coil inductance while the coupling efficiency varies with the Q value and discharge conditions such as pressure and input power. The coupling efficiency increases with the increase of pressure and input power, which is in accordance with the transformer model. However, the prediction given in the model that an increase in coil Q value improves power coupling efficiency is only applicable for coils with the same inductance. The study on power coupling efficiency for single multi-turn coil has been applied as an experimental reference for a large-area, high density inductive discharge source using four parallel multi-turn coils.
2006, 55 (10): 5318-5324. doi: 10.7498/aps.55.5318
The formulation of conductivity and dielectric susceptibility for the dust plasma at weak ionization is deduced by solving the Boltzmann’s equation and Shukla’s equation, which are the governing equations on dust particle charge and discharge processes, provided that the weak external electromagnetic field is imposed and the space dispersion neglected. The proper parameters of a solid rocket exhaust plume are then substituted into the derived formulae. The calculated results show that the radius and concentration of dust particles have significant influence on the conductivity and dielectric susceptibility.
Stimulated Raman cascade-into-photon condensation and ultra-intense EM solitons in laser plasma interaction
2006, 55 (10): 5325-5337. doi: 10.7498/aps.55.5325
Stimulated Raman scattering, stimulated Raman cascade and the transition from Raman cascade into photon condensation, induced by linearly-polarized intense laser beam interacting with underdense collisionless homogeneous plasmas, are studied by particle simulations. It is found that, at appropriate laser amplitude and plasma condition, a large-amplitude relativistic EM soliton is formed due to the strong photon condensation. The standing, backward- and forward-accelerated large-amplitude relativistic electromagnetic solitons induced by intense laser pulses in underdense collisionless homogeneous plasmas are studied by particle simulations. In addition to the inhomogeneity of the plasma density, we found that the acceleration of the solitons depends upon both the laser intensity and the plasma length. The electromagnetic frequency of the solitons is about one-half of the unperturbed electron plasma frequency. The transverse electric, magnetic and electrostatic fields have half-, one- and one-cycle structure in space, respectively.
2006, 55 (10): 5338-5343. doi: 10.7498/aps.55.5338
The present paper studies the influence of the interaction of incident pulsed laser and cold plasmas on the laser pulse in the relativistic laser-plasma system, taking the electron density fluctuation into account. For different initial parameters, the change of the laser-pulse width is analyzed in detail. The self-compression of the laser pulse is particularly discussed. Numerical calculation demonstrates that the pulse self-compression can be effectively achieved with the increase of the intensity and width of the laser pulse and the decrease of background plasma density. For initial laser-pulse parameters a0=0.12 and τ=70 and plasma density n0＝0.3, the ratio of compressed laser pulse to initial one is near to 1/10. And hence optimized theoretical parameters for the self-compression of the laser pulse are given.
2006, 55 (10): 5344-5348. doi: 10.7498/aps.55.5344
This paper discusses the space-charge-limited current and its energy distribution in the coaxial drifting pipe. In order to bypass the potential depression problem, the triaxial output cavity of relativistic keystron amplifier was implemented. The triaxial output cavity was designed and simulated. A hollow electron beam of 590kV, 5kA generates 1GW rf power in S band klystron amplifier using the triaxial output cavity. The efficiency is about 35%, which is 9% bigger than that of the coaxial output cavity. The results agree well with the experiment.
2006, 55 (10): 5349-5353. doi: 10.7498/aps.55.5349
The angular distribution and energy spectrum of hot electrons produced in the interaction of ultra-short ultra-intense laser pulses with solid foil targets are investigated. Results show that bath the angular distribution and the energy spectrum reveal anisotropic behavior. This anisotropy is believed to be related to the electron generation mechanism. The existence of energy anisotropy explains why different experimental groups obtained quite different elctron temperatures under the same laser intensity.
2006, 55 (10): 5354-5361. doi: 10.7498/aps.55.5354
The relativistic effects on resonance absorption, occurring when a high intensity p-polarized laser pulse is incident obliquely onto inhomogeneous plasma, are discussed by use of one-dimensional particle-in-cell simulation. It is found that the absorption rate decreases with the increase of the amplitude of the incident pulse until the laser intensity reaches about 3.4×1017W/cm2. This is mainly owing to the relativistic effect of the electrostatic field driven near the critical surface. At high light intensities, because of the relativistic effect of the laser pulse itself in plasma the plasma wave breaking, and the excitation of the parameter instabilities, the absorption begins to increase with the light intensity. For a given scale-length, similar intensity-dependence of the absorption is found for different incident angles and different initial electron temperatures.
2006, 55 (10): 5362-5367. doi: 10.7498/aps.55.5362
The red-shifted second harmonic emission of the laser light is observed in the laser propagation direction on the rear side of a foil target irradiated by femtosecond laser pulses. The emission is attributed to the coherent transition radiation (CTR) when the hot electrons accelerated by the v×B heating process traverse the solid-vacuum boundary. The red shift is caused by the expansion of the critical density surface towards the vacuum side. With the increase of the prepulse energy, the peak of the CTR moves further to the long wavelength side causing the broadening of the spectrum. The measurements of the CTR provide a potential diagnosis to the movement of the critical surface in the laser-plasma interaction process.
Analysis of ion noise with beam-wave interaction in klystron by two dimensional particle simulation method
2006, 55 (10): 5368-5374. doi: 10.7498/aps.55.5368
Ion noise in output signal of klystrons was obtained by particle-in-cell method. The interactions between beam electron, ion, secondary electron and electromagnetic field are illustrated. The mechanism of ion noise is analyzed. It shows that phase fluctuation in output signal is caused by the change of the beam current DC velocity which is affected by the change of the amount of ions. The ion interacts with beam electron and has no equilibration state. The amount of secondary electrons is small and it has little effect on ion noise, but its behaviors reflect the process of ion noise. The amplitude fluctuation of output signal is caused by the change of beam velocity and beam radius. It is also affected by the ion behaviors.
2006, 55 (10): 5375-5379. doi: 10.7498/aps.55.5375
Stable square emission patterns are observed in argon discharge at atmospheric pressure by using a dielectric barrier discharge device with different lateral boundary conditions. The spatio-temporal dynamics of square pattern in nanosecond time scale is investigated. It is found that the square pattern is an interlacing of two oscillating square sublattices, which have time sequence inversion behavior. The influence of the wall charge distribution on the forming process and the spatio-temporal dynamics of the emission patterns is discussed.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2006, 55 (10): 5380-5385. doi: 10.7498/aps.55.5380
TiN/ZrN multilayers were fabricated using reactive radio-frequency magnetron sputtering methods. X-ray diffraction analysis was used to determine the modulation structure of the multilayers. Using high-resolution transmission electronic microscopy, the interface was found to be a mixed layer of 2—3 nm in thickness. The nano-indentation measurement showed that the hardness of TiN/ZrN multilayers varied with the modulation period. Both the hardness and elastic modulus had their maximums for the multilayer with a modulation period of about 15.24 nm. The enhancement in hardness is discussed with different hardening mechanisms. The interface states and preferred orientation are assumed to be the main causes of the enhancement of TiN/ZrN multilayers in hardness.
Simulation study of effect of cooling rate on evolution of microstructures during solidification of liquid metal Cu
2006, 55 (10): 5386-5393. doi: 10.7498/aps.55.5386
A molecular dynamics simulation has been performed on the solidification process of liquid metal Cu by adopting the quantum Sutton-Chen many-body potentials at four different cooling rates. Through the pair distribution function，bond-type indices, coordination number, MSD, and visualized analysis, it is found that the cooling rate plays a critical role in the evolution of microstructures of liquid metal Cu. At the cooling rate of 1.0×014K/s, the amorphous structures will be formed in the system; at the cooling rate of 1.0×1013K/s, 1.0×1012K/s and 1.3×1011K/s, the mixed crystal structures of fcc and hcp formed mainly with 1421 bond-type will coexist in the system, and their corresponding crystallization temperatures are 373K, 773K, 873K, respectively. Namely, slower the cooling rate, higher the crystallization temperature, and higher the degree of crystallization; and slower the cooling rate, greater the number of 1421 bond-type, greater the proportion occupied by fcc in the mixed crystal. At the same time, it is found that the variation of the mean coordination number of atoms is closely related to that of 1551, 1441, 1661 bond-types, which reflects that the varying rule of the symmetric configurations in the system is related to the variation of the coordination number. In visualized analysis, the amorphous and crystal structures in 2D cross sections and the concrete structures of both the basic clusters of fcc and hcp in 3D were displayed by means of center-atom method.
Study on free volume change in the NiP amorphous alloy under high pressure using synchrotron radiation
2006, 55 (10): 5394-5397. doi: 10.7498/aps.55.5394
In situ high pressure energy dispersive X-ray diffraction with a synchrotron radiation source has been used to investigated the free volume change in Ni77P23 amorphous alloy up to 30.5 GPa at room temperature in a diamond-anvil cell. The atomic configuration information such as coordination number and atomic spacing was derived by radial distribution function via Fourier transformation. The results show that in the pressure range of 0—30.5 GPa, the structure of Ni77P23 amorphous alloy is stable. The compression behavior is investigated using in-situ high pressure measurment. The equation of state -ΔV/V0=0.08606P-3.2×10-4P2+5.7×10-6P3 is determined by fitting the experimental data according to the Bridgman equation.
2006, 55 (10): 5398-5402. doi: 10.7498/aps.55.5398
In this paper, we report the use of combining holography and photo-induced polymerization techniques to fabricate 2D mesoscale Penrose quasicrystals using 5 coherent beams. The effects of exposure dosage and polarizations of laser beams on the structures are studied. It is demonstrated that the air holes in the 2D quasicrytals could be as small as 0.1μm for high exposure dosage samples. This setup can be used to fabricate versatile 2D mesoscale quasicrystals, and may also shed light on extending this method to 3D quasicrystals. Here we offer a novel method to fabricate quasicrystals which is simpler and cheaper than, if not superior to, the other traditional micro-fabrication methods.
2006, 55 (10): 5403-5408. doi: 10.7498/aps.55.5403
According to the processes of nucleation and growth of nanocrystalline silicon (nc-Si) with shape changing from sphere-like to disc-like in the a-SiNx/a-Si:H/a-SiNx sandwich structure or a-Si :H/a-SiNx multilayer structure, we have proposed the theoretical model of constrained crystallinzation based on the classical thermodynamics, in which the increase of the interfacial energy between nc-Si and a-SiNx causes the growth of nc-Si to halt, and concludes the critical thickness of a-Si sublayer (34 nm) for constrained crystallization, The model of constrained growth has been validated in a-SiNx/nc-Si/a-SiNx sandwich and nc-Si/a-SiNx multilayer structures formed by laser annealing and thermal annealing.
The field emission properties of the randomly oriented and the well-aligned ZnO nanorods synthesized by a thermal evaporation method were investigated in detail. It was found that the field emission of the well-aligned ZnO nanorods is seriously affected by the screening effect. While, compared with the ZnO arrays, the field emission measurements on the randomly oriented ZnO nanorods show a lower turn-on filed and a larger field enhancement factor, which are attributed to the weak screening effect and the surface perturbations. These features make the random ZnO nanorods as a competitive candidate for field emission flat panel display.
2006, 55 (10): 5413-5417. doi: 10.7498/aps.55.5413
It was found via high temperature crystal growth in situ observation device that the morphology of KABO crystal varies with the degree of supersaturation of the crystal growth solution. The existence of ［BP3］3- and ［AlO4］5- growth units was proved by the results of high temperature Raman measurement of KABO crystal growth solution. The mechanism of KABO crystal morphology evolution was analyzed through the growth-units model of anionic coordination-polyhedra. It was found that the morphology of KABO crystal was determined simultaneously by its inner structure and the growth units. The kinds and dimensions of KABO growth units vary in solutions with different supersaturation, so accordingly, the morphology of KABO crystal changes from hexagonal to triangular morphology, and then from triangular to hexagonal dendritic morphology.
2006, 55 (10): 5418-5423. doi: 10.7498/aps.55.5418
The ground states of TiH2,TiD2 and TiT2 are determined as 3A2 based on atomic and molecular statics and ground theory. The energy E, heat capacity Cv and entropy S of hydrogen isotopic molecules and its titanium compounds have been calculated using density functional theory (DFT) with basis set 6-311G**. The electronic and vibrational energy and entropy of single molecules TiH2,TiD2 and TiT2 are used as the energy and entropy in their solid states approximately, which is called the electron-vibration motion approximation theory(EVMAT). The calculated results of hydrogenation (and of its isotopes) thermodymical functions ΔH0, ΔS0, ΔG0 and equilibrium pressure of metallic titanium changing with temperature are in good agreement with experimental data, which confirms EVMAT theory further.
2006, 55 (10): 5424-5434. doi: 10.7498/aps.55.5424
Electromigration (EM) problem in Al interconnects is one of the most persistent and important challenges in the microelectronic industry. From 1990s, with the scaling down and new processes introduced, ultra-deep submicron (feature size≤0.18 μm) Al interconnects involve more complicated EM issues. In this paper, we summarized the basic formulae of the EM phenomena and got the important flux divergence equations. Based on the equations, the research methods for EM problems were reviewed. The main issues and solutions during the half century of investigation for Al EM challenges were reviewed as well. Finally, the essentials and challenges of current ultra-deep submicron Al EM reliability are analyzed, and some prospective solutions were also proposed.
2006, 55 (10): 5435-5440. doi: 10.7498/aps.55.5435
In this paper the epitaxial growth mechanism on vicinal GaAs(001) surface is studied using the kinetic Monte Carlo simulation method. The Ehrlich-Schwoebel barrier has great influence on the growth mechanism of the vicinal surface. The simulation results show that the downward movement to a lower step of the adatoms can be inhibited by Ehrlich-Schwoebel barrier at low temperature, while the adatoms can move to the lower step at high temperature. At the beginning of growth, the adatoms are almost distributed uniformly on the steps. When the surface coverage reaches to certain value, the step nucleation begins. Meanwhile, the adatoms begin to accumulate at the upper step because of the Ehrlich-Schwoebel barrier. If there were no Ehrlich-Schwoebel barrier, the adatoms at the upper step could be depleted completely. The Ehrlich-Schwoebel barrier has great influence on the growth mode of the vicinal surface, and it will increase the temperature for onset of the step growth mode.
2006, 55 (10): 5441-5443. doi: 10.7498/aps.55.5441
Cubic boron nitride (c-BN) thin films with approximate 100% cubic phase and lower compressive stress were prepared on n-Si(111) substrates by radio frequency sputtering. The infrared spectra showed that the negative substrate bias had important effect on the content of cubic phase and the compressive stress of films. In addition, a relatively higher substrate resistivity favored the c-BN formation and reduced the compressive stress.
2006, 55 (10): 5444-5450. doi: 10.7498/aps.55.5444
A series of iron films has been successfully fabricated by deposition on silicone oil surfaces using the DC-magnetron sputtering method, and the growth mechanism and ordered surface morphologies have been systematically studied. It is found that the growth mechanism of the iron films is similar to that of nonmagnetic films on liquid substrates,in accordance with a two-stage growth model. Large disk-shaped patterns (disks) are observed in the continuous films and their growth behaviors are mainly related to the sputtering power, deposition time and growth duration in vacuum. The experiment indicates that the disks may result from the spontaneous, free organization and gathering of the iron atoms and atomic clusters driven by the internal stress. If the sputtering power and deposition time are comparatively large, wavy buckles with a nearly uniform wavelength of about 10 μm are observed in the continuous films, generally aligning parallel to the boundaries of the disks. Further analysis shows that the top surface of the silicone oil is modified to form a soft polymer layer during deposition. Subsequent cooling of the system creates compressive stress in the iron film, which is relieved by buckling to form the wavy structures.
2006, 55 (10): 5451-5454. doi: 10.7498/aps.55.5451
An optical apparatus based on substrate curvature method was developed for stress measurement of thin films, which offeres such advantages as overall field, non-contact, high precision, nondestructive, easy operation and quick response. Using the apparatus, the residual stress in porous silicon (PS) layers prepared by electrochemical etching using a solution of HF/ethanol with composition ratio of 1∶1 on heavily or gently doped (100) silicon as a function of the electric current density were obtained. It is found that the residual tensile stress tends to increase with the porosity increasing and the doping concentration of the silicon wafer increasing. The results show that there is a deep connection between the micro-structure PS and the residual stress distribution.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2006, 55 (10): 5455-5459. doi: 10.7498/aps.55.5455
Motion of single-walled carbon nanotubes on graphite substrate is investigated by using molecular dynamics simulation in this paper. Following a relaxation to the equilibrium state, a uniform force is applied to carbon nanotubes for a period of time to set them into motion. After the applied force being removed, carbon nanotubes move relative to the substrate in decelerating speed until they come to a full rest in the end. Different tube radius and chiral angles are selected during simulation. The results show that motion of carbon nanotubes is mainly affected by the chiral angle but independent of tube radius. When the chiral angle is 30°, periodic transition between sliding and rolling is observed due to the periodic change of atomic configuration during the motion. When chiral angle is between 28.3° and 30°, sliding and rotating take place at the same time. When chiral angle is less than 26.3°, only sliding is observed. Different chiral angles result in different atomic configurations in the contact region between carbon nanotubes and graphite substrate, which gives rise to different styles of motion.
2006, 55 (10): 5460-5465. doi: 10.7498/aps.55.5460
We have fabricated p-type and n-type carbon nanotube transistors (CNTFETs) by using high and low work-function metals Pt and Al as contact electrodes， respectively. The band structures indicate that the work functions of contact metals play an important role in operation mechanism of CNTFETs. We can obtain fine-tuning of Schottky barrier heights for p- and n-channel conductions by changing the contact metals. These results can be explained by taking into account the work functions of the contact metals.
2006, 55 (10): 5466-5470. doi: 10.7498/aps.55.5466
By employing the full potential augmented plane wave and local orbital method (APW+lO), we studied some possible hydrogen-related defect sites in ZnO. In view of the calculated defect formation energy, the most possible defect site should inhabit BC∥ local structure position. But the calculated local vibrational modes (LVMs) of the defect sites, when compared with the infrared absorption result, leads to the conclusion that the hydrogen-related defect sites in ZnO can inhabit both BC∥ and ABo∥ local structure positions.
The effect of doping CsNiCl3 crystal with Mg2+ on its ground level and Zero-field splitting parameters with Jahn-Teller effect
2006, 55 (10): 5471-5478. doi: 10.7498/aps.55.5471
The completely diagonalized Hamiltonian matrices of 3d2/3d8 ion configuration in the trigonal symmetry have been established by irreducible representation method. Taken into account the influence of the spin-spin coupling interactions omitted in previous publications, the spectra and the constants of crystal structure and zero-field splitting parameters of CsNiCl3 crystal and CsNiCl3: Mg2+ crystal are calculated and the influence of the doping to the spectra, the constants of crystal structure, zero-field splitting parameters and Jahn-Teller effect are studied. The results show that doping can change the structure of crystal which brings about the changes in the spectra and zero-field splitting parameters as well as Jahn-Teller effect.
Influence of working pressure on the crystallinity and growth behavior of ZnO films deposited by reactive radio-frequency magnetron sputtering
2006, 55 (10): 5479-5486. doi: 10.7498/aps.55.5479
Using the reactive radio-frequency magnetron sputtering method, ZnO films were deposited on Si (001) and quartz substrates at different pressures with a fixed flow ratio of Ar to O2. The influence of working pressure on the crystallinity and growth behavior were studied with the help of characterization of the morphology, microstructure and optical properties of the films by atomic force microscopy (AFM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and transmittance spectra,respectively. It is found that a critical working pressure can be taken as 0.5—1.0 Pa. With increasing the working pressure from 0.1 Pa up to the critical working pressure, the density of ZnO grains decreases and the films have high c-axis orientation with strong in-plane textured feature. When the working pressure exceeds the critical working pressure, the density of ZnO grains is roughtly a constant and the in-plane textured feature disappears. The influence of working pressure on the refractive index, extinction coefficient and optical energy gap is also discussed in the paper.
Broadband yellow luminescence in the photoluminescence spectra of n-GaN implanted by the different ions
2006, 55 (10): 5487-5493. doi: 10.7498/aps.55.5487
The n-type gallium nitride (GaN) films were implanted with oxygen, nitrogen, magnesium, silicon and gallium ions at room temperature in the dose range from 1013 to 1016 cm-2. All implanted samples were annealed at 900℃ for 10 min in a flowing nitrogen environment. The effects of the implantation ions on the broad yellow luminescence (YL) band were systematically investigated using the photoluminescence (PL) spectra taken at room temperature. A formula based on a semi-empirical model which was proposed by us was deduced, and with it, the experimental data was analyzed and the influence of implanted ions on the intensity of YL band was determined. We can confirm that the effects of the Mg (1016/cm2), Si (≤1014/cm2) and Ga(≥1015/cm2) implanted ions on the YL band are larger than that of the N and O implanted ions.
2006, 55 (10): 5494-5498. doi: 10.7498/aps.55.5494
The energy transfer and the luminescence properties of polyvinyl-carbazole (PVK) and oligomeric phenylenevinylene derivative (2,5-dodecyloxy-1,4-(biphenyl-enevinyl )phenyl)(DBVP)blend system were studied. The energy transfer between PVK and DBVP was investigated by the UV-vis absorption spectra, photoluminescent excitation (PLE) spectra and photoluminescent (PL) spectra of PVK/DBVP blend system. The electroluminescence (EL) properties of the blend system were investigated by characterization with the device ITO/PEDOT/PVK∶DBVP (w/w)/LiF/Al. The PL and EL spectra of PVK in the PVK/DBVP system were effectively quenched, which means the effective energy transfer between PVK and DBVP. Because PVK matrix acted as solid solvent, the emission performance of the blend system could be adjusted and improved by changing the ratio of PVK and DBVP. The luminescence efficiency is up to 1.06cd/A at 52cd/m2, when the weight ratio of PVK∶DBVP was 1:2 and the bright blue and green light emission were obtained when the ratio of PVK∶DBVP was changed from 20∶2 to 1∶2.
2006, 55 (10): 5499-5505. doi: 10.7498/aps.55.5499
Based on the NM/FI/FI/NM double spin filter junction (NM represents the nonmagnetic metal layer and FI the ferromagnetic insulator or semiconductor layer), a new type of double spin filter junction NM/FI/NI/FI/NM (NI represents the nonmagnetic insulator layer) is discussed. By inserting an nonmagnetic insulator layer between the ferromagnetic insulator layers, the adverse influence on the tunneling magnetic resistance (TMR) caused by the magnetic coupling at the interface between the ferromagnetic insulator (FI) layers can be avoided. Using the free-electron approximation and transfer matrix method the dependence of the tunneling conductance and TMR on the thickness of the FI layer and the NI layer and on the bias voltage in the double spin filter junction NM/FI/NI/FI/NM are studied.
Study on the magnetic entropy change and magnetic phase transition of NaZn13-type LaFe13－xAlxCy compounds
2006, 55 (10): 5506-5510. doi: 10.7498/aps.55.5506
The refrigerant capacity and magnetic phase transition of NaZn13-type LaFe13-xAlxC0.1(x=1.6，1.8) interstitial compounds are investigated. The magnetic entropy change |ΔS|m, which is calculated from one of the Maxwell’s relationships ΔS(T,H)=-∫( M/T)HdH, is lower than that of carbides with low Al content. Although the magnetic entropy change peak broadens with increasing Al content, the value of q, which is used to evaluate the refrigerant capacity, decreases due to the sharp derease of the magnetic entropy change. Taking the spin fluctuation into account, the magnetic free energy can be expanded up to the M6 term based on the Landau phase transition theory. The order of phase transition is distinguished by the the signs of a3(T), which is the coefficient of M4 term. The order of phase transition for LaFe13-xAlx carbides changes from the first one that is weak to the second one with the increase of Al content.
2006, 55 (10): 5511-5515. doi: 10.7498/aps.55.5511
Within the t-J model, the spin dynamics of the quasi-one-dimensional strongly correlated zigzag type materials is studied based on the fermion-spin theory. It is shown that the pattern of the neutron scattering peaks depends on both the next-nearest neighbor coupling and doping. The weight of the incommensurate neutron scattering peaks decreases with increasing energy.
2006, 55 (10): 5516-5520. doi: 10.7498/aps.55.5516
Fe100-xPdx nanowire arrays with different compositions have been fabricated in anodic aluminum oxide templates by electrodeposition. Around x=30, the nanowire arrays still show rather high coercivity (7.48 kA/m) and axial anisotropy. But increasing the Pd content to x=50, the magnetization easy axis is tuned to be perpendicular to the nanowires. It is attributed to the discontinuous magnetic layer being separated by non-ferromagnetic sheets grown in the Fe50Pd50 nanowires, such that the shape anisotropy overturns the easy axis. The formation of the laminated structure in Fe50Pd50 nanowires has been discussed based on the growth kinetics.
Diluted magnetic semiconductor Zn1-xFexO and Zn1-xFexO:Cu crystals were synthesized by hydrothermal method with 3molL-1 KOH as mineralizer, with 35% fill factor, under the reaction temperature of 430℃ for 24h. When Zn(OH)2 doped with FeCl2·6H2O was used as precursor, different shapes of Fe doped ZnO crystals were synthesized, of which the atomic percentage of Fe in the bigger crystals were 0.49%—0.52%. The magnetization of the crystals lowered with increasing temperature, a superconducting quantum interference device (SQUID) was used for measuring magnetism. Compared with Zn1-xFexO crystals the magnetization of Zn1-xFexO:Cu crystals doped with Cu increased obviously in the high temperature region, and at room temperature they were ferromagnetic.
2006, 55 (10): 5525-5530. doi: 10.7498/aps.55.5525
The spectral reflectance is measured after 60 keV proton irradiation by the spectrophotometer. The microscopic mechanism of irradiation damage of Al film reflector is studied by the slow positron annihilation technique and X-ray diffraction. The results show that the spectral reflectance of Al film reflectors decreases in the wavelength range of 200—800nm with increasing proton irradiation fluence and the radiation damage is mainly concentrated on the Al film of the reflector. The implanted protons may fill the dcfccts in Al film layer, thus decreases the electron density of Al film and enhances the interband transition of loose bound electrons. The interband transition can be excited by electromagnetic waves ranging from UV to visible and the spectral reflectance decreases in the corresponding wave band, which eventually results of the degradation of optical property of the reflector.
2006, 55 (10): 5531-5534. doi: 10.7498/aps.55.5531
We have studied the field emission properties of tetrapod-like ZnO nanostructures and the fabrication of flat panel displays. Stable field emission and full-screen lighting have been realized. It is shown by our experimental results that ZnO nanometerials are good field-emission cathode materials.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2006, 55 (10): 5535-5538. doi: 10.7498/aps.55.5535
In this paper, composite coating (about 400 μm thick) was prepared by SHS plasma spraying technology using micro-dimensional Fe2O3-Al composite feedstock, which was fabricated by mechanical glomeration. The composition and microstructure of the coating were analyzed by X-Ray diffraction, scanning electron microscopy and transmission electron microscopy. Meanwhile, the microhardness, fracture toughness and wear resistance were also measured. It shows that the skeleton of the coating is mainly composed of nanostructured FeAl2O4 and Al2O3, and the dispersed phase is nanosized Fe. The composite coating possesses satisfactory microhardness of about Hv870. Compared with conventional alumina coating, the fracture toughness and wear resistance of composite coating are increased by one and 1.5 times, respectively.
2006, 55 (10): 5539-5544. doi: 10.7498/aps.55.5539
Single-phase β-Zn4Sb3 bulk sample and several samples based on β-Zn4Sb3 with different amounts of Zn were produced by melting in an evacuated quartz ampoule followed by slow cooling and their thermoelectric properties were investigated at 300 to 700K. The distribution of Zn in the samples was observed and the effects of excess of Zn on thermoelectric properties of β-Zn4Sb3 compound were investigated systematically. With the amount of Zn increasing, electrical and thermal conductivities of the sample increase, and the Seebeck coefficient declines. The excess of Zn leads to an obvious improvement to the power factor of the β-Zn4Sb3 based materials. The ZTmax of the sample is 1.10 at 700K when the amount of excessive Zn is 2at%.
Molecular dynamic simulation of shock-induced phase transformation in single crystal iron with nano-void inclusion
2006, 55 (10): 5545-5550. doi: 10.7498/aps.55.5545
Shock-induced phase transformation (body-centered cubic α phase to hexagonal close-packed ε phase) in single crystal iron with a nano-void inclusion has been investigated by means of molecular dynamic (MD) simulation. The simulated sample is 17.2nm×17.2nm×17.2nm in size with 428341 atoms, and in the center of the sample settled a void of 1.12nm in diameter. The shock wave compression is generated by using a piston impact with the sample at velocities of 350m/s, 500m/s and 1087m/s, respectively. Shock wave propagates along the ［100］ direction in the sample. Results indicate that the existence of void is an important factor for inducing the phase transformation, which initially occurs around the void and mainly on the (011) and (011) planes, while with the increase of compression time it expands to the rest of the sample. By analyzing the moving history of atoms under shock wave compression, the phase transformation mechanism has been outlined. It is found that when the atoms at (011) planes slide to the void along ［011］ direction, they may have relatively different displacement, such that results in alternative positions compared to their initial location and yields the new structure (hcp).
2006, 55 (10): 5551-5554. doi: 10.7498/aps.55.5551
The Bi4Ti3O12 and Bi3.25La0.75Ti3O12 thin films are prepared on the Pt/Ti/SiO2/Si substrate using sol-gel method. The structures Pt/Bi3.25La0.75Ti3O12/Pt and Pt/Bi4Ti3O12/Pt are fabricated. The effects of La doping on the microstructures, and ferroelectric properties of Bi4Ti3O12 films are investigated. The 2Pr with test voltage 6V for the sample annealed at 700℃ increased from 12.5 μC/cm2 to 18.6 μC/cm2, and 2Vc is still 2.8 V when the La3+ ions occupy part of Bi3+ sites. The Bi3.25La0.75Ti3O12 films showed fatigue-free behavior. The mechanism of improvement of La-doped Bi4Ti3O12 ferroelectric thin films is discussed.
The effect of O4 absorption on the measurement of atmospheric trace gases with zenith-sky scattering light observations
2006, 55 (10): 5555-5561. doi: 10.7498/aps.55.5555
During the measurement of atmospheric trace gases with zenith-sky scattering light observations, the absorption feature of O4 in the ultraviolet-visible region can affect the results. The principle, equipment and method of measurent, as well as the processes of spectra analysis and concentration retrieval are presented in detail. Experiment proves that the accuracy of NO2 and O3 retrievals can be improved when considering the profile of O4 absorption. A brief comparison between our ground-based experiment results of ozone vertical column density with that measured by TOMS is also given in the last part of article.
2006, 55 (10): 5562-5567. doi: 10.7498/aps.55.5562
According to the tight-binding model of the single electron, we establish a one-dimensional random binary solid model for DNA molecules. Using the transfer-matrix approach, we calculate numerically the localization length and the conductivity of a DNA sequence with 50000 nucleotides base pairs. The results show that the random DNA sequence is an insulator with very small conductivity, that the localization length and conductivity strongly depend on energies, and there exist greater localization lengths at the band center than at the band edge, which implies there is higher conductivity at the band center. The results also show the localization lengths are affected by disorder degrees to some extent and decrease with the increasing of the degree of disorder for all energies. Especially with finite-size DNA sequence, the localization length and conductivity have obvious effect on nucleotide base pairs’ mol percentage.
2006, 55 (10): 5568-5574. doi: 10.7498/aps.55.5568
Through building some initial shapes which are similar to target shapes in Surface Evolver, after a long time of evolvement, we obtain the starfish vesicles with D2h and D3h symmetry, which are supported by experiment. Through tracing the eigenvalues of Hessian matrix of different shapes, we find that between the oblate and the star-fish vesicles, and between the oblate and prolate vesicles, there are two discontinuous phase transformation, and the biconcave triangular shapes and the biconcave elliptic shapes are usually unstable in the SC model.