Vol. 57, No. 9 (2008)
2008, 57 (9): 5500-5505. doi: 10.7498/aps.57.5500
The size effects of SrTiO3 nanoparticles are investigated by Raman spectroscopy and UV-Visible absorption spectra with changing grain size in the range of 10—80 nm. It is found that the intensity for the first-order TO2 mode increases significantly as the grain size decreases from 80 to 10 nm. Such behavior suggests the presence of the micropolar regions on the grain boundary induced by the enhanced surface-defect dipoles. Moreover, the first-order TO2 and TO3 modes show red-shifts, indicating the increase of the Ti—O bond-length with decreasing grain size of SrTiO3 nanoparticles. The softening of the Raman mode is consistent with the lattice expansion investigated by XRD. In addition, the UV-Visible absorption spectra indicates the enhancement of absorption due to surface distortion states and hence the lattice expansion, which results in the increase of Eg-value.
2008, 57 (9): 5893-5898. doi: 10.7498/aps.57.5893
A simple, high efficiency and mini-sized surface plasmon polariton (SPP) modulator based on electro-optic polymer is proposed. The modulator is constructed by metallic stripes of Mach-Zender (M-Z) interferometric structure and with electro-optic polymer surrounding the stripes. The reflectivity index of the electro-optic polymer is modulated when the modulating voltage is applied to the two arms of the M-Z interferometer. Through the M-Z interferometer, the modulation of the reflectivity index can be transferred into the modulation of the SPP intensity. By calculating the electric field near the metallic stripes and taking the distribution of SPP field into account, the working principle of the SPP modulator is demonstrated in detail and the half-wave modulating voltage is evaluated as 2.8V.
2008, 57 (9): 5361-5365. doi: 10.7498/aps.57.5361
Within the scope of the two_dimensional space with the energy and intensity of γ-ray as coordinates, we brought forward the concept of the two_dimensional fuzzy set about spectra, and established the membership function. We also introduced the fundamental principles and method for identifying the γ-ray fingerprints by fuzzy recognition technique. By regularizing the spectra, we succeeded in identifying the types and individuals of nuclear materials. Further more, we introduced the multiplying factor, and thus obtained high degree of confidence in identifying the spectra. We identified the simulation materials as radiation sources with the method, and studied the influence of the detecting distance and the detecting system fluctuation on the membership degree. The results show that the method has strong capabilities of identifying the types and the individuals of radiation sources, and can be applied to the nuclear materials safeguard.
2008, 57 (9): 5366-5368. doi: 10.7498/aps.57.5366
Using Mawhin’s continuation theorem,the periodic solutions for a class of nonlinear problem are first discussed.An El Nio atmospheric physicsal mechanism is applied and the periodic solutions for its model are obtained.
2008, 57 (9): 5369-5373. doi: 10.7498/aps.57.5369
Conformal invariance and conserved quantities of Lagrange system under Lie point transformation are studied. Firstly, the definition of conformal invariance and determining equation for the Lagrange system are provided. Secondly, the relationship between the system’s conformal invariance and Lie symmetry are discussed; the necessary and sufficient condition on which the system’s conformal invariance would be Lie symmetry under the infinitesimal one-parameter point transformation group is deduced; and the conserved quantities of the system are given. Lastly, an illustration example is introduced.
Reduction of Birkhoffian systems is studied. First, the differential equations of motion for the Birkhoffian systems are established and their cyclic integrals are given. Second, the Routh functions of Birkhoffian systems are constructed, and the order of the systems is reduced by using the cyclic integrals and the Birkhoffian form made to hold. Finally, an example is given to illustrate the application of the results.
The three Hamaker hypotheses are the basic principle of the micro-continuum medium. On the basis of the actual crystalline structure, the problem that, the Hamaker idea of continuum medium may not hold is discovered. There are gaps among the crystal structures. In order the micro-object to be a continuum, a close-packed Wigner-Seitz model is put forward by the object structure principle. By analysis of the double Wigner-Seitz model and the classic Lennard-Jones potential, the Hamaker medium amendatory factors for fcc and bcc are derived. The Hamaker additivity hypothesis and homogeneous hypothesis are revised. The micro-continuum medium form including the repulsive force is revised too. The application area of the micro-continuum medium is extended from the attractive force to the repulsive force, which provids an approach to the practical problems in engineering.
2008, 57 (9): 5384-5389. doi: 10.7498/aps.57.5384
The available range of the homoclinic bifurcation criterions are extended from the weakly nonlinear oscillation system to the strongly nonlinear oscillation system. It combines the analysis method of the strongly nonlinear oscillation system with the former criterions based on the improved complex normal form method. The periodic solution of this kind of system with a single degree of freedom is obtained by introducing the fundamental frequency under determination into the complex normal form computation. Then two different analytical criteria to predict the critical values of homoclinic bifurcation are adapted to the new system. It includes the undertermined fundamental frequency approaching zero and the collision of the periodic orbit with the saddle point. The results derived from different methods are compared in the specific systems with numerical simulation to testify the correctness and efficiency of the theoretical results.
2008, 57 (9): 5390-5394. doi: 10.7498/aps.57.5390
The new periodic wave solution for the (2+1)-dimensional Boussinesq equation is presented by using of Hirota method and Riemann theta function, from which the soliton solution can be obtained via an appropriate limited procedure.
2008, 57 (9): 5395-5399. doi: 10.7498/aps.57.5395
We investigate the impurity entanglement of 3-qutrit XXX-type Heisenberg chains in the presence of a uniform magnetic field along z axis by means of negativity. The entanglement is calculated as a function of the coupling constants J, impurity parameter J1, magnetic fields B and temperature T. Through calculating the negativity between sites 1 and (2,3) N1-23 and sites 3 and (1,2) N12-3, we show that the critical temperature Tc above which the entanglement vanishes increases with the increase of J1. The existence of magnetic fields B can obviously reduce the entanglement, and it is found that the limiting temperature Tc depends on the impurity parameter J1 but not on the magnetic field.
2008, 57 (9): 5400-5406. doi: 10.7498/aps.57.5400
Using a FitzHugh-Nagumo system as an example, we studied the stabilities of spiral waves in two-dimensional small-world network. It was found that there exists a critical rewiring probability p such that the spiral instability appears for p>pc due to the small-world connectivity. It was also confirmed that this spiral instability is different from the Eckhaus instability and the Doppler instability.
2008, 57 (9): 5407-5412. doi: 10.7498/aps.57.5407
A new fractional-order hyperchaotic system is reported. A synchronization method for the new chaotic systems is established and its mathematical proof is provided. The nonlinear terms in the response system are not dropped.The good agreement between theoretical analysis and numerical simulation shows the efficiency of the method.
2008, 57 (9): 5413-5418. doi: 10.7498/aps.57.5413
True random number generator (TRNG) is usually more secure than pseudo-random number generator.In this paper,a novel TRNG which produces random bits by noving the mouse casually is proposed which is cheap,convenient and universal for personal computer (PC) platforms.To eliminate the patterns among mouse movements of the same user,two approaches based on image encryption algorithm and Hash function were poposed,both making use of the sensitivity of chaos system.Abundant random bits generated by three users were tested strictly using U.S. NIST’s 16 statistical tests.All TRNGs passed the test successfully,and the revised TRNG is believed to be applicable practically on PC platforms.
2008, 57 (9): 5419-5424. doi: 10.7498/aps.57.5419
We investigate and simulate the evolution process and topological features of the virtual community networks.We founded that the joint of nodes, joint of edges, networks’ degree distribution, average degree and the correlation between the node’s degree and its time in the network are different from the scale-free network model.With statistics and analysis of some of the characteristics of an actual Internet forum, we propose a new network evolution algorithm, namely the virtual community network construction algorithm.The simulation results show that the networks generated from our algorithm has the same characteristics as the real virtual community networks.
2008, 57 (9): 5425-5428. doi: 10.7498/aps.57.5425
Based on the Larmor formula, a mathematic model is established to calculate the power of THz wave radiated form the photoconductive antenna. The power of THz waves radiated by GaAs photoconductive antenna under different experimental conditions was calculated by Monte Carlo simulations. The results show that the power of THz radiation can be improved by increasing the bias electric field or the energy of triggering light pulse, and large-aperture photoconductive antenna can emit THz wave with higher power compared with photoconductive antennas with small apertures because the former can carry more photo-generated carriers.
Design and assembly of split-sphere high pressure apparatus based on the hinge-type cubic-anvil press
2008, 57 (9): 5429-5434. doi: 10.7498/aps.57.5429
A new split-sphere large-volume high pressure apparatus has been developed to generate high pressure above 10 GPa. The apparatus is based on a domestic hinge-type cubic-anvil press known as the DS6×800T press. In this work, the split-sphere parts are directly placed in the cubic-anvil cell, and the effect of the gasket dimension and phyrophyllite density on pressure transmitting efficiency has been investigated. The relationship of cell pressure versus press load was calibrated at room temperature for the 14/8 (octahedral edge-length/anvil truncation edge-length, in millimeters) cell assembly using the phase transitions of Bi Ⅰ-Ⅱ(2.55 GPa), Ⅲ-Ⅴ(7.7 GPa), and SnⅠ-Ⅱ(9.4 GPa).The experimental results show that the cell pressure can reach about 10 GPa with a sample volume of 3—4 mm3 under an applied load of 290 ton.
Exact calculation of the optical path difference and lateral displacement of modified large optical path difference Sagnac interferometer in full view field used in upper atmospheric wind field measurement
2008, 57 (9): 5435-5441. doi: 10.7498/aps.57.5435
The shearing principle of modified large optical path difference Sagnac interferometer for upper atmospheric wind field measurement is presented. The exact expression of the optical path difference and lateral displacement in the full view field of modified Sagnac interferometer are calculated by analysing the relation between space beeline and its projection and the notion of ray index at random incidence angle. The theoretical and practical guidance are thereby provided for the study and design of the spatially modulated interference imaging spectrometers.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2008, 57 (9): 5442-5447. doi: 10.7498/aps.57.5442
We calculate the unpolarized differential cross section in magnetic dipole field, electric dipole field and uniform electrostatic and magnetostatic fields, respectively,by the Feynman perturbation technique. It is found that in electric dipole field, the differential cross section vanishes in both the same and the opposite propagating directions of the photon flux. In the magnetic dipole field the differential cross section generally has non-vanishing values in both directions,but when the propagating direction of photon flux is parallel to the magnetic dipole vector, the differential cross section is equal to zero. In the uniform electrostatic and magnetostatic fields, non-vanishing differential cross sections occur in the same and opposite propagating directions of the photon flux, but in the latter case it is weaker than in the former. When the mass of axion approaches to zero,the above process shows similar characters as the conversion of the photons to the gravitons.
2008, 57 (9): 5448-5451. doi: 10.7498/aps.57.5448
The neutrino energy loss rate of modified URCA process in strong magnetic field of neutron star core is investigated based on the n-p-e model. Both neutron and proton branches of modified URCA process are considered. The result shows that a strong magnetic field makes the neutrino energy loss rate of modified URCA process to oscillate intensively. Compared with the neutron branch, neutrino energy loss rate of the proton branch is weaker. But the total neutrino energy loss rate will increase due to the proton branch of modified URCA processes. The result will contribute to the research of cooling mechanism of neutron stars.
Analysis of the experiment data of vertical migration of radon and its daughters under ideal conditions
2008, 57 (9): 5452-5457. doi: 10.7498/aps.57.5452
We analyzed the vertical long distance migration experiment data of radon and its daughters,and found that the number of α particles is insufficient to explain the fast upward migration of radon by helium- radon clustering. If assume that radon has very strong ability to adsorb the helium from the air to form helium-radon clusters for vertical migration, then there is an inconsistency between the tentative and that experimental conclusion,that the upward and downward migration probability of radon and its daughters in natural state is equal to that when helium gas is added.So we propose that helium- radon clustering may not be the main reason of radon and its daughters′ fast upward migration. There may be other more complex reasons. The phenomenon needs further research.
2008, 57 (9): 5458-5463. doi: 10.7498/aps.57.5458
The isospin effects of isoscaling parameter α on the nucleon-nucleon cross section are investigated for two couples of central nuclear reactions 40C+ 40Ca with 60Ca + 40Ca and 112Sn+ 112Sn with 124Sn+ 124Sn within an isospin dependent quantum molecular dynamics. It is found that the isospin effect of isoscaling parameter α on the isospin dependent nucleon-nucleon cross section σmedNN(αm) compared with that on the isospin independent nucleon-nucleon cross sections σ1NN(αm) is very obvious. However, the isospin effect of isoscaling parameter α on σmedNN(αm) compared with that on the isospin independent nucleon-nucleon cross section σ2NN(αm) is small. The mechanisms for the above difference are investigated in detail.
ATOMIC AND MOLECULAR PHYSICS
2008, 57 (9): 5464-5468. doi: 10.7498/aps.57.5464
The structure optimization and frequency calculation of hexaazatriphenylene, triphenylene and their derivatives were carried out at the level of B3LYP/6-31G**, and the most stable configurations were obtained. On the basis of the most stable geometries, the relationships of the total energy with rotation degrees between the dimers were studied, and the lowest energy point was obtained. Based on the semi-classical model of the charge transport, our results predict that hexaazatriphenylene molecules have the largest positive charge transport rate and the smallest negative charge transport rate. Introduction of SH, OH, OR and F groups make the positive charge transport to increase, and the negative charge transport to decrease. The length of alkoxy group has little effect on charge transport properties.
2008, 57 (9): 5469-5475. doi: 10.7498/aps.57.5469
A Mathematica program is developed to calculate the energy and relativistic correction of helium-like atoms in 1sns configuration. A new set of trial functions for 1sns configuration in helium has been suggested. By virtue of the Rayleigh-Ritz variational method, the non-relativistic energies of 1sns configuration in helium (n=2—5) have been calculated, the relativistic corrections, which include mass correction, one- and two-body Darwin correction and spin-spin contact interaction, have been further calculated with the theory of perturbation. The calculated results are in good agreement with experimental data.
2008, 57 (9): 5476-5484. doi: 10.7498/aps.57.5476
The effective permittivity, effective permeability and the phase factor of a rectangular waveguide filled with an anisotropic metamaterial is derived through solving the wave equation. A group of important conclusions is obtained through discussing the relations between transmission characteristics of the waveguide and constitutive parameters of the filling metamaterial. It is shown that characteristics of the waveguide are determined by the transversal constitutive parameters when the operating frequency is higher than the cut_off frequency, and they are independent on the longitudinal constitutive parameters. However, below the cut off frequency, the characteristics of the waveguide are determined by both the transversal and longitudinal constitutive parameters. Two examples are calculated to demonstrate the above conclusions, and it is shown that calculated results are in a good agreement with the theoretical predictions. These results play important role in the applications of metamaterials to waveguide.
2008, 57 (9): 5485-5490. doi: 10.7498/aps.57.5485
In this paper, we present experimental study of effects of laser power and interaction length on collimation of chromium atomic beam by one-dimensional Doppler laser with large collimating slit of 5 mm in length, where the fluorescence is treated by Matlab. In addition, calculation by an adaptive step size, fourth-order Runge-Kutta type algorithm is done corresponding to the experiment. Both results show that with fixed interaction length, when the laser power becomes larger, or with fixed laser power, when the interaction length becomes longer, the FWHM of collimated atomic beam becomes smaller, and the peak becomes higher.
2008, 57 (9): 5491-5499. doi: 10.7498/aps.57.5491
Based on the first-principle, all geometric structures of Bn and BnNi clusters with n=6—12 have been optimized by using density functional theory with generalized gradient approximation, the equilibrium geometries for different spin multiplicities and ground-state structures have been determined. The results of Bn clusters are in good agreement with previous conclusions. When the Ni atom is doped in Bn clusters, the ground-state structure of the BnNi clusters favor three dimensional, but B12Ni cluster has the planar structure. The spin multiplicity of ground-state structures, except for n=8, obey the 2 and 1 alternate rule. The average atomic binding energies (Eb), second-order energy differences (Δ2E) and the HOMO-LUMO (gap) of ground-state structures have been calculated and discussed. The results indicated that n= 8 is the magic number of BnNi(n=6—12) clusters, implying that B8Ni cluster possess relatively higher stability. Calculated results on the magnetic moments show that the magnetic moment of B8Ni cluster is the biggest (2μB), the total magnetic moment and the average magnetic moment of clusters show the odd-even oscillation tendency along with the size increasing, and the magnetic moment is mainly provided by the 3 d orbital of Ni atom.
CLASSICAL AREA OF PHENOMENOLOGY
2008, 57 (9): 5506-5512. doi: 10.7498/aps.57.5506
The model of trapping force on microsphere based on the conservation of momentum are presented. Using 2-D FDTD algorithm, we calculated the effects of the wave length, waist of the Gaussian beam, the radius and refractive index of the microsphere on the trapping force. The results show that the microsphere located in a certain zone of focused laser optical electromagnetic fields will be trapped, and the trapping force deceases with the increase of the distance of the observed point away from the axis. When the refractive index of the surrounding medium is greater than that of the microsphere (such as an air bubble), it will be pushed out of the laser beam. The simulation results are in good aggrement with the experimental observation.
2008, 57 (9): 5513-5518. doi: 10.7498/aps.57.5513
Different dispersion properties are imparted to nonradiative dielectric (NRD) waveguides by split ring resonator metamaterials. Both longitudinal-section magnetic and longitudinal-section electric modes are capable of propagating very slowly due to the metamaterial bianisotropic effects, and can even approach zero velocity. Enhanced energy flow in the considered structure is also demonstrated under certain conditions. Finally, miniaturization of NRD waveguide based on these unusual properties is proposed.
Propagation and localization of plane waves in two-dimensional homogeneous and isotropic random medium
2008, 57 (9): 5519-5528. doi: 10.7498/aps.57.5519
Propagation and localization of plane waves in two-dimensional homogeneous and isotropic random medium is studied. The approximate stochastic solution of the plane wave and the propagation behaviors are obtained by means of stochastic functional approach. The results verify the phenomenon of localization of waves in random medium. The agreements between the theory and the computer simulations are shown to be satisfactory in spite of the use of approximate theoretical formulas.
Investigation of the scattered field from a two-dimensional dielectric target above the planar surface with a Gaussian beam incidence
2008, 57 (9): 5529-5536. doi: 10.7498/aps.57.5529
Differential scattering field of vertical incident Gaussian beam from a two-dimensional target near a plane interface is studied by means of a new hybrid method based on the reciprocity theorem (RT), the image theory (IT) and the method of moment (MoM). By application of IT, the plane interface is replaced by the virtual image of the actual target, and an equivalent model of the scattering problem is presented. In the equivalent model, the scattered field from the actual target and the virtual one are numerically calculated by employing MoM, and the rescattered coupling fields between the actual target and the virtual one are evaluated utilizing the combination of MoM and RT. The numerical results of these tests are presented and compared with previously published calculations for the same problems.
Analysis and simulation on propagation characteristics in waveguide filled with single-negative medium layers
2008, 57 (9): 5537-5541. doi: 10.7498/aps.57.5537
The propagation characteristics of rectangular waveguide filled with two layers of single-negative medium are analyzed in this paper. The Drude-FDTD model is adapted to the application in three-dimension simulation program. Simulation results show that a subwavelength transmission mode exists in the waveguide. Based on the simulation results for different frequency and different medium parameter, energy propagation rule in this kind of waveguide is obtained. Especialy, the band width of microwave devices and antennas can be significantly widened with ENG-MNG filling method.
Composite optical vortices formed by two flattened Gaussian vortex beams and their propagation in free space
2008, 57 (9): 5542-5549. doi: 10.7498/aps.57.5542
The composite optical vortices (OVs) in the superimposed field of two parallel, off-axis flattened Gaussian vortex beams with topological charge m1, 2=±1 at the waist plane and their propagation dynamics in free space are studied. Detailed numerical calculations and analysis show that the number, position and net topological charge of composite OVs depend on the control parameter, such as the relative phase, amplitude ratio, waist-width ratio, relative off-axis distance, beam order, and on the propagation distance, but the topological charge is not always conserved.
2008, 57 (9): 5550-5557. doi: 10.7498/aps.57.5550
The spatial distributions of energy in a random medium and the spectrum characteristics of some regions in this medium are studied and the results show that the energy is localized in some regions and the spatial distribution of the energy is both related with positions of the particles in the medium and the wavelength of excitation light. And the regions of energy congregation are related with the quasi-closed structures formed from the particles but no one to one correspondence exists between them. Under the stimulating of the same excitation light, different spectra appear in different quasi-closed structures and they change with time. And under the stimulating of different excitation light sources, the spectra of the same quasi-closed structure are different. When the wavelength of exci tation light does not match the configuration parameter of a quasi-closed structure, the peaks of its spectrum will change frequently and the energies of the peaks are attenuated quickly. When the wavelength of the light be ther matches the configuration parameter of the quasi-closed structure, a certain peak will retain its leading position in height in the spectrums and its energy attenuate but slowly. So photon-localization is both related with the configuration of medium and the wavelength of excitation light, and the random lasing can be regarded as the result of the general scattering effect of the excitation light by the random medium.
2008, 57 (9): 5558-5564. doi: 10.7498/aps.57.5558
The characteristics of laser induced damage morphology in the bulk of the K9 glass caused by focused nanosecond laser pulse is analyzed in detail. The damage shape looks like a spindle with a large front-end and its thickness gradually decreases on going to the rear end. According to the experimental results, the damaged range can be divided into four zones, namely the filamentary plasma channel, fractures, the fusion zone and the region of varying refractive index. The function of laser pulse energy deposition in space and the expansion pressure of shock wave are deduced, and the corresponding damage morphology is analyzed based on the spatial distribution of pressure. The theoretical analysis agrees with the experimental results.
Retrieval of the optical thickness and effective radius of aerosols from reflected solar radiation measurements
2008, 57 (9): 5565-5570. doi: 10.7498/aps.57.5565
A method for determining the optical thickness and effective particle radius of spherical aerosols with sun light of a single wavelength is presented. Based on the vector radiative transfer theory, the reflection matrix of the aerosols is calculated by using the adding-doubling method for λ=0.75μm and 3.3μm, the effective radii of aerosol particles were 0.01—1.5μm, and the optical thickness were 0.05—1. We modeled the retrieval process by computer simulation. From the numerical results, we conclude that the radiance combined with polarization is capable of uniquely retrieving optical thickness and effective radius with high accuracy. Especially, when the effective radius is less than 0.4μm, a visible light wavelength can be used for retrieval; when the effective radius is larger than 1.0μm, an infrared light wavelength can be used for retrieval; when the effective radius lies between 0.4 and 1.0μm, both of the two wave bands can be used to obtain a unique result with high accuracy.
2008, 57 (9): 5571-5577. doi: 10.7498/aps.57.5571
A theoretical model has been put forward to describe the dynamic properties of photoinduced anisotropy in photochromic diarylethene/PMMA film. The kinetic curves of molecule concentration, photoinduced dichroism and birefringence are calculated under the condition of excitation by linearly polarized light. The results show that the color molecule concentration decreases with the increase of the excitation exposure until the saturation point is reached. The photoinduced anisotropy increases to a maximum and then decreases with the exposure increasing. The optimal exposure is 260 J/cm2. Using the orthogonal polarization detection, the transmittance of probe beam reflecting the anisotropy is measured. The experimental result and the theoretical calculation are essentially consistent.
2008, 57 (9): 5578-5583. doi: 10.7498/aps.57.5578
According to the affected images generated by the thermal imaging system which incorporates a front wire grid, with the help of classical optical theory, we analyzed the diffractive functional principle character of light wave, and also analyzed the case of non-concolorous targets, and further established the mathematic model. The results indicated that after putting in parameters of real instance and generating simulated images using MATLAB, the simulated images have good comparability with the images obtained in reality. The research achieved the expected aim of the modelling. Finally we put forward the questions and key technology pending further research.
2008, 57 (9): 5584-5588. doi: 10.7498/aps.57.5584
A two-level atom passing through double spatially separated single-mode cavity fields is studied. We investigate the effecting factors of photon emission probabilities of the atom, which include the kinetic energy of the atom, the length of the cavity and the separation between the two cavities. The results show that in the case of ultra-cold atom, when the kinetic energy of the atom is small (k/k0k/k0>1), the length of the cavity has great effect on the photon emission probabilities. The present work shows that the photon emission probabilities may be modulated by controlling the center-of-mass motion of the atom.
2008, 57 (9): 5589-5592. doi: 10.7498/aps.57.5589
We study the realization of quantum logic gates in the interacting system of a two-dimensional trapped ion and two laser beams. We simplify the Hamiltonian of the system by Choosing the frequency detuning of laser fields and the transition frequency between the internal states of the ion, and furthermore，we describe the realization of a C-NOT gate, a swap gate and a phase gate. During these processes, the system needs to meet the Lamb-Dicke limit, and the Rabi oscillation frequency should be far smaller than the phonon frequency.
2008, 57 (9): 5593-5599. doi: 10.7498/aps.57.5593
A novel and high resolution method for measuring quantum states with incoherent light in the time-domain is presented. Taking Autler-Townes effect as an example, the physical process and the evolution rule during measurement are discussed by an explicit analytical formulation in detail; and the influence of measuring process on the quantum state is disclosed. With this method, very small splitting of the energy-level and large energy-level space can be measured readily at the same time, while the transverse relaxation rate of the system can be obtained directly by checking the decay time of the signal. Compared with the characteristics of the measuring methods between the time-domain and frequency-domain, we found that the measuring quantum states with incoherent light in the time-domain is robust and valid for disclosing information of the quantum state completely.
2008, 57 (9): 5600-5604. doi: 10.7498/aps.57.5600
We propose a new method of decoy state quantum key distribution with a heralded single-photon source. Alice uses the parametric down-conversion to generate entangled photon-pairs, one of the pair is used as heralding photon. According to the results of the trigger detector the heralded photons are divided into trigger and non-trigger sets.The states of the photons in the trigger set are used as the signal states and the ones in the non-trigger sets are used as the decoy states. Because of the efficiency of the trigger detector, the two sets both have photons. The yield and error rate of the single-photon are estimated through the yield and error rate of the two sets. This method does not need changing the intensity of the photon source, is easy to implement. Analysis results show that this method can reach the same security distance as with a perfect single photon source; the key generation rate is increased a lot compared with the method with a heralded photon source and is approximately two thirds the rate of the three intensities decoy state quantum key distribution with a heralded photon source.
2008, 57 (9): 5605-5611. doi: 10.7498/aps.57.5605
We propose one kind of improved QKD scheme based on time coding and phase coding. The pulse which had been discarded on the BB84 protocol phase coding QKD system is used to realize the time coding protocol, thus the useful bits rate in the present scheme can be doubled. At the same time, the phase coding keys and the time coding keys are obtained, we may combine both as new keys which can enhancethe generated rate and the sensitivity of monitor. At Bob’s side, a Fraday-Michelson is used instead of a traditional M-Z interferometer, which improves the stability of the interference visibility. With the proposed experimental setup, a stable quantum key distribution was performed over 90 km fiber. It is shown in our experiment that the characteristics of our system are as follows: secure, stable and economical.
Optical forces on moving atom were investigated in micro-cavity using fully quantum theory. In terms of the models of moving atom interacting with micro-cavity field, using algebraic dynamics method, the Hamiltonian can be diagonalized by introducing a canonical transformation. The expression of evolution operator of the system and reduced density operators are calculated straightforwardly. Analytical expressions for the forces are obtained, and the forces are discussed for a traveling-wave field and a standing-wave field respectively.
A new circuit model for avalanche photodiodes to detect infrared single photon by transient process of transmission lines
2008, 57 (9): 5620-5626. doi: 10.7498/aps.57.5620
A new circuit model for using the avalanche photodiodes to detect infrared single photon is proposed, which combines the requirements of a single photon detector control circuit and features of the electric pulses generator by transient process of transmission lines. The simulation results are given for the new circuit model and the emphasis is laid on the analysis of the feasibility of the circuit model in using the gate mode scheme of the avalanche photodiodes to detect infrared single photon and the influence of each electrical component on the performance of the circuit model. Finally, optimal parameters of the electrical components and the gate-mode with the quenching circuit model are demonstrated.
2008, 57 (9): 5627-5631. doi: 10.7498/aps.57.5627
The phase-locking of two photonic crystal fiber (PCF) lasers is studied experimentally by using Michelson cavity technique, and 47 W coherent output power is obtained. The phenomenon of interference-enhancement and interference-loss on the two arms of the Michelson cavity is theoretically explained by analyzing the optical path difference. Experiment shows that the Michelson cavity setup can improve the spectra of the combined laser significantly. The bandwidth of the combined laser is less than 5nm in our experiment.
2008, 57 (9): 5632-5638. doi: 10.7498/aps.57.5632
Output beam quality of InnoSlab laser with hybrid resonator is analyzed in this paper for the thermal lens effect and mirror misalignment. Many aspects, such as far-field light intensity distribution, far-field divergence angle, beam waist radius, beam quality factor M2 and PIB curve, etc, are discussed. Especially, in the off-axis unstable resonator direction, the influence of beam quality is discussed with respect to mirror misalignment by M2 and PIB curve. This gives valuable reference to unstable resonator beam quality evaluation, for which a unified standard has not been set up as yet.
2008, 57 (9): 5639-5645. doi: 10.7498/aps.57.5639
As it is difficult to solve a large number of rate equations including doubly excited states of various ions, block matrix method is expected to dramatically reduce the machine time by dividing the large number of equations into pieces of small units, and solving them one by one, on condition that the ionization and recombination between excited states of ions can be ignored. In this paper, the influence of ionization and recombination between excited states on plasma status was studied, and detailed analysis of its mechanism was made. The effect on gain of Ne-like Ge 19.6nm X-ray laser respectively driven by 1.0ns pulse, 100ps pulse and 5ps pre-pulse and main pulse was studied. The simulation shows that for the 5ps driving pulse case, the ionization and recombination between excited states has relatively large influence, and it can not be ignored and that for the two quasi-stable state cases, in the gain region with electron density less than 5×1020cm－3, the FWHM temporal width of gain increases by～10%, and the FWHM spatial width of gain increases respectively by～13% and ～-23%, and the time the peak gain appears is delayed respectively by～1.4% and ～6.9%, which is tolerable, implying that the block matrix method could be applied in the qualitative modeling of QSS scheme X-ray laser. However, for accurate study, the ionization between the excited states could not be neglected.
2008, 57 (9): 5646-5650. doi: 10.7498/aps.57.5646
We numerically simulated the dymamics of mode locking in pure positive dipersion lasers by NLS. Different from soliton lasers operating in net negative dispersion regime or dispersion mananged soliton and similariton lasers operationg in net positive dispersion regime with disperion compensation components, gain saturation and narrowing plays an important role in pulse formation in lasers composed of pure positive dispersion medium, in which the pulses evolve to gain-guided solitons. Stable gain-guided soliton was obtain in two kinds of mode locked fiber lasers operating in the positive dipersion regime, and experimental results confirmed the numerical simulation.
2008, 57 (9): 5651-5661. doi: 10.7498/aps.57.5651
The propagation and switching of fundamental solitons in three-core fiber nonlinear directional coupler with three cores in an equilateral-triangle arrangement have been investigated with two methods. Firstly, by using variational method, we obtained the equation of transmission coefficient with respect to distance. Secondly, we used the split-step Fourier method (SSFM) to solve the nonlinear Schrdinger equations. The results of both variational method and SSFM indicate that the energy of optical pulses transfer periodically between the three cores and have sharp switching characteristics when the first order intermodal dispersion coefficient is small. Otherwise, the periodicity of the coupling transmission characteristics of optical solitons in fiber coupler and the sharpness of switching are destroyed. The second order intermodal dispersion coefficient and initiative chirp reduce the coupling length, shorten the periods of the energy transfer of optical pulses between the three cores, and increase the threshold switching power. Though the cross phase modulation coefficient has weaker impact on transmission characteristics, it increases the threshold switching power of couplers.
Theoretical study of tunable terahertz radiation based on difference-frequency generation in GaSe and ZnGeP2 crystals
2008, 57 (9): 5662-5669. doi: 10.7498/aps.57.5662
Based on the theory of nonlinear optical frequency conversion, the phase-match angle, walk-off angle, acceptance angle and effective nonlinear coefficient of difference-frequency in GaSe and ZnGeP2 crystals are calculated under different phase-matched conditions. In the theoretical simulation, the experimental parameters which were reported to generate widely tunable terahertz waves by nonlinear optical difference-frequency method are adopted. The optimum phase-matched conditions corresponding to different terahertz wave bands are summarized through comparing the whole calculated results. The calculated results provide a sound and comprehensive theoretical basis for using optical difference-frequency method to generate tunable terahertz wave in the nonlinear crystals.
2008, 57 (9): 5670-5674. doi: 10.7498/aps.57.5670
Pure and MgO doped near stoichiometric lithium tantalate has been grown by adding flux method. The observation of the crystal wafers etched by hydrofluoric acid under metallographic microscope indicate that the domain structure of near stoichiometric lithium tantalate is hexagonal. Polarization experiments have been done by using the equipment made by ourselves. By using short-impulsed polarization electric field, several parameters, including the positive and negative direction coercive force field and polarization time were investigated. Polarization current and entirely reversed domain structure were obtained.
Chromatic bistability and luminescence switching of visible-infrared emission in Tm-doped laser crystal
2008, 57 (9): 5675-5683. doi: 10.7498/aps.57.5675
Optical bistability and luminescence switching of visible-infrared emission in Tm-doped laser crystal pumped at 648nm avalanche wavelength is predicted theoretically and studied numerically. The analytical formula of luminescence switching threshold is deduced using the theory of nonlinear rate equations. The evolutions of populations of Tm3+ energy levels, emission spectrum and fluorescence intensity versus pump power are investigated numerically. The numerical results predict that the luminescence switching between 452/469nm blue and 1716nm infrared spectra can be experimentally realized under 648nm laser pumping. Moreover, the bistability of emission spectra, chromatic fluorescence and luminescence intensity in Tm-doped crystal can be observed in the vicinity of photon avalanche threshold. The characteristics of chromatic bistability and luminescence switching in Tm-doped crystal allow for the tailoring of pump-controlled all-solid luminescent switcher and bistable wavelength switch operating in visible-infrared spectral range.
2008, 57 (9): 5684-5689. doi: 10.7498/aps.57.5684
The reduced Lagrange density of nonlocal nonlinear Schrdinger equation(NNLSE) is obtained by expanding the real symmetric response function in Taylor’s series in strongly nonlocal Kerr media. The problem of higher-order beam propagation can be analyzed by a variational approach, the equations are obtained for the evolution during propagation of the parameters of the trial solution and exact analytical Hermite-Gaussian(HG) solutions are found. HG solitons are formed when the input power is equal to the critical power. We demonstrated that the analytical HG solutions are in good agreement with the numerical simulations in the case of strong nonlocality.
2008, 57 (9): 5690-5698. doi: 10.7498/aps.57.5690
In this paper, we investigate the effect of the boundary of the nonlocal nonlinear medium on the propagation of soliton. On the basic of NNLSE and the Poisson equation, using the Green function approach, we obtain the response function of the lead glass of finite-size, which is a strong nonlocal medium. Starting with the paraxial ray equation, we obtain the analytical solutions of the oscillation trajectory and period of the beam. Comparing the analytical solutions with numerical simulations, we found that our analytical solutions are precise when the point of incidence is not near the boundary of the medium.
Investigation on up-conversion luminescence of Tm3+ and Yb3+ codoped oxy-fluorosilicate glass ceramics
2008, 57 (9): 5699-5704. doi: 10.7498/aps.57.5699
Two series of Tm3+ and Yb3+codoped oxy-fluorosilicate glass ceramics with the composition of 30SiO2-(20-x-y)Al2O3-40PbF2-10CdF2-xTm2O3-yYb2O3 were prepared and characterized. The up-conversion spectra of the samples were investigated and the up-conversion luminescence mechanisms of Tm3+/Yb3+ system were analyzed. The effects of Tm3+ and Yb3+ concentration on up-conversion luminescence spectra weresystematically studied. The results suggest that blue up-conversion emission intensity decreases when Tm3+ concentration increases due to the cross relaxation interaction between Tm3+ ions. The optimum Tm3+ concentration is 0.025mol%. Three-photon process and Yb3+ ion cooperative up-conversion energy transfer process co-exist in the Tm3+/Yb3+ up-conversion luminescence system. When Yb3+ concentration increases, due to the energy back-transfer process of 3H4(Tm3+)→2F5/2(Yb3+), the blue up-conversion emission intensity would decrease. With the help of Yb3+ ion cooperative up-conversion energy transfer, the blue up-conversion emission intensity actually increases, which is in accordance with the experimental results.
2008, 57 (9): 5705-5708. doi: 10.7498/aps.57.5705
As solid-state dye lasers exhibit the attractive features of compactness， being intoxic, and low cost, the development of tunable solid-state dye lasers is an area of active research. Solid state dyes based on polymethyl methacylate (PMMA) doped with new high efficiency pyrromethene-580 were prepared. First, the absorption and fluorescence of the samples were obtained. Pumped by the second harmonic of Q switched Nd:YAG laser, the output characteristics of the solid state dye lasers with different dye concentrations were studied. The central wavelength of the lasing emission peak increases with increasing dye concentration. The slope efficiencies of the samples were also obtained. The highest slope efficiency of 53.8% was obtained with dye concentration of about 2×10－4 mol/L. Pumped at 410mJ, the pulse energy of the solid dye laser reached 220mJ with the band width～8nm.
2008, 57 (9): 5709-5712. doi: 10.7498/aps.57.5709
A one-dimensional photonic crystal containing multilayered half-wave defects is designed and the transmission spectrum is studied by using transfer matrix theory. Under the first-order approximation of Taylor expansion, the analytic expression for the defect mode frequency is derived, from which the coupling factor is deduced. Our results are fitted with the experimental results or numerical simulation, and can be used to describe the characteristics of the defect modes. The result is helpful for designing a multiple channel filter.
2008, 57 (9): 5713-5717. doi: 10.7498/aps.57.5713
The laser beam automatic alignment system is applied to a high power laser facility for inertial confinement fusion. The far-field detection is a key technique of the automatic alignment system. Utilizing the image of spatial filter’s pinhole of the high power laser system and diffraction of sampling grating, a new method for far-field detection of laser beam is proposed and fully demonstrated on the experimental system. The experimental results indicate that, unlike the traditional method, this far-field detection system can fully use the space through off-axial grating sampling, and the average far-field alignment error is less than 0.9% of spatial filter pinhole diameter, which meets the alignment system requirements of less than 5% of spatial filter pinhole diameter.
2008, 57 (9): 5718-5721. doi: 10.7498/aps.57.5718
We proposed a theoretical model of magnetron photonic switching circuit (MPSC) in photonic crystal (PC) and investigated the properties of MPSC using the plane wave expansion method in combination with supercell method. This model is a PC composed of dielectric pillars set in air, in which one row of dielectric pillars is replaced by ferrite material with the dielectric constant same as that of the original dielectric pillars. When external static magnetic field is applied, the permeability of the ferrite pillars will not be equal to one and guide modes along the row of ferrite pillars may be generated in band gap. When the external field is removed, this system reverts to a perfect PC. Thus, this system forms a photonic switching circuit controlled by the external field. In calculation, we take square pillars set in square lattice. The calculation results show that this MPSC is reasonable and realizable, and some valuable results are obtained.
Modal characteristics and leakage loss of hollow-core photonic-bandgap fibers based on a square lattice
2008, 57 (9): 5722-5728. doi: 10.7498/aps.57.5722
In this paper the modal characteristics and leakage loss of hollow-core photonic bandgap fibers based on a square lattice with rounded square air holes was investigated by using a full-vector finite element method. It was found that hollow-core photonic bandgap fibers with air core arranged in square lattice can operate in the broad bandgap single mode. The leakage loss was analyzed comprehensively. Simulations show that the core diameter and the hole-to-hole spacing have a small influence on leakage loss, but for a given wavelength the desired lowest leakage loss could be obtained by tuning the value of hole-to-hole spacing, while the rounded diameter has a larger influence on leakage loss than the former factors and it has an optimal value dc/d=0.4. The number of cladding rings plays a key role in the leakage loss and the leakage loss is reduced by nearly 2 orders of magnitude per 2 additional cladding rings.
2008, 57 (9): 5729-5734. doi: 10.7498/aps.57.5729
A new type of microstructured optical fiber with a high birefringence tunable effect is designed by introducing two large air holes in a core region to induce local birefringence and reducing the hole lattices in the x-direction to induce global birefringence. Polarization properties and modal field characteristics of this fiber based on polymethyl methacrylate materials are investigated by using the full vectorial plane wave method. The results show that the fundamental mode birefringence has two maxima in an optical communication wavelength band, and the magnitude and position of the maximum birefringence can be adjusted by changing the wavelength and the structure parameter of this fiber. By adjusting the air holes diameter and hole lattices in the x-direction , the simulation results show the optimized design parameters of this fiber with high birefringence and zero polarization mode dispersion.
Design and characteristics of a near-elliptic inner cladding High birefringent polarization-stable photonic crystal fiber
2008, 57 (9): 5735-5741. doi: 10.7498/aps.57.5735
A new near-elliptic inner cladding (NEIC) structure of polarization-stable highly birefringent photonic crystal fiber (HB-PCF) is proposed and analyzed numerically by using the full-vector finite element method (FEM) under the condition of anisotropic perfectly matched layers. The result confirmed that the birefringence degradation of the proposed NEIC-PCF is less than 1.2×10-5 when the air hole diameter of the inner cladding along the short axis varies from 1.30μm to 1.18μm (varied by ～10%)，while the average birefringence is of the order of 10-3 at 1.55μm and the mode field diameters along long axis and short axis of the elliptic are 9.2μm and 2.4μm，respectively，which shows that the proposed PCF have excellent polarization stability.
2008, 57 (9): 5742-5748. doi: 10.7498/aps.57.5742
The vector field of normal modes in Pekeris waveguide is studied，and the expression of horizontal and vertical complex acoustic intensity are proposed，especially their characteristics are analyzed in this paper. For the single order mode，the form in the horizontal direction is traveling wave，the corresponding complex acoustic intensity is active，and the vertical form is standing wave，the corresponding complex acoustic intensity is reactive. But for the multi-order mode，either the horizontal or vertical complex acoustic intensity has both active and reactive component because of the interference between the normal modes. Only the active component can transport energy，but the reactive component also carries important information of sound field. The numerical analysis shows that，for the very low frequency sound field of point source，the sign of the active component of horizontal complex acoustic intensity and the reactive component of vertical complex acoustic intensity changed regularly with the change of the depth of acoustic source，so the target depths can be classified by comparing with a critical depth when the receiving transducer is placed in appropriate depths，especially the active component of horizontal complex acoustic intensity，can be used to tell whether the sound source is near the surface or underwater. Further more，the phase angle of complex acoustic intensity is discussed and its distribution regularities are analyzed.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
An acoustic gas concentration measurement algorithm for carbon monoxide in mixtures based on molecular multi-relaxation model
2008, 57 (9): 5749-5755. doi: 10.7498/aps.57.5749
In this paper，we disclose the relations between multi-relaxation absorption and the acoustic parameters when ultrasound propagates in gas mixtures，such as the relation between concentrations of constituents and acoustic frequencies. In the meantime，the dependence of acoustic velocity on the same parameters is discussed. Based on the sample consisting of carbon monoxide，water vapor，nitrogen and oxygen，we establish the three dimensional model for the relation between concentrations of mixture constituents and relaxation absorption and acoustic velocity，respectively. Further more，we give the two dimensional dependence between relaxation absorption and acoustic frequency. We propose a simplified algorithm to calculate the carbon monoxide concentration by measuring the relaxation absorption and acoustic velocity. Simulation results proved the feasibility of this method and showed the appropriate range of acoustic frequency. The origins of errors arising in the application of the method are indicated in this paper.
2008, 57 (9): 5756-5760. doi: 10.7498/aps.57.5756
Based on Monte Carlo simulation of neutron penumbral imaging，the linear space invariance is researched. In the field of view，the points broadening linearly depends on the axial distance on the object plane，but the integrated intensity keeps linear space invariance. Using this result，the alignment precision is analyzed. The axial error of the targets center on the object plane should be controlled within 50μm. The point source should be less than 300μm away from the object plane. The aperture rotation should be within 0.1mrad.
Introduction of 6-band P-1 radiation model for numerical analysis of three-dimensional air arc plasma
2008, 57 (9): 5761-5767. doi: 10.7498/aps.57.5761
6-band P-1 radiation model is introduced to implement the simulation of three-dimensional air arc plasma. The calculation has the specific feature that both radiation emission and self-absorption are taken into account. The distributions of temperature and radiation flux density are obtained and analyzed. Comparing with the net emission coefficient (NEC) method，its temperature distribution range is wider and the arc column voltage is more close to the experimental test value，which shows that the P-1 model can be used to solve the arc radiation problem more accurately.
Experimental investigation of square superlattice pattern formation in a dielectric barrier discharge
2008, 57 (9): 5768-5773. doi: 10.7498/aps.57.5768
The formation of the square superlattice pattern in discharge in the mixture of argon and air is investigated by using a dielectric barrier discharge device with water electrode. It is found that the bifurcation process of the patterns follows goes through the stages of square pattern，quasisuperlattice pattern，square superlattice pattern and the stripe or hexagonal pattern. Their spatial Fourier spectra are analyzed and the variation of the wave vector as a function of the applied voltage is determined. In addition，two types of square superlattice patterns with different spatial scales are observed with the applied voltage increasing. They all satisfy the standing wave condition. The role of wall charge accumulated in the dielectric layers in the formation of the square superlattice pattern is analyzed. Both the phase diagram on the plot of pattern type against the gas gap width and applied voltage and the phase diagram on the plot of the square superlattice pattern against the gas gap width and the gas pressure are obtained. In addition，the changes of the breakdown voltage and the voltage of the square superlattice pattern as a function of the air concentration are determined. It is found that they increase with the increasing of the air concentration.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Structural evolution and grain growth kinetics of the mechanically alloyed Fe42.5Al42.5Ti5B10 induced by annealing
2008, 57 (9): 5774-5781. doi: 10.7498/aps.57.5774
The XRD and TEM techniques were used to study the structural evolution in the mechanical alloying and annealing of Fe42.5Al42.5Ti5B10. The mechanical alloying mechanism during ball milling and the grain growth mechanism during annealing of the powder are also discussed. The results show that the diffusion of Al，Ti and B atoms into Fe lattice occurs during milling，leading to the formation of Fe(Al，Ti，B) solid solution. The process is controlled by continuous diffusion mixing mechanism. The alloying reaction is completed after 50h and the final product is a powder composed of nanocrystalline Fe(Al，Ti，B). Besides the relaxation of crystal defaults and lattice stress，the decomposition of Fe(Al，Ti，B) occurs to form FeAl and TiB2 during heat treatment of the 50h milled powder. The activation energy for the nanocrystalline FeAl growth was calculated to be 525.6kJ/mol according to kinetics theory of nanocrystalline growth.
2008, 57 (9): 5782-5787. doi: 10.7498/aps.57.5782
In this work，the microscopic defects in Ti-Mo alloy hydrides were studied by using small-angle X-ray scattering (SAXS) technique. The results show that the SAXS intensity measured for hydride of 5at％ Mo alloy was lower than that of other hydrides in the high scattering angle range. The crystal grains and its internal sub-structures in the hydrides are the scatterers which cause SAXS. The sub-structures are induced by the large number of dislocations in the hydrides produced during hydrogenation. The crystal structure of Mo 5at％ alloy is mainly hcp，but that of the other alloys is bcc. The hydrides of all these alloys, however, have a fcc crystal structure. Therefore，it is indicated that the Ti-Mo alloys with hcp and bcc crystal structures form the same hydride structure，but induce different types of dislocation defects during hydrogenation.
2008, 57 (9): 5788-5792. doi: 10.7498/aps.57.5788
Pulsed laser deposition (PLD) method was used to fabricate Ni1-xFexO (x=0.02，0.05) dilute magnetic semiconductor thin films with room temperature ferromagnetism. For the Ni0.98Fe0.03O sample with a lower Fe content，the crystalline structures of the Ni1-xFexO films are of the NaCl type as determined by X-ray diffraction. For the Ni0.95Fe0.05O sample with a higher Fe content，some additional weak diffraction peaks corresponding to α-Fe2O3 phase can be observed. From the X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS)， it is shown that the doped Fe impurities in Ni0.98Fe0.02O are substitutionally incorporated into the NiO host and no secondary phases with room temperature ferromagnetism are found. These results show the intrinsic ferromagnetism of the Ni1-xFexO samples.
2008, 57 (9): 5793-5799. doi: 10.7498/aps.57.5793
TiO2 nanoparticles were prepared by sol-gel method，and were annealed at different temperatures from 300 to 800℃. Their interfacial and fractal characteristics as well as and phase transition were investigated by using synchrotron radiation SAXS and XRD techniques. The change of nanoparticle size with annealing temperature was determined. The relationship between the interfacial characteristics and phase transition was discussed in this paper.
Investigation of the controllable growth of the TiO2 nanotube arrays fabricated by anodic oxidation method
2008, 57 (9): 5800-5805. doi: 10.7498/aps.57.5800
The highly ordered and uniform TiO2 nanotube arrays were fabricated by anodic oxidation of titanium foil in HF aqueous solution or ethylene glycol containing NH4F and deionized water. The diameter，density，length and wall thickness of nanotube arrays can be controlled effectively by varying the anodization parameters including electrolyte composition，voltage，and time. The microstructures of the titania nanotube arrays were characterized by X-ray diffraction (XRD). The results showed that the as-anodized titania nanotubes were amorphous. And when annealed in vacuum or in oxygen ambient at 500℃，the samples prepared in HF aqueous solution showed only anatase phase，and the samples prepared in ethylene glycol containing NH4F and deionized water showed both anatase and rutile phases. And the former and the latter batch of samples became better crystallized when annealed in oxygen and in vacuum，respectively. Furthermore，the controllable growth mechanism of nanotube arrays is discussed.
2008, 57 (9): 5806-5809. doi: 10.7498/aps.57.5806
TiO2 nanotubes were synthesized from commercial rutile powder by means of the hydrothermal method in alkaline solution at temperature of 150℃ for 48hours. The morphology and structure evolutions were characterized with SEM，TEM and X-ray diffraction. The TiO2 nanotubes mixed with Triton X-100 and acetyl acetone were screen-printed onto the glass substrate coated with a transparent conducting oxide (ITO，or tin-doped indium oxide)，then sintered at 450℃ for 30 minutes to form porous photoanode of dye-sensitized solar cells. A solar cell withactive area of 0.28cm2 was assembled with N719-coated nanotube-TiO2 electrode，Pt-coated ITO glass and iodide-based ionic liquid electrolyte. The J-V curve was measured using a standard solar simulator (AM1.5 spectrum，100mW/cm2)，and a photoelectric conversion efficiency of 2.17% was obtained.
2008, 57 (9): 5810-5816. doi: 10.7498/aps.57.5810
The time of flight mass spectrometric technique was used to determine the initial mean kinetic energy of small fragment ions C+n (n≤11) produced from C60 excited by 532nm nanosecond laser pulses. The measured kinetic energy shows little variation with the fragment mass and the laser fluence in a broad range. Based on the assumption that C+30 is produced predominantly by a single electron emission followed by successive C2 evaporation from hot C60 in the nanosecond laser field，the formation of small fragments is interpreted as the complete breakup of the unstable C+30 cage structure. The interpretation is consistent with the previously observed results.
Modeling the inter-molecular orientational correlation in orientational glassformers and the simulation analysis
2008, 57 (9): 5817-5822. doi: 10.7498/aps.57.5817
An effective bond model is proposed to describe the inter-molecule orientational correlation in orientational glassformers. The topological structures of the orientational correlation in the system are computer-smulated based upon the model. The results indicate that most of the bonding molecules appear in the form of molecular strings，and the phenomenon is explained using the probability theory. Furthermore，the simulated results are analyzed according to the string-model，and the rigourousness and feasibility of the model are discussed.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2008, 57 (9): 5823-5827. doi: 10.7498/aps.57.5823
The SnO2：(Cu，In) thin films are deposited on glass substrates by reaction evaporation. The photoluminecence(PL) of the films is researched. The films have amorphous structure. The transmittance is measured in the range 220—1100nm. The width of optical band gap is Eoptg=4.645eV. At room temperature，the photoluminescence is measured at different wavelengths，and continuous spectrum of photoluminescence is obtained in the range of 276—550nm. Especially，the density distributing in band tail states is determined by analyzing the emission spectrum.
The geometric structure，band structure and density of state of pure and N-Ga，2N-Ga codoped wurtzite ZnO have been investigated by first-principles ultrasoft pseudopotential method in the generalized gradient approximation. The calculation results show that the codoped structure N-Ga has better stability. Our work indicates that，the carrier concentration is increased in the 2N-Ga codoped configuration where the delocalized features are obvious，and this structure is more in favor of the formation of p-type ZnO.
2008, 57 (9): 5833-5837. doi: 10.7498/aps.57.5833
Molecular dynamics simulations have been used to study the three kinds of multi-wall nanotube oscillators. The results show that the shorter the inner tube of the oscillators，the larger the oscillation frequency，and the fluctuations ofthe axial force acted on the inter tube are also larger. The inner tube rotatesabout the tube axis while oscillating along the tube axis. The rotational kinetic energy is fluctuating and closely related to the length of the inner tube. The study results can be used in developing new technology of producing carbon nanotubes.
2008, 57 (9): 5838-5843. doi: 10.7498/aps.57.5838
The density functional theory and full-potential linearized augmented plane wave (FLAPW) method are used to study the anisotropic optical properties of superconductor MgB2. The optical conductivity spectra，the reflectivity spectra and electron energy loss spectra have been calculated. The calculated optical conductivity spectra along xx-axis display quite different features in comparison with that along the zz-axis，while the reflectivity spectra coincide well with the corresponding electron energy loss spectra，especially with respect to the characteristic peaks. In the optical conductivity spectra，the first intra-band absorption peak along xx-axis appears at 20000cm-1 while along zz-axis it appears at a high frequency of about 40000cm-1. In order to simulate the temperature effect in these spectra，the Lorentz expansion (δ=0.10eV) is added to the optical matrix elements in the calculation for 0K. In comparison with existing experimental data，a minor discrepancy of 1000cm-1 (～0.124eV) has been found in the calculated optical spectra.
2008, 57 (9): 5844-5852. doi: 10.7498/aps.57.5844
ZnO-based varistors with different doping levels of antimony and bismuth are prepared and their electrical properties are measured. It is found that when the doping level of Sb is small，with the amount of Sb2O3 increasing，the leakage current changes little，both nonlinear coefficient αL and breakdown nonlinear coefficient αB decrease but both field strength EL and breakdown field strength EB increase; when the doping level of Sb is high，with more Sb2O3 added，the leakage current increases sharply，αL and αB decrease further，and EL and EB drop down suddenly. With doping level of Bi increasing，the leakage current increases，αL and αB increase，but EL and EB decrease.
Direct generation of isolated sub-50 attosecond pulse via controlling quantum paths by a low frequency field
2008, 57 (9): 5853-5858. doi: 10.7498/aps.57.5853
We propose a new method to directly generate an isolated sub-50 attosecond pulse. The combination of a 5fs driving laser pulse with the wavelength of 800nm and a low frequency field with the wavelength of 10μm is adopted. The intensity of the low frequency field is 10% that of the driving pulse. It is shown that the harmonic spectrum is extended to Ip+8.2Up and the harmonics above Ip+4.2Up become continuous. By adjusting the phase of the carrier-envelope of the few-cycle pulse，the bandwidth of the supercontinuum can be further broadened and a close-to-Fourier-limit sub-50as pulse is directly obtained.
Significantly improved charge deposit properties of the cellular polypropylene film modified by gaseous fluorine
2008, 57 (9): 5859-5862. doi: 10.7498/aps.57.5859
Fluorination modification and electret properties were studied on the cellular polypropylene (PP) films modified by gaseous fluorine by attenuated total reflection (ATR) infrared analysis and the measurment of open-circuit thermally stimulated discharge (TSD) current，in situ TSD charge and isothermal charge decay. The results showed that the PP cellular films，especially the preoxidized ones，can be effectively fluorinated by gaseous fluorine，and that charge storage thermal stability of the fluorinated films，especially the fluorinated preoxidized ones，is significantly improved compared with that of the virginal PP film，even under conditions of negative pressure with a low partial pressure of gaseous fluorine，low reaction temperature about 60℃ and short reaction time of 15min.
Electronic properties of quantum wires in surface-acoustic-wave based single-electron transport devices
2008, 57 (9): 5863-5868. doi: 10.7498/aps.57.5863
By fabricating a split gate on the surface of AlxGa1-xAs/GaAs heterostructure，we experimentally obtain a quasi-one-dimensional quantum wire. This structure could be used to implement single-electron transport driven by surface acoustic waves. Based on structures of conduction band and distribution of electrons in the fabricated quantum wires，the influence of quantum-wire widths on the confining potential of the electrons is also discussed. Especially，we numerically study how the linear electron concentration depends on the applied split-gate voltage. For the quantum wires fabricated，we find that the calculated pinch-off voltages agree well with the relevant experimental values measured at 0.3K.
2008, 57 (9): 5869-5874. doi: 10.7498/aps.57.5869
Based on the analysis of the mechanism of irradiation damage and total dose effect on Schottky barrier diodes (SBD), using the model of the carrier mobility fluctuation and carrier number fluctuation of 1/f noise, the effect of irradiation damage on 1/f noise of SBD was studied in this paper. The research shows that, the irradiation induced interface states change the distributing of interface state density, and, moreover, modulate the Schottky barrier height and increase the velocity of recombination in the surface, leading to the degradation of device performance as well as the significant increasing of 1/f noise level. So, 1/f noise is closely related to SBD's degradation, namely, the larger the magnitude of 1/f noise and the deviation from standard value, the worse the reliability of device, and it's also an indicator of bad radiation-proof performance, which causes its high failure rate in radiation environment. Thus the 1/f noise acts as a researching tool on the mechanism of irradiation damage of SBD, also provides the theoretical basis for nondestructive irradiation hardness assessment.
2008, 57 (9): 5875-5880. doi: 10.7498/aps.57.5875
The lattice vibrations of diluted magnetic semiconductor GaMnN epitaxial films grown on sapphire substrates by metalorganic chemical vapor deposition have been investigated using infrared reflectance spectroscopy. The revised genetic algorithm was successfully used to extract the Lorentz oscillator model parameters of GaMnN from infrared reflectance spectra. Comparing the Lorentz oscillator model parameters of GaMnN with those of GaN, it was found that ωTO moved to higher frequencies, γ, ε∞ and εs increased, but the ωLO was almost not changed. The effects of Mn on the properties of lattice vibration and the mechanisms of variations of the dielectric function were also analyzed and discussed in this paper.
2008, 57 (9): 5881-5886. doi: 10.7498/aps.57.5881
The distribution of current diffusion of the quaternary AlGaInP LED has been simulated by finite element method to study the effect of electrode shape on the current spreading layer GaP. By comparing traditional circular-shape with cross-shape, arrow-shape, floriated-shape and gammadion-shape electrodes, we found that the electrode shape has an important effect on the output efficiency of light, and the light extraction efficiency of gammadion electrode is the highest. As the area of the whole electrode has an effect on the output efficiency, by optimizing the width of the electrode, the light extraction efficiency will be upgraded. For the gammadion electrode, when the width equals to 6.2204 μm, its light extraction efficiency is the highest, which is more than twice that of the traditional round electrode’s.
2008, 57 (9): 5887-5892. doi: 10.7498/aps.57.5887
The ZnO nanowire-based insulation gate field effect transistors were fabricated by connecting single ZnO nanowires across three kinds of symmetrical metal trenches (Au, Zn and Al thin films) with different widths. In the testing processes, the traditional ion beam eroding technology, electronic probe, and atom force microscopy probe methods were employed. The I-V characteristics of various synthesized ZnO nanowire-based devices were researched. The results showed that the main effecting factor on the I-V characteristic is the type of contact between the ZnO nanowire and the surface of different trenches, which may be of the Ohmic or the Schottky contact type in different cases. Finally, the I-V characteristics of the fabricated devices had been discussed by using the electron transport mechanism.
2008, 57 (9): 5899-5905. doi: 10.7498/aps.57.5899
By using the scattering matrix method, the properties of two-dimensional electron gas spin polarized transport through step-magnetic barrier structure at different bias voltage are investigated. The results show that (i) the degree of spin polarization is cyclically reducing if the incidence energy increases at zero bias voltage, and (ii) it is reduced slower and the maximum of spin polarization decreases when the number of steps increase in this structure, and (iii) it is enhanced significantly in a wider energy range under applied bias voltage, and more distinct spin-filtering properties are observed in the step-magnetic barriers.
Using a slow positron beam and the program VEPFIT, we found there exists a barrier in the interface between GaN and SiC, which is caused by lots of band-like defects existing in it. The existence of the barrier induced two backing electric fields in diverse directions close to the interface. These fields can produce a longer diffusion length in the SiC region where no field exists compared with that of SiC region, which has an electric field at a set value. The fitted value of the electric field offers a good reference for studying the situation in a real the interface.
Study of the characteristics of organic thin film transistors based on different active layers of pentacene and CuPc thin films
2008, 57 (9): 5911-5917. doi: 10.7498/aps.57.5911
The surface morphology and crystallization of pentacene and CuPc films deposited on SiO2 substrate are characterized by X-ray diffraction (XRD) and scaning electron microscopy (SEM). It was observed that the pentacene film has island structure, the sizes of islands were about 100nm. The pentacene has clearer orientation than CuPc. We also studied organic thin film transistors (OTFTs) with different active layers of pentacene and CuPc, fabricated by shadow mask to investigate the characteristics of the device. The active layers pentacene and CuPc have the thickness of 40nm, the thickness of gate insulator layer SiO2 is 250nm and the ratio of width to length (W/L) of device channel is 20. We analyzed the property of devices by Keithley 2410 I-V. The results presented here show that OTFTs devices in which pentacene and CuPc are used as active layer exhibited the field-effect mobility (μEF) of 1.201cm2/V·s and 0.0694cm2/V·s, threshold voltage (Vth) of -20V and -15V, and (on/off) current radio of 104 and 105, respectively.
2008, 57 (9): 5918-5922. doi: 10.7498/aps.57.5918
There has been a great interest in the strained Si CMOS technology lately, especially the modification of band structures which provides a theoretical basis for the design of the high-speed and high-performance devices and circuits. Calculations were performed on the band structures in strained Si/(111)Si1-xGex(0≤x≤0.4) by the first-principle pseudopotential approach of the plane wave based upon the density functional theory. It was found that the conduction band (CB) edge is characterized by the six valleys all the same, that valence band (VB) edge degeneracies are partially removed and that the electron mass in CB is unaltered under strain while the hole mass decreases along the ［100］ direction with increasing x. In addition, the fitted dependence of bandgap on x are in good agreement with KP theoretical calculation, from which the quantitative data supply valuable references to the devices design.
Study on electrical properties of n-GaN grown at low temperature by metal-organic vapor phase epitaxy
2008, 57 (9): 5923-5927. doi: 10.7498/aps.57.5923
Electrical properties of n-GaN grown at 740℃ and 900℃ by metal-organic vapor phase epitaxy were studied in detail. According to the electrochemical capacitance-voltage measurement, it is helpful to reduce the background impurity concentration in unintendedly-doped n-GaN grown at low temperature using TEGa as Ga precursor rather than TMGa. The results of Hall effect measurement of heavily Si-doped n-GaN show that, as Si concentration increases, the electron concentration increases almost linearly, which exhibits the dopant band conducting effect, while the electron mobility decreases. Atomic force microscope and X-ray diffraction measurements show that the surface morphology and crystal quality of most samples were determined by growth temperature and Si doping level. The surface morphology of all samples had a visible change only when the doping level was much higher at the same growth temperature. On the other hand, after the samples were annealed in oxygen, the electron mobility of all the samples remained almost constant, but the electron concentration decreased when the Si concentration was larger than 6×1019 cm-3. This result indicates that in the heavily Si-doped n-GaN grown at low temperature, the annealing process could result in the formation of acceptors due to the replacement of N by Si atoms.
2008, 57 (9): 5928-5932. doi: 10.7498/aps.57.5928
A numerical model of organic light emitting device (OLED) with metal/organic/metal structure was discussed on the basis of drift-diffusion equations in this paper. First，the influence of charges localized near the electrodes to the J-V curve was calculated and we got the same result of the literature. Second, the J-V curve of OLED with structure of ITO/PPV/Ca was simulated. In the simulation, the case of positive charge distribution localized near the anode was considered. The calculated J-V curve was in good agreement with the experiment. The charge creates an additional barrier and has a noted influence on the current density.
2008, 57 (9): 5933-5936. doi: 10.7498/aps.57.5933
In the process of theoretical fitting the switching current distributions of Josephson junction,macroscopic quantum tunneling (MQT) and thermally activated process are usually considered.Analysis of the results for a Bi2Sr2CaCu2O8+δ surface intrinsic Josephson junction (SIJJ), quantum corrections are considered at the intermediate areas between MQT and thermally activated process. It is found that quantum corrections lead to a perfect fit to the experimental data, which may be useful for the future studies of MQT in SIJJs and their possible applications as a superconducting qubit.
Spin-polarized transport in ferromagnetic semiconductor/ferromagnetic d-wave superconductor tunnel junction
2008, 57 (9): 5937-5943. doi: 10.7498/aps.57.5937
By solving a self-consistent equation for the d-wave superconducting gap and the magnetization, and applying an extended Blonder-Tinkham-Klapwijk approach, we study the spin-polarized quasiparticle transport coefficients and the differential conductance in ferromagnetic semiconductor/ferromagnetic d-wave superconductor junction. It is shown that (1) the exchange energy h0 in the ferromagnetic d-wave superconductor may make the zero-bias conductance peak and energy gap peak split into two peaks, and the energy difference between the two splitting peaks is equal to 2h0; (2) the exchange energy hFS in the ferromagnetic semiconductor can decrease the height of the two peaks resulting from splitting of the zero-bias conductance peak. For the splitting of the energy gap conductance peak, however, with hFS increased the left-hand peak is lowered and the right-hand peak is raised in the parallel configuration, but the left-hand peak is raised and the right-hand peak is lowered in the antiparallel configuration.
2008, 57 (9): 5944-5950. doi: 10.7498/aps.57.5944
Using the mean-field Jordan-Wigner transformation analysis, we have studied the one-dimensional spin-1/2 XY chain with Z-directional uniform long-range interactions in the external magnetic field. We have obtained such results as the Helmholtz free energy, internal energy, specific heat, magnetization and isothermal susceptibility. We also discuss the first and second-order phase transitions of the system at a finite temperature. Our results agree with results published in literature.
Single magnetic field-driven magnetoelectric effect in Tb1-xDyxFe2－y/Pb(Zr, Ti)O3 laminate composites
2008, 57 (9): 5951-5955. doi: 10.7498/aps.57.5951
In this paper we discuss the preparation of Tb1-xDyxFe2－y/Pb(Zr,Ti)O3 trilayers and a technique of single magnetic field-driven magnetoelectric coupling. A colossal ME voltage has been measured in the trilayers with the technique. The results obtained are far from that observed from that driven by two-field ME effect for the same material and probably predict some new physical effect. This technique can be expected to simplify the applications of ME effect in some fields.
2008, 57 (9): 5956-5961. doi: 10.7498/aps.57.5956
A new multi-exponential inversion method for NMR relaxation signals is presented and tested, which is based on differential evolution (DE) algorithm. The inversion of T2 spectrum in NMR is reduced to a non-negative constraint optimization problem, and solved directly by DE algorithm without pre-assigning the distribution of relaxation time T2. The validity and effectiveness of our method is demonstrated by computer simulations and the inversion of practical NMR data under low SNR.
X-ray diffraction and phase transition analysis for (K, Na)NbO3-based lead-free piezoelectric ceramics
2008, 57 (9): 5962-5967. doi: 10.7498/aps.57.5962
Characteristic of the orthorhombic and tetragonal phase of (K, Na)NbO3-based lead-free piezoelectric ceramics was analyzed in theory. X-ray diffraction differences between the orthorhombic and tetragonal phase were clarified in the 2θ range from 20° to 60°. For the orthorhombic (K, Na)NbO3-based piezoelectric ceramics, the number and relative intensity of X-ray diffraction peaks were calculated from a monoclinic primitive cell. A method distinguishing orthorhombic and tetragonal phase from the X-ray diffraction patterns was proposed. It is found that the phases of (K, Na)NbO3-based piezoelectric ceramics can be distingwished exactly from peaks of the primitive cell planes (1 0 2) and (1 2 1). For the powder diffraction, the phases can be distinguished more easily by relative intensities of the diffraction peaks for the peak-split position at around 22° or 45°.
2008, 57 (9): 5968-5972. doi: 10.7498/aps.57.5968
The uniform, dense, and crack-free PbZr0.4Ti0.6O3/PbZr0.5Ti0.5O3 bilayer with (100)-preferred crystal orientation and a single perovskite phase was fabricated on LaNiO3-coated Si substrate by using chemical solution deposition. The bilayer exhibits excellent ferroelectric properties, remnant polarization of 64μC/cm2 and coercive field of 43.6kV/cm. The prism-film coupling measurement indicates that four transverse electric modes can be excited in the system of Si/LaNiO3/PbZr0.5Ti0.5O3/PbZr0.4Ti0.6O3 and the light can be effectively confined to propagate in the guiding-layer. The refractive index and thickness for each film were obtained by solving the mode eigen-equation of the waveguide.
2008, 57 (9): 5973-5977. doi: 10.7498/aps.57.5973
We report the generation of anti-Stokes emissions with wavelength 480—550nm in the secondary cores of a dual-core photonic crystal fiber from 800nm femto second laser pulses. The conversion efficiency is as high as 28%. The anti-Stokes frequency conversion of laser pulses has strong polarization dependence of the pump. The simulation of light propagation in the waveguide well explains the experimental results.
2008, 57 (9): 5978-5982. doi: 10.7498/aps.57.5978
Tungsten-tellurite glasses with the molar compositions of (60+x)TeO2-(30-x)WO3-8BaO-2Na2O-0.5Er2O3 (x=0,5,10,15,20) have been prepared. Effects of WO3 on optical properties of Er3+-doped tungsten-tellurite glasses have been discussed. Along with the WO3 content increasing, Ω2 and Ω6 first increase and then decrease, and the stimulated emission cross-section also behaves in like manner, while Ω4 changes contrarily. According to the McCumber theory, the maximum peak of σe is calculate to be 1.00×10-21cm2 at 1.55μm. The maximum FWHM of Er3+ 4I13/2→4I15/2 emission spectrum is 82nm. In addition, the intensity of upconversion luminescence of the Er3+-doped tungsten-tellurite glasses decreases rapidly with the increasing of WO3 content.
2008, 57 (9): 5983-5988. doi: 10.7498/aps.57.5983
A.c. electrical properties of the heterostructured polymer light-emitting diode consisting of poly［2-methoxy-5-(2′-ethyl-hexyloxy)- 1, 4-phenylenevinylene］(MEH-PPV) as the light-emitting layer, and poly［(9,9 - bis(3′-(N,N-dimethylamino) propyl)-2,7- fluorene)-alt-2,7-(9,9-dioctylfluorene)］ (PF-NR2) as the electron-injecting layer, are studied by using impedance spectroscopy. Negative capacitance in impedance spectroscopic data has been observed. According to the Cole-Cole plot of the device ITO/PEDOT/MEH-PPV/PF-NR2/Al, the a.c. response of MEH-PPV/PF-NR2 interface can be explained in terms of the equivalent circuit model of a parallel combination of an inductance L and a resistance RL. The experiments showed that PF-NR2 could act as an electron injecting and hole blocking layer. We propose an energy band structure schematic diagram to explain the enhancement of the EL efficiency in the ITO/PEDOT/MEH-PPV/PF-NR2/Al structure.
2008, 57 (9): 5989-5995. doi: 10.7498/aps.57.5989
Absorption spectra, emission spectra of nanoized erbium implanted mesoporous silica functionalized with and without bis(perfluoromethylsulfonyl)amine as ligand were studied. Luminescence with high intensity has been obtained. The Judd-Ofelt strength parameters Ωt(t=2,4,6)were calculated as Ω2＝1.88×10-20cm2，Ω4＝5.45×10-20cm2 and Ω6＝3.11×10-20cm2, respectively. Oscillator strength, spontaneous emission probability, branching ratio and emission lifetime of each energy levels of Er3+were given. The peak intensity of emission spectra varying with the pump power was discussed. Stimulated emission cross section (σem＝10.9×10-21cm2) was calculated and compared with that of other host materials.
A fast algorithm for reflectivity calculation of micro/nano deep trench structures by corrected effective medium approximation
2008, 57 (9): 5996-6001. doi: 10.7498/aps.57.5996
This paper proposes a fast algorithm for reflectivity calculation of micro/nano scale high-aspect-ratio deep trench structures by the novel method of corrected effective medium approximation (CEMA). Extensive comparative investigation on the infrared reflection spectra of deep trench structures by means of effective medium approximation (EMA) and rigorous coupled-wave analysis (RCWA) reveals that the RCWA based method is accurate but time consuming while the EMA based calculation is much faster but less accurate. The proposed CEMA method is based on EMA but a dispersion corrected factor is added to calculate the refractive index of each effective medium. The dispersion corrected factor is found to be in inverse proportion to the square of the wavelength, and relates to the period, material and void fraction of trench structures. Simulations carried out on a lot of complex multi-layered trench structures, such as the bottle trench structure, demonstrate that the CEMA method is not only fast in calculation but also accurate enough in comparison with the RCWA based method. It is expected that the proposed CEMA method can be applied to deep trench measurement by model-based infrared spectroscopy (MBIR), thus has further potential applications such as real time etching process monitoring of micro/nano scale high-aspect-ratio deep trench structures in manufacturing microelectronics and microelectromechanical system (MEMS) devices.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2008, 57 (9): 6002-6006. doi: 10.7498/aps.57.6002
The μc-Si:H films were deposited by VHF-PECVD, the effects of silane concentration, power density, deposition pressure and total flow rate on the deposition rate and crystallization of μc-Si:H were extensively studied. Phase diagram in the plot of deposition pressure against power was determined. The deposition rate of μc-Si:H has reached 0.75nm/s. Incorporating such μc-Si:H films as i-layer, the single-junction solar cell on glass substrate showed an conversion efficiency of 5.5%.
2008, 57 (9): 6007-6012. doi: 10.7498/aps.57.6007
SiCGe layers were grown on 6H-SiC (0001) substrates by low pressure hot wall chemical vapor deposition at different temperatures (1100℃—1250℃) and with different GeH4 flow-rate ratios (6.3%—25%). Surface morphology, growth characteristics, and Ge contents of the samples were studied. Results of scan electron microscope images show that the SiCGe layers tend to grow in an island growth mode at lower temperatures, and the growth mode will change to the layer by layer mode accompanied by changes in island form and density as the growth temperature increases. X-ray photoelectron spectroscopy tests show that the Ge contents in the samples are in a range of 0.15％ to 0.62％, and they increase with the increase of GeH4 flow rates and the decrease of growth temperatures when other growth parameters are kept constant. Additionally, antiphase boundary (APB) defects in the SiCGe layers were analyzed qualitatively.
Influence of annealing on structure and optical band gap of nitrogen doping fluorinated amorphous carbon films
2008, 57 (9): 6013-6017. doi: 10.7498/aps.57.6013
Radio frequency plasma enhance chemical vapor deposition (RF-PECVD) was used todeposit nitrogen doped fluorinated amorphous carbon (a -C:F,N) films with CF4, CH4 and N2 as source gases. We focused on the influence of annealing temperature on the structure and optical band gap (Eg) of the films. The as-deposited films undergo significant chemical and optical changes during annealing. The films are thermally stable at 350℃. The optical band gap shows decrease of different degrees with increasing annealing temperature. Raman and Fourier transform infrared absorption spectra show that the relative content of F in the films decreased, while the content of sp2 carbon increased, and as a result, the density of states near the band edgye of σ-σ* decreases, which is responsible for the increasing Eg.
2008, 57 (9): 6018-6023. doi: 10.7498/aps.57.6018
The technique of passive differential optical absorption spectroscopy (DOAS) is based on fingerprint absorption of probed gas species, which enables simultaneous monitoring of a variety of pollutants found in the atmosphere using scattering light as light source. We describe an optical remote-sensing instrument which is based on imaging spectrometer that permits spatially resolved mapping of atmospheric trace gases by passive DOAS method. The applications of one spatial dimensional measurement of gas cell and imaging of the nitrogen dioxide over city main road were also reported in this paper. With scattered sunlight as the light source, the system based on imaging spectrometer simultaneously acquiring spectral information in one spatial dimension, the second spatial dimension is scanned by a moving mirror.
Backscattered Mueller matrix patterns of optically active media and its application in noninvasive glucose monitoring
2008, 57 (9): 6024-6029. doi: 10.7498/aps.57.6024
In this paper Stokes/Mueller formula was used to trace the polarization state of photon packet. Single scattering model and Monte Carlo method were used to investigate the influence of glucose on polarized light in turbid media. Some Mueller matrix elements show optical rotation in the presence of glucose. Using image subtraction and integration, an approximately linear relationship between low glucose concentration in the physiological range and optical rotation degree was found.
2008, 57 (9): 6030-6035. doi: 10.7498/aps.57.6030
Due to strong scattering, most optical tomography techniques can’t achieve practical imaging depth in turbid media such as bio-tissues. In this paper a new inner-light-source model was proposed and Monte Carlo method was used to analyze related problems. The distribution of backscattered photon number against the number of their scattering events was studied, and various illumination geometries and detecting methods were simulated. The results show that instead of rashly assuming that the number of photons reemitted from the tissue monotomically increases or decreases as scattering events accumulates; the backscattered photon number actually increases firstly and decreases later. The peak position, peak value and curve shape depend on the illumination geometry, monitoring method and tissue optical parameters.