Vol. 61, No. 1 (2012)
Layered optimization algorithm about a kind of nonlinear partial differential equation with initial-boundary value problem
2012, 61 (1): 010201. doi: 10.7498/aps.61.010201
For non-linear partial differential equations with initial-boundary value problems, based on the difference method and the optimization method with dynamic design variables, using unknown function values on discrete node points on time layer as design variables, the difference equations sets of all the discrete node points are constructed as stylized objective function. A layered accurate optimization algorithm about computing unknown function value on discrete node point is proposed. Universal computing program is designed, and practical examples are analyzed. Through comparing computation results with exact results, the effectiveness and the feasibility of proposed method are verified. The method can provide the condition for engineering application.
2012, 61 (1): 010202. doi: 10.7498/aps.61.010202
The dynamics of four-order modified Chua's circuit with slow-fast effect has been investigated in this letter. Different types of bursting phenomena can be observed in numerical simulations. By introducing slow-fast analysis, the bifurcation mechanism for the periodic bursting solutions, especially for Fold/Fold bursting and Fold/Hopf bursting, is presented, which is different from the usual case. With the variation of the parameter, the periodic bursting can evolve to chaotic bursting.
2012, 61 (1): 010203. doi: 10.7498/aps.61.010203
Scale-free connectivity, small-world pattern, hierarchical modularity and disassortative mixing are prominent features shared by most biological networks. Up to now, various network growth models invoking gene duplication and divergence have been proposed to understand the evolutionary mechanisms shaping the scale-free connectivity, small-world pattern and disassortative mixing . In this paper, we present an evolutionary model by introducing a rule of small preference duplication of a node and sequently divergence plus non-uniform heterodimerization meaning that the probability that an heterodimerization link is added between duplicated nodes is proportional to the number of common neighbors shared by these nodes based on biological background, showing that our model can almost display series of topological characteristics of real protein interaction networks, such as scale-free connectivity, small-world pattern, disassortativity of degree-degree correlation and hierarchical modularity. Our model may yield relevant insights into the evolutionary mechanism of protein interaction networks behind it.
2012, 61 (1): 010204. doi: 10.7498/aps.61.010204
Through building “surface-molecule” interfacial adsorption structure model, the physical and the chemical absorptions of (001) interface and (010) interface of KDP crystal are studied by using molecular dynamics and density functional theory method, and the effect of temperature on physical absorption behavior is investigated. The result indicates that the absorption process and the growth habit of KDP surface are dominated by the chemical absorption, and the binding energy on (001) surface is 2.86 times that on (010) surface of KDP crystal. Near the saturation temperature, the binding energy between [H2PO4]- anion and crystal surface presents obviously an oscillation characteristic with the temperature varying, and the solution becomes unstable with the formation of anion clusters. With temperature decreasing from 323 K to 308 K, the binding energy of H2O decreases in general, but the binding energy of KDP molecular increases obviously, which indicates the dehydration process results from the competitive absorption between H2O and [H2PO4]-. The results obtained are of significance in identifying the surface kinetics process and developing more sophisticated crystal growth theories.
2012, 61 (1): 010205. doi: 10.7498/aps.61.010205
To solve the precision machining problem in the structural surface mould manufacturing process, a new no-tool precision machining method based on softness abrasive flow machining (SAFM) is proposed. The key technology of SAFM is the characteristic analysis of two-phase flow. To solve this problem, a two-dimensional model of the two-phase flow is established by the topological structure transformation of level set method. This mechanics model is used to simulate the motion of the turbulent flow and work out the characteristic parameters of abrasive two-phase flow. The simulation results show that this model can preferably simulate the motion of the two-phase flow and calculate velocity and pressure with k- model and Preston equation. Therefore the feasibility of SAFM can be confirmed and a good reference can be provided for the further research.
2012, 61 (1): 010301. doi: 10.7498/aps.61.010301
The collective excitations of a one-dimensional superfluid Fermi gas in an anharmonic trap are investigated. By using the variational approach, the frequency shifts about the dipole mode of the center-of-mass variations and the breathing mode of width variations are derived. It is found that the frequency shift in a unitary region is more significant. Under the excitations of different driving amplitudes, the two low-energy modes are coupled due to the contribution of the quartic item, and the quantum beating phenomenon comes into being. The frequency of beating increases with the driving amplitude. The dynamics of the width exhibits complex characteristics, especially, in the unitary region.
2012, 61 (1): 010501. doi: 10.7498/aps.61.010501
Short-term traffic flow prediction for multi traffic states on urban expressway network is carried out in this paper. The model for multi traffic states is proposed by integrating the spatial and the temporal distribution characteristics of traffic flow parameters under free traffic, congested traffic and jam traffic respectively. Based on the classical traffic flow conservation equation, the ideology of spatial and temporal dispersions in partial differential equations is adopted to establish short-time traffic flow prediction model. Meanwhile, the impact factors, such as on and off ramp, lane change and road slope are considered, which convertes short-term traffic flow prediction model into short-time traffic flow prediction state space model. Finally, the short-term traffic flow prediction for multi traffic states on urban expressway network is realized. The empirical research shows that compared with the classic ARMA model, the proposed method can not only realize short-term traffic flow prediction for multi traffic states on urban expressway network but also achieve an accuracy of 90.23%. In the same condition, the accuracy of ARMA model is 81%.
Brownian heat engine driven by temperature difference in a periodic double-barrier sawtooth potential
2012, 61 (1): 010502. doi: 10.7498/aps.61.010502
This paper has studied the thermodynamic performance of a Brownian heat engine, which is driven by temperature difference. Brownian particles move in the periodic double-barrier sawtooth potential with an external load force and contact with an alternating hot and cold reservoir. The kinetic energy change of the Brownian particles and the heat leak between hot and cold reservoir are considered simultaneously. The influence of the main parameters, including the height of barrier, the ratio of the low barrier to high barrier and the external load force, on the efficiency of Brownian heat engine is discussed in detail. When the heat leak between the two reservoirs is taken into account, the Brownian heat engine is irreversible, the efficiency is less than the Carnot efficiency. When the heat leak is small, the ratio of the low barrier to high barrier can increase the efficiency. The curve of the power output versus the efficiency is a loop-shaped one. When the heat leak is negligible, the curve of the power output versus the efficiency is an open-shaped one. The efficiency is still less than the Carnot efficiency, because the heat flow via kinetic energy change of the particles is irreversible.
2012, 61 (1): 010503. doi: 10.7498/aps.61.010503
The colored noise induced switch in the gene transcriptional regulatory system is investigated. The approximate Fokker-Planck equation is obtained based on the Novikov theorem and the Fox approach. The explicit expressions of the steady state probability distribution, the mean value, and the mean first passage time are derived. After the numerical computations, these results show that the TF-A monomer concentration switches from the off position to the on position with the self-correlation time of the multiplicative noise increasing. The TF-A monomer concentration switches from the on position to the off position with the self-correlation time of the additive noise increasing. With the two kinds of the self-correlation time increasing, the mean first passage time becomes large, namely, the TF-A monomer concentration switch becomes difficult. The theoretical predictions are found to be in basic agreement with numerical results.
2012, 61 (1): 010504. doi: 10.7498/aps.61.010504
We proposed a new chaotic system using the closed loop self-feedback frequency modulation (FM) technique where the current sample of the output signal of voltage-controlled oscillator (VCO) is transformed and used as the next input of VCO. The dynamical behavior of the system is investigated by Bifurcation diagram and Lyapunov exponents. The performance of the system is analyzed in terms of peak to average power ratio (PAPR), frequency spectrum and the correlation function of the output signal. The results show that the developed system has complicated dynamical behaviors, including bifurcation, multi-stability and chaos, and the generated chaotic signals have low PAPR and wide bandwidth. We also discussed the synchronization of the system by FM code. In circuit experiments, VCO is implemented by digital frequency synthesis. The experimental results are consistent with our theoretical analysis.
2012, 61 (1): 010505. doi: 10.7498/aps.61.010505
Under the excitations of the high-frequency and weak low-frequency signals, the effects of linear time delay feedback on the vibrational resonance in overdamped bistable system and Duffing systems are investigated respectively. Both the analytical and the numerical results show that the response amplitude of the system to the low-frequency signal varies periodically with the delay parameter simultaneously (with two different periods, i.e., the periods of the two exciting signals). Numerical results also indicate that the delay feedback can induce vibrational resonance in the monostable Duffing system in which there exists no traditional vibrational resonance. By adjusting the delay parameter, not only the vibrational resonance can be effectively controlled, but also the response of the system to the weak low-frequency signal can be further improved.
Second harmonic multi-beam laser heterodyne measurement for small angle based on oscillating mirror sinusoidal modulation
2012, 61 (1): 010601. doi: 10.7498/aps.61.010601
In this paper, we propose a novel method of multi-beam laser heterodyne measurement for small angle based on sinusoidal modulation of simple harmonic motion oscillating mirror. By using the Doppler effect and heterodyne technology, by loading the information about small angle into the frequency difference of the multi-beam laser heterodyne signal, by using the frequency modulation of the oscillating mirror, this method can give many values of small angle after the multi-beam laser heterodyne signal demodulation simultaneously. Processing these values by weighted-average, small angle can be obtained accurately. This novel method is used to simulate measurement for small angle by MATLAB, the obtained result shows that the relative measurement error of this method is just 0.789677%.
Electrical read out of nano-electromechanical system signal by using graphene resonant channel transistor
2012, 61 (1): 010701. doi: 10.7498/aps.61.010701
The direct radio frequency read out method based on local back-gate graphene resonant channel transistor (RCT) is studied by combining the operation principles of graphene field-effect transistor and mechanical resonator. A novel method of fabricating local gate graphene RCT is proposed, and a graphene RCT with 1 m 1 m dimension channel is realized based on exfoliation graphene. The measured resonant frequency of graphene RCT is in a range of 57.5-88.25 MHz at room temperature. This work is useful to pave the way of graphene application to Nano-eletromechanical system and high frequency low-noise amplifier.
2012, 61 (1): 010702. doi: 10.7498/aps.61.010702
Based on the nonlinearity of metal rubber components and its different elastic damping mechanical properties with different structures, the mechanical model of hysteresis loop boundary deformation process of metal rubber components with different relative densities was established by the experiment method combining theory. Dynamic characteristics of metal rubber damping ring were analyzed under harmonic excitation load and experimental study was conducted. The elastic damping performance of the damper with preliminary deformation was researched and the experimental result showed good agreement with the theoretical analysis one, which provides a theoretical basis for practical application of this kind of damper.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Relation analysis between starting voltage and input voltage for a magneticaly insulated linear oscillator
2012, 61 (1): 012901. doi: 10.7498/aps.61.012901
Resorting to particle-in-cell (PIC), simulation and experimental investigation, the phenomenon is observed that the starting voltage increases with the increase of input operation voltage of a magnetically insulated transmission linear oscillator (MILO). Therefore, PIC simulation and theoretical analysis are carried out for further study. The key factor responsible for the phenomenon is found, that is, the bigger the operation voltage and the bigger the rise slope of the operation voltage is, and the bigger the starting voltage is; when the rise slope of the operation voltage is infinite, the starting voltage is equal to the operation voltage. Therefore, the variation of the rise slope of the input voltage is the key factor that causes the variation of the starting spot for an MILO; when there is no change of the rise slope of the voltage, the starting spot for the same MILO will not change, and the starting voltage will not change either; when there is the increase of the rise slope of the input voltage, the starting voltage for the same MILO will increase accordingly. In addition, the expression of the self-insulating critical current for an MILO is modified partly.
ATOMIC AND MOLECULAR PHYSICS
2012, 61 (1): 013101. doi: 10.7498/aps.61.013101
The molecular structures of ground state O2,TiO and TiO2 are calculated on the level of BP86/6-311++g(d, p) using density function theory method in Gaussian09 programs. The results show that the electron states of the ground states of the molecules respectively are O2(X3g),TiO(X3g) and TiO2(X1 A1).The stable structure of TiO2 molecule is of C2v symmetry. Each potential energy curve is obtained via scanning the single point energies of TiO and O2, which match well with those fitted with the four-parameter Murrell-Sorbie Function,according to which spectral data and force constants are deduced. The whole special analytical potential energy function of TiO2 is derived from the many-body expansion theory. And there exists a potential trap of 15.09 eV depth at 0.1652 nm (RTi-O) when the OTiO angle is fixed at 110.5, which suggests that a stable TiO2 molecule could be formed easily.
2012, 61 (1): 013301. doi: 10.7498/aps.61.013301
Multiphoton ionization of formaldehyde hydrated clusters is studied by time-of-flight mass spectrometry using 5 ns, 355 nm Nd: YAG laser beam with a power intensity of 10111012 W/cm2. The main products including protonated formaldehyde cluster series (CH2O)nH+(n=1-4), deprotonated formaldehyde clusters series (CH2O)nCHO+ (n=1-3, and two series based on molecules originating from H2CO ( the deprotonated and protonated forms ), H3CO+(H2O)n(n=1, 3, 5) and HCO+(H2O)n(n=1,3,5) are observed, and the simple structures are gave for some clusters. The transformation of formaldehyde mass peak is studied in different laser power density conditions. We find the ion peaks of formaldehyde monomer and water molecle ar a laser intensity of about 9.3 1011 W/cm2. Those mass peaks exist in envelope form and cannot be resolved under our experiment condition. The simple dynamic plasma sheath accelerating model is proposed to explain the physical mechanism of the envelope phenomenon.
2012, 61 (1): 013401. doi: 10.7498/aps.61.013401
Based on the group theory and the theory of atomic-molecular reaction statics, the reasonable dissociation limit for the ground state (X2) of TiN molecule is derived. Optimization calculation is performed using different groups of density functional method including BP86, B3P86, B3LYP, B3PW91 with different basis sets. The results show that the BP86 method with D95V++ (d, P) basis set for nitrogen atom and 6-311++G** basis set for titanium atom is the best group for calculating the geometric structure, the vibration frequency and the dissociation energy. The potential energy curves and the relevant spectroscopic constants for the ground state of TiN are obtained by least square fitting to the Murrell-Sorbie analytical potential function. All calculation results are in good agreement with the experimental data.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
Theory and simulation of the folded waveguide traveling-wave tube working in low voltage with changed period and big size
2012, 61 (1): 014101. doi: 10.7498/aps.61.014101
The folded waveguide traveling-wave tube which works at 3 mm band and above the band is limited to machining accuracy and power capacity. So a slow-wave folded waveguide structure which has a finite number of cycles and whose period can be changed nonasymptotically is proposed. Firstly, the theory for effectively increasing the high-order space harmonic coupling impedance of the structure is given. And the expressions for dispersion and coupling impedance are derived. Then through the simulation, a set of optimized design parameters is achieved. Thus the operating point of the traveling-wave tube is determined. Finally, it is simulated by MAFIA. And an effective gain is obtained. The traveling-wave tube which works at low voltage, relatively large size and relatively large period, is designed.
2012, 61 (1): 014102. doi: 10.7498/aps.61.014102
A simple structured left-handed metamaterials composed of single square ring cell is fabricated. Its permittivity and permeability are simultaneously negative in 4.8-5.25 GHz. A 5.0 GHz microstrip antenna is proposed, and we use this single square ring structured left-handed metamaterials (SSR-LHMs) as covering layer. Simulation and experiment results show that compared with conventional microstrip antenna, the performance of the new microstrip antenna with SSR-LHMs has been improved remarkably. The -3 dB beam of E-plane and H-plane can be reduced respectively by 25 and 20, so the directional property of the antenna is enhanced. The gain is improved by 3dB and the -10 dB bandwidth is increased by 600 MHz.
2012, 61 (1): 014201. doi: 10.7498/aps.61.014201
The preconditions and controlling factors of coherence collapse (CC) are analyzed by the rate equations and dual fiber Bragg grating (FBG) couple mode theory based on the physical process of dual FBG external cavity semiconductor lasers. A method of achieving and controlling CC multi-mode stable state is put forward for dual FBG external cavity semiconductor lasers. When the dual FBG external cavity semiconductor laser operates at the multi-mode stable state under the CC regime, the CC length reduces. The spectrum of the laser is relatively stable within the CC length. The experimental results show the output power of the laser is stable while the laser with the 3% external reflectivity is operating under the CC regime. The side mode suppression ratio is more than 45 dB. The full wave at half maximum broadens from 0.5 nm to 0.9 nm dramatically as soon as the laser operates from the incoherence collapse regime to the CC regime. The wavelength shift is less than 0.5 nm at the operating temperature of 0 ℃70 ℃. The minimum of the CC length is less than 0.5 m. The CC application of dual FBG external cavity semiconductor lasers is vital to improve the performance of optical fiber amplifiers and fiber lasers.
2012, 61 (1): 014202. doi: 10.7498/aps.61.014202
Reconstruction of focused high order Bessel-Gauss beam by using thin lens is proposed. Based on the diffraction theory, reconstruction behavior of focused high order Bessel-Gauss beam is analyzed. The three-dimensional optical intensity distribution and the cross-section optical intensity distribution of the high order Bessel-Gauss beam focused by first thin lens, and then reconstructed by the second thin lens are numerical simulated. Result shows that the high order Bessel-Gauss beam passing through the single thin lens can generate Bottle beam, and the bright ring is obtained at focus. To rectify the beam divergence after focus, another thin lens is introduced at suitable position. After that, the beam keeps the Bessel distribution. Experiment is conducted, and experimental results are in agrement with the theoretical analyses. Research result shows its significance in providing a guidance for optical tweezers, particle trapping and controlling.
2012, 61 (1): 014203. doi: 10.7498/aps.61.014203
Cross phase modulation based time lens and four-wave mixing based time lens are realized by utilizing cross phase modulation effect and four-wave mixing effect in the high nonlinear fiber, respectively. The nonlinear process in the high nonlinear fiber of cross phase modulation based time lens is simulated and analyzed. The simulation and the analysis show that the main influence factors are dispersion, self phase modulation and four-wave mixing, which can be eliminated by using the high nonlinear fiber with a certain amount of dispersion slope. Besides, the zero-dispersion wavelength of the high nonlinear fiber should be around the centre between the signal pulse and pump pulse. Then, the nonlinear process in the high nonlinear fiber of four-wave mixing based time lens is simulated and analyzed. The simulation and the analysis show that the main influence factors are dispersion, self phase modulation and other four-wave mixing, which can be eliminated by using the signal pulse and pump pulse with a certain amount of power. Besides, the powers of the signal pulse and the pump pulse can be improved by using the high non-linear fiber with a certain amount of dispersion, then the power of the output pulse can be improved, too. Finally, two kinds of time lenes are compared with each other.
The distribution of intensity of incident irradiation in photo-resist during exposure is figured out, and it is shown that the pattern in photo-resist on surface with high reflectivity will suffer standing wave due to the fact that the incidence irradiation interferences with the reflective beam from the photo-resist-substrate interface. The higher the reflectivity, the worse the effect of standing wave is, and it is shown that the standing wave will have adverse effects on the profile and the duty cycle of photo-resist grating and restricts the most groove depth. Inserting a layer of anti-reflection coating (ARC) can minimize the effect of standing wave. Experimental results show that it is a good way to use ARC between photo-resist and substrate to attenuate standing wave.
Electromagnetically induced grating in a Λ-type three-level atomic system modulated by a microwave field
2012, 61 (1): 014205. doi: 10.7498/aps.61.014205
We investigate the electromagnetically induced grating in a Λ -type three-level atomic system with a microwave field coupling the two ground states. The results show that the intensity of diffraction, especially the first-order diffraction, is increased remarkably due to the modulation and gain of the microwave field. If the parameters of the system are chosen properly, the intensity of the first-order diffraction goes up exponentially as the microwave intensity increases.
Continuous-variable three-color tripartite entangled state generated by a non-degenerate optical parameter oscillator
2012, 61 (1): 014206. doi: 10.7498/aps.61.014206
The quantum correlations between the output signal, the output idler and the reflected pump fields generated by non-degenerate optical parametric oscillator operating above the oscillation threshold are theoretically calculated with the semi-classical formulae. According to the multipartite entanglement criteria for the continuous variables, proposed by P. van Loock and A. Furusawa, the calculated results prove the existence of the quantum correlations between the amplitude and the phase quadrature for the three optical fields, i. e. they form a tripartite entangled state. We numerically calculate the dependence of the entanglement on the physical parameters of the optical oscillator and find the optimum operating conditions of the oscillator to produce the three-color tripartite entangled state, which provide the direct references for the design of the continuous variable multipartite entanglement generation systems.
Broad-bandwidth and ultrafast electromagnetic response of coupled bimetal nanoantennas in few-cycle laser applications
2012, 61 (1): 014207. doi: 10.7498/aps.61.014207
We explore the field enhancement and temporal response of coupled bi-metal Ag/Au core-shell nanoparticle antennas. The bimetal antennas exhibit ultra-broadband resonances and allow exploiting the local field enhancement for few-cycle laser applications such as elements with an ultrafast response in nanoplasmonic device. We study dimer, trimer and heptamer arrangements and find that the Ag/Au core-shell trimer shows that a very high enhancement factor with an amplitude exceeds 120, but still facilitates an ultrafast response. Such systems may be ideal for the generation of attosecond light pulses based on high harmonic generation by employing nanoplasmonic field enhancement.
2012, 61 (1): 014208. doi: 10.7498/aps.61.014208
Under the non-rotating wave approximation, the quantum evolution of entanglement property of a two-qubit and oscillator coupling system is accurately investigated by the method of coherent-state orthogonalization expansion. The property of the ground state for qubit-oscillator system and the difference between qubit-oscillator entanglement and qubit-qubit entanglement when resonant vibration occurs are discussed. The calculation results show that when the external field is not taken into consideration, the qubit-qubit entanglement reduces from 1 to 0 rapidly with the increase of coupling strength, indicating the strong sensitivity of the entanglement to the coupling strength. On the contrary, with the increase of the coupling the qubit-oscillator entanglement rises from 0, but does not reach the maximum value 2. At the beginning, when the two qubits do not entangle, the vacuum field does not lead to the entanglement in weak coupling. However, the strong coupling can induce the sudden appearance of the entanglement.
Basing on the theory of quantum feedback by Steixner and his coworkers, we develop the master equation of Doppler cooling with feedback in an ion trap. The result of simulation shows the property of speedup the cooling,besides the influences of those arguments and whether we could realize it in experiment.
Experimental and theoretical analysis of the dispersion of laser-induced surface acoustic wave due to surface roughness
2012, 61 (1): 014210. doi: 10.7498/aps.61.014210
In the process of producing materials, the surface roughness always exists. And it can change the velocity of surface acoustic wave (SAW) which propagates in the material. To assess the properties of materials by laser induced SAW, an inverse method based on the wide-band velocity dispersion characteristic of laser-induced SAW is most commonly used. To study whether the surface roughness can be one of the inversion characteristic parameters, an experimental apparatus is constructed in this article. In the apparatus, the SAW is induced in the surface roughness sample by laser, and it is received by a polyvinylidene fluoride transducer with wide frequency band. Using this apparatus, we study the influences of different surface roughnesses on SAW velocity. In the paper a physical model of laser-induced SAW propagating in roughness surface is established theoretically. The time domain characteristic of SAW is obtained by the finite element method, and then the velocity dispersion curve of SAW is achieved. It is concluded that the theoretical result and the experimental result are in good agreement with each other. The studies in this article form theoretical and experimental bases for assessing surface roughness by means of laser-induced SAW technique.
2012, 61 (1): 014211. doi: 10.7498/aps.61.014211
According to the requirements for design and manufacture, we choose double-chirped method for designing the initial structure of the chirped coatings, and analyze the dependencs of reflectivity and group delay dispersion on the parameters of coatings such as the double-chirped modulation factor and the the proportion of double-chirped layers on the total thin film stack. Further more, we establish their optimal values. Based on the analysis, a chirped mirror pair, whose reflectivity is more than 99.5% and average group delay dispersion is -40 fs2 with a residual ripple of less than 20 fs2 in a wavelength range of 600 nm-1050 nm, is demonstrated, which is to be used in the Ti: Sapphire femtosecond laser system for dispersion compensation.
Unidirectional open-loop chaotic synchronization communication based on a semiconductor laser with double optical feedback
2012, 61 (1): 014212. doi: 10.7498/aps.61.014212
Using a semiconductor laser with double optical feedback as a chaos transmitter, a unidirectional chaotic synchronization communication system is constructed, and the performances of such a system are investigated numerically. The results show that by selecting reasonable parameters, the time delay behaviour of chaotic carrier generated by the semiconductor laser with double optical feedback can be suppressed efficiently; through the strong injection from transmitter to receiver, the perfect synchronization between transmitter and receiver can be realized, and the synchronization quality has a high tolerance to frequency detuning between transmitted laser and received laser; under the additive chaos modulation encryption scheme, the 500 Mbits/s encoded message can be hidden efficiently in the chaotic carrier and successfully extracted at the receiver.
2012, 61 (1): 014213. doi: 10.7498/aps.61.014213
In the paper, the demonstration of a high-power LD-pumped Yb, Na:CaF2 femtosecond laser is presented, which the cavity is optimized concerning the numerical simulation for the thermal lens effect. With a 2% output coupler, a continuous-wave mode-locked pulse train with a pulsewidth of 190 fs, the average output power of 503 mW, the center wavelength at 1034 nm and a repetition frequency of 82.4 MHz is obtained under the absorbed pump power of 7.8 W. If other forms of output are recorded, such as the reflection of the crystal surface, the total output power is 905 mW.
2012, 61 (1): 014214. doi: 10.7498/aps.61.014214
We fabricate a high Q photonic crystal cavity on the top of SOI (silicon on insulator) with EBL (electron beam lithography) and ICP (inductively coupled plasma). The value of Q can reach 7 104. It provides basic condition for the following experiments, for example for the study of interaction between light and substance. The high Q cavity also provides good circumstance for the quantum information. The theoretical result of the value of Q is 1.2105 from FDTD (finite difference time domain) simulation.
2012, 61 (1): 014215. doi: 10.7498/aps.61.014215
The dependence of slowing light on the saturation effect in the vertical-cavity surface-emitting laser (VCSEL) is demonstrated. Combining the boundary conditions with the optical field distribution in VCSEL, the phase expression and the delay expression of the signal are derived. Based on these expressions and the rate equation, the relation between signal power and time delay is presented. Then the experimental demonstration shows the delays and the eye diagrams of a 2.5 Gbps pseudo-random binary sequence (PRBS) signal, when the VCSEL is working in the saturation condition. The theoretical and experimental results show that the high-power signal transmitted in the VCSEL could achieve better signal quality at the expense of the lower time delay. In order to obtain larger delay, on the one hand, the signal power should be controlled. On the other hand, the signal wavelength should be carefully adjusted to track the peak gain wavelength of the VCSEL caused by the saturation effect.
A vibration detection system based on two-stage polarization maintaining fiber Sagnac loop fiber laser
2012, 61 (1): 014216. doi: 10.7498/aps.61.014216
A novel fiber grating sensing technique utilized for vibration detection is proposed and experimentally demonstrated. A single wavelength laser is formed by polarization controllers and polarization maintaining fiber (PMF) to construct the high birefringence (Hi-Bi) Sagnac loop, PMF combined with erbium-doped fiber, single mode fiber and polarizer. The cantilever glued to an FBG is used as a sensor probe, and the linear edge of Sagnac ring laser are used to demodulate fiber optic seismic vibration signal. Sagnac ring theory and its edge effects are described in detail, and numerical simulation and experiment show that the vibration signal detection system is adjusted periodically in a range from L1 to L1 + L2, sensitivity goes up to 38.2 W/nm of discrimination, the linearity is 0.9996, and the dynamic range is 4070 dB, these meeting the requirements for vibration detection technical parameters.
All-optical format conversion from non-return-to-zero to return-to-zero based on four-wave mixing in photonic crystal fiber
2012, 61 (1): 014217. doi: 10.7498/aps.61.014217
The conversion from all-optical non-return-to-zero (NRZ) to return-to-zero (RZ) format is a crucial technology in interfacing WDM and OTDM of future transparent photonic network. The conversion from all-optical single-to-dual NRZ to RZ format conversion is presented and experimentally demonstrated based on four-wave mixing (FWM) in a 50 m dispersion-flattened highly-nonlinear photon crystal fiber (DF-HNL-PCF). The original NRZ format is converted into RZ format by injecting synchronized clock signal into the DF-HNL-PCF. The FWM effect generates two sideband components, which carry the same data information as the original NRZ signal with RZ format. The proposed format converter has a wide and tunable operation wavelength range of 19.3 nm. The optimum conversion efficiency, extinct ratio and Q factor are -21 dB, 11.9 dB and 7.2, respectively. The system is transparent to both bit rate and modulation format. The advantage of this scheme consists in the ability of bandwidth scalable due to the fact that the dispersion flattening of HNL - PCF is used. Furthermore, it is all optical fiber, compact and robust, which makes it more competitive as well as easily accessible for use in practical optical communication systems.
2012, 61 (1): 014601. doi: 10.7498/aps.61.014601
Torsion strain spectrum refers to the variation of the torsion strain of a specimen with external field, such as temperature, electric and magnetic fields, which facilitates the research of its dynamic behavior. We demonstrate that a torsion strain spectrum can be achieved in a high accuracy by making use of the conventional inverted torsion pendulum. By measuring its torsion strain spectrum of ferroelectric relaxor PMN-32%PT, we verify that its tetragonal-cubic transformation belongs to a burst-type martensite transformation.
2012, 61 (1): 014401. doi: 10.7498/aps.61.014401
Forced convection heat transfer in porous medium is involved mainly with the seepage, convection heat transfer, thermal dispersion and thermal radiation. Their research statuses and development trends are reviewed in this paper. The primary theoretical models, experimental research and empirical correlations were systemized and their features, application range and limitation were summarized too. Furthermore, the future research area and the difficulty are presented on the convection heat transfer of porous medium according to the comparative analysis of the past research results. In addition, when the radiation heat transfer can be considered in the cooling process of high temperature porous medium is determined by the simplifing calculation. All of these will be helpful to the theoretic research and engineering application of the porous medium.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2012, 61 (1): 015201. doi: 10.7498/aps.61.015201
In this article, the atomic structure and processes for Al are calculated in details by using the flexible atomic code. With these atomic parameters, the rate equations are established and resolved in order to obtain the level populations. The X ray radiation from Z-pinch Al plasma is then calculated. The experimental spectra are identified in details according to our theoretical results.
2012, 61 (1): 015202. doi: 10.7498/aps.61.015202
In the study of new energy resource, hydrogen energy has become a green energy the same as solar energy and wind energy. Under the action of certain catalytic materials (such as Ar+), the hydrogen atom of fractional hydrogen plasma can transit from the ground state to the fractional principal quantum number energy levels lower than the ground level, meanwhile the energy is largely released. By the study of the law of Balmer line's abnormal broadening of atomic hydrogen in argon and hydrogen plasma, the possibility of hydrogen plasma reaction with such a large amount of releasing energy is discussed. The research is in two aspects: by using hollow cathode discharge tube, the existence of fast hydrogen is confirmed and the relationship between the abnormal broadening and the ratio of argon to hydrogen is found to be consistent with the feature of catalytic reaction; by the comparative approach and experiments of strengthening reaction of fractional hydrogen plasma, we have obtained the broader Balmer line's abnormal broadening (the half height broadening reaches 0.245 nm).
Numerical study on coherent keV x ray generation by the interaction of ultra-short intense lasers with thin solid foils
2012, 61 (1): 015203. doi: 10.7498/aps.61.015203
The scheme of x ray generation by the interaction of ultra-short intense laser puls with two thin solid foils is re-investigated by one-dimensional numerical simulation. Attention is paid particularly to the effects of the thickness and the density distribution of the source target on the frequency spectrum and the conversion efficiency of the produced x ray emission, where the source target provides a relativistic electron layer. When the thickness of the source target is comparable to or smaller than the wavelength of x ray /4x2 ( is the wavelength of the incident laser), quasi-monochromatic x ray spectrum can be generated. Otherwise the spectrum will be broadened significantly and the maximum frequency will decrease rapidly. In addition, the presence of inhomogeneous preplasma in front of the foil will induce a similar change of the spectrum.
2012, 61 (1): 015204. doi: 10.7498/aps.61.015204
The influences on dual frequency capacitively coupled plasma radial uniformity are studied with a newly developed complete floating double probe. It is found that low frequency power, discharge pressure and gap have significant effects on radial uniformity. The results show that a suitable low frequency power, discharge pressure and larger discharge gap can achieve more uniform plasma. Finally, the improved two-dimensional fluid model simulations are performed with the same discharge parameters in experiment. The radial ion density distributions are obtained for different discharge gaps. The results are almost consistent with each other.
CONDENSED MATTER: STRUCTURAL, THERMAL AND MECHANICAL PROPERTIES
2012, 61 (1): 016101. doi: 10.7498/aps.61.016101
The vacuum sintered alloy with nominal composition of FeTe was analyzed using powder X-ray diffraction and refined with Rietveld method. It is shown that FeTe alloy crystallizes a tetragonal structure with space group of P/4nmm and its lattice constant is a = 3.8214(3)Å, c = 6.2875(3) Å, Z = 2. Fe at 2a and 2c positions and Te at 2c positions. FeTe films prepared by pulsed laser deposition showed superconducting transition with starting transition temperature Tc,onset of 13.2 K and Tc,0 of 9.8 K.
Thermodynamic study and cellular automaton simulation of thermal stability of nanocrystalline SmCo7 alloy
2012, 61 (1): 016102. doi: 10.7498/aps.61.016102
The accurate quantitative relationship between the excess volume at the grain boundary and the nanograin size in nanocrystalline alloy is deduced. The fundamental thermodynamic function of nanocrystalline alloy is derived as a function of nanograin size and temperature. By taking the SmCo7 alloy for example, the thermal stability of the nanocrystalline alloy, as well as its evolution characteristics, is studied based on the calculated excess Gibbs free energy of nanograin boundary. The results show that the nanostructure with grain size below a critical value that corresponds to the maximum excess Gibbs free energy can have higher thermal stability than a coarser nanograin structure. Once the grain size is larger than the critical value, the nanostructure may lose its stability and undergo discontinuous grain growth. By combining the nanothermodynamic model with the cellular automaton algorithm, the quantitative and visual simulations of nanograin growth in nanocrystalline SmCo7 alloy are performed. The nanograin growth behavior described by the two approaches are consistent with each other, which validates the conclusion of the thermal stability of nanocrystalline alloy, drawn from the present thermodynamic study.
2012, 61 (1): 016103. doi: 10.7498/aps.61.016103
Based on the outstanding optical properties of CdS and excellent electronic properties of single walled carbon nanotube (SWCNT), nano-CdS particle/SWCNT composite materials and nano-CdS/polyethyleneimine (PEI) functionalized SWCNT composite materials are prepared. Their optical and the electrical properties are investigated by using fluorescent light simulated sunlight. The results show that nano-CdS/SWCNT composite material displays a significant negative photo-conductivity phenomenon, while nano-CdS/PEI-SWCNT composite material displays a positive photo-conductivity phenomenon, which can be were explained by using electron-transfer theory. The optical and the electrical properties of two samples are unchanged in the case of large angle bending. Therefore, the nano-CdS/SWCNT composite materials in optical and electrical areas, especially in the emerging field of flexible opto-electronics have a good prospect.
2012, 61 (1): 016104. doi: 10.7498/aps.61.016104
A detailed knowledge of the structure and composition of NiAl compound is essential for understanding its oxidation resistance and the fracture process. The atomic distribution, concentration and long range order parameters in interior and (110) surface layer of NiAl compound at 1273 K are calculated by the grand canonical Monte Carlo simulation method. We find a quasi-exponentid relationship between the component deviations from the stoichiometry in surface layer and interior of NiAl in Al-rich region. It is observed that the deviation of component from stoichiometry in surface layer is over 30 times greater than that in interior.
2012, 61 (1): 016105. doi: 10.7498/aps.61.016105
The influence of copper precipitation on the formation of denuded zone (DZ) in Czochralski silicon has been systematically investigated by means of optical microscopy. It was found that, for conventional furnace high-low-high annealing, the copper precipitates colonies generated along the whole crosssection in the specimens contaminated by copper impurity at the first step of the heat treatment, thus no DZ generated. While in other specimens, DZ formed. Additionally, it was found that the contamination temperature can influence significantly the thermodynamics and kinetic process of the formation of copper precipitates. The phenomena also occurred in the specimens underwent rapid thermal-low-high annealing. On the basis of the step by step investigation, it was revealed that the copper precipitates temperature and point defects type can influence the formation of DZ to a great extent.
Total ionizing dose effects on n-channel metal oxide semiconductor transistors with annular-gate and ring-gate layouts
2012, 61 (1): 016106. doi: 10.7498/aps.61.016106
Two-edged-gate, annular-gate and ring-gate N-channel metal oxide semiconductor (NMOS) transistors with two different values of gate oxide thickness (tox) are fabricated in a commercial 0.35 m complementary metal oxide semiconductor (CMOS) process. The tests for the total ionizing dose (TID) effects of the transistors are carried out with a total dose up to 2000 Gy(Si). The results show that the dependence of radiation-induced threshold voltage shift on tox is larger than the power-law tox3. The TID tolerance of the low voltage NMOS (tox=11 nm) is improved from 300 Gy(Si) to over 2000 Gy(Si) by the annular-gate or ring-gate layout. For the high voltage NMOS (tox=26 nm), the annular-gate or ring-gate layout can only mitigate the growth of the off-state leakage current when the total dose is less than 1000 Gy(Si). As radiation hardening techniques, the annular-gate and ring-gate layouts have similar effects, but the annular-gate layout is slightly more effective in terms of the radiation-induced threshold voltage shift and off-state leakage current increase. The test results are theoretically explained by examining and analyzing the experimental data.
2012, 61 (1): 016107. doi: 10.7498/aps.61.016107
In this paper we characterize the microstructures of Mo/si multilager in space solar telescope induced by proton irradiation by transmission electron microscope (TEM). The optical performances of the Mo/Si multilayer mirror before and after proton irradiation are also determined. The experimental results show that some defect structures are introduced after proton irradiation. The Mo/Si periodic structure is destructed in some irradiation regions. The widths of Mo layer and Si layer significantly change and the Mo/Si interface is much rougher than before irradiation. Moreover, the obvious distortions of the Mo/Si interface and the formation of the small islands in Mo layer are also found. Furthermore, proton irradiation reduces the reflectivity of Mo/Si multilayer mirror. The dominante mechanism of optical degeneration of the Mo/Si multilayer induced by proton irradiation should be attributed to the formation of the defect structures.
2012, 61 (1): 016108. doi: 10.7498/aps.61.016108
Using first-principles pseudopotential plane wave method, the energy, atomic geometry and electronic density of states of FCC Cu crystal and its (111), (110) and (100) surface models were calculated and analyzed. According to the calculated results of the surface energy, the structural stability of the Cu surfaces increases for Cu (110), Cu (100), Cu (111) surfaces successively. The relaxation extent of the surface atoms decreases successively with the increasing the number of the layers. For the inwards relaxation of the surface layer atoms, Cu (110) surface moves maximum, Cu (100) takes second place, Cu (111) surface moves least. It was found that the relaxation of the surface atom layers not only causes the change of geometrical structures of the surface models but also leads to the change of peak contour of density of states (DOS) of surface layer atoms comparing with crystal inside. The increment of the total energy caused by these change is the main reason of the surface energy. And that the Cu (110) surface having higher activity than that of Cu(111) and Cu(100) surfaces may be attributed to its apparent rising of the surface layer atoms DOS in the high energy level.
2012, 61 (1): 016201. doi: 10.7498/aps.61.016201
Large-scale molecular dynamics simulations are performed to study the adhesive contact between a rigid spherical tip and an elastic flat substrate. We focus on he relations between the real contact area and the external load and between the repulsive force and attractive force on contact interface. The simulated results are consistent with the corresponding continuum contact theories, which are Hertz model, Ggeenwood-Williamson (or Persson) model and Maugis-Dugdale model according to surface roughness and interfacial adhesion. We show that there are same relations between the real contact area and the repulsive force for both non-adhesive and adhesive contact, which means that the effect of adhesion on contact behavior can be equivalent to that of a virtual load. We demonstrate that the attractive force on contact interface increases with the real contact area in a power-law function, with a power exponent larger than 1 for the atomic-scale smooth tip and with a power exponent smaller than 1 for the atomic-scale rough tip.
2012, 61 (1): 016202. doi: 10.7498/aps.61.016202
The load effect on the anisotropic friction property of gecko seta arrays have been experimentally investigated on a homemade micro adhesive and friction force detect device with isolated seta arrays. The result shows that when sliding against the direction of the seta curvature to grip out, the friction force is proportional to the normal load with a friction coefficient of about 0.6. When sliding along the direction of the seta curvature to grip in, the normal preload force could be fully or partly transformed into adhesion force and repulsive force while friction force rapidly rose with the increment of the applied preload. Under the same normal preload, the lateral friction force in grip in is more than twice of that in grip out. These properties of anisotropy in friction and adhesion are determined by the micro and nano-structures of setae.
2012, 61 (1): 016401. doi: 10.7498/aps.61.016401
Ab-initio calculation method is employed to determine the potential functions and the unknown parameters in pair-potential-based mean filed model for metals. Using the mean fields constructed from the potential functions, the vibration free volumes of atoms of metals Al, Cu, Ni, Na, and K at melting points are evaluated. The results indicate that the widely used hypothesis that the ratio of vibration free volume to the primitive cell volume of atoms in melting curve is a constant, is not correct. We provide a ratio model which can be usd to obtain much more accurate results of melting curve.
2012, 61 (1): 016801. doi: 10.7498/aps.61.016801
The Monte Carlo method of grand canonical ensemble is used to simulate the adsorption process of hydrogen storage in carbon nanotube. Results show that the hydrogen storage capacity of (30,30) armchair carbon nanotubes is 3.74 wt% at 77 K and 2 MPa and at 77 K 7.4 wt% and 10 MPa. H2 molecules are distributed mainly at the surface of carbon nanotube.
2012, 61 (1): 016802. doi: 10.7498/aps.61.016802
A relation between grain size and metal film is given by combining the Marom model with experiment data. Based on available theory model, taking into account the surface scattering, boundary scattering and grain size effect, an analytical resistivity model is presented for the 1050 nm thick Cu films. In particular, within a range of 1020 nm, the findings show that the proposed model with consideration of grain size effects is in good agreement with experimental results. Compared with Lim, Wang and Marom' models, the proposed method can reduce the relative standard deviations by 74.24%, 54.85% and 78.29%, respectively.
The variations in composition and bonding configuration of SiNx film under high annealing temperature treatment
2012, 61 (1): 016803. doi: 10.7498/aps.61.016803
Non-stoichiometric silicon nitride (SiNx) thin films are deposited on p-type crystalline silicon substrates at low temperature (200 ℃) using ammonia and silane mixtures by plasma enhanced chemical vapor deposition. The evolutions of SiN, SiH and NH bonding configurations, the variations of Si 2p and N 1s electron binding energy and the ratio R of nitrogen to silicon atoms in SiNx films annealed at temperature in a range of 5001100 ℃ are investigated at room temperature by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), respectively. The relationship between the evolutions of FTIR and XPS spectroscopy of the samples at different annealing temperatures and the variations of bonding configurations of Si, N and H atoms is discussed in detail. According to the arguments about FTIR and XPS spectroscopy we conclude that when the annealing temperature is lower than 800 ℃, the breakings of SiH and NH bonds in the SiNx films lead mainly to the formation of SiN bonds; when the annealing temperature is higher than 800 ℃, the breakings of SiH and NH bonds are conducible to the effusion of N atoms and the formation of silicon nanoparticles; when the annealing temperature equals 1100 ℃, the N2 react on the SiNx films to cause the ratio R of nitrogen to silicon atoms to inerease. These results are useful for controlling the probable chemical reaction in SiNx films under high annealing temperatures and optimizing the fabrication parameters of silicon nanoparticles embedded in SiNx films.
Underlying strain-induced growth of the self-assembled Ge quantum-dots prepared by ion beam sputtering deposition
2012, 61 (1): 016804. doi: 10.7498/aps.61.016804
The quantum-dot samples with single Ge layer and twofold stacked Ge layers are prepared by ion beam sputtering deposition. The different sizes and morphologies of quantum-dots are characterized using atomic force microscope technique. The effects of strain from the capped Ge quantum-dots on the upper Ge wetting layer and the nucleation are also investigated by the buried strain model. The results show that the non-uniform strain in the Si spacing layer which caps the buried quantum-dot layer, leads to the decrease of Ge critical thickness in the upper layer, which increases the upper dot size. The strain intensity increases with the decrease of Si spacer thickness, which results in the changes of dot shape and size in the upper layer. Furthermore, the strain also modulates the distribution of upper quantum-dot layer.
2012, 61 (1): 016805. doi: 10.7498/aps.61.016805
The deposition processes for Al atoms on Pb (Al/Pb system) surface and Pb atoms on Al surface (Pb/Al system) are studied using molecular dynamic simulations. Under the same deposition conditions, the morphologies of the two systems are very different due to the difference in energy barrier between the interfaces. The substrate temperature, the atom incident energy, and the surface orientation are discussed in terms of their effects on the atom mixing between interfaces. The simulation results show that with the substrate temperature increasing, atomic mobility is enhanced and the degree of atoms mixing between interfaces becomes greater. However, the change of the atom incident energy has little effect on the atoms mixing between interfaces. The atoms mixing is obviously different due to the change of the surface orientation. The analysis on the pair correlation function g(r) indicates that the film formed with higher incident energy has a better quality. The radial distribution function in peak of the intermixing region reveals that a PbAl intermetallic compound may be formed at the interface between Pb and Al.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2012, 61 (1): 017101. doi: 10.7498/aps.61.017101
First-principles calculations based on the density functional theory are used to study the crystal structure, electronic and optical properties of Nb doped anatase and rutile TiO2. The calculated results reveal that anatase TiO2:Nb has a smaller effective mass and carriers nearly twice lager than those of rutile TiO2:Nb under the same doping concentration. And anatase TiO2:Nb also exhibits a greater room-temperature ionization of donors. Besides, the calculated optical properties indicate that anatase TiO2:Nb has a more excellent transparency than rutile TiO2:Nb. All the results suggest that anatase TiO2:Nb is more applicable to transparent conductive oxides. The calculated results consist well with the available experimental results.
First principles study of the electronic structure and optical properties of Magnli phase titanium suboxides Ti8O15
2012, 61 (1): 017102. doi: 10.7498/aps.61.017102
The electronic structure and the optical properties of Magnli phase titanium suboxide Ti8O15 are studied by using the plane-wave ultrasoft pesudopotential method based on the density functional theory. The band structure reveals that the energy band gap of Ti8O15 is reduced a lot compared with that of anatase TiO2, which is due to the fact that O 2p, Ti 3p and Ti 3d of Ti8O15 shift toward the left compared with those of TiO2, and a new electron energy level formed by the redundant electrons of Ti 3d and Ti 3p of Ti8O15 due to the lack of oxygen atom in lattice. The results from DOS analysis show that electron distribution near the Fermi level of Ti8O15 is different from that of anatase TiO2, contribution of O 2p to Fermi level decreases and that of Ti 3d increases. Compared with anatase TiO2 which only has high ultraviolet light absorption, Ti8O15 has high light absorptivity both in ultraviolet spectrum and visible spectrum, because its narrow forbidden band width results in the red shift toward visible-light region. The light absorptivity calculated results are consistent with those from UV-vis diffuse absorption test results of anatase TiO2 and Magnli phase titanium suboxides.
First principles study of effects of the concentration of Ga/N highly doped p-type ZnO on electric conductivity performance and red shift
2012, 61 (1): 017103. doi: 10.7498/aps.61.017103
Based on first principles within the density-functional theory, using the plane-wave ultrasoft pseudopotential method, the models of unit cell pure ZnO and two highly Ga/N co-doped supercells of Zn0.9375Ga0.0625O0.9375N0.0625 and Zn0.875Ga0.125O0.75N0.25 with different doping concentrations are constructed, and the geometry optimizations for the three models are carried out. The total density of states and the band structures are also calculated. The calculation results show that at a higher doping concentration, when the co-doping concentration is more than a special value, the conductivity decreases with the increase of Ga/N co-doping concentration in ZnO, furthermore the red shift effect is more prominent which is consistent with the change trend of the experimental results.
Formation and inhibition mechanisms of space charges in direct current polyethylene insulation explained by energy band theory
2012, 61 (1): 017104. doi: 10.7498/aps.61.017104
The key factor for developing cable plastic cross-linked polyethylene cable is to eliminate space charge in the bulk. Nowadays, it is universally received that the suppression mechanism of charge accumulation in polyethylene/nano-particle composite is the formation of deep traps for trapping charges, which, in fact, is contrary to the principles of electrical field. So in this paper, the formation and the suppression mechanisms of space charge are elaborated by the energy band theory of polymeric dielectric. Then based on the first order trap model, the formation of space charge in polymeric dielectric is deduced by dynamical equation of the trapped and detraped charges. When the deep traps are introduced into polymeric dielectric, a displacement of Fermi energy level in dielectric occurs and the electric contact of interface between electrode and dielectric changes from ohmic contact to blocking contact. The width of the depletion region associated with blocking contact is less than 100 , due to huge density of traps existing in amorphous polyethylene (PE). The tunnel effect of electron makes the electrical contact of interface a neutral contact. The space charges cannot be formed in PE dielectric under electrical stress. Finally, the conductive current as a function of electrical stress and the space charge distribution are measured respectively on both PE samples, one is pure PE and the other is the nano-particle modified PE filled with deep traps. The test results are consistent with the theoretical results.
2012, 61 (1): 017105. doi: 10.7498/aps.61.017105
In this paper,we propose a new device structure called HMG SSDOI (hetero-materiel gate strained Si directly on insulator), which combines the advantages of strained-silicon and hetero-material gate technology. By solving 2D Poisson's equation, we present models of the surface potential, surface electric field and threshold voltage for the new structure. These models take into account the effects of the gate length, the work function and the energy band. ISE TCAD is also used to simulate the performance of new device structure. The comparison results of model calculation and mathematic simulation show that the new structure of HMG SSDOI can enhance the carrier transport efficiency and suppress short channel effect, drain induction barrier lower and hot carrier effect, which improves device performance greatly.
2012, 61 (1): 017106. doi: 10.7498/aps.61.017106
A numerical algorithm is proposed for multi-orbital slave-boson mean field approach through the integrating pattern search method, the generalized Lagrange multiplier method, and the Rosenbrock method. Since the crystal field splitting, inter-orbital hopping and realistic band structures can be considered, the proposed slave-boson mean field approach can be utilized to study realistic material. To validate our algorithm, the Mott transitions in twoorbital Hubbard models are studied with the elliptical density of states. The results are consistent with the reported ones available. Then we use this method to study the correlation effect on the three-orbital Hubbard model for NaxCoO2. It is shown that the six small Fermi surfaces constructed by the eg' orbital vanish in the intermediate Coulomb correlations. The physical reason is that the hole occupations of eg' orbital decrease with U increasing. All the calculated results verify the accuracy and the efficiency of our numerical algorithm.
2012, 61 (1): 017107. doi: 10.7498/aps.61.017107
We theoretically investigate the spin relaxation of polaron, which arises from the electron interactions with the longitudinal optical phonon between the sublevel Zeeman splitting of the polaron ground state by using the vibrational and the unitary transformation methods in a two-dimensional quantum dot, where the Rashba spin-orbital coupling is taken into account. In fact, this process occurs by means of the absorption (or emitting) of a deformation potential acoustic phonon (or a piezoelectric one). The relaxation rate dependences of the magnetic, the quantum dot radius, the lander parameter, the Rashba spin-orbital coupling parameter are studied under the conditions of the strong coupling limitation and the weak one.
2012, 61 (1): 017108. doi: 10.7498/aps.61.017108
In consideration of the preparation of CdS/CdTe solar cell back contact layer, the band structure and the density of states of undoped and (Y, Gd) doped in ZnTe were caculated from the plane wave ultra soft pseudo potential method based on density functional theory and generalized gradient approximation. We acquired the system total energy and lattice parameter. As a result, the structural stability improve after doping, the lattice match between ZnTe and CdTe are better when Y doped. (Y, Gd) doped make the ZnTe semiconductor degeneration. Compared with Gd, the electronic effective mass of ZnTe doped with Y are lighter. The carrier concentration order of magnitude in different doping system are same. We analysed the influence on ZnTe used for back contact layer when doped with (Y, Gd).
2012, 61 (1): 017201. doi: 10.7498/aps.61.017201
In this paper, characteristics of charge trapping and detrapping in low density polyethylene under dc electric field are investigated using the pulsed electroacoustic technique. It is found that the charge decay shows very different features for the samples with different periods of applied electric field. A simple trapping and detrapping model based on two trapping levels is proposed to qualitatively explain the observation. At the same time, numerical simulation based on the above model is carried out to extract parameters (trap depths and concentration) related to the material. It is found that the space charge decaying in the first few hundred seconds, corresponding to the fast changing part of the slope, is trapped in a shallow trap with a depth in a range between 0.77 and 0.81 eV, and the trapped charge density reaches (1.1681.553) 1019 m-3 in the sample volume measured. At the same time, the space charge that decays at longer time, corresponding to the slower part of the slope, is trapped in a deep trap with a depth in a range of 0.96 and 1.01 eV, and the trapped charge density is (1.1944.615) 1018 m-3. The trap depths and charge densities of both shallow and deep traps may increase with ageing, and the parameters of two energy wells can be used as an indication of the material aging.
2012, 61 (1): 017202. doi: 10.7498/aps.61.017202
The geometry structure, electronic structure and optical properties of zinc bende CdS:M (M = Ag,Zn) were studied systemically using density functional theory based on first-principles ultrasoft pseudopotential method and GGA.The relationship between the distribution of the electronic states and their structures has been analyzed. The dielectric function and the complex refractive index function on doping CdS system have been obtained. The calculation results showed that the hole concentration of Ag-doped CdS is increased, enhanced the conductivity of the material. But the carrier concentration of Al-doped CdS was not changed; the optical band gap were narrowed for Ag-doping, Zn-doping CdS. The mechanism of luminescence has been explained in terms of an analysis of the dielectric function and the complex refractive index function.
2012, 61 (1): 017501. doi: 10.7498/aps.61.017501
Fe doped TiO2 films are deposited on glass substrates using dc magnetron sputtering. The crystal structures and the magnetic properties of these films are studied. Room temperature ferromagnetism is observed in each of all the Fe doped TiO2 films. The source of magnetism is related to an exchange interaction between the transition-metal (Fe) ions and localized strapped holes. The maximal magnetization is observed in a TiO2 film with Fe concentration 7%. With the increase of Fe concentration, the crystal structure of TiO2 film transforms gradually from anatase phase to rutile phases, and magnetism in the film weakened. The changes of crystal structure and crystallization in TiO2 film resulting from Fe doping affect the change of ferromagnetism in the film.
Measuring and analyzing the cooling dielectric spectra of the -relaxation in dimethyl phthalate series materials
2012, 61 (1): 017701. doi: 10.7498/aps.61.017701
The cooling dielectric spectra of the -relaxation in dimethyl phthalate, diethyl phthalate, dibutyl phthalate, and dioctyl phthalate series materials are measured, and the average relaxation time of the -relaxation a as a function of temperature T is obtained. By fitting the a data to the empirical Vogel-Fulcher-Tammann law a = 0 exp (A/(T-T0)), the values of 0, A and T0 of the series materials are obtained. The results of 0, A, T0 and Tg show some variation regularities with the carbon number n in the side-group of dimethyl phthalate series molecules. And specifically, with the increase of n, the internal degrees of freedoms of the molecules, A and Tg indicate almost the same tendencies, i.e. first coming down and then going up, while 1/0 and T0 have quite similar behaviors, i.e. first reducing rapidly and then keeping at near constant values.
2012, 61 (1): 017702. doi: 10.7498/aps.61.017702
The single crystalline Tm2O3 films are deposited on Si(001) substrates by molecular beam epitaxy, by using x-ray photoelectron spectroscopy, the valence and the conduction-band shifts of Tm2O3 to Si are obtained to be 3.1 0.2 eV and 1.9 0.3 eV, respectively. The energy gap of Er2O3 is determined to be 6.1 0.2 eV. The results of the study show that the Tm2O3 could be a promising candidate for high-k gate dielectrics.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2012, 61 (1): 018101. doi: 10.7498/aps.61.018101
To improve the uniformity of crystalline volume fraction (Xc) along the deposition direction in microcrystalline silicon films, very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD), combined with parameters smoothly changed two-step method, is adopted to prepare high-rate microcrystalline silicon films on glass subtrates. With a power density of 2.1 W/cm2, silane concentration between 6% and 9.6%, a difference between Xc measured in the film direction and that in the glass direction, is just 2 percent. With a silane concentration of 9.6%, Xc, measured in the film direction and the glass direction respectively reach 50% and 48%, close to 2 percent, relative difference just 4 percent, whereas the deposition rate reaches 3.43 nm/s. What is more, Xc difference can reduce to 1 percent by strictly controlling the transitional parameters. It shows that the new deposition method not only curb the incubation layers and improve the vertical structure, but also give a larger range for film optimizing in the future.
Eliminating the influence of attitude on brightness temperatures measurement for polarimetric microwave radiometer
2012, 61 (1): 018401. doi: 10.7498/aps.61.018401
In order to meet the requirement of accurate detection for polarimetric microwave radiometer, in this paper, we study on the influence of attitude on brightness temperatures received by the radiometer. Correction for brightness temperatures errors is also analyzed. The relationship between the misspecification of the attitude and the incidence angle together with polarization rotation angle is established. The variation of brightness temperatures with the change of incidence angle and polarization rotation angle is simulated. We simulate the original observational brightness temperatures of the radiometer. A method based on the radiative transfer model for compensating attitude offset to correct brightness temperatures errors is presented. Taking vertical brightness temperature and the third Stokes parameter brightness temperature for example, our method can eliminate the influence of attitude offset on the observation of brightness temperatures effectively, the result can satisfy the accuracy requirement of data preprocessing for polarimetric microwave radiometer.
2012, 61 (1): 018501. doi: 10.7498/aps.61.018501
A microstructure-based electromigration model of Cu interconnects is proposed. Mechanisms of scaling and critical length effects of Cu electromigration are studied by transmission electron microscopy and statistical failure analysis. The results show that the lifetime of electromigration is reduced with Cu grain size decreasing when the width of interconnect is scaled down. Electromigration failure is not observed when the interconnect length is smaller than the critical length due to insufficient vacancies for voiding the whole Cu grains. Some small grains are vacated at the cathode end when the interconnect length is larger than the critical length during the testing. The proportion of failures increases and the lifetime decreases with interconnect length increasing. The failure time is dependent mainly on Cu grain size, and the failure lifetime and failure proportion fluctuate with grain size varying when the interconnect length is beyond the diffusion length.
High stability and linear tuning wavelength tunable resonant cavity enhanced photo-detector grown on GaAs
2012, 61 (1): 018502. doi: 10.7498/aps.61.018502
A wavelength tunable resonant cavity enhanced photo-detector grown on GaAs is fabricated. The quantum wells of In0.25Ga0.75As/GaAs in the active region are grown by molecular beam epitaxy. The peak of the response spectrum at 0 work bias is located at 1071 nm. When the tuning voltage rises from 0 V to 21 V, the peak shows a blue shift of 23 nm, reaching 1048 nm. Statistical results show that there is a stable accurate corresponding relation between the tuning voltage and the response peak. The relation is approximately linear when the tuning voltage is greater than 5 V. Some theoretical analysis is performed on the test results.
2012, 61 (1): 018503. doi: 10.7498/aps.61.018503
Dielectric distributed Bragg reflectors (DDBRs) with SiO2/Si3N4 are grown by PECVD alternately. For the etching of DDBR, dry and wet etching methods are both used. The reflectivity of DDBR is calculated by transfer matrix method, and the high performance DDBR structure is fabricated to obtain optimal reliability, we find that the enhancement factor along the cavity axis and the integrated emission enhancement factor of RCLED with 1.5 RC DDBR are 1.058 and 1.5 respectively, a full width at half maximum is 10.5 nm by PL analysis. Then, high performance RCLEDs are fabricated by using an optimal DDBR structure. The devices with DDBR show many advantages: a lower turn-on voltage of 1.78 V, under 20 mA injection current, the output power and the luminous efficiency of the device with/without DDBR gain the improvements of 27.7% and 26.8% respectively, under 0-100 mA injection current, the output power has unconspicuous downtrend, better characteristic saturation of optical power and temperature stability.
2012, 61 (1): 018701. doi: 10.7498/aps.61.018701
In coherent x-ray diffractive imaging, the oversampled far-field diffraction pattern for phase retrieval iterative algorithm is used in order to reconstruct the information about the real space. The support constraint is one of the most important steps of the 3D phase retrieval process. Here we use a small nonperiodic 2D digital image as an object for studying the algorithm of pursuing support constraint automatically and noise correction for different types of noises in the diffraction pattern. We find an efficient method of noise correction while the traditional methods do not work well in the high noise condition. The result shows that this method can be used to reduce the effect effectively for the reconstruction. We also study the 3D reconstruction for the electron density distribution of Au nano-particles. We achieve a good reconstruction separately with and without noise effect in the diffraction pattern and we find that the signal-to-noise ratio should be bigger than 27 for successful 3D reconstruction.
2012, 61 (1): 018801. doi: 10.7498/aps.61.018801
After accounting for a contact resistance between carbon nanotube (CNT) and substrate, the local electric filed of top of CNT were calculated by combining an improved floated sphere model and the Fowler-Nordheim theory for understand the effect of the contact resistance on field emission from CNT. It is found that the field emission current is limited and current saturation and nonlinear characteristics of the Fowler-Nordheim plots are produced by the contact resistance in region of high electric field. The origin can be attributed to the local electric filed of top of CNT remarkably debases as compared to without the contact resistance.
GEOPHYSICS, ASTRONOMY AND ASTROPHYSICS
2012, 61 (1): 019701. doi: 10.7498/aps.61.019701
A prototype of x-ray photon counting detector is proposed for x-ray pulsar navigation. The detector consists of CsI photocathode, micro-channel plate (MCP) electron multiplier, collect anode and electronic readout. The sensitivity, the temporal resolution, and the dead time are tested, and the results show that the sensitivity of the detector is 5.2× 103 A/W at 5 keV, the temporal resolution is 1.1 ns, and dead time is 100 ns.