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Chin. Phys. B  
  Chin. Phys. B--2016, Vol.25, No.4
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Theoretical calculation and experiment of microwave electromagnetic property of Ni(C) nanocapsules

Dan-Feng Zhang, Zhi-Feng Hao, Bi Zeng, Yan-Nan Qian, Ying-Xin Huang, Zhen-Da Yang
Chin. Phys. B 2016, 25 (4): 040201;  doi: 10.1088/1674-1056/25/4/040201
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With the combination of the dielectric loss of the carbon layer with the magnetic loss of the ferromagnetic metal core, carbon-coated nickel (Ni(C)) nanoparticles are expected to be the promising microwave absorbers. Microwave electromagnetic parameters and reflection loss in a frequency range of 2 GHz-18 GHz for paraffin-Ni(C) composites are investigated. The values of relative complex permittivity and permeability, the dielectric and magnetic loss tangent of paraffin-Ni(C) composites are measured, respectively, when the weight ratios of Ni(C) nanoparticles are equal to 10 wt%, 40 wt%, 50 wt%, 70 wt%, and 80 wt% in paraffin-Ni(C) composites. The results reveal that Ni(C) nanoparticles exhibit a peak of magnetic loss at about 13 GHz, suggesting that magnetic loss and a natural resonance could be found at that frequency. Based on the measured complex permittivity and permeability, the reflection losses of paraffin-Ni(C) composites with different weight ratios of Ni(C) nanoparticles and coating thickness values are simulated according to the transmission line theory. An excellent microwave absorption is obtained. To be proved by the experimental results, the reflection loss of composite with a coating thickness of 2 mm is measured by the Arch method. The results indicate that the maximum reflection loss reaches -26.73 dB at 12.7 GHz, and below -10 dB, the bandwidth is about 4 GHz. The fact that the measured absorption position is consistent with the calculated results suggests that a good electromagnetic match and a strong microwave absorption can be established in Ni(C) nanoparticles. The excellent Ni(C) microwave absorber is prepared by choosing an optimum layer number and the weight ratio of Ni(C) nanoparticles in paraffin-Ni(C) composites.

(2+1)-dimensional dissipation nonlinear Schrödinger equation for envelope Rossby solitary waves and chirp effect

Jin-Yuan Li, Nian-Qiao Fang, Ji Zhang, Yu-Long Xue, Xue-Mu Wang, Xiao-Bo Yuan
Chin. Phys. B 2016, 25 (4): 040202;  doi: 10.1088/1674-1056/25/4/040202
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In the past few decades, the (1+1)-dimensional nonlinear Schrödinger (NLS) equation had been derived for envelope Rossby solitary waves in a line by employing the perturbation expansion method. But, with the development of theory, we note that the (1+1)-dimensional model cannot reflect the evolution of envelope Rossby solitary waves in a plane. In this paper, by constructing a new (2+1)-dimensional multiscale transform, we derive the (2+1)-dimensional dissipation nonlinear Schrödinger equation (DNLS) to describe envelope Rossby solitary waves under the influence of dissipation which propagate in a plane. Especially, the previous researches about envelope Rossby solitary waves were established in the zonal area and could not be applied directly to the spherical earth, while we adopt the plane polar coordinate and overcome the problem. By theoretical analyses, the conservation laws of (2+1)-dimensional envelope Rossby solitary waves as well as their variation under the influence of dissipation are studied. Finally, the one-soliton and two-soliton solutions of the (2+1)-dimensional NLS equation are obtained with the Hirota method. Based on these solutions, by virtue of the chirp concept from fiber soliton communication, the chirp effect of envelope Rossby solitary waves is discussed, and the related impact factors of the chirp effect are given.

Two-dimensional fracture analysis of piezoelectric material based on the scaled boundary node method

Shen-Shen Chen, Juan Wang, Qing-Hua Li
Chin. Phys. B 2016, 25 (4): 040203;  doi: 10.1088/1674-1056/25/4/040203
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A scaled boundary node method (SBNM) is developed for two-dimensional fracture analysis of piezoelectric material, which allows the stress and electric displacement intensity factors to be calculated directly and accurately. As a boundary-type meshless method, the SBNM employs the moving Kriging (MK) interpolation technique to an approximate unknown field in the circumferential direction and therefore only a set of scattered nodes are required to discretize the boundary. As the shape functions satisfy Kronecker delta property, no special techniques are required to impose the essential boundary conditions. In the radial direction, the SBNM seeks analytical solutions by making use of analytical techniques available to solve ordinary differential equations. Numerical examples are investigated and satisfactory solutions are obtained, which validates the accuracy and simplicity of the proposed approach.

New analytical exact solutions of time fractional KdV–KZK equation by Kudryashov methods

S Saha Ray
Chin. Phys. B 2016, 25 (4): 040204;  doi: 10.1088/1674-1056/25/4/040204
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In this paper, new exact solutions of the time fractional KdV-Khokhlov-Zabolotskaya-Kuznetsov (KdV-KZK) equation are obtained by the classical Kudryashov method and modified Kudryashov method respectively. For this purpose, the modified Riemann-Liouville derivative is used to convert the nonlinear time fractional KdV-KZK equation into the nonlinear ordinary differential equation. In the present analysis, the classical Kudryashov method and modified Kudryashov method are both used successively to compute the analytical solutions of the time fractional KdV-KZK equation. As a result, new exact solutions involving the symmetrical Fibonacci function, hyperbolic function and exponential function are obtained for the first time. The methods under consideration are reliable and efficient, and can be used as an alternative to establish new exact solutions of different types of fractional differential equations arising from mathematical physics. The obtained results are exhibited graphically in order to demonstrate the efficiencies and applicabilities of these proposed methods of solving the nonlinear time fractional KdV-KZK equation.

Nonrelativistic Shannon information entropy for Kratzer potential

Najafizade S A, Hassanabadi H, Zarrinkamar S
Chin. Phys. B 2016, 25 (4): 040301;  doi: 10.1088/1674-1056/25/4/040301
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The Shannon information entropy is investigated within the nonrelativistic framework. The Kratzer potential is considered as the interaction and the problem is solved in a quasi-exact analytical manner to discuss the ground and first excited states. Some interesting features of the information entropy densities as well as the probability densities are demonstrated. The Bialynicki-Birula-Mycielski inequality is also tested and found to hold for these cases.

Kraus operator solutions to a fermionic master equation describing a thermal bath and their matrix representation

Xiang-Guo Meng, Ji-Suo Wang, Hong-Yi Fan, Cheng-Wei Xia
Chin. Phys. B 2016, 25 (4): 040302;  doi: 10.1088/1674-1056/25/4/040302
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We solve the fermionic master equation for a thermal bath to obtain its explicit Kraus operator solutions via the fermionic state approach. The normalization condition of the Kraus operators is proved. The matrix representation for these solutions is obtained, which is incongruous with the result in the book completed by Nielsen and Chuang [Quantum Computation and Quantum Information, Cambridge University Press, 2000]. As especial cases, we also present the Kraus operator solutions to master equations for describing the amplitude-decay model and the diffusion process at finite temperature.

Deformed photon-added entangled squeezed vacuum and one-photon states: Entanglement, polarization, and nonclassical properties

A Karimi, M K Tavassoly
Chin. Phys. B 2016, 25 (4): 040303;  doi: 10.1088/1674-1056/25/4/040303
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In this paper, after a brief review on the entangled squeezed states, we produce a new class of the continuous-variable-type entangled states, namely, deformed photon-added entangled squeezed states. These states are obtained via the iterated action of the f-deformed creation operator A=f(n)a on the entangled squeezed states. In the continuation, by studying the criteria such as the degree of entanglement, quantum polarization as well as sub-Poissonian photon statistics, the two-mode correlation function, one-mode and two-mode squeezing, we investigate the nonclassical behaviors of the introduced states in detail by choosing a particular f-deformation function. It is revealed that the above-mentioned physical properties can be affected and so may be tuned by justifying the excitation number, after choosing a nonlinearity function. Finally, to generate the introduced states, we propose a theoretical scheme using the nonlinear Jaynes-Cummings model.

Fidelity between Gaussian mixed states with quantum state quadrature variances

Hai-Long Zhang, Chun Zhou, Jian-Hong Shi, Wan-Su Bao
Chin. Phys. B 2016, 25 (4): 040304;  doi: 10.1088/1674-1056/25/4/040304
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In this paper, from the original definition of fidelity in a pure state, we first give a well-defined expansion fidelity between two Gaussian mixed states. It is related to the variances of output and input states in quantum information processing. It is convenient to quantify the quantum teleportation (quantum clone) experiment since the variances of the input (output) state are measurable. Furthermore, we also give a conclusion that the fidelity of a pure input state is smaller than the fidelity of a mixed input state in the same quantum information processing.

Weakly interacting spinor Bose-Einstein condensates with three-dimensional spin-orbit coupling

Shu-Wei Song, Rui Sun, Hong Zhao, Xuan Wang, Bao-Zhong Han
Chin. Phys. B 2016, 25 (4): 040305;  doi: 10.1088/1674-1056/25/4/040305
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Starting from the Hamiltonian of the second quantization form, the weakly interacting Bose-Einstein condensate with spin-orbit coupling of Weyl type is investigated. It is found that the SU(2) nonsymmetric term, i.e., the spin-dependent interaction, can lift the degeneracy of the ground states with respect to the z component of the total angular momentum Jz, casting the ground condensate state into a configuration of zero Jz. This ground state density profile can also be affirmed by minimizing the full Gross-Pitaevskii energy functional. The spin texture of the zero Jz state indicates that it is a knot structure, whose fundamental group is π3(M)π3(S2)=Z.

Dynamics of spinor Bose-Einstein condensate subject to dissipation

Man-Man Pang, Ya-Jiang Hao
Chin. Phys. B 2016, 25 (4): 040501;  doi: 10.1088/1674-1056/25/4/040501
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We investigate the internal dynamics of the spinor Bose-Einstein condensates subject to dissipation by solving the Lindblad master equation. It is shown that for the condensates without dissipation its dynamics always evolve along a specific orbital in the phase space of (n0, θ) and display three kinds of dynamical properties including Josephson-like oscillation, self-trapping-like oscillation, and ‘running phase'. In contrast, the condensates subject to dissipation will not evolve along the specific dynamical orbital. If component-1 and component-(-1) dissipate at different rates, the magnetization m will not conserve and the system transits between different dynamical regions. The dynamical properties can be exhibited in the phase space of (n0, θ, m).

Phase sensitivity of two nonlinear interferometers with inputting entangled coherent states

Chao-Ping Wei, Xiao-Yu Hu, Ya-Fei Yu, Zhi-Ming Zhang
Chin. Phys. B 2016, 25 (4): 040601;  doi: 10.1088/1674-1056/25/4/040601
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We investigate the phase sensitivity of the SU(1,1) interfereometer [SU(1,1)I] and the modified Mach-Zehnder interferometer (MMZI) with the entangled coherent states (ECS) as inputs. We consider the ideal case and the situations in which the photon losses are taken into account. We find that, under ideal conditions, the phase sensitivity of both the MMZI and the SU(1,1)I can beat the shot-noise limit (SNL) and approach the Heisenberg limit (HL). In the presence of photon losses, the ECS can beat the coherent and squeezed states as inputs in the SU(1,1)I, and the MMZI is more robust against internal photon losses than the SU(1,1)I.

Compressed sensing sparse reconstruction for coherent field imaging

Bei Cao, Xiu-Juan Luo, Yu Zhang, Hui Liu, Ming-Lai Chen
Chin. Phys. B 2016, 25 (4): 040701;  doi: 10.1088/1674-1056/25/4/040701
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Return signal processing and reconstruction plays a pivotal role in coherent field imaging, having a significant influence on the quality of the reconstructed image. To reduce the required samples and accelerate the sampling process, we propose a genuine sparse reconstruction scheme based on compressed sensing theory. By analyzing the sparsity of the received signal in the Fourier spectrum domain, we accomplish an effective random projection and then reconstruct the return signal from as little as 10% of traditional samples, finally acquiring the target image precisely. The results of the numerical simulations and practical experiments verify the correctness of the proposed method, providing an efficient processing approach for imaging fast-moving targets in the future.

Preparation and room temperature NO2-sensing performances of porous silicon/V2O5 nanorods

Wen-Jun Yan, Ming Hu, Ji-Ran Liang, Deng-Feng Wang, Yu-Long Wei, Yu-Xiang Qin
Chin. Phys. B 2016, 25 (4): 040702;  doi: 10.1088/1674-1056/25/4/040702
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In this paper, porous silicon/V2O5 nanorod composites are prepared by a heating process of as-sputtered V film on porous silicon (PS) at 600 ℃ for different times (15, 30, and 45 min) in air. The morphologies and crystal structures of the samples are investigated by field emission scanning electron microscope (FESEM), x-ray diffractometer (XRD), x-ray photoelectron spectroscopy (XPS), and Raman spectrum (RS). An improved understanding of the growth process of V2O5 nanorods on PS is presented. The gas sensing properties of samples are measured for NO2 gas of 0.25 ppm~3 ppm at 25 ℃. We investigate the effects of the annealing time on the NO2-sensing performances of the samples. The sample obtained at 600 ℃ for 30 min exhibits a very strong response and fast response-recovery rate to ppm level NO2, indicating a p-type semiconducting behavior. The XPS analysis reveals that the heating process for 30 min produces the biggest number of oxygen vacancies in the nanorods, which is highly beneficial to gas sensing. The significant NO2 sensing performance of the sample obtained at 600 ℃ for 30 min probably is due to the strong amplification effect of the heterojunction between PS and V2O5 and a large number of oxygen vacancies in the nanorods.

Ab initio study on the electronic states and laser cooling of AlCl and AlBr

Rong Yang, Bin Tang, Tao Gao
Chin. Phys. B 2016, 25 (4): 043101;  doi: 10.1088/1674-1056/25/4/043101
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We investigate whether AlCl and AlBr are promising candidates for laser cooling. We report new ab initio calculations on the ground state X1Σ+ and two low-lying states (A1Π and a3Π) of AlCl and AlBr. The calculated spectroscopic constants show good agreement with available theoretical and experimental results. We also obtain the permanent dipole moments (PDMs) curve at multi-reference configuration interaction (MRCI) level of theory. The transition properties of A1Π and a3Π states are predicted, including the transition dipole moments (TDMs), Franck-Condon factors (FCFs), radiative times and radiative width. The calculated radiative lifetimes are of the order of a nanosecond, implying that they are sufficiently short for rapid laser cooling. Both AlCl and AlBr have highly diagonally distributed FCFs which are crucial requirement for molecular laser cooling. The results demonstrate the feasibility of laser cooling AlCl and AlBr, and we propose laser cooling schemes for AlCl and AlBr.

Comment on “Atomic structure calculations for F-like tungsten” by S. Aggarwal [Chin. Phys B 23 (2014) 093203]

Kanti M Aggarwal
Chin. Phys. B 2016, 25 (4): 043201;  doi: 10.1088/1674-1056/25/4/043201
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Recently, S. Aggarwal [Chin. Phys. B 23 (2014) 093203] reported energy levels, radiative rates, and the lifetimes for the lowest 60 levels belonging to the 2s22p5, 2s2p6, and 2s22p43l configurations of F-like tungsten. There is no discrepancy for his calculated energies for the levels and the radiative rates for the limited number of E1 transitions, but the reported results for the lifetimes are highly inaccurate. According to our calculations, errors in his reported lifetimes are up to 6 orders of magnitude for several levels. Here we report the correct lifetimes for future comparisons and applications, and also explain the reason for the discrepancies.

High-order harmonic generation of the N2 molecule in two-color circularly polarized laser fields Hot!

Hui Du(杜慧), Jun Zhang(张军), Shuai Ben(贲帅), Hui-Ying Zhong(钟慧英), Tong-Tong Xu(徐彤彤), Jing Guo(郭静), Xue-Shen Liu(刘学深)
Chin. Phys. B 2016, 25 (4): 043202;  doi: 10.1088/1674-1056/25/4/043202
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The generation of high-order harmonics and the attosecond pulse of the N2 molecule in two-color circularly polarized laser fields are investigated by the strong-field Lewenstein model. We show that the plateau of spectra is dramatically extended and a continuous harmonic spectrum with the bandwidth of 113 eV is obtained. When a static field is added to the x direction, the quantum path control is realized and a supercontinuum spectrum can be obtained, which is beneficial to obtain a shorter attosecond pulse. The underlying physical mechanism is well explained by the time-frequency analysis and the semi-classical three-step model with a finite initial transverse velocity. By superposing several orders of harmonics in the combination of two-color circularly polarized laser fields and a static field, an isolated attosecond pulse with a duration of 30 as can be generated.

Differential cross sections for electron impact excitation of molecular hydrogen using the momentum-space multichannel optical method

Yuan-Cheng Wang, Jia Ma, Ya-Jun Zhou
Chin. Phys. B 2016, 25 (4): 043401;  doi: 10.1088/1674-1056/25/4/043401
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In the present work, the momentum-space multichannel optical method is employed in four-state close-coupling calculations to study the electronic excitation of H2 molecules by electron-impact. Particularly, differential cross sections for the X1Σg+→b3Σu+, X1Σg+→a3Σg+, and X1Σg+→c3Πu transitions are reported. Comparison is made with the available experimental and theoretical results.
SPECIAL TOPIC—Soft matter and biological physics (Review)

Soliton excitation in the pass band of the transmission line based on modulation

Guoying Zhao, Feng Tao, Weizhong Chen
Chin. Phys. B 2016, 25 (4): 044101;  doi: 10.1088/1674-1056/25/4/044101
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We numerically investigate the excitation of soliton waves in the nonlinear electrical transmission line formed by many cells. When the periodic driving voltage with frequency in the pass band closing to the cutoff frequency is applied to the endpoint of the whole line, the soliton wave can be generated. The numerical results show that the soliton wave generation mainly depends on the self modulation associated with the nonlinear effect. In this study, the lower subharmonic component is also observed in the frequency spectrum. To further understand this phenomenon, we study the dependence of the subharmonic power spectrum and frequency on the forcing amplitude and frequency numerically, and find that the subharmonic frequency increases with the gradual growth of the driving amplitude.

Propagation of Airy Gaussian vortex beams in uniaxial crystals

Weihao Yu, Ruihuang Zhao, Fu Deng, Jiayao Huang, Chidao Chen, Xiangbo Yang, Yanping Zhao, Dongmei Deng
Chin. Phys. B 2016, 25 (4): 044201;  doi: 10.1088/1674-1056/25/4/044201
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The propagation dynamics of the Airy Gaussian vortex beams in uniaxial crystals orthogonal to the optical axis has been investigated analytically and numerically. The propagation expression of the beams has been obtained. The propagation features of the Airy Gaussian vortex beams are shown with changes of the distribution factor and the ratio of the extraordinary refractive index to the ordinary refractive index. The correlations between the ratio and the maximum intensity value during the propagation, and its appearing distance have been investigated.

The effect of a permanent dipole moment on the polar molecule cavity quantum electrodynamics

Jing-Yun Zhao, Li-Guo Qin, Xun-Ming Cai, Qiang Lin, Zhong-Yang Wang
Chin. Phys. B 2016, 25 (4): 044202;  doi: 10.1088/1674-1056/25/4/044202
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A dressed-state perturbation theory beyond the rotating wave approximation (RWA) is presented to investigate the interaction between a two-level electronic transition of polar molecules and a quantized cavity field. Analytical expressions can be explicitly derived for both the ground-and excited-state-energy spectrums and wave functions of the system, where the contribution of permanent dipole moments (PDM) and the counter-rotating wave term (CRT) can be shown separately. The validity of these explicit results is discussed by comparison with the direct numerical simulation. Compared to the CRT coupling, PDM results in the coupling of more dressed states and the energy shift is proportional to the square of the normalized permanent dipole difference, and a greater Bloch-Siegert shift can be produced in the giant dipole molecule cavity QED. In addition, our method can also be extended to the solution of the two-level atom Rabi model Hamiltonian beyond the RWA.

Dynamics of a three-level V-type atom driven by a cavity photon and microwave field

Yan-Li Xue, Shi-Deng Zhu, Ju Liu, Ting-Hui Xiao, Bao-Hua Feng, Zhi-Yuan Li
Chin. Phys. B 2016, 25 (4): 044203;  doi: 10.1088/1674-1056/25/4/044203
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We discuss the dynamics of a three-level V-type atom driven simultaneously by a cavity photon and microwave field by examining the atomic population evolution. Owing to the coupling effect of the cavity photon, periodical oscillation of the population between the two upper states and the ground state takes place, which is the well-known vacuum Rabi oscillation. Meanwhile, the population exchange between the upmost level and the middle level can occur due to the driving action of the external microwave field. The general dynamic behavior is the superposition of a fast and a slow periodical oscillation under the cooperative and competitive effect of the cavity photon and the microwave field. Numerical results demonstrate that the time evolution of the population is strongly dependent on the atom-cavity coupling coefficient g and Rabi frequency Ωe that reflects the intensity of the external microwave field. By modulating the two parameters g and Ωe, a large number of population transfer behaviors can be achieved.

Laser frequency locking based on the normal and abnormal saturated absorption spectroscopy of 87Rb

Jian-Hong Wan(万剑宏), Chang Liu(刘畅), Yan-Hui Wang(王延辉)
Chin. Phys. B 2016, 25 (4): 044204;  doi: 10.1088/1674-1056/25/4/044204
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We present a practical method to avoid the mis-locking phenomenon in the saturated-absorption-spectrum laser-frequency-locking system and set up a simple theoretical model to explain the abnormal saturated absorption spectrum. The method uses the normal and abnormal saturated absorption spectra of the same transition 52S1/2, F=2-52P3/2, F'=3 saturated absorption of the 87Rb D2 resonance line. After subtracting these two signals with the help of electronics, we can obtain a spectrum with a single peak to lock the laser. In our experiment, we use the normal and inverse signals of the transitions 52S1/2, F=2-52P3/2, F'=3 saturated absorption of the 87Rb D2 resonance line to lock a 780-nm distributed feedback (DFB) diode laser. This method improves the long-term locking performance and is suitable for other kinds of diode lasers.

Monolithic CEO-stabilization scheme-based frequency comb from an octave-spanning laser Hot!

Zi-Jiao Yu(于子蛟), Hai-Nian Han(韩海年), Yang Xie(谢阳), Hao Teng(滕浩), Zhao-Hua Wang(王兆华), Zhi-Yi Wei(魏志义)
Chin. Phys. B 2016, 25 (4): 044205;  doi: 10.1088/1674-1056/25/4/044205
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We demonstrate a carrier-envelope phase-stabilized octave-spanning oscillator based on the monolithic scheme. A wide output spectrum extending from 480 nm to 1050 nm was generated directly from an all-chirped mirror Ti:sapphire laser. After several improvements, the carrier-envelope offset (CEO) beat frequency accessed nearly 60 dB under a resolution of 100 kHz. Using a feedback system with 50-kHz bandwidth, we compressed the residual phase noise to 55 mrad (integrated from 1 Hz to 1 MHz) for the stabilized CEO, corresponding to 23-as timing jitter at the central wavelength of 790 nm. This is, to the best of our knowledge, the smallest timing jitter achieved among the existing octave-spanning laser based frequency combs.

A closed form of a kurtosis parameter of a hypergeometric-Gaussian type-II beam

Khannous F, Ebrahim A A A, Belafhal A
Chin. Phys. B 2016, 25 (4): 044206;  doi: 10.1088/1674-1056/25/4/044206
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Based on the irradiance moment definition and the analytical expression of waveform propagation for hypergeometric-Gaussian type-II beams passing through an ABCD system, the kurtosis parameter is derived analytically and illustrated numerically. The kurtosis parameters of the Gaussian beam, modified Bessel modulated Gaussian beam with quadrature radial and elegant Laguerre-Gaussian beams are obtained by treating them as special cases of the present treatment. The obtained results show that the kurtosis parameter depends on the change of the beam order m and the hollowness parameter p, such as its decrease with increasing m and increase with increasing p.

Spectral distortion of dual-comb spectrometry due to repetition rate fluctuation

Hong-Lei Yang, Hao-Yun Wei, Yan Li
Chin. Phys. B 2016, 25 (4): 044207;  doi: 10.1088/1674-1056/25/4/044207
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Dual-comb spectrometry suffers the fluctuations of parameters in combs. We demonstrate that the repetition rate is more important than any other parameter, since the fluctuation of the repetition rate leads to a change of difference in the repetition rate between both combs, consequently causing the conversion factor variation and spectral frequency misalignment. The measured frequency noise power spectral density of the repetition rate exhibits an integrated residual frequency modulation of 1.4 Hz from 1 Hz to 100 kHz in our system. This value corresponds to the absorption peak fluctuation within a root mean square value of 0.19 cm-1 that is verified by both simulation and experimental result. Further, we can also simulate spectrum degradation as the fluctuation varies. After modifying misaligned spectra and averaging, the measured result agrees well with the simulated spectrum based on the GEISA database.

Frequency-stabilized Yb:fiber comb with a tapered single-mode fiber

Yang Xie, Hai-Nian Han, Long Zhang, Zi-Jiao Yu, Zheng Zhu, Lei Hou, Li-Hui Pang, Zhi-Yi Wei
Chin. Phys. B 2016, 25 (4): 044208;  doi: 10.1088/1674-1056/25/4/044208
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We demonstrate a stable Yb:fiber frequency comb with supercontinuum generation by using a specially designed tapered single-mode fiber, in which a spectrum spanning from 500 nm to 1500 nm is produced. The carrier-envelope offset signal of the Yb:fiber comb is measured with a signal-to-noise ratio of more than 40 dB and a linewidth narrower than 120 kHz. The repetition rate and carrier-envelope offset signals are simultaneously phase locked to a microwave reference frequency.

Modulation of terahertz generation in dual-color filaments by an external electric field and preformed plasma

Min Li, An-Yuan Li, Bo-Qu He, Shuai Yuan, He-Ping Zeng
Chin. Phys. B 2016, 25 (4): 044209;  doi: 10.1088/1674-1056/25/4/044209
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Terahertz generation driven by dual-color filaments in air is demonstrated to be remarkably enhanced by applying an external electric field to the filaments. As terahertz generation is sensitive to the dual-color phase difference, a preformed plasma is verified efficiently in modulating terahertz radiation from linear to elliptical polarization. In the presence of preformed plasma, a dual-color filament generates terahertz pulses of elliptical polarization and the corresponding ellipse rotates regularly with the change of the preformed plasma density. The observed terahertz modulation with the external electric field and the preformed plasma provides a simple way to estimate the plasma density and evaluate the photocurrent dynamics of the dual-color filaments. It provides further experimental evidence of the photo-current model in governing the dual-color filament driven terahertz generation processes.

Strip silicon waveguide for code synchronization in all-optical analog-to-digital conversion based on a lumped time-delay compensation scheme

Sha Li, Zhi-Guo Shi, Zhe Kang, Chong-Xiu Yu, Jian-Ping Wang
Chin. Phys. B 2016, 25 (4): 044210;  doi: 10.1088/1674-1056/25/4/044210
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An all-optical analog-to-digital converter (ADC) based on the nonlinear effect in a silicon waveguide is a promising candidate for overcoming the limitation of electronic devices and is suitable for photonic integration. In this paper, a lumped time-delay compensation scheme with 2-bit quantization resolution is proposed. A strip silicon waveguide is designed and used to compensate for the entire time-delays of the optical pulses after a soliton self-frequency shift (SSFS) module within a wavelength range of 1550 nm-1580 nm. A dispersion coefficient as high as -19800 ps/(km·nm) with ± 0.5 ps/(km·nm) variation is predicted for the strip waveguide. The simulation results show that the maximum supportable sampling rate (MSSR) is 50.45 GSa/s with full width at half maximum (FWHM) variation less than 2.52 ps, along with the 2-bit effective-number-of-bit and Gray code output.

Planar waveguides in neodymium-doped calcium niobium gallium garnet crystals produced by proton implantation

Chun-Xiao Liu, Meng Chen, Li-Li Fu, Rui-Lin Zheng, Hai-Tao Guo, Zhi-Guang Zhou, Wei-Nan Li, She-Bao Lin, Wei Wei
Chin. Phys. B 2016, 25 (4): 044211;  doi: 10.1088/1674-1056/25/4/044211
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In this work, the fabrication and optical properties of a planar waveguide in a neodymium-doped calcium niobium gallium garnet (Nd:CNGG) crystal are reported. The waveguide is produced by proton (H+) implantation at 480 keV and a fluence of 1.0×1017 ions/cm2. The prism-coupling measurement is performed to obtain the dark mode of the waveguide at a wavelength of 632.8 nm. The reflectivity calculation method (RCM) is used to reconstruct the refractive index profile. The finite-difference beam propagation method (FD-BPM) is employed to calculate the guided mode profile of the waveguide. The stopping and range of ions in matter 2010 (SRIM 2010) code is used to simulate the damage profile induced by the ion implantation. The experimental and theoretical results indicate that the waveguide can confine the light propagation.

Study of the temperature rise induced by a focusing transducer with a wide aperture angle on biological tissue containing ribs

Xin Wang, Jiexing Lin, Xiaozhou Liu, Jiehui Liu, Xiufen Gong
Chin. Phys. B 2016, 25 (4): 044301;  doi: 10.1088/1674-1056/25/4/044301
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We used the spheroidal beam equation to calculate the sound field created by focusing a transducer with a wide aperture angle to obtain the heat deposition, and then we used the Pennes bioheat equation to calculate the temperature field in biological tissue with ribs and to ascertain the effects of rib parameters on the temperature field. The results show that the location and the gap width between the ribs have a great influence on the axial and radial temperature rise of multilayer biological tissue. With a decreasing gap width, the location of the maximum temperature rise moves forward; as the ribs are closer to the transducer surface, the sound energy that passes through the gap between the ribs at the focus decreases, the maximum temperature rise decreases, and the location of the maximum temperature rise moves forward with the ribs.

Analytical solution based on the wavenumber integration method for the acoustic field in a Pekeris waveguide

Wen-Yu Luo, Xiao-Lin Yu, Xue-Feng Yang, Ren-He Zhang
Chin. Phys. B 2016, 25 (4): 044302;  doi: 10.1088/1674-1056/25/4/044302
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An exact solution based on the wavenumber integration method is proposed and implemented in a numerical model for the acoustic field in a Pekeris waveguide excited by either a point source in cylindrical geometry or a line source in plane geometry. Besides, an unconditionally stable numerical solution is also presented, which entirely resolves the stability problem in previous methods. Generally the branch line integral contributes to the total field only at short ranges, and hence is usually ignored in traditional normal mode models. However, for the special case where a mode lies near the branch cut, the branch line integral can contribute to the total field significantly at all ranges. The wavenumber integration method is well-suited for such problems. Numerical results are also provided, which show that the present model can serve as a benchmark for sound propagation in a Pekeris waveguide.

Initiation of vacuum breakdown and failure mechanism of the carbon nanotube during thermal field emission

Dan Cai, Lie Liu, Jin-Chuan Ju, Xue-Long Zhao, Hong-Yu Zhou, Xiao Wang
Chin. Phys. B 2016, 25 (4): 045101;  doi: 10.1088/1674-1056/25/4/045101
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The carbon nanotube (CNT)-based materials can be used as vacuum device cathodes. Owing to the excellent field emission properties of CNT, it has great potentials in the applications of an explosive field emission cathode. The falling off of CNT from the substrate, which frequently appears in experiments, restricts its application. In addition, the onset time of vacuum breakdown limits the performance of the high-power explosive-emission-cathode-based diode. In this paper, the characteristics of the CNT, electric field strength, contact resistance and the kind of substrate material are varied to study the parameter effects on the onset time of vacuum breakdown and failure mechanism of the CNT by using the finite element method.

Numerical analysis of the optimized performance of the electron cyclotron wave system in a HL-2M tokamak

Jing-Chun Li, Xue-Yu Gong, Jia-Qi Dong, Jun Wang, Lan Yin
Chin. Phys. B 2016, 25 (4): 045201;  doi: 10.1088/1674-1056/25/4/045201
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The capabilities of current drive, neoclassical tearing mode (NTM) stabilization, and sawtooth control are analyzed for the electron-cyclotron wave (ECW) system in a HL-2M tokamak. Better performance of the upper launcher is demonstrated in comparison with that of a dropped upper launcher, in terms of JEC/Jbs for NTM stabilization and IECCD/(Δρtor)2 for sawtooth control. 1-MW ECW power is enough for the 3/2 NTM stabilization, and 1.8-MW ECW power is required to suppress 2/1 NTM in a single null divertor equilibrium with 1.2-MA toroidal current with the upper launcher. Optimization simulation of electron-cyclotron current drive (ECCD) is carried out for three mirrors in an equatorial port, indicating that the middle mirror has a good performance compared with the top and bottom mirrors. The results for balanced co-and counter-ECCD in an equatorial port are also presented.

Surface diffuse discharge mechanism of well-aligned atmospheric pressure microplasma arrays

Ren-Wu Zhou, Ru-Sen Zhou, Jin-Xing Zhuang, Jiang-Wei Li, Mao-Dong Chen, Xian-Hui Zhang, Dong-Ping Liu, Kostya Ostrikov, Si-Ze Yang
Chin. Phys. B 2016, 25 (4): 045202;  doi: 10.1088/1674-1056/25/4/045202
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A stable and homogeneous well-aligned air microplasma device for application at atmospheric pressure is designed and its electrical and optical characteristics are investigated. Current-voltage measurements and intensified charge coupled device (ICCD) images show that the well-aligned air microplasma device is able to generate a large-area and homogeneous discharge at the applied voltages ranging from 12 kV to 14 kV, with a repetition frequency of 5 kHz, which is attributed to the diffusion effect of plasma on dielectric surface. Moreover, this well-aligned microplasma device may result in the uniform and large-area surface modification of heat-sensitive PET polymers without damage, such as optimization in hydrophobicity and biocompatibility. In the biomedical field, the utility of this well-aligned microplasma device is further testified. It proves to be very efficient for the large-area and uniform inactivation of E. coli cells with a density of 103/cm2 on LB agar plate culture medium, and inactivation efficiency can reach up to 99% for 2-min treatment.

Electrical and optical characteristics of the radio frequency surface dielectric barrier discharge plasma actuation

Wei-Long Wang, Hui-Min Song, Jun Li, Min Jia, Yun Wu, Di Jin
Chin. Phys. B 2016, 25 (4): 045203;  doi: 10.1088/1674-1056/25/4/045203
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Electrical characteristics and optical emission spectrum of the radio frequency (RF) surface dielectric barrier discharge (SDBD) plasma actuation are investigated experimentally in this paper. Influences of operating pressure, duty cycle and load power on the discharge are analyzed. When the operating pressure reaches 30 kPa, the discharge energy calculated from the Charge-Voltage (Q-V) Lissajous figure increases significantly, while the effective capacitance decreases remarkably. As the duty cycle of the applied voltage increases, the voltage-current waveforms, the area of Q-V loop and the capacity show no distinct changes. Below 40 W, effective capacitance increases with the increase of load power, but it almost remains unchanged when load power is between 40 W and 95 W. The relative intensity I391.4peak/I380.5peak changes little as the operating pressure varies from 4 kPa to 100 kPa, while it rises evidently with the pressure below 4 kPa, which indicates that the RF discharge mode shifts from filamentary discharge to glow discharge at around 4 kPa. With the increase of load power, the relative intensity I391.4peak/I380.5peak rises evidently. Additionally, the relative intensity I371.1peak/I380.5peak is insensitive to the pressure, the duty cycle, and the load power.

Characteristics of droplets ejected from liquid glycerol doped with carbon in laser ablation propulsion

Zhi-Yuan Zheng, Si-Qi Zhang, Tian Liang, Lu Gao, Hua Gao, Zi-Li Zhang
Chin. Phys. B 2016, 25 (4): 045204;  doi: 10.1088/1674-1056/25/4/045204
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The characteristics of droplets ejected from liquid glycerol doped with carbon are investigated in laser ablation propulsion. Results show that carbon content has an effect on both the coupling coefficient and the specific impulse. The doped-carbon moves the laser focal position from the glycerol interior to the surface. This results in a less consumed glycerol and a high specific impulse. An optimal propulsion can be realized by varying carbon content in glycerol.

Microstructure and lateral conductivity control of hydrogenated nanocrystalline silicon oxide and its application in a-Si:H/a-SiGe:H tandem solar cells

Tian-Tian Li, Tie Yang, Jia Fang, De-Kun Zhang, Jian Sun, Chang-Chun Wei, Sheng-Zhi Xu, Guang-Cai Wang, Cai-Chi Liu, Ying Zhao, Xiao-Dan Zhang
Chin. Phys. B 2016, 25 (4): 046101;  doi: 10.1088/1674-1056/25/4/046101
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Phosphorous-doped hydrogenated nanocrystalline silicon oxide (n-nc-SiOx:H) films are prepared via radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). Increasing deposition power during n-nc-SiOx:H film growth process can enhance the formation of nanocrystalline and obtain a uniform microstructure of n-nc-SiOx:H film. In addition, in 20s interval before increasing the deposition power, high density small grains are formed in amorphous SiOx matrix with higher crystalline volume fraction (Ic) and have a lower lateral conductivity. This uniform microstructure indicates that the higher Ic can leads to better vertical conductivity, lower refractive index, wider optical band-gap. It improves the back reflection in a-Si:H/a-SiGe:H tandem solar cells acting as an n-nc-SiOx:H back reflector prepared by the gradient power during deposition. Compared with the sample with SiOx back reflector, with a constant power used in deposition process, the sample with gradient power SiOx back reflector can enhance the total short-circuit current density (Jsc) and the initial efficiency of a-Si:H/a-SiGe:H tandem solar cells by 8.3% and 15.5%, respectively.

Pressure-induced solidifications of liquid sulfur below and above λ-transition

Fei Tang, Lin-Ji Zhang, Feng-Liang Liu, Fei Sun, Wen-Ge Yang, Jun-Long Wang, Xiu-Ru Liu, Ru Shen
Chin. Phys. B 2016, 25 (4): 046102;  doi: 10.1088/1674-1056/25/4/046102
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Two kinds of glassy sulfurs are synthesized by the rapid compression method from liquid sulfur at temperatures below and above the λ-transition point. The glassy sulfur has different colors and transparencies, depending on temperature, which may inherit some structural information from the λ-transition. Raman spectrum studies of these samples show that a large fraction of polymeric chains exist in the glassy sulfur, even in the one solidified from T < Tλ. We find that a higher compression rate instead of a higher temperature of the parent liquid captures more polymeric chains. Pressure-induced glassy sulfur presents high thermal stability compared with temperature quenched glassy sulfur and could transform into liquid sulfur directly without crystallization through an abnormal exothermic melting course. High energy x-ray diffraction is utilized to study the local order of the pressure-induced glassy sulfur.

Convenient synthesis of stable silver quantum dots with enhanced photoluminescence emission by laser fragmentation

Shuang Li, Ming Chen
Chin. Phys. B 2016, 25 (4): 046103;  doi: 10.1088/1674-1056/25/4/046103
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A new strategy for the facile synthesis of very stable and mono-dispersed silver (Ag) quantum dots (QDs) is developed by laser fragmentation of bulk Ag in water using polysorbate 80 as a dispersing and stabilizing agent. The surfactant plays an important role in the formation of size-controlled Ag nano-structures. The Ag QDs have excellent photo-stability of ~500 h and enhanced photoluminescence (PL) at 510 nm. This has significant implications for selective and ultrasensitive PL probes. Based on laser fragmentation in the biocompatible surfactant solution, our results have opened up a novel paradigm to obtain stable metal QDs directly from bulk targets. This is a breakthrough in the toxicity problems that arise from standard chemical fabrication.

Radiation-induced 1/f noise degradation of PNP bipolar junction transistors at different dose rates

Qi-Feng Zhao, Yi-Qi Zhuang, Jun-Lin Bao, Wei Hu
Chin. Phys. B 2016, 25 (4): 046104;  doi: 10.1088/1674-1056/25/4/046104
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It is found that ionizing-radiation can lead to the base current and the 1/f noise degradations in PNP bipolar junction transistors. In this paper, it is suggested that the surface of the space charge region of the emitter-base junction is the main source of the base surface 1/f noise. A model is developed which identifies the parameters and describes their interactive contributions to the recombination current at the surface of the space charge region. Based on the theory of carrier number fluctuation and the model of surface recombination current, a 1/f noise model is developed. This model suggests that 1/f noise degradations are the result of the accumulation of oxide-trapped charges and interface states. Combining models of ELDRS, this model can explain the reason why the 1/f noise degradation is more severe at a low dose rate than at a high dose rate. The radiations were performed in a Co60 source up to a total dose of 700 Gy(Si). The low dose rate was 0.001 Gy(Si)/s and the high dose rate was 0.1 Gy(Si)/s. The model accords well with the experimental results.

Large scale silver nanowires network fabricated by MeV hydrogen (H+) ion beam irradiation

Honey S, Naseem S, Ishaq A, Maaza M, Bhatti M T, Wan D
Chin. Phys. B 2016, 25 (4): 046105;  doi: 10.1088/1674-1056/25/4/046105
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A random two-dimensional large scale nano-network of silver nanowires (Ag-NWs) is fabricated by MeV hydrogen (H+) ion beam irradiation. Ag-NWs are irradiated under H+ ion beam at different ion fluences at room temperature. The Ag-NW network is fabricated by H+ ion beam-induced welding of Ag-NWs at intersecting positions. H+ ion beam induced welding is confirmed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Moreover, the structure of Ag NWs remains stable under H+ ion beam, and networks are optically transparent. Morphology also remains stable under H+ ion beam irradiation. No slicings or cuttings of Ag-NWs are observed under MeV H+ ion beam irradiation. The results exhibit that the formation of Ag-NW network proceeds through three steps: ion beam induced thermal spikes lead to the local heating of Ag-NWs, the formation of simple junctions on small scale, and the formation of a large scale network. This observation is useful for using Ag-NWs based devices in upper space where protons are abandoned in an energy range from MeV to GeV. This high-quality Ag-NW network can also be used as a transparent electrode for optoelectronics devices.

Channeling of fast ions through the bent carbon nanotubes: The extended two-fluid hydrodynamic model

Lazar Karbunar, Duško Borka, Ivan Radović, Zoran L Mišković
Chin. Phys. B 2016, 25 (4): 046106;  doi: 10.1088/1674-1056/25/4/046106
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We investigate the interactions of charged particles with straight and bent single-walled carbon nanotubes (SWNTs) under channeling conditions in the presence of dynamic polarization of the valence electrons in carbon. This polarization is described by a cylindrical, two-fluid hydrodynamic model with the parameters taken from the recent modelling of several independent experiments on electron energy loss spectroscopy of carbon nano-structures. We use the hydrodynamic model to calculate the image potential for protons moving through four types of SWNTs at a speed of 3 atomic units. The image potential is then combined with the Doyle-Turner atomic potential to obtain the total potential in the bent carbon nanotubes. Using that potential, we also compute the spatial and angular distributions of protons channeled through the bent carbon nanotubes, and compare the results with the distributions obtained without taking into account the image potential.

Complete low-frequency bandgap in a two-dimensional phononic crystal with spindle-shaped inclusions

Ting Wang, Hui Wang, Mei-Ping Sheng, Qing-Hua Qin
Chin. Phys. B 2016, 25 (4): 046301;  doi: 10.1088/1674-1056/25/4/046301
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A two-dimensional phononic crystal (PC) structure possessing a relatively low frequency range of complete bandgap is presented. The structure is composed of periodic spindle-shaped plumbum inclusions in a rubber matrix which forms a square lattice. The dispersion relation, transmission spectrum and displacement field are studied using the finite element method in conjunction with the Bloch theorem. Numerical results show that the present PC structure can achieve a large complete bandgap in a relatively low frequency range compared with two inclusions of different materials, which is useful in low-frequency noise and vibration control and can be designed as a low frequency acoustic filter and waveguides. Moreover, the transmission spectrum and effective mass are evaluated to validate the obtained band structure. It is interesting to see that within the band gap the effective mass becomes negative, resulting in an imaginary wave speed and wave exponential attenuation. Finally, sensitivity analysis of the effect of geometrical parameters of the presented PC structure on the lowest bandgap is performed to investigate the variations of the bandgap width and frequency.

Structure phase transformation and equation of state of cerium metal under pressures up to 51 GPa

Ce Ma, Zuo-Yong Dou, Hong-Yang Zhu, Guang-Yan Fu, Xiao Tan, Bin Bai, Peng-Cheng Zhang, Qi-Liang Cui
Chin. Phys. B 2016, 25 (4): 046401;  doi: 10.1088/1674-1056/25/4/046401
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This study presents high pressure phase transitions and equation of states of cerium under pressures up to 51 GPa at room temperature. The angle-dispersive x-ray diffraction experiments are carried out using a high energy synchrotron x-ray source. The bulk moduli of high pressure phases of cerium are calculated using the Birch-Murnaghan equation. We discuss and correct several previous controversial conclusions, which are caused by the measurement accuracy or personal explanation. The c/a axial ratio of ε-Ce has a maximum value at about 29 GPa, i.e., c/a ≈ 1.690.

Optoelectronic properties of SnO2 thin films sprayed at different deposition times

Allag Abdelkrim, Saâd Rahmane, Ouahab Abdelouahab, Attouche Hafida, Kouidri Nabila
Chin. Phys. B 2016, 25 (4): 046801;  doi: 10.1088/1674-1056/25/4/046801
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This article presents the elaboration of tin oxide (SnO2) thin films on glass substrates by using a home-made spray pyrolysis system. Effects of film thickness on the structural, optical, and electrical film properties are investigated. The films are characterized by several techniques such as x-ray diffraction (XRD), atomic force microscopy (AFM), ultraviolet-visible (UV-Vis) transmission, and four-probe point measurements, and the results suggest that the prepared films are uniform and well adherent to the substrates. X-ray diffraction (XRD) patterns show that SnO2 film is of polycrystal with cassiterite tetragonal crystal structure and a preferential orientation along the (110) plane. The calculated grain sizes are in a range from 32.93 nm to 56.88 nm. Optical transmittance spectra of the films show that their high transparency average transmittances are greater than 65% in the visible region. The optical gaps of SnO2 thin films are found to be in a range of 3.64 eV-3.94 eV. Figures of merit for SnO2 thin films reveal that their maximum value is about 1.15×10-4 Ω-1 at λ = 550 nm. Moreover, the measured electrical resistivity at room temperature is on the order of 10-2 Ω·cm.

Investigations of mechanical, electronic, and magnetic properties of non-magnetic MgTe and ferro-magnetic Mg0.75TM0.25Te (TM=Fe, Co, Ni): An ab-initio calculation

Mahmood Q, Alay-e-Abbas S M, Mahmood I, Asif Mahmood, Noor N A
Chin. Phys. B 2016, 25 (4): 047101;  doi: 10.1088/1674-1056/25/4/047101
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The mechanical, electronic and magnetic properties of non-magnetic MgTe and ferro-magnetic (FM) Mg0.75TM0.25Te (TM = Fe, Co, Ni) in the zinc-blende phase are studied by ab-initio calculations for the first time. We use the generalized gradient approximation functional for computing the structural stability, and mechanical properties, while the modified Becke and Johnson local (spin) density approximation (mBJLDA) is utilized for determining the electronic and magnetic properties. By comparing the energies of non-magnetic and FM calculations, we find that the compounds are stable in the FM phase, which is confirmed by their structural stabilities in terms of enthalpy of formation. Detailed descriptions of elastic properties of Mg0.75TM0.25Te alloys in the FM phase are also presented. For electronic properties, the spin-polarized electronic band structures and density of states are computed, showing that these compounds are direct bandgap materials with strong hybridizations of TM 3d states and Te p states. Further, the ferromagnetism is discussed in terms of the Zener free electron model, RKKY model and double exchange model. The charge density contours in the (110) plane are calculated to study bonding properties. The spin exchange splitting and crystal field splitting energies are also calculated. The distribution of electron spin density is employed in computing the magnetic moments appearing at the magnetic sites (Fe, Co, Ni), as well as at the non-magnetic sites (Mg, Te). It is found that the p-d hybridization causes not only magnetic moments on the magnetic sites but also induces negligibly small magnetic moments at the non-magnetic sites.

Fabrications and characterizations of high performance 1.2 kV, 3.3 kV, and 5.0 kV class 4H-SiC power SBDs

Qing-Wen Song, Xiao-Yan Tang, Hao Yuan, Yue-Hu Wang, Yi-Meng Zhang, Hui Guo, Ren-Xu Jia, Hong-Liang Lv, Yi-Men Zhang, Yu-Ming Zhang
Chin. Phys. B 2016, 25 (4): 047102;  doi: 10.1088/1674-1056/25/4/047102
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In this paper, 1.2 kV, 3.3 kV, and 5.0 kV class 4H-SiC power Schottky barrier diodes(SBDs)are fabricated with three N-type drift layer thickness values of 10 μm, 30 μm, and 50 μm, respectively. The avalanche breakdown capabilities, static and transient characteristics of the fabricated devices are measured in detail and compared with the theoretical predictions. It is found that the experimental results match well with the theoretical calculation results and are very close to the 4H-SiC theoretical limit line. The best achieved breakdown voltages (BVs) of the diodes on the 10 μm, 30 μm, and 50 μm epilayers are 1400 V, 3320 V, and 5200 V, respectively. Differential specific-on resistances (Ron-sp) are 2.1 mΩ ·cm2, 7.34 mΩ·cm2, and 30.3 mΩ·cm2, respectively.

Inverted polymer solar cells with employing of electrochemical-anodizing synthesized TiO2 nanotubes

Mehdi Ahmadi, Sajjad Rashidi Dafeh, Hamed Fatehy
Chin. Phys. B 2016, 25 (4): 047201;  doi: 10.1088/1674-1056/25/4/047201
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An inverted structure of polymer solar cells based on Poly(3-hexylthiophene)(P3HT):[6-6] Phenyl-(6) butyric acid methyl ester (PCBM) with using thin films of TiO2 nanotubes and nanoparticles as an efficient cathode buffer layer is developed. A total of three cells employing TiO2 thin films with different thickness values are fabricated. Two cells use layers of TiO2 nanotubes prepared via self-organized electrochemical-anodizing leading to thickness values of 203 and 423.7 nm, while the other cell uses only a simple sol-gel synthesized TiO2 thin film of nanoparticles with a thickness of 100 nm as electron transport layer. Experimental results demonstrate that TiO2 nanotubes with these thickness values are inefficient as the power conversion efficiency of the cell using 100-nm TiO2 thin film is 1.55%, which is more than the best power conversion efficiency of other cells. This can be a result of the weakness of the electrochemical anodizing method to grow nanotubes with lower thickness values. In fact as the TiO2 nanotubes grow in length the series resistance (Rs) between the active polymer layer and electron transport layer increases, meanwhile the fill factor of cells falls dramatically which finally downgrades the power conversion efficiency of the cells as the fill factor falls.

Design of terahertz beam splitter based on surface plasmon resonance transition

Xiang Liu, Dong-Xiao Yang
Chin. Phys. B 2016, 25 (4): 047301;  doi: 10.1088/1674-1056/25/4/047301
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According to the resonance transition between propagating surface plasmon and localized surface plasmon, we demonstrate a design of beam splitter that can split terahertz wave beams in a relatively broad frequency range. The transmission properties of the beam splitter are analyzed utilizing the finite element method. The resonance transition between two kinds of plasmons can be explained by a model of coherent electron cloud displacement.

Excitonic transitions in Be-doped GaAs/AlAs multiple quantum well

Wei-Min Zheng, Su-Mei Li, Wei-Yan Cong, Ai-Fang Wang, Bin Li, Hai-Bei Huang
Chin. Phys. B 2016, 25 (4): 047302;  doi: 10.1088/1674-1056/25/4/047302
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A series of GaAs/AlAs multiple-quantum wells doped with Be is grown by molecular beam epitaxy. The photoluminescence spectra are measured at 4, 20, 40, 80, 120, and 200 K, respectively. The recombination transition emission of heavy-hole and light-hole free excitons is clearly observed and the transition energies are measured with different quantum well widths. In addition, a theoretical model of excitonic states in the quantum wells is used, in which the symmetry of the component of the exciton wave function representing the relative motion is allowed to vary between the two-and three-dimensional limits. Then, within the effective mass and envelope function approximation, the recombination transition energies of the heavy-and light-hole excitons in GaAs/AlAs multiple-quantum wells are calculated each as a function of quantum well width by the shooting method and variational principle with two variational parameters. The results show that the excitons are neither 2D nor 3D like, but are in between in character and that the theoretical calculation is in good agreement with the experimental results.

Dirac operator on the sphere with attached wires

E N Grishanov, D A Eremin, D A Ivanov, I Yu Popov
Chin. Phys. B 2016, 25 (4): 047303;  doi: 10.1088/1674-1056/25/4/047303
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An explicitly solvable model for tunnelling of relativistic spinless particles through a sphere is suggested. The model operator is constructed by an operator extensions theory method from the orthogonal sum of the Dirac operators on a semi-axis and on the sphere. The transmission coefficient is obtained. The dependence of the transmission coefficient on the particle energy has a resonant character. One observes pairs of the Breit-Wigner and the Fano resonances. It correlates with the corresponding results for a non-relativistic particle.

Study on electrical defects level in single layer two-dimensional Ta2O5

Dahai Li, Xiongfei Song, Linfeng Hu, Ziyi Wang, Rongjun Zhang, Liangyao Chen, David Wei Zhang, Peng Zhou
Chin. Phys. B 2016, 25 (4): 047304;  doi: 10.1088/1674-1056/25/4/047304
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Two-dimensional atomic-layered material is a recent research focus, and single layer Ta2O5 used as gate dielectric in field-effect transistors is obtained via assemblies of Ta2O5 nanosheets. However, the electrical performance is seriously affected by electronic defects existing in Ta2O5. Therefore, spectroscopic ellipsometry is used to calculate the transition energies and corresponding probabilities for two different charged oxygen vacancies, whose existence is revealed by x-ray photoelectron spectroscopy analysis. Spectroscopic ellipsometry fitting also calculates the thickness of single layer Ta2O5, exhibiting good agreement with atomic force microscopy measurement. Nondestructive and noncontact spectroscopic ellipsometry is appropriate for detecting the electrical defects level of single layer Ta2O5.

An analytical model for nanowire junctionless SOI FinFETs with considering three-dimensional coupling effect

Fan-Yu Liu, Heng-Zhu Liu, Bi-Wei Liu, Yu-Feng Guo
Chin. Phys. B 2016, 25 (4): 047305;  doi: 10.1088/1674-1056/25/4/047305
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In this paper, the three-dimensional (3D) coupling effect is discussed for nanowire junctionless silicon-on-insulator (SOI) FinFETs. With fin width decreasing from 100 nm to 7 nm, the electric field induced by the lateral gates increases and therefore the influence of back gate on the threshold voltage weakens. For a narrow and tall fin, the lateral gates mainly control the channel and therefore the effect of back gate decreases. A simple two-dimensional (2D) potential model is proposed for the subthreshold region of junctionless SOI FinFET. TCAD simulations validate our model. It can be used to extract the threshold voltage and doping concentration. In addition, the tuning of back gate on the threshold voltage can be predicted.

Numerical simulation of the magnetoresistance effect controlled by electric field in p-n junction

Pan Yang, Wen-Jie Chen, Jiao Wang, Zhao-Wen Yan, Jian-Li Qiao, Tong Xiao, Xin Wang, Zheng-Peng Pang, Jian-Hong Yang
Chin. Phys. B 2016, 25 (4): 047306;  doi: 10.1088/1674-1056/25/4/047306
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The magnetoresistance effect of a p-n junction under an electric field which is introduced by the gate voltage at room temperature is investigated by simulation. As auxiliary models, the Lombardi CVT model and carrier generation-recombination model are introduced into a drift-diffusion transport model and carrier continuity equations. All the equations are discretized by the finite-difference method and the box integration method and then solved by Newton iteration. Taking advantage of those models and methods, an abrupt junction with uniform doping is studied systematically, and the magnetoresistance as a function of doping concentration, SiO2 thickness and geometrical size is also investigated. The simulation results show that the magnetoresistance (MR) can be controlled substantially by the gate and is dependent on the polarity of the magnetic field.

Effects of Mg substitution on the structural and magnetic properties of Co0.5Ni0.5-xMgxFe2O4 nanoparticle ferrites

R M Rosnan, Z Othaman, R Hussin, Ali A Ati, Alireza Samavati, Shadab Dabagh, Samad Zare
Chin. Phys. B 2016, 25 (4): 047501;  doi: 10.1088/1674-1056/25/4/047501
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In this study, nanocrystalline Co-Ni-Mg ferrite powders with composition Co0.5Ni0.5-xMgxFe2O4 are successfully synthesized by the co-precipitation method. A systematic investigation on the structural, morphological and magnetic properties of un-doped and Mg-doped Co-Ni ferrite nanoparticles is carried out. The prepared samples are characterized using x-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and vibrating sample magnetometry (VSM). The XRD analyses of the synthesized samples confirm the formation of single-phase cubic spinel structures with crystallite sizes in a range of ~32 nm to ~36 nm. The lattice constant increases with increasing Mg content. FESEM images show that the synthesized samples are homogeneous with a uniformly distributed grain. The results of IR spectroscopy analysis indicate the formation of functional groups of spinel ferrite in the co-precipitation process. By increasing Mg2+ substitution, room temperature magnetic measurement shows that maximum magnetization and coercivity increase from ~57.35 emu/g to ~61.49 emu/g and ~603.26 Oe to ~684.11 Oe (1 Oe=79.5775 A·m-1), respectively. The higher values of magnetization Ms and Mr suggest that the optimum composition is Co0.5Ni0.4Mg0.1Fe2O4 that can be applied to high-density recording media and microwave devices.

Spin-cluster glass state in U(Ga0.95Mn0.05)3

Dong-Hua Xie, Wen Zhang, Yi Liu, Wei Feng, Yun Zhang, Shi-Yong Tan, Xie-Gang Zhu, Qiu-Yun Chen, Qin Liu, Bing-Kai Yuan, Xin-Chun Lai
Chin. Phys. B 2016, 25 (4): 047502;  doi: 10.1088/1674-1056/25/4/047502
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We report the study of a low temperature cluster glass state in 5% Mn-doped UGa3} heavy fermion compound. This compound transforms from a paramagnetic state to a spin-cluster glass state, which is confirmed by measuring the dc susceptibility and magnetization. The ac susceptibility exhibits a frequency-dependent peak around Tf, which provides direct evidence of the cluster glass state. By analyzing the field-dependent magnetization and frequency-dependent ac susceptibility in detail, we deduce that this compound forms a spin-cluster glass state below Tf.

Study of magnetization reversal and anisotropy of single crystalline ultrathin Fe/MgO (001) film by magneto-optic Kerr effect

Miao-Ling Zhang, Jun Ye, Rui Liu, Shu Mi, Yong Xie, Hao-Liang Liu, Chris Van Haesendonck, Zi-Yu Chen
Chin. Phys. B 2016, 25 (4): 047503;  doi: 10.1088/1674-1056/25/4/047503
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The magnetization reversal process of Fe/MgO (001) thin film is investigated by combining transverse and longitudinal hysteresis loops. Owing to the competition between domain wall pinning energy and weak uniaxial magnetic anisotropy,the typical magnetization reversal process of Fe ultrathin film can take place via either an “l-jump” process near the easy axis, or a “2-jump” process near the hard axis, depending on the applied field orientation. Besides, the hysteresis loop presents strong asymmetry resulting from the variation of the detected light intensity due to the quadratic magneto-optic effect. Furthermore, we modify the detectable light intensity formula and simulate the hysteresis loops of the Kerr signal. The results show that they are in good agreement with the experimental data.

Magnetic transition behavior of perovskite manganites Nd0.5Sr0.3Ca0.2MnO3 polycrystalline

Ru Xing, Su-Lei Wan, Wen-Qing Wang, Lin Zheng, Xiang Jin, Min Zhou, Yi Lu, Jian-Jun Zhao
Chin. Phys. B 2016, 25 (4): 047601;  doi: 10.1088/1674-1056/25/4/047601
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A polycrystalline sample Nd0.5Sr0.3Ca0.2MnO3 is prepared by the conventional solid state reaction method. The structure and magnetic properties are investigated with x-ray diffraction (XRD) patterns, a superconducting quantum interference device (SQUID), and electron spin resonance (ESR). The sample is in single phase with the space group Pbnm symmetry. With the decrease of temperature, Nd0.5Sr0.3Ca0.2MnO3 undergoes three magnetic transitions: ferromagnetic transition at TC ≈ 210 K, charge-ordering at TCO ≈ 175 K, and antiferromagnetic transition at TN=155 K. In addition, the activation energy Ea ≈ 52.78 meV can be extracted by curve fitting.

Apparent directional spectral emissivity determination of semitransparent materials

Chun-Yang Niu, Hong Qi, Ya-Tao Ren, Li-Ming Ruan
Chin. Phys. B 2016, 25 (4): 047801;  doi: 10.1088/1674-1056/25/4/047801
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An inverse estimation method and corresponding measurement system are developed to measure the apparent spectral directional emissivities of semitransparent materials. The normal spectral emissivity and transmissivity serve as input for the inverse analysis. Consequently, the refractive index and absorption coefficient of the semitransparent material could be retrieved by using the pseudo source adding method as the forward method and the stochastic particle swarm optimization algorithm as the inverse method. Finally, the arbitrary apparent spectral directional emissivity of semitransparent material is estimated by using the pseudo source adding method given the retrieval refractive index and absorption coefficient. The present system has the advantage of a simple experimental structure, high accuracy, and excellent capability to measure the emissivity in an arbitrary direction. Furthermore, the apparent spectral directional emissivity of sapphire at 773 K is measured by using this system in a spectral range of 3 μm-12 μm and a viewing range of 0°-90°. The present method paves the way for a new directional spectral emissivity measurement strategy.

Effect of co-doped metal caions on the properties of Y2O3:Eu3+ phosphors synthesized by gel-combustion method

Hui Shi, Xi-Yan Zhang, Wei-Li Dong, Xiao-Yun Mi, Neng-Li Wang, Yan Li, Hong-Wei Liu
Chin. Phys. B 2016, 25 (4): 047802;  doi: 10.1088/1674-1056/25/4/047802
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Y2O3:Eu3+ phosphors co-doped with different metal cations (Li+, Na+, K+, Mg2+, Ca2+) are prepared by the gel-combustion method with Y2O3, Eu2O3, and R(NO3)x (R=Li, Na, K, Mg, Ca) serving as raw materials and glycine as fuel, calcined at 1000 ℃ for 2 h. The synthesized Y2O3:Eu3+ phosphors doped with different metal cations and doping ratios are characterized by x-ray diffractometry (XRD), fluorescence and phosphorescent spectrophotometer. The co-doping metal cations are advantageous to the development of Y2O3:Eu3+ lattice. All the samples can emit red light peaked at 611 nm under 254-nm excited. The luminescence intensities of co-doping samples are increased because the cations increase the electron transition probability of Eu3+ from 5D0 level to 7F level. The fluorescence lifetime of Eu3+ (5D07F2) is increased by doping metal cations.
SPECIAL TOPIC—Non-equilibrium phenomena in soft matters

Field emission properties of a-C and a-C:H films deposited on silicon surfaces modified with nickel nanoparticles

Jin-Long Jiang, Yu-Bao Wang, Qiong Wang, Hao Huang, Zhi-Qiang Wei, Jun-Ying Hao
Chin. Phys. B 2016, 25 (4): 048101;  doi: 10.1088/1674-1056/25/4/048101
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The a-C and a-C:H films are deposited on silicon surfaces modified with and without nickel nanoparticles by using mid-frequency magnetron sputtering. The microstructures and morphologies of the films are analyzed by Raman spectroscopy and atomic force microscopy. Field emission behaviors of the deposited films with and without nickel nanoparticles modification are comparatively investigated. It is found that the hydrogen-free carbon film exhibits a high field emission current density and low turn-on electric field compared with the hydrogenated carbon film. Nickel modifying could increase the current density, whereas it has no significant effect on the turn-on electric field. The mechanism of field electron emission of a sample is discussed from the surface morphologies of the films and nickel nanoparticle roles in the interface between film and substrate.

Graphene/polyaniline composite sponge of three-dimensional porous network structure as supercapacitor electrode

Jiu-Xing Jiang, Xu-Zhi Zhang, Zhen-Hua Wang, Jian-Jun Xu
Chin. Phys. B 2016, 25 (4): 048102;  doi: 10.1088/1674-1056/25/4/048102
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As a supercapacitor electrode, the graphene/polyaniline (PANI) composite sponge with a three-dimensional (3D) porous network structure is synthesized by a simple three-step method. The three steps include an in situ polymerization, freeze-drying and reduction by hydrazine vapor. The prepared sponge has a large specific surface area and porous network structure, so it is in favor of spreading the electrolyte ion and increasing the charge transfer efficiency of the system. The process of preparation is simple, easy to operate and low cost. The composite sponge shows better electrochemical performance than the pure individual graphene sponge while PANI cannot keep the shape of a sponge. Such a composite sponge exhibits specific capacitances of 487 F·g-1 at 2 mV/s compared to pristine PANI of 397 F·g-1.

Effects of catalyst height on diamond crystal morphology under high pressure and high temperature

Ya-Dong Li, Xiao-Peng Jia, Bing-Min Yan, Ning Chen, Chao Fang, Yong Li, Hong-An Ma
Chin. Phys. B 2016, 25 (4): 048103;  doi: 10.1088/1674-1056/25/4/048103
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The effect of the catalyst height on the morphology of diamond crystal is investigated by means of temperature gradient growth (TGG) under high pressure and high temperature (HPHT) conditions with using a Ni-based catalyst in this article. The experimental results show that the morphology of diamond changes from an octahedral shape to a cub-octahedral shape as the catalyst height rises. Moreover, the finite element method (FEM) is used to simulate the temperature field of the melted catalyst/solvent. The results show that the temperature at the location of the seed diamond continues to decrease with the increase of catalyst height, which is conducive to changing the morphology of diamond. This work provides a new way to change the diamond crystal morphology.

Subsurface defect characterization and laser-induced damage performance of fused silica optics polished with colloidal silica and ceria

Xiang He, Gang Wang, Heng Zhao, Ping Ma
Chin. Phys. B 2016, 25 (4): 048104;  doi: 10.1088/1674-1056/25/4/048104
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This paper mainly focuses on the influence of colloidal silica polishing on the damage performance of fused silica optics. In this paper, nanometer sized colloidal silica and micron sized ceria are used to polish fused silica optics. The colloidal silica polished samples and ceria polished samples exhibit that the root-mean-squared (RMS) average surface roughness values are 0.7 nm and 1.0 nm, respectively. The subsurface defects and damage performance of the polished optics are analyzed and discussed. It is revealed that colloidal silica polishing will introduce much fewer absorptive contaminant elements and subsurface damages especially no trailing indentation fracture. The 355-nm laser damage test reveals that each of the fused silica samples polished with colloidal silica has a much higher damage threshold and lower damage density than ceria polished samples. Colloidal silica polishing is potential in manufacturing high power laser optics.

Aluminum incorporation efficiencies in A-and C-plane AlGaN grown by MOVPE

Dong-Yue Han, Hui-Jie Li, Gui-Juan Zhao, Hong-Yuan Wei, Shao-Yan Yang, Lian-Shan Wang
Chin. Phys. B 2016, 25 (4): 048105;  doi: 10.1088/1674-1056/25/4/048105
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The aluminum incorporation efficiencies in nonpolar A-plane and polar C-plane AlGaN films grown by metalorganic vapour phase epitaxy (MOVPE) are investigated. It is found that the aluminum content in A-plane AlGaN film is obviously higher than that in the C-plane sample when the growth temperature is above 1070 ℃. The high aluminum incorporation efficiency is beneficial to fabricating deep ultraviolet optoelectronic devices. Moreover, the influences of the gas inlet ratio, the V/III ratio, and the chamber pressure on the aluminum content are studied. The results are important for growing the AlGaN films, especially nonpolar AlGaN epilayers.

Computational analysis of the roles of biochemical reactions in anomalous diffusion dynamics

Naruemon Rueangkham, Charin Modchang
Chin. Phys. B 2016, 25 (4): 048201;  doi: 10.1088/1674-1056/25/4/048201
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Most biochemical processes in cells are usually modeled by reaction-diffusion (RD) equations. In these RD models, the diffusive process is assumed to be Gaussian. However, a growing number of studies have noted that intracellular diffusion is anomalous at some or all times, which may result from a crowded environment and chemical kinetics. This work aims to computationally study the effects of chemical reactions on the diffusive dynamics of RD systems by using both stochastic and deterministic algorithms. Numerical method to estimate the mean-square displacement (MSD) from a deterministic algorithm is also investigated. Our computational results show that anomalous diffusion can be solely due to chemical reactions. The chemical reactions alone can cause anomalous sub-diffusion in the RD system at some or all times. The time-dependent anomalous diffusion exponent is found to depend on many parameters, including chemical reaction rates, reaction orders, and chemical concentrations.

Effects of Shannon entropy and electric field on polaron in RbCl triangular quantum dot

M Tiotsop, A J Fotue, S C Kenfack, N Issofa, H Fotsin, L C Fai
Chin. Phys. B 2016, 25 (4): 048401;  doi: 10.1088/1674-1056/25/4/048401
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In this paper, the time evolution of the quantum mechanical state of a polaron is examined using the Pekar type variational method on the condition of the electric-LO-phonon strong-coupling and polar angle in RbCl triangular quantum dot. We obtain the eigenenergies, and the eigenfunctions of the ground state, and the first excited state respectively. This system in a quantum dot can be treated as a two-level quantum system qubit and the numerical calculations are performed. The effects of Shannon entropy and electric field on the polaron in the RbCl triangular quantum dot are also studied.

Analysis and experiments of self-injection magnetron

Yi Zhang, Wen-Jun Ye, Ping Yuan, Huan-Cheng Zhu, Yang Yang, Ka-Ma Huang
Chin. Phys. B 2016, 25 (4): 048402;  doi: 10.1088/1674-1056/25/4/048402
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Magnetrons are widely used in microwave-based industrial applications, which are rapidly developing. However, the coupling between their output frequency and power as well as their wideband spectra restricts their further application. In this work, the output frequency and power of a magnetron are decoupled by self-injection. Moreover, the spectral bandwidth is narrowed, and the phase noise is reduced for most loop phase values. In order to predict the frequency variation with loop phase and injection ratio, a theoretical model based on a circuit equivalent to the magnetron is developed. Furthermore, the developed model also shows that the self-injection magnetron is stabler than the free-running magnetron and that the magnetron's phase noise can be reduced significantly for most loop phase values. Experimental results confirm the conclusions obtained using the proposed model.

Extraction of temperature dependences of small-signal model parameters in SiGe HBT HICUM model

Ya-Bin Sun, Jun Fu, Yu-Dong Wang, Wei Zhou, Wei Zhang, and Zhi-Hong Liu
Chin. Phys. B 2016, 25 (4): 048501;  doi: 10.1088/1674-1056/25/4/048501
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In this work, temperature dependences of small-signal model parameters in the SiGe HBT HICUM model are presented. Electrical elements in the small-signal equivalent circuit are first extracted at each temperature, then the temperature dependences are determined by the series of extracted temperature coefficients, based on the established temperature formulas for corresponding model parameters. The proposed method is validated by a 1×0.2×16 μm2 SiGe HBT over a wide temperature range (from 218 K to 473 K), and good matching is obtained between the extracted and modeled results. Therefore, we believe that the proposed extraction flow of model parameter temperature dependence is reliable for characterizing the transistor performance and guiding the circuit design over a wide temperature range.

Ultra-low specific on-resistance high-voltage vertical double diffusion metal-oxide-semiconductor field-effect transistor with continuous electron accumulation layer

Da Ma, Xiao-Rong Luo, Jie Wei, Qiao Tan, Kun Zhou, Jun-Feng Wu
Chin. Phys. B 2016, 25 (4): 048502;  doi: 10.1088/1674-1056/25/4/048502
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A new ultra-low specific on-resistance (Ron,sp) vertical double diffusion metal-oxide-semiconductor field-effect transistor (VDMOS) with continuous electron accumulation (CEA) layer, denoted as CEA-VDMOS, is proposed and its new current transport mechanism is investigated. It features a trench gate directly extended to the drain, which includes two PN junctions. In on-state, the electron accumulation layers are formed along the sides of the extended gate and introduce two continuous low-resistance current paths from the source to the drain in a cell pitch. This mechanism not only dramatically reduces the Ron,sp but also makes the Ron,sp almost independent of the n-pillar doping concentration (Nn). In off-state, the depletion between the n-pillar and p-pillar within the extended trench gate increases the Nn, and further reduces the Ron,sp. Especially, the two PN junctions within the trench gate support a high gate-drain voltage in the off-state and on-state, respectively. However, the extended gate increases the gate capacitance and thus weakens the dynamic performance to some extent. Therefore, the CEA-VDMOS is more suitable for low and medium frequencies application. Simulation indicates that the CEA-VDMOS reduces the Ron,sp by 80% compared with the conventional super-junction VDMOS (CSJ-VDMOS) at the same high breakdown voltage (BV).

Damage effect and mechanism of the GaAs pseudomorphic high electron mobility transistor induced by the electromagnetic pulse

Xiao-Wen Xi, Chang-Chun Chai, Gang Zhao, Yin-Tang Yang, Xin-Hai Yu, Yang Liu
Chin. Phys. B 2016, 25 (4): 048503;  doi: 10.1088/1674-1056/25/4/048503
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The damage effect and mechanism of the electromagnetic pulse (EMP) on the GaAs pseudomorphic high electron mobility transistor (PHEMT) are investigated in this paper. By using the device simulation software, the distributions and variations of the electric field, the current density and the temperature are analyzed. The simulation results show that there are three physical effects, i.e., the forward-biased effect of the gate Schottky junction, the avalanche breakdown, and the thermal breakdown of the barrier layer, which influence the device current in the damage process. It is found that the damage position of the device changes with the amplitude of the step voltage pulse. The damage appears under the gate near the drain when the amplitude of the pulse is low, and it also occurs under the gate near the source when the amplitude is sufficiently high, which is consistent with the experimental results.

Damage effect and mechanism of the GaAs high electron mobility transistor induced by high power microwave

Yang Liu, Chang-Chun Chai, Yin-Tang Yang, Jing Sun, Zhi-Peng Li
Chin. Phys. B 2016, 25 (4): 048504;  doi: 10.1088/1674-1056/25/4/048504
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In this paper, we present the damage effect and mechanism of high power microwave (HPM) on AlGaAs/GaAs pseudomorphic high-electron-mobility transistor (pHEMT) of low-noise amplifier (LNA). A detailed investigation is carried out by simulation and experiment study. A two-dimensional electro-thermal model of the typical GaAs pHEMT induced by HPM is established in this paper. The simulation result reveals that avalanche breakdown, intrinsic excitation, and thermal breakdown all contribute to damage process. Heat accumulation occurs during the positive half cycle and the cylinder under the gate near the source side is most susceptible to burn-out. Experiment is carried out by injecting high power microwave into GaAs pHEMT LNA samples. It is found that the damage to LNA is because of the burn-out at first stage pHEMT. The interiors of the damaged samples are observed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). Experimental results accord well with the simulation of our model.

Comparison of blue-green response between transmission-mode GaAsP-and GaAs-based photocathodes grown by molecular beam epitaxy

Gang-Cheng Jiao, Zheng-Tang Liu, Hui Guo, Yi-Jun Zhang
Chin. Phys. B 2016, 25 (4): 048505;  doi: 10.1088/1674-1056/25/4/048505
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In order to develop the photodetector for effective blue-green response, the 18-mm-diameter vacuum image tube combined with the transmission-mode Al0.7Ga0.3As0.9P0.1/GaAs0.9P0.1 photocathode grown by molecular beam epitaxy is tentatively fabricated. A comparison of photoelectric property, spectral characteristic and performance parameter between the transmission-mode GaAsP-based and blue-extended GaAs-based photocathodes shows that the GaAsP-based photocathode possesses better absorption and higher quantum efficiency in the blue-green waveband, combined with a larger surface electron escape probability. Especially, the quantum efficiency at 532 nm for the GaAsP-based photocathode achieves as high as 59%, nearly twice that for the blue-extended GaAs-based one, which would be more conducive to the underwater range-gated imaging based on laser illumination. Moreover, the simulation results show that the favorable blue-green response can be achieved by optimizing the emission-layer thickness in a range of 0.4 μ-0.6 μ.

X-ray absorption near-edge structure study on the configuration of Cu2+/histidine complexes at different pH values

Mei-Juan Yu, Yu Wang, Wei Xu
Chin. Phys. B 2016, 25 (4): 048701;  doi: 10.1088/1674-1056/25/4/048701
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The local configurations around metal ions in metalloproteins are of great significance for understanding their biological functions. Cu2+/histidine (His) is a typical complex existing in many metalloproteins and plays an important role in lots of physiological functions. The three-dimensional (3D) structural configurations of Cu2+/His complexes at different pH values (2.5, 6.5, and 8.5) are quantitatively determined by x-ray absorption near-edge structure (XANES). Generally Cu2+/His complex keeps an octahedral configuration consisting of oxygen atoms from water molecules and oxygen or nitrogen atoms from histidine molecules coordinated around Cu2+. It is proved in this work that the oxygen atoms from water molecules, when increasing the pH value from acid to basic value, are gradually substituted by the Ocarboxyl, Nam, and Nim from hisitidine molecules. Furthermore, the symmetries of Cu2+/His complexes at pH 6.5 and pH 8.5 are found to be lower than at pH 2.5.

A new traffic model on compulsive lane-changing caused by off-ramp

Xiao-He Liu, Hung-Tang Ko, Ming-Min Guo, Zheng Wu
Chin. Phys. B 2016, 25 (4): 048901;  doi: 10.1088/1674-1056/25/4/048901
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In the field of traffic flow studies, compulsive lane-changing refers to lane-changing (LC) behaviors due to traffic rules or bad road conditions, while free LC happens when drivers change lanes to drive on a faster or less crowded lane. LC studies based on differential equation models accurately reveal LC influence on traffic environment. This paper presents a second-order partial differential equation (PDE) model that simulates both compulsive LC behavior and free LC behavior, with lane-changing source terms in the continuity equation and a lane-changing viscosity term in the momentum equation. A specific form of this model focusing on a typical compulsive LC behavior, the ‘off-ramp problem’, is derived. Numerical simulations are given in several cases, which are consistent with real traffic phenomenon.

Pedestrian evacuation at the subway station under fire

Xiao-Xia Yang, Hai-Rong Dong, Xiu-Ming Yao, Xu-Bin Sun
Chin. Phys. B 2016, 25 (4): 048902;  doi: 10.1088/1674-1056/25/4/048902
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With the development of urban rail transit, ensuring the safe evacuation of pedestrians at subway stations has become an important issue in the case of an emergency such as a fire. This paper chooses the platform of line 4 at the Beijing Xuanwumen subway station to study the emergency evacuation process under fire. Based on the established platform, effects of the fire dynamics, different initial pedestrian densities, and positions of fire on evacuation are investigated. According to simulation results, it is found that the fire increases the air temperature and the smoke density, and decreases pedestrians' visibility and walking velocity. Also, there is a critical initial density at the platform if achieving a safe evacuation within the required 6 minutes. Furthermore, different positions of fire set in this paper have little difference on crowd evacuation if the fire is not large enough. The suggestions provided in this paper are helpful for the subway operators to prevent major casualties.

Effect of supply voltage and body-biasing on single-event transient pulse quenching in bulk fin field-effect-transistor process

Jun-Ting Yu, Shu-Ming Chen, Jian-Jun Chen, Peng-Cheng Huang, Rui-Qiang Song
Chin. Phys. B 2016, 25 (4): 049401;  doi: 10.1088/1674-1056/25/4/049401
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Charge sharing is becoming an important topic as the feature size scales down in fin field-effect-transistor (FinFET) technology. However, the studies of charge sharing induced single-event transient (SET) pulse quenching with bulk FinFET are reported seldomly. Using three-dimensional technology computer aided design (3DTCAD) mixed-mode simulations, the effects of supply voltage and body-biasing on SET pulse quenching are investigated for the first time in bulk FinFET process. Research results indicate that due to an enhanced charge sharing effect, the propagating SET pulse width decreases with reducing supply voltage. Moreover, compared with reverse body-biasing (RBB), the circuit with forward body-biasing (FBB) is vulnerable to charge sharing and can effectively mitigate the propagating SET pulse width up to 53% at least. This can provide guidance for radiation-hardened bulk FinFET technology especially in low power and high performance applications.
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