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Chin. Phys. B  
  Chin. Phys. B--2018, Vol.27, No.4
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TOPIC REVIEW—Thermal and thermoelectric properties of nano materials

An extension of integrable equations related to AKNS and WKI spectral problems and their reductions

Xian-Guo Geng, Yun-Yun Zhai
Chin. Phys. B 2018, 27 (4): 040201;  doi: 10.1088/1674-1056/27/4/040201
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A novel hierarchy of integrable nonlinear evolution equations related to the combined Ablowitz-Kaup-Newell-Segur (AKNS) and Wadati-Konno-Ichikawa (WKI) spectral problems is proposed, from which the Lax pair for a corresponding negative flow and its infinite many conservation laws are obtained. Furthermore, a reduction of this hierarchy is discussed, by which a generalized sinh-Gordon equation is derived on the basis of its negative flow.

Integrability classification and exact solutions to generalized variable-coefficient nonlinear evolution equation

Han-Ze Liu, Li-Xiang Zhang
Chin. Phys. B 2018, 27 (4): 040202;  doi: 10.1088/1674-1056/27/4/040202
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This paper is concerned with the generalized variable-coefficient nonlinear evolution equation (vc-NLEE). The complete integrability classification is presented, and the integrable conditions for the generalized variable-coefficient equations are obtained by the Painlevé analysis. Then, the exact explicit solutions to these vc-NLEEs are investigated by the truncated expansion method, and the Lax pairs (LP) of the vc-NLEEs are constructed in terms of the integrable conditions.

Constructing (2+1)-dimensional N=1 supersymmetric integrable systems from the Hirota formalism in the superspace

Jian-Yong Wang, Xiao-Yan Tang, Zu-Feng Liang
Chin. Phys. B 2018, 27 (4): 040203;  doi: 10.1088/1674-1056/27/4/040203
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The N=1 supersymmetric extensions of two integrable systems, a special negative Kadomtsev-Petviashvili (NKP) system and a (2+1)-dimensional modified Korteweg-de Vries (MKdV) system, are constructed from the Hirota formalism in the superspace. The integrability of both systems in the sense of possessing infinitely many generalized symmetries are confirmed by extending the formal series symmetry approach to the supersymmetric framework. It is found that both systems admit a generalization of W type algebra and a Kac-Moody-Virasoro type subalgebra. Interestingly, the first one of the positive flow of the supersymmetric NKP system is another N=1 supersymmetric extension of the (2+1)-dimensional MKdV system. Based on our work, a hypothesis is put forward on a series of (2+1)-dimensional supersymmetric integrable systems. It is hoped that our work may develop a straightforward way to obtain supersymmetric integrable systems in high dimensions.

Shannon information entropies for rectangular multiple quantum well systems with constant total lengths

M Solaimani, Guo-Hua Sun, Shi-Hai Dong
Chin. Phys. B 2018, 27 (4): 040301;  doi: 10.1088/1674-1056/27/4/040301
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We first study the Shannon information entropies of constant total length multiple quantum well systems and then explore the effects of the number of wells and confining potential depth on position and momentum information entropy density as well as the corresponding Shannon entropy. We find that for small full width at half maximum (FWHM) of the position entropy density, the FWHM of the momentum entropy density is large and vice versa. By increasing the confined potential depth, the FWHM of the position entropy density decreases while the FWHM of the momentum entropy density increases. By increasing the potential depth, the frequency of the position entropy density oscillation within the quantum barrier decreases while that of the position entropy density oscillation within the quantum well increases. By increasing the number of wells, the frequency of the position entropy density oscillation decreases inside the barriers while it increases inside the quantum well. As an example, we might localize the ground state as well as the position entropy densities of the 1st, 2nd, and 6th excited states for a four-well quantum system. Also, we verify the Bialynicki-Birula-Mycieslki (BBM) inequality.

Comparative investigation of freezing phenomena for quantum coherence and correlations

Lian-Wu Yang, Wei Han, Yun-Jie Xia
Chin. Phys. B 2018, 27 (4): 040302;  doi: 10.1088/1674-1056/27/4/040302
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We show that the freezing phenomenon, exhibited by a specific class of two-qubit state under local nondissipative decoherent evolutions, is a common feature of the relative entropy measure of quantum coherence and correlation. All those measurement outcomes, preserve a constant value in the considered noisy channels, but the condition, property and mechanism of the freezing phenomenon for quantum coherence are different from those of the quantum correlation.

Dynamics of entanglement protection of two qubits using a driven laser field and detunings: Independent and common, Markovian and/or non-Markovian regimes

S Golkar, M K Tavassoly
Chin. Phys. B 2018, 27 (4): 040303;  doi: 10.1088/1674-1056/27/4/040303
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Preventing quantum entanglement from decoherence effect is of theoretical and practical importance in the quantum information processing technologies. In this regard, we consider the entanglement dynamics of two identical qubits where the qubits which are coupled to two independent (Markovian and/or non-Markovian) as well as a common reservoir at zero temperature are further interacted with a classical driving laser field. Then, we study the preservation of generated two-qubit entanglement in various situations using the concurrence measure. It is shown that by applying the classical driving field and so the possibility of controlling the Rabi frequency, the amount of entanglement of the two-qubit system is improved in the off-resonance condition between the qubit and the central cavity frequencies (central detuning) in both non-Markovian and Markovian reservoirs. While the central detuning has a constructive role, the detuning between the qubit and the classical field (laser detuning) affects negatively on the entanglement protection. The obtained results show that long-living entanglement in the non-Markovian reservoir is more accessible than in the Markovian reservoir. We demonstrate that, in a common reservoir non-zero stationary entanglement is achievable whenever the two-qubit system is coupled to the reservoir with appropriate values of relative coupling strengths.

Controlling the entanglement of mechanical oscillators in composite optomechanical system

Jun Zhang, Qing-Xia Mu, Wen-Zhao Zhang
Chin. Phys. B 2018, 27 (4): 040304;  doi: 10.1088/1674-1056/27/4/040304
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A controllable entanglement scheme of two mechanical oscillators is proposed in a composite optomechanical system. In the case of strong driving and high dissipation, the dynamics of the movable mirror of the optomechanical cavity is characterized by an effective frequency in the long-time evolution of the system. Considering the classical nonlinear effects in an optomechanical system, we investigate the relationship between the effective frequency of the movable mirror and the adjustable parameters of the cavity. It shows that the effective frequency of the movable mirror can be adjusted ranging from ωm (the resonance frequency of the coupling oscillator) to -ωm. Under the condition of experimental realization, we can generate and control steady-state entanglement between two oscillators by adjusting the effective frequency of the movable mirror and reducing the effective dissipation by selecting the parameter of the cavity driving laser appropriately. Our scheme provides a promising platform to control the steady-state behavior of solid-state qubits using classical manipulation, which is significant for quantum information processing and fundamental research.

Geometrical optics-based ray field tracing method for complex source beam applications

Min Gao, Feng Yang, Xue-Wu Cui, Rui Wang
Chin. Phys. B 2018, 27 (4): 040401;  doi: 10.1088/1674-1056/27/4/040401
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Due to the fact that traditional ray field tracking approaches require a large number of geometrical optical (GO) ray tubes, they are very inefficient in many practical applications. An improved ray model scheme for a complex source beam (CSB) tracking technique is proposed in this paper. The source field can be expressed by a superposition of CSBs, then every CSB basis function has a Gaussian-type amplitude distribution and is suitable for replacing a GO ray tube in the ray tracing approach. The complex phase matching technique is adopted to find the reflected beam in the reflection point where local approximation is used to represent the curved surface in its neighborhood. A new solution to multiple reflections using the conventional right-handed reflected system is used to track the field easily. Numerical results show the accuracy of the proposed method.

Nucleus-acoustic solitary waves in self-gravitating degenerate quantum plasmas

D M S Zaman, M Amina, P R Dip, A A Mamun
Chin. Phys. B 2018, 27 (4): 040402;  doi: 10.1088/1674-1056/27/4/040402
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Nucleus-acoustic (NA) solitary waves (SWs) propagating in a self-gravitating degenerate quantum plasma (SDQP) system (containing non-relativistically degenerate heavy and light nuclei, and non-/ultra-relativistically degenerate electrons) have been theoretically investigated. The modified Korteweg-de Vries (mK-dV) equation has been derived for both planar and non-planar geometry by employing the reductive perturbation technique. It is shown that the NA SWs exist with positive (negative) electrostatic (self-gravitational) potential. It is also observed that the effects of non-/ultra-relativistically degenerate electron pressure, dynamics of non-relativistically light nuclei, spherical geometry, etc. significantly modify the basic features (e.g., amplitude, width, speed, etc.) of the NA SWs. The applications of our results, which are relevant to astrophysical compact objects, like white dwarfs and neutron stars, are briefly discussed.

Stochastic resonance and synchronization behaviors of excitatory-inhibitory small-world network subjected to electromagnetic induction

Xiao-Han Zhang, Shen-Quan Liu
Chin. Phys. B 2018, 27 (4): 040501;  doi: 10.1088/1674-1056/27/4/040501
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The phenomenon of stochastic resonance and synchronization on some complex neuronal networks have been investigated extensively. These studies are of great significance for us to understand the weak signal detection and information transmission in neural systems. Moreover, the complex electrical activities of a cell can induce time-varying electromagnetic fields, of which the internal fluctuation can change collective electrical activities of neuronal networks. However, in the past there have been a few corresponding research papers on the influence of the electromagnetic induction among neurons on the collective dynamics of the complex system. Therefore, modeling each node by imposing electromagnetic radiation on the networks and investigating stochastic resonance in a hybrid network can extend the interest of the work to the understanding of these network dynamics. In this paper, we construct a small-world network consisting of excitatory neurons and inhibitory neurons, in which the effect of electromagnetic induction that is considered by using magnetic flow and the modulation of magnetic flow on membrane potential is described by using memristor coupling. According to our proposed network model, we investigate the effect of induced electric field generated by magnetic stimulation on the transition of bursting phase synchronization of neuronal system under electromagnetic radiation. It is shown that the intensity and frequency of the electric field can induce the transition of the network bursting phase synchronization. Moreover, we also analyze the effect of magnetic flow on the detection of weak signals and stochastic resonance by introducing a subthreshold pacemaker into a single cell of the network and we find that there is an optimal electromagnetic radiation intensity, where the phenomenon of stochastic resonance occurs and the degree of response to the weak signal is maximized. Simulation results show that the extension of the subthreshold pacemaker in the network also depends greatly on coupling strength. The presented results may have important implications for the theoretical study of magnetic stimulation technology, thus promoting further development of transcranial magnetic stimulation (TMS) as an effective means of treating certain neurological diseases.

A new nonlinear oscillator with infinite number of coexisting hidden and self-excited attractors

Yan-Xia Tang, Abdul Jalil M Khalaf, Karthikeyan Rajagopal, Viet-Thanh Pham, Sajad Jafari, Ye Tian
Chin. Phys. B 2018, 27 (4): 040502;  doi: 10.1088/1674-1056/27/4/040502
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In this paper, we introduce a new two-dimensional nonlinear oscillator with an infinite number of coexisting limit cycles. These limit cycles form a layer-by-layer structure which is very unusual. Forty percent of these limit cycles are self-excited attractors while sixty percent of them are hidden attractors. Changing this new system to its forced version, we introduce a new chaotic system with an infinite number of coexisting strange attractors. We implement this system through field programmable gate arrays.

A new four-dimensional chaotic system with first Lyapunov exponent of about 22, hyperbolic curve and circular paraboloid types of equilibria and its switching synchronization by an adaptive global integral sliding mode control

Jay Prakash Singh, Binoy Krishna Roy, Zhouchao Wei
Chin. Phys. B 2018, 27 (4): 040503;  doi: 10.1088/1674-1056/27/4/040503
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This paper presents a new four-dimensional (4D) autonomous chaotic system which has first Lyapunov exponent of about 22 and is comparatively larger than many existing three-dimensional (3D) and 4D chaotic systems. The proposed system exhibits hyperbolic curve and circular paraboloid types of equilibria. The system has all zero eigenvalues for a particular case of an equilibrium point. The system has various dynamical behaviors like hyperchaotic, chaotic, periodic, and quasi-periodic. The system also exhibits coexistence of attractors. Dynamical behavior of the new system is validated using circuit implementation. Further an interesting switching synchronization phenomenon is proposed for the new chaotic system. An adaptive global integral sliding mode control is designed for the switching synchronization of the proposed system. In the switching synchronization, the synchronization is shown for the switching chaotic, stable, periodic, and hybrid synchronization behaviors. Performance of the controller designed in the paper is compared with an existing controller.

Time-varying formation for general linear multi-agent systems via distributed event-triggered control under switching topologies

Jin-Huan Wang, Yu-Ling Xu, Jian Zhang, De-Dong Yang
Chin. Phys. B 2018, 27 (4): 040504;  doi: 10.1088/1674-1056/27/4/040504
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This paper investigates the time-varying formation problem for general linear multi-agent systems using distributed event-triggered control strategy. Different from the previous works, to achieve the desired time-varying formation, a distributed control scheme is designed in an event-triggered way, in which for each agent the controller is triggered only at its own event times. The interaction topology among agents is assumed to be switching. The common Lyapunov function as well as Riccati inequality is applied to solve the time-varying formation problem. Moreover, the Zeno behavior of triggering time sequences can be excluded for each agent. Finally, a simulation example is presented to illustrate the effectiveness of the theoretical results.

Symmetry and asymmetry rogue waves in two-component coupled nonlinear Schrödinger equations

Zai-Dong Li, Cong-Zhe Huo, Qiu-Yan Li, Peng-Bin He, Tian-Fu Xu
Chin. Phys. B 2018, 27 (4): 040505;  doi: 10.1088/1674-1056/27/4/040505
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By means of the modified Darboux transformation we obtain some types of rogue waves in two-coupled nonlinear Schrödinger equations. Our results show that the two components admits the symmetry and asymmetry rogue wave solutions, which arises from the joint action of self-phase, cross-phase modulation, and coherent coupling term. We also obtain the analytical transformation from the initial seed solution to unique rogue waves with the bountiful pair structure. In a special case, the asymmetry rogue wave can own the spatial and temporal symmetry gradually, which is controlled by one parameter. It is worth pointing out that the rogue wave of two components can share the temporal inversion symmetry.

Quantum parameter estimation in a spin-boson dephasing quantum system by periodical projective measurements

Le Yang, Hong-Yi Dai, Ming Zhang
Chin. Phys. B 2018, 27 (4): 040601;  doi: 10.1088/1674-1056/27/4/040601
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In this paper, we explore how to estimate the phase damping parameter γ and the tunneling amplitude parameter from a spin-boson dephasing quantum model by periodical projective measurements. The preparation of initial states is accomplished by performing the period measurements in our scheme. The parameter γ can be always estimated when projective measurement bases are chosen as θ=π/2 and φ=0. Based on the estimated value of γ and the interval information of , we can select another measurement bases (θ=π/4 and φ=π/2) to obtain the estimated value of . A coherent control is indispensable to estimate if γ is in the interval of ; whereas the control is not necessary if γ is out of the known interval of . We establish the relation between the optimal period time and the parameter γ or in terms of Fisher information. Although the optimal measurement period cannot be selected beforehand, the aforementioned relation can be utilized to adjust the measurement period to approach the optimal one.

Highly-sensitive NO, NO2, and NH3 measurements with an open-multipass cell based on mid-infrared wavelength modulation spectroscopy

Xiang Chen, Chen-Guang Yang, Mai Hu, Jian-Kang Shen, Er-Chao Niu, Zhen-Yu Xu, Xue-Li Fan, Min Wei, Lu Yao, Ya-Bai He, Jian-Guo Liu, Rui-Feng Kan
Chin. Phys. B 2018, 27 (4): 040701;  doi: 10.1088/1674-1056/27/4/040701
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A compact prototype based on mid-infrared wavelength modulation spectroscopy (WMS) is developed for the simultaneous monitoring of NO, NO2, and NH3 in the urban area. Three quantum cascade lasers (QCLs) with central frequencies around 1900.0 cm-1, 1600.0 cm-1, and 1103.4 cm-1 are used for NO, NO2, and NH3 detections, respectively, by time-division multiplex. An open-path multi-pass cell of 60-m optical path length is applied to the instrument for high sensitivity and reducing the response time to less than 1 s. The prototype achieves a sub-ppb detection limit for all the three target gases with an average time of about 100 s. The instrument is installed in the Jiangsu environmental monitoring center to conduct performance tests on ambient air. Continuous 24-hour measurements show good agreement with the results of a reference instrument based on the chemiluminescence technique.

Selection rules for electric multipole transition of triatomic molecule in scattering experiments

Hong-Chun Tian, Long-Quan Xu, Lin-Fan Zhu
Chin. Phys. B 2018, 27 (4): 043101;  doi: 10.1088/1674-1056/27/4/043101
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In the electron or x-ray scattering experiment, the measured spectra at larger momentum transfer are dominated by the electric dipole-forbidden transitions, while the corresponding selection rules for triatomic molecules have not been clearly elucidated. In this work, based on the molecular point group, the selection rules for the electric multipolarities of the electronic transitions of triatomic molecules are derived and summarized into several tables with the variation of molecular geometry in the transition process being considered. Based on the summarized selection rules, the electron energy loss spectra of H2O, CO2, and N2O are identified, and the momentum transfer dependence behaviors of their valence-shell excitations are explained.

High-level theoretical study of the evolution of abundances and interconversion of glycine conformers

Fan Liu, Jing Yu, Yan-Ru Huang
Chin. Phys. B 2018, 27 (4): 043102;  doi: 10.1088/1674-1056/27/4/043102
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The relative conformer energies of glycine are evaluated by using a focal point analysis expressed as (HF →MP2 →MP3 →CCSD →CCSD(T)). The conformer abundances at various temperatures (298-500 K) are calculated based on the relative energies and Boltzmann statistical thermostatistical analysis with and without considering internal hindered rotations. A comparison between the available Raman spectrum and the electron momentum spectrum confirms that the influence of rigid-rotor hindered rotation on the conformational proportions of glycine is considerable, especially for the Ⅲp structure. The conformational interconversions are discussed. It is found that with increasing temperature, the mole fraction of Ⅱn keeps constant and Ip structure can convert into IVn and Ⅲp, leading to the decrease in the weight of Ip and the increase in the weights of IVn and Ⅲp conformers, which is in accordance with experimental observations.

Density functional theory study of structural stability for gas hydrate

Ping Guo, Yi-Long Qiu, Long-Long Li, Qiang Luo, Jian-Fei Zhao, Yi-Kun Pan
Chin. Phys. B 2018, 27 (4): 043103;  doi: 10.1088/1674-1056/27/4/043103
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Using the first-principles method based on the density functional theory (DFT), the structures and electronic properties of different gas hydrates (CO2, CO, CH4, and H2) are investigated within the generalized gradient approximation. The structural stability of methane hydrate is studied in this paper. The results show that the carbon dioxide hydrate is more stable than the other three gas hydrates and its binding energy is -2.36 eV, and that the hydrogen hydrate is less stable and the binding energy is -0.36 eV. Water cages experience repulsion from inner gas molecules, which makes the hydrate structure more stable. Comparing the electronic properties of two kinds of water cages, the energy region of the hydrate with methane is low and the peak is close to the left, indicating that the existence of methane increases the stability of the hydrate structure. Comparing the methane molecule in water cages and a single methane molecule, the energy of electron distribution area of the former is low, showing that the filling of methane enhances the stability of hydrate structure.

Novel potential energy surface-based quantum dynamics of ion-molecule reaction O++D2 →OD++D

Xian-Long Wang, Feng Gao, Shou-Bao Gao, Lu-Lu Zhang, Yu-Zhi Song, Qing-Tian Meng
Chin. Phys. B 2018, 27 (4): 043104;  doi: 10.1088/1674-1056/27/4/043104
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According to a novel electronic ground-state potential energy surface of H2O+(X4A"), we calculate the reaction probabilities and the integral cross section for the titled reaction O++D2 →OD++D by the Chebyshev wave packet propagation method. The reaction probabilities in a collision-energy range of 0.0 eV-1.0 eV show an oscillatory structure for the O++D2 reaction due to the existence of the potential well. Compared with the results of Martínez et al., the present integral cross section is large, which is in line with experimental data.

Dynamic stabilization of Na atom in an intense pulsed laser field

Xiao-Li Guo, Song-Feng Zhao, Guo-Li Wang, Xiao-Xin Zhou
Chin. Phys. B 2018, 27 (4): 043201;  doi: 10.1088/1674-1056/27/4/043201
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We investigate theoretically the ionization properties of the valence electron for the alkali metal atom Na in an intense pulsed laser field by solving numerically the time-dependent Schrödinger equation with an accurate l-dependent model potential. By calculating the variations of the ionization probabilities with laser peak intensity for wavelengths ranging from 200 nm to 600 nm, our results present a dynamic stabilization trend for the Na atom initially in its ground state (3s) and the excited states (3p and 4s) exposed to an intense pulsed laser field. Especially a clear “window” of dynamic stabilization at lower laser intensities and longer wavelengths for the initial state 4s (the second excited state) is found. By analyzing the time-dependent population distributions of the valence electron in the bound states with the different values of principal quantum number n and orbital quantum number l, we can attribute the dynamic stabilization to the periodic population in the low-excited states since the valence electron oscillates rapidly between the lowly excited states and the continuum states.

Corrections to atomic ground state energy due to interaction between atomic electric quadrupole and optical field

Jie Hu, Yu Chen, Yi-Xiu Bai, Pei-Song He, Qing Sun, An-Chun Ji
Chin. Phys. B 2018, 27 (4): 043202;  doi: 10.1088/1674-1056/27/4/043202
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We study the ground state energy of an atom interacting with an oscillating optical field with electric dipole and quadrupole coupling. Under the rotating wave approximation, we derive the effective atomic Hamiltonians of the dipole/quadrupole coupling term within the perturbation theory up to the second order. Based on the effective Hamiltonians, we analyze the atomic ground-state energy corrections of these two processes in detail. As an application, we find that for alkali-like atoms, the energy correction from the quadrupole coupling is negligible small in comparison with that from the dipole coupling, which justifies the so-called dipole approximation used in literatures. Some special cases where the quadrupole interaction may have considerable energy corrections are also discussed. Our results would be beneficial for the study of atom-light interaction beyond dipole approximation.

Quantitative evaluation of space charge effects of laser-cooled three-dimensional ion system on a secular motion period scale

Li-Jun Du, Hong-Fang Song, Shao-Long Chen, Yao Huang, Xin Tong, Hua Guan, Ke-Lin Gao
Chin. Phys. B 2018, 27 (4): 043701;  doi: 10.1088/1674-1056/27/4/043701
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In this paper, we introduce a method of quantitatively evaluating and controlling the space charge effect of a laser-cooled three-dimensional (3D) ion system in a linear Paul trap. The relationship among cooling efficiency, ion quantity, and trapping strength is analyzed quantitatively, and the dynamic space distribution and temporal evolution of the 3D ion system on a secular motion period time scale in the cooling process are obtained. The ion number influences the eigen-micromotion feature of the ion system. When trapping parameter q is~0.3, relatively ideal cooling efficiency and equilibrium temperature can be obtained. The decrease of axial electrostatic potential is helpful in reducing the micromotion heating effect and the degradation in the total energy. Within a single secular motion period under different cooling conditions, ions transform from the cloud state (each ion disperses throughout the envelope of the ion system) to the liquid state (each ion is concentrated at a specific location in the ion system) and then to the crystal state (each ion is subjected to a fixed motion track). These results are conducive to long-term storage and precise control, motion effect suppression, high-efficiency cooling, and increasing the precision of spectroscopy for a 3D ion system.


Design of scale model of plate-shaped absorber in a wide frequency range

Li-Ming Yuan, Yong-Gang Xu, Wei Gao, Fei Dai, Qi-Lin Wu
Chin. Phys. B 2018, 27 (4): 044101;  doi: 10.1088/1674-1056/27/4/044101
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In order to design the scale model in a wide frequency range, a method based on the reflective loss is proposed according to the high-frequency approximation algorithm, and an example of designing the scale model of a plate-shaped absorber is given in this paper. In the example, the frequency of the full-size measurement ranges from 2.0 GHz to 2.4 GHz, the thickness of the full-size absorber is 1 mm and the scale ratio is 1/5. A two-layer scale absorber is obtained by the proposed method. The thickness values of the bottom and top layer are 0.4 mm and 0.5 mm, respectively. Furthermore, the scattering properties of a plate model and an SLICY model are studied by FEKO to verify the effectiveness of the designed scale absorber. Compared with the corresponding values from the theoretical scale model, the average values of the absolute deviations in 10 GHz~12 GHz are 0.53 dBm2, 0.65 dBm2, 0.76 dBm2 for the plate model and 0.20 dBm2, 0.95 dBm2, 0.77 dBm2 for the SLICY model while the incident angles are 0°, 30°, and 60°, respectively. These deviations fall within the Radar cross section (RCS) measurement tolerance. Thus, the work in this paper has important theoretical and practical significance.

All-fiber linearly polarized laser oscillator by fiber coiling loss control

Yu-Sheng Huang, Qi-Rong Xiao, Dan Li, Ze-Hui Wang, Xue-Jiao Wang, Ping Yan, Ma-Li Gong
Chin. Phys. B 2018, 27 (4): 044201;  doi: 10.1088/1674-1056/27/4/044201
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In this paper, we demonstrate an all-fiber linearly polarized fiber laser oscillator. The single polarization of the oscillator is achieved through the careful designing of the active fiber coiling. The relationship between fiber coiling diameter and polarization extinction ratio and optical efficiency is studied, whose results lead to an optimized system. The thermal management of the oscillator is also refined, which allows the oscillator to reach a maximum output power of 44.1 W with an optical-to-optical efficiency of 57.9%. A high average polarization extinction ratio of 21.6 dB is achieved during a 2-hour stability test. The oscillator also owns a narrow 3-dB bandwidth of 0.1 nm, as well as near-diffraction-limit beam quality of M2~1.14.

Observation of self-Q-switching in bulk Yb: GdYSiO laser

Shuang Gong, Jin-Rong Tian, He-Yang Guo Yu, Zi-Kai Dong, Chang-Xing Xu, Wen-Ping Zhang, Yan-Rong Song
Chin. Phys. B 2018, 27 (4): 044202;  doi: 10.1088/1674-1056/27/4/044202
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We report the first self-Q-switched Yb-doped GdYSiO5 (Yb:GYSO) laser operating at 1080 nm. Stable Q-switched pulses with a repetition rate of 18.1 kHz and pulse duration of 9.45 μs are obtained. A maximum average output power of 452.6 mW is achieved with a 1% transmission output coupler. With a 3% transmission output coupler, the shortest pulse width of 6.6 μs is obtained. It demonstrates that Yb:GYSO crystal can be simultaneously employed as a saturable absorber and a gain medium to generate microsecond Q-switched pulses in the near infrared region.

Fundamental and dressed annular solitons in saturable nonlinearity with parity-time symmetric Bessel potential

Hong-Cheng Wang, Ya-Dong Wei, Xiao-Yuan Huang, Gui-Hua Chen, Hai Ye
Chin. Phys. B 2018, 27 (4): 044203;  doi: 10.1088/1674-1056/27/4/044203
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We theoretically study the existence and stability of optical solitons in saturable nonlinearity with a two-dimensional parity-time (PT) symmetric Bessel potential. Besides the fundamental solitons, a novel type of dressed soliton, whose intensity looks like a ring dressed on an intensity hump, are presented. It is found that both the fundamental solitons and dressed solitons can exist when the propagation constant is beyond a certain critical value. The propagation stability is investigated with a linear stability analysis corroborated by a beam propagation method. All the fundamental solitons are stable, while dressed solitons are unstable for low values of saturable parameter. As the value of saturable parameter increases, the dressed solitons tend to be stable at high powers.

Photonic crystal structures: Beam deflector and beam router

Utku Erdiven, Erkan Tetik, Faruk Karadag
Chin. Phys. B 2018, 27 (4): 044204;  doi: 10.1088/1674-1056/27/4/044204
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We investigate the optical characteristic, transverse magnetic (TM) and transverse electric (TE) band of two-dimensional (2D) square lattice photonic crystal structure, which is composed of cylindrical air regions positioned at the corners of the square shaped dielectric rods. We obtain the wide photonic bandwidths between TM1-TM2 and TM3-TM4 bands. According to the results, we demonstrate the band gaps close to each other in the TM and TE frequencies for proposed structures. The resulting photonic gaps are formed to be about 8% at the higher frequencies of TE modes (TE4-TE5) and TM modes (TM7-TM8 and TM9-TM10). In addition, we examine isotropically generated structures for light guiding properties and observe that the light is directed in a particular route without using any deflection. We also investigate the self-collimation effect with the designed structure. The obtained results reveal the influences of the radius of cylindrical air holes and the angle between these air holes on absolute and partial photonic band gaps. Moreover, we observe the TM and TE band gaps that overlap. It is thought that the obtained band overlap will provide an easy way to produce the photonic crystals in practical applications like photonic insensitive waveguide. It is also believed that these results can provide the photonic crystal structures to work as a beam deflecting and beam router in integrated optical circuit applications.

Head-on collision between two solitary waves in a one-dimensional bead chain

Fu-Gang Wang, Yang-Yang Yang, Juan-Fang Han, Wen-Shan Duan
Chin. Phys. B 2018, 27 (4): 044501;  doi: 10.1088/1674-1056/27/4/044501
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The head on collision between two opposite propagating solitary waves is studied in the present paper both numerically and analytically. The interesting result is that no phase shift is observed which is different from that found in other branches of physics. It is found that the maximum amplitude in the process of the head on collision is close to the linear sum of two colliding solitary waves.

Oxidation during the production of FGH4095 superalloy powders by electrode induction-melt inert gas atomization

Shan Feng, Min Xia, Chang-Chun Ge
Chin. Phys. B 2018, 27 (4): 044701;  doi: 10.1088/1674-1056/27/4/044701
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Super-clean and super-spherical FGH4095 superalloy powder is produced by the ceramic-free electrode induction-melt inert gas atomization (EIGA) technique. A continuous and steady-state liquid metal flow is achieved at high-frequency (350 kHz) alternating current and high electric power (100 kW). The superalloy is immersed in a high-frequency induction coil, and the liquid metal falling into a supersonic nozzle is atomized by an Ar gas of high kinetic gas energy. Numerical calculations are performed to optimize the structure parameters for the nozzle tip. The undesired oxidation reaction of alloying elements starts at 1000℃ with the reaction originating from the active sites on the powder surfaces, leading to the formation of oxides, MexOy. The role of active sites and kinetic factors associated with the diffusion of oxygen present in the atomization gas streams are also examined. The observed results reveal that the oxidation process occurring at the surface of the produced powders gradually moves toward the core, and that there exists a clear interface between the product layer and the reactant. The present study lays a theoretical foundation for controlling the oxidation of nickel-based superalloy powders from the powder process step.


Particle-in-cell simulation for the effect of magnetic cusp on discharge characteristics in a cylindrical Hall thruster

Sheng-Tao Liang, Hui Liu, Da-Ren Yu
Chin. Phys. B 2018, 27 (4): 045201;  doi: 10.1088/1674-1056/27/4/045201
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The cylindrical Hall thruster has the good prospect of serving as a miniaturized electric propulsion device. A 2D-3V particle-in-cell plus Monte Carlo (PIC-MCC) method is used to study the effect of the magnetic cusp on discharge characteristics of a cylindrical Hall thruster. The simulation results show that the main ionization region and the main potential drop of the thruster are located at the upstream of the discharge channel. When the magnetic cusp moves toward the anode side, the main ionization region is compressed and weakened, moving upstream correspondingly. The ionization near the cusp is enhanced, and the interaction between the plasma and the wall increases. The simulation results suggest that the magnetic cusp should be located near the channel exit.

Phase shift effects of radio-frequency bias on ion energy distribution in continuous wave and pulse modulated inductively coupled plasmas

Chan Xue, Fei Gao, Yong-Xin Liu, Jia Liu, You-Nian Wang
Chin. Phys. B 2018, 27 (4): 045202;  doi: 10.1088/1674-1056/27/4/045202
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A retarding field energy analyzer (RFEA) is used to measure the time-averaged ion energy distributions (IEDs) on the substrate in both continuous wave (CW) and synchronous pulse modulated radio-frequency (RF) inductively coupled Ar plasmas (ICPs). The effects of the phase shift θ between the RF bias voltage and the RF source on the IED is investigated under various discharge conditions. It is found that as θ increases from 0 to π, the IED moves towards the low-energy side, and its energy width becomes narrower. In order to figure out the physical mechanism, the voltage waveforms on the substrate are also measured. The results show that as θ increases from 0 to π, the amplitude of the voltage waveform decreases and, meanwhile, the average sheath potential decreases as well. Specifically, the potential drop in the sheath on the substrate exhibits a maximum value at the same phase (i.e., θ=0) and a minimum value at the opposite phase (i.e., θ=π). Therefore, when ions traverse across the sheath region above the substrate, they obtain less energies at lower sheath potential drop, leading to lower ion energy. Besides, as θ increases from π to 2π, the IEDs and their energy widths change reversely.


Wettability of Si and Al-12Si alloy on Pd-implanted 6H-SiC

Ting-Ting Wang, Gui-Wu Liu, Zhi-Kun Huang, Xiang-Zhao Zhang, Zi-Wei Xu, Guan-Jun Qiao
Chin. Phys. B 2018, 27 (4): 046101;  doi: 10.1088/1674-1056/27/4/046101
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SiC monocrystal substrates are implanted by Pd ions with different ion-beam energies and fluences, and the effects of Pd ion implantation on wettability of Si/SiC and Al-12Si/SiC systems are investigated by the sessile drop technique. The decreases of contact angles of the two systems are disclosed after the ion implantation, which can be attributed to the increase of surface energy (σSV) of SiC substrate derived from high concentration of defects induced by the ion-implantation and to the decrease of solid-liquid surface energy (σSL) resulting from the increasing interfacial interactions. This study can provide guidance in improving the wettability of metals on SiC and the electronic packaging process of SiC substrate.

The influence of surface effects on Frederiks transition in nematic liquid crystal doped with ferroelectric nanoparticles

Erfan Kadivar, Mojtaba Farrokhbin
Chin. Phys. B 2018, 27 (4): 046801;  doi: 10.1088/1674-1056/27/4/046801
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Motivated by our recent work, in this work, we present the numerical study of the anchoring effect on the Frederiks threshold field in a nematic liquid crystal doped with ferroelectric colloidal nanoparticles. Assuming weak anchoring conditions, we employ the relaxation method and Maxwell construction to numerically solve the Euler-Lagrangian differential equation for the total free energy together the Rapini-Papoular surface energy to take into account anchoring of nematic liquid crystal molecules at the substrates. In this study, we focus our attention on obtaining the phase diagrams of Frederiks transition for different values of anchoring strength which have been not computed in our previous work. In this way, the effect of nanoparticle radius, nanoparticle volume fraction, nanoparticle polarization, and cell thickness on the Frederiks transition for different values of anchoring conditions are summarized in the phase diagrams. The numerical results show that by increasing the nanoparticles size and nanoparticle volume fraction in the ferronematic system, the Frederiks threshold field is strongly reduced.

Two-dimensional electron gas characteristics of InP-based high electron mobility transistor terahertz detector

Jin-Lun Li, Shao-Hui Cui, Jian-Xing Xu, Xiao-Ran Cui, Chun-Yan Guo, Ben Ma, Hai-Qiao Ni, Zhi-Chuan Niu
Chin. Phys. B 2018, 27 (4): 047101;  doi: 10.1088/1674-1056/27/4/047101
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The samples of InxGa1-xAs/In0.52Al0.48As two-dimensional electron gas (2DEG) are grown by molecular beam epitaxy (MBE). In the sample preparation process, the In content and spacer layer thickness are changed and two kinds of methods, i.e., contrast body doping and δ-doping are used. The samples are analyzed by the Hall measurements at 300 K and 77 K. The InxGa1-xAs/In0.52Al0.48As 2DEG channel structures with mobilities as high as 10289 cm2/V·(300 K) and 42040 cm2/V·(77 K) are obtained, and the values of carrier concentration (Nc) are 3.465×1012/cm2 and 2.502×1012/cm2, respectively. The THz response rates of InP-based high electron mobility transistor (HEMT) structures with different gate lengths at 300 K and 77 K temperatures are calculated based on the shallow water wave instability theory. The results provide a reference for the research and preparation of InP-based HEMT THz detectors.

The effect of replacing pnictogen elements on the physical properties of SrMg2X2 (X=N, P, As, Sb, Bi) Zintl compounds

G Murtaza, Abdul Ahad Khan, M Yaseen, A Laref, Naeem Ullah, Inayat ur Rahman
Chin. Phys. B 2018, 27 (4): 047102;  doi: 10.1088/1674-1056/27/4/047102
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The effect of replacing the anion from N to Bi down the group in the periodic table is investigated on SrMg2X2 (X=N, P, As, Sb, Bi). A full potential linearized augmented plane wave plus local orbitals method is used along with different exchange-correlation potentials to obtain the lattice constants, phonons, electronic, and optical properties of the SrMg2X2 (X=N, P, As, Sb, Bi) Zintl compounds. A good agreement is achieved and our calculations are validated by previous experimental and theoretical data. All compounds have shown stable dynamical behavior with gamma centered longitudinal response having no imaginary frequencies. Electronic band structures reveal the semiconducting nature of the compounds. The Pnictogen (X)-p state contributed mainly in the valence band and the Sr-d state forms the conduction of the compounds. Relative charge transfer and low overlapping of the atomic densities indicates the preferable ionic bonding character of these materials. In the optical properties, real and imaginary parts of dielectric function, complex refractive index, birefringence, reflectivity, and optical conductivity are calculated. These compounds can be utilized in the optical and optoelectronic devices.

Passivation of carbon dimer defects in amorphous SiO2/4H-SiC (0001) interface: A first-principles study

Yi-Jie Zhang, Zhi-Peng Yin, Yan Su, De-Jun Wang
Chin. Phys. B 2018, 27 (4): 047103;  doi: 10.1088/1674-1056/27/4/047103
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An amorphous SiO2/4H-SiC (0001) interface model with carbon dimer defects is established based on density functional theory of the first-principle plane wave pseudopotential method. The structures of carbon dimer defects after passivation by H2 and NO molecules are established, and the interface states before and after passivation are calculated by the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional scheme. Calculation results indicate that H2 can be adsorbed on the O2-C=C-O2 defect and the carbon-carbon double bond is converted into a single bond. However, H2 cannot be adsorbed on the O2-(C=C)'-O2 defect. The NO molecules can be bonded by N and C atoms to transform the carbon-carbon double bonds, thereby passivating the two defects. This study shows that the mechanism for the passivation of SiO2/4H-SiC (0001) interface carbon dimer defects is to convert the carbon-carbon double bonds into carbon dimers. Moreover, some intermediate structures that can be introduced into the interface state in the band gap should be avoided.

Influence of spin-orbit coupling on spin-polarized electronic transport in magnetic semiconductor nanowires with nanosized sharp domain walls

Lian Liu, Wen-Xiang Chen, Rui-Qiang Wang, Liang-Bin Hu
Chin. Phys. B 2018, 27 (4): 047201;  doi: 10.1088/1674-1056/27/4/047201
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Influence of spin-orbit coupling on spin-polarized electronic transport in magnetic semiconductor nanowires with nanosized sharp domain walls is investigated theoretically. It is shown that the Rashba spin-orbit coupling can enhance significantly the spin-flip scattering of charge carriers from a nanosized sharp domain wall whose extension is much smaller than the carrier's Fermi wavelength. When there are more than one domain wall presented in a magnetic semiconductor nanowire, not only the spin-flip scattering of charge carriers from the domain walls but the quantum interference of charge carriers in the intermediate domain regions between neighboring domain walls may play important roles on spin-polarized electronic transport, and in such cases the influences of the Rashba spin-orbit coupling will depend sensitively both on the domain walls' width and the domain walls' separation.

Effect of depositing PCBM on perovskite-based metal-oxide-semiconductor field effect transistors

Su-Zhen Luan, Yu-Cheng Wang, Yin-Tao Liu, Ren-Xu Jia
Chin. Phys. B 2018, 27 (4): 047208;  doi: 10.1088/1674-1056/27/4/047208
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In this manuscript, the perovskite-based metal-oxide-semiconductor field effect transistors (MOSFETs) with phenyl-C61-butyric acid methylester (PCBM) layers are studied. The MOSFETs are fabricated on perovskites, and characterized by photoluminescence spectra (PL), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). With PCBM layers, the current-voltage hysteresis phenomenon is effetely inhibited, and both the transfer and output current values increase. The band energy diagrams are proposed, which indicate that the electrons are transferred into the PCBM layer, resulting in the increase of photocurrent. The electron mobility and hole mobility are extracted from the transfer curves, which are about one order of magnitude as large as those of PCBM deposited, which is the reason why the electrons are transferred into the PCBM layer and the holes are still in the perovskites, and the effects of ionized impurity scattering on carrier transport become smaller.

Room-temperature operating extended short wavelength infrared photodetector based on interband transition of InAsSb/GaSb quantum well

Ling Sun, Lu Wang, Jin-Lei Lu, Jie Liu, Jun Fang, Li-Li Xie, Zhi-Biao Hao, Hai-Qiang Jia, Wen-Xin Wang, Hong Chen
Chin. Phys. B 2018, 27 (4): 047209;  doi: 10.1088/1674-1056/27/4/047209
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Here in this paper, we report a room-temperature operating infrared photodetector based on the interband transition of an InAsSb/GaSb quantum well. The interband transition energy of 5-nm thick InAs0.91Sb0.09 embedded in the GaSb barrier is calculated to be 0.53 eV (2.35 μm), which makes the absorption range of InAsSb cover an entire range from short-wavelength infrared to long-wavelength infrared spectrum. The fabricated photodetector exhibits a narrow response range from 2.0 μm to 2.3 μm with a peak around 2.1 μm at 300 K. The peak responsivity is 0.4 A/W under -500 -mV applied bias voltage, corresponding to a peak quantum efficiency of 23.8% in the case without any anti-reflection coating. At 300 K, the photodetector exhibits a dark current density of 6.05×10-3 A/cm2 under -400-mV applied bias voltage and 3.25×10-5 A/cm2 under zero, separately. The peak detectivity is 6.91×1010 cm·Hz1/2/W under zero bias voltage at 300 K.

Conductivity and band alignment of LaCrO3/SrTiO3 (111) heterostructure

Yan-Peng Hong, Xin-Xin Wang, Guo-Liang Qu, Cheng-Jian Li, Hong-Xia Xue, Ke-Jian Liu, Yong-Chun Li, Chang-Min Xiong, Rui-Fen Dou, Lin He, Jia-Cai Nie
Chin. Phys. B 2018, 27 (4): 047301;  doi: 10.1088/1674-1056/27/4/047301
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In this work, we investigate the electrical transport property and electronic structure of oxide heterostructure LaCrO3/SrTiO3 (111). The interface grown under relatively low oxygen partial pressure is found to be metallic with a conducting critical thickness of 11 unit cells of LaCrO3. This criticality is also observed by x-ray photoelectron spectroscopy, in which the Ti3+ signal intensity at the spectrum edge of the Ti-2p3/2 core level increases rapidly when the critical thickness is reached. The variations of the valence band offset and full width at half maximum of the core-level spectrum with LaCrO3 thickness suggest that the built-in fields exist both in LaCrO3 and in SrTiO3. Two possible origins are proposed:the charge transfer from LaCrO3 and the formation of a quantum well in SrTiO3. Our results shed light on the understanding of the doping mechanism at the polar/non-polar oxide interface. Moreover, due to the interesting lattice and spin structure of LCO in the (111) direction, our work provides a basis for further exploring the novel topological quantum phenomena in this system.

Gap plasmon-enhanced photoluminescence of monolayer MoS2 in hybrid nanostructure Hot!

Le Yu, Di Liu, Xiao-Zhuo Qi, Xiao Xiong, Lan-Tian Feng, Ming Li, Guo-Ping Guo, Guang-Can Guo, Xi-Feng Ren
Chin. Phys. B 2018, 27 (4): 047302;  doi: 10.1088/1674-1056/27/4/047302
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Monolayer transition-metal dichalcogenides (TMDs) have attracted a lot of attention for their applications in optics and optoelectronics. Molybdenum disulfide (MoS2), as one of those important materials, has been widely investigated due to its direct band gap and photoluminescence (PL) in visible range. Owing to the fact that the monolayer MoS2 suffers low light absorption and emission, surface plasmon polaritons (SPPs) are used to enhance both the excitation and emission efficiencies. Here, we demonstrate that the PL of MoS2 sandwiched between 200-nm-diameter gold nanoparticle (AuNP) and 150-nm-thick gold film is improved by more than 4 times compared with bare MoS2 sample. This study shows that gap plasmons can possess more optical and optoelectronic applications incorporating with many other emerging two-dimensional materials.

Double band-inversions of bilayer phosphorene under strain and their effects on optical absorption

Shi He, Mou Yang, Rui-Qiang Wang
Chin. Phys. B 2018, 27 (4): 047303;  doi: 10.1088/1674-1056/27/4/047303
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Strain is a powerful tool to engineer the band structure of bilayer phosphorene. The band gap can be decreased by vertical tensile strain or in-plane compressive strain. At a critical strain, the gap is closed and the bilayer phosphorene is turn to be a semi-Dirac semimetal material. If the strain is stronger than the criterion, a band-inversion occurs and it re-happens when the strain is larger than another certain value. For the zigzag bilayer phosphorene ribbon, there are two edge band dispersions and each dispersion curve represents two degenerate edge bands. When the first band-inversion happens, one of the edge band dispersion disappears between the band-cross points while the other survives, and the latter will be eliminated between another pair of band-cross points of the second band-inversion. The optical absorption of bilayer phosphorene is highly polarized along armchair direction. When the strain is turn on, the optical absorption edge changes. The absorption rate for armchair polarized light is decreased by gap shrinking, while that for zigzag polarized light increases. The band-touch and band-inversion respectively result in the sublinear and linear of absorption curve versus light frequency in low frequency limit.

Bias polarity-dependent unipolar switching behavior in NiO/SrTiO3 stacked layer

Xian-Wen Sun, Cai-Hong Jia, Xian-Sheng Liu, Guo-Qiang Li, Wei-Feng Zhang
Chin. Phys. B 2018, 27 (4): 047304;  doi: 10.1088/1674-1056/27/4/047304
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The identification of the switching location has been a key technology to tune the physical properties of unipolar resistive switching (RS) cells. Here we report the RS properties of Au/NiO/SrTiO3(STO)/Pt memory cells. The switching repeatability is closely related to the applied bias polarity, which is different from the scenario of the Au/STO/Pt cells reported in our previous researches. The high resistance in positive bias is greater than that in negative bias. The R(T)-R0I2R(T) plot of the on-state I-V curve shows a regular shape only with a slight bend and an abnormal shape with an abrupt increase and decrease under negative and positive bias, respectively. These comparative experimental results reveal that the conductance filament consisting of oxygen vacancies grows from the cathode to the anode. The spatial RS location is identified with the weaker part along the conductance filament length direction, which should be near the NiO/STO interface and STO/Pt interface under positive and negative bias, respectively.

Low specific on-resistance GaN-based vertical heterostructure field effect transistors with nonuniform doping superjunctions

Wei Mao, Hai-Yong Wang, Peng-Hao Shi, Xiao-Fei Wang, Ming Du, Xue-Feng Zheng, Chong Wang, Xiao-Hua Ma, Jin-Cheng Zhang, Yue Hao
Chin. Phys. B 2018, 27 (4): 047305;  doi: 10.1088/1674-1056/27/4/047305
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A novel GaN-based vertical heterostructure field effect transistor (HFET) with nonuniform doping superjunctions (non-SJ HFET) is proposed and studied by Silvaco-ATLAS, for minimizing the specific on-resistance (RonA) at no expense of breakdown voltage (BV). The feature of non-SJ HFET lies in the nonuniform doping concentration from top to bottom in the n-and p-pillars, which is different from that of the conventional GaN-based vertical HFET with uniform doping superjunctions (un-SJ HFET). A physically intrinsic mechanism for the nonuniform doping superjunction (non-SJ) to further reduce RonA at no expense of BV is investigated and revealed in detail. The design, related to the structure parameters of non-SJ, is optimized to minimize the RonA on the basis of the same BV as that of un-SJ HFET. Optimized simulation results show that the reduction in RonA depends on the doping concentrations and thickness values of the light and heavy doping parts in non-SJ. The maximum reduction of more than 51% in RonA could be achieved with a BV of 1890 V. These results could demonstrate the superiority of non-SJ HFET in minimizing RonA and provide a useful reference for further developing the GaN-based vertical HFETs.

Influence of fin architectures on linearity characteristics of AlGaN/GaNFinFETs

Ting-Ting Liu, Kai Zhang, Guang-Run Zhu, Jian-Jun Zhou, Yue-Chan Kong, Xin-Xin Yu, Tang-Sheng Chen
Chin. Phys. B 2018, 27 (4): 047307;  doi: 10.1088/1674-1056/27/4/047307
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We investigate the influence of fin architecture on linearity characteristics of AlGaN/GaNFinFET. It is found that the FinFET with scaled fin dimensions exhibits much flatter Gm characteristics than the one with long fins as well as planar HEMT. According to the comparative study, we provide direct proof that source resistance rather than tri-gate structure itself dominates the Gm behavior. Furthermore, power measurements show that the optimized FinFET is capable of delivering a much higher output power density along with significant improvement in linearity characteristics than conventional planar HEMT. This study also highlights the importance of fin design in GaN-based FinFET for microwave power application, especially high-linearity applications.

Topological phase diagrams and Majorana zero modes of the Kitaev ladder and tube

Yiming Wang, Zhidan Li, Qiang Han
Chin. Phys. B 2018, 27 (4): 047401;  doi: 10.1088/1674-1056/27/4/047401
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In this paper, we study two quasi-one-dimensional (1D) Kitaev models with ladder-like and tube-like spatial structures, respectively. Our results provide the phase diagrams and explicit expressions of the Majorana zero modes. The topological phase diagrams are obtained by decomposing the topological invariants and the topological conditions for topologically nontrivial phases are given precisely. For systems which belongs to topological class BDI, we obtain the regions in the phase diagrams where the topological numbers show even-odd effect. For the Kitaev tube model a phase factor induced by the magnetic flux in the axial direction of the tube is introduced to alter the classification of the tube Hamiltonian from class BDI to D. The Kitaev tube of class D is characterized by the Z2 index when the number of chains is odd while 0, 1, 2 when the number of chains is even. The phase diagrams show periodic behaviors with respect to the magnetic flux. The bulk-boundary correspondence is demonstrated by the observations that the topological conditions for the bulk topological invariant to take nontrivial values are precisely those for the existence of the Majorana zero modes.

The structure and elasticity of phase B silicates under high pressure by first principles simulation

Lei Liu, Li Yi, Hong Liu, Ying Li, Chun-Qiang Zhuang, Long-Xing Yang, Gui-Ping Liu
Chin. Phys. B 2018, 27 (4): 047402;  doi: 10.1088/1674-1056/27/4/047402
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The structures and elasticities of phase B silicates with different water and iron (Fe) content are obtained by first-principles simulation to understand the effects of water and Fe on their properties under high pressure. The lattice constants a and b decrease with increasing water content. On the contrary, c increases with increasing water content. On the other hand, the b and c decrease with increasing Fe content while a increases with increasing Fe content. The decrease of M (metal)-O octahedral volume is greater than the decrease of SiO polyhedral volume over the same pressure range. The density, bulk modulus and shear modulus of phase B increase with increasing Fe content and decrease with increasing water content. The compressional wave velocity (Vp) and shear wave velocity (Vs) of phase B decrease with increasing water and Fe content. The comparisons of density and wave velocity between phase B silicate and the Earth typical structure provide the evidence for understanding the formation of the X-discontinuity zone of the mantle.

Distinction between critical current effects and intrinsic anomalies in the point-contact Andreev reflection spectra of unconventional superconductors Hot!

Ge He, Zhong-Xu Wei, Jérémy Brisbois, Yan-Li Jia, Yu-Long Huang, Hua-Xue Zhou, Shun-Li Ni, Alejandro V Silhanek, Lei Shan, Bei-Yi Zhu, Jie Yuan, Xiao-Li Dong, Fang Zhou, Zhong-Xian Zhao, Kui Jin
Chin. Phys. B 2018, 27 (4): 047403;  doi: 10.1088/1674-1056/27/4/047403
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In this work, we discuss the origin of several anomalies present in the point-contact Andreev reflection spectra of (Li1-xFex)OHFeSe, LiTi2O4, and La2-xCexCuO4. While these features are similar to those stemming from intrinsic superconducting properties, such as Andreev reflection, electron-boson coupling, multigap superconductivity, d-wave and p-wave pairing symmetry, they cannot be accounted for by the modified Blonder-Tinkham-Klapwijk (BTK) model, but require to consider critical current effects arising from the junction geometry. Our results point to the importance of tracking the evolution of the dips and peaks in the differential conductance as a function of the bias voltage, in order to correctly deduce the properties of the superconducting state.

Composition design for (PrNd-La–Ce)2Fe14B melt-spun magnets by machine learning technique

Rui Li, Yao Liu, Shu-Lan Zuo, Tong-Yun Zhao, Feng-Xia Hu, Ji-Rong Sun, Bao-Gen Shen
Chin. Phys. B 2018, 27 (4): 047501;  doi: 10.1088/1674-1056/27/4/047501
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Data-driven technique is a powerful and efficient tool for guiding materials design, which could supply as an alternative to trial-and-error experiments. In order to accelerate composition design for low-cost rare-earth permanent magnets, an approach using composition to estimate coercivity (Hcj) and maximum magnetic energy product ((BH)max) via machine learning has been applied to (PrNd-La-Ce)2Fe14B melt-spun magnets. A set of machine learning algorithms are employed to build property prediction models, in which the algorithm of Gradient Boosted Regression Trees is the best for predicting both Hcj and (BH)max, with high accuracies of R2=0.88 and 0.89, respectively. Using the best models, predicted datasets of Hcj or (BH)max in high-dimensional composition space can be constructed. Exploring these virtual datasets could provide efficient guidance for materials design, and facilitate the composition optimization of 2:14:1 structure melt-spun magnets. Combined with magnets' cost performance, the candidate cost-effective magnets with targeted properties can also be accurately and rapidly identified. Such data analytics, which involves property prediction and composition design, is of great time-saving and economical significance for the development and application of LaCe-containing melt-spun magnets.

Investigation of magnetization reversal process in pinned CoFeB thin film by in-situ Lorentz TEM

Ke Pei, Wei-Xing Xia, Bao-Min Wang, Xing-Cheng Wen, Ping Sheng, Jia-Ping Liu, Xin-Cai Liu, Run-Wei Li
Chin. Phys. B 2018, 27 (4): 047502;  doi: 10.1088/1674-1056/27/4/047502
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Exchange bias effect has been widely employed for various magnetic devices. The experimentally reported magnitude of exchange bias field is often smaller than that predicted theoretically, which is considered to be due to the partly pinned spins of ferromagnetic layer by antiferromagnetic layer. However, mapping the distribution of pinned spins is challenging. In this work, we directly image the reverse domain nucleation and domain wall movement process in the exchange biased CoFeB/IrMn bilayers by Lorentz transmission electron microscopy. From the in-situ experiments, we obtain the distribution mapping of the pinning strength, showing that only 1/6 of the ferromagnetic layer at the interface is strongly pinned by the antiferromagnetic layer. Our results prove the existence of an inhomogeneous pinning effect in exchange bias systems.

First-order reversal curve investigated magnetization switching in Pd/Co/Pd wedge film

Yan Li, Wei He, Rui Sun, Zi-Zhao Gong, Na Li, Qeemat Gul, Xiang-Qun Zhang, Zhao-Hua Cheng
Chin. Phys. B 2018, 27 (4): 047503;  doi: 10.1088/1674-1056/27/4/047503
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The magnetization switching plays an essential role in spintronic devices. In this study, a Pd(3 nm)/Co(0.14-1.68 nm)/Pd(5 nm) wedge film is deposited on an MgO (111) substrate by molecular beam epitaxy. We investigate the polar magneto-optical Kerr effect (MOKE) and carry out the first-order reversal curve (FORC) measurements. For the wedge system, it is observed that the Co thickness could drive the spin reorientation transition (SRT) from out-of-plane to in-plane. Meanwhile, we find the different types of magnetization switchings in the continuous SRT process, which can originate from the formation of different magnetic compositions. Our work provides the possibility of tuning the interfacial effect, and paves the way to analyzing magnetization switching.

Linear and nonlinear optical analysis on semiorganic L-proline cadmium chloride single crystal

Mohd Anis, M I Baig, S S Hussaini, M D Shirsat, Mohd Shkir, H A Ghramh
Chin. Phys. B 2018, 27 (4): 047801;  doi: 10.1088/1674-1056/27/4/047801
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In the current investigation, L-proline cadmium chloride monohydrate (LPCC) single crystal is grown by a slow solvent evaporation technique to identify its credibility for nonlinear optical device applications. The constituent elements of LPCC crystal are determined by the energy dispersive spectroscopic (EDS) technique. The single crystal x-ray diffraction technique is used to determine the structural dimensions of LPCC crystal. The UV-visible studies are carried out within a wavelength range of 200 nm-1100 nm to determine the optical transmittance of LPCC crystal. The linear optical parameters of LPCC crystal are evaluated using the transmittance data to discuss its importance for distinct optical devices. The Nd:YAG laser assisted Kurtz-Perry test is carried out to determine the enhancement in second harmonic generation efficiency of LPCC crystal with reference to KDP crystal. The Z-scan technique is employed to assess the third order nonlinear optical (TONLO) properties of LPCC crystal at 632.8 nm. The Z-scan data are utilized to evaluate the TONLO refraction, absorption and susceptibility of LPCC crystal. The color oriented luminescence behavior of LPCC crystal is investigated within a spectral range of 350 nm-700 nm. The dependence of dielectric constant and dielectric loss on temperature and frequency is evaluated through the dielectric measurement studies.

Structural, electronic, vibrational, and thermodynamic properties of Zr1-xHfxCo: A first-principles-based study

Jun-Chao Liu, Zhi-Hong Yuan, Shi-Chang Li, Xiang-Gang Kong, You Yu, Sheng-Gui Ma, Ge Sang, Tao Gao
Chin. Phys. B 2018, 27 (4): 047802;  doi: 10.1088/1674-1056/27/4/047802
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The physical properties including structural, electronic, vibrational and thermodynamic properties of Zr1-xHfxCo (x is the concentration of constituent element Hf, and changes from 0 to 1) are investigated in terms of the ABINIT program. The results reveal that all of Zr1-xHfxCo have similar physical properties. When Hf concentration x gradually increases from 0.0 to 1.0, the lattice constant decreases from 3.217 Å to 3.195 Å very slowly. The calculated density of states (DOS) indicates that the metallic nature is enhanced and the electrical conductivity turns better with the increase of Hf. Moreover, as Hf concentration increases from 0 to 1, the Fermi energy gradually increases from -6.96 eV to -6.21 eV, and the electronic density of states at the Fermi level (N(Ef)) decreases from 2.795 electrons/eV f.u. down to 2.594 electrons/eV f.u., both of which imply the decrease of chemical stability. The calculated vibrational properties show that the increase of Hf concentration from 0 to 1 causes the maximum vibrational frequency to decrease gradually from about 223 cm-1 to 186 cm-1, which suggests a lower dispersion gradient and lower phonon group velocities for these modes. Finally, the phonon related thermodynamic properties are obtained and discussed.

Characteristic improvements of thin film AlGaInP red light emitting diodes on a metallic substrate

Bin Zhao, Wei Hu, Xian-Sheng Tang, Wen-Xue Huo, Li-Li Han, Ming-Long Zhao, Zi-Guang Ma, Wen-Xin Wang, Hai-Qiang Jia, Hong Chen
Chin. Phys. B 2018, 27 (4): 047803;  doi: 10.1088/1674-1056/27/4/047803
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We report a type of thin film AlGaInP red light emitting diode (RLED) on a metallic substrate by electroplating copper (Cu) to eliminate the absorption of GaAs grown substrate. The fabrication of the thin film RLED is presented in detail. Almost no degradations of epilayers properties are observed after this substrate transferred process. Photoluminescence and electroluminescence are measured to investigate the luminous characteristics. The thin film RLED shows a significant enhancement of light output power (LOP) by improving the injection efficiency and light extraction efficiency compared with the reference RLED on the GaAs parent substrate. The LOPs are specifically enhanced by 73.5% and 142% at typical injections of 2 A/cm2 and 35 A/cm2 respectively from electroluminescence. Moreover, reduced forward voltages, stable peak wavelengths and full widths at half maximum are obtained with the injected current increasing. These characteristic improvements are due to the Cu substrate with great current spreading and the back reflection by bottom electrodes. The substrate transferred technology based on electroplating provides an optional way to prepare high-performance optoelectronic devices, especially for thin film types.

Hot spots enriched plasmonic nanostructure-induced random lasing of quantum dots thin film

Feng Shan, Xiao-Yang Zhang, Jing-Yuan Wu, Tong Zhang
Chin. Phys. B 2018, 27 (4): 047804;  doi: 10.1088/1674-1056/27/4/047804
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Here, a plasmon-enhanced random laser was achieved by incorporating gold nanostars (NS) into disordered polymer and CdSe/ZnS quantum dots (QDs) gain medium films, in which the surface plasmon resonance of gold NS can greatly enhance the scattering cross section and bring a large gain volume. The random distribution of gold NS in the gain medium film formed a laser-mode resonator. Under a single-pulse pumping, the scattering center of gold NS-based random laser exhibits enhanced performance of a lasing threshold of 0.8 mJ/cm2 and a full width as narrow as 6 nm at half maximum. By utilizing the local enhancement characteristic of the electric field at the sharp apexes of the gold NS, the emission intensity of the random laser was increased. In addition, the gold NS showed higher thermal stability than the silver nanoparticles, withstanding high temperature heating up to 200℃. The results of metal nanostructures with enriched hot spots and excellent temperature stability have tremendous potential applications in the fields of biological identification, medical diagnostics, lighting, and display devices.

Off-stoichiometry indexation of BiFeO3 thin film on silicon by Rutherford backscattering spectrometry

Ze-Song Wang, Ren-Zheng Xiao, Chang-Wei Zou, Wei Xie, Can-Xin Tian, Shu-Wen Xue, Gui-Ang Liu, Neena Devi, De-Jun Fu
Chin. Phys. B 2018, 27 (4): 047901;  doi: 10.1088/1674-1056/27/4/047901
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BiFeO3 is a multiferroic material with physical properties very sensitive to its stoichiometry. BiFeO3 thin films on silicon substrate are prepared by the sol-gel method combined with layer-by-layer annealing and final annealing schemes. X-ray diffraction and scanning electron microscopy are employed to probe the phase structures and surface morphologies. Using Rutherford backscattering spectrometry to quantify the nonstoichiometries of BiFeO3 thin films annealed at 100℃-650℃. The results indicate that Bi and Fe cations are close to the stoichiometry of BiFeO3, whereas the deficiency of O anions possibly plays a key role in contributing to the leakage current of 10-5 A/cm2 in a wide range of applied voltage rather than the ferroelectric polarizations of BiFeO3 thin films annealed at high temperature.

Effects of growth conditions on optical quality and surface morphology of InGaAsBi

Jia-Kai Li, Li-Kun Ai, Ming Qi, An-Hui Xu, Shu-Min Wang
Chin. Phys. B 2018, 27 (4): 048101;  doi: 10.1088/1674-1056/27/4/048101
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The effects of Bi flux and pressure of AsH3 on Bi incorporation, surface morphology and optical properties of InGaAsBi grown by gas source molecular beam epitaxy are studied. It is found that using relatively low pressure of AsH3 and high Bi flux can strengthen the effect on the incorporation of Bi and increase its content linearly with Bi flux until it nearly reaches a saturation value. The result from Rutherford backscattering spectroscopy (RBS) confirms that the Bi incorporation can increase up to 1.13%. By adjusting Bi and As flux, we could improve the surface morphology of InGaAsBi sample. Room temperature photoluminescence shows strong and broad light emission at energy levels much smaller than the InGaAs bandgap.

Structural and electrical properties of reactive magnetron sputtered yttrium-doped HfO2 films

Yu Zhang, Jun Xu, Da-Yu Zhou, Hang-Hang Wang, Wen-Qi Lu, Chi-Kyu Choi
Chin. Phys. B 2018, 27 (4): 048103;  doi: 10.1088/1674-1056/27/4/048103
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Hafnium oxide thin films doped with different concentrations of yttrium are prepared on Si (100) substrates at room temperature using a reactive magnetron sputtering system. The effects of Y content on the bonding structure, crystallographic structure, and electrical properties of Y-doped HfO2 films are investigated. The x-ray photoelectron spectrum (XPS) indicates that the core level peak positions of Hf 4f and O 1s shift toward lower energy due to the structure change after Y doping. The depth profiling of XPS shows that the surface of the film is completely oxidized while the oxygen deficiency emerges after the stripping depths have increased. The x-ray diffraction and high resolution transmission electron microscopy (HRTEM) analyses reveal the evolution from monoclinic HfO2 phase towards stabilized cubic HfO2 phase and the preferred orientation of (111) appears with increasing Y content, while pure HfO2 shows the monoclinic phase only. The leakage current and permittivity are determined as a function of the Y content. The best combination of low leakage current of 10-7 A/cm2 at 1 V and a highest permittivity value of 29 is achieved when the doping ratio of Y increases to 9 mol%. A correlation among Y content, phase evolution and electrical properties of Y-doped HfO2 ultra-thin film is investigated.

Low-temperature synthesis of apatite-type La9.33Ge6O26 as electrolytes with high conductivity

Guang-Chao Yin, Guo-Dong Zhao, Hong Yin, Fu-Chao Jia, Qiang Jing, Sheng-Gui Fu, Mei-Ling Sun, Wei Gao
Chin. Phys. B 2018, 27 (4): 048201;  doi: 10.1088/1674-1056/27/4/048201
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In the present study, high-quality apatite-type La9.33Ge6O26 powders are successfully synthesized by a facile molten-salt synthesis method (MSSM) at low temperatures, using LiCl, LiCl/NaCl mixture (mass ratio 1:1) as molten salt, respectively. Experimental results indicate that the optimal mass ratio between reactant and molten salt is 1:2, and LiCl/NaCl mixed molten-salt is more beneficial for forming high-quality La9.33Ge6O26 powders than LiCl individual molten-salt. Comparing with the conventional solid-state reaction method (SSRM), the synthesis temperature of apatite-type La9.33Ge6O26 powders using the MSSM decreases more than 350℃, which can effectively avoid Ge loss in the preparation process of precursor powders. Furthermore, the powders obtained by the MSSM are homogeneous, non-agglomerated and well crystallized, which are very favorable for gaining dense pellets in the premise of avoiding Ge loss. On the basis of high-quality precursor powders, the dense and pure ceramic pellets of La9.33Ge6O26 are gained at a low temperature of 1100℃ for 2 h, which exhibit higher conductivities (σ 850℃(LiCl)=2.3×10-2 S·cm-1, σ 850℃(LiCl/NaCl)=4.9×10-2 S·cm-1) and lower activation energies (Ea(LiCl)=1.02 eV, Ea(LiCl/NaCl)=0.99 eV) than that synthesized by the SSRM.

Scalability of dark current in silicon PIN photodiode

Ya-Jie Feng, Chong Li, Qiao-Li Liu, Hua-Qiang Wang, An-Qi Hu, Xiao-Ying He, Xia Guo
Chin. Phys. B 2018, 27 (4): 048501;  doi: 10.1088/1674-1056/27/4/048501
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The mechanism for electrical conduction is investigated by the dark temperature-dependent current-voltage characteristics of Si PIN photodiodes with different photosensitive areas. The characteristic tunneling energy E00 can be obtained to be 1.40 meV, 1.53 meV, 1.74 meV, 1.87 meV, and 2.01 meV, respectively, for the photodiodes with L=0.25 mm, 0.5 mm, 1 mm, 1.5 mm, and 2 mm by fitting the ideality factor n versus temperature curves according to the tunneling-enhanced recombination mechanism. The trap-assisted tunneling-enhanced recombination in the i-layer plays an important role in our device, which is consistent with the experimental result that area-dependent leakage current is dominant with the side length larger than 1 mm of the photosensitive area. Our results reveal that the quality of the bulk material plays an important role in the electrical conduction mechanism of the devices with the side length larger than 1 mm of the photosensitive area.

Closed-form breakdown voltage/specific on-resistance model using charge superposition technique for vertical power double-diffused metal-oxide-semiconductor device with high-κ insulator

Xue Chen, Zhi-Gang Wang, Xi Wang, James B Kuo
Chin. Phys. B 2018, 27 (4): 048502;  doi: 10.1088/1674-1056/27/4/048502
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An improved vertical power double-diffused metal-oxide-semiconductor (DMOS) device with a p-region(P1) and high-κ insulator vertical double-diffusion metal-oxide-semiconductor (HKP-VDMOS) is proposed to achieve a better performance on breakdown voltage (BV)/specific on-resistance (Ron,sp) than conventional VDMOS with a high-κ insulator (CHK-VDMOS). The main mechanism is that with the introduction of the P-region, an extra electric field peak is generated in the drift region of HKP-VDMOS to enhance the breakdown voltage. Due to the assisted depletion effect of this p-region, the specific on-resistance of the device could be reduced because of the high doping density of the N-type drift region. Meanwhile, based on the superposition of the depleted charges, a closed-form model for electric field/breakdown voltage is generally derived, which is in good agreement with the simulation result within 10% of error. An HKP-VDMOS device with a breakdown voltage of 600 V, a reduced specific on-resistance of 11.5 mΩ·cm2 and a figure of merit (FOM) (BV2/Ron,sp) of 31.2 MW·cm-2 shows a substantial improvement compared with the CHK-VDMOS device.

Research on the radiation hardened SOI devices with single-step Si ion implantation

Li-Hua Dai, Da-Wei Bi, Zhi-Yuan Hu, Xiao-Nian Liu, Meng-Ying Zhang, Zheng-Xuan Zhang, Shi-Chang Zou
Chin. Phys. B 2018, 27 (4): 048503;  doi: 10.1088/1674-1056/27/4/048503
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Silicon-on-insulator (SOI) devices are sensitive to the total ionizing dose effect due to the existence of buried oxide. In this paper, an extra single-step Si ion implantation into buried oxide layer prior to the normal complementary metal-oxide-semiconductor transistor (CMOS) process is used to harden the SOI wafer. The top-Si quality of the hardened SOI wafer is confirmed to be good enough for device manufacturing through various characterization methods. The radiation experiments show that the total ionizing dose tolerance of the Si implanted SOI device is improved significantly. The metastable electron traps introduced by Si implantation is also investigated by electrical stress. The results show that these traps are very instable, and electrons will tunnel into or out of the metastable electron traps quickly after hot-electron-injection or hot-hole-injection.

Water-based processed and alkoxide-based processed indium oxide thin-film transistors at different annealing temperatures

Xu-Yang Li, Zhi-Nong Yu, Jin Cheng, Yong-Hua Chen, Jian-She Xue, Jian Guo, Wei Xue
Chin. Phys. B 2018, 27 (4): 048504;  doi: 10.1088/1674-1056/27/4/048504
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In this study, indium oxide (In2O3) thin-film transistors (TFTs) are fabricated by two kinds of low temperature solution-processed technologies (Ta ≤ 300℃), i.e., water-based (DIW-based) process and alkoxide-based (2-ME-based) process. The thickness values, crystallization properties, chemical structures, surface roughness values, and optical properties of In2O3 thin-films and the electrical characteristics of In2O3 TFTs are studied at different annealing temperatures. Thermal annealing at higher temperature leads to an increase in the saturation mobility (μsat) and a negative shift in the threshold voltage (VTH). The DIW-based processed In2O3-TFT annealed at 300℃ exhibits excellent device performance, and one annealed at 200℃ exhibits an acceptable μsat of 0.86 cm2/V·s comparable to that of a-Si:H TFTs, whereas the 2-ME-based TFT annealed at 300℃ exhibits an abundant μsat of 1.65 cm2/Vs and one annealed at 200℃ is inactive. The results are attributed to the fact that the DIW-based process induces a higher degree of oxidation and less defect states than the 2-ME-based process at the same temperature. The DIW-based process for fabricating the In2O3 TFT opens the way for the development of nontoxic, low-cost, and low-temperature oxide electronics.

Analytically determining frequency and amplitude of spontaneous alpha oscillation in Jansen's neural mass model using the describing function method

Yao Xu, Chun-Hui Zhang, Ernst Niebur, Jun-Song Wang
Chin. Phys. B 2018, 27 (4): 048701;  doi: 10.1088/1674-1056/27/4/048701
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Spontaneous alpha oscillations are a ubiquitous phenomenon in the brain and play a key role in neural information processing and various cognitive functions. Jansen's neural mass model (NMM) was initially proposed to study the origin of alpha oscillations. Most of previous studies of the spontaneous alpha oscillations in the NMM were conducted using numerical methods. In this study, we aim to propose an analytical approach using the describing function method to elucidate the spontaneous alpha oscillation mechanism in the NMM. First, the sigmoid nonlinear function in the NMM is approximated by its describing function, allowing us to reformulate the NMM and derive its standard form composed of one nonlinear part and one linear part. Second, by conducting a theoretical analysis, we can assess whether or not the spontaneous alpha oscillation would occur in the NMM and, furthermore, accurately determine its amplitude and frequency. The results reveal analytically that the interaction between linearity and nonlinearity of the NMM plays a key role in generating the spontaneous alpha oscillations. Furthermore, strong nonlinearity and large linear strength are required to generate the spontaneous alpha oscillations.

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