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Chin. Phys. B  
  Chin. Phys. B--2020, Vol.29, No.3
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SPECIAL TOPIC—Recent advances in thermoelectric materials and devices

Cherenkov terahertz radiation from Dirac semimetals surface plasmon polaritons excited by an electron beam

Tao Zhao, Zhenhua Wu
Chin. Phys. B 2020, 29 (3): 034101;  doi: 10.1088/1674-1056/ab6840
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We demonstrate a physical mechanism for terahertz (THz) generation from surface plasmon polaritons (SPPs). In a structure with a bulk Dirac semimetals (BDSs) film deposited on a dielectric substrate, the energy of the asymmetric SPP mode can be significantly enhanced to cross the light line of the substrate due to the SPP-coupling between the interfaces of the film. Therefore, the SPPs can be immediately transformed into Cherenkov radiation without removing the wavevector mismatch. Additionally, the symmetric SPP mode can also be dramatically lifted to cross the substrate light line when a buffer layer with low permittivity relative to the substrate is introduced. In this case, dual-frequency THz radiation from the two SPP modes can be generated simultaneously. The radiation intensity is significantly enhanced by over two orders due to the field enhancement of the SPPs. The radiation frequency can be tuned in the THz frequency regime by adjusting the beam energy and the chemical potential of the BDSs. Our results could find potential applications in developing room temperature, tunable, coherent, and intense THz radiation sources to cover the entire THz band.

Paraxial propagation of cosh-Airy vortex beams in chiral medium

Xiao-Jin Yang, Zhen-Sen Wu, Tan Qu
Chin. Phys. B 2020, 29 (3): 034201;  doi: 10.1088/1674-1056/ab683f
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Propagation dynamics of the cosh-Airy vortex (CAiV) beams in a chiral medium is investigated analytically with Huygens-Fresnel diffraction integral formula. The results show that the CAiV beams are split into the left circularly polarized vortex (LCPV) beams and the right circularly polarized vortex (RCPV) beams with different propagation trajectories in the chiral medium. We mainly investigate the effect of the cosh parameter on the propagation process of the CAiV beams. The propagation characteristics, including intensity distribution, propagation trajectory, peak intensity, main lobe's intensity, Poynting vector, and angular momentum are discussed in detail. We find that the cosh parameter affects the intensity distribution of the CAiV beams but not its propagation trajectory. As the cosh parameter increases, the distribution areas of the LCPV and RCPV beams become wider, and the side lobe's intensity and peak intensity become larger. Besides, the main lobe's intensity of the LCPV and RCPV beams increase with the increase of the cosh parameter at a farther propagation distance, which is confirmed by the variation trend of the Poynting vector. It is significant that we can vary the cosh parameter to control the intensity distribution, main lobe's intensity, and peak intensity of the CAiV beams without changing the propagation trajectory. Our results may provide some support for applications of the CAiV beams in optical micromanipulation.

Far-field vector-diffraction of off-axis parabolic mirror under oblique incidence

Xia-Hui Zeng, Xi-Yao Chen
Chin. Phys. B 2020, 29 (3): 034202;  doi: 10.1088/1674-1056/ab683e
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Based on a full vector-diffraction theory, a detailed theoretical study is carried out, aiming at providing a clear insight into the effects of different focusing and off-axis parabola parameters on far-field vector-diffraction properties of an off-axis parabolic mirror in the presence of misalignments of the incoming beam. The physical origin of these effects is also explored. The results show that the far-field intensity profile is altered by the distortion-, coma-, and astigmatism-like aberrations, which are caused by oblique incidence rather than inherent aberrations for the off-axis configuration. The radius of 90% encircled energy also increases but does not change monotonically with incident beam size increasing, or rather, it first decreases and then increases. The focal shift strongly depends on the effective focal length and oblique incidence angle, but it is almost independent of the beam size, which affects the focusing spot patterns. The intensity distribution produces a higher astigmatic image with off-axis angle increasing. Coma-like aberration starts to become dominant with beam size increasing and results in larger curved propagation trajectory. The incident polarization also affects the intensity distribution. The variation in the Strehl ratio with oblique incidence angle strongly depends on the misalignment direction and beam size as well. In addition, we find that the difference in locus between the catacaustic and the diffraction focus in the meridian is small. But the locus of the sagittal foci is obviously different from the locus of the meridian foci and the catacaustic focus. Moreover, the peak intensity of the sagittal focus is maximum, and the ratio of the peak intensity to that in the meridian plane is approximately 1.5. Understanding these effects is valuable for assessing a practical focused intensity and describing the motion of charged particles under a strong electric field in ultraintense laser-matter interaction.

Optical enhanced interferometry with two-mode squeezed twin-Fock states and parity detection

Li-Li Hou, Shuai Wang, Xue-Fen Xu
Chin. Phys. B 2020, 29 (3): 034203;  doi: 10.1088/1674-1056/ab6837
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We theoretically investigate the quantum enhanced metrology using two-mode squeezed twin-Fock states and parity detection. Our results indicate that, for a given initial squeezing parameter, compared with the two-mode squeezed vacuum state, both phase sensitivity and resolution can be enhanced when the two-mode squeezed twin-Fock state is considered as an input state of a Mach-Zehnder interferometer. Within a constraint on the total photon number, although the two-mode squeezed vacuum state gives the better phase sensitivity when the phase shift φ to be estimated approaches to zero, the phase sensitivity offered by these non-Gaussian entangled Gaussian states is relatively stable with respect to the phase shift itself. When the phase shift slightly deviates from φ=0, the phase sensitivity can be still enhanced by the two-mode squeezed twin-Fock state over a broad range of the total mean photon number where the phase uncertainty is still below the quantum standard noise limit. Finally, we numerically prove that the quantum Cramér-Rao bound can be approached with the parity detection.

Dynamic manipulation of probe pulse and coherent generation of beating signals based on tunneling-induced inference in triangular quantum dot molecules

Nuo Ba, Jin-You Fei, Dong-Fei Li, Xin Zhong, Dan Wang, Lei Wang, Hai-Hua Wang, Qian-Qian Bao
Chin. Phys. B 2020, 29 (3): 034204;  doi: 10.1088/1674-1056/ab683d
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We investigate the dynamic propagation of a probe field via the tunneling-induced interference effect in a triple model of quantum dot molecules. By theoretical analysis and numerical simulation, we find that the number of transparency window relate to the energy splitting and the group velocity of probe field can be effectively controlled by the tunneling coupling intensity. In addition, in the process of light storage and retrieval, when the excited states have no energy splitting in the storage stage but opposite values of the energy splitting in the retrieval stage, the beating signals can be generated.

A low-noise, high-SNR balanced homodyne detector for the bright squeezed state measurement in 1-100 kHz range

Jin-Rong Wang, Qing-Wei Wang, Long Tian, Jing Su, Yao-Hui Zheng
Chin. Phys. B 2020, 29 (3): 034205;  doi: 10.1088/1674-1056/ab683b
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We report a low-noise, high-signal-to-noise-ratio (SNR) balanced homodyne detector based on the standard transimpedance amplifier circuit and the inductance and capacitance combination for the measurement of the bright squeezed state in the range from 1 kHz to 100 kHz. A capacitance is mounted at the input end of the AC branch to prevent the DC photocurrent from entering the AC branch and avoid AC branch saturation. By adding a switch at the DC branch, the DC branch can be flexibly turned on and off on different occasions. When the switch is on, the DC output provides a monitor signal for laser beam alignment. When the switch is off, the electronic noise of the AC branch is greatly reduced at audio-frequency band due to immunity to the impedance of the DC branch, hence the SNR of the AC branch is significantly improved. As a result, the electronic noise of the AC branch is close to -125 dBm, and the maximum SNR of the AC branch is 48 dB with the incident power of 8 mW in the range from 1 kHz to 100 kHz. The developed photodetector paves a path for measuring the bright squeezed state at audio-frequency band.

Evaluation of polarization field in InGaN/GaN multiple quantum well structures by using electroluminescence spectra shift

Ping Chen, De-Gang Zhao, De-Sheng Jiang, Jing Yang, Jian-Jun Zhu, Zong-Shun Liu, Wei Liu, Feng Liang, Shuang-Tao Liu, Yao Xing, Li-Qun Zhang
Chin. Phys. B 2020, 29 (3): 034206;  doi: 10.1088/1674-1056/ab6967
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In order to investigate the inherent polarization intensity in InGaN/GaN multiple quantum well (MQW) structures, the electroluminescence (EL) spectra of three samples with different GaN barrier thicknesses of 21.3 nm, 11.4 nm, and 6.5 nm are experimentally studied. All of the EL spectra present a similar blue-shift under the low-level current injection, and then turns to a red-shift tendency when the current increases to a specific value, which is defined as the turning point. The value of this turning point differs from one another for the three InGaN/GaN MQW samples. Sample A, which has the GaN barrier thickness of 21.3 nm, shows the highest current injection level at the turning point as well as the largest value of blue-shift. It indicates that sample A has the maximum intensity of the polarization field. The red-shift of the EL spectra results from the vertical electron leakage in InGaN/GaN MQWs and the corresponding self-heating effect under the high-level current injection. As a result, it is an effective approach to evaluate the polarization field in the InGaN/GaN MQW structures by using the injection current level at the turning point and the blue-shift of the EL spectra profiles.

Eigenvalue spectrum analysis for temporal signals of Kerr optical frequency combs based on nonlinear Fourier transform

Jia Wang, Ai-Guo Sheng, Xin Huang, Rong-Yu Li, Guang-Qiang He
Chin. Phys. B 2020, 29 (3): 034207;  doi: 10.1088/1674-1056/ab683a
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Based on the nonlinear Schrödinger equation (NLSE) with damping, detuning, and driving terms describing the evolution of signals in a Kerr microresonator, we apply periodic nonlinear Fourier transform (NFT) to the study of signals during the generation of the Kerr optical frequency combs (OFCs). We find that the signals in different states, including the Turing pattern, the chaos, the single soliton state, and the multi-solitons state, can be distinguished according to different distributions of the eigenvalue spectrum. Specially, the eigenvalue spectrum of the single soliton pulse is composed of a pair of conjugate symmetric discrete eigenvalues and the quasi-continuous eigenvalue spectrum with eye-like structure. Moreover, we have successfully demonstrated that the number of discrete eigenvalue pairs in the eigenvalue spectrum corresponds to the number of solitons formed in a round-trip time inside the Kerr microresonator. This work shows that some characteristics of the time-domain signal can be well reflected in the nonlinear domain.

Design of diamond-shape photonic crystal fiber polarization filter based on surface plasma resonance effect

Yongxia Zhang, Jinhui Yuan, Yuwei Qu, Xian Zhou, Binbin Yan, Qiang Wu, Kuiru Wang, Xinzhu Sang, Keping Long, Chongxiu Yu
Chin. Phys. B 2020, 29 (3): 034208;  doi: 10.1088/1674-1056/ab683c
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A novel plasmonic polarization filter based on the diamond-shape photonic crystal fiber (PCF) is proposed. The resonant coupling characteristics of the PCF polarization filter are investigated by the full-vector finite-element method. By optimizing the geometric parameters of the PCF, when the fiber length is 5 mm, the polarization filter has a bandwidth of 990 nm and an extinction ratio (ER) of lower than -20 dB. Moreover, a single wavelength polarization filter can also be achieved, along with an ER of -279.78 dB at wavelength 1.55 μm. It is believed that the proposed PCF polarization filter will be very useful in laser and optical communication systems.

A compact electro-absorption modulator based on graphene photonic crystal fiber

Guangwei Fu, Ying Wang, Bilin Wang, Kaili Yang, Xiaoyu Wang, Xinghu Fu, Wa Jin, Weihong Bi
Chin. Phys. B 2020, 29 (3): 034209;  doi: 10.1088/1674-1056/ab6838
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A compact electro-absorption modulator based on graphene photonic crystal fiber is proposed. To enhance the graphene-light interaction efficiency, the innermost six air-holes of photonic crystal fiber are replaced by two large semicircular holes, and monolayer graphene is deposited on the two large semicircular holes. By optimizing the structure parameters, a strong graphene-light interaction is obtained. Moreover, the switch on-off point of the modulator is unchangeable, which is only related to the frequency of the incident light. The influence factors of this composite structure have been analyzed. The proposed modulator is compared with other graphene-based modulators, and the results show that it is filled without dielectric spacer. There are some excellent performances, such as an extinction ratio 7 dB of y-polarization mode, 3-dB modulation bandwidth of 70 GHz with small footprint of 205 μm, and a consumption of energy per bit 59 pJ/bit.

The optical nonreciprocal response based on a four-mode optomechanical system

Jing Wang
Chin. Phys. B 2020, 29 (3): 034210;  doi: 10.1088/1674-1056/ab6836
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We propose a scheme for realizing the optical nonreciprocal response based a four-mode optomechanical system, consisting of two charged mechanical modes and two linearly coupled optical modes. Two charged mechanical modes are coupled by Coulomb interaction, and two optical modes are coupled to one of mechanical modes by radiation pressure. We numerically evaluate the transmission probability of the probe field to obtain the optimum optical nonreciprocal response parameters. Also, we show that the optical nonreciprocal response is caused by the quantum interference between the optomechanical couplings and the linearly coupled interaction that breaks the time-reversal symmetry.

High-contrast imaging based on wavefront shaping to improve low signal-to-noise ratio photoacoustic signals using superpixel method

Xinjing Lv, Xinyu Xu, Qi Feng, Bin Zhang, Yingchun Ding, Qiang Liu
Chin. Phys. B 2020, 29 (3): 034301;  doi: 10.1088/1674-1056/ab6842
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Photoacoustic (PA) imaging has drawn tremendous research interest for various applications in biomedicine and experienced exponential growth over the past decade. Since the scattering effect of biological tissue on ultrasound is two- to three-orders magnitude weaker than that of light, photoacoustic imaging can effectively improve the imaging depth. However, as the depth of imaging further increases, the incident light is seriously affected by scattering that the generated photoacoustic signal is very weak and the signal-to-noise ratio (SNR) is quite low. Low SNR signals can reduce imaging quality and even cause imaging failure. In this paper, we proposed a new wavefront shaping and imaging method of low SNR photoacoustic signal using digital micromirror device (DMD) based superpixel method. We combined the superpixel method with DMD to modulate the phase and amplitude of the incident light, and the genetic algorithm (GA) was used as the wavefront shaping algorithm. The enhancement of the photoacoustic signal reached 10.46. Then we performed scanning imaging by moving the absorber with the translation stage. A clear image with contrast of 8.57 was obtained while imaging with original photoacoustic signals could not be achieved. The proposed method opens new perspectives for imaging with weak photoacoustic signals.

Second harmonic magnetoacoustic responses of magnetic nanoparticles in magnetoacoustic tomography with magnetic induction

Gepu Guo, Ya Gao, Yuzhi Li, Qingyu Ma, Juan Tu, Dong Zhang
Chin. Phys. B 2020, 29 (3): 034302;  doi: 10.1088/1674-1056/ab6843
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Due to the unique magnetic, mechanical and thermal properties, magnetic nanoparticles (MNPs) have comprehensive applications as the contrast and therapeutic agents in biomedical imaging and magnetic hyperthermia. The linear and nonlinear magnetoacoustic responses determined by the magnetic properties of MNPs have attracted more and more attention in biomedical engineering. By considering the relaxation time of MNPs, we derive the formulae of second harmonic magnetoacoustic responses (2H-MARs) for a cylindrical MNP solution model based on the mechanical oscillations of MNPs in magnetoacoustic tomography with magnetic induction (MAT-MI). It is proved that only the second harmonic magnetoacoustic oscillations can be generated by MNPs under an alternating magnetic excitation. The acoustic pressure of the 2H-MAR is proportional to the square of the magnetic field intensity and exhibits a linear increase with the concentration of MNPs. Numerical simulations of the 2H-MAR are confirmed by the experimental measurements for various magnetic field intensities and solution concentrations using a laser vibrometer. The favorable results demonstrate the feasibility of the harmonic measurements without the fundamental interference of the electromagnetic excitation, and suggest a new harmonic imaging strategy of MAT-MI for MNPs with enhanced spatial resolution and improved signal-to-noise ratio in biomedical applications.

Bubble translation driven by pulsation in a double-bubble system

Ling-Ling Zhang, Wei-Zhong Chen, Yuan-Yuan Zhang, Yao-Rong Wu, Xun Wang, Guo-Ying Zhao
Chin. Phys. B 2020, 29 (3): 034303;  doi: 10.1088/1674-1056/ab69ee
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The pulsation and translation of two cavitation bubbles are studied numerically in sound field. The results show that bubbles' pulsation driven by the sound makes them translate. Different pulsations lead to different translations. Two bubbles will be mutually attractive to each other if they pulsate in phase, while they will be repulsive if out of phase. Furthermore, the secondary Bjerknes force for small phase difference is attractive, and it becomes repulsive for other phase differences up to π phase difference due to the nonlinear effect, although the attractive strength between two bubbles is much larger than the repulsive strength. Finally, one bubble pulsation and the other bubble stationary make the bubbles repel each other.

Ultrasonic beam focusing characteristics of shear-vertical waves for contact-type linear phased array in solid

Yu-Xiang Dai, Shou-Guo Yan, Bi-Xing Zhang
Chin. Phys. B 2020, 29 (3): 034304;  doi: 10.1088/1674-1056/ab69ed
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We investigate the beam focusing technology of shear-vertical (SV) waves for a contact-type linear phased array to overcome the shortcomings of conventional wedge transducer arrays. The numerical simulation reveals the transient excitation and propagation characteristics of SV waves. It is found that the element size plays an important role in determining the transient radiation directivity of SV waves. The transient beam focusing characteristics of SV waves for various array parameters are deeply studied. It is particularly interesting to see that smaller element width will provide the focused beam of SV waves with higher quality, while larger element width may result in erratic fluctuation of focusing energy around the focal point. There exists a specific range of inter-element spacing for optimum focusing performance. Moreover, good beam focusing performance of SV waves can be achieved only at high steering angles.

Influence of dynamic tissue properties on temperature elevation and lesions during HIFU scanning therapy: Numerical simulation

Xiao Zou, Hu Dong, Sheng-You Qian
Chin. Phys. B 2020, 29 (3): 034305;  doi: 10.1088/1674-1056/ab6c4f
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When large tumors are treated, ablation of the entire volume of tumors requires multiple treatment spots formed by high intensity-focused ultrasound (HIFU) scanning therapy. The heating effect of HIFU on biological tissue is mainly reflected in temperature elevation and tissue lesions. Tissue property parameters vary with temperature and, in turn, the distribution of temperature as well as the heating effects change accordingly. In this study, an HIFU scanning therapy model considering dynamic tissue properties is provided. The acoustic fields and temperature fields are solved combining the Helmholtz wave equation with Pennes bio-heat transfer equation based on the finite element method (FEM) to investigate the effects of various tissue properties (i.e., the attenuation coefficient, acoustic velocity, thermal conductivity, specific heat capacity, density, and blood perfusion rate) on heating performance. Comparisons of the temperature distribution and thermal lesions under static and dynamic properties are made based on the data of tissue property parameters varying with temperature. The results show that the dynamic changes of thermal conductivity, specific heat capacity, and acoustic velocity may account for the decrease of temperature elevation in HIFU treatment, while the dynamic changes of attenuation coefficient, density, and blood perfusion rate aggravate the increase of temperature on treatment spots. Compared with other properties, the dynamic change of attenuation coefficient has a greater impact on tissue temperature elevation. During HIFU scanning therapy, the temperature elevation and tissue lesions of the first treatment spot are smaller than those of the subsequent treatment spots, but the temperature on the last treatment spot drops faster during the cooling period. The ellipsoidal tissue lesion is not symmetrical; specifically, the part facing toward the previous treatment spot tends to be larger. Under the condition of the same doses, the temperature elevation and the size of tissue lesions under dynamic properties present significant growth in comparison to static properties. Besides, the tissue lesion begins to form earlier with a more unsymmetrical shape and is connected to the tissue lesion around the previous treatment spot. As a result, lesions around all the treatment spots are connected with each other to form a closed lesion region. The findings in this study reveal the influence of dynamic tissue properties on temperature elevation and lesions during HIFU scanning therapy, providing useful support for the optimization of treatment programs to guarantee higher efficacy and safety.

Simulation-based optimization of inner layout of a theater considering the effect of pedestrians

Qing-Fei Gao, Yi-Zhou Tao, Yan-Fang Wei, Cheng Wu, Li-Yun Dong
Chin. Phys. B 2020, 29 (3): 034501;  doi: 10.1088/1674-1056/ab6c44
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We propose an extended cellular automaton model based on the floor field. The floor field can be changed accordingly in the presence of pedestrians. Furthermore, the effects of pedestrians with different speeds are distinguished, i.e., still pedestrians result in more increment of the floor field than moving ones. The improved floor field reflects impact of pedestrians as movable obstacles on evacuation process. The presented model was calibrated by comparing with previous studies. It is shown that this model provides a better description of crowd evacuation both qualitatively and quantitatively. Then we investigated crowd evacuation from a middle-size theater. Four possible designs of aisles in the theater are studied and one of them is the actual design in reality. Numerical simulation shows that the actual design of the theater is reasonable. Then we optimize the position of the side exit in order to reduce the evacuation time. It is shown that the utilization of the two exits at bottom is less than that of the side exits. When the position of the side exit is shifted upwards by about 1.6 m, it is found that the evacuation time reaches its minimum.

A mass-conserved multiphase lattice Boltzmann method based on high-order difference

Zhang-Rong Qin, Yan-Yan Chen, Feng-Ru Ling, Ling-Juan Meng, Chao-Ying Zhang
Chin. Phys. B 2020, 29 (3): 034701;  doi: 10.1088/1674-1056/ab6834
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The Z-S-C multiphase lattice Boltzmann model [Zheng, Shu, and Chew (ZSC), J. Comput. Phys. 218, 353 (2006)] is favored due to its good stability, high efficiency, and large density ratio. However, in terms of mass conservation, this model is not satisfactory during the simulation computations. In this paper, a mass correction is introduced into the ZSC model to make up the mass leakage, while a high-order difference is used to calculate the gradient of the order parameter to improve the accuracy. To verify the improved model, several three-dimensional multiphase flow simulations are carried out, including a bubble in a stationary flow, the merging of two bubbles, and the bubble rising under buoyancy. The numerical simulations show that the results from the present model are in good agreement with those from previous experiments and simulations. The present model not only retains the good properties of the original ZSC model, but also achieves the mass conservation and higher accuracy.

Multi-bubble motion behavior of uniform magnetic field based on phase field model

Chang-Sheng Zhu, Zhen Hu, Kai-Ming Wang
Chin. Phys. B 2020, 29 (3): 034702;  doi: 10.1088/1674-1056/ab6839
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Aiming at the interaction and coalescence of bubbles in gas-liquid two-phase flow, a multi-field coupling model was established to simulate deformation and dynamics of multi-bubble in gas-liquid two-phase flow by coupling magnetic field, phase field, continuity equation, and momentum equation. Using the phase field method to capture the interface of two phases, the geometric deformation and dynamics of a pair of coaxial vertical rising bubbles under the applied uniform magnetic field in the vertical direction were investigated. The correctness of results is verified by mass conservation method and the comparison of the existing results. The results show that the applied uniform magnetic field can effectively shorten the distance between the leading bubble and the trailing bubble, the time of bubbles coalescence, and increase the velocity of bubbles coalescence. Within a certain range, as the intensity of the applied uniform magnetic field increases, the velocity of bubbles coalescence is proportional to the intensity of the magnetic field, and the time of bubbles coalescence is inversely proportional to the intensity of the magnetic field.

Electrohydrodynamic behaviors of droplet under a uniform direct current electric field

Zi-Long Deng, Mei-Mei Sun, Cheng Yu
Chin. Phys. B 2020, 29 (3): 034703;  doi: 10.1088/1674-1056/ab6835
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The electrohydrodynamic behaviors and evolution processes of silicone oil droplet in castor oil under uniform direct current (DC) electric field are visually observed based on a high-speed microscopic platform. Subsequently, the effects of different working conditions, such as electric field strength, droplet size, etc., on droplet behaviors are roundly discussed. It can be found that there are four droplet behavior modes, including Taylor deformation, typical oblique rotation, periodic oscillation, and fracture, which change with the increase of electric field strength. It is also demonstrated that the degree of flat ellipse deformation gets larger under a stronger electric field. Moreover, both of the stronger electric field and smaller droplet size lead to an increase in the rotation angle of the droplet.

Interface coupling effects of weakly nonlinear Rayleigh-Taylor instability with double interfaces

Zhiyuan Li, Lifeng Wang, Junfeng Wu, Wenhua Ye
Chin. Phys. B 2020, 29 (3): 034704;  doi: 10.1088/1674-1056/ab6965
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Taking the Rayleigh-Taylor instability with double interfaces as the research object, the interface coupling effects in the weakly nonlinear regime are studied numerically. The variation of Atwood numbers on the two interfaces and the variation of the thickness between them are taken into consideration. It is shown that, when the Atwood number on the lower interface is small, the amplitude of perturbation growth on the lower interface is positively related with the Atwood number on the upper interface. However, it is negatively related when the Atwood number on the lower interface is large. The above phenomenon is quantitatively studied using an analytical formula and the underlying physical mechanism is presented.

Fractional variant of Stokes-Einstein relation in aqueous ionic solutions under external static electric fields

Gan Ren, Shikai Tian
Chin. Phys. B 2020, 29 (3): 036101;  doi: 10.1088/1674-1056/ab695b
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Both ionic solutions under an external applied static electric field E and glassy-forming liquids under undercooled state are in non-equilibrium state. In this work, molecular dynamics (MD) simulations with three aqueous alkali ion chloride (NaCl, KCl, and RbCl) ionic solutions are performed to exploit whether the glass-forming liquid analogous fractional variant of the Stokes-Einstein relation also exists in ionic solutions under E. Our results indicate that the diffusion constant decouples from the structural relaxation time under E, and a fractional variant of the Stokes-Einstein relation is observed as well as a crossover analogous to the glass-forming liquids under cooling. The fractional variant of the Stokes-Einstein relation is attributed to the E introduced deviations from Gaussian and the nonlinear effect.

Synthesis, structure, and properties of Ba9Co3Se15 with one-dimensional spin chains Hot!

Lei Duan, Xian-Cheng Wang, Jun Zhang, Jian-Fa Zhao, Li-Peng Cao, Wen-Min Li, Run-Ze Yu, Zheng Deng, Chang-Qing Jin
Chin. Phys. B 2020, 29 (3): 036102;  doi: 10.1088/1674-1056/ab69ea
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A new compound with one-dimensional spin chains, Ba9Co3Se15, was synthesized under high pressure and high temperature conditions and systematically characterized via structural, transport and magnetic measurements. Ba9Co3Se15 crystallizes in a hexagonal structure with the space group P-6c2 (No. 188) and lattice constants of a =b = 9.6765 Å and c = 18.9562 Å. The structure consists of trimeric face-sharing octahedral CoSe6 chains, which are arranged in a triangular lattice in the ab-plane and separated by Ba atoms. The distance of the nearest neighbor of CoSe6 chains is very large, given by the lattice constant a= 9.6765 Å. The Weiss temperature Tθ associated with the intra-chain coupling strength is about -346 K. However, no long-range magnetic order but a spin glass transition at ~3 K has been observed. Our results indicate that the spin glass behavior in Ba9Co3Se15 mainly arises from the magnetic frustration due to the geometrically frustrated triangular lattice.

First-principles investigation on ideal strength of B2 NiAl and NiTi alloys

Chun-Yao Zhang, Fu-Yang Tian, Xiao-Dong Ni
Chin. Phys. B 2020, 29 (3): 036201;  doi: 10.1088/1674-1056/ab7440
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For B2 NiAl and NiTi intermetallic compounds, the ideal stress-strain image is lack from the perspective of elastic constants. We use first-principles calculation to investigate the ideal strength and elastic behavior under the tensile and shear loads. The relation between the ideal strength and elastic constants is found. The uniaxial tension of NiAl and NiTi along <001> crystal direction leads to the change from tetragonal path to orthogonal path, which is driven by the vanishing of the shear constant C66. The shear failure under {110}<111> shear deformation occurring in process of tension may result in a small ideal tensile strength (~2 GPa) for NiTi. The unlikeness in the ideal strength of NiAl and NiTi alloys is discussed based on the charge density difference.


Effect of overdrive voltage on PBTI trapping behavior in GaN MIS-HEMT with LPCVD SiNx gate dielectric

Tao-Tao Que, Ya-Wen Zhao, Liu-An Li, Liang He, Qiu-Ling Qiu, Zhen-Xing Liu, Jin-Wei Zhang, Jia Chen, Zhi-Sheng Wu, Yang Liu
Chin. Phys. B 2020, 29 (3): 037201;  doi: 10.1088/1674-1056/ab696b
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The effect of high overdrive voltage on the positive bias temperature instability (PBTI) trapping behavior is investigated for GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT) with LPCVD-SiNx gate dielectric. A higher overdrive voltage is more effective to accelerate the electrons trapping process, resulting in a unique trapping behavior, i.e., a larger threshold voltage shift with a weaker time dependence and a weaker temperature dependence. Combining the degradation of electrical parameters with the frequency-conductance measurements, the unique trapping behavior is ascribed to the defect energy profile inside the gate dielectric changing with stress time, new interface/border traps with a broad distribution above the channel Fermi level are introduced by high overdrive voltage.

High-mobility SiC MOSFET with low density of interface traps using high pressure microwave plasma oxidation

Xin-Yu Liu, Ji-Long Hao, Nan-Nan You, Yun Bai, Yi-Dan Tang, Cheng-Yue Yang, Sheng-Kai Wang
Chin. Phys. B 2020, 29 (3): 037301;  doi: 10.1088/1674-1056/ab68c0
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The microwave plasma oxidation under the relatively high pressure (6 kPa) region is introduced into the fabrication process of SiO2/4H-SiC stack. By controlling the oxidation pressure, species, and temperature, the record low density of interface traps (~ 4×1010 cm-2·eV-1@Ec - 0.2 eV) is demonstrated on SiO2/SiC stack formed by microwave plasma oxidation. And high quality SiO2 with very flat interface (0.27-nm root-mean-square roughness) is obtained. High performance SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) with peak field effect mobility of 44 cm-2·eV-1 is realized without additional treatment. These results show the potential of a high-pressure plasma oxidation step for improving the channel mobility in SiC MOSFETs.

Defect engineering on the electronic and transport properties of one-dimensional armchair phosphorene nanoribbons

Huakai Xu, Gang Ouyang
Chin. Phys. B 2020, 29 (3): 037302;  doi: 10.1088/1674-1056/ab69ec
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We investigate the electronic and transport properties of one-dimensional armchair phosphorene nanoribbons (APNRs) containing atomic vacancies with different distributions and concentrations using ab initio density functional calculations. It is found that the atomic vacancies are easier to form and detain at the edge region rather than a random distribution through analyzing formation energy and diffusion barrier. The highly local defect states are generated at the vicinity of the Fermi level, and emerge a deep-to-shallow transformation as the width increases after introducing vacancies in APNRs. Moreover, the electrical transport of APNRs with vacancies is enhanced compared to that of the perfect counterparts. Our results provide a theoretical guidance for the further research and applications of PNRs through defect engineering.

Influence of Zr50Cu50 thin film metallic glass as buffer layer on the structural and optoelectrical properties of AZO films

Bao-Qing Zhang, Gao-Peng Liu, Hai-Tao Zong, Li-Ge Fu, Zhi-Fei Wei, Xiao-Wei Yang, Guo-Hua Cao
Chin. Phys. B 2020, 29 (3): 037303;  doi: 10.1088/1674-1056/ab6c50
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Aluminum-doped ZnO (AZO) thin films with thin film metallic glass of Zr50Cu50 as buffer are prepared on glass substrates by the pulsed laser deposition. The influence of buffer thickness and substrate temperature on structural, optical, and electrical properties of AZO thin film are investigated. Increasing the thickness of buffer layer and substrate temperature can both promote the transformation of AZO from amorphous to crystalline structure, while they show (100) and (002) unique preferential orientations, respectively. After inserting Zr50Cu50 layer between the glass substrate and AZO film, the sheet resistance and visible transmittance decrease, but the infrared transmittance increases. With substrate temperature increasing from 25 ℃ to 520 ℃, the sheet resistance of AZO(100 nm)/ Zr50Cu50(4 nm) film first increases and then decreases, and the infrared transmittance is improved. The AZO(100 nm)/Zr50Cu50(4 nm) film deposited at a substrate temperature of 360 ℃ exhibits a low sheet resistance of 26.7 Ω/□, high transmittance of 82.1% in the visible light region, 81.6% in near-infrared region, and low surface roughness of 0.85 nm, which are useful properties for their potential applications in tandem solar cell and infrared technology.

Comparative study on transport properties of N-, P-, and As-doped SiC nanowires: Calculated based on first principles

Ya-Lin Li, Pei Gong, Xiao-Yong Fang
Chin. Phys. B 2020, 29 (3): 037304;  doi: 10.1088/1674-1056/ab6c4c
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According to the one-dimensional quantum state distribution, carrier scattering, and fixed range hopping model, the structural stability and electron transport properties of N-, P-, and As-doped SiC nanowires (N-SiCNWs, P-SiCNWs, and As-SiCNWs) are simulated by using the first principles calculations. The results show that the lattice structure of N-SiCNWs is the most stable in the lattice structures of the above three kinds of doped SiCNWs. At room temperature, for unpassivated SiCNWs, the doping effect of P and As are better than that of N. After passivation, the conductivities of all doped SiCNWs increase by approximately two orders of magnitude. The N-SiCNW has the lowest conductivity. In addition, the N-, P-, As-doped SiCNWs before and after passivation have the same conductivity-temperature characteristics, that is, above room temperature, the conductivity values of the doped SiCNWs all increase with temperature increasing. These results contribute to the electronic application of nanodevices.

General principles to high-throughput constructing two-dimensional carbon allotropes Hot!

Qing Xie, Lei Wang, Jiangxu Li, Ronghan Li, Xing-Qiu Chen
Chin. Phys. B 2020, 29 (3): 037306;  doi: 10.1088/1674-1056/ab6c4b
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We propose general principles to construct two-dimensional (2D) single-atom-thick carbon allotropes. They can be viewed as the generalization of patterning Stone-Walse defects (SWDs) by manipulating bond rotation and of patterning inverse SWDs by adding (or removing) carbon pairs on the pristine graphene, respectively. With these principles, numerous 2D allotropes of carbon can be systematically constructed. Using 20 constructed 2D allotropes as prototypical and benchmark examples, besides nicely reproducing all well-known ones, such as pentaheptites, T-graphene, OPGs, etc, we still discover 13 new allotropes. Their structural, thermodynamic, dynamical, and electronic properties are calculated by means of first-principles calculations. All these allotropes are metastable in energy compared with that of graphene and, except for OPG-A and C3-10-H allotropes, the other phonon spectra of 18 selected allotropes are dynamically stable. In particular, the proposed C3-11 allotrope is energetically favorable than graphene when the temperature is increased up to 1043 K according to the derived free energies. The electronic band structures demonstrate that (i) the C3-8 allotrope is a semiconductor with an indirect DFT band gap of 1.04 eV, (ii) another unusual allotrope is C3-12 which exhibits a highly flat band just crossing the Fermi level, (iii) four allotropes are Dirac semimetals with the appearance of Dirac cones at the Fermi level in the lattices without hexagonal symmetry, and (vi) without the spin-orbit coupling (SOC) effect, the hexagonal C3-11 allotrope exhibits two Dirac cones at K and K' points in its Brillouin zone in similarity with graphene.

Time-dependent Ginzburg-Landau equations for multi-gap superconductors

Minsi Li, Jiahong Gu, Long Du, Hongwei Zhong, Lijuan Zhou, Qinghua Chen
Chin. Phys. B 2020, 29 (3): 037401;  doi: 10.1088/1674-1056/ab69ef
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We numerically solve the time-dependent Ginzburg-Landau equations for two-gap superconductors using the finite-element technique. The real-time simulation shows that at low magnetic field, the vortices in small-size samples tend to form clusters or other disorder structures. When the sample size is large, stripes appear in the pattern. These results are in good agreement with the previous experimental observations of the intriguing anomalous vortex pattern, providing a reliable theoretical basis for the future applications of multi-gap superconductors.

Three- and two-dimensional calculations for the interface anisotropy dependence of magnetic properties of exchange-spring Nd2Fe14B/α-Fe multilayers with out-of-plane easy axes

Qian Zhao, Xin-Xin He, Francois-Jacques Morvan, Guo-Ping Zhao, Zhu-Bai Li
Chin. Phys. B 2020, 29 (3): 037501;  doi: 10.1088/1674-1056/ab69e9
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Hysteresis loops, energy products and magnetic moment distributions of perpendicularly oriented Nd2Fe14B/α-Fe exchange-spring multilayers are studied systematically based on both three-dimensional (3D) and one-dimensional (1D) micromagnetic methods, focused on the influence of the interface anisotropy. The calculated results are carefully compared with each other. The interface anisotropy effect is very palpable on the nucleation, pinning and coercive fields when the soft layer is very thin. However, as the soft layer thickness increases, the pinning and coercive fields are almost unchanged with the increment of interface anisotropy though the nucleation field still monotonically rises. Negative interface anisotropy decreases the maximum energy products and increases slightly the angles between the magnetization and applied field. The magnetic moment distributions in the thickness direction at various applied fields demonstrate a progress of three-step magnetic reversal, i.e., nucleation, evolution and irreversible motion of the domain wall. The above results calculated by two models are in good agreement with each other. Moreover, the in-plane magnetic moment orientations based on two models are different. The 3D calculation shows a progress of generation and disappearance of vortex state, however, the magnetization orientations within the film plane calculated by the 1D model are coherent. Simulation results suggest that negative interface anisotropy is necessarily avoided experimentally.

Giant low-field magnetocaloric effect in EuTi1-xNbxO3 (x=0.05, 0.1, 0.15, and 0.2) compounds

Wen-Hao Jiang, Zhao-Jun Mo, Jia-Wei Luo, Zhe-Xuan Zheng, Qiu-Jie Lu, Guo-Dong Liu, Jun Shen, Lan Li
Chin. Phys. B 2020, 29 (3): 037502;  doi: 10.1088/1674-1056/ab69e7
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The magnetic properties and magnetocaloric effect (MCE) of EuTi1-xNbxO3 (x=0.05, 0.1, 0.15, and 0.2) compounds are investigated. Owing to electronic doping, parts of Ti ions are replaced by Nb ions, the lattice constant increases and a small number of Ti4+ (3d0) ions change into Ti3+ (3d1). It is the ferromagnetism state that is dominant in the derivative balance. The values of the maximum magnetic entropy change (-ΔSMmax) are 10.3 J/kg·K, 9.6 J/kg·K, 13.1 J/kg·K, and 11.9 J/kg·K for EuTi1-xNbxO3 (x=0.05, 0.1, 0.15, and 0.2) compounds and the values of refrigeration capacity are 36, 33, 86, and 80 J/kg as magnetic field changes in a range of 0 T-1 T. The EuTi1-xNbxO3 (x=0.05, 0.1, 0.15, and 0.2) compounds with giant reversible MCE are considered as a good candidate for magnetic refrigerant working at low-temperature and low-field.

Magnetoelectric effects in multiferroic Y-type hexaferrites Ba0.3Sr1.7CoxMg2-xFe12O22

Yanfen Chang, Kun Zhai, Young Sun
Chin. Phys. B 2020, 29 (3): 037701;  doi: 10.1088/1674-1056/ab696c
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Y-type hexaferrites with tunable conical magnetic structures are promising single-phase multiferroics that exhibit large magnetoelectric effects. We have investigated the influence of Co substitution on the magnetoelectric properties in the Y-type hexaferrites Ba0.3Sr1.7CoxMg2-xFe12O22 (x = 0.0, 0.4, 1.0, 1.6). The spin-induced electric polarization can be reversed by applying a low magnetic field for all the samples. The magnetoelectric phase diagrams of Ba0.3Sr1.7CoxMg2-xFe12O22 are obtained based on the measurements of magnetic field dependence of dielectric constant at selected temperatures. It is found that the substitution of Co ions can preserve the ferroelectric phase up to a higher temperature, and thus is beneficial for achieving single-phase multiferroics at room temperature.

Surface passivation in n-type silicon and its application insilicon drift detector

Yiqing Wu, Ke Tao, Shuai Jiang, Rui Jia, Ye Huang
Chin. Phys. B 2020, 29 (3): 037702;  doi: 10.1088/1674-1056/ab695e
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Based on the surface passivation of n-type silicon in a silicon drift detector (SDD), we propose a new passivation structure of SiO2/Al2O3/SiO2 passivation stacks. Since the SiO2 formed by the nitric-acid-oxidation-of-silicon (NAOS) method has good compactness and simple process, the first layer film is formed by the NAOS method. The Al2O3 film is also introduced into the passivation stacks owing to exceptional advantages such as good interface characteristic and simple process. In addition, for requirements of thickness and deposition temperature, the third layer of the SiO2 film is deposited by plasma enhanced chemical vapor deposition (PECVD). The deposition of the SiO2 film by PECVD is a low-temperature process and has a high deposition rate, which causes little damage to the device and makes the SiO2 film very suitable for serving as the third passivation layer. The passivation approach of stacks can saturate dangling bonds at the interface between stacks and the silicon substrate, and provide positive charge to optimize the field passivation of the n-type substrate. The passivation method ultimately achieves a good combination of chemical and field passivations. Experimental results show that with the passivation structure of SiO2/Al2O3/SiO2, the final minority carrier lifetime reaches 5223 μs at injection of 5×1015 cm-3. When it is applied to the passivation of SDD, the leakage current is reduced to the order of nA.

Processes underlying the laser photochromic effect in colloidal plasmonic nanoparticle aggregates

A E Ershov, V S Gerasimov, I L Isaev, A P Gavrilyuk, S V Karpov
Chin. Phys. B 2020, 29 (3): 037802;  doi: 10.1088/1674-1056/ab6551
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We have studied the dynamic and static processes occurring in disordered multiparticle colloidal Ag aggregates with natural structure and affecting their plasmonic absorption spectra under pico- and nanosecond pulsed laser radiations, as well as the physical origin responsible for these processes. We have shown that depending on the duration of the laser pulse, the mechanisms of laser modification of such aggregates can be associated both with changes in the resonant properties of the particles due to their heating and melting (picosecond irradiation mode) and with the particle shifts in the resonant domains of the aggregates (nanosecond pulses) which depend on the wavelength, intensity, and polarization of the radiation. These mechanisms result in formation of a narrow dip in the plasmonic absorption spectrum of the aggregates near the laser radiation wavelength and affect the shape and position of the dip. The effect of polydispersity of nanoparticle aggregates on laser photochromic reaction has been studied.

A low-dimensional crystal growth model on an isotropic and quasi-free sustained substrate

Chenxi Lu, Senjiang Yu, Lingwei Li, Bo Yang, Xiangming Tao, Gaoxiang Ye
Chin. Phys. B 2020, 29 (3): 038101;  doi: 10.1088/1674-1056/ab6968
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A new crystal growth theoretical model is established for the low-dimensional nanocrystals on an isotropic and quasi-free sustained substrate. The driven mechanism of the model is based on the competitive growth among the preferential growth directions of the crystals possessing anisotropic crystal structures, such as the hexagonal close-packed and wurtzite structures. The calculation results are in good agreement with the experimental findings in the growth process of the low-dimensional Zn nanocrystals on silicone oil surfaces. Our model shows a growth mechanism of various low-dimensional crystals on/in the isotropic substrates.

Low-temperature plasma enhanced atomic layer deposition of large area HfS2 nanocrystal thin films

Ailing Chang, Yichen Mao, Zhiwei Huang, Haiyang Hong, Jianfang Xu, Wei Huang, Songyan Chen, Cheng Li
Chin. Phys. B 2020, 29 (3): 038102;  doi: 10.1088/1674-1056/ab6c4a
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Hafnium disulfide (HfS2) is a promising two-dimensional material for scaling electronic devices due to its higher carrier mobility, in which the combination of two-dimensional materials with traditional semiconductors in the framework of CMOS-compatible technology is necessary. We reported on the deposition of HfS2 nanocrystals by remote plasma enhanced atomic layer deposition at low temperature using Hf(N(CH3)(C2H5))4 and H2S as the reaction precursors. Self-limiting reaction behavior was observed at the deposition temperatures ranging from 150℃ to 350℃, and the film thickness increased linearly with the growth cycles. The uniform HfS2 nanocrystal thin films were obtained with the size of nanocrystal grain up to 27 nm. It was demonstrated that higher deposition temperature could enlarge the grain size and improve the HfS2 crystallinity, while causing crystallization of the mixed HfO2 above 450℃. These results suggested that atomic layer deposition is a low-temperature route to synthesize high quality HfS2 nanocrystals for electronic device or electrochemical applications.

Comparison study of GaN films grown on porous andplanar GaN templates

Shan Ding, Yue-Wen Li, Xiang-Qian Xiu, Xue-Mei Hua, Zi-Li Xie, Tao Tao, Peng Chen, Bin Liu, Rong Zhang, You-Dou Zheng
Chin. Phys. B 2020, 29 (3): 038103;  doi: 10.1088/1674-1056/ab6c48
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The GaN thick films have been grown on porous GaN template and planar metal-organic chemical vapor deposition (MOCVD)-GaN template by halide vapor phase epitaxy (HVPE). The analysis results indicated that the GaN films grown on porous and planar GaN templates under the same growth conditions have similar structural, optical, and electrical properties. But the porous GaN templates could significantly reduce the stress in the HVPE-GaN epilayer and enhance the photoluminescence (PL) intensity. The voids in the porous template were critical for the strain relaxation in the GaN films and the increase of the PL intensity. Thus, the porous GaN converted from β-Ga2O3 film as a novel promising template is suitable for the growth of stress-free GaN films.

Coulomb blockade and hopping transport behaviors of donor-induced quantum dots in junctionless transistors

Liu-Hong Ma, Wei-Hua Han, Fu-Hua Yang
Chin. Phys. B 2020, 29 (3): 038104;  doi: 10.1088/1674-1056/ab74ce
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The ionized dopants, working as quantum dots in silicon nanowires, exhibit potential advantages for the development of atomic-scale transistors. We investigate single electron tunneling through a phosphorus dopant induced quantum dots array in heavily n-doped junctionless nanowire transistors. Several subpeaks splittings in current oscillations are clearly observed due to the coupling of the quantum dots at the temperature of 6 K. The transport behaviors change from resonance tunneling to hoping conduction with increased temperature. The charging energy of the phosphorus donors is approximately 12.8 meV. This work helps clear the basic mechanism of electron transport through donor-induced quantum dots and electron transport properties in the heavily doped nanowire through dopant engineering.

Theoretical study on the relationship between the position of the substituent and the ESIPT fluorescence characteristic of HPIP

Xin Zhang, Jian-Hui Han, You Li, Chao-Fan Sun, Xing Su, Ying Shi, Hang Yin
Chin. Phys. B 2020, 29 (3): 038201;  doi: 10.1088/1674-1056/ab6d50
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The influences of the substituent base position on the excited state intramolecular proton transfer fluorescence properties were explored in 2-(2'-hydroxyphenyl)imidazo[1,2-a]-pyridine (HPIP) and HPIP's derivatives (5'Br-HPIP and 6'Br-HPIP). And the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods were used to calculate the molecule structures. The calculated results showed that the influence of 5'Br-HPIP on the fluorescence intensity is stronger than that of 6'Br-HPIP. The fluorescence emission peak of 5'Br-HPIP occurred a blue shift compared with HPIP, and 6'Br-HPIP exhibited an opposite red shift. The change of the fluorescence emission peak was attributed to the decrease of the energy gap from 6'Br-HPIP to 5'Br-HPIP. Our work on the substituent position influence could be helpful to design and develop new materials.

Investigation of gate oxide traps effect on NAND flash memory by TCAD simulation

He-Kun Zhang, Xuan Tian, Jun-Peng He, Zhe Song, Qian-Qian Yu, Liang Li, Ming Li, Lian-Cheng Zhao, Li-Ming Gao
Chin. Phys. B 2020, 29 (3): 038501;  doi: 10.1088/1674-1056/ab695f
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The effects of gate oxide traps on gate leakage current and device performance of metal-oxide-nitride-oxide-silicon (MONOS)-structured NAND flash memory are investigated through Sentaurus TCAD. The trap-assisted tunneling (TAT) model is implemented to simulate the leakage current of MONOS-structured memory cell. In this study, trap position, trap density, and trap energy are systematically analyzed for ascertaining their influences on gate leakage current, program/erase speed, and data retention properties. The results show that the traps in blocking layer significantly enhance the gate leakage current and also facilitates the cell program/erase. Trap density ~1018 cm-3 and trap energy ~1 eV in blocking layer can considerably improve cell program/erase speed without deteriorating data retention. The result conduces to understanding the role of gate oxide traps in cell degradation of MONOS-structured NAND flash memory.

Enhancement of radiation hardness of InP-based HEMT with double Si-doped plane

Ying-Hui Zhong, Bo Yang, Ming-Ming Chang, Peng Ding, Liu-Hong Ma, Meng-Ke Li, Zhi-Yong Duan, Jie Yang, Zhi Jin, Zhi-Chao Wei
Chin. Phys. B 2020, 29 (3): 038502;  doi: 10.1088/1674-1056/ab6962
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An anti-radiation structure of InP-based high electron mobility transistor (HEMT) has been proposed and optimized with double Si-doped planes. The additional Si-doped plane under channel layer has made a huge promotion in channel current, transconductance, current gain cut-off frequency, and maximum oscillation frequency of InP-based HEMTs. Moreover, direct current (DC) and radio frequency (RF) characteristic properties and their reduction rates have been compared in detail between single Si-doped and double Si-doped structures after 75-keV proton irradiation with dose of 5×1011 cm-2, 1×1012 cm-2, and 5×1012 cm-2. DC and RF characteristics for both structures are observed to decrease gradually as irradiation dose rises, which particularly show a drastic drop at dose of 5×1012 cm-2. Besides, characteristic degradation degree of the double Si-doped structure is significantly lower than that of the single Si-doped structure, especially at large proton irradiation dose. The enhancement of proton radiation tolerance by the insertion of another Si-doped plane could be accounted for the tremendously increased native carriers, which are bound to weaken substantially the carrier removal effect by irradiation-induced defects.

Numerical and analytical investigations for the SOI LDMOS with alternated high-k dielectric and step doped silicon pillars

Jia-Fei Yao, Yu-Feng Guo, Zhen-Yu Zhang, Ke-Meng Yang, Mao-Lin Zhang, Tian Xia
Chin. Phys. B 2020, 29 (3): 038503;  doi: 10.1088/1674-1056/ab6960
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This paper presents a new silicon-on-insulator (SOI) lateral-double-diffused metal-oxide-semiconductor transistor (LDMOST) device with alternated high-k dielectric and step doped silicon pillars (HKSD device). Due to the modulation of step doping technology and high-k dielectric on the electric field and doped profile of each zone, the HKSD device shows a greater performance. The analytical models of the potential, electric field, optimal breakdown voltage, and optimal doped profile are derived. The analytical results and the simulated results are basically consistent, which confirms the proposed model suitable for the HKSD device. The potential and electric field modulation mechanism are investigated based on the simulation and analytical models. Furthermore, the influence of the parameters on the breakdown voltage (BV) and specific on-resistance (Ron,sp) are obtained. The results indicate that the HKSD device has a higher BV and lower Ron,sp compared to the SD device and HK device.

A method to extend wavelength into middle-wavelength infrared based on InAsSb/(Al)GaSb interband transition quantum well infrared photodetector

Xuan-Zhang Li, Ling Sun, Jin-Lei Lu, Jie Liu, Chen Yue, Li-Li Xie, Wen-Xin Wang, Hong Chen, Hai-Qiang Jia, Lu Wang
Chin. Phys. B 2020, 29 (3): 038504;  doi: 10.1088/1674-1056/ab6969
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We present a method to extend the operating wavelength of the interband transition quantum well photodetector from an extended short-wavelength infrared region to a middle-wavelength infrared region. In the modified InAsSb quantum well, GaSb is replaced with AlSb/AlGaSb, the valence band of the barrier material is lowered, the first restricted energy level is higher than the valence band of the barrier material, the energy band structure forms type-II structure. The photocurrent spectrum manifest that the fabricated photodetector exhibits a response range from 1.9 μm to 3.2 μm with two peaks at 2.18 μm and 3.03 μm at 78 K.

Role of remote Coulomb scattering on the hole mobility at cryogenic temperatures in SOI p-MOSFETs

Xian-Le Zhang, Peng-Ying Chang, Gang Du, Xiao-Yan Liu
Chin. Phys. B 2020, 29 (3): 038505;  doi: 10.1088/1674-1056/ab6966
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The impacts of remote Coulomb scattering (RCS) on hole mobility in ultra-thin body silicon-on-insulator (UTB SOI) p-MOSFETs at cryogenic temperatures are investigated. The physical models including phonon scattering, surface roughness scattering, and remote Coulomb scatterings are considered, and the results are verified by the experimental results at different temperatures for both bulk (from 300 K to 30 K) and UTB SOI (300 K and 25 K) p-MOSFETs. The impacts of the interfacial trap charges at both front and bottom interfaces on the hole mobility are mainly evaluated for the UTB SOI p-MOSFETs at liquid helium temperature (4.2 K). The results reveal that as the temperature decreases, the RCS due to the interfacial trap charges plays an important role in the hole mobility.

Microstructure evolution and passivation quality of hydrogenated amorphous silicon oxide (a-SiOx:H) on <100>- and <111>-orientated c-Si wafers

Jun-Fan Chen, Sheng-Sheng Zhao, Ling-Ling Yan, Hui-Zhi Ren, Can Han, De-Kun Zhang, Chang-Chun Wei, Guang-Cai Wang, Guo-Fu Hou, Ying Zhao, Xiao-Dan Zhang
Chin. Phys. B 2020, 29 (3): 038801;  doi: 10.1088/1674-1056/ab6c47
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Hydrogenated amorphous silicon oxide (a-SiOx:H) is an attractive passivation material to suppress epitaxial growth and reduce the parasitic absorption loss in silicon heterojunction (SHJ) solar cells. In this paper, a-SiOx:H layers on different orientated c-Si substrates are fabricated. An optimal effective lifetime (τeff) of 4743 μs and corresponding implied open-circuit voltage (iVoc) of 724 mV are obtained on <100>-orientated c-Si wafers. While τeff of 2429 μs and iVoc of 699 mV are achieved on <111>-orientated substrate. The FTIR and XPS results indicate that the a-SiOx:H network consists of SiOx (Si-rich), Si-OH, Si-O-SiHx, SiO2≡Si-Si, and O3≡Si-Si. A passivation evolution mechanism is proposed to explain the different passivation results on different c-Si wafers. By modulating the a-SiOx:H layer, the planar silicon heterojunction solar cell can achieve an efficiency of 18.15%.

Simulation study on cooperation behaviors and crowd dynamics in pedestrian evacuation

Ya-Ping Ma, Hui Zhang
Chin. Phys. B 2020, 29 (3): 038901;  doi: 10.1088/1674-1056/ab6b14
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Pedestrian evacuation is actually a process of behavioral evolution. Interaction behaviors between pedestrians affect not only the evolution of their cooperation strategy, but also their evacuation paths-scheduling and dynamics features. The existence of interaction behaviors and cooperation evolution is therefore critical for pedestrian evacuation. To address this issue, an extended cellular automaton (CA) evacuation model considering the effects of interaction behaviors and cooperation evolution is proposed here. The influence mechanism of the environment factor and interaction behaviors between neighbors on the decision-making of one pedestrian to path scheduling is focused. Average payoffs interacting with neighbors are used to represent the competitive ability of one pedestrian, aiming to solve the conflicts when more than one pedestrian competes for the same position based on a new method. Influences of interaction behaviors, the panic degree and the conflict cost on the evacuation dynamics and cooperation evolution of pedestrians are discussed. Simulation results of the room evacuation show that the interaction behaviors between pedestrians to a certain extent are beneficial to the evacuation efficiency and the formation of cooperation behaviors as well. The increase of conflict cost prolongs the evacuation time. Panic emotions of pedestrians are bad for cooperation behaviors of the crowd and have complex effects on evacuation time. A new self-organization effect is also presented.
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