Chin. Phys. B

Revealing Chern number from quantum metric

Anwei Zhang(张安伟)

Chin. Phys. B, 2022, 31 (4): 040201. DOI: 10.1088/1674-1056/ac2f2c

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Chern number is usually characterized by Berry curvature. Here, by investigating the Dirac model of even-dimensional Chern insulator, we give the general relation between Berry curvature and quantum metric, which indicates that the Chern number can be encoded in quantum metric as well as the surface area of the Brillouin zone on the hypersphere embedded in Euclidean parameter space. We find that there is a corresponding relationship between the quantum metric and the metric on such a hypersphere. We give the geometrical property of quantum metric. Besides, we give a protocol to measure the quantum metric in the degenerate system.

Anti-function solution of uniaxial anisotropic Stoner-Wohlfarth model Suggested by editors

Kun Zheng(郑坤), Yu Miao(缪宇), Tong Li(李通), Shuang-Long Yang(杨双龙), Li Xi(席力), Yang Yang(杨洋), Dun Zhao(赵敦), and De-Sheng Xue(薛德胜)

Chin. Phys. B, 2022, 31 (4): 040202. DOI: 10.1088/1674-1056/ac401e

Abstract ( 342 )

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The anti-trigonometric function is used to strictly solve the uniaxial anisotropic Stoner-Wohlfarth (SW) model, which can obtain the relation of the angle α (θ) between the magnetization (the anisotropy field) and the applied magnetic field. Using this analytic solution, the hysteresis loops of uniaxial anisotropic SW particles magnetized in typical directions could be numerically calculated. Then, the hysteresis loops are obtained in randomly distributed SW particle ensembles while ignoring the dipole interaction among them with the analytic solution. Finally, the correctness of the analytic solution is verified by the exact solutions of remanence, switching field, and coercivity from the SW model. The analytic solution provides an important reference for understanding the magnetizing and magnetization reversal processes of magnetic materials.

Ultra-broadband absorber based on cascaded nanodisk arrays

Qi Wang(王琦), Rui Li(李瑞), Xu-Feng Gao(高旭峰), Shi-Jie Zhang(张世杰), Rui-Jin Hong(洪瑞金), Bang-Lian Xu(徐邦联), and Da-Wei Zhang(张大伟)

Chin. Phys. B, 2022, 31 (4): 040203. DOI: 10.1088/1674-1056/ac2d1d

Abstract ( 287 )

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An ultra-broadband perfect absorber consisting of cascaded nanodisk arrays is demonstrated by placing insulator-metal-insulator-metal nanodisks on insulator-metal film stacks. The absorber shows over 90% absorption in a wavelength range between 600 nm and 4000 nm under transverse magnetic (TM) polarization, with an average absorptivity of 91.5% and a relative absorption bandwidth of 147.8%. The analysis of the electric field and magnetic field show that the synergy of localized surface plasmons, propagating surface plasmons, and plasmonic resonant cavity modes leads to the ultra-broadband perfect absorption, which accords well with the results of impedance-matched analysis. The influences of structural parameters and different metal materials on absorption performance are discussed. Furthermore, the absorber is polarization-independent, and the absorption remains more than 90% at a wide incident angle up to 40° under TE polarization and TM polarization. The designed ultra-broadband absorber has promising prospects in photoelectric detection and imaging.

Self-adaptive behavior of nunchakus-like tracer induced by active Brownian particles

Yi-Qi Xia(夏益祺), Guo-Qiang Feng(冯国强), and Zhuang-Lin Shen(谌庄琳)

Chin. Phys. B, 2022, 31 (4): 040204. DOI: 10.1088/1674-1056/ac29b1

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We design a nunchakus-like tracer and investigate its self-adaptive behavior in an active Brownian particle (ABP) bath via systematically tuning the self-propelled capability and density of ABPs. Specifically, the nunchakus-like tracer will have a stable wedge-like shape in the ABP bath when the self-propelled force is high enough. We analyze the angle between the two arms of the tracer and the velocity of the joint point of the tracer. The angle exhibits a non-monotonic phenomenon as a function of active force. However, it increases with density of ABPs increasing monotonically. A simple linear relationship between the velocity and the self-propelled force is found under the highly active force. In other words, the joint points of the tracer diffuse and the super-diffusive behavior can make the relation between the self-propelled force and the density of ABPs persist longer. In addition, we find that the tracer can flip at high density of ABPs. Our results also suggest the new self-adaptive model research of the transport properties in a non-equilibrium medium.

Dynamics and intermittent stochastic stabilization of a rumor spreading model with guidance mechanism in heterogeneous network

Xiaojing Zhong(钟晓静), Yukun Yang(杨宇琨), Runqing Miao(苗润青), Yuqing Peng(彭雨晴), and Guiyun Liu(刘贵云)

Chin. Phys. B, 2022, 31 (4): 040205. DOI: 10.1088/1674-1056/ac587d

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We propose a novel rumor propagation model with guidance mechanism in heterogeneous complex networks. Firstly, the sharp threshold of rumor propagation, global stability of the information-equilibrium and information-prevailing-equilibrium under R₀ <1 and R₀> 1 is carried out by Lyapunov method and LaSalle's invariant principle. Next, we design an aperiodically intermittent stochastic stabilization method to suppress the rumor propagation. By using the Itô formula and exponential martingale inequality, the expression of the minimum control intensity is calculated. This method can effectively stabilize the rumor propagation by choosing a suitable perturb intensity and a perturb time ratio, while minimizing the control cost. Finally, numerical examples are given to illustrate the analysis and method of the paper.

Exact solutions of the Schrödinger equation for a class of hyperbolic potential well

Xiao-Hua Wang(王晓华), Chang-Yuan Chen(陈昌远), Yuan You(尤源), Fa-Lin Lu(陆法林), Dong-Sheng Sun(孙东升), and Shi-Hai Dong(董世海)

Chin. Phys. B, 2022, 31 (4): 040301. DOI: 10.1088/1674-1056/ac3392

Abstract ( 405 )

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We propose a new scheme to study the exact solutions of a class of hyperbolic potential well. We first apply different forms of function transformation and variable substitution to transform the Schrödinger equation into a confluent Heun differential equation and then construct a Wronskian determinant by finding two linearly dependent solutions for the same eigenstate. And then in terms of the energy spectrum equation which is obtained from the Wronskian determinant, we are able to graphically decide the quantum number with respect to each eigenstate and the total number of bound states for a given potential well. Such a procedure allows us to calculate the eigenvalues for different quantum states via Maple and then substitute them into the wave function to obtain the expected analytical eigenfunction expressed by the confluent Heun function. The linearly dependent relation between two eigenfunctions is also studied.

Quantum watermarking based on threshold segmentation using quantum informational entropy

Jia Luo(罗佳), Ri-Gui Zhou(周日贵), Wen-Wen Hu(胡文文), YaoChong Li(李尧翀), and Gao-Feng Luo(罗高峰)

Chin. Phys. B, 2022, 31 (4): 040302. DOI: 10.1088/1674-1056/ac2803

Abstract ( 336 )

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We propose a new quantum watermarking scheme based on threshold selection using informational entropy of quantum image. The core idea of this scheme is to embed information into object and background of cover image in different ways. First, a threshold method adopting the quantum informational entropy is employed to determine a threshold value. The threshold value can then be further used for segmenting the cover image to a binary image, which is an authentication key for embedding and extraction information. By a careful analysis of the quantum circuits of the scheme, that is, translating into the basic gate sequences which show the low complexity of the scheme. One of the simulation-based experimental results is entropy difference which measures the similarity of two images by calculating the difference in quantum image informational entropy between watermarked image and cover image. Furthermore, the analyses of peak signal-to-noise ratio, histogram and capacity of the scheme are also provided.

Quantum private comparison of arbitrary single qubit states based on swap test

Xi Huang(黄曦), Yan Chang(昌燕), Wen Cheng(程稳), Min Hou(侯敏), and Shi-Bin Zhang(张仕斌)

Chin. Phys. B, 2022, 31 (4): 040303. DOI: 10.1088/1674-1056/ac4103

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By using swap test, a quantum private comparison (QPC) protocol of arbitrary single qubit states with a semi-honest third party is proposed. The semi-honest third party (TP) is required to help two participants perform the comparison. She can record intermediate results and do some calculations in the whole process of the protocol execution, but she cannot conspire with any of participants. In the process of comparison, the TP cannot get two participants' private information except the comparison results. According to the security analysis, the proposed protocol can resist both outsider attacks and participants' attacks. Compared with the existing QPC protocols, the proposed one does not require any entanglement swapping technology, but it can compare two participants' qubits by performing swap test, which is easier to implement with current technology. Meanwhile, the proposed protocol can compare secret integers. It encodes secret integers into the amplitude of quantum state rather than transfer them as binary representations, and the encoded quantum state is compared by performing the swap test. Additionally, the proposed QPC protocol is extended to the QPC of arbitrary single qubit states by using multi-qubit swap test.

Deterministic remote state preparation of arbitrary three-qubit state through noisy cluster-GHZ channel

Zhihang Xu(许智航), Yuzhen Wei(魏玉震), Cong Jiang(江聪), and Min Jiang(姜敏)

Chin. Phys. B, 2022, 31 (4): 040304. DOI: 10.1088/1674-1056/ac2b17

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We propose a novel scheme for remote state preparation of an arbitrary three-qubit state with unit success probability, utilizing a nine-qubit cluster-GHZ state without introducing auxiliary qubits. Furthermore, we proceed to investigate the effects of different quantum noises (e.g., amplitude-damping, phase-damping, bit-flip and phase-flip noises) on the systems. The fidelity results of three-qubit target state are presented, which are usually used to illustrate how close the output state is to the target state. To compare the different effects between the four common types of quantum noises, the fidelities under one specific identical target state are also calculated and discussed. It is found that the fidelity of the phase-flip noisy channel drops the fastest through the four types of noisy channels, while the fidelity is found to always maintain at 1 in bit-flip noisy channel.

Low-overhead fault-tolerant error correction scheme based on quantum stabilizer codes Suggested by editors

Xiu-Bo Chen(陈秀波), Li-Yun Zhao(赵立云), Gang Xu(徐刚), Xing-Bo Pan(潘兴博), Si-Yi Chen(陈思怡), Zhen-Wen Cheng(程振文), and Yi-Xian Yang(杨义先)

Chin. Phys. B, 2022, 31 (4): 040305. DOI: 10.1088/1674-1056/ac3817

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Fault-tolerant error-correction (FTEC) circuit is the foundation for achieving reliable quantum computation and remote communication. However, designing a fault-tolerant error correction scheme with a solid error-correction ability and low overhead remains a significant challenge. In this paper, a low-overhead fault-tolerant error correction scheme is proposed for quantum communication systems. Firstly, syndrome ancillas are prepared into Bell states to detect errors caused by channel noise. We propose a detection approach that reduces the propagation path of quantum gate fault and reduces the circuit depth by splitting the stabilizer generator into X-type and Z-type. Additionally, a syndrome extraction circuit is equipped with two flag qubits to detect quantum gate faults, which may also introduce errors into the code block during the error detection process. Finally, analytical results are provided to demonstrate the fault-tolerant performance of the proposed FTEC scheme with the lower overhead of the ancillary qubits and circuit depth.

Manipulating vortices in F=2 Bose-Einstein condensates through magnetic field and spin-orbit coupling Suggested by editors

Hao Zhu(朱浩), Shou-Gen Yin(印寿根), and Wu-Ming Liu(刘伍明)

Chin. Phys. B, 2022, 31 (4): 040306. DOI: 10.1088/1674-1056/ac398f

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We investigate the vortex structures excited by Ioffe-Pritchard magnetic field and Dresselhaus-type spin-orbit coupling in F=2 ferromagnetic Bose-Einstein condensates. In the weakly interatomic interacting regime, an external magnetic field can generate a polar-core vortex in which the canonical particle current is zero. With the combined effect of spin-orbit coupling and magnetic field, the ground state experiences a transition from polar-core vortex to Mermin-Ho vortex, in which the canonical particle current is anticlockwise. For fixed spin-orbit coupling strengths, the evolution of phase winding, magnetization, and degree of phase separation with magnetic field are studied. Additionally, with further increasing spin-orbit coupling strength, the condensate exhibits symmetrical density domains separated by radial vortex arrays. Our work paves the way to explore exotic topological excitations in high-spin systems.

Quantum walk search algorithm for multi-objective searching with iteration auto-controlling on hypercube

Yao-Yao Jiang(姜瑶瑶), Peng-Cheng Chu(初鹏程), Wen-Bin Zhang(张文彬), and Hong-Yang Ma(马鸿洋)

Chin. Phys. B, 2022, 31 (4): 040307. DOI: 10.1088/1674-1056/ac2806

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Shenvi et al. have proposed a quantum algorithm based on quantum walking called Shenvi-Kempe-Whaley (SKW) algorithm, but this search algorithm can only search one target state and use a specific search target state vector. Therefore, when there are more than two target nodes in the search space, the algorithm has certain limitations. Even though a multi-objective SKW search algorithm was proposed later, when the number of target nodes is more than two, the SKW search algorithm cannot be mapped to the same quotient graph. In addition, the calculation of the optimal target state depends on the number of target states m. In previous studies, quantum computing and testing algorithms were used to solve this problem. But these solutions require more Oracle calls and cannot get a high accuracy rate. Therefore, to solve the above problems, we improve the multi-target quantum walk search algorithm, and construct a controllable quantum walk search algorithm under the condition of unknown number of target states. By dividing the Hilbert space into multiple subspaces, the accuracy of the search algorithm is improved from p_c=(1/2)-O(1/n) to p_c=1-O(1/n). And by adding detection gate phase, the algorithm can stop when the amplitude of the target state becomes the maximum for the first time, and the algorithm can always maintain the optimal number of iterations, so as to reduce the number of unnecessary iterations in the algorithm process and make the number of iterations reach $ t_{\rm f}=(\pi /2)\sqrt{2^{n-2}} $.

Protecting geometric quantum discord via partially collapsing measurements of two qubits in multiple bosonic reservoirs

Xue-Yun Bai(白雪云) and Su-Ying Zhang(张素英)

Chin. Phys. B, 2022, 31 (4): 040308. DOI: 10.1088/1674-1056/ac4f54

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We study the dynamics of geometric quantum discord (GQD) between two qubits, each qubit interacting at the same time with K independent multiple bosonic reservoirs at zero temperature. In both weak and strong qubit-reservoirs coupling regimes, we find that the increase of the number K of reservoirs can induce the damped oscillation of GQD, and enhance the memory effects of the overall environment. And the Hilbert-Schmidt norm GQD (two-norm GQD) is always smaller than the trace norm geometric quantum discord (one-norm GQD). Therefore, the one-norm GQD is a better way to measure the quantum correlation. Finally, we propose an effective strategy to improve GQD by using partially collapsing measurements, and we find that the protection effect is better with the increase of the weak measurement strength.

Beating standard quantum limit via two-axis magnetic susceptibility measurement Suggested by editors

Zheng-An Wang(王正安), Yi Peng(彭益), Dapeng Yu(俞大鹏), and Heng Fan(范桁)

Chin. Phys. B, 2022, 31 (4): 040309. DOI: 10.1088/1674-1056/ac4229

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We report a metrology scheme which measures the magnetic susceptibility of an atomic spin ensemble along the $x$ and $z$ directions and produces parameter estimation with precision beating the standard quantum limit. The atomic ensemble is initialized via one-axis spin squeezing with optimized squeezing time and parameter $\phi$ (to be estimated) assumed as uniformly distributed between 0 and $2\pi$ while fixed in each estimation. One estimation of $\phi$ can be produced with every two magnetic susceptibility data measured along the two axes respectively, which has an imprecision scaling $({1.43\pm0.02})/N^{0.687\pm0.003}$ with respect to the number $N$ of the atomic spins. The measurement scheme is easy to implement and is robust against the measurement fluctuation caused by environment noise and measurement defects.

Neural-mechanism-driven image block encryption algorithm incorporating a hyperchaotic system and cloud model

Peng-Fei Fang(方鹏飞), Han Liu(刘涵), Cheng-Mao Wu(吴成茂), and Min Liu(刘旻)

Chin. Phys. B, 2022, 31 (4): 040501. DOI: 10.1088/1674-1056/ac272d

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An image encryption algorithm is proposed in this paper based on a new four-dimensional hyperchaotic system, a neural mechanism, a Galois field and an improved Feistel block structure, which improves the efficiency and enhances the security of the encryption algorithm. Firstly, a four-dimensional hyperchaotic system with a large key space and chaotic dynamics performance is proposed and combined with a cloud model, in which a more complex and random sequence is constructed as the key stream, and the problem of chaotic periodicity is solved. Then, the key stream is combined with the neural mechanism, Galois field and improved Feistel block structure to scramble and diffuse the image encryption. Finally, the experimental results and security analysis show that the encryption algorithm has a good encryption effect and high encryption efficiency, is secure, and can meet the requirements of practical applications.

Traffic flow prediction based on BILSTM model and data denoising scheme

Zhong-Yu Li(李中昱), Hong-Xia Ge(葛红霞), and Rong-Jun Cheng(程荣军)

Chin. Phys. B, 2022, 31 (4): 040502. DOI: 10.1088/1674-1056/ac3647

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Accurate prediction of road traffic flow is a significant part in the intelligent transportation systems. Accurate prediction can alleviate traffic congestion, and reduce environmental pollution. For the management department, it can make effective use of road resources. For individuals, it can help people plan their own travel paths, avoid congestion, and save time. Owing to complex factors on the road, such as damage to the detector and disturbances from environment, the measured traffic volume can contain noise. Reducing the influence of noise on traffic flow prediction is a piece of very important work. Therefore, in this paper we propose a combination algorithm of denoising and BILSTM to effectively improve the performance of traffic flow prediction. At the same time, three denoising algorithms are compared to find the best combination mode. In this paper, the wavelet (WL) denoising scheme, the empirical mode decomposition (EMD) denoising scheme, and the ensemble empirical mode decomposition (EEMD) denoising scheme are all introduced to suppress outliers in traffic flow data. In addition, we combine the denoising schemes with bidirectional long short-term memory (BILSTM) network to predict the traffic flow. The data in this paper are cited from performance measurement system (PeMS). We choose three kinds of road data (mainline, off ramp, on ramp) to predict traffic flow. The results for mainline show that data denoising can improve prediction accuracy. Moreover, prediction accuracy of BILSTM+EEMD scheme is the highest in the three methods (BILSTM+WL, BILSTM+EMD, BILSTM+EEMD). The results for off ramp and on ramp show the same performance as the results for mainline. It is indicated that this model is suitable for different road sections and long-term prediction.

Ratchet transport of self-propelled chimeras in an asymmetric periodic structure

Wei-Jing Zhu(朱薇静) and Bao-Quan Ai(艾保全)

Chin. Phys. B, 2022, 31 (4): 040503. DOI: 10.1088/1674-1056/ac3391

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We studied the rectified transport of underdamped particles subject to phase lag in an asymmetric periodic structure. When the inertia effect is considered, it is possible to observe reversals of the average velocity with small self-propelled force, whereas particles always move in the positive direction with large self-propelled force. The introduction of phase lag leads particles to follow circular orbits and suppress the polar motion. In addition, this can adjust the direction of particle motion. There exists an optimal value of polar interaction strength at which the rectification is maximal. These results open the way for many application processes, such as spatial sorting of particles mixture and separation based on their physical properties.

Solving quantum rotor model with different Monte Carlo techniques ^Hot!

Weilun Jiang(姜伟伦), Gaopei Pan(潘高培), Yuzhi Liu(刘毓智), and Zi-Yang Meng(孟子杨)

Chin. Phys. B, 2022, 31 (4): 040504. DOI: 10.1088/1674-1056/ac4f52

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We systematically test the performance of several Monte Carlo update schemes for the (2+1)d XY phase transition of quantum rotor model. By comparing the local Metropolis (LM), LM plus over-relaxation (OR), Wolff-cluster (WC), hybrid Monte Carlo (HM), hybrid Monte Carlo with Fourier acceleration (FA) schemes, it is clear that among the five different update schemes, at the quantum critical point, the WC and FA schemes acquire the smallest autocorrelation time and cost the least amount of CPU hours in achieving the same level of relative error, and FA enjoys a further advantage of easily implementable for more complicated interactions such as the long-range ones. These results bestow one with the necessary knowledge of extending the quantum rotor model, which plays the role of ferromagnetic/antiferromagnetic critical bosons or Z₂ topological order, to more realistic and yet challenging models such as Fermi surface Yukawa-coupled to quantum rotor models.

Investigating the thermal conductivity of materials by analyzing the temperature distribution in diamond anvils cell under high pressure

Caihong Jia(贾彩红), Min Cao(曹敏), Tingting Ji(冀婷婷), Dawei Jiang(蒋大伟), and Chunxiao Gao(高春晓)

Chin. Phys. B, 2022, 31 (4): 040701. DOI: 10.1088/1674-1056/ac29aa

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Investigating the thermal transport properties of materials is of great importance in the field of earth science and for the development of materials under extremely high temperatures and pressures. However, it is an enormous challenge to characterize the thermal and physical properties of materials using the diamond anvil cell (DAC) platform. In the present study, a steady-state method is used with a DAC and a combination of thermocouple temperature measurement and numerical analysis is performed to calculate the thermal conductivity of the material. To this end, temperature distributions in the DAC under high pressure are analyzed. We propose a three-dimensional radiative-conductive coupled heat transfer model to simulate the temperature field in the main components of the DAC and calculate in situ thermal conductivity under high-temperature and high-pressure conditions. The proposed model is based on the finite volume method. The obtained results show that heat radiation has a great impact on the temperature field of the DAC, so that ignoring the radiation effect leads to large errors in calculating the heat transport properties of materials. Furthermore, the feasibility of studying the thermal conductivity of different materials is discussed through a numerical model combined with locally measured temperature in the DAC. This article is expected to become a reference for accurate measurement of in situ thermal conductivity in DACs at high-temperature and high-pressure conditions.

Memristor-based multi-synaptic spiking neuron circuit for spiking neural network Suggested by editors

Wenwu Jiang(蒋文武), Jie Li(李杰), Hongbo Liu(刘洪波), Xicong Qian(钱曦聪), Yuan Ge(葛源), Lidan Wang(王丽丹), and Shukai Duan(段书凯)

Chin. Phys. B, 2022, 31 (4): 040702. DOI: 10.1088/1674-1056/ac380b

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Spiking neural networks (SNNs) are widely used in many fields because they work closer to biological neurons. However, due to its computational complexity, many SNNs implementations are limited to computer programs. First, this paper proposes a multi-synaptic circuit (MSC) based on memristor, which realizes the multi-synapse connection between neurons and the multi-delay transmission of pulse signals. The synapse circuit participates in the calculation of the network while transmitting the pulse signal, and completes the complex calculations on the software with hardware. Secondly, a new spiking neuron circuit based on the leaky integrate-and-fire (LIF) model is designed in this paper. The amplitude and width of the pulse emitted by the spiking neuron circuit can be adjusted as required. The combination of spiking neuron circuit and MSC forms the multi-synaptic spiking neuron (MSSN). The MSSN was simulated in PSPICE and the expected result was obtained, which verified the feasibility of the circuit. Finally, a small SNN was designed based on the mathematical model of MSSN. After the SNN is trained and optimized, it obtains a good accuracy in the classification of the IRIS-dataset, which verifies the practicability of the design in the network.

Design of cylindrical conformal transmitted metasurface for orbital angular momentum vortex wave generation

Ben Fu(付犇), Shi-Xing Yu(余世星), Na Kou(寇娜), Zhao Ding(丁召), and Zheng-Ping Zhang(张正平)

Chin. Phys. B, 2022, 31 (4): 040703. DOI: 10.1088/1674-1056/ac3a65

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We propose a cylindrical conformal transmitted metasurface for orbital angular momentum vortex wave generation. Formulas for calculating the phase distributions of cylindrical conformal transmitted metasurface is presented. A prototype of the proposed conformal transmitted metasurface is designed, fabricated and measured. Measured results shows that the proposed conformal transmitted metasurface can effectively generate vortex waves, which verifies the effectiveness of our method. The proposed method may pave the way of vortex wave generation with cylindrical conformal devices.

Copper ion beam emission in solid electrolyte Rb₄Cu₁₆I_6.5Cl_13.5

Tushagu Abudouwufu(吐沙姑·阿不都吾甫), Xiangyu Zhang (张翔宇), Wenbin Zuo (左文彬), Jinbao Luo(罗进宝), Yueqiang Lan(兰越强), Canxin Tian (田灿鑫), Changwei Zou(邹长伟), Alexander Tolstoguzov, and Dejun Fu(付德君)

Chin. Phys. B, 2022, 31 (4): 040704. DOI: 10.1088/1674-1056/ac2f31

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Copper ion conducting solid electrolyte Rb$_{4}$Cu$_{16}$I$_{6.5}$Cl$_{13.5 }$ was prepared by means of mechano-chemical method. The structure and morphology of the powder was investigated by x-ray diffraction and scanning electron microscopy. The grain size was estimated to be 0.2-0.9 μm and the ionic conductivity at room temperature was approximately 0.206 S/cm. The solid electrolyte Rb$_{4}$Cu$_{16}$I$_{6.5}$Cl$_{13.5 }$ was exploited for copper ion beam generation. The copper ion emission current of several nA was successfully obtained at acceleration voltages of 15 kV and temperature of 197 $^\circ$C in vacuum of 2.1$\times10^{-4}$ Pa. A good linear correlation between the logarithmic ion current $(\log I)$ and the square root of the acceleration voltage ($U_{\rm acc}$) at high voltage range was obtained, suggesting the Schottky emission mechanism in the process of copper ion beam generation.

Wide dynamic detection range of methane gas based on enhanced cavity absorption spectroscopy

Yu Wang(汪玉), Bo-Kun Ding(丁伯坤), Kun-Yang Wang(王坤阳), Jiao-Xu Mei(梅教旭), Ze-Lin Han(韩泽林), Tu Tan(谈图), and Xiao-Ming Gao(高晓明)

Chin. Phys. B, 2022, 31 (4): 040705. DOI: 10.1088/1674-1056/ac2484

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Integrated cavity output spectroscopy (ICOS) is an effective technique in trace gase detection. The strong absorption due to the long optical path of this method makes it challenging in the application scenes that have large gas concentration fluctuation, especially when the gas concentration is high. In this paper, we demonstrate an extension of the dynamic range of ICOS by using a detuned laser combined with an off-axis integrating cavity. With this, we improve the upper limit of the dynamic detection range from 0.1% (1000 ppm) to 20% of the gas concentration. This method provides a way of using ICOS in the applications with unpredictable gas concentrations such as gas leak detection, ocean acidification, carbon sequestration, etc.

High-precision nuclear magnetic resonance probe suitable for in situ studies of high-temperature metallic melts Suggested by editors

Ao Li(李傲), Wei Xu(许巍), Xiao Chen(陈霄), Bing-Nan Yao(姚冰楠), Jun-Tao Huo(霍军涛), Jun-Qiang Wang(王军强), and Run-Wei Li(李润伟)

Chin. Phys. B, 2022, 31 (4): 040706. DOI: 10.1088/1674-1056/ac4a70

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High-temperature nuclear magnetic resonance (NMR) has proven to be very useful for detecting the temperature-induced structural evolution and dynamics in melts. However, the sensitivity and precision of high-temperature NMR probes are limited. Here we report a sensitive and stable high-temperature NMR probe based on laser-heating, suitable for in situ studies of metallic melts, which can work stably at the temperature of up to 2000 K. In our design, a well-designed optical path and the use of a water-cooled copper radio-frequency (RF) coil significantly optimize the signal-to-noise ratio (S/NR) at high temperatures. Additionally, a precise temperature controlling system with an error of less than ±1 K has been designed. After temperature calibration, the temperature measurement error is controlled within ±2 K. As a performance testing, ²⁷Al NMR spectra are measured in Zr-based metallic glass-forming liquid in situ. Results show that the S/NR reaches 45 within 90 s even when the sample's temperature is up to 1500 K and that the isothermal signal drift is better than 0.001 ppm per hour. This high-temperature NMR probe can be used to clarify some highly debated issues about metallic liquids, such as glass transition and liquid-liquid transition.

Theoretical calculation of the quadratic Zeeman shift coefficient of the ³P₀^o clock state for strontium optical lattice clock

Benquan Lu(卢本全), Xiaotong Lu(卢晓同), Jiguang Li(李冀光), and Hong Chang(常宏)

Chin. Phys. B, 2022, 31 (4): 043101. DOI: 10.1088/1674-1056/ac29a6

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In the weak-magnetic-field approximation, we derived an expression of quadratic Zeeman shift coefficient of $^3P^{\rm o}_0$ clock state for $^{88}$Sr and $^{87}$Sr atoms. By using this formula and the multi-configuration Dirac-Hartree-Fock theory, the quadratic Zeeman shift coefficients were calculated. The calculated values $C_2$ = $-23.38(5)$ MHz/T$^2$ for $^{88}$Sr and the $^3P^{\rm o}_0$, $F = 9/2$, $M_F = \pm9/2$ clock states for $^{87}$Sr agree well with the other available theoretical and experimental values, especially the most accurate measurement recently. In addition, the calculated values of the $^3P^{\rm o}_0$, $F = 9/2$, $M_F = \pm9/2$ clock states were also determined in our $^{87}$Sr optical lattice clock. The consistency with measurements verifies the validation of our calculation model. Our theory is also useful to evaluate the second-order Zeeman shift of the clock transition, for example, the new proposed $^1S_0$, $F = 9/2$, $M_F = \pm5/2$-${}^3P^{\rm o}_0$, $F = 9/2$, $M_F = \pm3/2$ transitions.

Quantum and quasiclassical dynamics of C($^{3} P$) + H$_{2}(^{1} \varSigma_{\text{g}}^+)\rightarrow H(^{2} S)$ + CH($^{2} \varPi$) reaction: Coriolis coupling effects and stereodynamics Suggested by editors

Dong Liu(刘栋), Lulu Zhang(张路路), Juan Zhao(赵娟), Qin Zhang(张芹), Yuzhi Song(宋玉志), and Qingtian Meng(孟庆田)

Chin. Phys. B, 2022, 31 (4): 043102. DOI: 10.1088/1674-1056/ac3989

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The dynamics of ${\rm C}+{\rm H_2}\rightarrow {\rm H}+{\rm CH}$ reaction is theoretically studied using the quasiclassical trajectory and quantum mechanical wave packet methods. The analysis of reaction probabilities, integral cross sections, and rate coefficients reveal the essential Coriolis coupling effects in the quantum mechanical wave packet calculations.The calculated polarization-dependent differential cross section, $P$($\theta_r$) and $P$($\phi_r$) show that the $\bm j'$ of product rotational angular momentum is not only aligned along the $y$ axis and the direction of the vector $\bm x+\bm z$, but also strongly oriented along the positive $y$ axis.

Spectroscopy and scattering matrices with nitrogen atom: Rydberg states and optical oscillator strengths

Yuhao Zhu(朱宇豪), Rui Jin(金锐), Yong Wu(吴勇), and Jianguo Wang(王建国)

Chin. Phys. B, 2022, 31 (4): 043103. DOI: 10.1088/1674-1056/ac1f05

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The scattering matrices of ${\rm e}+ {\rm N}^{+}$ with $J^\pi=1.5^{+}$ in discrete energy regions are calculated using the eigenchannel R-matrix method. We obtain good parameters of multichannel quantum defect theory (MQDT) that vary smoothly as the function of the energy resulting from the analytical continuation property of the scattering matrices. By employing the MQDT, all discrete energy levels for N could be calculated accurately without missing anyone. The MQDT parameters (i.e., scattering matrices) can be calibrated with the available precise spectroscopy values. In this work, the optical oscillator strengths for the transition between the ground state and Rydberg series are obtained, which provide rich data for the diagnostic analysis of plasma.

High-performance coherent population trapping clock based on laser-cooled atoms

Xiaochi Liu(刘小赤), Ning Ru(茹宁), Junyi Duan(段俊毅), Peter Yun(云恩学), Minghao Yao(姚明昊), and Jifeng Qu(屈继峰)

Chin. Phys. B, 2022, 31 (4): 043201. DOI: 10.1088/1674-1056/ac2d21

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We present a coherent population trapping clock system based on laser-cooled $^{87}$Rb atoms. The clock consists of a frequency-stabilized CPT interrogation laser and a cooling laser as well as a compact magneto-optical trap, a high-performance microwave synthesizer, and a signal detection system. The resonance signal in the continuous wave regime exhibits an absorption contrast of $\sim 50$%. In the Ramsey interrogation method, the linewidth of the central fringe is 31.25 Hz. The system achieves fractional frequency stability of ${2.4\times }{{10}}^{{-11}}/\sqrt \tau $, which goes down to ${1.8\times }{{10}}^{{-13}}$ at 20000 s. The results validate that cold atom interrogation can improve the long-term frequency stability of coherent population trapping clocks and holds the potential for developing compact/miniature cold atoms clocks.

Quantum mechanical solution to spectral lineshape in strongly-coupled atom-nanocavity system Suggested by editors

Jian Zeng(曾健) and Zhi-Yuan Li(李志远)

Chin. Phys. B, 2022, 31 (4): 043202. DOI: 10.1088/1674-1056/ac40fc

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The strongly coupled system composed of atoms, molecules, molecule aggregates, and semiconductor quantum dots embedded within an optical microcavity/nanocavity with high quality factor and/or low modal volume has become an excellent platform to study cavity quantum electrodynamics (CQED), where a prominent quantum effect called Rabi splitting can occur due to strong interaction of cavity-mode single-photon with the two-level atomic states. In this paper, we build a new quantum model that can describe the optical response of the strongly-coupled system under the action of an external probing light and the spectral lineshape. We take the Hamiltonian for the strongly-coupled photon-atom system as the unperturbed Hamiltonian $\bm{H}$₀ and the interaction Hamiltonian of the probe light upon the coupled-system quantum states as the perturbed Hamiltonian $\bm{V}$. The theory yields a double Lorentzian lineshape for the permittivity function, which agrees well with experimental observation of Rabi splitting in terms of spectral splitting. This quantum theory will pave the way to construct a complete understanding for the microscopic strongly-coupled system that will become an important element for quantum information processing, nano-optical integrated circuits, and polariton chemistry.

Generation of elliptical isolated attosecond pulse from oriented H₂⁺ in a linearly polarized laser field Suggested by editors

Yun-He Xing(邢云鹤), Jun Zhang(张军), Xiao-Xin Huo(霍晓鑫), Qing-Yun Xu(徐清芸), and Xue-Shen Liu(刘学深)

Chin. Phys. B, 2022, 31 (4): 043203. DOI: 10.1088/1674-1056/ac398b

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We investigate the ellipticity of the high-order harmonic generation from the oriented H₂⁺ exposed to a linearly polarized laser field by numerically solving the two-dimensional time-dependent Schrödinger equation (2D TDSE). Numerical simulations show that the harmonic ellipticity is remarkably sensitive to the alignment angle. The harmonic spectrum is highly elliptically polarized at a specific alignment angle θ=30°, which is insensitive to the variation of the laser parameters. The position of the harmonic intensity minima indicates the high ellipticity, which can be attributed to the two-center interference effect. The high ellipticity can be explained by the phase difference of the harmonics. This result facilitates the synthesis of a highly elliptical isolated attosecond pulse with duration down to 65 as, which can be served as a powerful tool to explore the ultrafast dynamics of molecules and study chiral light-matter interaction.

Decoding the electron dynamics in high-order harmonic generation from asymmetric molecular ions in elliptically polarized laser fields

Cai-Ping Zhang(张彩萍) and Xiang-Yang Miao(苗向阳)

Chin. Phys. B, 2022, 31 (4): 043301. DOI: 10.1088/1674-1056/ac29b0

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The high-order harmonic generation from an asymmetric molecular ion is theoretically investigated based on the Born-Oppenheimer model with two-dimensional electron dynamics. It is shown that the harmonic intensity changes periodically in elliptically polarized laser fields. The periodical character is ellipticity-dependent. By establishing the physical image, the periodicity of the harmonic intensity can be ascribed to the contributions of the ground state and the excited state. Furthermore, the electron dynamics from different electronic states can be selected via combining the elliptically polarized laser field with a static electric field. The harmonics dominated either by ground state or excited state are emitted once in an optical cycle in the combined laser field.

Enhancement of isolated attosecond pulse generation by using long gas medium

Yueying Liang(梁玥瑛), Xinkui He(贺新奎), Kun Zhao(赵昆), Hao Teng(滕浩), and Zhiyi Wei(魏志义)

Chin. Phys. B, 2022, 31 (4): 043302. DOI: 10.1088/1674-1056/ac29a8

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Isolated attosecond pulse generation in argon is theoretically investigated for different gas pressures and medium lengths. The output of attosecond pulse is effectively enhanced by using a longer gas medium with optimized pressure. The peak intensity of the attosecond pulse by using 6 mm gas medium is doubled compared with that of 1-3 mm gas cell, which is usually used in the experiment. Our simulation shows that the distortion of the driving laser waveform and the absorption are the main factors that limit the output of the attosecond pulse for the long gas medium. Optimized generation condition could be found by balancing the medium length and pressure.

Debye-screening effect on electron-impact excitation of helium-like Al¹¹⁺ and Fe²⁴⁺ ions

Yu-Long Ma(马玉龙), Ling Liu(刘玲), Lu-You Xie(颉录有), Yong Wu(吴勇), Deng-Hong Zhang(张登红), Chen-Zhong Dong(董晨钟), Yi-Zhi Qu(屈一至), and Jian-Guo Wang(王建国)

Chin. Phys. B, 2022, 31 (4): 043401. DOI: 10.1088/1674-1056/ac2e65

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Debye-screening effects on the electron-impact excitation (EIE) processes for the dipole-allowed transition 1s$^{2}$ $^{1}{\rm S} \to 1$s2p $^{1}$P in He-like Al$^{11+}$ and Fe$^{24+}$ ions are investigated using the fully relativistic distorted-wave methods with the-Hückel (DH) model potential. Debye-screening effects on the continuum-bound (CB) interaction and target ion are discussed, both of which result in reduction of EIE cross sections. This reduction due to screening on the CB interaction is dominant. The non-spherical and spherical DH potentials are adopted for considering the screening effect on the CB interaction. It is found that the spherical DH potential could significantly overestimate the influence of plasma screening on EIE cross sections for multielectron He-like ions.

Strong chirality in twisted bilayer α-MoO₃

Bi-Yuan Wu(吴必园), Zhang-Xing Shi(石章兴), Feng Wu(吴丰), Ming-Jun Wang(王明军), and Xiao-Hu Wu(吴小虎)

Chin. Phys. B, 2022, 31 (4): 044101. DOI: 10.1088/1674-1056/ac3740

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Chiral structures are promising in many applications, such as biological sensing and analytical chemistry, and have been extensively explored. In this paper, we theoretically investigate the chiral response of twisted bilayer α-MoO₃. Firstly, the analytical formula for the transmissivity is derived when the structure is illuminated with circularly polarized plane waves. Furthermore, the results demonstrate that the twisted bilayer α-MoO₃ can excite the strong chirality with the maximum circular dichroism (CD) of 0.89. In this case, the chirality is due to the simultaneous breaking the rotational symmetry and mirror symmetry, which originates from the relative rotation of two α-MoO₃ layers. To better understand the physical mechanism, the polarization conversion between the left-hand circular polarization (LCP) and right-hand circular polarization (RCP) waves is discussed as well. Moreover, it is found that the structure can maintain the strong chirality (CD> 0.8) when the twisted angle varies from 69° to 80°, which effectively reduces the strictness in the requirement for rotation angle. In addition, the CD can be larger than 0.85 when the incidence angle of circularly polarized plane wave is less than 40°, implying that the chirality is robust against the angle of incidence. Our work not only provides an insight into chirality induced by the twisted bilayer α-MoO₃, but also looks forward to applications in biological sensing.

High-sensitivity Bloch surface wave sensor with Fano resonance in grating-coupled multilayer structures

Daohan Ge(葛道晗), Yujie Zhou(周宇杰), Mengcheng Lv(吕梦成), Jiakang Shi(石家康), Abubakar A. Babangida, Liqiang Zhang(张立强), and Shining Zhu(祝世宁)

Chin. Phys. B, 2022, 31 (4): 044102. DOI: 10.1088/1674-1056/ac2e60

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A new type of device consisting of a lithium niobate film coupled with a distributed Bragg reflector (DBR) was theoretically proposed to explore and release Bloch surface waves for applications in sensing and detection. The film and grating made of lithium niobate (LiNbO₃) were placed on both sides of the DBR and a concentrated electromagnetic field was formed at the film layer. By adjusting the spatial incidence angle of the incident light, two detection and analysis modes were obtained, including surface diffraction detection and guided Bloch detection. Surface diffraction detection was used to detect the gas molecule concentrations, while guided Bloch detection was applied for the concentration detection of biomolecule-modulated biological solutions. According to the drift of the Fano curve, the average sensor sensitivities from the analysis of the two modes were 1560 °/RIU and 1161 °/RIU, and the maximum detection sensitivity reached 2320 °/RIU and 2200 °/RIU, respectively. This study revealed the potential application of LiNbO₃ as a tunable material when combined with DBR to construct a new type of biosensor, which offered broad application prospects in Bloch surface wave biosensors.

Smith-Purcell radiation improved by multi-grating structure

Jing Shu(舒靖), Ping Zhang(张平), Man Liang(梁满), Sheng-Peng Yang(杨生鹏), Shao-Meng Wang(王少萌), and Yu-Bin Gong(宫玉彬)

Chin. Phys. B, 2022, 31 (4): 044103. DOI: 10.1088/1674-1056/ac5390

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The photonic crystal structure has attracted much attention due to its ability to confine light. In this paper, we present our study on an improved Smith-Purcell radiation from a simple metal photonic crystal excited by moving electrons. Different from the wide-band Smith-Purcell radiation from a single metal grating, the results show that the injected electrons could induce more dipole oscillations inside the multi-grating structure, and it leads to the enhancement of the radiation intensity. In addition, there are strong resonances in metal multi-grating structure, and the resonance characteristics may narrow the radiation band, which leads to a radiation with an obvious peak in the spectrum. Therefore, the multi-grating structure has the ability to enhance the radiation intensity and shape the radiation frequency band. By optimizing the structure parameters, coherent and tunable Smith-Purcell radiation can be realized, and it provides a potential way to develop band-controllable light or THz radiation source.

Reconstruction resolution enhancement of EPISM based holographic stereogram with hogel spatial multiplexing Suggested by editors

Yunpeng Liu(刘云鹏), Teng Zhang(张腾), Jian Su(苏健), Tao Jing(荆涛), Min Lin(蔺敏), Pei Li(李沛), and Xingpeng Yan(闫兴鹏)

Chin. Phys. B, 2022, 31 (4): 044201. DOI: 10.1088/1674-1056/ac306f

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We investigate how the splicing mode of a holographic element (hogel) affects the reconstruction of a 3D scene to improve the reconstruction resolution of a holographic stereogram fabricated using the effective perspective image segmentation and mosaicking method (EPISM). First, the effect of hogel spatial multiplexing on holographic recording and reconstruction is studied based on the mechanism of recording interference fringes in the holographic recording medium. Second, combined with the influence of multiple exposures on the hologram's diffraction efficiency, the diffraction efficiency of the holographic stereogram is analyzed in the spatial multiplexing mode. The holographic stereogram is then regarded as a special optical imaging system. The theory of spatial bandwidth product is adopted to describe the comprehensive resolution of the holographic stereogram, which explains why hogel spatial multiplexing can significantly improve the reconstruction resolution of a holographic stereogram. Compared with the traditional printing method under the same parameters in optical experiments, hogel spatial multiplexing has a lower diffraction efficiency but a higher quality of reconstructed image, consistent with the theoretical analysis.

Switchable instantaneous frequency measurement by optical power monitoring based on DP-QPSK modulator

Yu-Lin Zhu(朱昱琳), Bei-Lei Wu(武蓓蕾), Jing Li(李晶), Mu-Guang Wang(王目光), Shi-Ying Xiao(肖世莹), and Feng-Ping Yan(延凤平)

Chin. Phys. B, 2022, 31 (4): 044202. DOI: 10.1088/1674-1056/ac40ff

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We propose and analyze an instantaneous frequency measurement system by using optical power monitoring technique with improved resolution. The primary component adopted in the proposal is a dual-polarization quadrature phase shift keying (DP-QPSK) modulator which is used to modulate the microwave signal that has a designed time delay and phase shifting. The generated optical signal is sent to polarization beam splitter (PBS) in DP-QPSK modulator. Owing to the complementary transmission nature of polarization interference introduced by PBS, the frequency information is converted into the optical power and the relationship between the amplitude comparison function (ACF) and microwave frequency to be measured is established. Thus, the frequency of the microwave signal can be easily measured through monitoring the optical powers of the two output ports of the PBS. Furthermore, by adjusting the direct current (DC) biases of the DP-QPSK modulator instead of changing the electrical delay, the measurement range and resolution can be switched. In this paper, the basic principle of the instantaneous frequency measurement system is derived in detail, and simulation has been performed to investigate the resolution, the measurement range, and the influence of imperfection devices. The proposed scheme is wavelength-independent and its measurement range is switchable, which can avoid the laser wavelength drifting problem and thus greatly increasing the system flexibility.

Nonlinear optical properties in n-type quadruple δ-doped GaAs quantum wells

Humberto Noverola-Gamas, Luis Manuel Gaggero-Sager, and Outmane Oubram

Chin. Phys. B, 2022, 31 (4): 044203. DOI: 10.1088/1674-1056/ac248e

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The effects of the interlayer distance on the nonlinear optical properties of n-type quadruple δ-doped GaAs quantum well were theoretically investigated. Particularly, the absorption coefficient and the relative refraction index change were determined. In the effective mass approach and within the framework of the Thomas-Fermi theory, the Schrödinger equation was resolved. Thereby, the subband energy levels and their respective wave functions were calculated. The variations in the nonlinear optical properties were determined by using the density matrix solutions. The achieved results demonstrate that the interlayer distance causes optical red-shift on nonlinear optical properties. Therefore, it can be deduced that the suitably chosen interlayer distance can be used to tune optical properties within the infrared spectrum region in optoelectronic devices such as far-infrared photo-detectors, high-speed electronic-optical modulators, and infrared lasers.

Orientation and ellipticity dependence of high-order harmonic generation in nanowires Suggested by editors

Fan Yang(杨帆), Yinghui Zheng(郑颖辉), Luyao Zhang(张路遥), Xiaochun Ge(葛晓春), and Zhinan Zeng(曾志男)

Chin. Phys. B, 2022, 31 (4): 044204. DOI: 10.1088/1674-1056/ac3ed0

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It has been predicted that high-order harmonic generation (HHG) in nanowires has the potential to scale up photon energy and harmonic yield. However, studies on HHG in nanowires are still theoretical and no relevant experimental results have been reported as yet. Our experimental observation of the high-order harmonic in cadmium sulfide nanowires (CdS NWs) excited by a mid-infrared laser is, to our knowledge, the first of such study, and it verifies some of the theoretical results. Our experimental results show that the observed harmonics are strongest when a pump laser is parallel to the nanowires. Therefore, the theoretical prediction that harmonics are strongest under the nanowires parallel to the laser field is confirmed experimentally, and this can be used to determine the orientation of the nanowire. In addition, harmonics are sensitive to the variation of pump light ellipticities. This orientation dependence opens new opportunities to access the ultrafast and strong-field physics of nanowires.

Creation of multi-frequency terahertz waves by optimized cascaded difference frequency generation

Zhong-Yang Li(李忠洋), Jia Zhao(赵佳), Sheng Yuan(袁胜), Bin-Zhe Jiao(焦彬哲), Pi-Bin Bing(邴丕彬), Hong-Tao Zhang(张红涛), Zhi-Liang Chen(陈治良), Lian Tan(谭联), and Jian-Quan Yao(姚建铨)

Chin. Phys. B, 2022, 31 (4): 044205. DOI: 10.1088/1674-1056/ac29b4

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A new scheme which generates multi-frequency terahertz (THz) waves from planar waveguide by the optimized cascaded difference frequency generation (OCDFG) is proposed. A THz wave with frequency ω_T1 is generated by the OCDFG with two infrared pump waves, and simultaneously a series of cascaded optical waves with a frequency interval ω_T1 is generated. The THz wave with a frequency of M-times ω_T1 is generated by mixing the m-th-order and the (m+M)-th-order cascaded optical wave. The phase mismatch distributions of cascaded difference frequency generation (CDFG) are modulated by changing the thickness of planar waveguide step by step, thereby satisfying the phase-matching condition from first-order to high-order cascaded Stokes process step by step. As a result, the intensity of THz wave can be enhanced and modulated by controlling the cascading order of OCDFG.

Rotational manipulation of massive particles in a 2D acoustofluidic chamber constituted by multiple nonlinear vibration sources

Qiang Tang(汤强), Pengzhan Liu(刘鹏展), and Shuai Tang(唐帅)

Chin. Phys. B, 2022, 31 (4): 044301. DOI: 10.1088/1674-1056/ac1f0e

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Rotational manipulation of massive particles and biological samples is essential for the development of miniaturized lab-on-a-chip platforms in the fields of chemical, medical, and biological applications. In this paper, a device concept of a two-dimensional acoustofluidic chamber actuated by multiple nonlinear vibration sources is proposed. The functional chamber enables the generation of acoustic streaming vortices for potential applications that include strong mixing of multi-phase flows and rotational manipulation of micro-/nano-scale objects without any rotating component. Using numerical simulations, we find that diversified acoustofluidic fields can be generated in the chamber under various actuations, and massive polystyrene beads inside can experience different acoustophoretic motions under the combined effect of an acoustic radiation force and acoustic streaming. Moreover, we investigate and clarify the effects of structural design on modulation of the acoustofluidic fields in the chamber. We believe the presented study could not only provide a promising potential tool for rotational acoustofluidic manipulation, but could also bring this community some useful design insights into the achievement of desired acoustofluidic fields for assorted microfluidic applications.

Acoustic radiation force on a rigid cylinder near rigid corner boundaries exerted by a Gaussian beam field

Qin Chang(常钦), Yuchen Zang(臧雨宸), Weijun Lin(林伟军), Chang Su(苏畅), and Pengfei Wu(吴鹏飞)

Chin. Phys. B, 2022, 31 (4): 044302. DOI: 10.1088/1674-1056/ac2d1f

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Acoustic manipulation is one of the well-known technologies of particle control and a top research in acoustic field. Calculation of acoustic radiation force on a particle nearby boundaries is one of the critical tasks, as it approximates realistic applications. Nevertheless, it is quite difficult to solve the problem by theoretical method when the boundary conditions are intricate. In this study, we present a finite element method numerical model for the acoustic radiation force exerting on a rigid cylindrical particle immersed in fluid near a rigid corner. The effects of the boundaries on acoustic radiation force of a rigid cylinder are analyzed with particular emphasis on the non-dimensional frequency and the distance from the center of cylinder to each boundary. The results reveal that these parameters play important roles in acoustic manipulation for particle-nearby complicated rigid boundaries. This study verifies the feasibility of numerical analysis on the issue of acoustic radiation force calculation close to complex boundaries, which may provide a new idea on analyzing the acoustic particle manipulation in confined space.

Effect of nonlinear translations on the pulsation of cavitation bubbles

Lingling Zhang(张玲玲), Weizhong Chen(陈伟中), Yang Shen(沈阳), Yaorong Wu(武耀蓉), Guoying Zhao(赵帼英), and Shaoyang Kou(寇少杨)

Chin. Phys. B, 2022, 31 (4): 044303. DOI: 10.1088/1674-1056/ac1e18

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The pulsations and translations of cavitation bubbles obey combined ordinary differential equations, and their nonlinearities are studied by the bifurcation diagram and the phase diagram in a strong ultrasonic field. Bubble pulsation can change regularly or irregularly with changing driving pressure in the time domain. The bifurcation diagrams of the pulsation versus driving pressure show that the pulsations and translations of bubbles have nonlinear characteristics, and the nonlinear translations of bubbles can disorder the pulsations for certain parameters. Disorder of the pulsation can also be caused by nonlinear pulsation itself. In addition, the phase diagrams also show that the nonlinear translations make a large contribution to the pulsations. The same result can also be obtained when the ambient radii of two bubbles are different.

Non-invasive and low-artifact in vivo brain imaging by using a scanning acoustic-photoacoustic dual mode microscopy ^Hot!

Wentian Chen(陈文天), Chao Tao(陶超), Zizhong Hu(胡仔仲), Songtao Yuan(袁松涛), Qinghuai Liu(刘庆淮), and Xiaojun Liu(刘晓峻)

Chin. Phys. B, 2022, 31 (4): 044304. DOI: 10.1088/1674-1056/ac4a6f

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Photoacoustic imaging is a potential candidate for in vivo brain imaging, whereas, its imaging performance could be degraded by inhomogeneous multi-layered media, consisted of scalp and skull. In this work, we propose a low-artifact photoacoustic microscopy (LAPAM) scheme, which combines conventional acoustic-resolution photoacoustic microscopy with scanning acoustic microscopy to suppress the reflection artifacts induced by multi-layers. Based on similar propagation characteristics of photoacoustic signals and ultrasonic echoes, the ultrasonic echoes can be employed as the filters to suppress the reflection artifacts to obtain low-artifact photoacoustic images. Phantom experiment is used to validate the effectiveness of this method. Furthermore, LAPAM is applied for in-vivo imaging mouse brain without removing the scalp and the skull. Experimental results show that the proposed method successfully achieves the low-artifact brain image, which demonstrates the practical applicability of LAPAM. This work might improve the photoacoustic imaging quality in many biomedical applications which involve tissues with complex acoustic properties, such as brain imaging through scalp and skull.

A quantitative analysis method for contact force of mechanism with a clearance joint based on entropy weight and its application in a six-bar mechanism

Zhen-Nan Chen(陈镇男), Meng-Bo Qian(钱孟波), Fu-Xing Sun(孙福兴), and Jia-Xuan Pan(潘佳煊)

Chin. Phys. B, 2022, 31 (4): 044501. DOI: 10.1088/1674-1056/ac338f

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Contact force in a clearance joint affects the dynamic characteristics and leads to nonlinear response of the mechanism. It is necessary to assess the nonlinearity of contact force quantitatively. Therefore, a new method named contact-force entropy weight is proposed in this paper. This method presents a comprehensive description of the judgment matrix in the X, Y, and Z directions. To assess the influence degrees of different clearances and angular velocities on the contact force, the method is applied to numerical calculation and simulation of a six-bar mechanism with a clearance joint to illustrate its application and investigate the influence degree of angular velocity and clearance on the contact force. By combining the simulation results and theoretical calculations, the influence degrees of different clearances and angular velocities on the contact-force entropy weight of the six-bar mechanism with a clearance joint are revealed. It is found that the angular velocity has a significant influence on the contact force entropy weight of the clearance joint, showing that the contact-force entropy weight is a feasible new method of assessing non-linearity of contact force quantitatively. The method gives a theoretical reference for quantitatively analyzing the nonlinear dynamics.

Influence of various shapes of nanoparticles on unsteady stagnation-point flow of Cu-H₂O nanofluid on a flat surface in a porous medium: A stability analysis

Astick Banerjee, Krishnendu Bhattacharyya, Sanat Kumar Mahato, and Ali J. Chamkha

Chin. Phys. B, 2022, 31 (4): 044701. DOI: 10.1088/1674-1056/ac229b

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The nanofluid and porous medium together are able to fulfill the requirement of high cooling rate in many engineering problems. So, here the impact of various shapes of nanoparticles on unsteady stagnation-point flow of Cu-H₂O nanofluid on a flat surface in a porous medium is examined. Moreover, the thermal radiation and viscous dissipation effects are considered. The problem governing partial differential equations are converted into self-similar coupled ordinary differential equations and those are numerically solved by the shooting method. The computed results can reveal many vital findings of practical importance. Firstly, dual solutions exist for decelerating unsteady flow and for accelerating unsteady and steady flows, the solution is unique. The presence of nanoparticles affects the existence of dual solution in decelerating unsteady flow only when the medium of the flow is a porous medium. But different shapes of nanoparticles are not disturbing the dual solution existence range, though it has a considerable impact on thermal conductivity of the mixture. Different shapes of nanoparticles act differently to enhance the heat transfer characteristics of the base fluid, i.e., the water here. On the other hand, the existence range of dual solutions becomes wider for a larger permeability parameter related to the porous medium. Regarding the cooling rate of the heated surface, it rises with the permeability parameter, shape factor (related to various shapes of Cu-nanoparticles), and radiation parameter. The surface drag force becomes stronger with the permeability parameter. Also, with growing values of nanoparticle volume fraction, the boundary layer thickness (BLT) increases and the thermal BLT becomes thicker with larger values of shape factor. For decelerating unsteady flow, the nanofluid velocity rises with permeability parameter in the case of upper branch solution and an opposite trend for the lower branch is witnessed. The thermal BLT is thicker with radiation parameter. Due to the existence of dual solutions, a linear stability analysis is made and it is concluded that the upper branch and unique solutions are stable solutions.

Shedding vortex simulation method based on viscous compensation technology research

Hao Zhou(周昊), Lei Wang(汪雷), Zhang-Feng Huang(黄章峰), and Jing-Zhi Ren(任晶志)

Chin. Phys. B, 2022, 31 (4): 044702. DOI: 10.1088/1674-1056/ac29ae

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Owing to the influence of the viscosity of the flow field, the strength of the shedding vortex decreases gradually in the process of backward propagation. Large-scale vortexes constantly break up, forming smaller vortexes. In engineering, when numerical simulation of vortex evolution process is carried out, a large grid is needed to be arranged in the area of outflow field far from the boundary layer in order to ensure the calculation efficiency. As a result, small scale vortexes at the far end of the flow field cannot be captured by the sparse grid in this region, resulting in the dissipation or even disappearance of vortexes. In this paper, the effect of grid scale is quantified and compared with the viscous effect through theoretical derivation. The theoretical relationship between the mesh viscosity and the original viscosity of the flow field is established, and the viscosity term in the turbulence model is modified. This method proves to be able to effectively improve the intensity of small-scale shedding vortexes at the far end of the flow field under the condition of sparse grid. The error between the simulation results and the results obtained by using fine mesh is greatly reduced, the calculation time is shortened, and the high-precision and efficient simulation of the flow field is realized.

Studies on aluminum powder combustion in detonation environment Suggested by editors

Jian-Xin Nie(聂建新), Run-Zhe Kan(阚润哲), Qing-Jie Jiao(焦清介), Qiu-Shi Wang(王秋实), Xue-Yong Guo(郭学永), and Shi Yan(闫石)

Chin. Phys. B, 2022, 31 (4): 044703. DOI: 10.1088/1674-1056/ac373e

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The combustion mechanism of aluminum particles in a detonation environment characterized by high temperature (in unit 10³ K), high pressure (in unit GPa), and high-speed motion (in units km/s) was studied, and a combustion model of the aluminum particles in detonation environment was established. Based on this model, a combustion control equation for aluminum particles in detonation environment was obtained. It can be seen from the control equation that the burning time of aluminum particle is mainly affected by the particle size, system temperature, and diffusion coefficient. The calculation result shows that a higher system temperature, larger diffusion coefficient, and smaller particle size lead to a faster burn rate and shorter burning time for aluminum particles. After considering the particle size distribution characteristics of aluminum powder, the application of the combustion control equation was extended from single aluminum particles to nonuniform aluminum powder, and the calculated time corresponding to the peak burn rate of aluminum powder was in good agreement with the experimental electrical conductivity results. This equation can quantitatively describe the combustion behavior of aluminum powder in different detonation environments and provides technical means for quantitative calculation of the aluminum powder combustion process in detonation environment.

Diffusion of a chemically active colloidal particle in composite channels Suggested by editors

Xin Lou(娄辛), Rui Liu(刘锐), Ke Chen(陈科), Xin Zhou(周昕), Rudolf Podgornik, and Mingcheng Yang(杨明成)

Chin. Phys. B, 2022, 31 (4): 044704. DOI: 10.1088/1674-1056/ac381b

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Diffusion of colloidal particles in microchannels has been extensively investigated, where the channel wall is either a no-slip or a slip-passive boundary. However, in the context of active fluids, driving boundary walls are ubiquitous and are expected to have a substantial effect on the particle dynamics. By mesoscale simulations, we study the diffusion of a chemically active colloidal particle in composite channels, which are constructed by alternately arranging the no-slip and diffusio-osmotic boundary walls. In this case, the chemical reaction catalyzed by the active colloidal particle creates a local chemical gradient along the channel wall, which drives a diffusio-osmotic flow parallel to the wall. We show that the diffusio-osmotic flow can significantly change the spatial distribution and diffusion dynamics of the colloidal particle in the composite channels. By modulating the surface properties of the channel wall, we can achieve different patterns of colloidal position distribution. The findings thus propose a novel possibility to manipulate colloidal diffusion in microfluidics, and highlight the importance of driving boundary walls in dynamics of colloidal particles in microchannels.

Distribution of charged lunar dust in the south polar region of the moon

Qing Xia(夏清), Ming-Hui Cai(蔡明辉), Liang-Liang Xu(许亮亮), Rui-Long Han(韩瑞龙), Tao Yang(杨涛), and Jian-Wei Han(韩建伟)

Chin. Phys. B, 2022, 31 (4): 045201. DOI: 10.1088/1674-1056/ac2e61

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Lunar dust is one of the most threatening problems confronting the return of human beings to the moon. In this work we studied the spatial distribution behavior of charged lunar dust in the solar wind plasma environment in the south polar region of the moon and considered the influence of a mini-crater using Spacecraft Plasma Interactions Software. The distribution of dust and plasma at low solar altitude angles of 20° and 0° was studied, and the spatial density of lunar dust was ~10^10.4 m^-3 and ~10^11.5 m^-3, respectively. This is because a higher surface potential will result in transportation of small dust particles and photoelectrons can also neutralize positively charged lunar dust. The dust density in the plasma void region created by a mini-crater with a 5 m high wall was studied. We obtained a quasi-neutral electric environment in the plasma void region of the mini-crater, and the dust density was about a magnitude lower than that in other regions. The dust risk to a spacesuit is much lower on the nightside than on the dayside, but there is severe charged lunar dust transport in the region between light and shade, which is dominated by the difference in surface and plasma potential caused by photoelectrons.

The intermittent excitation of geodesic acoustic mode by resonant Instanton of electron drift wave envelope in L-mode discharge near tokamak edge Suggested by editors

Zhao-Yang Liu(刘朝阳), Yang-Zhong Zhang(章扬忠), Swadesh Mitter Mahajan, A-Di Liu(刘阿娣), Chu Zhou(周楚), and Tao Xie(谢涛)

Chin. Phys. B, 2022, 31 (4): 045202. DOI: 10.1088/1674-1056/ac43ac

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There are two distinct phases in the evolution of drift wave envelope in the presence of zonal flow. A long-lived standing wave phase, which we call the Caviton, and a short-lived traveling wave phase (in radial direction) we call the Instanton. Several abrupt phenomena observed in tokamaks, such as intermittent excitation of geodesic acoustic mode (GAM) shown in this paper, could be attributed to the sudden and fast radial motion of Instanton. The composite drift wave—zonal flow system evolves at the two well-separate scales:the micro-scale and the meso-scale. The eigenmode equation of the model defines the zero-order (micro-scale) variation; it is solved by making use of the two-dimensional (2D) weakly asymmetric ballooning theory (WABT), a theory suitable for modes localized to rational surface like drift waves, and then refined by shifted inverse power method, an iterative finite difference method. The next order is the equation of electron drift wave (EDW) envelope (containing group velocity of EDW) which is modulated by the zonal flow generated by Reynolds stress of EDW. This equation is coupled to the zonal flow equation, and numerically solved in spatiotemporal representation; the results are displayed in self-explanatory graphs. One observes a strong correlation between the Caviton-Instanton transition and the zero-crossing of radial group velocity of EDW. The calculation brings out the defining characteristics of the Instanton:it begins as a linear traveling wave right after the transition. Then, it evolves to a nonlinear stage with increasing frequency all the way to 20 kHz. The modulation to Reynolds stress in zonal flow equation brought in by the nonlinear Instanton will cause resonant excitation to GAM. The intermittency is shown due to the random phase mixing between multiple central rational surfaces in the reaction region.

Morphological and structural damage investigation of nanostructured molybdenum fuzzy surface after pulsed plasma bombardment

Yu-Chuan Luo(罗玉川), Rong Yan(鄢容), Guo Pu(蒲国), Hong-Bin Wang(王宏彬), Zhi-Jun Wang(王志君), Chi Yang(杨驰), Li Yang(杨黎), Heng-Xin Guo(郭恒鑫), Zhi-Bing Zhou(周志兵), Bo Chen(陈波), Jian-Jun Chen(陈建军), Fu-Jun Gou(芶富均), Zong-Biao Ye(叶宗标), and Kun Zhang(张坤)

Chin. Phys. B, 2022, 31 (4): 045203. DOI: 10.1088/1674-1056/ac3395

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Steady high-flux helium (He) plasma with energy ranging from 50 eV to 90 eV is used to fabricate a fiber-form nanostructure called fuzz on a polycrystalline molybdenum (Mo) surface. Enhanced hydrogen (H) pulsed plasma in a wide power density range of 12 MW/m²-35 MW/m² is subsequently used to bombard the fuzzy Mo, thereby simulating the damage of edge localized mode (ELM) to fuzz. The comparisons of surface morphologies, crystalline structures, and optical reflectivity between the original Mo and the Mo treated with various He⁺ energy and transient power densities are performed. With the increase of He ion energy, the Mo nano-fuzz evolved density is enlarged due to the decrease of filament diameter and optical reflectivity. The fuzz-enhanced He release should be the consequence of crystalline growth and the lattice shrinkage inside the Mo-irradiated layers (~200 nm). The fuzz induced by lower energy experiences more severe melting damage and dust release under the condition of the identical transient H plasma-bombardment. The H and He are less likely to be trapped due to aggravated melting evidenced by the enhanced crystalline size and distinct lattice shrinkage. As the transient power density rises, the thermal effect is enhanced, thereby causing the fuzz melting loss to aggravate and finally to completely disappear when the power density exceeds 21 MW/m². Irreversible grain expansion results in huge tensile stress, leading to the observable brittle cracking. The effects of transient thermal load and He ion energy play a crucial role in etching Mo fuzz during ELM transient events.

A simple analytical model of laser direct-drive thin shell target implosion

Bo Yu(余波), Tianxuan Huang(黄天晅), Li Yao(姚立), Chuankui Sun(孙传奎), Wanli Shang(尚万里), Peng Wang(王鹏), Xiaoshi Peng(彭晓世), Qi Tang(唐琦), Zifeng Song(宋仔峰), Wei Jiang(蒋炜), Zhongjing Chen(陈忠靖), Yudong Pu(蒲昱东), Ji Yan(晏骥), Yunsong Dong(董云松), Jiamin Yang(杨家敏), Yongkun Ding(丁永坤), and Jian Zheng(郑坚)

Chin. Phys. B, 2022, 31 (4): 045204. DOI: 10.1088/1674-1056/ac21bd

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A high-neutron yield platform imploded by a thin shell target is generally built to probe nuclear science problems, and it has the advantages of high neutron yield, ultrashort fusion time, micro fusion zone, isotropic and monoenergetic neutron. Some analytical models have been proposed to interpret exploding-pusher target implosion driven by a long wavelength laser, whereas they are imperfect for a 0.35 μm laser implosion experiment. When using the 0.35 μm laser, the shell is ablated and accelerated to high implosion velocity governed by Newton's law, ablation acceleration and quasi-adiabatic compression models are suitable to explain the implosion of a laser direct-drive thin shell target. The new analytical model scales bang time, ion temperature and neutron yield for large variations in laser power, target radius, shell thickness, and fuel pressure. The predicted results of the analytical model are in agreement with experimental data on the Shenguang-III prototype laser facility, 100 kJ laser facility, Omega, and NIF, it demonstrates that the analytical model benefits the understanding of experiment performance and optimizing the target design of high neutron yield implosion.

Post-solitons and electron vortices generated by femtosecond intense laser interacting with uniform near-critical-density plasmas Suggested by editors

Dong-Ning Yue(岳东宁), Min Chen(陈民), Yao Zhao(赵耀), Pan-Fei Geng(耿盼飞), Xiao-Hui Yuan(远晓辉), Quan-Li Dong(董全力), Zheng-Ming Sheng(盛政明), and Jie Zhang(张杰)

Chin. Phys. B, 2022, 31 (4): 045205. DOI: 10.1088/1674-1056/ac46c5

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Generation of nonlinear structures, such as stimulated Raman side scattering waves, post-solitons and electron vortices, during ultra-short intense laser pulse transportation in near-critical-density (NCD) plasmas is studied by using multi-dimensional particle-in-cell (PIC) simulations. In two-dimensional geometries, both P- and S-polarized laser pulses are used to drive these nonlinear structures and to check the polarization effects on them. In the S-polarized case, the scattered waves can be captured by surrounding plasmas leading to the generation of post-solitons, while the main pulse excites convective electric currents leading to the formation of electron vortices through Kelvin-Helmholtz instability (KHI). In the P-polarized case, the scattered waves dissipate their energy by heating surrounding plasmas. Electron vortices are excited due to the hosing instability of the drive laser. These polarization dependent physical processes are reproduced in two different planes perpendicular to the laser propagation direction in three-dimensional simulation with linearly polarized laser driver. The current work provides inspiration for future experiments of laser-NCD plasma interactions.

Temperature-dependent structure and magnetization of YCrO₃ compound

Qian Zhao(赵前), Ying-Hao Zhu(朱英浩), Si Wu(吴思), Jun-Chao Xia(夏俊超), Peng-Fei Zhou(周鹏飞), Kai-Tong Sun(孙楷橦), and Hai-Feng Li(李海峰)

Chin. Phys. B, 2022, 31 (4): 046101. DOI: 10.1088/1674-1056/ac2b23

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We have grown a YCrO$_3$ single crystal by the floating-zone method and studied its temperature-dependent crystalline structure and magnetization by x-ray powder diffraction and PPMS DynaCool measurements. All diffraction patterns were well indexed by an orthorhombic structure with space group of $Pbnm$ (No. 62). From 36 K to 300 K, no structural phase transition occurs in the pulverized YCrO$_3$ single crystal. The antiferromagnetic phase transition temperature was determined as $T_\textrm{N} = 141.58(5)$ K by the magnetization versus temperature measurements. We found weak ferromagnetic behavior in the magnetic hysteresis loops below $T_\textrm{N}$. Especially, we demonstrated that the antiferromagnetism and weak ferromagnetism appear simultaneously upon cooling. The lattice parameters ($a$, $b$, $c$, and $V$) deviate downward from the Grüneisen law, displaying an anisotropic magnetostriction effect. We extracted temperature variation of the local distortion parameter $\varDelta$. Compared to the $\varDelta$ value of Cr ions, Y, O1, and O2 ions show one order of magnitude larger $\varDelta$ values indicative of much stronger local lattice distortions. Moreover, the calculated bond valence states of Y and O2 ions have obvious subduction charges.

Helium bubble formation and evolution in NiMo-Y₂O₃ alloy under He ion irradiation Suggested by editors

Awen Liu(刘阿文), Hefei Huang(黄鹤飞), Jizhao Liu(刘继召), Zhenbo Zhu(朱振博), and Yan Li(李燕)

Chin. Phys. B, 2022, 31 (4): 046102. DOI: 10.1088/1674-1056/ac3654

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We report helium ion irradiation experiments for a new type of dispersion-strengthened NiMo-Y₂O₃ alloy with three different irradiation doses and varying irradiation dose rates at 750 ℃ to evaluate its helium-induced damage behavior. Transmission electron microscopy was used to reveal the evolution of helium bubbles after irradiation. The experimental results show that with increasing ion dose, the number density of helium bubbles increases continuously. However, the mean size of helium bubbles first increases and then decreases, mainly due to the varied ion dose rates. The volume fractions of helium bubbles in the three investigated samples after irradiation are 0.15%, 0.32%, and 0.27%, which are lower than that of the Hastelloy N alloy (0.58%) after similar irradiation conditions. This indicates that the NiMo-Y₂O₃ alloy exhibits better helium-induced-swelling resistance than the Hastelloy N alloy, highlighting its potential applicability to MSRs, from the perspective of irradiation performance.

Surface chemical disorder and lattice strain of GaN implanted by 3-MeV Fe¹⁰⁺ ions Suggested by editors

Jun-Yuan Yang(杨浚源), Zong-Kai Feng(冯棕楷), Ling Jiang(蒋领), Jie Song(宋杰), Xiao-Xun He(何晓珣), Li-Ming Chen(陈黎明), Qing Liao(廖庆), Jiao Wang(王姣), and Bing-Sheng Li(李炳生)

Chin. Phys. B, 2022, 31 (4): 046103. DOI: 10.1088/1674-1056/ac373f

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Chemical disorder on the surface and lattice strain in GaN implanted by Fe¹⁰⁺ ions are investigated. In this study, 3-MeV Fe¹⁰⁺ ions fluence ranges from 1×10¹³ ions/cm² to 5×10¹⁵ ions/cm² at room temperature. X-ray photoelectron spectroscopy, high-resolution x-ray diffraction, and high-resolution transmission electron microscopy were used to characterize lattice disorder. The transition of Ga-N bonds to oxynitride bonding is caused by ion sputtering. The change of tensile strain out-of-plane with fluence was measured. Lattice disorder due to the formation of stacking faults prefers to occur on the basal plane.

Theoretical study on the improvement of the doping efficiency of Al in 4H-SiC by co-doping group-IVB elements Suggested by editors

Yuanchao Huang(黄渊超), Rong Wang(王蓉), Yixiao Qian(钱怡潇), Yiqiang Zhang(张懿强), Deren Yang(杨德仁), and Xiaodong Pi(皮孝东)

Chin. Phys. B, 2022, 31 (4): 046104. DOI: 10.1088/1674-1056/ac20ca

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The p-type doping efficiency of 4H silicon carbide (4H-SiC) is rather low due to the large ionization energies of p-type dopants. Such an issue impedes the exploration of the full advantage of 4H-SiC for semiconductor devices. In this study, we show that co-doping group-IVB elements effectively decreases the ionization energy of the most widely used p-type dopant, i.e., aluminum (Al), through the defect-level repulsion between the energy levels of group-IVB elements and that of Al in 4H-SiC. Among group-IVB elements Ti has the most prominent effectiveness. Ti decreases the ionization energy of Al by nearly 50%, leading to a value as low as ~0.13 eV. As a result, the ionization rate of Al with Ti co-doping is up to ~5 times larger than that without co-doping at room temperature when the doping concentration is up to 10¹⁸ cm^-3. This work may encourage the experimental co-doping of group-IVB elements such as Ti and Al to significantly improve the p-type doping efficiency of 4H-SiC.

Evolution of defects and deformation mechanisms in different tensile directions of solidified lamellar Ti-Al alloy

Yutao Liu(刘玉涛), Tinghong Gao(高廷红), Yue Gao(高越), Lianxin Li(李连欣), Min Tan(谭敏), Quan Xie(谢泉), Qian Chen(陈茜), Zean Tian(田泽安), Yongchao Liang(梁永超), and Bei Wang(王蓓)

Chin. Phys. B, 2022, 31 (4): 046105. DOI: 10.1088/1674-1056/ac1f0b

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Two-phase γ-TiAl/α₂-Ti₃Al lamellar intermetallics have attracted considerable attention because of their excellent strength and plasticity. However, the exact deformation mechanisms remain to be investigated. In this paper, a solidified lamellar Ti-Al alloy with lamellar orientation at 0°, 17°, and 73° with respect to the loading direction was stretched by utilizing molecular dynamics (MD) simulations. The results show that the mechanical properties of the sample are considerably influenced by solidified defects and tensile directions. The structure deformation and fracture were primarily attributed to an intrinsic stacking fault (ISF) accompanied by the nucleated Shockley dislocation, and the adjacent extrinsic stacking fault (ESF) and ISF formed by solidification tend to form large HCP structures during the tensile process loading at 73°. Moreover, cleavage cracking easily occurs on the γ/α₂ interface under tensile deformation. The fracture loading mechanism at 17° is grain boundary slide whereas, at 73° and 0°, the dislocation piles up to form a dislocation junction.

Stability and luminescence properties of CsPbBr₃/CdSe/Al core-shell quantum dots

Heng Yao(姚恒), Anjiang Lu(陆安江), Zhongchen Bai(白忠臣), Jinguo Jiang(蒋劲国), and Shuijie Qin(秦水介)

Chin. Phys. B, 2022, 31 (4): 046106. DOI: 10.1088/1674-1056/ac5978

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To improve the stability and luminescence properties of CsPbBr₃ QDs, we proposed a new core-shell structure for CsPbBr₃/CdSe/Al quantum dots (QDs). By using a simple method of ion layer adsorption and a reaction method, CdSe and Al were respectively packaged on the surface of CsPbBr₃ QDs to form the core-shell CsPbBr₃/CdSe/Al QDs. After one week in a natural environment, the photoluminescence quantum yields of CsPbBr₃/CdSe/Al QDs were greater than 80%, and the PL intensity remained at 71% of the original intensity. Furthermore, the CsPbBr₃/CdSe/Al QDs were used as green emitters for white light-emitting diodes (LEDs), with the LEDs spectrum covering 129% of the national television system committee (NTSC) standard color gamut. The core-shell structure of QDs can effectively improve the stability of CsPbBr₃ QDs, which has promising prospects in optoelectronic devices.

Dependence of nitrogen vacancy color centers on nitrogen concentration in synthetic diamond

Yong Li(李勇), Xiaozhou Chen(陈孝洲), Maowu Ran(冉茂武), Yanchao She(佘彦超), Zhengguo Xiao(肖政国), Meihua Hu(胡美华), Ying Wang(王应), and Jun An(安军)

Chin. Phys. B, 2022, 31 (4): 046107. DOI: 10.1088/1674-1056/ac3220

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Crystallization of diamond with different nitrogen concentrations was carried out with a FeNiCo-C system at pressure of 6.5 GPa. As the nitrogen concentration in diamond increased, the color of the synthesized diamond crystals changed from colorless to yellow and finally to atrovirens (a dark green). All the Raman peaks for the obtained crystals were located at about 1330 cm^-1 and contained only the sp³ hybrid diamond phase. Based on Fourier transform infrared results, the nitrogen concentration of the colorless diamond was < 1 ppm and absorption peaks corresponding to nitrogen impurities were not detected. However, the C-center nitrogen concentration of the atrovirens diamond reached 1030 ppm and the value of A-center nitrogen was approximately 180 ppm with a characteristic absorption peak at 1282 cm^-1. Furthermore, neither the NV⁰ nor the NV^- optical color center existed in diamond crystal with nitrogen impurities of less than 1 ppm by photoluminescence measurement. However, Ni-related centers located at 695 nm and 793.6 nm were observed in colorless diamond. The NE8 color center at 793.6 nm has more potential for application than the common NV centers. NV⁰ and NV^- optical color centers coexist in diamond without any additives in the synthesis system. Importantly, only the NV^- color center was noticed in diamond with a higher nitrogen concentration, which maximized optimization of the NV^-/NV⁰ ratio in the diamond structure. This study has provided a new way to prepare diamond containing only NV^- optical color centers.

Formation of L1₀-FeNi hard magnetic material from FeNi-based amorphous alloys

Yaocen Wang(汪姚岑), Ziyan Hao(郝梓焱), Yan Zhang(张岩), Xiaoyu Liang(梁晓宇), Xiaojun Bai(白晓军), and Chongde Cao(曹崇德)

Chin. Phys. B, 2022, 31 (4): 046301. DOI: 10.1088/1674-1056/ac280a

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L1₀-FeNi hard magnetic alloy with coercivity reaching 861 Oe was synthesized through annealing Fe₄₂Ni_41.3Si₈B₄P₄Cu_0.7 amorphous alloy, and the L1₀-FeNi formation mechanism has been studied. It is found the L1₀-FeNi in annealed samples at 400 ℃ mainly originated from the residual amorphous phase during the second stage of crystallization which could take place over 60 ℃ lower than the measured onset temperature of the second stage with a 5 ℃/min heating rate. Annealing at 400 ℃ after fully crystallization still caused a slight increase of coercivity, which was probably contributed by the limited transformation from other high temperature crystalline phases towards L1₀ phase, or the removal of B from L1₀ lattice and improvement of the ordering quality of L1₀ phase due to the reduced temperature from 520 ℃ to 400 ℃. The first stage of crystallization has hardly direct contribution to L1₀-FeNi formation. Ab initio simulations show that the addition of Si or Co in L1₀-FeNi has the effect of enhancing the thermal stability of L1₀ phase without seriously deteriorating its magnetic hardness. The non-monotonic feature of direction dependent coercivity in ribbon segments resulted from the combination of domain wall pinning and demagnetization effects. The approaches of synthesizing L1₀-FeNi magnets by adding Si or Co and decreasing the onset crystallization temperature have been discussed in detail.

Insights into the adsorption of water and oxygen on the cubic CsPbBr₃ surfaces: A first-principles study Suggested by editors

Xin Zhang(张鑫), Ruge Quhe(屈贺如歌), and Ming Lei(雷鸣)

Chin. Phys. B, 2022, 31 (4): 046401. DOI: 10.1088/1674-1056/ac3987

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The degradation mechanism of the all-inorganic perovskite solar cells in the ambient environment remains unclear. In this paper, water and oxygen molecule adsorptions on the all-inorganic perovskite (CsPbBr₃) surface are studied by density-functional theory calculations. In terms of the adsorption energy, the water molecules are more susceptible than the oxygen molecules to be adsorbed on the CsPbBr₃ surface. The water molecules can be adsorbed on both the CsBr- and PbBr-terminated surfaces, but the oxygen molecules tend to be selectively adsorbed on the CsBr-terminated surface instead of the PbBr-terminated one due to the significant adsorption energy difference. While the adsorbed water molecules only contribute deep states, the oxygen molecules introduce interfacial states inside the bandgap of the perovskite, which would significantly impact the chemical and transport properties of the perovskite. Therefore, special attention should be paid to reduce the oxygen concentration in the environment during the device fabrication process so as to improve the stability and performance of the CsPbBr₃-based devices.

Zero thermal expansion in metal-organic framework with imidazole dicarboxylate ligands Suggested by editors

Qilong Gao(高其龙), Yixin Jiao(焦怡馨), and Gang Li(李纲)

Chin. Phys. B, 2022, 31 (4): 046501. DOI: 10.1088/1674-1056/ac3ecf

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Exploring new abnormal thermal expansion materials is important to understand the nature of thermal expansion. Metal-organic framework (MOF) with unique structure flexibility is an ideal material to study the thermal expansion. This work adopts the high-resolution variable-temperature powder x-ray diffraction to investigate the structure and intrinsic thermal expansion in Sr-MOF ([Sr(DMPhH₂IDC)₂]_n). It has the unique honeycomb structure with one-dimensional (1D) channels along the c-axis direction, the a-b plane displays layer structure. The thermal expansion behavior has strong relationship with the structure, ZTE appears in the a-b plane and large PTE along the c-axis direction. The possible mechanism is that the a/b layers have enough space for the transverse thermal vibration of polydentate ligands, while along the c-axis direction is not. This work not only reports one interesting zero thermal expansion material, but also provides new understanding for thermal expansion mechanism from the perspective of the structural model.

Near-zero thermal expansion in β-CuZnV₂O₇ in a large temperature range Suggested by editors

Yaguang Hao(郝亚光), Hengli Xie(谢恒立), Gaojie Zeng(曾高杰), Huanli Yuan(袁焕丽), Yangming Hu(胡杨明), Juan Guo(郭娟), Qilong Gao(高其龙), Mingju Chao(晁明举), Xiao Ren(任霄), and Er-Jun Liang(梁二军)

Chin. Phys. B, 2022, 31 (4): 046502. DOI: 10.1088/1674-1056/ac3393

Abstract ( 393 )

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We report a new type of near-zero thermal expansion material β-CuZnV₂O₇ in a large temperature range from 173 K to 673 K. It belongs to a monoclinic structure (C2/c space group) in the whole temperature range. No structural phase transition is observed at atmospheric pressure based on the x-ray diffraction and Raman experiment. The high-pressure Raman experiment demonstrates that two structural phase transitions exist at 0.94 GPa and 6.53 GPa, respectively. The mechanism of negative thermal expansion in β-CuZnV₂O₇ is interpreted by the variations of the angles between atoms intuitively and the phonon anharmonicity intrinsically resorting to the negative Grüneisen parameter.

Numerical simulation of two droplets impacting upon a dynamic liquid film

Quan-Yuan Zeng(曾全元), Xiao-Hua Zhang(张小华), and Dao-Bin Ji(纪道斌)

Chin. Phys. B, 2022, 31 (4): 046801. DOI: 10.1088/1674-1056/ac22a0

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The impact of droplets on the liquid film is widely involved in industrial and agricultural fields. In recent years, plenty of works are limited to dry walls or stationary liquid films, and the research of multi-droplet impact dynamic films is not sufficient. Based on this, this paper employs a coupled level set and volume of fluid (CLSVOF) method to numerically simulate two-droplet impingement on a dynamic liquid film. In our work, the dynamic film thickness, horizontal central distance between the droplets, droplets' initial impact speed, and simultaneously the flow velocity of the moving film are analyzed. The evolution phenomenon and mechanism caused by the collision are analyzed in detail. We find that within a certain period of time, the droplet spacing does not affect the peripheral crown height; when the droplet spacing decreases or the initial impact velocity increases, the height of the peripheral crown increases at the beginning, and then, because the crown splashed under Rayleigh-Plateau instability, this results in the reduction of the crown height. At the same time, it is found that when the initial impact velocity increases, the angle between the upstream peripheral jet and the dynamic film becomes larger. The more obvious the horizontal movement characteristics, the more restrained the crown height; the spread length increases with the increase of the dynamic film speed, droplet spacing and the initial impact velocity. When the liquid film is thicker, more fluid enters the crown, due to the crown being unstable, the surface tension is not enough to overcome the weight of the rim at the end of the crown, resulting in droplets falling off.

TiS₂-graphene heterostructures enabling polysulfide anchoring and fast electrocatalyst for lithium-sulfur batteries: A first-principles calculation

Wenyang Zhao(赵文阳), Li-Chun Xu(徐利春), Yuhong Guo(郭宇宏), Zhi Yang(杨致), Ruiping Liu(刘瑞萍), and Xiuyan Li(李秀燕)

Chin. Phys. B, 2022, 31 (4): 047101. DOI: 10.1088/1674-1056/ac3227

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Lithium-sulfur batteries have attracted attention because of their high energy density. However, the "shuttle effect" caused by the dissolving of polysulfide in the electrolyte has greatly hindered the widespread commercial use of lithium-sulfur batteries. In this paper, a novel two-dimensional TiS₂/graphene heterostructure is theoretically designed as the anchoring material for lithium-sulfur batteries to suppress the shuttle effect. This heterostructure formed by the stacking of graphene and TiS₂ monolayer is the van der Waals type, which retains the intrinsic metallic electronic structure of graphene and TiS₂ monolayer. Graphene improves the electronic conductivity of the sulfur cathode, and the transferred electrons from graphene enhance the polarity of the TiS₂ monolayer. Simulations of the polysulfide adsorption show that the TiS₂/graphene heterostructure can maintain good metallic properties and the appropriate adsorption energies of 0.98-3.72 eV, which can effectively anchor polysulfides. Charge transfer analysis suggests that further enhancement of polarity is beneficial to reduce the high proportion of van der Waals (vdW) force in the adsorption energy, thereby further enhancing the anchoring ability. Low Li₂S decomposition barrier and Li-ion migration barrier imply that the heterostructure has the ability to catalyze fast electrochemical kinetic processes. Therefore, TiS₂/graphene heterostructure could be an important candidate for ideal anchoring materials of lithium-sulfur batteries.

Tunable electronic properties of GaS-SnS₂ heterostructure by strain and electric field

Da-Hua Ren(任达华), Qiang Li(李强), Kai Qian(钱楷), and Xing-Yi Tan(谭兴毅)

Chin. Phys. B, 2022, 31 (4): 047102. DOI: 10.1088/1674-1056/ac3a62

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Vertically stacked heterostructures have received extensive attention because of their tunable electronic structures and outstanding optical properties. In this work, we study the structural, electronic, and optical properties of vertically stacked GaS-SnS₂ heterostructure under the frame of density functional theory. We find that the stacked GaS-SnS₂ heterostructure is a semiconductor with a suitable indirect band gap of 1.82 eV, exhibiting a type-II band alignment for easily separating the photo-generated carriers. The electronic properties of GaS-SnS₂ heterostructure can be effectively tuned by an external strain and electric field. The optical absorption of GaS-SnS₂ heterostructure is more enhanced than those of the GaS monolayer and SnS₂ monolayer in the visible light region. Our results suggest that the GaS-SnS₂ heterostructure is a promising candidate for the photocatalyst and photoelectronic devices in the visible light region.

Self-screening of the polarized electric field in wurtzite gallium nitride along [0001] direction ^Hot!

Qiu-Ling Qiu(丘秋凌), Shi-Xu Yang(杨世旭), Qian-Shu Wu(吴千树), Cheng-Lang Li(黎城朗), Qi Zhang(张琦), Jin-Wei Zhang(张津玮), Zhen-Xing Liu(刘振兴), Yuan-Tao Zhang(张源涛), and Yang Liu(刘扬)

Chin. Phys. B, 2022, 31 (4): 047103. DOI: 10.1088/1674-1056/ac4746

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The strong polarization effect of GaN-based materials is widely used in high-performance devices such as white-light-emitting diodes (white LEDs), high electron mobility transistors (HEMTs), and GaN polarization superjunctions. However, the current researches on the polarization mechanism of GaN-based materials are not sufficient. In this paper, we studied the influence of polarization on electric field and energy band characteristics of Ga-face GaN bulk materials by using a combination of theoretical analysis and semiconductor technology computer-aided design (TCAD) simulation. The self-screening effect in Ga-face bulk GaN under ideal and non-ideal conditions is studied respectively. We believe that the formation of high-density two-dimensional electron gas (2DEG) in GaN is the accumulation of screening charges. We also clarify the source and accumulation of the screening charges caused by the GaN self-screening effect in this paper and aim to guide the design and optimization of high-performance GaN-based devices.

Doublet luminescence due to coexistence of excitons and electron-hole plasmas in optically excited CH₃NH₃PbBr₃ single crystal Suggested by editors

Jie Wang(王杰), Guang-Zhe Ma(马广哲), Lu Cao(曹露), Min Gao(高敏), and Dong Shi(石东)

Chin. Phys. B, 2022, 31 (4): 047104. DOI: 10.1088/1674-1056/ac29b5

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Doublet luminescence from hybrid metal trihalide perovskite semiconductors is observed along with materials processing when high-quality single crystals are obtainable. Yet, the underlying physical mechanism remains poorly understood. Here, we report controllable solution-processed crystallization that affords high-quality CH₃NH₃PbBr₃ single crystals with atomically flat pristine surfaces. Front-face photoluminescence (PL) shows doublet luminescence components with variable relative intensities depending on the crystal surface conditions. We further find that the low-energy PL component with asymmetric spectral line-shape becomes predominant when the atomically flat crystal surfaces are passivated in the ion-abundant saturated solutions, while poor-quality single crystal with visually rough surface only gives the high-energy PL with symmetric line-shape. The asymmetric spectral line-shape of the low-energy PL matches perfectly with the simulated bandedge emission. Therefore, the low-energy PL component is attributable to the intrinsic bandedge emission from the crystal bulk while the high-energy one to surface-specific emission. Elliott fitting to the absorption data and multi-exponential fitting to the time-resolved photoluminescence traces jointly indicate the coexistence of excitons and electron-hole plasmas in optically excited CH₃NH₃PbBr₃ single crystals, thereby catching the physical merit that leads to the occurrence of doublet luminescence.

Topological properties of Sb(111) surface: A first-principles study

Shuangxi Wang(王双喜) and Ping Zhang(张平)

Chin. Phys. B, 2022, 31 (4): 047105. DOI: 10.1088/1674-1056/ac46bc

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First-principles calculations based on the density functional theory were performed to systematically study the electronic properties of the thin film of antimony in (111) orientation. By considering the spin-orbit interaction, for stoichiometric surface, the topological states keep robust for six-bilayer case, and can be recovered in the three-bilayer film, which are guaranteed by time-reversal symmetry and inverse symmetry. For reduced surface doped by non-magnetic Bi or magnetic Mn atom, localized three-fold symmetric features can be identified. Moreover, band structures show that the non-trivial topological states stand for non-magnetic substitutional Bi atom, while can be eliminated by adsorbed or substitutional magnetic Mn atom.

Thermoelectric performance of XI₂ (X = Ge, Sn, Pb) bilayers Suggested by editors

Nan Lu(陆楠) and Jie Guan(管杰)

Chin. Phys. B, 2022, 31 (4): 047201. DOI: 10.1088/1674-1056/ac474c

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We study the thermal and electronic transport properties as well as the thermoelectric (TE) performance of three two-dimensional (2D) XI₂ (X=Ge, Sn, Pb) bilayers using density functional theory and Boltzmann transport theory. We compared the lattice thermal conductivity, electrical conductivity, Seebeck coefficient, and dimensionless figure of merit (ZT) for the XI₂ monolayers and bilayers. Our results show that the lattice thermal conductivity at room temperature for the bilayers is as low as ~1.1 W·m^{-1·K^-1-1.7 W}·m^{-1·K^-1, which is about 1.6 times as large as the monolayers for all the three materials. Electronic structure calculations show that all the}XI₂ bilayers are indirect-gap semiconductors with the band gap values between 1.84 eV and 1.96 eV at PBE level, which is similar as the corresponding monolayers. The calculated results of ZT show that the bilayer structures display much less direction-dependent TE efficiency and have much larger n-type ZT values compared with the monolayers. The dramatic difference between the monolayer and bilayer indicates that the inter-layer interaction plays an important role in the TE performance of XI₂, which provides the tunability on their TE characteristics.

Theoretical design of thermal spin molecular logic gates by using a combinational molecular junction

Yi Guo(郭逸), Peng Zhao(赵朋), and Gang Chen(陈刚)

Chin. Phys. B, 2022, 31 (4): 047202. DOI: 10.1088/1674-1056/ac3a5f

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Based on the density functional theory combined with the nonequilibrium Green function methodology, we have studied the thermally-driven spin-dependent transport properties of a combinational molecular junction consisting of a planar four-coordinate Fe molecule and a 15,16-dinitrile dihydropyrene/cyclophanediene molecule, with single-walled carbon nanotube bridge and electrode. Our results show that the magnetic field and light can effectively regulate the thermally-driven spin-dependent currents. Perfect thermal spin-filtering effect and good thermal switching effect are realized. The results are explained by the Fermi-Dirac distribution function, the spin-resolved transmission spectra, the spatial distribution of molecular projected self-consistent Hamiltonian orbitals, and the spin-resolved current spectra. On the basis of these thermally-driven spin-dependent transport properties, we have further designed three basic thermal spin molecular AND, OR, and NOT gates.

Effect of carbon nanotubes addition on thermoelectric properties of Ca₃Co₄O₉ ceramics Suggested by editors

Ya-Nan Li(李亚男), Ping Wu(吴平), Shi-Ping Zhang(张师平), Yi-Li Pei(裴艺丽), Jin-Guang Yang(杨金光), Sen Chen(陈森), and Li Wang(王立)

Chin. Phys. B, 2022, 31 (4): 047203. DOI: 10.1088/1674-1056/ac4bd2

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Increasing the phonon scattering center by adding nanoparticles to thermoelectric materials is an effective method of regulating the thermal conductivity. In this study, a series of Ca$_{3}$Co$_{4}$O$_{9}/x$ wt.% CNTs ($x=0$, 3, 5, 7, 10) polycrystalline ceramic thermoelectric materials by adding carbon nanotubes (CNTs) were prepared with sol-gel method and cold-pressing sintering technology. The results of x-ray diffraction and field emission scanning electron microscopy show that the materials have a single-phase structure with high orientation and sheet like microstructure. The effect of adding carbon nanotubes to the thermoelectric properties of Ca$_{3}$Co$_{4}$O$_{9}$ was systematically measured. The test results of thermoelectric properties show that the addition of carbon nanotubes reduces the electrical conductivity and Seebeck coefficient of the material. Nevertheless, the thermal conductivity of the samples with carbon nanotubes addition is lower than that of the samples without carbon nanotubes. At 625 K, the thermal conductivity of Ca$_{3}$Co$_{4}$O$_{9}$/10 wt.% CNTs sample is reduced to 0.408 W$\cdot$m$^{-1}\cdot$K$^{-1}$, which is about 73% lower than that of the original sample. When the three parameters are coupled, the figure of merit of Ca$_{3}$Co$_{4}$O$_{9}$/3 wt.% CNTs sample reaches 0.052, which is 29% higher than that of the original sample. This shows that an appropriate amount of carbon nanotubes addition can reduce the thermal conductivity of Ca$_{3}$Co$_{4}$O$_{9}$ ceramic samples and improve their thermoelectric properties.

Micro thermoelectric devices: From principles to innovative applications

Qiulin Liu(刘求林), Guodong Li(李国栋), Hangtian Zhu(朱航天), and Huaizhou Zhao(赵怀周)

Chin. Phys. B, 2022, 31 (4): 047204. DOI: 10.1088/1674-1056/ac5609

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Thermoelectric devices (TEDs), including thermoelectric generators (TEGs) and thermoelectric coolers (TECs) based on the Seebeck and Peltier effects, respectively, are capable of converting heat directly into electricity and vice versa. Tough suffering from low energy conversion efficiency and relatively high capital cost, TEDs have found niche applications, such as the remote power source for spacecraft, solid-state refrigerators, waste heat recycling, and so on. In particular, on-chip integrable micro thermoelectric devices (μ-TEDs), which can realize local thermal management, on-site temperature sensing, and energy harvesting under minor temperature gradient, could play an important role in biological sensing and cell cultivation, self-powered Internet of Things (IoT), and wearable electronics. In this review, starting from the basic principles of thermoelectric devices, we summarize the most critical parameters for μ-TEDs, design guidelines, and most recent advances in the fabrication process. In addition, some innovative applications of μ-TEDs, such as in combination with microfluidics and photonics, are demonstrated in detail.

Light-modulated electron retroreflection and Klein tunneling in a graphene-based n-p-n junction

Xingfei Zhou(周兴飞), Ziying Wu(吴子瀛), Yuchen Bai(白宇晨), Qicheng Wang(王起程), Zhentao Zhu(朱震涛), Wei Yan(闫巍), and Yafang Xu(许亚芳)

Chin. Phys. B, 2022, 31 (4): 047301. DOI: 10.1088/1674-1056/ac2b94

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We investigate the electron retroreflection and the Klein tunneling across a graphene-based n-p-n junction irradiated by linearly polarized off-resonant light with the polarization along the x direction. The linearly polarized off-resonant light modifies the band structure of graphene, which leads to the anisotropy of band structure. By adjusting the linearly polarized light and the direction of n-p-n junction simultaneously, the electron retroreflection appears and the anomalous Klein tunneling, the perfect transmission at a nonzero incident angle regardless of the width and height of potential barrier, happens, which arises from the fact that the light-induced anisotropic band structure changes the relation of wavevector and velocity of electron. Our finding provides an alternative and flexible method to modulate electron retroreflection and Klein tunneling.

Lateral β-Ga₂O₃ Schottky barrier diode fabricated on (-201) single crystal substrate and its temperature-dependent current-voltage characteristics Suggested by editors

Pei-Pei Ma(马培培), Jun Zheng(郑军), Ya-Bao Zhang(张亚宝), Xiang-Quan Liu(刘香全), Zhi Liu(刘智), Yu-Hua Zuo(左玉华), Chun-Lai Xue(薛春来), and Bu-Wen Cheng(成步文)

Chin. Phys. B, 2022, 31 (4): 047302. DOI: 10.1088/1674-1056/ac2729

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Lateral β-Ga₂O₃ Schottky barrier diodes (SBDs) each are fabricated on an unintentionally doped (-201) n-type β-Ga₂O₃ single crystal substrate by designing L-shaped electrodes. By introducing sidewall electrodes on both sides of the conductive channel, the SBD demonstrates a high current density of 223 mA/mm and low specific on-resistance of 4.7 mΩ ·cm². Temperature-dependent performance is studied and the Schottky barrier height is extracted to be in a range between 1.3 eV and 1.35 eV at temperatures ranging from 20 ℃ to 150 ℃. These results suggest that the lateral β-Ga₂O₃ SBD has a tremendous potential for future power electronic applications.

Extrinsic equivalent circuit modeling of InP HEMTs based on full-wave electromagnetic simulation Suggested by editors

Shi-Yu Feng(冯识谕), Yong-Bo Su(苏永波), Peng Ding(丁芃), Jing-Tao Zhou(周静涛), Song-Ang Peng(彭松昂), Wu-Chang Ding(丁武昌), and Zhi Jin(金智)

Chin. Phys. B, 2022, 31 (4): 047303. DOI: 10.1088/1674-1056/ac2b1d

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With the widespread utilization of indium-phosphide-based high-electron-mobility transistors (InP HEMTs) in the millimeter-wave (mmW) band, the distributed and high-frequency parasitic coupling behavior of the device is particularly prominent. We present an InP HEMT extrinsic parasitic equivalent circuit, in which the conductance between the device electrodes and a new gate-drain mutual inductance term L_mgd are taken into account for the high-frequency magnetic field coupling between device electrodes. Based on the suggested parasitic equivalent circuit, through HFSS and advanced design system (ADS) co-simulation, the equivalent circuit parameters are directly extracted in the multi-step system. The HFSS simulation prediction, measurement data, and modeled frequency response are compared with each other to verify the feasibility of the extraction method and the accuracy of the equivalent circuit. The proposed model demonstrates the distributed and radio-frequency behavior of the device and solves the problem that the equivalent circuit parameters of the conventional InP HEMTs device are limited by the device model and inaccurate at high frequencies when being extracted.

Fast-switching SOI-LIGBT with compound dielectric buried layer and assistant-depletion trench

Chunzao Wang(王春早), Baoxing Duan(段宝兴), Licheng Sun(孙李诚), and Yintang Yang(杨银堂)

Chin. Phys. B, 2022, 31 (4): 047304. DOI: 10.1088/1674-1056/ac29ac

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A lateral insulated gate bipolar transistor (LIGBT) based on silicon-on-insulator (SOI) structure is proposed and investigated. This device features a compound dielectric buried layer (CDBL) and an assistant-depletion trench (ADT). The CDBL is employed to introduce two high electric field peaks that optimize the electric field distributions and that, under the same breakdown voltage (BV) condition, allow the CDBL to acquire a drift region of shorter length and a smaller number of stored carriers. Reducing their numbers helps in fast-switching. Furthermore, the ADT contributes to the rapid extraction of the stored carriers from the drift region as well as the formation of an additional heat-flow channel. The simulation results show that the BV of the proposed LIGBT is increased by 113% compared with the conventional SOI LIGBT of the same length L_D. Contrastingly, the length of the drift region of the proposed device (11.2 μ) is about one third that of a traditional device (33 μ) with the same BV of 141 V. Therefore, the turn-off loss (E_OFF) of the CDBL SOI LIGBT is decreased by 88.7% compared with a conventional SOI LIGBT when the forward voltage drop (V_F) is 1.64 V. Moreover, the short-circuit failure time of the proposed device is 45% longer than that of the conventional SOI LIGBT. Therefor, the proposed CDBL SOI LIGBT exhibits a better V_F-E_OFF tradeoff and an improved short-circuit robustness.

Anomalous Hall effect of facing-target sputtered ferrimagnetic Mn₄N epitaxial films with perpendicular magnetic anisotropy

Zeyu Zhang(张泽宇), Qiang Zhang(张强), and Wenbo Mi(米文博)

Chin. Phys. B, 2022, 31 (4): 047305. DOI: 10.1088/1674-1056/ac2b90

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Epitaxial Mn$_{4}$N films with different thicknesses were fabricated by facing-target reactive sputtering and their anomalous Hall effect (AHE) is investigated systematically. The Hall resistivity shows a reversed magnetic hysteresis loop with the magnetic field. The magnitude of the anomalous Hall resistivity sharply decreases with decreasing temperature from 300 K to 150 K. The AHE scaling law in Mn$_{4}$N films is influenced by the temperature-dependent magnetization, carrier concentration and interfacial scattering. Different scaling laws are used to distinguish the various contributions of AHE mechanisms. The scaling exponent $\gamma > 2$ for the conventional scaling in Mn$_{4}$N films could be attributed to the residual resistivity $\rho_{xx0}$. The longitudinal conductivity $\sigma_{xx}$ falls into the dirty regime. The scaling of $\rho_{\rm AH}=\alpha \rho_{xx0} +b\rho_{xx}^{n}$ is used to separate out the temperature-independent $\rho_{xx0}$ from extrinsic contribution. Moreover, the relationship between $\rho_{\rm AH}$ and $\rho_{xx}$ is fitted by the proper scaling to clarify the contributions from extrinsic and intrinsic mechanisms of AHE, which demonstrates that the dominant mechanism of AHE in the Mn$_{4}$N films can be ascribed to the competition between skew scattering, side jump and the intrinsic mechanisms.

Laser-induced phase conversion of n-type SnSe₂ to p-type SnSe Suggested by editors

Qi Zheng(郑琦), Rong Yang(杨蓉), Kang Wu(吴康), Xiao Lin(林晓), Shixuan Du(杜世萱), Chengmin Shen(申承民), Lihong Bao(鲍丽宏), and Hong-Jun Gao(高鸿钧)

Chin. Phys. B, 2022, 31 (4): 047306. DOI: 10.1088/1674-1056/ac4901

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We report a facile phase conversion method that can locally convert n-type SnSe₂ into p-type SnSe by direct laser irradiation. Raman spectra of SnSe₂ flakes before and after laser irradiation confirm the phase conversion of SnSe₂ to SnSe. By performing the laser irradiation on SnSe₂ flakes at different temperatures, it is found that laser heating effect induces the removal of Se atoms from SnSe₂ and results in the phase conversion of SnSe₂ to SnSe. Lattice-revolved transmission electron microscope images of SnSe₂ flakes before and after laser irradiation further confirm such conversion. By selective laser irradiation on SnSe₂ flakes, a pattern with SnSe₂/SnSe heteostructures is created. This indicates that the laser induced phase conversion technique has relatively high spatial resolution and enables the creation of micron-sized in-plane p-n junction at predefined region.

Research status and performance optimization of medium-temperature thermoelectric material SnTe

Pan-Pan Peng(彭盼盼), Chao Wang(王超), Lan-Wei Li(李岚伟), Shu-Yao Li(李淑瑶), and Yan-Qun Chen(陈艳群)

Chin. Phys. B, 2022, 31 (4): 047307. DOI: 10.1088/1674-1056/ac20c9

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Thermoelectric materials have the ability to directly convert heat into electricity, which have been extensively studied for decades to solve global energy shortages and environmental problems. As a medium temperature (400-800 K) thermoelectric material, SnTe has attracted extensive attention as a promising substitute for PbTe due to its non-toxic characteristics. In this paper, the research status of SnTe thermoelectric materials is reviewed, and the strategies to improve its performance are summarized and discussed in terms of electrical and thermal transport properties. This comprehensive discussion will provides guidance and inspiration for the research on SnTe.

Advances in thermoelectric (GeTe)_x(AgSbTe₂)_100-x

Hongxia Liu(刘虹霞), Xinyue Zhang(张馨月), Wen Li(李文), and Yanzhong Pei(裴艳中)

Chin. Phys. B, 2022, 31 (4): 047401. DOI: 10.1088/1674-1056/ac3cae

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The (GeTe)_x(AgSbTe₂)_100-x alloys, also called TAGS-x in short, have long been demonstrated as a promising candidate for thermoelectric applications with successful services as the p-type leg in radioisotope thermoelectric generators for space missions. This largely stems from the complex band structure for a superior electronic performance and strong anharmonicity for a low lattice thermal conductivity. Utilization of the proven strategies including carrier concentration optimization, band and defects engineering, an extraordinary thermoelectric figure of merit, zT, has been achieved in TAGS-based alloys. Here, crystal structure, band structure, microstructure, synthesis techniques and thermoelectric transport properties of TAGS-based alloys, as well as successful strategies for manipulating the thermoelectric performance, are surveyed with opportunities for further advancements. These strategies involved are believed to be in principle applicable for advancing many other thermoelectrics.

Incommensurate-commensurate magnetic phase transition in double tungstate Li₂Co(WO₄)₂ Suggested by editors

Xiyu Chen(陈西煜), Ning Ding(丁宁), Meifeng Liu(刘美风), Tao Zou(邹涛), V. Ovidiu Garlea, Jingwen Gong(龚婧雯), Fei Liu(刘飞), Yunlong Xie(谢云龙), Lun Yang(杨伦), Shuhan Zheng(郑书翰), Xiuzhang Wang(王秀章), Shuai Dong(董帅), T. Charlton, and Jun-Ming Liu(刘俊明)

Chin. Phys. B, 2022, 31 (4): 047501. DOI: 10.1088/1674-1056/ac3818

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Magnetic susceptibility, specific heat, and neutron powder diffraction measurements have been performed on polycrystalline Li$_{2}$Co(WO$_{4}$)$_{2}$ samples. Under zero magnetic field, two successive magnetic transitions at $T_{\rm N1}\sim 9.4$ K and $T_{\rm N2}\sim 7.4$ K are observed. The magnetic ordering temperatures gradually decrease as the magnetic field increases. Neutron diffraction reveals that Li$_{2}$Co(WO$_{4}$)$_{2}$ enters an incommensurate magnetic state with a temperature dependent $\bm k$ between $T_{\rm N1}$ and $T_{\rm N2}$. The magnetic propagation vector locks-in to a commensurate value $\bm k = (1/2, 1/4, 1/4)$ below $T_{\rm N2}$. The antiferromagnetic structure is refined at 1.7 K with Co$^{2+}$ magnetic moment 2.8(1) $\mu_{\rm B}$, consistent with our first-principles calculations.

Enhancement of magnetic and dielectric properties of low temperature sintered NiCuZn ferrite by Bi₂O₃-CuO additives

Jie Li(李颉), Bing Lu(卢冰), Ying Zhang(张颖), Jian Wu(武剑), Yan Yang(杨燕), Xue-Ning Han(韩雪宁), Dan-Dan Wen(文丹丹), Zheng Liang(梁峥), and Huai-Wu Zhang(张怀武)

Chin. Phys. B, 2022, 31 (4): 047502. DOI: 10.1088/1674-1056/ac3399

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With a series of 1.0 wt%Bi$_{2}$O$_{3}$-$x$ wt% CuO ($x =0.0$, 0.2, 0.4, 0.6, and 0.8) serving as sintering additives, Ni$_{0.23}$Cu$_{0.32}$Zn$_{0.45}$Fe$_{2}$O$_{4}$ ferrites are successfully synthesized at a low temperature (900 $^\circ$C) by using the solid state reaction method. The effects of the additives on the phase formation, magnetic and dielectric properties as well as the structural and gyromagnetic properties are investigated. The x-ray diffraction (XRD) results indicate that the added Bi$_{2}$O$_{3}$-CuO can lower the synthesis temperature significantly without the appearing of the second phase. The scanning electron microscope (SEM) images confirm that Bi$_{2}$O$_{3}$ is an important factor that determines the sintering behaviors, while CuO affects the grain size and densification. With CuO content $x=0.4$ or 0.6, the sample shows high saturation magnetization, low coercivity, high real part of magnetic permeability, dielectric permittivity, and small ferromagnetic resonance linewidth ($\Delta H$). The NiCuZn ferrites are a promising new generation of high-performance microwave devices, such as phase shifters and isolators.

Comprehensive performance of a ball-milled La_0.5Pr_0.5Fe_11.4Si_1.6B_0.2H_y/Al magnetocaloric composite

Jiao-Hong Huang(黄焦宏), Ying-De Zhang(张英德), Nai-Kun Sun(孙乃坤), Yang Zhang(张扬), Xin-Guo Zhao(赵新国), and Zhi-Dong Zhang(张志东)

Chin. Phys. B, 2022, 31 (4): 047503. DOI: 10.1088/1674-1056/ac280b

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Due to the hydrogen embrittlement effect, La(Fe,Si)₁₃-based hydrides can only exist in powder form, which limits their practical application. In this work, ductile and thermally conductive Al metal was homogeneously mixed with La_0.5Pr_0.5Fe_11.4Si_1.6B_0.2 using the ball milling method. Then hydrogenation and compactness shaping of the magnetocaloric composites were performed in one step via a sintering process under high hydrogen pressure. As the Al content reached 9 wt.%, the La_0.5Pr_0.5Fe_11.4Si_1.6B_0.2H_y/Al composite showed the mechanical behavior of a ductile material with a yield strength of ~44 MPa and an ultimate strength of 269 MPa accompanied by a pronounced improvement in thermal conductivity. Due to the ease of formation of Fe-Al-Si phases and the several micron and submicron sizes of the composite particles caused by ball milling process, the magnetic entropy change of the composites was substantially reduced to ~1.2 J/kg· K-1.5 J/kg· K at 0 T-1.5 T.

Effect of anode area on the sensing mechanism of vertical GaN Schottky barrier diode temperature sensor Suggested by editors

Ji-Yao Du(都继瑶), Xiao-Bo Li(李小波), Tao-Fei Pu(蒲涛飞), and Jin-Ping Ao(敖金平)

Chin. Phys. B, 2022, 31 (4): 047701. DOI: 10.1088/1674-1056/ac3223

Abstract ( 366 )

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Effect of anode area on temperature sensing ability is investigated for a vertical GaN Schottky-barrier-diode sensor. The current-voltage-temperature characteristics are comparable to each other for Schottky barrier diodes with different anode areas, excepting the series resistance. In the sub-threshold region, the contribution of series resistance on the sensitivity can be ignored due to the relatively small current. The sensitivity is dominated by the current density. A large anode area is helpful for enhancing the sensitivity at the same current level. In the fully turn-on region, the contribution of series resistance dominates the sensitivity. Unfortunately, a large series resistance degrades the temperature error and linearity, implying that a larger anode area will help to decrease the series resistance and to improve the sensing ability.

Improving the performance of a GaAs nanowire photodetector using surface plasmon polaritons

Xiaotian Zhu(朱笑天), Bingheng Meng(孟兵恒), Dengkui Wang(王登魁), Xue Chen(陈雪), Lei Liao(廖蕾), Mingming Jiang(姜明明), and Zhipeng Wei(魏志鹏)

Chin. Phys. B, 2022, 31 (4): 047801. DOI: 10.1088/1674-1056/ac1e15

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GaAs nanowires (NWs) are ideal materials for preparing near-infrared photodetectors owing to their high charge carrier mobility and direct band gap. Although the performance of GaAs NW photodetectors can be enhanced by surface passivation or doping, it still cannot meet the requirement for applications. In this paper we propose a method to greatly improve the performances of GaAs NW photodetectors by hot-hole injection via surface plasmon polaritons. In this case, the responsivity of a single GaAs NW photodetector is increased by a fact of 3.2 to 6.56 A· W^-1 by attaching capsule-like Au nanoparticles to its surface. This research uses an efficient route to improve the NW photocurrent, which is also important for the development of a high-performance near-infrared NW photodetecor.

Effect of Cu doping on the secondary electron yield of carbon films on Ag-plated aluminum alloy Suggested by editors

Tiancun Hu(胡天存), Shukai Zhu(朱淑凯), Yanan Zhao(赵亚楠), Xuan Sun(孙璇), Jing Yang(杨晶), Yun He(何鋆), Xinbo Wang(王新波), Chunjiang Bai(白春江), He Bai(白鹤), Huan Wei(魏焕), Meng Cao(曹猛), Zhongqiang Hu(胡忠强), Ming Liu(刘明), and Wanzhao Cui(崔万照)

Chin. Phys. B, 2022, 31 (4): 047901. DOI: 10.1088/1674-1056/ac322c

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Reducing the secondary electron yield (SEY) of Ag-plated aluminum alloy is important for high-power microwave components. In this work, Cu doped carbon films are prepared and the secondary electron emission characteristics are studied systematically. The secondary electron coefficient δ_max of carbon films increases with the Cu contents increasing at first, and then decreases to 1.53 at a high doping ratio of 0.645. From the viewpoint of surface structure, the higher the content of Cu is, the rougher the surface is, since more cluster particles appear on the surface due to the small solid solubility of Cu in the amorphous carbon network. However, from viewpoint of the electronic structure, the reduction of the sp² hybrid bonds will increase the SEY effect as the content of Cu increases, due to the decreasing probability of collision with free electrons. Thus, the two mechanisms would compete and coexist to affect the SEY characteristics in Cu doped carbon films.

Butt-joint regrowth method by MOCVD for integration of evanescent wave coupled photodetector and multi-quantum well semiconductor optical amplifier

Feng Xiao(肖峰), Qin Han(韩勤), Han Ye(叶焓), Shuai Wang(王帅), Zi-Qing Lu(陆子晴), and Fan Xiao(肖帆)

Chin. Phys. B, 2022, 31 (4): 048101. DOI: 10.1088/1674-1056/ac272b

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We have realized integration of evanescent wave coupled photodetector (ECPD) and multi-quantum well (MQW) semiconductor optical amplifier (SOA) on MOCVD platform by investigating butt-joint regrowth method of thick InP/InGaAsP waveguides to deep etched SOA mesas. The combination of inductively coupled plasma etching and wet chemical etching technique has been studied to define the final mesa shape before regrowth. By comparing the etching profiles of different non-selective etchants, we have obtained a controllable non-reentrant mesa shape with smooth sidewall by applying one step 2HBr:2H₃PO₄:K₂Cr₂O₇ wet etching. A high growth temperature of 680 ℃ is found helpful to enhance planar regrowth. By comparing the growth morphologies and simulating optical transmission along different directions, we determined that waveguides should travel across the regrowth interface along the [110] direction. The relation between growth rate and mask design has been extensively studied and the result can provide an important guidance for future mask design and vertical alignment between the active and passive cores. ECPD-SOA integrated device has been successfully achieved by this method without further regrowth steps and provided a responsivity of 7.8 A/W. The butt-joint interface insertion loss is estimated to be 1.05 dB/interface.

Edge assisted epitaxy of CsPbBr₃ nanoplates on Bi₂O₂Se nanosheets for enhanced photoresponse

Haotian Jiang(蒋浩天), Xing Xu(徐兴), Chao Fan(樊超), Beibei Dai(代贝贝), Zhuodong Qi(亓卓栋), Sha Jiang(蒋莎), Mengqiu Cai(蔡孟秋), and Qinglin Zhang(张清林)

Chin. Phys. B, 2022, 31 (4): 048102. DOI: 10.1088/1674-1056/ac2b20

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Bi$_{2}$O$_{2}$Se has been proved to be a promising candidate for electronic and optoelectronic devices due to their unique physical properties. However, it is still a great challenge to construct the heterostructures with direct epitaxy of hetero semiconductor materials on Bi$_{2}$O$_{2}$Se nanosheets. Here, a two-step chemical vapor deposition (CVD) route was used to directly grow the CsPbBr$_{3}$ nanoplate-Bi$_{2}$O$_{2}$Se nanosheet heterostructures. The CsPbBr$_{3}$ nanoplates were selectively grown on the Bi$_{2}$O$_{2}$Se nanosheet along the edges, where the dangling bonds provide the nucleation sites. The epitaxial relationships between CsPbBr$_{3}$ and Bi$_{2}$O$_{2}$Se were determined as ${[200]}_{\rm Bi_{2}O_{2}Se}||{[110]}_{\rm CsPbBr_{3}}$ and ${[110]}_{\rm Bi_{2}O_{2}Se}||{[200]}_{\rm CsPbBr_{3}}$ by transmission electron microscopy characterization. The photoluminescence (PL) results reveal that the formation of heterostructures results in the remarkable PL quenching due to the type-I band arrangement at CsPbBr$_{3}$/Bi$_{2}$O$_{2}$Se interface, which was confirmed by ultraviolet photoelectron spectroscopy (UPS) and Kelvin probe measurements, and makes the photogenerated carriers transfer from CsPbBr$_{3}$ to Bi$_{2}$O$_{2}$Se. Importantly, the photodetectors based on the heterostructures exhibit a 4-time increase in the responsivity compared to those based on the pristine Bi$_{2}$O$_{2}$Se sheets, and the fast rise and decay time in microsecond. These results indicate that the direct epitaxy of the CsPbBr$_{3}$ plates on the Bi$_{2}$O$_{2}$Se sheet may improve the optoelectronic performance of Bi$_{2}$O$_{2}$Se based devices.

Comparative study of high temperature anti-oxidation property of sputtering deposited stoichiometric and Si-rich SiC films

Hang-Hang Wang(王行行), Wen-Qi Lu(陆文琪), Jiao Zhang(张娇), and Jun Xu(徐军)

Chin. Phys. B, 2022, 31 (4): 048103. DOI: 10.1088/1674-1056/ac3a61

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Stoichiometric and silicon-rich (Si-rich) SiC films were deposited by microwave electron cyclotron resonance (MW-ECR) plasma enhanced RF magnetron sputtering method. As-deposited films were oxidized at 800 ℃, 900 ℃, and 1000 ℃ in air for 60 min. The chemical composition and structure of the films were analyzed by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Fourier transform infrared spectroscopy (FT-IR). The surface morphology of the films before and after the high temperature oxidation was measured by atomic force microscopy. The mechanical property of the films was measured by a nano-indenter. The anti-oxidation temperature of the Si-rich SiC film is 100 ℃ higher than that of the stoichiometric SiC film. The oxidation layer thickness of the Si-rich SiC film is thinner than that of the stoichiometric SiC film in depth direction. The large amount of extra silicon in the Si-rich SiC film plays an important role in the improvement of its high temperature anti-oxidation property.

Phase-field modeling of faceted growth in solidification of alloys

Hui Xing(邢辉), Qi An(安琪), Xianglei Dong(董祥雷), and Yongsheng Han(韩永生)

Chin. Phys. B, 2022, 31 (4): 048104. DOI: 10.1088/1674-1056/ac3398

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A regularization of the surface tension anisotropic function used in vapor-liquid-solid nanowire growth was introduced into the quantitative phase-field model to simulate the faceted growth in solidification of alloys. Predicted results show that the value of δ can only affect the region near the tip, and the convergence with respect to δ can be achieved with the decrease of δ near the tip. It can be found that the steady growth velocity is not a monotonic function of the cusp amplitude, and the maximum value is approximately at ε=0.8 when the supersaturation is fixed. Moreover, the growth velocity is an increasing function of supersaturation with the morphological transition from facet to dendrite.

Thermodynamically consistent model for diblock copolymer melts coupled with an electric field

Xiaowen Shen(沈晓文) and Qi Wang(王奇)

Chin. Phys. B, 2022, 31 (4): 048201. DOI: 10.1088/1674-1056/ac2728

Abstract ( 357 )

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We present a thermodynamically consistent model for diblock copolymer melts coupled with an electric field derived using the Onsager linear response theory. We compare the model with the thermodynamically inconsistent one previously used for the coupled system to highlight their differences in describing transient dynamics.

Theoretical study on the mechanism for the excited-state double proton transfer process of an asymmetric Schiff base ligand

Zhengran Wang(王正然), Qiao Zhou(周悄), Bifa Cao(曹必发), Bo Li(栗博), Lixia Zhu(朱丽霞), Xinglei Zhang(张星蕾), Hang Yin(尹航), and Ying Shi(石英)

Chin. Phys. B, 2022, 31 (4): 048202. DOI: 10.1088/1674-1056/ac21c2

Abstract ( 285 )

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Excited-state double proton transfer (ESDPT) in the 1-[(2-hydroxy-3-methoxy-benzylidene)-hydrazonomethyl]-naphthalen-2-ol (HYDRAVH₂) ligand was studied by the density functional theory and time-dependent density functional theory method. The analysis of frontier molecular orbitals, infrared spectra, and non-covalent interactions have cross-validated that the asymmetric structure has an influence on the proton transfer, which makes the proton transfer ability of the two hydrogen protons different. The potential energy surfaces in both S₀ and S₁ states were scanned with varying O-H bond lengths. The results of potential energy surface analysis adequately proved that the HYDRAVH₂ can undergo the ESDPT process in the S₁ state and the double proton transfer process is a stepwise proton transfer mechanism. Our work can pave the way towards the design and synthesis of new molecules.

Fast-speed self-powered PEDOT: PSS/α-Ga₂O₃ nanorod array/FTO photodetector with solar-blind UV/visible dual-band photodetection

Ming-Ming Fan(范明明), Kang-Li Xu(许康丽), Ling Cao(曹铃), and Xiu-Yan Li(李秀燕)

Chin. Phys. B, 2022, 31 (4): 048501. DOI: 10.1088/1674-1056/ac3814

Abstract ( 373 )

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The $\alpha $-Ga$_{2}$O$_{3}$ nanorod array is grown on FTO by hydrothermal and annealing processes. And a self-powered PEDOT:PSS/$\alpha $-Ga$_{2}$O$_{3}$ nanorod array/FTO (PGF) photodetector has been demonstrated by spin coating PEDOT:PSS on the $\alpha $-Ga$_{2}$O$_{3}$ nanorod array. Successfully, the PGF photodetector shows solar-blind UV/visible dual-band photodetection. Our device possesses comparable solar-blind UV responsivity (0.18 mA/W at 235 nm) and much faster response speed (0.102 s) than most of the reported self-powered $\alpha $-Ga$_{2}$O$_{3}$ nanorod array solar-blind UV photodetectors. And it presents the featured and distinguished visible band photoresponse with a response speed of 0.136 s at 540 nm. The response time is also much faster than the other non-self-powered $\beta $-Ga$_{2}$O$_{3 }$ DUV/visible dual-band photodetectors due to the fast-speed separation of photogenerated carries by the built-in electric field in the depletion regions of PEDOT:PSS/$\alpha $-Ga$_{2}$O$_{3}$ heterojunction. The results herein may prove a promising way to realize fast-speed self-powered $\alpha $-Ga$_{2}$O$_{3}$ photodetectors with solar-blind UV/visible dual-band photodetection by simple processes for the applications of multiple-target tracking, imaging, machine vision and communication.

Module-level design and characterization of thermoelectric power generator

Kang Zhu(朱康), Shengqiang Bai(柏胜强), Hee Seok Kim, and Weishu Liu(刘玮书)

Chin. Phys. B, 2022, 31 (4): 048502. DOI: 10.1088/1674-1056/ac1b8f

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Thermoelectric power generation provides us the unique capability to explore the deep space and holds promise for harvesting the waste heat and providing a battery-free power supply for IoTs. The past years have witnessed massive progress in thermoelectric materials, while the module-level development is still lagged behind. We would like to shine some light on the module-level design and characterization of thermoelectric power generators (TEGs). In the module-level design, we review material selection, thermal management, and the determination of structural parameters. We also look into the module-level characterization, with particular attention on the heat flux measurement. Finally, the challenge in the optimal design and reliable characterization of thermoelectric power generators is discussed, together with a calling to establish a standard test procedure.

The 50 nm-thick yttrium iron garnet films with perpendicular magnetic anisotropy ^Hot!

Shuyao Chen(陈姝瑶), Yunfei Xie(谢云飞), Yucong Yang(杨玉聪), Dong Gao(高栋), Donghua Liu(刘冬华), Lin Qin(秦林), Wei Yan(严巍), Bi Tan(谭碧), Qiuli Chen(陈秋丽), Tao Gong(龚涛), En Li(李恩), Lei Bi(毕磊), Tao Liu(刘涛), and Longjiang Deng(邓龙江)

Chin. Phys. B, 2022, 31 (4): 048503. DOI: 10.1088/1674-1056/ac4cc4

Abstract ( 663 )

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Yttrium iron garnet (YIG) films possessing both perpendicular magnetic anisotropy (PMA) and low damping would serve as ideal candidates for high-speed energy-efficient spintronic and magnonic devices. However, it is still challenging to achieve PMA in YIG films thicker than 20 nm, which is a major bottleneck for their development. In this work, we demonstrate that this problem can be solved by using substrates with moderate lattice mismatch with YIG so as to suppress the excessive strain-induced stress release as increasing the YIG thickness. After carefully optimizing the growth and annealing conditions, we have achieved out-of-plane spontaneous magnetization in YIG films grown on sGGG substrates, even when they are as thick as 50 nm. Furthermore, ferromagnetic resonance and spin pumping induced inverse spin Hall effect measurements further verify the good spin transparency at the surface of our YIG films.

Evaluation on performance of MM/PBSA in nucleic acid-protein systems Suggested by editors

Yuan-Qiang Chen(陈远强), Yan-Jing Sheng(盛艳静), Hong-Ming Ding(丁泓铭), and Yu-Qiang Ma(马余强)

Chin. Phys. B, 2022, 31 (4): 048701. DOI: 10.1088/1674-1056/ac3a5c

Abstract ( 348 )

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The molecular mechanics/Poisson-Boltzmann surface area (MM/PBSA) method has been widely used in predicting the binding affinity among ligands, proteins, and nucleic acids. However, the accuracy of the predicted binding energy by the standard MM/PBSA is not always good, especially in highly charged systems. In this work, we take the protein-nucleic acid complexes as an example, and showed that the use of screening electrostatic energy (instead of Coulomb electrostatic energy) in molecular mechanics can greatly improve the performance of MM/PBSA. In particular, the Pearson correlation coefficient of dataset II in the modified MM/PBSA (i.e., screening MM/PBSA) is about 0.52, much better than that (< 0.33) in the standard MM/PBSA. Further, we also evaluate the effect of solute dielectric constant and salt concentration on the performance of the screening MM/PBSA. The present study highlights the potential power of the screening MM/PBSA for predicting the binding energy in highly charged bio-systems.

Molecular dynamics simulations of A-DNA in bivalent metal ions salt solution

Jingjing Xue(薛晶晶), Xinpeng Li(李新朋), Rongri Tan(谈荣日), and Wenjun Zong(宗文军)

Chin. Phys. B, 2022, 31 (4): 048702. DOI: 10.1088/1674-1056/ac3caa

Abstract ( 434 )

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A-form DNA is one of the biologically active double helical structure. The study of A-DNA structure has an extensive application for developing the field of DNA packaging in biotechnology. In aqueous solution, the A-DNA structure will have a free transformation, the A-DNA structure will be translated into B-form structure with the evolution of time, and eventually stabilized in the B-DNA structure. To explore the stability function of the bivalent metal ions on the A-DNA structure, a series of molecular dynamics simulations have been performed on the A-DNA of sequence (CCCGGCCGGG). The results show that bivalent metal ions (Mg²⁺, Zn²⁺, Ca²⁺) generate a great effect on the structural stability of A-DNA in the environment of high concentration. As the interaction between metal ions and electronegative DNA chains, the stability of A-DNA in solution is gradually improved with the increasing solution concentration of ions. In metal salt solution with high concentration, metal ions can be easily distributed in the solvation shells around the phosphate groups and further lead to the formation of shorter and more compact DNA structure. Also, under the condition of the same concentration and valency of the metal ions, the stability of A-DNA structure is different. The calculations indicate that the structure of A-DNA in CaCl₂ solution is less stable than in MgCl₂ and ZnCl₂ solution.

Transmembrane transport of multicomponent liposome-nanoparticles into giant vesicles

Hui-Fang Wang(王慧芳), Chun-Rong Li(李春蓉), Min-Na Sun(孙敏娜), Jun-Xing Pan(潘俊星), and Jin-Jun Zhang(张进军)

Chin. Phys. B, 2022, 31 (4): 048703. DOI: 10.1088/1674-1056/ac380f

Abstract ( 326 )

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With the emergence and rapid development of nanotechnology, the nanoparticles hybridized with multicomponent lipids are more and more used in gene delivery. These vectors interact with the cell membrane before entering into the cell. Therefore, the nature of this interaction is important in investigating multicomponent liposome-nanoparticle (MLP) transport across the cell membrane. In this paper the transport of MLPs across the membranes of giant vesicles (GVs) in solvents is studied by using the self-consistent field theory (SCFT). Based on the analysis of the MLP permeating the GV membranes, a simple transport model is proposed. The effects of the difference in membrane morphology and the size of the nanoparticle on the endocytosis are discussed systematically. The role of energy barriers in quasi-equilibrium is also examined. The results indicate that the interaction between MLP and GV is a spontaneous process and the energy barrier needs overcoming to form metastable intermediates. The results provide theoretical reference for better understanding the transmembrane transport process of nanoparticles, and guidance for relevant experimental studies as well.

Optimized quantum singular value thresholding algorithm based on a hybrid quantum computer Suggested by editors

Yangyang Ge(葛阳阳), Zhimin Wang(王治旻), Wen Zheng(郑文), Yu Zhang(张钰), Xiangmin Yu(喻祥敏), Renjie Kang(康人杰), Wei Xin(辛蔚), Dong Lan(兰栋), Jie Zhao(赵杰), Xinsheng Tan(谭新生), Shaoxiong Li(李邵雄), and Yang Yu(于扬)

Chin. Phys. B, 2022, 31 (4): 048704. DOI: 10.1088/1674-1056/ac40fb

Abstract ( 334 )

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Quantum singular value thresholding (QSVT) algorithm, as a core module of many mathematical models, seeks the singular values of a sparse and low rank matrix exceeding a threshold and their associated singular vectors. The existing all-qubit QSVT algorithm demands lots of ancillary qubits, remaining a huge challenge for realization on nearterm intermediate-scale quantum computers. In this paper, we propose a hybrid QSVT (HQSVT) algorithm utilizing both discrete variables (DVs) and continuous variables (CVs). In our algorithm, raw data vectors are encoded into a qubit system and the following data processing is fulfilled by hybrid quantum operations. Our algorithm requires O[log(MN)] qubits with O(1) qumodes and totally performs O(1) operations, which significantly reduces the space and runtime consumption.

Deep learning facilitated whole live cell fast super-resolution imaging Suggested by editors

Yun-Qing Tang(唐云青), Cai-Wei Zhou(周才微), Hui-Wen Hao(蒿慧文), and Yu-Jie Sun(孙育杰)

Chin. Phys. B, 2022, 31 (4): 048705. DOI: 10.1088/1674-1056/ac1b93

Abstract ( 365 )

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A fully convolutional encoder-decoder network (FCEDN), a deep learning model, was developed and applied to image scanning microscopy (ISM). Super-resolution imaging was achieved with a 78 μm×78 μm field of view and 12.5 Hz-40 Hz imaging frequency. Mono and dual-color continuous super-resolution images of microtubules and cargo in cells were obtained by ISM. The signal-to-noise ratio of the obtained images was improved from 3.94 to 22.81 and the positioning accuracy of cargoes was enhanced by FCEDN from 15.83±2.79 nm to 2.83±0.83 nm. As a general image enhancement method, FCEDN can be applied to various types of microscopy systems. Application with conventional spinning disk confocal microscopy was demonstrated and significantly improved images were obtained.

Increasing the ·OH radical concentration synergistically with plasma electrolysis and ultrasound in aqueous DMSO solution Suggested by editors

Chao Li(李超), De-Long Xu(徐德龙), Wen-Quan Xie(谢文泉), Xian-Hui Zhang(张先徽), and Si-Ze Yang(杨思泽)

Chin. Phys. B, 2022, 31 (4): 048706. DOI: 10.1088/1674-1056/ac523d

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In recent years, significant increases in waste processing and material engineering have been seen by using advanced oxidation processes. The treatment results and energy yields of these processes are largely determined by the generation and retention of reactive oxygen species (ROS). However, increasing the amount of ROS remains a key challenge because of the unavailability of performance- and energy-efficient techniques. In this study, plasma electrolysis, ultrasound, and plasma electrolysis combined with ultrasound were used to treat dimethyl sulfoxide (DMSO) solutions, and the results showed that the two methods can synergistically convert filament discharge into spark discharge, and the conversion of the discharge mode can significantly increase the concentration of OH radicals and effectively improve the efficiency of DMSO degradation. We verified the rationality of the results by analyzing the mass transfer path of ROS based on the reaction coefficients and found that the ·OH radicals in aqueous solution were mainly derived from the decomposition of hydrogen peroxide. These findings indicated that the synergistic action of plasma electrolysis and ultrasound can enhance the production of chemically reactive species, and provide new insights and guiding principles for the future translation of this combined strategy into real-life applications. Our results demonstrated that the synergistic strategy of ultrasound and plasma electrolysis is feasible in the switching mode and increasing the ROS, and may open new routes for materials engineering and pollutant degradation.

Synchronization in multilayer networks through different coupling mechanisms

Xiang Ling(凌翔), Bo Hua(华博), Ning Guo(郭宁), Kong-Jin Zhu(朱孔金), Jia-Jia Chen(陈佳佳), Chao-Yun Wu(吴超云), and Qing-Yi Hao(郝庆一)

Chin. Phys. B, 2022, 31 (4): 048901. DOI: 10.1088/1674-1056/ac2b19

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In recent years, most studies of complex networks have focused on a single network and ignored the interaction of multiple networks, much less the coupling mechanisms between multiplex networks. In this paper we investigate synchronization phenomena in multilayer networks with nonidentical topological structures based on three specific coupling mechanisms:assortative, disassortative, and anti-assortative couplings. We find rich and complex synchronous dynamic phenomena in coupled networks. We also study the behavior of effective frequencies for layers I and II to understand the underlying microscopic dynamics occurring under the three different coupling mechanisms. In particular, the coupling mechanisms proposed here have strong robustness and effectiveness and can produce abundant synchronization phenomena in coupled networks.

Characteristics of vapor based on complex networks in China Suggested by editors

Ai-Xia Feng(冯爱霞), Qi-Guang Wang(王启光), Shi-Xuan Zhang(张世轩), Takeshi Enomoto(榎本刚), Zhi-Qiang Gong(龚志强), Ying-Ying Hu(胡莹莹), and Guo-Lin Feng(封国林)

Chin. Phys. B, 2022, 31 (4): 049201. DOI: 10.1088/1674-1056/ac43a3

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The uneven spatial distribution of stations providing precipitable water vapor (PWV) observations in China hinders the effective use of these data in assimilation, nowcasting, and prediction. In this study, we proposed a complex network framework for exploring the topological structure and the collective behavior of PWV in the mainland of China. We used the Pearson correlation coefficient and transfer entropy to measure the linear and nonlinear relationships of PWV amongst different stations and to set up the undirected and directed complex networks, respectively. Our findings revealed the statistical and geographical distribution of the variables influencing PWV networks and identified the vapor information source and sink stations. Specifically, the findings showed that the statistical and spatial distributions of the undirected and directed complex vapor networks in terms of degree and distance were similar to each other (the common interaction mode for vapor stations and their locations). The betweenness results displayed different features. The largest betweenness ratio for directed networks tended to be larger than that of the undirected networks, implying that the transfer of directed PWV networks was more efficient than that of the undirected networks. The findings of this study are heuristic and will be useful for constructing the best strategy for the PWV data in applications such as vapor observational networks design and precipitation prediction.

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