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High-Performance Organic Field-Effect Transistors Based on Two-Dimensional Vat Orange 3 Crystals
Ning Yan, Zhiren Xiong, Chengbing Qin, and Xiaoxi Li
Chin. Phys. Lett.    2024, 41 (2): 028101 .   DOI: 10.1088/0256-307X/41/2/028101
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The exploration and research of low-cost, environmentally friendly, and sustainable organic semiconductor materials are of immense significance in various fields, including electronics, optoelectronics, and energy conversion. Unfortunately, these semiconductors have almost poor charge transport properties, which range from $\sim$ $10^{-4}$ cm$^{2}\cdot$V$^{-1}\cdot$s$^{-1}$ to $\sim$ $10^{-2}$ cm$^{2}\cdot$V$^{-1}\cdot$s$^{-1}$. Vat orange 3, as one of these organic semiconductors, has great potential due to its highly conjugated structure. We obtain high-quality multilayered Vat orange 3 crystals with two-dimensional (2D) growth on h-BN surfaces with thickness of 10–100 nm using physical vapor transport. Raman's results confirm the stability of the chemical structure of Vat orange 3 during growth. Furthermore, by leveraging the structural advantages of 2D materials, an organic field-effect transistor with a 2D vdW vertical heterostructure is further realized with h-BN encapsulation and multilayered graphene contact electrodes, resulting in an excellent transistor performance with On/Off ratio of $10^{4}$ and high field-effect mobility of 0.14 cm$^{2}\cdot$V$^{-1}\cdot$s$^{-1}$. Our results show the great potential of Vat orange 3 with 2D structures in future nano-electronic applications. Furthermore, we showcase an approach that integrates organic semiconductors with 2D materials, aiming to offer new insights into the study of organic semiconductors.
Determination of Work Function for p- and n-Type 4H-SiC Single Crystals via Scanning Kelvin Probe Force Microscopy
Hui Li, Guobin Wang, Jingyu Yang, Zesheng Zhang, Jun Deng, and Shixuan Du
Chin. Phys. Lett.    2023, 40 (12): 128101 .   DOI: 10.1088/0256-307X/40/12/128101
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Silicon carbide (SiC) is a promising platform for fabricating high-voltage, high-frequency and high-temperature electronic devices such as metal oxide semiconductor field effect transistors in which many junctions or interfaces are involved. The work function (WF) plays an essential role in these devices. However, studies of the effect of conductive type and polar surfaces on the WF of SiC are limited. Here, we report the measurement of WFs of Si- and C-terminated polar surfaces for both p-type and n-type conductive 4H-SiC single crystals by scanning Kelvin probe microscopy (SKPFM). The results show that p-type SiC exhibits a higher WF than n-type SiC. The WF of a C-terminated polar surface is higher than that of a Si-terminated polar surface, which is further confirmed by first-principles calculations. By revealing this long-standing knowledge gap, our work facilitates the fabrication and development of SiC-based electronic devices, which have tremendous potential applications in electric vehicles, photovoltaics, and so on. This work also shows that SKPFM is a good method for identifying polar surfaces of SiC and other polar materials nondestructively, quickly and conveniently.
Performance Improvement of a Direct Carbon Fuel Cell through an Irreversible Vacuum Thermionic Generator
Yuan Wang and Shanhe Su
Chin. Phys. Lett.    2023, 40 (12): 128201 .   DOI: 10.1088/0256-307X/40/12/128201
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A novel hybrid system consisting of a direct carbon fuel cell (DCFC), a thermionic generator (TIG), and a regenerator is developed to recover the exhaust heat from the fuel cell. Expressions for the power output and efficiency of subsystems and the hybrid system are derived. Based on the energy balance equation, the area matching problem between the DCFC and the TIG is discussed and solved. By considering the main irreversibilities, the influences of the DCFC's current density and the TIG's voltage on the performance of the hybrid system are revealed. The maximum power output density and the corresponding efficiency of the hybrid system are, respectively, equal to 379 W/m$^{2}$ and 36%. To enhance the maximum power density of the single DCFC, the optimal regions of the main parameters are determined.
Characteristics of Speed–Acceleration Phase Diagram of Migrating Cells
Yikai Ma and Wei Chen
Chin. Phys. Lett.    2023, 40 (12): 128701 .   DOI: 10.1088/0256-307X/40/12/128701
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Cell movement behavior is one of the most interesting biological problems in physics, biology, and medicine. We experimentally investigate the characteristics of random cell motion during migration. Observing cell motion trajectories under a microscope, we employ a nonlinear dynamics method to construct a speed–acceleration phase diagram. Our analysis reveals the presence of a fixed point in this phase diagram, which suggests that migrating cells possess a stable state. Cells that deviate from this stable state display a tendency to return to it, following the streamline trends of an attractor structure in the phase diagram. We derive a set of characteristic values describing cell motion, encompassing inherent speed, inherent acceleration, characteristic time for speed change, and characteristic time for acceleration change. We develop a differential equation model based on experimental data and conduct numerical calculations. The computational results align with the findings obtained from experiments. Our research suggests that the asymmetrical characteristics observed in cell motion near an inherent speed primarily arise from properties of inherent acceleration of cells.
Magneto-Orientated Graphite Double-Layer Homo-Structure with Broadband Microwave Absorption
Jun-Song Wang, Wei Ding, Cheng-Hong Zhang, Kang Qiu, You-Lin Gao, Mian-Ke Chen, Muhammad Adnan Aslam, Mahmoud A. Khalifa, Jia-Liang Luo, Jun Fang, and Zhi-Gao Sheng
Chin. Phys. Lett.    2023, 40 (11): 118101 .   DOI: 10.1088/0256-307X/40/11/118101
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We utilized magnetic fields as an efficient tool to manipulate the orientation and electromagnetic properties of graphite micro-flakes (GMFs). As a result, we successfully developed a GMF double-layer homo-structure, which shows excellent electromagnetic absorption properties. By tuning the direction of a small magnetic field (850 G), vertical and horizontal aligned GMFs are produced. Their electromagnetic parameters are effectively tailored by this magneto-orientation effect, and the vertical and horizontal aligned GMFs achieve good results in terms of impedance matching and microwave absorption. With the combination of these two magneto-orientated layers, vertically oriented as the surficial impedance matching layer and horizontally oriented as the inner loss layer, we design a GMF-based double-layer homo-structure. After thickness optimization, $-38.2$ dB minimum reflection loss and 6.4 GHz (11.6–18.0 GHz) absorption bandwidth are achieved. Our findings further emphasize the importance of material orientation freedom and provide a magneto-strategy to design multiple-layer structures and to produce high-performance microwave devices.
Parallel DNA G-Quadruplex Induced and Stabilized by Curaxin CBL0137
Jing-Wei Kong, Shuo-Xing Dou, Wei Li, Hui Li, and Peng-Ye Wang
Chin. Phys. Lett.    2023, 40 (7): 078701 .   DOI: 10.1088/0256-307X/40/7/078701
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G-quadruplex (G4) is one of the higher-order DNA structures in guanine-rich sequences which are widely distributed across the genome. Due to their presence in oncogenic promoters and telomeres, G4 DNA structures become the novel targets in anticancer drug designs. Curaxin CBL0137, as an important candidate anticancer drug, can effectively inhibit the growth of multiple cancers. Although there is evidence that anticancer activity of curaxin is associated with its ability to bind DNA and to change the DNA topology, its therapeutic target and the underlying anti-cancer mechanism are still unclear. Here we show, for the first time, that curaxin CBL0137 induces G4 folding from anti-parallel to parallel structures, by single-molecule fluorescence resonance energy transfer technique. More importantly, we find that curaxin CBL0137 promotes G4 folding as well as stabilizes the folded G4 structures with long loops, giving a novel insight into effects of curaxin CBL0137 on DNA structures. Our work provides new ideas for the therapeutic mechanism of curaxin CBL0137 and for designs of new G4-targeting anticancer drugs.
Intrinsic Electronic Properties of BN-Encapsulated, van der Waals Contacted MoSe$_{2}$ Field-Effect Transistors
Yinjiang Shao, Jian Zhou, Ning Xu, Jian Chen, Kenji Watanabe, Takashi Taniguchi, Yi Shi, and Songlin Li
Chin. Phys. Lett.    2023, 40 (6): 068501 .   DOI: 10.1088/0256-307X/40/6/068501
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Two-dimensional (2D) semiconductors have attracted considerable interest for their unique physical properties. Here, we report the intrinsic cryogenic electronic transport properties in few-layer MoSe$_{2}$ field-effect transistors (FETs) that are fully encapsulated in ultraclean hexagonal boron nitride dielectrics and are simultaneously van der Waals contacted with gold electrodes. The FETs exhibit electronically favorable channel/dielectric interfaces with low densities of interfacial traps ($ < $ $10^{10}$ cm$^{-2}$), which lead to outstanding device characteristics at room temperature, including near-Boltzmann-limit subthreshold swings (65 mV/dec), high carrier mobilities (53–68 cm$^{2}\cdot$V$^{-1}\cdot$s$^{-1}$), and negligible scanning hystereses ($ < $ $15$ mV). The dependence of various contact-related parameters with temperature and carrier density is also systematically characterized to understand the van der Waals contacts between gold and MoSe$_{2}$. The results provide insightful information about the device physics in van der Waals contacted and encapsulated 2D FETs.
Giant Tunneling Magnetoresistance in Spin-Filter Magnetic Tunnel Junctions Based on van der Waals A-Type Antiferromagnet CrSBr
Guibin Lan, Hongjun Xu, Yu Zhang, Chen Cheng, Bin He, Jiahui Li, Congli He, Caihua Wan, Jiafeng Feng, Hongxiang Wei, Jia Zhang, Xiufeng Han, and Guoqiang Yu
Chin. Phys. Lett.    2023, 40 (5): 058501 .   DOI: 10.1088/0256-307X/40/5/058501
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Two-dimensional van der Waals magnetic materials have demonstrated great potential for new-generation high-performance and versatile spintronic devices. Among them, magnetic tunnel junctions (MTJs) based on A-type antiferromagnets, such as CrI$_{3}$, possess record-high tunneling magnetoresistance (TMR) because of the spin filter effect of each insulating unit ferromagnetic layer. However, the relatively low working temperature and the instability of the chromium halides hinder applications of this system. Using a different technical scheme, we fabricated the MTJs based on an air-stable A-type antiferromagnet, CrSBr, and observed a giant TMR of up to 47000% at 5 K. Meanwhile, because of a relatively high Néel temperature of CrSBr, a sizable TMR of about 50% was observed at 130 K, which makes a big step towards spintronic devices at room temperature. Our results reveal the potential of realizing magnetic information storage in CrSBr-based spin-filter MTJs.
Enhancement of Carrier Mobility in Semiconductor Nanostructures by Carrier Distribution Engineering
Binxi Liang, Luhao Liu, Jiachen Tang, Jian Chen, Yi Shi, and Songlin Li
Chin. Phys. Lett.    2023, 40 (5): 058503 .   DOI: 10.1088/0256-307X/40/5/058503
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Two-dimensional (2D) van der Waals semiconductors are appealing for low-power transistors. Here, we show the feasibility in enhancing carrier mobility in 2D semiconductors through engineering the vertical distribution of carriers confined inside ultrathin channels via symmetrizing gate configuration or increasing channel thickness. Through self-consistently solving the Schrödinger–Poisson equations, the shapes of electron envelope functions are extensively investigated by clarifying their relationship with gate configuration, channel thickness, dielectric permittivity, and electron density. The impacts of electron distribution variation on various carrier scattering matrix elements and overall carrier mobility are insightfully clarified. It is found that the carrier mobility can be generally enhanced in the dual-gated configuration due to the centralization of carrier redistribution in the nanometer-thick semiconductor channels and the rate of increase reaches up to 23% in HfO$_{2}$ dual-gated 10-layer MoS$_{2}$ channels. This finding represents a viable strategy for performance optimization in transistors consisting of 2D semiconductors.
A 700 W$\cdot$h$\cdot$kg$^{-1}$ Rechargeable Pouch Type Lithium Battery
Quan Li, Yang Yang, Xiqian Yu, and Hong Li
Chin. Phys. Lett.    2023, 40 (4): 048201 .   DOI: 10.1088/0256-307X/40/4/048201
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High-energy-density rechargeable lithium batteries are being pursued by researchers because of their revolutionary potential nature. Current advanced practical lithium-ion batteries have an energy density of around 300 W$\cdot$h$\cdot$kg$^{-1}$. Continuing to increase the energy density of batteries to a higher level could lead to a major explosion development in some fields, such as electric aviation. Here, we have manufactured practical pouch-type rechargeable lithium batteries with both a gravimetric energy density of 711.3 W$\cdot$h$\cdot$kg$^{-1}$ and a volumetric energy density of 1653.65 W$\cdot$h$\cdot$L$^{-1}$. This is achieved through the use of high-performance battery materials including high-capacity lithium-rich manganese-based cathode and thin lithium metal anode with high specific energy, combined with extremely advanced process technologies such as high-loading electrode preparation and lean electrolyte injection. In this battery material system, the structural stability of cathode material in a widened charge/discharge voltage range and the deposition/dissolution behavior of interfacial modified thin lithium electrode are studied.
Large-Area Monolayer n-Type Molecular Semiconductors with Improved Thermal Stability and Charge Injection
Sai Jiang, Lichao Peng, Xiaosong Du, Qinyong Dai, Jianhang Guo, Jianhui Gu, Jian Su, Ding Gu, Qijing Wang, Huafei Guo, Jianhua Qiu, and Yun Li
Chin. Phys. Lett.    2023, 40 (3): 038101 .   DOI: 10.1088/0256-307X/40/3/038101
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We fabricated monolayer n-type two-dimensional crystalline semiconducting films with millimeter-sized areas and remarkable morphological uniformity using an antisolvent-confined spin-coating method. The antisolvent can cause a downstream Marangoni flow, which improves the film morphologies. The deposited crystalline monolayer films exhibit excellent thermal stabilities after annealing, which reveals the annealing-induced enhancement of crystallinity. The transistors based on the n-type monolayer crystalline films show linear output characteristics and superior electron mobilities. The improved charge injection between monolayer films and Au electrodes results from the energy level shift as the films decrease to the monolayer, which leads to a lower injection barrier. This work demonstrates a promising method for fabricating air-stable, low-cost, high-performance, and large-area organic electronics.
Achieving 1.2 fm/Hz$^{1/2}$ Displacement Sensitivity with Laser Interferometry in Two-Dimensional Nanomechanical Resonators: Pathways towards Quantum-Noise-Limited Measurement at Room Temperature
Jiankai Zhu, Luming Wang, Jiaqi Wu, Yachun Liang, Fei Xiao, Bo Xu, Zejuan Zhang, Xiulian Fan, Yu Zhou, Juan Xia, and Zenghui Wang
Chin. Phys. Lett.    2023, 40 (3): 038102 .   DOI: 10.1088/0256-307X/40/3/038102
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Laser interferometry is an important technique for ultrasensitive detection of motion and displacement. We push the limit of laser interferometry through noise optimization and device engineering. The contribution of noises other than shot noise is reduced from 92.6% to 62.4%, demonstrating the possibility towards shot-noise-limited measurement. Using noise thermometry, we quantify the laser heating effect and determine the range of laser power values for room-temperature measurements. With detailed analysis and optimization of signal transduction, we achieve 1.2 fm/Hz$^{1/2}$ displacement measurement sensitivity at room temperature in two-dimensional (2D) CaNb$_{2}$O$_{6}$ nanomechanical resonators, the best value reported to date among all resonators based on 2D materials. Our work demonstrates a possible pathway towards quantum-noise-limited measurement at room temperature.
A Ferroelectric Domain-Wall Transistor
Yang-Jun Ou, Jie Sun, Yi-Ming Li, and An-Quan Jiang
Chin. Phys. Lett.    2023, 40 (3): 038501 .   DOI: 10.1088/0256-307X/40/3/038501
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On the basis of novel properties of ferroelectric conducting domain walls, the domain wall nanoelectronics emerges and provides a brand-new dimension for the development of high-density, high-speed and energy-efficient nanodevices. For in-memory computing, three-terminal devices with both logic and memory functions such as transistors purely based on ferroelectric domain walls are urgently required. Here, a prototype ferroelectric domain-wall transistor with a well-designed coplanar electrode geometry is demonstrated on epitaxial BiFeO$_{3}$ thin films. For the logic function, the current switching between on/off states of the transistor depends on the creation or elimination of conducting domain walls between drain and source electrodes. For the data storage, the transistor can maintain nonvolatile on/off states after the write/erase operations, providing an innovative approach for the development of the domain wall nanoelectronics.
Low-Temperature Aqueous Na-Ion Batteries: Strategies and Challenges of Electrolyte Design
Qiubo Guo, Shuai Han, Yaxiang Lu, Liquan Chen, and Yong-Sheng Hu
Chin. Phys. Lett.    2023, 40 (2): 028801 .   DOI: 10.1088/0256-307X/40/2/028801
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Aqueous Na-ion batteries (ANIBs) are considered to be promising secondary battery systems for grid-scale energy storage applications and have attracted widespread attention due to their unique merits of rich resources of Na, as well as the inherent safety and low cost of aqueous electrolytes. However, the narrow electrochemical stability widow and high freezing point of traditional dilute aqueous electrolytes restrict their multi-scenario applications. Considering the charge-storage mechanism of ANIBs, the optimization and design of aqueous Na-based electrolytes dominate their low-temperature performance, which is also hot off the press in this field. In this review, we first systematically comb the research progress of the novel electrolytes and point out their remaining challenges in ANIBs. Then our perspectives on how to further improve the low-temperature performance of ANIBs will also be discussed. Finally, this review briefly sheds light on the potential direction of low-temperature ANIBs, which would guide the future design of high-performance aqueous rechargeable batteries.
A $dC/dV$ Measurement for Quantum-Dot Light-Emitting Diodes
Jingrui Ma, Haodong Tang, Xiangwei Qu, Guohong Xiang, Siqi Jia, Pai Liu, Kai Wang, and Xiao Wei Sun
Chin. Phys. Lett.    2022, 39 (12): 128401 .   DOI: 10.1088/0256-307X/39/12/128401
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We present $dC/dV$ analysis based on the capacitance-voltage ($C$–$V$) measurement of quantum-dot light-emitting diodes (QLEDs), and find that some key device operating parameters (electrical and optical turn-on voltage, peak capacitance, maximum efficiency) can be directly related to the turning points and maximum/minimum of the $dC/dV$ (versus voltage) curve. By the $dC/dV$ study, the behaviors such as low turn-on voltage, simultaneous electrical and optical turn-on process, and carrier accumulation during the device aging can be well explained. Moreover, we perform the $C$–$V$ and $dC/dV$ measurement of aged devices, and confirm that our $dC/dV$ analysis is correct for them. Thus, our $dC/dV$ analysis method can be applied universally for QLED devices. It provides an in-depth understanding of carrier dynamics in QLEDs through simple $C$–$V$ measurement.
Large Room-Temperature Magnetoresistance in van der Waals Ferromagnet/Semiconductor Junctions
Wenkai Zhu, Shihong Xie, Hailong Lin, Gaojie Zhang, Hao Wu, Tiangui Hu, Ziao Wang, Xiaomin Zhang, Jiahan Xu, Yujing Wang, Yuanhui Zheng, Faguang Yan, Jing Zhang, Lixia Zhao, Amalia Patanè, Jia Zhang, Haixin Chang, and Kaiyou Wang
Chin. Phys. Lett.    2022, 39 (12): 128501 .   DOI: 10.1088/0256-307X/39/12/128501
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A magnetic tunnel junction (MTJ) is the core component in memory technologies, such as the magnetic random-access memory, magnetic sensors and programmable logic devices. In particular, MTJs based on two-dimensional van der Waals (vdW) heterostructures offer unprecedented opportunities for low power consumption and miniaturization of spintronic devices. However, their operation at room temperature remains a challenge. Here, we report a large tunnel magnetoresistance (TMR) of up to 85% at room temperature ($T = 300$ K) in vdW MTJs based on a thin ($ < 10$ nm) semiconductor spacer WSe$_{2}$ layer embedded between two Fe$_{3}$GaTe$_{2}$ electrodes with intrinsic above-room-temperature ferromagnetism. The TMR in the MTJ increases with decreasing temperature up to 164% at $T = 10$ K. The demonstration of TMR in ultra-thin MTJs at room temperature opens a realistic and promising route for next-generation spintronic applications beyond the current state of the art.
High-Performance Indium-Gallium-Zinc-Oxide Thin-Film Transistors with Stacked Al$_{2}$O$_{3}$/HfO$_{2}$ Dielectrics
Yue Li, Li Zhu, Chunsheng Chen, Ying Zhu, Changjin Wan, and Qing Wan
Chin. Phys. Lett.    2022, 39 (11): 118501 .   DOI: 10.1088/0256-307X/39/11/118501
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High-performance amorphous indium-gallium-zinc-oxide thin-film transistors (a-IGZO TFTs) gated by Al$_{2}$O$_{3}$/ HfO$_{2}$ stacked dielectric films are investigated. The optimized TFTs with Al$_{2}$O$_{3}$ (2.0 nm)/HfO$_{2}$ (13 nm) stacked gate dielectrics demonstrate the best performance, including low total trap density $N_{\rm t}$, low subthreshold swing voltage, large switching ratio $I_{\rm ON/OFF}$, high mobility $\mu_{_{\scriptstyle \rm FE}}$, and low operating voltage, equal to $1.35 \times 10^{12}$ cm$^{-2}$, 88 mV/dec, $5.24 \times 10^{8}$, 14.2 cm$^{2}$/V$\cdot$s, and 2.0 V, respectively. Furthermore, a low-voltage-operated resistor-loaded inverter has been fabricated based on such an a-IGZO TFT, showing ideal full swing characteristics and high gain of $\sim $27 at 3.0 V. These results indicate a-IGZO TFTs gated by optimized Al$_{2}$O$_{3}$/HfO$_{2}$ stacked dielectrics are of great interests for low-power, high performance, and large-area display and emerging electronics.
New Insight of Fe Valence State Change Using Leaves: A Combined Experimental and Theoretical Study
Zejun Zhang, Yizhou Yang, Jie Jiang, Liang Chen, Shanshan Liang, and Haiping Fang
Chin. Phys. Lett.    2022, 39 (10): 108201 .   DOI: 10.1088/0256-307X/39/10/108201
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Fe$^{2+}$ is of considerable importance in plant growth and crop production. However, most Fe elements in nature favor existing in the trivalent state, which often causes the deficiency of Fe$^{2+}$ in plants. Here, we report the Fe valence state change from Fe$^{3+}$ to Fe$^{2+}$ by using leaves. This valence state change was confirmed by x-ray photoelectron spectroscopy in Fe-Cl@leaves. Fourier transform infrared and ultraviolet-visible spectroscopy demonstrated that aromatic ring groups were included in leaves, and cation-$\pi$ interactions between Fe cations and the components containing aromatic rings in leaves were measured. Further, density functional theory calculations revealed that the most stable adsorption site for hydrated Fe$^{3+}$ cation was the region where hydroxyl groups and aromatic rings coexist. Moreover, molecular orbital and charge decomposition analysis revealed that the aromatic rings took the major part (59%) of the whole net charge transfer between leaves and Fe cations. This work provides a high-efficiency and eco-friendly way to transform the Fe valence state from Fe$^{3+}$ to Fe$^{2+}$, and affords a new insight into the valance change between plant organisms with cations.
Enhanced Anomalous Hall Effect of Pt on an Antiferromagnetic Insulator with Fully Compensated Surface
Yu Bai, Zhe Wang, Na Lei, Wisal Muhammad, Lifeng Xiang, Qiang Li, Huilin Lai, Yinyan Zhu, Wenbing Wang, Hangwen Guo, Lifeng Yin, Ruqian Wu, and Jian Shen
Chin. Phys. Lett.    2022, 39 (10): 108501 .   DOI: 10.1088/0256-307X/39/10/108501
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We report a significantly enhanced anomalous Hall effect (AHE) of Pt on antiferromagnetic insulator thin film (3-unit-cell La$_{0.7}$Sr$_{0.3}$MnO$_{3}$, abbreviated as LSMO), which is one order of magnitude larger than that of Pt on other ferromagnetic (e.g. Y$_{3}$Fe$_{5}$O$_{12}$) and antiferromagnetic (e.g. Cr$_{2}$O$_{3}$) insulator thin films. Our experiments demonstrate that the antiferromagnetic La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ with fully compensated surface suppresses the positive anomalous Hall resistivity induced by the magnetic proximity effect and facilitates the negative anomalous Hall resistivity induced by the spin Hall effect. By changing the substrate's temperature during Pt deposition, we observed that the diffusion of Mn atoms into Pt layer can further enhance the AHE. The anomalous Hall resistivity increases with increasing temperature and persists even well above the Neel temperature ($T_{\rm N}$) of LSMO. The Monte Carlo simulations manifest that the unusual rise of anomalous Hall resistivity above $T_{\rm N}$ originates from the thermal induced magnetization in the antiferromagnetic insulator.
Characteristics and Applications of Current-Driven Magnetic Skyrmion Strings
Zhaonian Jin, Minhang Song, Henan Fang, Lin Chen, Jiangwei Chen, and Zhikuo Tao
Chin. Phys. Lett.    2022, 39 (10): 108502 .   DOI: 10.1088/0256-307X/39/10/108502
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We investigate the current-driven characteristics and applications of magnetic skyrmion strings by micromagnetic simulations. Under the spin-polarized driving current, the skyrmion string presents different moving trajectories in different layers due to the skyrmion Hall effect. Moreover, a series of skyrmion bobbers can be generated with a notch defect placed in the surface and the skyrmion bobbers will follow the skyrmion string. By varying the current density, the bobbers' characteristics such as number and velocity can be manipulated, which inspires us to propose a skyrmion string-based diode. In addition, an AND logic gate and an OR logic gate in the identical scheme based on the skyrmion string are proposed. AND logic and OR logic behaviors can be realized by varying the driving current densities. Our findings will contribute to further research of magnetic skyrmion strings for data storage, processing, and energy-efficient computing.
Molecular Insights into Striking Antibody Evasion of SARS-CoV-2 Omicron Variant
Zeng-Shuai Yan, Yao Xu, Hong-Ming Ding, and Yu-Qiang Ma
Chin. Phys. Lett.    2022, 39 (10): 108701 .   DOI: 10.1088/0256-307X/39/10/108701
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The SARS-CoV-2 Omicron variant has become the dominant variant in the world. Uncovering the structural basis of altered immune response and enhanced transmission of Omicron is particularly important. Here, taking twenty-five antibodies from four groups as examples, we comprehensively reveal the underlying mechanism of how mutations in Omicron induces the weak neutralization by using molecular simulations. Overall, the binding strength of 68% antibodies is weakened in Omicron, much larger than that in Delta (40%). Specifically, the percentage of the weakened antibodies vary largely in different groups. Moreover, the mutation-induced repulsion is mainly responsive for the weak neutralization in AB/CD groups but does not take effect in EF group. Significantly, we demonstrate that the disappearance of hydrophobic interaction and salt bridges due to residue deletions contributes to the decreased binding energy in NTD group. This work provides unprecedented atomistic details for the distinct neutralization of WT/Delta/Omicron, which informs prospective efforts to design antibodies/vaccines against Omicron.
Modulated Collective Motions and Condensation of Bacteria
Mei-Mei Bao, Isaiah Eze Igwe, Kang Chen, and Tian-Hui Zhang
Chin. Phys. Lett.    2022, 39 (10): 108702 .   DOI: 10.1088/0256-307X/39/10/108702
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Bacteria can spontaneously develop collective motions by aligning their motions in dense systems. Here we show that bacteria can also respond collectively to an alternating electrical field and form dynamic clusters oscillating at the same frequency of the field. As the dynamic clusters go beyond a critical size, they split into smaller ones spontaneously. The critical size for splitting depends on the frequency of electric field and the concentration of bacteria. We show that, instead of their biological activity, the physical properties of bacteria as charged particles are responsible for the formation of dynamic clusters. Electroconvective flows across the system play the key role in stabilizing the clusters. However, to form clusters, collective hydrodynamic cooperation between bacteria is important such that no aggregation occurs in dilute suspensions. The findings in this study illustrate that bio-systems can respond collectively to an external field, promising an effective way to control and modulate the behavior of organisms. Moreover, the controlled aggregation and condensation of bacteria offer a robust approach to improve the local concentration of bacteria for early and rapid detection, which has wide applications in clinics.
Indium-Gallium-Zinc-Oxide-Based Photoelectric Neuromorphic Transistors for Spiking Morse Coding
Xinhuang Lin, Haotian Long, Shuo Ke, Yuyuan Wang, Ying Zhu, Chunsheng Chen, Changjin Wan, and Qing Wan
Chin. Phys. Lett.    2022, 39 (6): 068501 .   DOI: 10.1088/0256-307X/39/6/068501
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The human brain that relies on neural networks communicated by spikes is featured with ultralow energy consumption, which is more robust and adaptive than any digital system. Inspired by the spiking framework of the brain, spike-based neuromorphic systems have recently inspired intensive attention. Therefore, neuromorphic devices with spike-based synaptic functions are considered as the first step toward this aim. Photoelectric neuromorphic devices are promising candidates for spike-based synaptic devices with low latency, broad bandwidth, and superior parallelism. Here, the indium-gallium-zinc-oxide-based photoelectric neuromorphic transistors are fabricated for Morse coding based on spike processing, 405-nm light spikes are used as synaptic inputs, and some essential synaptic plasticity, including excitatory postsynaptic current, short-term plasticity, and high-pass filtering, can be mimicked. More interestingly, Morse codes encoded by light spikes are decoded using our devices and translated into amplitudes. Furthermore, such devices are compatible with standard integrated processes suitable for large-scale integrated neuromorphic systems.
In Situ Epitaxy of Pure Phase Ultra-Thin InAs-Al Nanowires for Quantum Devices
Dong Pan, Huading Song, Shan Zhang, Lei Liu, Lianjun Wen, Dunyuan Liao, Ran Zhuo, Zhichuan Wang, Zitong Zhang, Shuai Yang, Jianghua Ying, Wentao Miao, Runan Shang, Hao Zhang, and Jianhua Zhao
Chin. Phys. Lett.    2022, 39 (5): 058101 .   DOI: 10.1088/0256-307X/39/5/058101
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We demonstrate the in situ growth of ultra-thin InAs nanowires with an epitaxial Al film by molecular-beam epitaxy. Our InAs nanowire diameter ($\sim $30 nm) is much thinner than before ($\sim $100 nm). The ultra-thin InAs nanowires are pure phase crystals for various different growth directions. Transmission electron microscopy confirms an atomically abrupt and uniform interface between the Al shell and the InAs wire. Quantum transport study on these devices resolves a hard induced superconducting gap and 2$e$-periodic Coulomb blockade at zero magnetic field, a necessary step for future Majorana experiments. By reducing wire diameter, our work presents a promising route for reaching fewer sub-band regime in Majorana nanowire devices.
Highly Sensitive Mid-Infrared Photodetector Enabled by Plasmonic Hot Carriers in the First Atmospheric Window
Yuan-Fang Yu, Ye Zhang, Fan Zhong, Lin Bai, Hui Liu, Jun-Peng Lu, and Zhen-Hua Ni
Chin. Phys. Lett.    2022, 39 (5): 058501 .   DOI: 10.1088/0256-307X/39/5/058501
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The first atmospheric window of 3–5 µm in the mid-infrared (MIR) spectral range pertains to crucial application fields, with particular scientific and technological importance. However, conventional narrow-bandgap semiconductors operating at this band, represented by mercury cadmium telluride and indium antimonide, suffer from limited specific detectivity at room temperature and hindered optoelectronic integration. In this study, a plasmonic hot electron-empowered MIR photodetector based on Al-doped ZnO (AZO)/bi-layer graphene heterostructure is demonstrated. Free electrons oscillate coherently in AZO disk arrays, resulting in strong localized surface plasmon resonance (LSPR) in the MIR region. The photoelectric conversion efficiency at 3–5 µm is significantly improved due to plasmon-induced hot-electron extraction and LSPR-enhanced light absorption. The specific detectivity reaches about $1.4 \times 10^{11}$ Jones and responsivity is up to 4712.3 A/W at wavelength of 3 µm at room temperature. The device's specific detectivity is among the highest performance of commercial state-of-the-art photodetectors and superior to most of the other 2D materials based photodetectors in the MIR region. These results demonstrate that a plasmonic heavily doped metal oxides/2D material heterostructure is a suitable architecture for constructing highly sensitive room-temperature MIR photodetectors.
Epitaxial Growth and Characteristics of Nonpolar $a$-Plane InGaN Films with Blue-Green-Red Emission and Entire In Content Range
Jianguo Zhao, Kai Chen, Maogao Gong, Wenxiao Hu, Bin Liu, Tao Tao, Yu Yan, Zili Xie, Yuanyuan Li, Jianhua Chang, Xiaoxuan Wang, Qiannan Cui, Chunxiang Xu, Rong Zhang, and Youdou Zheng
Chin. Phys. Lett.    2022, 39 (4): 048101 .   DOI: 10.1088/0256-307X/39/4/048101
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Nonpolar (11$\bar{2}$0) plane In$_{x}$Ga$_{1- x}$N epilayers comprising the entire In content ($x$) range were successfully grown on nanoscale GaN islands by metal-organic chemical vapor deposition. The structural and optical properties were studied intensively. It was found that the surface morphology was gradually smoothed when $x$ increased from 0.06 to 0.33, even though the crystalline quality was gradually declined, which was accompanied by the appearance of phase separation in the In$_{x}$Ga$_{1- x}$N layer. Photoluminescence wavelengths of 478 and 674 nm for blue and red light were achieved for $x$ varied from 0.06 to 0.33. Furthermore, the corresponding average lifetime ($\tau_{1/e}$) of carriers for the nonpolar InGaN film was decreased from 406 ps to 267 ps, indicating that a high-speed modulation bandwidth can be expected for nonpolar InGaN-based light-emitting diodes. Moreover, the bowing coefficient ($b$) of the (11$\bar{2}$0) plane InGaN was determined to be 1.91 eV for the bandgap energy as a function of $x$.
Probing the Air Storage Failure Mechanism of Ni-Rich Layered Cathode Materials
Qingyu Dong, Ruowei Yi, Jizhen Qi, Yanbin Shen, and Liwei Chen
Chin. Phys. Lett.    2022, 39 (3): 038201 .   DOI: 10.1088/0256-307X/39/3/038201
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Ni-rich layered oxide cathode materials, such as LiNi$_{0.83}$Co$_{0.12}$Mn$_{0.05}$O$_{2}$ (NCM811), exhibit high specific capacity and low cost, and become cathode material preference of high-energy-density Li-ion batteries. However, these cathode materials are not stable and will form Li-poor reconstructed layers and alkaline compounds (Li$_{2}$CO$_{3}$, LiOH) on the surface during the storage and processing in humid air, resulting in serious deterioration of electrochemical properties. During the past two decades, the consensus on the surface instability mechanism during humid air storage has not been reached. The main controversy focuses on the unstable octahedron mechanism and the Li/H exchange mechanism. Herein, we investigate the instability mechanism in the humid air by conducting scanning electronic microscopy, scanning transmission electron microscopy, and x-ray photoelectron spectroscopy analysis on NCM811 samples stored in designed atmospheres, etc., and realize that the surface instability of the NCM811 during storage should be mainly originated from Li/H exchange when it contacts with moisture.
Fluorination Increases Hydrophobicity at the Macroscopic Level but not at the Microscopic Level
Weishuai Di, Xin Wang, Yanyan Zhou, Yuehai Mei, Wei Wang, and Yi Cao
Chin. Phys. Lett.    2022, 39 (3): 038701 .   DOI: 10.1088/0256-307X/39/3/038701
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Hydrophobic interactions have been studied before in detail based on hydrophobic polymers, such as polystyrene (PS). Because fluorinated materials have relatively low surface energy, they often show both oleophobicity and hydrophobicity at the macroscopic level. However, it remains unknown how fluorination of hydrophobic polymer influences hydrophobicity at the microscopic level. We synthesized PS and fluorine-substituted PS (FPS) by employing the reversible addition-fragmentation chain transfer polymerization method. Contact angle measurements confirmed that FPS is more hydrophobic than PS at the macroscopic level due to the introduction of fluorine. However, single molecule force spectroscopy experiments showed that the forces required to unfold the PS and FPS nanoparticles in water are indistinguishable, indicating that the strength of the hydrophobic effect that drives the self-assembly of PS and FPS nanoparticles is the same at the microscopic level. The divergence of hydrophobic effect at the macroscopic and microscopic level may hint different underlying mechanisms: the hydrophobicity is dominated by the solvent hydration at the microscopic level and the surface-associated interaction at the macroscopic level.
Wet Mechanical Milling Induced Phase Transition to Cubic Anti-Perovskite Li$_{2}$OHCl
Di-Xing Ni, Yao-Dong Liu, Zhi Deng, Dian-Cheng Chen, Xin-Xin Zhang, Tao Wang, Shuai Li, and Yu-Sheng Zhao
Chin. Phys. Lett.    2022, 39 (2): 028201 .   DOI: 10.1088/0256-307X/39/2/028201
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Anti-perovskite solid-state electrolyte Li$_{2}$OHCl usually exhibits orthorhombic phase and low ionic conductivity at room temperature. However, its ionic conductivity increases greatly when the temperature is up to 40 ℃, while it goes through an orthorhombic-to-cubic phase transition. The cubic Li$_{2}$OHCl with high ionic conductivity is stabilized at room temperature and even lower temperature about 10 ℃ by a simple synthesis method of wet mechanical milling. The cubic Li$_{2}$OHCl prepared by this method performs an ionic conductivity of $4.27 \times 10^{-6}$ S/cm at room temperature, about one order of magnitude higher than that of the orthorhombic Li$_{2}$OHCl. The phase-transition temperature is decreased to around 10 ℃. Moreover, it can still remain cubic phase after heat treatment at 210 ℃. This work delivers a huge potential of fabricating high ionic conductivity phase anti-perovskite solid-state electrolyte materials by wet mechanical milling.
Electrochemical Role of Transition Metals in Sn–Fe Alloy Revealed by Operando Magnetometry
Le-Qing Zhang, Qing-Tao Xia, Zhao-Hui Li, Yuan-Yuan Han, Xi-Xiang Xu, Xin-Long Zhao, Xia Wang, Yuan-Yuan Pan, Hong-Sen Li, and Qiang Li
Chin. Phys. Lett.    2022, 39 (2): 028202 .   DOI: 10.1088/0256-307X/39/2/028202
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As promising materials, alloy-type anode materials have been intensively investigated in both academia and industry. To release huge volume expansion during alloying/dealloying process, they are usually doped with transition metals. However, the electrochemical role of transition metals has not been fully understood. Here, pure Sn$_{3}$Fe films were deposited by sputtering, and the electrochemical mechanism was systematically investigated by operando magnetometry. We confirmed that Fe particles liberated by Li insertion recombine partially with Sn during the delithiation, while the stepwise increase in magnetization with the cycles demonstrates growth of Fe nanoparticles. In addition, we also found an unconventional increase of magnetization in the charging process, which can be attributed to the space charge storage at the interface of Fe/Li$_{x}$Sn. These critical findings pave the way for the mechanism understanding and development of high-performance Sn based alloy electrode materials.
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