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Non-van der Waals AgCrS_(2) nanosheet: a new member of 2D realm

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Science China Chemistry 2022年第3期65卷 419-420页

作者： Kaihui Liu state key laboratory for mesoscopic physics School of PhysicsPeking UniversityBeijing 100871China

Layered materials with strong interlayer interaction have gained tremendous attention for accessing two-dimensional(2 D) structures, since the charged layers with diverse dangling bonds enrich such atomic-thick structures with exotic properties and versatile functionalization [1–3]. However,unlike van der Waals(vd W) materials that can be directly torn by various routes, the stronger interactions between neighboring layers make them more difficult to laminate.

关键词： versatile gained neighboring

From Topological Nodal-Line Semimetals to Quantum Spin Hall Insulators in Tetragonal SnX Monolayers(X=F,Cl,Br,I)

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Chinese physics Letters 2024年第6期41卷 98-111页

作者：朱晔赵宝薛阳徐玮徐文婷杨中芹 state key laboratory of Surface physics Key Laboratory of Computational Physical Sciences(MOE)and Department of PhysicsFudan UniversityShanghai 200433China Shandong key laboratory of Optical Communication Science and Technology School of Physics Science and Information TechnologyLiaocheng UniversityLiaocheng 252059China school of physics East China University of Science and TechnologyShanghai 200237China Shanghai Qi Zhi Institute Shanghai 200030China

Two-dimensional(2D)topological materials have recently garnered significant interest due to their profound physical properties and promising applications for future quantum nanoelectronics.Achieving various topological states within one type of materials is,however,seldom reported.Based on first-principles calculations and tightbinding models,we investigate topological electronic states in a novel family of 2D halogenated tetragonal stanene(T-SnX,X=F,Cl,Br,I).All the four monolayers are found to be unusual topological nodal-line semimetals(NLSs),protected by a glide mirror symmetry.When spin-orbit coupling(SOC)is turned on,T-SnF and TSnCl are still ascertained as topological NLSs due to the remaining band inversion,primarily composed of Sn pxy orbitals,while T-Sn Br and T-SnI become quantum spin Hall insulators.The phase transition is ascribed to moving up in energy of Sn s orbitals and increasing of SOC strengths.The topology origin in the materials is uniformly rationalized through elementary band representations.The robust and diverse topological states found in the 2D T-SnX monolayers position them as an excellent material platform for development of innovative topological electronics.

关键词： topological metals quantum

Compact and high-efficient wavelength demultiplexing coupler based on high-index dielectric nanoantennas

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Chinese physics B 2018年第9期27卷 327-332页

作者：谭敬丰庞画孟凤凯蒋进 state key laboratory for mesoscopic physics School of Physics Peking University

Wavelength demultiplexing waveguide couplers have important applications in integrated nanophotonic devices. Two of the most important indicators of the quality of a wavelength demultiplexing coupler are coupling efficiency and splitting ratio. In this study, we utilize two asymmetric high-index dielectric nanoantennas directly positioned on top of a silicon-on insulator waveguide to realize a compact wavelength demultiplexing coupler in a communication band, which is based on the interference of the waveguide modes coupled by the two nanoantennas. We add a Au substrate for further increasing the coupling efficiency. This has constructive and destructive influences on the antenna＇s in-coupling efficiency owing to the Fabry-Perot（FP） resonance in the SiO2 layer. Therefore, we can realize a wavelength demultiplexing coupler with compact size and high coupling efficiency. This coupler has widespread applications in the areas of wavelength filters,on-chip signal processing, and integrated nanophotonic circuits.

关键词： wavelength demultiplexing coupler high-index dielectric nanoantenna coupling efficiency Fabry-Perot（FP） resonance

Importance of ligands on TiO_2 nanocrystals for perovskite solar cells

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Chinese physics B 2018年第1期27卷 92-97页

作者：赵耀赵怡程周文可伏睿李琪俞大鹏赵清 state key laboratory for mesoscopic physics and Electron Microscopy laboratory School of Physics Peking University

The fabrication of high-quality electron-selective layers at low temperature is a prerequisite to realizing efficient flexible and tandem perovskite solar cells （PSCs）. A colloidal-quantum-dot ink that contains TiO2 nanocrystals enables the deposition of a flat film with matched energy level for PSCs; however, the selection of ligands on the TiO2 surface is still unexplored. Here, we systematically studied the effect of the titanium diisopropoxide bis（acetylacetonate）（TiAc2） ligand on the performance of PSCs with a planar n-i-p architecture. We prepared TiO2 nanocrystals from TiCI4 and ethyl alcohol with C1- ligands attached on its surface and we found that a tiny amount of TiAc2 treatment of as-prepared TiO2 nanocrystals in a mixed solution of chloroform and methyl alcohol can enhance PSC power conversion efficiency （PCE） from 14.7% to 18.3%. To investigate the effect of TiAc2 ligand on PSCs, TiO2 samples with different TiAc2 content were prepared by adding TiAc2 into the as-obtained TiO2 nanocrystal solution. We use x-ray photoelectron spectroscopy to identify the content of C1 so as to reveal that C1 ligands can be substituted by TiAc2. We speculate that the improvement in PCE originates from amorphous TiO2 formation on the TiO2 nanocrystal surface, whereby a single-molecule layer of amorphous TiO2 facilitates charge transfer between the perovskite film and the TiO2 electronic transport layer, but excessive TiAc2 lowers the PSC performance dramatically. We further prove our hypothesis by x-ray diffraction measurements. We believe the PCE of PSCs can be further improved by carefully choosing the type and changing the content of surface ligands on TiO2 nanocrystal.

关键词： TiAc2 TiO2 nanocrystal surface ligand perovskite solar cells

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自旋输运揭示高阶棱态的拓扑性质

Science Bulletin 2022年第8期67卷 788-793,M0003页

作者：王安琦向鹏展赵彤阳廖志敏 state key laboratory for mesoscopic physics and Frontiers Science Center for Nano-optoelectronics School of PhysicsPeking UniversityBeijing 100871China

根据高阶拓扑相理论,在三维高阶拓扑材料中,除了常见的三维体态和二维表面态,还存在一维无能隙的拓扑棱态.由于很难通过传统的实验手段(如光谱和量子振荡测量)对一维电子态进行探测,到目前为止,人们对于棱态的拓扑性质仍然知之甚少.本... 详细信息

根据高阶拓扑相理论,在三维高阶拓扑材料中,除了常见的三维体态和二维表面态,还存在一维无能隙的拓扑棱态.由于很难通过传统的实验手段(如光谱和量子振荡测量)对一维电子态进行探测,到目前为止,人们对于棱态的拓扑性质仍然知之甚少.本文通过自旋电位测量的手段,揭示了高阶拓扑半金属Cd;As;纳米片中棱态的拓扑特性.实验发现,高阶棱态具有和量子自旋霍尔态类似的电子螺旋性特征,即棱态电子的自旋和动量是相互锁定的.棱态自旋极化信号能稳定维持到室温条件,且可以实现长距离的非局域传输,传输距离超过5μm.棱态自旋信号的温度鲁棒性和长程非局域传输特性,表明棱态由于受拓扑保护具备较强的抗环境干扰能力.该工作不但深化了人们对于高阶拓扑材料输运性质的理解,而且也为实现低功耗自旋电子学器件提供了重要的材料平台.

关键词： Topological nature Hinge states Higher-order topological materials Spin-polarized transport

Graphene-integrated waveguides:Properties,preparation,and applications

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Nano Research 2022年第11期15卷 9704-9726页

作者： Kaili Chang Zenghui Li Yuzong Gu Kaihui Liu Ke Chen Center for the physics of Low-Dimensional Materials School of Physics and ElectronicsHenan UniversityKaifeng 475004China state key laboratory for mesoscopic physics School of PhysicsPeking UniversityBeijing 100871China

Graphene-integrated waveguides(GIWGs)have shown immense potential for applications in next-generation datacom technology due to graphene’s compactness and its functional complementarity with traditional optical waveguides.However,the fabrication techniques of GIWGs lack scalability for commercial applications.Here we discuss the recent developments of GIWGs in two-dimensional optoelectronics by focusing on their properties,wave–matter interaction mechanisms,and fabrication techniques.We highlight representative advances on the advantages and potential applications of GIWGs in telecom networks.Finally,we outline major challenges and development trends to bridge the gap between proof-of-concept demonstrations and practical applications.

关键词： graphene waveguide integration process optoelectronics two-dimensional materials

Degradation behaviors of high power GaN-based blue light emitting diodes

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Chinese physics B 2013年第11期22卷 603-606页

作者：钟灿涛于彤军颜建陈志忠张国义 state key laboratory for mesoscopic physics School of Physics Peking University

The degradation mechanism of high power InGaN/GaN blue light emitting diodes （LEDs） is investigated in this paper. The LED samples were stressed at room temperature under 350-mA injection current for about 400 h. The light output power of the LEDs decreased by 35% during the first 100 h and then remained almost unchanged, and the reverse current at-5 V increased from 10^-9 A to 10^-7 A during the aging process. The power law, whose meaning was re-illustrated by the improved rate equation, was used to analyze the light output power-injection current （L-I） curves. The analysis results indicate that nonradiative recombination, Auger recombination, and the third-order term of carriers overflow increase during the aging process, all of which may be important reasons for the degradation of LEDs. Besides, simulating L-I curves with the improved rate equation reveal that higher-than-third-order terms of carriers overflow may not be the main degradation mechanism, because they change slightly when the LED is stressed.

关键词： light emitting diodes degradation rate equation

Spin logic devices based on negative differential resistance -enhanced anomalous Hall effect

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International Journal of Minerals,Metallurgy and Materials 2024年第6期31卷 1437-1448页

作者： Hongming Mou Ziyao Lu Yuchen Pu Zhaochu Luo Xiaozhong Zhang key laboratory of Advanced Materials(MOE) School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China state key laboratory of Artificial Microstructure and mesoscopic physics School of PhysicsPeking UniversityBeijing 100871China

Owing to rapid developments in spintronics,spin-based logic devices have emerged as promising tools for next-generation computing technologies.This paper provides a comprehensive review of recent advancements in spin logic devices,particularly focusing on fundamental device concepts rooted in nanomagnets,magnetoresistive random access memory,spin–orbit torques,electric-field modu-lation,and magnetic domain walls.The operation principles of these devices are comprehensively analyzed,and recent progress in spin logic devices based on negative differential resistance-enhanced anomalous Hall effect is summarized.These devices exhibit reconfigur-able logic capabilities and integrate nonvolatile data storage and computing functionalities.For current-driven spin logic devices,negative differential resistance elements are employed to nonlinearly enhance anomalous Hall effect signals from magnetic bits,enabling reconfig-urable Boolean logic operations.Besides,voltage-driven spin logic devices employ another type of negative differential resistance ele-ment to achieve logic functionalities with excellent cascading ability.By cascading several elementary logic gates,the logic circuit of a full adder can be obtained,and the potential of voltage-driven spin logic devices for implementing complex logic functions can be veri-fied.This review contributes to the understanding of the evolving landscape of spin logic devices and underscores the promising pro-spects they offer for the future of emerging computing schemes.

关键词： spin logic spin–orbit torque negative differential resistance full-adder

GaN substrate and GaN homo-epitaxy for LEDs:Progress and challenges

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Chinese physics B 2015年第6期24卷 65-74页

作者：吴洁君王昆于彤军张国义 state key laboratory for Artificial Microstructure and mesoscopic physics School of PhysicsPeking University

After a brief review on the progresses in GaN substrates by ammonothermal method and Na-flux method and hydride vapor phase epitaxy （HVPE） technology, our research results of growing GaN thick layer by a gas fow-rnodulated HVPE, removing the GaN layer through an efficient self-separation process from sapphire substrate, and modifying the uniformity of multiple wafer growth are presented. The effects of surface morphology and defect behaviors on the GaN homo-epitaxial growth on free standing substrate are also discussed, and followed by the advances of LEDs on GaN substrates and prospects of their applications in solid state lighting.

关键词： gallium nitride （GaN） free standing substrate hydride vapor phase epitaxy （HVPE） homo-epitaxy