二维原子晶体材料中的各向异性研究概述

二维原子晶体材料简称二维材料,因载流子迁移和热量扩散都被限制在二维平面内,展现出了许多奇特的性质而受到了广泛关注。二维材料的带隙可调特性在场效应管、光电器件、热电器件等领域应用广泛。另外二维材料的自旋自由度和谷自由度的可控性使得二维材料在自旋电子学和谷电子学等领域也引发了深入的研究。不同的二维材料由于晶体结构的特殊性质导致了不同的电学特性或者光学特性的各向异性,包括拉曼光谱、光致发光光谱、二阶谐波谱、光吸收谱、热导率、电导率等性质的各向异性。这些各向异性特性在偏振光电器件、偏振热电器件、仿生器件、偏振光探等领域拥有巨大的发展潜力。二维材料的各向异性还能够用于实现器件性能的最优化。文章介绍了各种二维材料的各向异性的最新研究进展。     

金属元素掺杂二维过渡族金属硫化物研究进展

传统二维材料具有丰富的电学、光学特性?在电子器件领域中占据着重要位置?金属元素掺杂二维过渡族金属硫化物不仅可以保持原过渡族金属硫化物所特有的优越性能?还可赋予二维材料特定的铁磁、铁电性能?使其在光学器件、自旋电子学器件以及信息和数据存储等领域得到更广泛的应用?重点介绍了金属元素掺杂过渡族金属硫化物的理论和制备方法?对其结构特性、电子特性以及磁学特性进行了详细讨论?并且着重论述了金属元素掺杂在过渡族金属硫化物中的实验合成方法?其中?化学气相沉积法、化学气相传输法被广泛使用?其他实验方法如固相法、磁控溅射法也可结合运用?最后展望了金属元素掺杂过渡族金属硫化物研究面临的挑战以及未来磁性二维材料的发展方向?     

二维磁性材料与自旋系统研究进展

自旋系统是一类基于电子自旋工作的器件,具有高速、低功耗等优点,其中磁存储器被认为是下一代存储器的领跑者之一。二维材料有着天然的界面性能优势,接近微缩极限的尺寸特点,以及二维结构带来的物理特性,在自旋系统中有望得到广泛运用。本文概述了二维材料在自旋领域的最新研究进展,介绍了一些常见的二维磁性材料,讨论了基于二维材料的二维自旋器件,以及回顾了基于二维材料的磁性调控,最后总结了这一领域仍然面临的挑战,并对未来发展进行了展望。     

单分子结中的有机自由基（英文）

空气稳定有机自由基的发现引起了人们对探究其在分子电子学和自旋电子学中应用的兴趣.这些自由基具有独特的开壳层电子结构,因而表现出特殊的电学特性.由于其较弱的旋轨耦合特性,也使得其成为自旋电子学的重要研究对象.此外,自由基还可以通过二聚、分子识别和机械互锁等分子间相互作用来构筑超分子器件.本文综述了空气稳定有机自由基在电子学及自旋电子学中的应用,通过详述其卓越的电磁性能来拓展启发分子设计的多样性.本综述还概述了超分子自由基的制备方法和相关性质的研究进展,拓宽了单分子研究的范围.此外,自由基介导的单分子反应是一个新兴的研究方向,本文也对该领域的未来发展方向进行了展望.通过阐明空气稳定有机自由基的应用潜力,本文将有望对分子电子学和自旋电子学的研究产生一定的指导意义.     

微型热电器件研究进展

历经了30年的低谷期后,伴随着新型热电材料的出现及增大材料优值系数ZT新思路的提出,热电材料和器件这一研究领域开始了复兴.由于自身的诸多优点,微型热电器件已成为该领域的研究热点.作为新型的热电器件,微型热电器件在发电、制冷和传感器等领域获得了重要应用.综述了微型热电器件在应用、结构和制备技术方面的研究进展.     

ReX_2(X=S,Se):二维各向异性材料发展的新机遇

二维材料因其不同于体相的超薄原子结构、大的比表面积和量子限域效应等受到了人们的广泛关注。二维各向异性材料作为二维材料家族的一员,其取向依赖的物理和化学性质,使得对该类材料性能的选择性优化成为可能。过渡金属Re基硫属化合物作为各向异性材料的典型代表,具有可调的可见光波段吸收带隙,极弱的层间耦合作用力,以及各向异性的光学、电学性能,现已成为电子和光电子领域的研究热点之一。本文主要介绍了ReX_2(X=S,Se)的晶体结构和基本性质,总结目前该材料体系主流的合成方法,研究其各向异性物理特性及优化的手段和条件,并对ReX_2的制备和发展进行了展望。     

调控La2/3Sr1/3MnO3基异质结中磁各向异性变化的进展(英文)

钙钛矿锰酸盐(La_2/3Sr_1/3MnO₃)基异质结由于存在强自旋轨道耦合作用、高温铁磁性、强金属导电性以及丰富的氧八面体变化等特点,近年来在氧化物自旋电子学、拓扑电子态以及磁存储功能材料等应用方面备受关注.本综述主要针对锰酸盐异质结中磁各向异性变化,及其在氧化物自旋电子学器件中可能的应用进行了及时系统的总结.首先,本文简要介绍了锰酸盐异质结中的热点研究内容以及本文的出发点;其次,介绍了利用应变和衬底取向对锰酸盐异质结磁各向异性的调控;再次,重点介绍了界面耦合效应、氧八面体旋转、对称性破缺等新型界面工程手段对磁各向异性的调控;最后,介绍了电场调控磁各向异性的可逆变化方法,并总结了一些新型调控磁各向异性的手段.本综述将有效推动锰氧化物中磁各向异性的进一步研究,并且为锰氧化物在高效磁存储器件中的应用指明方向.     

钙钛矿锰氧化物低维纳米结构研究进展

钙钛矿结构锰氧化物由于同时存在电荷、自旋、轨道、晶格等多种自由度, 它们之间很强的相互作用和相互竞争导致了一系列新颖的物理现象, 如庞磁电阻效应、巨磁熵效应、绝缘体-金属转变、电子相分离、电荷/轨道有序等现象, 使其成为凝聚态物理学研究的热点。随着微电子器件日趋集成化和微型化, 其特征尺寸越来越小, 目前基于钙钛矿结构锰氧化物微电子器件的特征尺寸已经进入纳米尺度。在纳米尺度钙钛矿结构锰氧化物具有显著的尺寸效应, 表现出与薄膜及块材不同的电、磁输运特性, 在新一代微电子器件领域具有重要的应用价值。近年来人们在钙钛矿锰氧化物低维纳米结构制备、电磁输运特性测量、微结构表征及理论模拟方面, 都取得了较大的研究进展, 本文对此进行了评述。首先, 概述了钙钛矿锰氧化物低维纳米结构的微结构研究进展; 介绍了钙钛矿锰氧化物低维纳米结构的电子相分离及电荷有序现象; 评述了其电磁输运特性的纳米尺度表征; 讨论了钙钛矿锰氧化物低维纳米结构在自旋电子学、磁随机存储器和传感器方面的应用进展。最后指出了未来钙钛矿锰氧化物低维纳米结构研究需要重点解决的一些问题。     

二维黑磷的制备及光电器件研究进展

黑磷有随层数可调的直接带隙和独特的各向异性结构等众多优异的性质,因此近年来受到科研人员的广泛关注.本文概述了二维黑磷的制备方法,重点综述了黑磷独特的非线性光学性质、各向异性光学性质及它在光电器件中的应用.最后,对黑磷的应用前景与一些亟待解决的问题做了简单的讨论.     

石墨烯基电子学中的平面异质结研究进展（英文）

二维平面晶体,由于能带结构的多样性和与半导体平面工艺兼容的特点,被认为在电子学中是延续摩尔定律的候选材料之一;同时它具备易转移、光学透明、能带可调等特点,在柔性电子学和光电子学方面展示出巨大的潜在应用。将电路所需的具有不同导电性能的二维材料在平面内实现空间上的可控集成,是实现单原子层二维电子学的首要问题。综述了最近在石墨烯基电子学中平面异质结的研究进展,包括石墨烯-绝缘体和石墨烯-半导体异质结,集中在可控制备、对界面结构的原子尺度研究、以及逻辑功能原型器件研究。最后简述当前该领域面临的挑战和研究前景。     

Recent advances in anisotropic two-dimensional materials and device applications

Two-dimensional(2D)materials,such as transition metal dichalcogenides(TMDs),black phosphorus(BP),MXene and borophene,have aroused extensive attention since the discovery of graphene in 2004.They have wide range of applications in many research fields,such as optoelectronic devices,energy storage,catalysis,owing to their striking physical and chemical properties.Among them,anisotropic 2D material is one kind of 2D materials that possess different properties along different directions caused by the intrinsic anisotropic atoms5 arrangement of the 2D materials,mainly including BP,borophene,low-symmetry TMDs(ReSe2 and ReSa)and group IV monochalcogenides(SnS,SnSe,GeS,and GeSe).Recently,a series of new devices has been fabricated based on these anisotropic 2D materials.In this review,we start from a brief introduction of the classifications,crystal structures,preparation techniques,stability,as well as the strategy to discriminate the anisotropic characteristics of 2D materials.Then,the recent advanced applications including electronic devices,optoelectronic devices,thermoelectric devices and nanomechanical devices based on the anisotropic 2D materials both in experiment and theory have been summarized.Finally,the current challenges and prospects in device designs,integration,mechanical analysis,and micro-/nano-fabrication techniques related to anisotropic 2D materials have been discussed.This review is aimed to give a generalized knowledge of anisotropic 2D materials and their current devices applications,and thus inspiring the exploration and development of other kinds of new anisotropic 2D materials and various novel device applications.     

Strain-Engineered Anisotropic Optical and Electrical Properties in 2D Chiral-Chain Tellurium

Atomically thin materials, leveraging their low-dimensional geometries and superior mechanical properties, are amenable to exquisite strain manipulation with a broad tunability inaccessible to bulk or thin-film materials. Such capability offers unexplored possibilities for probing intriguing physics and materials science in the 2D limit as well as enabling unprecedented device applications. Here, the strain-engineered anisotropic optical and electrical properties in solution-grown, sub-millimeter-size 2D Te are systematically investigated through designing and introducing a controlled buckled geometry in its intriguing chiral-chain lattice. The observed Raman spectra reveal anisotropic lattice vibrations under the corresponding straining conditions. The feasibility of using buckled 2D Te for ultrastretchable strain sensors with a high gauge factor (≈380) is further explored. 2D Te is an emerging material boasting attractive characteristics for electronics, sensors, quantum devices, and optoelectronics. The results suggest the potential of 2D Te as a promising candidate for designing and implementing flexible and stretchable devices with strain-engineered functionalities.     

Anisotropic optical and electronic properties of two-dimensional layered germanium sulfide

Two-dimensional (2D) layered materials,transition-metal dichalcogenides,and black phosphorus have attracted considerable interest from the viewpoints of fundamental physics and device applications.The establishment of new functionalities in anisotropic layered 2D materials is a challenging but rewarding frontier,owing to the remarkable optical properties of these materials and their prospects for new devices.Herein,we report the anisotropic and thicknessdependent optical properties of a 2D layered monochalcogenide of germanium sulfide (GeS).Three Raman-scattering peaks corresponding to the B3g,A1g,and A2g modes with a strong polarization dependence are demonstrated in the GeS flakes,which validates polarized Raman spectroscopy as an effective method for identifying the crystal orientation of anisotropic layered GeS.Photoluminescence (PL) is observed with a peak at ～1.66 eV that originates from the direct optical transition in GeS at room temperature.The polarization-dependent characteristics of the PL,which are revealed for the first time,along with the demonstration of anisotropic absorption,indicate an obvious anisotropic optical transition near the band edge of GeS,which is supported by density functional theory calculations.The significantly thickness-dependent PL is observed and discussed.This anisotropic layered GeS presents opportunities for the discovery of new physical phenomena and will find applications that exploit its anisotropic properties,such as polarization-sensitive photodetectors.     

Highly Anisotropic Sb2Se3 Nanosheets: Gentle Exfoliation from the Bulk Precursors Possessing 1D Crystal Structure

2D materials, particularly those bearing in‐plane anisotropic optical and electrical properties such as black phosphorus and ReS₂, have spurred great research interest very recently as promising building blocks for future electronics. However, current progress is limited to layered compounds that feature atomic arrangement asymmetry within the covalently bonded planes. Herein, a series of highly anisotropic nanosheets (Sb₂Se₃, Sb₂S₃, Bi₂S₃, and Sb₂(S, Se)₃), which are composed of 1D covalently linked ribbons stacked together via van der Waals force, is introduced as a new member to the anisotropic 2D material family. These unique anisotropic nanosheets are successfully fabricated from their polymer‐like bulk counterparts through a gentle water freezing‐thawing approach. Angle‐resolved polarized Raman spectroscopy characterization confirms the strong in‐plane asymmetry of Sb₂Se₃ nanosheets, and photodetection study reveals their high responsivity and anisotropic in‐plane transport. This work can enlighten the synthesis and application of new anisotropic 2D nanosheets that can be potentially applied for future electronic and optoelectronic devices.     

Alternative Plasmonic Materials: Beyond Gold and Silver

Materials research plays a vital role in transforming breakthrough scientific ideas into next‐generation technology. Similar to the way silicon revolutionized the microelectronics industry, the proper materials can greatly impact the field of plasmonics and metamaterials. Currently, research in plasmonics and metamaterials lacks good material building blocks in order to realize useful devices. Such devices suffer from many drawbacks arising from the undesirable properties of their material building blocks, especially metals. There are many materials, other than conventional metallic components such as gold and silver, that exhibit metallic properties and provide advantages in device performance, design flexibility, fabrication, integration, and tunability. This review explores different material classes for plasmonic and metamaterial applications, such as conventional semiconductors, transparent conducting oxides, perovskite oxides, metal nitrides, silicides, germanides, and 2D materials such as graphene. This review provides a summary of the recent developments in the search for better plasmonic materials and an outlook of further research directions.     

Highly Anisotropic Conductors

Composite materials with ordered microstructures often lead to enhanced functionalities that a single material can hardly achieve. Many biomaterials with unusual microstructures can be found in nature; among them, many possess anisotropic and even directional physical and chemical properties. With inspiration from nature, artificial composite materials can be rationally designed to achieve this anisotropic behavior with desired properties. Here, a metallic wood with metal continuously filling the wood vessels is developed, which demonstrates excellent anisotropic electrical, thermal, and mechanical properties. The well‐aligned metal rods are confined and separated by the wood vessels, which deliver directional electron transport parallel to the alignment direction. Thus, the novel metallic wood composite boasts an extraordinary anisotropic electrical conductivity (σ_||/σ_⊥) in the order of 10¹¹, and anisotropic thermal conductivity (κ_||/κ_⊥) of 18. These values exceed the highest reported values in existing anisotropic composite materials. The anisotropic functionality of the metallic wood enables it to be used for thermal management applications, such as thermal insulation and thermal dissipation. The highly anisotropic metallic wood serves as an example for further anisotropic materials design; other composite materials with different biotemplates/hosts and fillers can achieve even higher anisotropic ratios, allowing them to be implemented in a variety of applications.     

Recent Progress of Two-Dimensional Thermoelectric Materials

Thermoelectric generators have attracted a wide research interest owing to their ability to directly convert heat into electrical power.Moreover,the thermoelectric properties of traditional inorganic and organic materials have been significantly improved over the past few decades.Among these compounds,layered two-dimensional(2D)materials,such as graphene,black phosphorus,transition metal dichalcogenides,IVA–VIA compounds,and MXenes,have generated a large research attention as a group of potentially high-performance thermoelectric materials.Due to their unique electronic,mechanical,thermal,and optoelectronic properties,thermoelectric devices based on such materials can be applied in a variety of applications.Herein,a comprehensive review on the development of 2D materials for thermoelectric applications,as well as theoretical simulations and experimental preparation,is presented.In addition,nanodevice and new applications of 2D thermoelectric materials are also introduced.At last,current challenges are discussed and several prospects in this field are proposed.     

The Role of Graphene and Other 2D Materials in Solar Photovoltaics

2D materials have attracted considerable attention due to their exciting optical and electronic properties, and demonstrate immense potential for next‐generation solar cells and other optoelectronic devices. With the scaling trends in photovoltaics moving toward thinner active materials, the atomically thin bodies and high flexibility of 2D materials make them the obvious choice for integration with future‐generation photovoltaic technology. Not only can graphene, with its high transparency and conductivity, be used as the electrodes in solar cells, but also its ambipolar electrical transport enables it to serve as both the anode and the cathode. 2D materials beyond graphene, such as transition‐metal dichalcogenides, are direct‐bandgap semiconductors at the monolayer level, and they can be used as the active layer in ultrathin flexible solar cells. However, since no 2D material has been featured in the roadmap of standard photovoltaic technologies, a proper synergy is still lacking between the recently growing 2D community and the conventional solar community. A comprehensive review on the current state‐of‐the‐art of 2D‐materials‐based solar photovoltaics is presented here so that the recent advances of 2D materials for solar cells can be employed for formulating the future roadmap of various photovoltaic technologies.     

Van der Waals Epitaxy of III-Nitride Semiconductors Based on 2D Materials for Flexible Applications

III-nitride semiconductors have attracted considerable attention in recent years owing to their excellent physical properties and wide applications in solid-state lighting, flat-panel displays, and solar energy and power electronics. Generally, GaN-based devices are heteroepitaxially grown on c-plane sapphire, Si (111), or 6H-SiC substrates. However, it is very difficult to release the GaN-based films from such single-crystalline substrates and transfer them onto other foreign substrates. Consequently, it is difficult to meet the ever-increasing demand for wearable and foldable applications. On the other hand, sp²-bonded two-dimensional (2D) materials, which exhibit hexagonal in-plane lattice arrangements and weakly bonded layers, can be transferred onto flexible substrates with ease. Hence, flexible III-nitride devices can be implemented through such 2D release layers. In this progress report, the recent advances in the different strategies for the growth of III-nitrides based on 2D materials are reviewed, with a focus on van der Waals epitaxy and transfer printing. Various attempts are presented and discussed herein, including the different kinds of 2D materials (graphene, hexagonal boron nitride, and transition metal dichalcogenides) used as release layers. Finally, current challenges and future perspectives regarding the development of flexible III-nitride devices are discussed.