High-throughput Synthesis of Solution-Processable van der Waals Heterostructures through Electrochemistry

Two-dimensional van der Waals heterostructures (2D vdWHs) have recently gained widespread attention because of their abundant and exotic properties, which open up many new possibilities for next-generation nanoelectronics. However, practical applications remain challenging due to the lack of high-throughput techniques for fabricating high-quality vdWHs. Here, we demonstrate a general electrochemical strategy to prepare solution-processable high-quality vdWHs, in which electrostatic forces drive the stacking of electrochemically exfoliated individual assemblies with intact structures and clean interfaces into vdWHs with strong interlayer interactions. Thanks to the excellent combination of strong light absorption, interfacial charge transfer, and decent charge transport properties in individual layers, thin-film photodetectors based on graphene/In₂Se₃ vdWHs exhibit great promise for near-infrared (NIR) photodetection, owing to a high responsivity (267 mA W⁻¹), fast rise (72 ms) and decay (426 ms) times under NIR illumination. This approach enables various hybrid systems, including graphene/In₂Se₃, graphene/MoS₂ and graphene/MoSe₂ vdWHs, providing a broad avenue for exploring emerging electronic, photonic, and exotic quantum phenomena.     

Graphene-based electrochemical energy conversion and storage: fuel cells, supercapacitors and lithium ion batteries

Graphene has attracted extensive research interest due to its strictly 2-dimensional (2D) structure, which results in its unique electronic, thermal, mechanical, and chemical properties and potential technical applications. These remarkable characteristics of graphene, along with the inherent benefits of a carbon material, make it a promising candidate for application in electrochemical energy devices. This article reviews the methods of graphene preparation, introduces the unique electrochemical behavior of graphene, and summarizes the recent research and development on graphene-based fuel cells, supercapacitors and lithium ion batteries. In addition, promising areas are identified for the future development of graphene-based materials in electrochemical energy conversion and storage systems.     

From two-dimensional materials to heterostructures

Graphene, hexagonal boron nitride, molybdenum disulphide, and layered transition metal dichalcogenides (TMDCs) represent a class of two-dimensional (2D) atomic crystals with unique properties due to reduced dimensionality. Stacking these materials on top of each other in a controlled fashion can create heterostructures with tailored properties that offers another promising approach to design and fabricate novel electronic devices. In this report, we attempt to review this rapidly developing field of hybrid materials. We summarize the fabrication methods for different 2D materials, the layer-by-layer growth of various vertical heterostructures and their electronic properties. Particular interests are given to in-situ stack aforementioned 2D materials in controlled sequences, and the TMDCs heterostructures.     

二维半导体材料纳米电子器件和光电器件

近年来,随着各领域对微电子器件集成度及性能要求的不断提高,发展基于二维半导体材料的新型高性能功能性器件成为了突破当前技术瓶颈的重要环节和关键方向。目前,作为新型二维半导体材料的代表,二维过渡金属二硫化物、二维黑磷以及范德瓦尔斯异质结凭借其在电学、热学、机械、光学等方面的优异性能已经成为了发展高性能纳米电子器件和光电器件的最具潜力的材料之一。在本综述中,首先概述了几种用于纳米器件的常见二维材料,分析了材料的结构、性能及其在纳米器件中的应用,其次重点对基于过渡金属二硫化物、黑磷以及由其衍生的范德瓦尔斯异质结的纳米电子器件和光电器件的最新研究进展进行讨论,最后对目前二维半导体纳米器件所面临的挑战以及未来的发展方向进行总结及分析,从而为未来发展高性能功能性纳米器件提供支持。     

Graphene-based materials for polymer solar cells

Due to the remarkable electronic, optical, thermal, and mechanical properties, graphene-based materials have shown great potential in a wide range of technique applications. Particularly, the high transparency, conductivity, flexibility, and abundance make graphene materials highly attractive for polymer solar cells (PSCs). Graphene-based materials have been regarded as one promising candidate used in various parts in PSCs not only as electrodes, but also as interfacial layers and active layers with an aim to boost the power conversion efficiency of the devices. In this review, we summarize the recent progress about the design and synthesis of graphene-based materials for efficient PSCs along with the related challenges and future perspectives.     

表面电荷转移掺杂石墨烯的研究进展

表面电荷转移掺杂是调制石墨烯电学特性的重要手段。发展高效、稳定的表面电荷转移掺杂剂对于提高石墨烯的电学和光电性能、从而推动其在电子和光电领域中的应用具有重要意义。本文围绕高效与稳定两个方面综述了近年来石墨烯表面电荷转移掺杂剂的研究现状以及掺杂石墨烯在光电器件应用方面的进展。根据掺杂剂的类型，着重介绍了最新发展的高效p型和n型掺杂剂，并概述了稳定掺杂方面的重要研究工作。此外，专门介绍了基于掺杂石墨烯透明电极的高性能光电器件。最后，根据表面电荷转移掺杂研究面临的主要挑战，对其未来的发展方向进行了展望。     

功能化石墨烯材料：定义、分类及制备策略

自2004年被成功制备后,石墨烯因其独特迷人的性质在近十几年来备受关注,同时也引发了二维纳米材料的研究热潮。单原子层厚度的二维结构赋予石墨烯非同寻常的光学、电子学、磁学及力学等性质,使得石墨烯在生物学、医学、化学、物理学和环境科学等多个领域展现出极大的应用潜力。制得注意的是,石墨烯在应用时通常需要进行功能化,调节其组成、大小、形状和结构等,以便于加工处理或满足不同的应用需求。石墨烯功能化方法多样,功能化产物也是种类繁多。然而,到目前为止,石墨烯功能化产物并没有系统全面的分类和精确的定义。因此,本文在系统总结现有石墨烯功能化研究的基础上,给出了石墨烯功能化产物的系统分类、各类的精确定义和相应的制备策略,并通过典型示例进行了详细地阐述。石墨烯功能化的产物统称为“功能化石墨烯材料”,分为两类：“功能化石墨烯”和“功能化石墨烯复合材料”。功能化石墨烯材料的制备可由“自上而下”和“自下而上”两种策略实现。制备策略的选择取决于应用需求。系统分类、精确命名和制备策略的归纳必将有助于功能化石墨烯材料的进一步发展。     

Functionalization of 2D materials by intercalation

Since the discovery of graphene many studies focused on its functionalization by different methods. These strategies aim to find new pathways to overcome the main drawback of graphene, a missing band-gap, which strongly reduces its potential applications, particularly in the domain of nanoelectronics, despite its huge and unequaled charge carrier mobility. The necessity to contact this material with a metal has motivated a lot of studies of metal/graphene interactions and has led to the discovery of the intercalation process very early in the history of graphene. Intercalation, where the deposited atoms do not stay at the graphene surface but intercalate between the top layer and the substrate, may happen at room temperature or be induced by annealing, depending of the chemical nature of the metal. This kind of mechanism was already well-known in the earlier Graphite Intercalation Compounds (GICs), particularly famous for one current application, the Lithium-ion Battery, which is simply an application based on the intercalation of Lithium atoms between two sheets of graphene in a graphite anode. Among numerous discoveries the GICs community also found a way to obtain graphite with superconducting properties by using intercalated alkali metals. Graphene is now a playground to “revisit” and understand all these mechanisms and to discover possible new properties of graphene induced by intercalation. For example, the intercalation process may be used to decouple the graphene layer from its substrate, to change its doping level or even, in a more general way, to modify its electronic band structure and the nature of its Dirac fermions. In this paper we will focus on the functionalization of graphene by using intercalation of metal atoms but also of molecules. We will give an overview of the induced modifications of the electronic band structure possibly leading to spin-orbit coupling, superconductivity, …We will see how this concept of functionalization is also now used in the framework of other 2D materials beyond graphene and of van der Waals heterostructures based on these materials.     

Opening of Band Gap of Graphene with High Electronic Mobility by Codoping BN Pairs

Two-dimensional(2D) materials with a high density and low power consumption have become the most popular candidates for next-generation semiconductor electronic devices. As a prototype 2D material, graphene has attracted much attention owing to its stability and ultrahigh mobility. However, zero band gap of graphene leads to very low on-off ratios and thus limits its applications in electronic devices, such as transistors. Although some new 2D materials and doped graphene have nonzero band gaps, the electronic mobility is sacrificed. In this study, to open the band gap of graphene with high electronic mobility, the structure and property of BN-doped graphene were evaluated using first-principles calculations. The formation energies indicate that the six-membered BN rings doped graphene has the most favorable configuration. The band structures show that the band gaps can be opened by such type of doping. Also, the Dirac-cone-like band dispersion of graphene is mostly inhibited, ensuring high electronic mobility. Therefore, codoping BN into graphene might provide 2D materials with nonzero band gaps and high electronic mobility.     

Luminescent Graphene-Based Materials via Europium Complexation on Dipyridylpyridazine-Functionalized Graphene Sheets

Graphene-based materials exhibit outstanding physical properties and so are potentially applicable in a great variety of fields. Unlike their corresponding oxides, graphite and graphene are not prone to functionalization. Diels–Alder reactions are among the scarce reactions that they can occur without disrupting their conjugated sp² systems. Herein, the reaction between graphite and 3,6-di(2-pyridyl)-1,2,4,5-tetrazine under different conditions affords several graphene-based materials consisting of dipyridylpyridazine-functionalized few-layer graphene, multilayer graphene and graphite, the sheets of which act as ligands for the grafting of a europium complex. These three materials show strong red emission under 365 nm UV radiation. Their emitting particles can be visualized by confocal microscopy. The rich coordination chemistry of dipyridylpyridazine ligands has potential novel properties for similarly functionalized graphene-based materials grafted with other metal complexes.     

High‐Quality Three‐Dimensional Nanoporous Graphene

We report three‐dimensional (3D) nanoporous graphene with preserved 2D electronic properties, tunable pore sizes, and high electron mobility for electronic applications. The complex 3D network comprised of interconnected graphene retains a 2D coherent electron system of massless Dirac fermions. The transport properties of the nanoporous graphene show a semiconducting behavior and strong pore‐size dependence, together with unique angular independence. The free‐standing, large‐scale nanoporous graphene with 2D electronic properties and high electron mobility holds great promise for practical applications in 3D electronic devices.     

基于液相法二维异质结的空间结构可控制备

The research in two-dimensional (2D) materials, such as graphene, transition metal dichalcogenides (TMDs) and black phosphorus, has been further flourished with the recent emergence of heterostructures composed of dissimilar 2D materials. The interfacing/coupling between different constituent components in a heterostructure has given rise to interesting phenomena and useful properties. For example, depending on the type of 2D materials, the distance and the kind of bonding between them, as well as the crystalline property of the hetero-interface, the interface may provide charge traps, exciton recombination centers, or bridges for effective charge/energy transfer. It has also been found that the spatial arrangement in addition to the composition of the constituents is an important factor influencing the overall properties of the heterostructures. Although many methods, such as dry transfer and vapor-phased growth are able to yield heterostructures from pristine or highly crystalline 2D crystals with spatial control, such as vertical heterostructures and lateral heterostructures, these methods are generally not scalable, which has restricted the use of the obtained heterostructures mostly to fundamental studies. The solution-phased synthesis methods, such as solvothermal/hydrothermal synthesis, electrochemical deposition and hot-injection method, may be more suitable for mass production of functional heterostructures despite the relatively low product quality. In the past couple of years, a diverse kinds of hetero/hybrid structures of 2D materials have been prepared successfully in wet-chemical processes. However, precise control over the geometric arrangement of the constituent components has been challenging in solution. Currently, four types of heterostructures including 2D crystals grown on a larger 2D template, vertical heterostructures, lateral heterostructures, and core-shell heterostructures have been prepared in solution. For the first type, flexible 2D nanosheets such as graphene and monolayer TMDs are used as synthesis templates to support the nucleation and growth of other 2D crystals. For vertical heterostructures, relatively rigid nanoplates are used to allow continuous deposition of 2D layers of other materials to form sandwich-like structures. The formation of lateral heterostructures requires edge growth on existing 2D materials without basal deposition, and therefore other methods such as cation exchange can be used as alternative routes. The preparation of core-shell 2D heterostructures generally involves both epitaxial edge growth and basal deposition and has been realized in both metallic and semiconductor structures. In this review, these kinds of heterostructures based on 2D materials will be discussed in terms of their synthesis methods, properties and possible applications. In addition, we will discuss the challenges and possible opportunities in this research direction.     

Stacking of Exfoliated Two‐Dimensional Materials: A Review

In recent years, two‐dimensional (2D) atomic crystals represented by graphene have opened up new fields of 2D physics. Layered materials with atomic layer thickness are self‐assembled into van der Waals heterostructures by weak van der Waals forces without considering lattice matching. Van der Waals heterostructures can not only enhance the performance of its constituent materials but also show new characteristics. High‐quality heterostructures require mechanically cleaved intrinsic 2D materials and flexible 2D material stacking techniques. Here, we summarize in detail the reliable exfoliation methods for large‐area single‐layer 2D materials and the dry and wet stacking techniques with high success rates. The twisted bilayer graphene is used as an example to briefly introduce the single‐crystal tearing method, which is currently the most practical method for preparing isotropic twisted heterostructures with high‐precision rotation angles. We hope to provide a valuable reference for researchers of 2D materials.     

Fabrication of Large-Area Molybdenum Disulfide Device Arrays Using Graphene/Ti Contacts

Two-dimensional (2D) molybdenum disulfide (MoS₂) is the most mature material in 2D material fields owing to its relatively high mobility and scalability. Such noticeable properties enable it to realize practical electronic and optoelectronic applications. However, contact engineering for large-area MoS₂ films has not yet been established, although contact property is directly associated to the device performance. Herein, we introduce graphene-interlayered Ti contacts (graphene/Ti) into large-area MoS₂ device arrays using a wet-transfer method. We achieve MoS₂ devices with superior electrical and photoelectrical properties using graphene/Ti contacts, with a field-effect mobility of 18.3 cm²/V∙s, on/off current ratio of 3 × 10⁷, responsivity of 850 A/W, and detectivity of 2 × 10¹² Jones. This outstanding performance is attributable to a reduction in the Schottky barrier height of the resultant devices, which arises from the decreased work function of graphene induced by the charge transfer from Ti. Our research offers a direction toward large-scale electronic and optoelectronic applications based on 2D materials.     

石墨烯/聚合物纳米复合电流变材料

电流变智能流体在外电场刺激下能快速可逆地改变自身流变性能,具有重要技术应用价值.传统的基于微米颗粒的电流变流体易于沉降并且电致屈服强度不高限制了技术应用,最近基于纳米颗粒的非传统电流变材料研究受到重视,特别是具有各向异性形貌的纳米颗粒悬浮液被发现具有明显增强的电/磁流变效应.本文介绍了最近基于石墨烯的二维纳米复合电流变材料的研究进展,主要包括石墨烯/半导聚合物、石墨烯/极性聚合物、石墨烯/碳等几种典型的电流变材料的制备、结构和电流变行为.研究表明利用石墨烯独特的二维纳米结构、优异的电学和热学性质可能为制备新颖的高性能纳米电流变材料提供途径。     

Dependence of the Properties of 2D Nanocomposites Generated by Covalent Crosslinking of Nanosheets on the Interlayer Separation: A Combined Experimental and Theoretical Study

Covalently cross-linked heterostructures of 2D materials are a new class of materials which possess electrochemical and photochemical hydrogen evolution properties. It was of considerable interest to investigate the role of interlayer spacing in the nanocomposites involving MoS₂ and graphene sheets and its control over electronic structures and catalytic properties. We have investigated this problem with emphasis on the hydrogen evolution properties of these structures by a combined experimental and theoretical study. We have linked MoS₂ based nanocomposites with other 2D materials with varying interlayer spacing by changing the linker and studied their hydrogen evolution properties. The hydrogen evolution activity for these composites decreases with increasing linker length, which we can link to a decrease in magnitude of charge transfer across the layers with increasing interlayer spacing. Factors such as the nature of the sheets, interlayer distance as well as the nature of the linker provide pathways to tune the properties of covalently cross-linked 2D material rendering this new class of materials highly interesting.     

石墨烯作为硫载体在锂硫电池中的研究进展

锂硫电池因其超高的理论能量密度以及硫资源丰富、成本低廉、无毒的优点,被认为是极具发展潜力与应用前景的新一代储能设备。然而,硫正极导电性差、体积膨胀以及穿梭效应严重等问题严重制约了其商业化应用。石墨烯具有高比表面积、高导电性和高柔韧性,并且易于进行表面化学修饰及组装,是一种理想的硫载体材料。本文主要综述了近年来三维石墨烯、表面化学修饰的石墨烯、石墨烯基复合材料以及石墨烯基柔性材料在锂硫电池正极中的研究现状,并展望了石墨烯作为硫载体在锂硫电池正极中的发展趋势。     

Reversible chemical switches of functionalized nitrogen-doped graphene field-effect transistors

Nitrogen doping is a promising way to modulate the electrical properties of graphene to realize graphene-based electronics and promise fascinating properties and applications.Herein,we report a method to noncovalently assembly titanium(Ⅳ) bis(ammoniumlactato) dihydroxide(Ti complex) on nitrogen-doped graphene to create a reliable hybrids which can be used as a reversible chemical induced switching.As the adsorption and desorption of Ti complex in sequential treatments,the conductance of the nitrogen-doped graphene transistors was finely modulated.Control experiments with pristine graphene clearly demonstrated the important effort of the nitrogen in this chemical sensor.Under optimized conditions,nitrogen-doped graphene transistors open up new ways to develop multifunctional devices with high sensitivity.     

石墨烯基纤维储能器件的研究进展与展望

随着小型化、可穿戴等特征的智能电子以及物联网传感设备的发展,新型纤维状柔性化、小型化电化学储能器件已成为重要的研究方向。同时,对纤维材料和柔性储能器件的性能提出了更高的要求,如可任意弯折、可拉伸、可折叠、高储能密度等。石墨烯纤维具有独特的结构、优异的导电性、良好机械性能和电化学性质,已证明了是一种极具前景、高性能的新型纤维状柔性储能材料。目前,研究者已开发了多种石墨烯基纤维微观结构的调控策略来进一步改进其性能。本文首先系统总结了石墨烯基纤维的制备方法和其性能提升的策略,然后详细讨论其在柔性化纤维状超级电容器、金属离子电池、热电发电机、太阳能电池和相变材料等储能领域中的最新应用进展。最后,对石墨烯基纤维在能源存储和转换领域中存在的挑战和机会进行了展望。