Magnetic two-dimensional(2D)van derWaals(vdWs)materials and their heterostructures attract increasing attention in the spintronics community due to their various degrees of freedom such as spin,charge,and energy valle...Magnetic two-dimensional(2D)van derWaals(vdWs)materials and their heterostructures attract increasing attention in the spintronics community due to their various degrees of freedom such as spin,charge,and energy valley,which may stimulate potential applications in the field of low-power and high-speed spintronic devices in the future.This review begins with introducing the long-range magnetic order in 2D vdWs materials and the recent progress of tunning their properties by electrostatic doping and stress.Next,the proximity-effect,current-induced magnetization switching,and the related spintronic devices(such as magnetic tunnel junctions and spin valves)based on magnetic 2D vdWs materials are presented.Finally,the development trend of magnetic 2D vdWs materials is discussed.This review provides comprehensive understandings for the development of novel spintronic applications based on magnetic 2D vdWs materials.展开更多
The layered magnetic van der Waals materials have generated tremendous interest due to their potential applications and importance in fundamental research.Previous x-ray diffraction(XRD)studies on the magnetic van der...The layered magnetic van der Waals materials have generated tremendous interest due to their potential applications and importance in fundamental research.Previous x-ray diffraction(XRD)studies on the magnetic van der Waals compound VI3,revealed a structural transition above the magnetic transition but output controversial analysis on symmetry.In this paper we carried out polarized Raman scattering measurements on VI3 from 10 K to 300 K,with focus on the two Ag phonon modes at^71.1 cm^-1 and 128.4 cm-1.Our careful symmetry analysis based on the angle-dependent spectra demonstrates that the crystal symmetry can be well described by C2h rather than D3d both above and below structural phase transition.We further performed temperature-dependent Raman experiments to study the magnetism in VI3.Fano asymmetry and anomalous linewidth drop of two Ag phonon modes at low temperatures,point to a significant spin-phonon coupling.This is also supported by the softening of 71.1-cm^-1 mode above the magnetic transition.The study provides the fundamental information on lattice dynamics and clarifies the symmetry in VI3.And spin-phonon coupling existing in a wide temperature range revealed here may be meaningful in applications.展开更多
Perovskite solar cells(PSCs)offer low costs and high power conversion efficiency.However,the lack of long-term stability,primarily stemming from the interfacial defects and the sus-ceptible metal electrodes,hinders th...Perovskite solar cells(PSCs)offer low costs and high power conversion efficiency.However,the lack of long-term stability,primarily stemming from the interfacial defects and the sus-ceptible metal electrodes,hinders their practical application.In the past few years,two-dimensional(2D)materials(e.g.,graphene and its derivatives,transitional metal dichalcogenides,MXenes,and black phosphorus)have been identified as a promising solution to solving these problems because of their dangling bond-free surfaces,layer-dependent electronic band structures,tunable functional groups,and inherent compactness.Here,recent progress of 2D material toward efficient and stable PSCs is summarized,including its role as both interface materials and electrodes.We discuss their beneficial effects on perovskite growth,energy level alignment,defect passivation,as well as blocking external stimulus.In particular,the unique properties of 2D materials to form van der Waals heterojunction at the bottom interface are emphasized.Finally,perspectives on the further development of PSCs using 2D materials are provided,such as designing high-quality van der Waals heterojunction,enhancing the uniformity and coverage of 2D nanosheets,and developing new 2D materials-based electrodes.展开更多
As the family of magnetic materials is rapidly growing,two-dimensional(2D)van der Waals(vdW)magnets have attracted increasing attention as a platform to explore fundamental physical problems of magnetism and their pot...As the family of magnetic materials is rapidly growing,two-dimensional(2D)van der Waals(vdW)magnets have attracted increasing attention as a platform to explore fundamental physical problems of magnetism and their potential applications.This paper reviews the recent progress on emergent vd W magnetic compounds and their potential applications in devices.First,we summarize the current vd W magnetic materials and their synthetic methods.Then,we focus on their structure and the modulation of magnetic properties by analyzing the representative vd W magnetic materials with different magnetic structures.In addition,we pay attention to the heterostructures of vd W magnetic materials,which are expected to produce revolutionary applications of magnetism-related devices.To motivate the researchers in this area,we finally provide the challenges and outlook on 2D vd W magnetism.展开更多
Exploring the novel structural phase of van der Waals(vdW) magnets would promote the development of spintronics.Here, through first-principles calculations, we report a novel monoclinic structure of vdW layered 1T-CrT...Exploring the novel structural phase of van der Waals(vdW) magnets would promote the development of spintronics.Here, through first-principles calculations, we report a novel monoclinic structure of vdW layered 1T-CrTe2, which is one of the popular vdW magnets normally exhibiting a trigonal structure. The new monoclinic phase emerges from a switchable magnetic state between ferromagnetism and antiferromagnetism through changing hole doping concentration, which suggests a practical approach to obtain such a structure. The results of phonon dispersion and energy analysis convince us that the monoclinic structure is a metastable phase even without hole doping. When the hole doping concentration increases,the stability analysis indicates the preference for a novel monoclinic phase rather than a conventional trigonal phase, and meanwhile, the magnetic properties are accordingly tuned. This work provides new insights into the phase engineering of the chalcogenide family and the electrical control of magnetism of vdW layered magnets.展开更多
The self-intercalation of Cr into pristine two-dimensional(2D) van der Waals ferromagnetic CrTe_(2),which forms chromium tellurides(Cr_(x)Te_(2)),has garnered interest due to their remarkable magnetic characteristics ...The self-intercalation of Cr into pristine two-dimensional(2D) van der Waals ferromagnetic CrTe_(2),which forms chromium tellurides(Cr_(x)Te_(2)),has garnered interest due to their remarkable magnetic characteristics and the wide variety of chemical compositions available.Here,comprehensive basic characterization and magnetic studies are conducted on quasi-2D ferromagnetic Cr_(1.04)Te_(2) crystals.Measurements of the isothermal magnetization curves are conducted around the critical temperature to systematically investigate the critical behavior.Specifically,the critical exponents β=0.2399,γ=0.859,and δ=4.3498,as well as the Curie temperature T_(C)=249.56 K,are determined using various methods,including the modified Arrott plots,the Kouvel-Fisher method,the Widom scaling method,and the critical isotherm analysis.These results indicate that the tricritical mean-field model accurately represents the critical behavior of Cr_(1.04)Te_(2.A magnetic phase diagram with tricritical phenomenon is thus constructed.Further investigations confirm that the critical exponents obtained conform to the scalar equation near T_(C),indicating their self-consistency and reliability.Our work sheds light on the magnetic properties of quasi-2D Cr_(1.04)Te_(2),broadening the scope of the van der Waals crystals for developments of future spintronic devices operable at room temperature.展开更多
Flexible electronics and optoelectronics exhibit inevitable trends in next-generation intelligent industries,including healthcare and wellness,electronic skins,the automotive industry,and foldable or rollable displays...Flexible electronics and optoelectronics exhibit inevitable trends in next-generation intelligent industries,including healthcare and wellness,electronic skins,the automotive industry,and foldable or rollable displays.Traditional bulk-material-based flexible devices considerably rely on lattice-matched crystal structures and are usually plagued by unavoidable chemical disorders at the interface.Two-dimensional van der Waals materials(2D VdWMs)have exceptional multifunctional properties,including large specific area,dangling-bond-free interface,plane-to-plane van der Waals interactions,and excellent mechanical,electrical,and optical properties.Thus,2D VdWMs have considerable application potential in functional intelligent flexible devices.To utilize the unique properties of 2D VdWMs and their van der Waals heterostructures,new designs and configurations of electronics and optoelectronics have emerged.However,these new designs and configurations do not consider lattice mismatch and process incompatibility issues.In this review,we summarized the recently reported 2D VdWM-based flexible electronic and optoelectronic devices with various functions thoroughly.Moreover,we identified the challenges and opportunities for further applications of 2D VdWM-based flexible electronics and optoelectronics.展开更多
Research on two-dimensional(2D) materials and related van der Waals heterostructures(vdWHs) is intense and remains one of the leading topics in condensed matter physics.Lattice vibrations or phonons of a vdWH provide ...Research on two-dimensional(2D) materials and related van der Waals heterostructures(vdWHs) is intense and remains one of the leading topics in condensed matter physics.Lattice vibrations or phonons of a vdWH provide rich information,such as lattice structure,phonon dispersion,electronic band structure and electron–phonon coupling.Here,we provide a mini review on the lattice vibrations in vdWHs probed by Raman spectroscopy.First,we introduced different kinds of vdWHs,including their structures,properties and potential applications.Second,we discussed interlayer and intralayer phonon in twist multilayer graphene and MoS2.The frequencies of interlayer and intralayer modes can be reproduced by linear chain model(LCM)and phonon folding induced by periodical moiré potentials,respectively.Then,we extended LCM to vdWHs formed by distinct 2D materials,such as MoS2/graphene and hBN/WS2 heterostructures.We further demonstrated how to calculate Raman intensity of interlayer modes in vdWHs by interlayer polarizability model.展开更多
1. The transient absorption spectra of the WS2 monolayer sample.In the measurement of the transient absorption spectra of the WS2 monolayer sample, A 400-nm (3.1eV) pump pulse with a peak fluence of about 10μJ/cm2exc...1. The transient absorption spectra of the WS2 monolayer sample.In the measurement of the transient absorption spectra of the WS2 monolayer sample, A 400-nm (3.1eV) pump pulse with a peak fluence of about 10μJ/cm2excites the electrons from the valence band into the conduction band,the展开更多
Two-dimensional (2D) Van der Waals heterostructures have aroused extensive concerns in recent years. Their fabrica- tion calls for facile and efficient transfer techniques for achieving well-defined structures. In t...Two-dimensional (2D) Van der Waals heterostructures have aroused extensive concerns in recent years. Their fabrica- tion calls for facile and efficient transfer techniques for achieving well-defined structures. In this work, we report a simple and effective dry transfer method to fabricate 2D heterostructures with a clean interface. Using Propylene Carbonate (PC) films as stamps, we are able to pick up various 2D materials flakes from the substrates and unload them to the receiving substrates at an elevated temperature. Various multilayer heterostructures with ultra-clean interfaces were fabricated by this technique. Furthermore, the 2D materials can be pre-pattemed before transfer so as to fabricate desired device structures, demonstrating a facile way to promote the development of 2D heterostructures.展开更多
Exploring two-dimensional(2D)magnetic heterostructures is essential for future spintronic and optoelectronic devices.Herein,using first-principle calculations,stable ferromagnetic ordering and colorful electronic prop...Exploring two-dimensional(2D)magnetic heterostructures is essential for future spintronic and optoelectronic devices.Herein,using first-principle calculations,stable ferromagnetic ordering and colorful electronic properties are established by constructing the VS_(2)/C_(3)N van der Waals(vdW)heterostructure.Unlike the semiconductive properties with indirect band gaps in both the VS2 and C3N monolayers,our results indicate that a direct band gap with type-Ⅱband alignment and p-doping characters are realized in the spin-up channel of the VS_(2)/C_(3)N heterostructure,and a typical type-Ⅲband alignment with a broken-gap in the spin-down channel.Furthermore,the band alignments in the two spin channels can be effectively tuned by applying tensile strain.An interchangement between the type-Ⅱand type-Ⅲband alignments occurs in the two spin channels,as the tensile strain increases to 4%.The attractive magnetic properties and the unique band alignments could be useful for prospective applications in the next-generation tunneling devices and spintronic devices.展开更多
Van der Waals heterostructures(vdWHs) are showing considerable potential in both fundamental exploration and practical applications. Built upon the synthetic successes of(two-dimensional) 2D materials, several synthet...Van der Waals heterostructures(vdWHs) are showing considerable potential in both fundamental exploration and practical applications. Built upon the synthetic successes of(two-dimensional) 2D materials, several synthetic strategies of vdWHs have been developed,allowing the convenient fabrication of diverse vdWHs with decent controllability, quality, and scalability. This review first summarizes the current state of the art in synthetic strategies of vdWHs, including physical combination, deposition, solvothermal synthesis, and synchronous evolution. Then three major applications and their representative vdWH devices have been reviewed, including electronics(tunneling field effect transistors and 2D contact),optoelectronics(photodetector), and energy conversion(electrocatalysts and metal ion batteries), to unveil the potentials of vdWHs in practical applications and provide the general design principles of functional vdWHs for different applications. Besides, moiré superlattices based on vdWHs are discussed to showcase the importance of vdWHs as a platform for novel condensed matter physics. Finally, the crucial challenges towards ideal vdWHs with high performance are discussed, and the outlook for future development is presented. By the systematical integration of synthetic strategies and applications, we hope this review can further light up the rational designs of vdWHs for emerging applications.展开更多
With the development of Moore's law, the future trend of devices will inevitably be shrinking and integration to further achieve size reduction. The emergence of new two-dimensional non-layered materials(2DNLMs) n...With the development of Moore's law, the future trend of devices will inevitably be shrinking and integration to further achieve size reduction. The emergence of new two-dimensional non-layered materials(2DNLMs) not only enriches the 2D material family to meet future development, but also stimulates the global enthusiasm for basic research and application technologies in the 2D field. Van der Waals(vd W) heterostructures, in which two-dimensional layered materials(2DLMs)are physically stacked layer by layer, can also occur between 2DLMs and 2DNLMs hybrid heterostructures, providing an alternative platform for nanoelectronics and optoelectronic applications. Here, we outline the recent developments of2DLMs/2DNLMs hybrid heterostructures, with particular emphasis on major advances in synthetic methods and applications. And the categories and crystal structures of 2DLMs and 2DNLMs are also shown. We highlight some promising applications of the heterostructures in electronics, optoelectronics, and catalysis. Finally, we provide conclusions and future prospects in the 2D materials field.展开更多
Two-dimensional ferromagnetic van der Waals(2D vdW)heterostructures have opened new avenues for creating artificial materials with unprecedented electrical and optical functions beyond the reach of isolated 2D atomic ...Two-dimensional ferromagnetic van der Waals(2D vdW)heterostructures have opened new avenues for creating artificial materials with unprecedented electrical and optical functions beyond the reach of isolated 2D atomic layered materials,and for manipulating spin degree of freedom at the limit of few atomic layers,which empower next-generation spintronic and memory devices.However,to date,the electronic properties of 2D ferromagnetic heterostructures still remain elusive.Here,we report an unambiguous magnetoresistance behavior in CrI_(3)/graphene heterostructures,with a maximum magnetoresistance ratio of 2.8%.The magnetoresistance increases with increasing magnetic field,which leads to decreasing carrier densities through Lorentz force,and decreases with the increase of the bias voltage.This work highlights the feasibilities of applying two-dimensional ferromagnetic vdW heterostructures in spintronic and memory devices.展开更多
Geometrical frustration in low-dimensional magnetic systems has been an intriguing research aspect,where the suppression of conventional magnetic order may lead to exotic ground states such as spin glass or spin liqui...Geometrical frustration in low-dimensional magnetic systems has been an intriguing research aspect,where the suppression of conventional magnetic order may lead to exotic ground states such as spin glass or spin liquid.In this work we report the synthesis and magnetism study of the monocrystalline Mn_(2)Ga_(2)S_(5),featuring both the van derWaals structure and a bilayered triangular Mn lattice.Magnetic susceptibility reveals a significant antiferromagnetic interaction with a Curie-Weiss temperature θ_(w)~-260 K and a high spin S=5/2 Mn^(2+) state.However,no long range magnetic order has been found down to 2 K,and a spin freezing transition is found to occur at around 12 K well below its θ_(w).This yields a frustration index of f=-θ_(w)/T_(f)≈22,an indication that the system is highly frustrated.The absence of a double-peak structure in magnetic specific heat compared with the TM_(2)S_(4) compounds implies that the spin freezing behavior in Mn_(2)Ga_(2)S_(5)is a result of the competition between exchange interactions and the 2D crystalline structure.Our results suggest that the layered Mn_(2)Ga_(2)S_(5)would be an excellent candidate for investigating the physics of 2D magnetism and spin disordered state.展开更多
Spintronic devices are driving new paradigms of bio-inspired,energy efficient computation like neuromorphic stochastic computing and in-memory computing.They have also emerged as key candidates for non-volatile memori...Spintronic devices are driving new paradigms of bio-inspired,energy efficient computation like neuromorphic stochastic computing and in-memory computing.They have also emerged as key candidates for non-volatile memories for embedded systems as well as alternatives to persistent memories.To meet the growing demands from such diverse applications,there is need for innovation in materials and device designs which can be scaled and adapted according to the application.Two-dimensional(2D)magnetic materials address challenges facing bulk magnet systems by offering scalability while maintaining device integrity and allowing efficient control of magnetism.In this review,we highlight the progress made in experimental studies on 2D magnetic materials towards their integration into spintronic devices.We provide an account of the various relevant material discoveries,demonstrations of current and voltage-based control of magnetism and reported device systems,while also discussing the challenges and opportunities towards integration of 2D magnetic materials in commercial spintronic devices.展开更多
Detecting light from a wealth of physical degrees of freedom(e.g.wavelength,intensity,polarization state,phase,etc)enables the acquirement of more comprehensive information.In the past two decades,low-dimensional van ...Detecting light from a wealth of physical degrees of freedom(e.g.wavelength,intensity,polarization state,phase,etc)enables the acquirement of more comprehensive information.In the past two decades,low-dimensional van der Waals materials(vdWMs)have established themselves as transformative building blocks toward lensless polarization optoelectronics,which is highly beneficial for optoelectronic system miniaturization.This review provides a comprehensive overview on the recent development of low-dimensional vdWM polarized photodetectors.To begin with,the exploitation of pristine 1D/2D vdWMs with immanent in-plane anisotropy and related heterostructures for filterless polarization-sensitive photodetectors is introduced.Then,we have systematically epitomized the various strategies to induce polarization photosensitivity and enhance the degree of anisotropy for low-dimensional vdWM photodetectors,including quantum tailoring,construction of core–shell structures,rolling engineering,ferroelectric regulation,strain engineering,etc,with emphasis on the fundamental physical principles.Following that,the ingenious optoelectronic applications based on the low-dimensional vdWM polarized photodetectors,including multiplexing optical communications and enhanced-contrast imaging,have been presented.In the end,the current challenges along with the future prospects of this burgeoning research field have been underscored.On the whole,the review depicts a fascinating landscape for the next-generation high-integration multifunctional optoelectronic systems.展开更多
Chemical modification and vertical stacking of two-dimensional materials are promising techniques for new nanoelectronic devices. We present Density Functional Tight Binding(DFTB) calculations of a field-effect device...Chemical modification and vertical stacking of two-dimensional materials are promising techniques for new nanoelectronic devices. We present Density Functional Tight Binding(DFTB) calculations of a field-effect device,based on lateral and vertical heterostructures of 2D materials. The device consists of a phosphorene channel protected by graphene sheets, which work as contacts and are divided into the source and drain by local hydrogenation of graphene, which gives insulating graphane. In this device composed of only 3 layers, single sheets of graphene-graphane can work as both leads and oxide gate, while also acting as protective layers for a phosphorene channel. We show how for perfect vd W heterostructures of graphane/phosphorene/graphane and graphene/phosphorene/graphene the Schottky barrier is deeply influenced by normal electric fields, and we characterize electronic transport of such a device. Finally, we characterize phosphorene channel doping and defects, which, at very high densities in the transport direction, enables transport inside the phosphorene bandgap.展开更多
Ⅲ-nitride semiconductor materials have excellent optoelectronic properties,mechanical properties,and chemical stability,which have important applications in the field of optoelectronics and microelectronics.Two-dimen...Ⅲ-nitride semiconductor materials have excellent optoelectronic properties,mechanical properties,and chemical stability,which have important applications in the field of optoelectronics and microelectronics.Two-dimensional(2D)materials have been widely focused in recent years due to their peculiar properties.With the property of weak bonding between layers of 2D materials,the growth ofⅢ-nitrides on 2D materials has been proposed to solve the mismatch problem caused by heterogeneous epitaxy and to develop substrate stripping techniques to obtain high-quality,low-cost nitride materials for high-quality nitride devices and their extension in the field of flexible devices.In this progress report,the main methods for the preparation of 2D materials,and the recent progress and applications of different techniques for the growth ofⅢ-nitrides based on 2D materials are reviewed.展开更多
Heteroepitaxy can reduce the cost and widen the application range of semiconductor film synthesis and device fabrication.However,the lattice and thermal expansion coefficient mismatches between epilayers and substrate...Heteroepitaxy can reduce the cost and widen the application range of semiconductor film synthesis and device fabrication.However,the lattice and thermal expansion coefficient mismatches between epilayers and substrates limit the improvement of crystal quality and device performance.Two-dimensional(2D)material-assisted heteroepitaxy offers an effective solution to these challenges.The weak interaction at the interface between films and substrates facilitates the subsequent exfoliation and transfer of epilayer for the fabrication of flexible or high-power electronics.Herein,we summarize the modes of 2D material-assisted epitaxy,which can be classified into remote epitaxy,pinhole epitaxy and van der Waals epitaxy based on the interfacial interaction between the epilayers and substrates.Furthermore,we discuss in detail the improved crystal quality and functional applications,such as flexible devices,wavelength-modulated optoelectronic devices,and thermal management in high-power devices.Moreover,we highlight the challenges and prospects of 2D material-assisted epitaxy,providing roadmaps for lateral research and semiconductor production.展开更多
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0206200)the National Natural Science Foundation of China(Grant No.11874409)+2 种基金the Beijing Natural Science Foundation,China(Grant No.Z190009)the Science Center of the National Science Foundation of China(Grant No.52088101)the K.C.Wong Education Foundation(Grant No.GJTD-2019-14).
文摘Magnetic two-dimensional(2D)van derWaals(vdWs)materials and their heterostructures attract increasing attention in the spintronics community due to their various degrees of freedom such as spin,charge,and energy valley,which may stimulate potential applications in the field of low-power and high-speed spintronic devices in the future.This review begins with introducing the long-range magnetic order in 2D vdWs materials and the recent progress of tunning their properties by electrostatic doping and stress.Next,the proximity-effect,current-induced magnetization switching,and the related spintronic devices(such as magnetic tunnel junctions and spin valves)based on magnetic 2D vdWs materials are presented.Finally,the development trend of magnetic 2D vdWs materials is discussed.This review provides comprehensive understandings for the development of novel spintronic applications based on magnetic 2D vdWs materials.
基金Project supported by the Science Fund from the Ministry of Science and Technology of China(Grant Nos.2017YFA0302904 and 2016YFA0300504)the National Natural Science Foundation of China(Grant Nos.11774419,U1932215,11774423,and 11822412)+1 种基金the Fundamental Research Funds for the Central Universities,Chinathe Research Funds of Renmin University of China(RUC)(Grant Nos.15XNLQ07,18XNLG14,and 19XNLG17).
文摘The layered magnetic van der Waals materials have generated tremendous interest due to their potential applications and importance in fundamental research.Previous x-ray diffraction(XRD)studies on the magnetic van der Waals compound VI3,revealed a structural transition above the magnetic transition but output controversial analysis on symmetry.In this paper we carried out polarized Raman scattering measurements on VI3 from 10 K to 300 K,with focus on the two Ag phonon modes at^71.1 cm^-1 and 128.4 cm-1.Our careful symmetry analysis based on the angle-dependent spectra demonstrates that the crystal symmetry can be well described by C2h rather than D3d both above and below structural phase transition.We further performed temperature-dependent Raman experiments to study the magnetism in VI3.Fano asymmetry and anomalous linewidth drop of two Ag phonon modes at low temperatures,point to a significant spin-phonon coupling.This is also supported by the softening of 71.1-cm^-1 mode above the magnetic transition.The study provides the fundamental information on lattice dynamics and clarifies the symmetry in VI3.And spin-phonon coupling existing in a wide temperature range revealed here may be meaningful in applications.
基金the financial support of the National Natural Science Foundation of China(Nos.U21A20171,12074245,and 52102281)National Key R&D Program of China(Nos.2021YFB3800068 and 2020YFB1506400)+1 种基金Shanghai Sailing Program(No.21YF1421600)Young Elite Scientists Sponsorship Program by China Association for Science and Technology(No.2021QNRC001).
文摘Perovskite solar cells(PSCs)offer low costs and high power conversion efficiency.However,the lack of long-term stability,primarily stemming from the interfacial defects and the sus-ceptible metal electrodes,hinders their practical application.In the past few years,two-dimensional(2D)materials(e.g.,graphene and its derivatives,transitional metal dichalcogenides,MXenes,and black phosphorus)have been identified as a promising solution to solving these problems because of their dangling bond-free surfaces,layer-dependent electronic band structures,tunable functional groups,and inherent compactness.Here,recent progress of 2D material toward efficient and stable PSCs is summarized,including its role as both interface materials and electrodes.We discuss their beneficial effects on perovskite growth,energy level alignment,defect passivation,as well as blocking external stimulus.In particular,the unique properties of 2D materials to form van der Waals heterojunction at the bottom interface are emphasized.Finally,perspectives on the further development of PSCs using 2D materials are provided,such as designing high-quality van der Waals heterojunction,enhancing the uniformity and coverage of 2D nanosheets,and developing new 2D materials-based electrodes.
基金funding support of the National Natural Science Foundation of China(Grant Nos.11975035,51731001,11805006,and 11675006)the National Key Research and Development Program of China(Grant Nos.2017YFA0206303 and 2017YFA0403701)。
文摘As the family of magnetic materials is rapidly growing,two-dimensional(2D)van der Waals(vdW)magnets have attracted increasing attention as a platform to explore fundamental physical problems of magnetism and their potential applications.This paper reviews the recent progress on emergent vd W magnetic compounds and their potential applications in devices.First,we summarize the current vd W magnetic materials and their synthetic methods.Then,we focus on their structure and the modulation of magnetic properties by analyzing the representative vd W magnetic materials with different magnetic structures.In addition,we pay attention to the heterostructures of vd W magnetic materials,which are expected to produce revolutionary applications of magnetism-related devices.To motivate the researchers in this area,we finally provide the challenges and outlook on 2D vd W magnetism.
基金supported by the National Key Research and Development Program of China (Grant No. 2017YFA0403200)the National Natural Science Foundation of China (Grant No. 11774429)+1 种基金the NSAF (Grant No. U1830206)the Science and Technology Innovation Program of Hunan Province, China (Grant No. 2021RC4026)。
文摘Exploring the novel structural phase of van der Waals(vdW) magnets would promote the development of spintronics.Here, through first-principles calculations, we report a novel monoclinic structure of vdW layered 1T-CrTe2, which is one of the popular vdW magnets normally exhibiting a trigonal structure. The new monoclinic phase emerges from a switchable magnetic state between ferromagnetism and antiferromagnetism through changing hole doping concentration, which suggests a practical approach to obtain such a structure. The results of phonon dispersion and energy analysis convince us that the monoclinic structure is a metastable phase even without hole doping. When the hole doping concentration increases,the stability analysis indicates the preference for a novel monoclinic phase rather than a conventional trigonal phase, and meanwhile, the magnetic properties are accordingly tuned. This work provides new insights into the phase engineering of the chalcogenide family and the electrical control of magnetism of vdW layered magnets.
基金Project supported by the Natural Science Foundation of Nanjing University of Posts and Telecommunications(Grant No.NY222170)Jiangsu Specially-Appointed Professor Program,and Natural Science Foundation of Universities of Jiangsu Province(Grant No.TJ219008)the support of the open research fund of Key Laboratory of Quantum Materials and Devices(Southeast University),Ministry of Education。
文摘The self-intercalation of Cr into pristine two-dimensional(2D) van der Waals ferromagnetic CrTe_(2),which forms chromium tellurides(Cr_(x)Te_(2)),has garnered interest due to their remarkable magnetic characteristics and the wide variety of chemical compositions available.Here,comprehensive basic characterization and magnetic studies are conducted on quasi-2D ferromagnetic Cr_(1.04)Te_(2) crystals.Measurements of the isothermal magnetization curves are conducted around the critical temperature to systematically investigate the critical behavior.Specifically,the critical exponents β=0.2399,γ=0.859,and δ=4.3498,as well as the Curie temperature T_(C)=249.56 K,are determined using various methods,including the modified Arrott plots,the Kouvel-Fisher method,the Widom scaling method,and the critical isotherm analysis.These results indicate that the tricritical mean-field model accurately represents the critical behavior of Cr_(1.04)Te_(2.A magnetic phase diagram with tricritical phenomenon is thus constructed.Further investigations confirm that the critical exponents obtained conform to the scalar equation near T_(C),indicating their self-consistency and reliability.Our work sheds light on the magnetic properties of quasi-2D Cr_(1.04)Te_(2),broadening the scope of the van der Waals crystals for developments of future spintronic devices operable at room temperature.
基金supported by the Natural Science Foundation of Beijing Municipality(No.Z180011)the National Natural Science Foundation of China(Nos.51991340,51991342,51972022,92163205,and 52188101)+2 种基金the National Key Research and Development Program of China(No.2016YFA0202701)the Fundamental Research Funds for the Central Universities(No.FRF-TP-19-025A3)the Overseas Expertise Introduction Projects for Discipline Innovation(No.B14003)。
文摘Flexible electronics and optoelectronics exhibit inevitable trends in next-generation intelligent industries,including healthcare and wellness,electronic skins,the automotive industry,and foldable or rollable displays.Traditional bulk-material-based flexible devices considerably rely on lattice-matched crystal structures and are usually plagued by unavoidable chemical disorders at the interface.Two-dimensional van der Waals materials(2D VdWMs)have exceptional multifunctional properties,including large specific area,dangling-bond-free interface,plane-to-plane van der Waals interactions,and excellent mechanical,electrical,and optical properties.Thus,2D VdWMs have considerable application potential in functional intelligent flexible devices.To utilize the unique properties of 2D VdWMs and their van der Waals heterostructures,new designs and configurations of electronics and optoelectronics have emerged.However,these new designs and configurations do not consider lattice mismatch and process incompatibility issues.In this review,we summarized the recently reported 2D VdWM-based flexible electronic and optoelectronic devices with various functions thoroughly.Moreover,we identified the challenges and opportunities for further applications of 2D VdWM-based flexible electronics and optoelectronics.
基金the National Key Research and Development Program of China (Grant No.2016YFA0301204)the National Natural Science Foundation of China (Grant Nos.11874350 and 11434010)
文摘Research on two-dimensional(2D) materials and related van der Waals heterostructures(vdWHs) is intense and remains one of the leading topics in condensed matter physics.Lattice vibrations or phonons of a vdWH provide rich information,such as lattice structure,phonon dispersion,electronic band structure and electron–phonon coupling.Here,we provide a mini review on the lattice vibrations in vdWHs probed by Raman spectroscopy.First,we introduced different kinds of vdWHs,including their structures,properties and potential applications.Second,we discussed interlayer and intralayer phonon in twist multilayer graphene and MoS2.The frequencies of interlayer and intralayer modes can be reproduced by linear chain model(LCM)and phonon folding induced by periodical moiré potentials,respectively.Then,we extended LCM to vdWHs formed by distinct 2D materials,such as MoS2/graphene and hBN/WS2 heterostructures.We further demonstrated how to calculate Raman intensity of interlayer modes in vdWHs by interlayer polarizability model.
文摘1. The transient absorption spectra of the WS2 monolayer sample.In the measurement of the transient absorption spectra of the WS2 monolayer sample, A 400-nm (3.1eV) pump pulse with a peak fluence of about 10μJ/cm2excites the electrons from the valence band into the conduction band,the
基金supported by the National Basic Research Program of China(Grant Nos.2013CB934500 and 2013CBA01602)the National Natural Science Foundation of China(Grant Nos.61325021,11574361,and 51572289)+1 种基金the Key Research Program of Frontier Sciences,CAS,(Grant No.QYZDB-SSW-SLH004)the Strategic Priority Research Program(B),CAS(Grant No.XDB07010100)
文摘Two-dimensional (2D) Van der Waals heterostructures have aroused extensive concerns in recent years. Their fabrica- tion calls for facile and efficient transfer techniques for achieving well-defined structures. In this work, we report a simple and effective dry transfer method to fabricate 2D heterostructures with a clean interface. Using Propylene Carbonate (PC) films as stamps, we are able to pick up various 2D materials flakes from the substrates and unload them to the receiving substrates at an elevated temperature. Various multilayer heterostructures with ultra-clean interfaces were fabricated by this technique. Furthermore, the 2D materials can be pre-pattemed before transfer so as to fabricate desired device structures, demonstrating a facile way to promote the development of 2D heterostructures.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0207500)Natural Science Foundation of Henan Province,China(Grant No.202300410507)Key Research&Development and Promotion Projects in Henan Province,China(Grant No.212102210134).
文摘Exploring two-dimensional(2D)magnetic heterostructures is essential for future spintronic and optoelectronic devices.Herein,using first-principle calculations,stable ferromagnetic ordering and colorful electronic properties are established by constructing the VS_(2)/C_(3)N van der Waals(vdW)heterostructure.Unlike the semiconductive properties with indirect band gaps in both the VS2 and C3N monolayers,our results indicate that a direct band gap with type-Ⅱband alignment and p-doping characters are realized in the spin-up channel of the VS_(2)/C_(3)N heterostructure,and a typical type-Ⅲband alignment with a broken-gap in the spin-down channel.Furthermore,the band alignments in the two spin channels can be effectively tuned by applying tensile strain.An interchangement between the type-Ⅱand type-Ⅲband alignments occurs in the two spin channels,as the tensile strain increases to 4%.The attractive magnetic properties and the unique band alignments could be useful for prospective applications in the next-generation tunneling devices and spintronic devices.
基金support from the Grants (9229079, 9610482,7005468) from City University of Hong KongEarly Career Scheme Project 21302821 from Research Grants Council。
文摘Van der Waals heterostructures(vdWHs) are showing considerable potential in both fundamental exploration and practical applications. Built upon the synthetic successes of(two-dimensional) 2D materials, several synthetic strategies of vdWHs have been developed,allowing the convenient fabrication of diverse vdWHs with decent controllability, quality, and scalability. This review first summarizes the current state of the art in synthetic strategies of vdWHs, including physical combination, deposition, solvothermal synthesis, and synchronous evolution. Then three major applications and their representative vdWH devices have been reviewed, including electronics(tunneling field effect transistors and 2D contact),optoelectronics(photodetector), and energy conversion(electrocatalysts and metal ion batteries), to unveil the potentials of vdWHs in practical applications and provide the general design principles of functional vdWHs for different applications. Besides, moiré superlattices based on vdWHs are discussed to showcase the importance of vdWHs as a platform for novel condensed matter physics. Finally, the crucial challenges towards ideal vdWHs with high performance are discussed, and the outlook for future development is presented. By the systematical integration of synthetic strategies and applications, we hope this review can further light up the rational designs of vdWHs for emerging applications.
基金Project supported by the National Natural Science Fundation of China (Grant Nos. 61731019, 60908012, 61575008, and 61775007)the Beijing Natural Science Foundation (Grant Nos. 4182015 and 4202010)。
文摘With the development of Moore's law, the future trend of devices will inevitably be shrinking and integration to further achieve size reduction. The emergence of new two-dimensional non-layered materials(2DNLMs) not only enriches the 2D material family to meet future development, but also stimulates the global enthusiasm for basic research and application technologies in the 2D field. Van der Waals(vd W) heterostructures, in which two-dimensional layered materials(2DLMs)are physically stacked layer by layer, can also occur between 2DLMs and 2DNLMs hybrid heterostructures, providing an alternative platform for nanoelectronics and optoelectronic applications. Here, we outline the recent developments of2DLMs/2DNLMs hybrid heterostructures, with particular emphasis on major advances in synthetic methods and applications. And the categories and crystal structures of 2DLMs and 2DNLMs are also shown. We highlight some promising applications of the heterostructures in electronics, optoelectronics, and catalysis. Finally, we provide conclusions and future prospects in the 2D materials field.
基金Project supported by the National Natural Science Foundation of China(Grant No.51872039)Science and Technology Program of Sichuan,China(Grant No.M112018JY0025).
文摘Two-dimensional ferromagnetic van der Waals(2D vdW)heterostructures have opened new avenues for creating artificial materials with unprecedented electrical and optical functions beyond the reach of isolated 2D atomic layered materials,and for manipulating spin degree of freedom at the limit of few atomic layers,which empower next-generation spintronic and memory devices.However,to date,the electronic properties of 2D ferromagnetic heterostructures still remain elusive.Here,we report an unambiguous magnetoresistance behavior in CrI_(3)/graphene heterostructures,with a maximum magnetoresistance ratio of 2.8%.The magnetoresistance increases with increasing magnetic field,which leads to decreasing carrier densities through Lorentz force,and decreases with the increase of the bias voltage.This work highlights the feasibilities of applying two-dimensional ferromagnetic vdW heterostructures in spintronic and memory devices.
基金supported by the National Natural Science Foundation of China(Grant Nos.U1832214,11774007,U2032213,and 12104461).
文摘Geometrical frustration in low-dimensional magnetic systems has been an intriguing research aspect,where the suppression of conventional magnetic order may lead to exotic ground states such as spin glass or spin liquid.In this work we report the synthesis and magnetism study of the monocrystalline Mn_(2)Ga_(2)S_(5),featuring both the van derWaals structure and a bilayered triangular Mn lattice.Magnetic susceptibility reveals a significant antiferromagnetic interaction with a Curie-Weiss temperature θ_(w)~-260 K and a high spin S=5/2 Mn^(2+) state.However,no long range magnetic order has been found down to 2 K,and a spin freezing transition is found to occur at around 12 K well below its θ_(w).This yields a frustration index of f=-θ_(w)/T_(f)≈22,an indication that the system is highly frustrated.The absence of a double-peak structure in magnetic specific heat compared with the TM_(2)S_(4) compounds implies that the spin freezing behavior in Mn_(2)Ga_(2)S_(5)is a result of the competition between exchange interactions and the 2D crystalline structure.Our results suggest that the layered Mn_(2)Ga_(2)S_(5)would be an excellent candidate for investigating the physics of 2D magnetism and spin disordered state.
文摘Spintronic devices are driving new paradigms of bio-inspired,energy efficient computation like neuromorphic stochastic computing and in-memory computing.They have also emerged as key candidates for non-volatile memories for embedded systems as well as alternatives to persistent memories.To meet the growing demands from such diverse applications,there is need for innovation in materials and device designs which can be scaled and adapted according to the application.Two-dimensional(2D)magnetic materials address challenges facing bulk magnet systems by offering scalability while maintaining device integrity and allowing efficient control of magnetism.In this review,we highlight the progress made in experimental studies on 2D magnetic materials towards their integration into spintronic devices.We provide an account of the various relevant material discoveries,demonstrations of current and voltage-based control of magnetism and reported device systems,while also discussing the challenges and opportunities towards integration of 2D magnetic materials in commercial spintronic devices.
基金supported by the National Natural Science Foundation of China(Grant Nos.U2001215,52272175)the Natural Science Foundation of Guangdong Province(Grant Nos.2021A1515110403,2022A1515011487)+1 种基金the Science and Technology Projects in Guangzhou(Grant No.202201011232)the One-Hundred Talents Program of Sun Yat-sen University,and State Key Laboratory of Optoelectronic Materials and Technologies.
文摘Detecting light from a wealth of physical degrees of freedom(e.g.wavelength,intensity,polarization state,phase,etc)enables the acquirement of more comprehensive information.In the past two decades,low-dimensional van der Waals materials(vdWMs)have established themselves as transformative building blocks toward lensless polarization optoelectronics,which is highly beneficial for optoelectronic system miniaturization.This review provides a comprehensive overview on the recent development of low-dimensional vdWM polarized photodetectors.To begin with,the exploitation of pristine 1D/2D vdWMs with immanent in-plane anisotropy and related heterostructures for filterless polarization-sensitive photodetectors is introduced.Then,we have systematically epitomized the various strategies to induce polarization photosensitivity and enhance the degree of anisotropy for low-dimensional vdWM photodetectors,including quantum tailoring,construction of core–shell structures,rolling engineering,ferroelectric regulation,strain engineering,etc,with emphasis on the fundamental physical principles.Following that,the ingenious optoelectronic applications based on the low-dimensional vdWM polarized photodetectors,including multiplexing optical communications and enhanced-contrast imaging,have been presented.In the end,the current challenges along with the future prospects of this burgeoning research field have been underscored.On the whole,the review depicts a fascinating landscape for the next-generation high-integration multifunctional optoelectronic systems.
基金supported through the German Research Foundation within the project “Straintronics of imperfect quasi-two-dimensional materials: coplanar vs lamellar heterostructures” (CU 44/43).
文摘Chemical modification and vertical stacking of two-dimensional materials are promising techniques for new nanoelectronic devices. We present Density Functional Tight Binding(DFTB) calculations of a field-effect device,based on lateral and vertical heterostructures of 2D materials. The device consists of a phosphorene channel protected by graphene sheets, which work as contacts and are divided into the source and drain by local hydrogenation of graphene, which gives insulating graphane. In this device composed of only 3 layers, single sheets of graphene-graphane can work as both leads and oxide gate, while also acting as protective layers for a phosphorene channel. We show how for perfect vd W heterostructures of graphane/phosphorene/graphane and graphene/phosphorene/graphene the Schottky barrier is deeply influenced by normal electric fields, and we characterize electronic transport of such a device. Finally, we characterize phosphorene channel doping and defects, which, at very high densities in the transport direction, enables transport inside the phosphorene bandgap.
基金Project supported by the State Key Program of the National Natural Science Foundation of China(Grant No.61734008)the National Natural Science Foundation of China(Grant No.62174173)。
文摘Ⅲ-nitride semiconductor materials have excellent optoelectronic properties,mechanical properties,and chemical stability,which have important applications in the field of optoelectronics and microelectronics.Two-dimensional(2D)materials have been widely focused in recent years due to their peculiar properties.With the property of weak bonding between layers of 2D materials,the growth ofⅢ-nitrides on 2D materials has been proposed to solve the mismatch problem caused by heterogeneous epitaxy and to develop substrate stripping techniques to obtain high-quality,low-cost nitride materials for high-quality nitride devices and their extension in the field of flexible devices.In this progress report,the main methods for the preparation of 2D materials,and the recent progress and applications of different techniques for the growth ofⅢ-nitrides based on 2D materials are reviewed.
基金The work was supported by the National Key R&D Program of China(2019YFA0708200)the National Natural Science Foundation of China(T2188101,52125307,52021006 and 12074369)+1 种基金the“2011 Program”from the Peking-Tsinghua-IOP Collaborative Innovation Center of Quantum Matter,Youth Innovation Promotion Association,CASthe Youth Supporting Program of Institute of Semiconductors.
文摘Heteroepitaxy can reduce the cost and widen the application range of semiconductor film synthesis and device fabrication.However,the lattice and thermal expansion coefficient mismatches between epilayers and substrates limit the improvement of crystal quality and device performance.Two-dimensional(2D)material-assisted heteroepitaxy offers an effective solution to these challenges.The weak interaction at the interface between films and substrates facilitates the subsequent exfoliation and transfer of epilayer for the fabrication of flexible or high-power electronics.Herein,we summarize the modes of 2D material-assisted epitaxy,which can be classified into remote epitaxy,pinhole epitaxy and van der Waals epitaxy based on the interfacial interaction between the epilayers and substrates.Furthermore,we discuss in detail the improved crystal quality and functional applications,such as flexible devices,wavelength-modulated optoelectronic devices,and thermal management in high-power devices.Moreover,we highlight the challenges and prospects of 2D material-assisted epitaxy,providing roadmaps for lateral research and semiconductor production.