Two-dimensional(2D)transition metal dichalcogenide(TMDC)monolayers,a class of ultrathin materials with a direct bandgap and high exciton binding energies,provide an ideal platform to study the photoluminescence(PL)of ...Two-dimensional(2D)transition metal dichalcogenide(TMDC)monolayers,a class of ultrathin materials with a direct bandgap and high exciton binding energies,provide an ideal platform to study the photoluminescence(PL)of light-emitting devices.Atomically thin TMDCs usually contain various defects,which enrich the lattice structure and give rise to many intriguing properties.As the influences of defects can be either detrimental or beneficial,a comprehensive understanding of the internal mechanisms underlying defect behaviour is required for PL tailoring.Herein,recent advances in the defect influences on PL emission are summarized and discussed.Fundamental mechanisms are the focus of this review,such as radiative/nonradiative recombination kinetics and band structure modification.Both challenges and opportunities are present in the field of defect manipulation,and the exploration of mechanisms is expected tofacilitate the applications of 2D TMDCs in the future.展开更多
Transition metal dichalcogenides(TMDCs)have suitable and adjustable band gaps,high carrier mobility and yield.Layered TMDCs have attracted great attention due to the structure diversity,stable existence in normal temp...Transition metal dichalcogenides(TMDCs)have suitable and adjustable band gaps,high carrier mobility and yield.Layered TMDCs have attracted great attention due to the structure diversity,stable existence in normal temperature environment and the band gap corresponding to wavelength between infrared and visible region.The ultra-thin,flat,almost defect-free surface,excellent mechanical flexibility and chemical stability provide convenient conditions for the construction of different types of TMDCs heterojunctions.The optoelectric properties of heterojunctions based on TMDCs materials are summarized in this review.Special electronic band structures of TMDCs heterojunctions lead to excellent optoelectric properties.The emitter,p-n diodes,photodetectors and photosensitive devices based on TMDCs heterojunction materials show excellent performance.These devices provide a prototype for the design and development of future high-performance optoelectric devices.展开更多
Two-dimensional(2D) materials have attracted extensive interest due to their excellent electrical, thermal,mechanical, and optical properties. Graphene has been one of the most explored 2D materials. However, its zero...Two-dimensional(2D) materials have attracted extensive interest due to their excellent electrical, thermal,mechanical, and optical properties. Graphene has been one of the most explored 2D materials. However, its zero band gap has limited its applications in electronic devices. Transition metal dichalcogenide(TMDC), another kind of 2D material,has a nonzero direct band gap(same charge carrier momentum in valence and conduction band) at monolayer state,promising for the efficient switching devices(e.g., field-effect transistors). This review mainly focuses on the recent advances in charge carrier mobility and the challenges to achieve high mobility in the electronic devices based on 2DTMDC materials and also includes an introduction of 2D materials along with the synthesis techniques. Finally, this review describes the possible methodology and future prospective to enhance the charge carrier mobility for electronic devices.展开更多
Spintronics,exploiting the spin degree of electrons as the information vector,is an attractive field for implementing the beyond Complemetary metal-oxide-semiconductor(CMOS)devices.Recently,two-dimensional(2D)material...Spintronics,exploiting the spin degree of electrons as the information vector,is an attractive field for implementing the beyond Complemetary metal-oxide-semiconductor(CMOS)devices.Recently,two-dimensional(2D)materials have been drawing tremendous attention in spintronics owing to their distinctive spin-dependent properties,such as the ultralong spin relaxation time of graphene and the spin-valley locking of transition metal dichalcogenides.Moreover,the related heterostructures provide an unprecedented probability of combining the di erent characteristics via proximity e ect,which could remedy the limitation of individual 2D materials.Hence,the proximity engineering has been growing extremely fast and has made significant achievements in the spin injection and manipulation.Nevertheless,there are still challenges toward practical application;for example,the mechanism of spin relaxation in 2D materials is unclear,and the high-effciency spin gating is not yet achieved.In this review,we focus on 2D materials and related heterostructures to systematically summarize the progress of the spin injection,transport,manipulation,and application for information storage and processing.We also highlight the current challenges and future perspectives on the studies of spintronic devices based on 2D materials.展开更多
Atomically thin transition metal dichalcogenide films with distorted trigonal(1T') phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1T' film and experimental investi...Atomically thin transition metal dichalcogenide films with distorted trigonal(1T') phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1T' film and experimental investigation of its electronic structure are critical. Here we report the electronic structure of 1T'-MoTe2 films grown by molecular beam epitaxy(MBE).Growth of the 1T'-MoTe2 film depends critically on the substrate temperature, and successful growth of the film is indicated by streaky stripes in the reflection high energy electron diffraction(RHEED) and sharp diffraction spots in the low energy electron diffraction(LEED). Angle-resolved photoemission spectroscopy(ARPES) measurements reveal a metallic behavior in the as-grown film with an overlap between the conduction and valence bands. First principles calculation suggests that a suitable tensile strain along the a-axis direction is needed to induce a gap to make it an insulator. Our work not only reports the electronic structure of MBE grown 1T'-MoTe2 films, but also provides insights for strain engineering to make it possible for quantum spin Hall effect.展开更多
Monolayer transition-metal dichacolgenides (TMDCs) present a direct optical bandgap at the Brillouin zones, socalled valleys. Those energetically degenerate valleys (K and K’) present different valley pseudospins, em...Monolayer transition-metal dichacolgenides (TMDCs) present a direct optical bandgap at the Brillouin zones, socalled valleys. Those energetically degenerate valleys (K and K’) present different valley pseudospins, emitting the valley photons with opposite spin angular momentums due to nonlinear optical selection rules. Furthermore, although atomically thin, two-dimensional (2D) TMDCs have giant nonlinearity, which can be enhanced by the valley-excitons.展开更多
Monolayer transition-metal dichalcogenides possess rich excitonic physics and unique valley-contrasting optical selection rule,and offer a great platform for long spin/valley lifetime engineering and the associated sp...Monolayer transition-metal dichalcogenides possess rich excitonic physics and unique valley-contrasting optical selection rule,and offer a great platform for long spin/valley lifetime engineering and the associated spin/valleytronics exploration.Using two-color time-resolved Kerr rotation and time-resolved reflectivity spectroscopy,we investigate the spin/valley dynamics of different excitonic states in monolayer WSe_(2)grown by molecular beam epitaxy.With fine tuning of the photon energy of both pump and probe beams,the valley relaxation process for the neutral excitons and trions is found to be remarkably different-their characteristic spin/valley lifetimes vary from picoseconds to nanoseconds,respectively.The observed long trion spin lifetime of>2.0 ns is discussed to be associated with the dark trion states,which is evidenced by the photon-energy dependent valley polarization relaxation.Our results also reveal that valley depolarization for these different excitonic states is intimately connected with the strong Coulomb interaction when the optical excitation energy is above the exciton resonance.展开更多
Photonic topological insulators with robust boundary states can enable great applications for optical communication and quantum emission,such as unidirectional waveguide and single-mode laser.However,because of the di...Photonic topological insulators with robust boundary states can enable great applications for optical communication and quantum emission,such as unidirectional waveguide and single-mode laser.However,because of the diffraction limit of light,the physical insight of topological resonance remains unexplored in detail,like the dark line that exists with the crys-talline symmetry-protected topological edge state.Here,we experimentally observe the dark line of the Z_(2)photonic topo-logical insulator in the visible range by photoluminescence and specify its location by cathodoluminescence characteriza-tion,and elucidate its mechanism with the p-d orbital electromagnetic field distribution which calculated by numerical sim-ulation.Our investigation provides a deeper understanding of Z_(2)topological edge states and may have great signific-ance to the design of future on-chip topological devices.展开更多
基金the National Key R&D Program of China(Nos.2017YFA 0205700,2019YFA 0308000)the National Natural Science Foundation of China(NSFC)(Nos.61774034,91963130,11704068,61705106)Jiangsu Natural Science Foundation(No.BK20170694).The project is supported by"the Fundamental Research Funds for the Central Universities"。
文摘Two-dimensional(2D)transition metal dichalcogenide(TMDC)monolayers,a class of ultrathin materials with a direct bandgap and high exciton binding energies,provide an ideal platform to study the photoluminescence(PL)of light-emitting devices.Atomically thin TMDCs usually contain various defects,which enrich the lattice structure and give rise to many intriguing properties.As the influences of defects can be either detrimental or beneficial,a comprehensive understanding of the internal mechanisms underlying defect behaviour is required for PL tailoring.Herein,recent advances in the defect influences on PL emission are summarized and discussed.Fundamental mechanisms are the focus of this review,such as radiative/nonradiative recombination kinetics and band structure modification.Both challenges and opportunities are present in the field of defect manipulation,and the exploration of mechanisms is expected tofacilitate the applications of 2D TMDCs in the future.
基金supported by the National Natural Science Foundation of China(Grant Nos.91436102 and 11374353)and the Fundamental Research Funds for the Central Universities(Grant No.06500067).
文摘Transition metal dichalcogenides(TMDCs)have suitable and adjustable band gaps,high carrier mobility and yield.Layered TMDCs have attracted great attention due to the structure diversity,stable existence in normal temperature environment and the band gap corresponding to wavelength between infrared and visible region.The ultra-thin,flat,almost defect-free surface,excellent mechanical flexibility and chemical stability provide convenient conditions for the construction of different types of TMDCs heterojunctions.The optoelectric properties of heterojunctions based on TMDCs materials are summarized in this review.Special electronic band structures of TMDCs heterojunctions lead to excellent optoelectric properties.The emitter,p-n diodes,photodetectors and photosensitive devices based on TMDCs heterojunction materials show excellent performance.These devices provide a prototype for the design and development of future high-performance optoelectric devices.
基金funded by Australian Research Council discovery project DP140103041Future Fellowship FT160100205
文摘Two-dimensional(2D) materials have attracted extensive interest due to their excellent electrical, thermal,mechanical, and optical properties. Graphene has been one of the most explored 2D materials. However, its zero band gap has limited its applications in electronic devices. Transition metal dichalcogenide(TMDC), another kind of 2D material,has a nonzero direct band gap(same charge carrier momentum in valence and conduction band) at monolayer state,promising for the efficient switching devices(e.g., field-effect transistors). This review mainly focuses on the recent advances in charge carrier mobility and the challenges to achieve high mobility in the electronic devices based on 2DTMDC materials and also includes an introduction of 2D materials along with the synthesis techniques. Finally, this review describes the possible methodology and future prospective to enhance the charge carrier mobility for electronic devices.
基金partially supported by the National Natural Science Foundation of China(Grant No.61775241)the Youth Innovation Team(Grant No:2019012)of CSU+3 种基金the Hunan province key research and development project(Grant No:2019GK2233)Hunan Province Graduate Research and Innovation Project(Grant No:CX20190177)the Science and Technology Innovation Basic Research Project of Shenzhen(Grant No.JCYJ20180307151237242)the funding support from the Australian Research Council(ARC Discovery Project,DP180102976).
文摘Spintronics,exploiting the spin degree of electrons as the information vector,is an attractive field for implementing the beyond Complemetary metal-oxide-semiconductor(CMOS)devices.Recently,two-dimensional(2D)materials have been drawing tremendous attention in spintronics owing to their distinctive spin-dependent properties,such as the ultralong spin relaxation time of graphene and the spin-valley locking of transition metal dichalcogenides.Moreover,the related heterostructures provide an unprecedented probability of combining the di erent characteristics via proximity e ect,which could remedy the limitation of individual 2D materials.Hence,the proximity engineering has been growing extremely fast and has made significant achievements in the spin injection and manipulation.Nevertheless,there are still challenges toward practical application;for example,the mechanism of spin relaxation in 2D materials is unclear,and the high-effciency spin gating is not yet achieved.In this review,we focus on 2D materials and related heterostructures to systematically summarize the progress of the spin injection,transport,manipulation,and application for information storage and processing.We also highlight the current challenges and future perspectives on the studies of spintronic devices based on 2D materials.
基金Project supported by the National Basic Research Program of China(Grant Nos.2016YFA0301004 and 2015CB921001)the National Natural Science Foundation of China(Grant Nos.11334006,11725418,and 11674188)
文摘Atomically thin transition metal dichalcogenide films with distorted trigonal(1T') phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1T' film and experimental investigation of its electronic structure are critical. Here we report the electronic structure of 1T'-MoTe2 films grown by molecular beam epitaxy(MBE).Growth of the 1T'-MoTe2 film depends critically on the substrate temperature, and successful growth of the film is indicated by streaky stripes in the reflection high energy electron diffraction(RHEED) and sharp diffraction spots in the low energy electron diffraction(LEED). Angle-resolved photoemission spectroscopy(ARPES) measurements reveal a metallic behavior in the as-grown film with an overlap between the conduction and valence bands. First principles calculation suggests that a suitable tensile strain along the a-axis direction is needed to induce a gap to make it an insulator. Our work not only reports the electronic structure of MBE grown 1T'-MoTe2 films, but also provides insights for strain engineering to make it possible for quantum spin Hall effect.
文摘Monolayer transition-metal dichacolgenides (TMDCs) present a direct optical bandgap at the Brillouin zones, socalled valleys. Those energetically degenerate valleys (K and K’) present different valley pseudospins, emitting the valley photons with opposite spin angular momentums due to nonlinear optical selection rules. Furthermore, although atomically thin, two-dimensional (2D) TMDCs have giant nonlinearity, which can be enhanced by the valley-excitons.
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB43000000).
文摘Monolayer transition-metal dichalcogenides possess rich excitonic physics and unique valley-contrasting optical selection rule,and offer a great platform for long spin/valley lifetime engineering and the associated spin/valleytronics exploration.Using two-color time-resolved Kerr rotation and time-resolved reflectivity spectroscopy,we investigate the spin/valley dynamics of different excitonic states in monolayer WSe_(2)grown by molecular beam epitaxy.With fine tuning of the photon energy of both pump and probe beams,the valley relaxation process for the neutral excitons and trions is found to be remarkably different-their characteristic spin/valley lifetimes vary from picoseconds to nanoseconds,respectively.The observed long trion spin lifetime of>2.0 ns is discussed to be associated with the dark trion states,which is evidenced by the photon-energy dependent valley polarization relaxation.Our results also reveal that valley depolarization for these different excitonic states is intimately connected with the strong Coulomb interaction when the optical excitation energy is above the exciton resonance.
基金supported by the National Key Research and Development Program of China (grant no.2017YFA0206000)Beijing Natural Science Foundation (grant nos. Z180011)+3 种基金the National Key Research and Development Program of China (grant nos. 2020YFA0211300, 2017YFA0205700, 2019YFA0210203,2018YFA0306200)National Science Foundation of China (grant nos. 12027807, 61521004, 21790364 and 11625418)PKUBaidu Fund Project (grant no.2020BD023)High-performance Computing Platform of Peking University
文摘Photonic topological insulators with robust boundary states can enable great applications for optical communication and quantum emission,such as unidirectional waveguide and single-mode laser.However,because of the diffraction limit of light,the physical insight of topological resonance remains unexplored in detail,like the dark line that exists with the crys-talline symmetry-protected topological edge state.Here,we experimentally observe the dark line of the Z_(2)photonic topo-logical insulator in the visible range by photoluminescence and specify its location by cathodoluminescence characteriza-tion,and elucidate its mechanism with the p-d orbital electromagnetic field distribution which calculated by numerical sim-ulation.Our investigation provides a deeper understanding of Z_(2)topological edge states and may have great signific-ance to the design of future on-chip topological devices.
