Twist-angle two-dimensional systems,such as twisted bilayer graphene,twisted bilayer transition metal dichalcogenides,twisted bilayer phosphorene and their multilayer van der Waals heterostructures,exhibit novel and t...Twist-angle two-dimensional systems,such as twisted bilayer graphene,twisted bilayer transition metal dichalcogenides,twisted bilayer phosphorene and their multilayer van der Waals heterostructures,exhibit novel and tunable properties due to the formation of Moirésuperlattice and modulated Moirébands.The review presents a brief venation on the development of"twistronics"and subsequent applications based on band engineering by twisting.Theoretical predictions followed by experimental realization of magic-angle bilayer graphene ignited the flame of investigation on the new freedom degree,twistangle,to adjust(opto)electrical behaviors.Then,the merging of Dirac cones and the presence of flat bands gave rise to enhanced light-matter interaction and gate-dependent electrical phases,respectively,leading to applications in photodetectors and superconductor electronic devices.At the same time,the increasing amount of theoretical simulation on extended twisted 2D materials like TMDs and BPs called for further experimental verification.Finally,recently discovered properties in twisted bilayer h-BN evidenced h-BN could be an ideal candidate for dielectric and ferroelectric devices.Hence,both the predictions and confirmed properties imply twist-angle two-dimensional superlattice is a group of promising candidates for next-generation(opto)electronics.展开更多
Recent studies in van der Waals coupled two-dimensional(2D) bilayer materials have demonstrated a new freedom for material engineering by the formation of moiré pattern. By tuning the twist angle between two laye...Recent studies in van der Waals coupled two-dimensional(2D) bilayer materials have demonstrated a new freedom for material engineering by the formation of moiré pattern. By tuning the twist angle between two layers, one can modulate their electronic band structures and therefore the associated electrical transport and optical properties, which are distinct from the original ones of each individual layer. These new properties excite great passion in the exploration of new quantum states and possible applications of 2D bilayers. In this article, we will mainly review the prevailing fabrication methods and emerging physical properties of twisted bilayer materials and lastly give out a perspective of this topic.展开更多
Chiral perovskites(CPs)have attracted enormous attentions since they have combined chirality and optoelectrical properties well which is promising in circularly polarized luminescence(CPL)application and of great impo...Chiral perovskites(CPs)have attracted enormous attentions since they have combined chirality and optoelectrical properties well which is promising in circularly polarized luminescence(CPL)application and of great importance for future spin-optoelectronics.However,there is a key contradiction that in chiral perovskites chirality distorts the crystal structure,leading to poor photoluminescence(PL)properties.Achieving the balance between chirality and PL is a major challenge for strong CPL from chiral perovskites.Differently,two-dimensional(2D)chiral perovskite has shown fascinating chiral induced spin selectivity(CISS)effect which can act as spin injector under ambient conditions.Here,we propose an effective strategy to achieve high CPL activity generated from quantum dots(QDs)by introducing 2D chiral perovskite as a chiral source,providing spin polarized carriers through the CISS effect.The as-synthesized QDs/CP composites exhibit dissymmetry factors(glum)up to 9.06×10^(−3).For the first time,we performed grazing incident wide angle X-ray scattering(GIWAXS)measurements,showing the chirality originates from the distorted lattices caused by the large chiral organic cations.Besides,time-resolved PL(TR-PL)measurements verify the enhanced CPL activity should be attributed to the charge transport between two components.These findings provide a useful method to achieve CPL in QDs/2D chiral perovskite heterojunctions which could be promising in spinoptoelectronics application.展开更多
Based on fourth-order cumulant and ESPRIT algorithm, a novel joint frequency, two-dimensional angle of arrival (2D AOA) and the polarization estimation method of incoming multiple independent spatial narrow-band non-G...Based on fourth-order cumulant and ESPRIT algorithm, a novel joint frequency, two-dimensional angle of arrival (2D AOA) and the polarization estimation method of incoming multiple independent spatial narrow-band non-Gaussian signals in arbitrary Gaussian noise environment are proposed . The array is composed of crossed dipoles parallel to the coordinate axes. The crossed dipole positions are arbitrarily distributed. Computer simulation confirms its feasibility.展开更多
Based on nonuniformly spaced L-shape array, a novel algorithm using ESPRIT and inte-ger search is proposed to estimate the frequency, two-dimensional angles of arrival (2-D AOA) and polarizations of incoming multiple ...Based on nonuniformly spaced L-shape array, a novel algorithm using ESPRIT and inte-ger search is proposed to estimate the frequency, two-dimensional angles of arrival (2-D AOA) and polarizations of incoming multiple independent spatial narrow-band signals. The L-shape array is com-posed of crossed dipoles that are paralleled to the coordinate axis. Computer simulation confirms its availability.展开更多
The twist angle between two van der Waals coupled monolayers has emerged as a new and powerful degree of freedom for engineering physical properties of semiconductor homo-and hetero-bilayers.While the interlayer twist...The twist angle between two van der Waals coupled monolayers has emerged as a new and powerful degree of freedom for engineering physical properties of semiconductor homo-and hetero-bilayers.While the interlayer twist has shown prominent effect on electronic and optical properties of transition metal dichalcogenide(TMD)bilayers,it remains unclear how it could be used to manipulate the exciton dynamics,especially exciton-exciton annihilation(EEA)process which is the dominant energy loss channel in TMDs under moderate to high exciton density due to strong Coulomb interaction.Herein,we show that the twist angle in TMD bilayers can act as an effective knob to control the EEA process.Specifically,EEA rate constant increases from 1° twisted WSe_(2) bilayers(0.026 cm^(2)/s)by more than twice to 32° twisted bilayers(0.053 cm2/s)and then drops again in 60° twisted bilayers(0.019 cm^(2)/s).This twist-angle dependence can be attributed to the energy difference between indirect and direct excitons arising from the interlayer interaction.Our work opens up the possibility of artificially managing the exciton dynamics in TMD materials for optoelectronic applications via interlayer twist angle.展开更多
基金financially supported by the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB43000000)the CAS-JSPS Cooperative Research Project(No.GJHZ2021131)。
文摘Twist-angle two-dimensional systems,such as twisted bilayer graphene,twisted bilayer transition metal dichalcogenides,twisted bilayer phosphorene and their multilayer van der Waals heterostructures,exhibit novel and tunable properties due to the formation of Moirésuperlattice and modulated Moirébands.The review presents a brief venation on the development of"twistronics"and subsequent applications based on band engineering by twisting.Theoretical predictions followed by experimental realization of magic-angle bilayer graphene ignited the flame of investigation on the new freedom degree,twistangle,to adjust(opto)electrical behaviors.Then,the merging of Dirac cones and the presence of flat bands gave rise to enhanced light-matter interaction and gate-dependent electrical phases,respectively,leading to applications in photodetectors and superconductor electronic devices.At the same time,the increasing amount of theoretical simulation on extended twisted 2D materials like TMDs and BPs called for further experimental verification.Finally,recently discovered properties in twisted bilayer h-BN evidenced h-BN could be an ideal candidate for dielectric and ferroelectric devices.Hence,both the predictions and confirmed properties imply twist-angle two-dimensional superlattice is a group of promising candidates for next-generation(opto)electronics.
基金Project supported by the National Key R&D Program of China(Grant Nos.2016YFA0300903 and 2016YFA0300804)National Equipment Program of China(Grant No.ZDYZ2015-1)+3 种基金Beijing Graphene Innovation Program,China(Grant No.Z181100004818003)Beijing Municipal Science&Technology Commission,China(Grant No.Z181100004218006)Bureau of Industry and Information Technology of Shenzhen,China(Graphene platform contract No.201901161512)the Key R&D Program of Guangdong Province,China(Grant No.2019B010931001)
文摘Recent studies in van der Waals coupled two-dimensional(2D) bilayer materials have demonstrated a new freedom for material engineering by the formation of moiré pattern. By tuning the twist angle between two layers, one can modulate their electronic band structures and therefore the associated electrical transport and optical properties, which are distinct from the original ones of each individual layer. These new properties excite great passion in the exploration of new quantum states and possible applications of 2D bilayers. In this article, we will mainly review the prevailing fabrication methods and emerging physical properties of twisted bilayer materials and lastly give out a perspective of this topic.
基金Guangdong Basic and Applied Basic Research Foundation(Nos.2022A1515011071,2019A1515111093,and 2022A1515011614)the National Natural Science Foundation of China(Nos.62122034,61875082,61905107,62204107,and 62205138)+2 种基金Innovation Project of Department of Education of Guangdong Province(No.2019KTSCX157)Shenzhen Innovation Project(Nos.JCYJ20210324104413036 and JCYJ20190809152411655)Q.Q.W.and H.M.Z.acknowledge the support from China Postdoctoral Science Foundation(Nos.2021M691397 and 2021M691411).
文摘Chiral perovskites(CPs)have attracted enormous attentions since they have combined chirality and optoelectrical properties well which is promising in circularly polarized luminescence(CPL)application and of great importance for future spin-optoelectronics.However,there is a key contradiction that in chiral perovskites chirality distorts the crystal structure,leading to poor photoluminescence(PL)properties.Achieving the balance between chirality and PL is a major challenge for strong CPL from chiral perovskites.Differently,two-dimensional(2D)chiral perovskite has shown fascinating chiral induced spin selectivity(CISS)effect which can act as spin injector under ambient conditions.Here,we propose an effective strategy to achieve high CPL activity generated from quantum dots(QDs)by introducing 2D chiral perovskite as a chiral source,providing spin polarized carriers through the CISS effect.The as-synthesized QDs/CP composites exhibit dissymmetry factors(glum)up to 9.06×10^(−3).For the first time,we performed grazing incident wide angle X-ray scattering(GIWAXS)measurements,showing the chirality originates from the distorted lattices caused by the large chiral organic cations.Besides,time-resolved PL(TR-PL)measurements verify the enhanced CPL activity should be attributed to the charge transport between two components.These findings provide a useful method to achieve CPL in QDs/2D chiral perovskite heterojunctions which could be promising in spinoptoelectronics application.
文摘Based on fourth-order cumulant and ESPRIT algorithm, a novel joint frequency, two-dimensional angle of arrival (2D AOA) and the polarization estimation method of incoming multiple independent spatial narrow-band non-Gaussian signals in arbitrary Gaussian noise environment are proposed . The array is composed of crossed dipoles parallel to the coordinate axes. The crossed dipole positions are arbitrarily distributed. Computer simulation confirms its feasibility.
基金This work was supported by China Academy of Electronics & Information Technology ( Grant No. 28.5.3.3.).
文摘Based on nonuniformly spaced L-shape array, a novel algorithm using ESPRIT and inte-ger search is proposed to estimate the frequency, two-dimensional angles of arrival (2-D AOA) and polarizations of incoming multiple independent spatial narrow-band signals. The L-shape array is com-posed of crossed dipoles that are paralleled to the coordinate axis. Computer simulation confirms its availability.
基金We thank the financial support from the National Natural Science Foundation of China(Nos.22022305,21773208,21922305,and 21873080)the Fundamental Research Funds for the Central Universities(No.2020XZZX002-06)National Key Research and Development Program of China(No.2017YFA0207700).
文摘The twist angle between two van der Waals coupled monolayers has emerged as a new and powerful degree of freedom for engineering physical properties of semiconductor homo-and hetero-bilayers.While the interlayer twist has shown prominent effect on electronic and optical properties of transition metal dichalcogenide(TMD)bilayers,it remains unclear how it could be used to manipulate the exciton dynamics,especially exciton-exciton annihilation(EEA)process which is the dominant energy loss channel in TMDs under moderate to high exciton density due to strong Coulomb interaction.Herein,we show that the twist angle in TMD bilayers can act as an effective knob to control the EEA process.Specifically,EEA rate constant increases from 1° twisted WSe_(2) bilayers(0.026 cm^(2)/s)by more than twice to 32° twisted bilayers(0.053 cm2/s)and then drops again in 60° twisted bilayers(0.019 cm^(2)/s).This twist-angle dependence can be attributed to the energy difference between indirect and direct excitons arising from the interlayer interaction.Our work opens up the possibility of artificially managing the exciton dynamics in TMD materials for optoelectronic applications via interlayer twist angle.