Two-dimensional(2D)transition-metal dichalcogenide(TMD)materials have aroused noticeable interest due to their distinguished electronic and optical properties.However,little is known about their complex exciton proper...Two-dimensional(2D)transition-metal dichalcogenide(TMD)materials have aroused noticeable interest due to their distinguished electronic and optical properties.However,little is known about their complex exciton properties together with the exciton dynamics process which have been expected to influence the performance of optoelectronic devices.The process of fluorescence can well reveal the process of exciton transition after excitation.In this work,the room-temperature layer-dependent exciton dynamics properties in layered WSe2 are investigated by the fluorescence lifetime imaging microscopy(FLIM)for the first time.This paper focuses on two mainly kinds of excitons including the direct transition neutral excitons and trions.Compared with the lifetime of neutral excitons(<0.3 ns within four-layer),trions possess a longer lifetime(~6.6 ns within four-layer)which increases with the number of layers.We attribute the longer-lived lifetime to the increasing number of trions as well as the varieties of trion configurations in thicker WSe2.Besides,the whole average lifetime increases over 10%when WSe2 flakes added up from monolayer to four-layer.This paper provides a novel tuneable layer-dependent method to control the exciton dynamics process and finds a relatively longer transition lifetime of trions at room temperature,enabling to investigate in the charge transport in TMD-based optoelectronics devices in the future.展开更多
Two-dimensional(2D)heterostructures based on the combination of transition metal dichalcogenides(TMDs)and transition metal oxides(TMOs)have aroused growing attention due to their integrated merits of both components a...Two-dimensional(2D)heterostructures based on the combination of transition metal dichalcogenides(TMDs)and transition metal oxides(TMOs)have aroused growing attention due to their integrated merits of both components and multiple functionalities.However,nondestructive approaches of constructing TMD-TMO heterostructures are still very limited.Here,we develop a novel type of lateral TMD-TMO heterostructure(NbS2-Nb2O5-NbS2)using a simple lithography-free,direct laser-patterning technique.The perfect contact of an ultrathin TMO channel(Nb2O5)with two metallic TMDs(NbS2)electrodes guarantee strong electrical signals in a two-terminal sensor.Distinct from sensing mechanisms in separate TMOs or TMDs,this sensor works based on the modulation of surface conduction of the ultrathin TMO(Nb2O5)channel through an adsorbed layer of water molecules.The sensor thus exhibits high selectivity and ultrahigh sensitivity for room-temperature detection of NH3(ΔR/R=80%at 50 ppm),superior to the reported NH3 sensors based on 2D materials,and a positive temperature coefficient of resistance as high as 15%–20%/℃.Bending-invariant performance and high reliability are also demonstrated in flexible versions of sensors.Our work provides a new strategy of lithography-free processing of novel TMD-TMO heterostructures towards high-performance sensors,showing great potential in the applications of future portable and wearable electronics.展开更多
基金This work is supported by the National Natural Science Foundation of China(Nos.51527901,51575298,51705285,and 11890672)And we are grateful to Tsinghua-Nikon Imaging Core Facility for providing technical support and to Yanli Zhang for assistance with confocal microscopy and image processing.
文摘Two-dimensional(2D)transition-metal dichalcogenide(TMD)materials have aroused noticeable interest due to their distinguished electronic and optical properties.However,little is known about their complex exciton properties together with the exciton dynamics process which have been expected to influence the performance of optoelectronic devices.The process of fluorescence can well reveal the process of exciton transition after excitation.In this work,the room-temperature layer-dependent exciton dynamics properties in layered WSe2 are investigated by the fluorescence lifetime imaging microscopy(FLIM)for the first time.This paper focuses on two mainly kinds of excitons including the direct transition neutral excitons and trions.Compared with the lifetime of neutral excitons(<0.3 ns within four-layer),trions possess a longer lifetime(~6.6 ns within four-layer)which increases with the number of layers.We attribute the longer-lived lifetime to the increasing number of trions as well as the varieties of trion configurations in thicker WSe2.Besides,the whole average lifetime increases over 10%when WSe2 flakes added up from monolayer to four-layer.This paper provides a novel tuneable layer-dependent method to control the exciton dynamics process and finds a relatively longer transition lifetime of trions at room temperature,enabling to investigate in the charge transport in TMD-based optoelectronics devices in the future.
基金This work was financially supported by Basic Science Center Project of the National Natural Science Foundation of China(NSFC)(No.51788104)the National Key R&D Program of China(No.2018YFA0208400)+1 种基金the National Natural Science Foundation of China(Nos.51972193 and 11774191)Fok Ying-Tong Education Foundation(No.161042)。
文摘Two-dimensional(2D)heterostructures based on the combination of transition metal dichalcogenides(TMDs)and transition metal oxides(TMOs)have aroused growing attention due to their integrated merits of both components and multiple functionalities.However,nondestructive approaches of constructing TMD-TMO heterostructures are still very limited.Here,we develop a novel type of lateral TMD-TMO heterostructure(NbS2-Nb2O5-NbS2)using a simple lithography-free,direct laser-patterning technique.The perfect contact of an ultrathin TMO channel(Nb2O5)with two metallic TMDs(NbS2)electrodes guarantee strong electrical signals in a two-terminal sensor.Distinct from sensing mechanisms in separate TMOs or TMDs,this sensor works based on the modulation of surface conduction of the ultrathin TMO(Nb2O5)channel through an adsorbed layer of water molecules.The sensor thus exhibits high selectivity and ultrahigh sensitivity for room-temperature detection of NH3(ΔR/R=80%at 50 ppm),superior to the reported NH3 sensors based on 2D materials,and a positive temperature coefficient of resistance as high as 15%–20%/℃.Bending-invariant performance and high reliability are also demonstrated in flexible versions of sensors.Our work provides a new strategy of lithography-free processing of novel TMD-TMO heterostructures towards high-performance sensors,showing great potential in the applications of future portable and wearable electronics.