Lateral two-dimensional(2D) heterostructures have opened up unprecedented opportunities in modern electronic device and material science. In this work, electronic properties of size-dependent MoTe2/WTe2 lateral hetero...Lateral two-dimensional(2D) heterostructures have opened up unprecedented opportunities in modern electronic device and material science. In this work, electronic properties of size-dependent MoTe2/WTe2 lateral heterostructures(LHSs)are investigated through the first-principles density functional calculations. The constructed periodic multi-interfaces patterns can also be defined as superlattice structures. Consequently, the direct band gap character remains in all considered LHSs without any external modulation, while the gap size changes within little difference range with the building blocks increasing due to the perfect lattice matching. The location of the conduction band minimum(CBM) and the valence band maximum(VBM) will change from P-point to Γ-point when m plus n is a multiple of 3 for A-mn LHSs as a result of Brillouin zone folding. The bandgap located at high symmetry Γ-point is favourable to electron transition, which might be useful to optoelectronic device and could be achieved by band engineering. Type-II band alignment occurs in the MoTe2/WTe2 LHSs, for electrons and holes are separated on the opposite domains, which would reduce the recombination rate of the charge carriers and facilitate the quantum efficiency. Moreover, external biaxial strain leads to efficient bandgap engineering. MoTe2/WTe2 LHSs could serve as potential candidate materials for next-generation electronic devices.展开更多
Wireless Sensor Networks (WSNs) are used to sense certain parameters in an environment, manipulate the acquired data and transmit/receive the information in an intra or inter communication network. Innovative research...Wireless Sensor Networks (WSNs) are used to sense certain parameters in an environment, manipulate the acquired data and transmit/receive the information in an intra or inter communication network. Innovative researches in WSNs have resulted in the increase of application scenarios, which, at a time instant, were not even well-thought-of to be automated by WSNs. With this advent, it becomes necessary to customize sensor nodes depending on node specific characteristics and the deployment environment. Challenges for designing a WSN depend on the scenario in which it is implemented. Commercially available wireless motes are mostly generalized for usage in most of the applications. This survey work aims to provide an insight on the various wireless motes available in the market. This will enhance future researchers to select wireless modules which might be most suitable for their application needs. Various parameters related to the technical and implementation characteristics of WSNs were considered in this survey. This survey also concentrates with the survey on individual RF modules based on certain parameters like frequency of operation, transmission power, receiver sensitivity, interface mechanism, data rate, active, sleep & power-down current consumptions, range and cost involved.展开更多
The present study was conducted to analyze cotton cultivar and location differences in motes, and to determine the relationships among these and ginning outturn. Therefore, the seed cotton of five promising hybrids na...The present study was conducted to analyze cotton cultivar and location differences in motes, and to determine the relationships among these and ginning outturn. Therefore, the seed cotton of five promising hybrids namely;G.77 × Pima S6 and G.84 × (G.74 × G.68) growing in [Kafr El-Sheikh - Kafr El-Dawar - Etay El-Barood - Damietta], G.89 × Pima S6 growing in [El-Sharkia - El-Gharbiya - El-Dakahliya - El-Monofiya], G.83 × (G.75 × 5844) × G.80 and G.90 × Australian growing in [Sohag - El-Minia - Beni-Sueif - El-Faium] were used in this study. The results obtained indicate that the varieties exhibited different behavior responses to environmental conditions. On the whole, environmental factors associated with differences in place of growth, appeared to have much more influence on the number of motes than did varietal factors. Most of the locks for the promising hybrids at the different locations tend to cluster around the mean of 6 or 7 seeds per lock. There is a fairly marked tendency for the lock index, lint weight and lint percentage to decrease as the motes percentage increase. On the other hand, most of the promising hybrids under study tend to increase in the seed index as the motes percentage increase. However, the increasing in seed index as a result of the increasing in motes percentage for some cotton cultivars growing at different environments could be explain the difference in behavior for these cotton cultivars in lint percentage.展开更多
Wireless sensor networks have been identified as one of the key technologies for the 21st century. In order to overcome their limitations such as fault tolerance and conservation of energy, we propose a middleware sol...Wireless sensor networks have been identified as one of the key technologies for the 21st century. In order to overcome their limitations such as fault tolerance and conservation of energy, we propose a middleware solution, In-Motes. In-Motes stands as a fault tolerant platform for deploying and monitoring applications in real time offers a number of possibilities for the end user giving him in parallel the freedom to experiment with various parameters, in an effort the deployed applications to run in an energy efficient manner inside the network. The proposed scheme is evaluated through the In-Motes EYE application, aiming to test its merits under real time conditions. In-Motes EYE application which is an agent based real time In-Motes application developed for sensing acceleration variations in an environment. The application was tested in a prototype area, road alike, for a period of four months.展开更多
As one of the most popular novels in O'Connor's works, Wise Blood is heated discussed by critics home and abroad.Wise blood, as the major image in the novel, flows in the body of both Hazel Motes and Enoch Eme...As one of the most popular novels in O'Connor's works, Wise Blood is heated discussed by critics home and abroad.Wise blood, as the major image in the novel, flows in the body of both Hazel Motes and Enoch Emery who are the main protagonists. This thesis aims to analyzes the overtone behind wise blood so as to present a different angel of understanding this novel.展开更多
Two-dimensional (2D) heterostructures have shown great potential in advanced photovoltaics due to their restrained carrier recombination, prolonged exciton lifetime and improved light absorption. Herein, a 2D polarize...Two-dimensional (2D) heterostructures have shown great potential in advanced photovoltaics due to their restrained carrier recombination, prolonged exciton lifetime and improved light absorption. Herein, a 2D polarized heterostructure is constructed between Janus MoSSe and MoTe_(2) monolayers and is systematically investigated via first-principles calculations. Electronically, the valence band and conduction band of the MoSSe−MoTe_(2) (MoSeS−MoTe_(2)) are contributed by MoTe_(2) and MoSSe layers, respectively, and its bandgap is 0.71 (0.03) eV. A built-in electric field pointing from MoTe_(2) to MoSSe layers appears at the interface of heterostructures due to the interlayer carrier redistribution. Notably, the band alignment and built-in electric field make it a direct z-scheme heterostructure, benefiting the separation of photogenerated electron-hole pairs. Besides, the electronic structure and interlayer carrier reconstruction can be readily controlled by reversing the electric polarization of the MoSSe layer. Furthermore, the light absorption of the MoSSe/MoTe_(2) heterostructure is also improved in comparison with the separated monolayers. Consequently, in this work, a new z-scheme polarized heterostructure with polarization-controllable optoelectronic properties is designed for highly efficient optoelectronics.展开更多
In the past decade,molybdenum ditelluride(MoTe2)has received significant attention from the scientific community due to its structural features and unique properties originate from them.In the current review,the prope...In the past decade,molybdenum ditelluride(MoTe2)has received significant attention from the scientific community due to its structural features and unique properties originate from them.In the current review,the properties,various preparation approaches,and versatile applications of MoTe2 are presented.The review provides a brief update on the state of our fundamental understanding of MoTe2 material and also discusses the issues that need to be resolved.To introduce MoTe2,we briefly summarize its structural,optoelectronic,magnetic,and mechanical properties in the beginning.Then,different preparation meth-ods of MoTe2,such as exfoliation,laser treatment,deposition,hydrothermal,microwave,and molecular beam epitaxy,are included.The excellent electri-cal conductivity,strong optical activity,tunable bandgap,high sensitivity,and impressive stability make it an ideal contender for different applications,includ-ing energy storage,catalysis,sensors,solar cells,photodetectors,and transistors.The performance of MoTe2 in these applications is systematically introduced along with mechanistic insights.At the end of the article,the challenges and possible future directions are highlighted to further modify MoTe2 material for the numerous functionalities.Therefore,the availability of different phases and layer structures implies a potential for MoTe2 to lead an era of two-dimensional materials that began from the exfoliation of graphene.展开更多
The efficient near-infrared light detection of the MoTe2/germanium(Ge)heterojunction has been demonstrated.The fabricated MoTe2/Ge van der Waals heterojunction shows excellent photoresponse performances under the illu...The efficient near-infrared light detection of the MoTe2/germanium(Ge)heterojunction has been demonstrated.The fabricated MoTe2/Ge van der Waals heterojunction shows excellent photoresponse performances under the illumination of a 915 nm laser.The photoresponsivity and specific detectivity can reach to 12,460 A/W and 3.3×10^12 Jones,respectively.And the photoresponse time is 5 ms.However,the MoTe2/Ge heterojunction suffers from a large reverse current at dark due to the low barrier between MoTe2 and Ge.Therefore,to reduce the reverse current,an ultrathin GeO2 layer deposited by ozone oxidation has been introduced to the MoTe2/Ge heterojunction.The reverse current of the MoTe2/GeO2/Ge heterojunction at dark was suppressed from 0.44µA/µm^2 to 0.03 nA/µm^2,being reduced by more than four orders of magnitude.The MoTe2/Ge heterojunction with the GeO2 layer also exhibits good photoresponse performances,with a high responsivity of 15.6 A/W,short response time of 5 ms,and good specific detectivity of 4.86×10^11 Jones.These properties suggest that MoTe2/Ge heterostructure is one of the promising structures for the development of high performance near-infrared photodetectors.展开更多
Molybdenum ditelluride （MoTe2） has been demonstrated great potential in electronic and optoelectronic applications. However, the reported effective hole mobility remains far below its theoretical value. Herein, taki...Molybdenum ditelluride （MoTe2） has been demonstrated great potential in electronic and optoelectronic applications. However, the reported effective hole mobility remains far below its theoretical value. Herein, taking advantage of high-κ screening effect, we have fabricated back-gated MoTe2 transistors on an Al2O3 high-κ dielectric and systematically investigated the electronic and optoelectronic proper- ties. A high current on/off ratio exceeding 106 is achieved in the Al2O3-based MoTe2 transistors, and the hole mobility is demonstrated to be 150 cm2 V^-1 s^-1, compared to 0.2-20 cm^2 V^-1 s^-1 ever obtained from back-gated MoTe2 transistors in the literatures. Moreover, a considerable hole concentration of 1.2 × 10^13 cm 2 is attained in our Al2O3-based MoTe2 transistors owing to the strong gate control capa- bility, leading to a high on-state hole current of 6.1 μA μm^-1. After optimization, our Al2O3-based MoTe2 phototransistor exhibits outstanding photodetective performance, with a high responsivity of 543 AW^-1 and a high photogain of 1,662 at 405 nm light illumination, which are boosted around 419 times compared to the referential SiO2-based control devices. The mechanisms of photoconductivity in the Al2O3-based MoTe2 phototransistors have been analyzed in detail, and the photogating effect is considered to play an important role. This work may provide useful insight to improve carrier mobility in two-dimensional layered semiconductors and open opportunities to facilitate the development of high-performance photodetectors in the future.展开更多
Infrared(IR)light photodetection based on two dimensional(2D)materials of proper bandgap has attracted increasing attention.However,the weak IR absorption in 2D materials,due to their ultrathin attribute and indirect ...Infrared(IR)light photodetection based on two dimensional(2D)materials of proper bandgap has attracted increasing attention.However,the weak IR absorption in 2D materials,due to their ultrathin attribute and indirect bandgap in multilayer structures,degrades their performance when used as IR photodetectors.In this work,we utilize the fact that few-layer MoTe2 flake has a near-IR(NIR)bandgap and demonstrate a^60-fold enhancement of NIR response by introducing a gold hollow nanorods on the surface.Such gold hollow nanorods have distinct absorption peak located also at the NIR regime,therefore induces strong resonance,benefitting NIR absorption in MoTe2,resulting in strong near-field enhancement.With the evidence from steady and transient state optical spectra,we confirm that the enhancement of NIR response originates only photon absorption,rather than electron transport at interfaces as observed in other heterostructures,therefore,precluding the requirement of high-quality interfaces for commercial applications.展开更多
Doping can improve the band alignment at the metal-semiconductor interface to modify the corresponding Schottky barrier,which is crucial for the realization of high-performance logic components.Here,we systematically ...Doping can improve the band alignment at the metal-semiconductor interface to modify the corresponding Schottky barrier,which is crucial for the realization of high-performance logic components.Here,we systematically investigated a convenient and effective method,ultraviolet ozone treatment,for p-type doping of MoTe2 field-effect transistors to enormously enhance the corresponding electrical performance.The resulted hole concentration and mobility are near 100 times enhanced to be〜1.0×10^13 cm^-2 and 101.4 cm^2/(V·s),respectively,and the conductivity is improved by 5 orders of magnitude.These values are comparable to the highest ones ever obtained via annealing doping or non-lithographic fabrication methods at room temperature.Compared with the pristine one,the photoresponsivity(522 mA/W)is enhanced approximately 100 times.Such excellent performances can be attributed to the sharply reduced Schottky barrier because of the surface charge transfer from MoTe2 to MoOx(x<3),as proved by photoemission spectroscopy.Additionally,the p-doped devices exhibit excellent stability in ambient air.Our findings show significant potential in future nanoelectronic and optoelectronic applications.展开更多
Molybdenum ditelluride （MoTe2）, which is an important transition-metal dichalcogenide, has attracted considerable interest owing to its unique properties, such as its small bandgap and large Seebeck coefficient. How...Molybdenum ditelluride （MoTe2）, which is an important transition-metal dichalcogenide, has attracted considerable interest owing to its unique properties, such as its small bandgap and large Seebeck coefficient. However, the batch production of monolayer MoTe2 has been rarely reported. In this study, we demonstrate the synthesis of large-domain （edge length exceeding 30 μm）, monolayer MoTe2 from chemical vapor deposition-grown monolayer MoS2 using a chalcogen atom-exchange synthesis route. An in-depth investigation of the tellurization process reveals that the substitution of S atoms by Te is prevalently initiated at the edges and grain boundaries of the monolayer MoS2, which differs from the homogeneous selenization of MoS2 flakes with the formation of alloyed Mo-S-Se hybrids. Moreover, we detect a large compressive strain （approximately -10%） in the transformed MoTe2 lattice, which possibly drives the phase transition from 2H to 1T＇ at the reaction temperature of 500 ℃. This phase change is substantiated by experimental facts and first-principles calculations. This work introduces a novel route for the templated synthesis of two-dimensional layered materials through atom substitutional chemistry and provides a new pathway for engineering the strain and thus the intriguing physics and chemistry.展开更多
Flash memories and semiconductor p-n junctions are two elementary but incompatible building blocks of most electronic and optoelectronic devices.The pressing demand to efficiently transfer massive data between memorie...Flash memories and semiconductor p-n junctions are two elementary but incompatible building blocks of most electronic and optoelectronic devices.The pressing demand to efficiently transfer massive data between memories and logic circuits,as well as for high data storage capability and device integration density,has fueled the rapid growth of technique and material innovations.Two-dimensional(2D)materials are considered as one of the most promising candidates to solve this challenge.However,a key aspect for 2D materials to build functional devices requires effective and accurate control of the carrier polarity,concentration and spatial distribution in the atomically thin structures.Here,a non-volatile opto-electrical doping approach is demonstrated,which enables reversibly writing spatially resolved doping patterns in the MoTe2 conductance channel through a MoTe2/hexagonal boron nitride(h-BN)heterostructure.Based on the doping effect induced by the combination of electrostatic modulation and ultraviolet light illumination,a 3-bit flash memory and various homojunctions on the same MoTe2/BN heterostructure are successfully developed.The flash memory achieved 8 well distinguished memory states with a maximum on/off ratio over 10^4.Each state showed negligible decay during the retention time of 2,400 s.The heterostructure also allowed the formation of p-p,n-n,p-n,and n-p homojunctions and the free transition among these states.The MoTe2 p-n homojunction with a rectification ratio of 10^3 exhibited excellent photodetection and photovoltaic performance.Having the memory device and p-n junction built on the same structure makes it possible to bring memory and computational circuit on the same chip,one step further to realize near-memory computing.展开更多
Materials in the transition metal dichalcogenide family, including WS2, MoS2, WSe2, and MoSe2, etc., have captured a substantial amount of attention due to their remarkable nonlinearities and optoelectronic properties...Materials in the transition metal dichalcogenide family, including WS2, MoS2, WSe2, and MoSe2, etc., have captured a substantial amount of attention due to their remarkable nonlinearities and optoelectronic properties.Compared with WS2 and MoS2, the monolayered MoTe2 owns a smaller direct bandgap of 1.1 eV. It is beneficial for the applications in broadband absorption. In this letter, using the magnetron sputtering technique, MoTe2 is deposited on the surface of the tapered fiber to be assembled into the saturable absorber. We first implement the MoTe2-based Q-switched fiber laser operating at the wavelength of 1559 nm. The minimum pulse duration and signal-to-noise ratio are 677 ns and 63 dB, respectively. Moreover, the output power of 25 mW is impressive compared with previous work. We believe that MoTe2 is a promising 2D material for ultrafast photonic devices in the high-power Q-switched fiber lasers.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61674053 and 11881240254)the Natural Science Foundation of Henan Province,China(Grant No.162300410325)+1 种基金the Key Young Teachers of Henan Province,China(Grant No.2017GGJS179)the Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT030)
文摘Lateral two-dimensional(2D) heterostructures have opened up unprecedented opportunities in modern electronic device and material science. In this work, electronic properties of size-dependent MoTe2/WTe2 lateral heterostructures(LHSs)are investigated through the first-principles density functional calculations. The constructed periodic multi-interfaces patterns can also be defined as superlattice structures. Consequently, the direct band gap character remains in all considered LHSs without any external modulation, while the gap size changes within little difference range with the building blocks increasing due to the perfect lattice matching. The location of the conduction band minimum(CBM) and the valence band maximum(VBM) will change from P-point to Γ-point when m plus n is a multiple of 3 for A-mn LHSs as a result of Brillouin zone folding. The bandgap located at high symmetry Γ-point is favourable to electron transition, which might be useful to optoelectronic device and could be achieved by band engineering. Type-II band alignment occurs in the MoTe2/WTe2 LHSs, for electrons and holes are separated on the opposite domains, which would reduce the recombination rate of the charge carriers and facilitate the quantum efficiency. Moreover, external biaxial strain leads to efficient bandgap engineering. MoTe2/WTe2 LHSs could serve as potential candidate materials for next-generation electronic devices.
文摘Wireless Sensor Networks (WSNs) are used to sense certain parameters in an environment, manipulate the acquired data and transmit/receive the information in an intra or inter communication network. Innovative researches in WSNs have resulted in the increase of application scenarios, which, at a time instant, were not even well-thought-of to be automated by WSNs. With this advent, it becomes necessary to customize sensor nodes depending on node specific characteristics and the deployment environment. Challenges for designing a WSN depend on the scenario in which it is implemented. Commercially available wireless motes are mostly generalized for usage in most of the applications. This survey work aims to provide an insight on the various wireless motes available in the market. This will enhance future researchers to select wireless modules which might be most suitable for their application needs. Various parameters related to the technical and implementation characteristics of WSNs were considered in this survey. This survey also concentrates with the survey on individual RF modules based on certain parameters like frequency of operation, transmission power, receiver sensitivity, interface mechanism, data rate, active, sleep & power-down current consumptions, range and cost involved.
文摘The present study was conducted to analyze cotton cultivar and location differences in motes, and to determine the relationships among these and ginning outturn. Therefore, the seed cotton of five promising hybrids namely;G.77 × Pima S6 and G.84 × (G.74 × G.68) growing in [Kafr El-Sheikh - Kafr El-Dawar - Etay El-Barood - Damietta], G.89 × Pima S6 growing in [El-Sharkia - El-Gharbiya - El-Dakahliya - El-Monofiya], G.83 × (G.75 × 5844) × G.80 and G.90 × Australian growing in [Sohag - El-Minia - Beni-Sueif - El-Faium] were used in this study. The results obtained indicate that the varieties exhibited different behavior responses to environmental conditions. On the whole, environmental factors associated with differences in place of growth, appeared to have much more influence on the number of motes than did varietal factors. Most of the locks for the promising hybrids at the different locations tend to cluster around the mean of 6 or 7 seeds per lock. There is a fairly marked tendency for the lock index, lint weight and lint percentage to decrease as the motes percentage increase. On the other hand, most of the promising hybrids under study tend to increase in the seed index as the motes percentage increase. However, the increasing in seed index as a result of the increasing in motes percentage for some cotton cultivars growing at different environments could be explain the difference in behavior for these cotton cultivars in lint percentage.
文摘Wireless sensor networks have been identified as one of the key technologies for the 21st century. In order to overcome their limitations such as fault tolerance and conservation of energy, we propose a middleware solution, In-Motes. In-Motes stands as a fault tolerant platform for deploying and monitoring applications in real time offers a number of possibilities for the end user giving him in parallel the freedom to experiment with various parameters, in an effort the deployed applications to run in an energy efficient manner inside the network. The proposed scheme is evaluated through the In-Motes EYE application, aiming to test its merits under real time conditions. In-Motes EYE application which is an agent based real time In-Motes application developed for sensing acceleration variations in an environment. The application was tested in a prototype area, road alike, for a period of four months.
文摘As one of the most popular novels in O'Connor's works, Wise Blood is heated discussed by critics home and abroad.Wise blood, as the major image in the novel, flows in the body of both Hazel Motes and Enoch Emery who are the main protagonists. This thesis aims to analyzes the overtone behind wise blood so as to present a different angel of understanding this novel.
基金support of the Australian Research Council under Discovery Projects DP210100721 and DP210100331.
文摘Two-dimensional (2D) heterostructures have shown great potential in advanced photovoltaics due to their restrained carrier recombination, prolonged exciton lifetime and improved light absorption. Herein, a 2D polarized heterostructure is constructed between Janus MoSSe and MoTe_(2) monolayers and is systematically investigated via first-principles calculations. Electronically, the valence band and conduction band of the MoSSe−MoTe_(2) (MoSeS−MoTe_(2)) are contributed by MoTe_(2) and MoSSe layers, respectively, and its bandgap is 0.71 (0.03) eV. A built-in electric field pointing from MoTe_(2) to MoSSe layers appears at the interface of heterostructures due to the interlayer carrier redistribution. Notably, the band alignment and built-in electric field make it a direct z-scheme heterostructure, benefiting the separation of photogenerated electron-hole pairs. Besides, the electronic structure and interlayer carrier reconstruction can be readily controlled by reversing the electric polarization of the MoSSe layer. Furthermore, the light absorption of the MoSSe/MoTe_(2) heterostructure is also improved in comparison with the separated monolayers. Consequently, in this work, a new z-scheme polarized heterostructure with polarization-controllable optoelectronic properties is designed for highly efficient optoelectronics.
文摘In the past decade,molybdenum ditelluride(MoTe2)has received significant attention from the scientific community due to its structural features and unique properties originate from them.In the current review,the properties,various preparation approaches,and versatile applications of MoTe2 are presented.The review provides a brief update on the state of our fundamental understanding of MoTe2 material and also discusses the issues that need to be resolved.To introduce MoTe2,we briefly summarize its structural,optoelectronic,magnetic,and mechanical properties in the beginning.Then,different preparation meth-ods of MoTe2,such as exfoliation,laser treatment,deposition,hydrothermal,microwave,and molecular beam epitaxy,are included.The excellent electri-cal conductivity,strong optical activity,tunable bandgap,high sensitivity,and impressive stability make it an ideal contender for different applications,includ-ing energy storage,catalysis,sensors,solar cells,photodetectors,and transistors.The performance of MoTe2 in these applications is systematically introduced along with mechanistic insights.At the end of the article,the challenges and possible future directions are highlighted to further modify MoTe2 material for the numerous functionalities.Therefore,the availability of different phases and layer structures implies a potential for MoTe2 to lead an era of two-dimensional materials that began from the exfoliation of graphene.
基金supported by the National Key Research and Development Program of China(Nos.2016YFA0200400 and 2016YFA0302300)the National Science and Technology Major Project of China(No.2016ZX02301001).
文摘The efficient near-infrared light detection of the MoTe2/germanium(Ge)heterojunction has been demonstrated.The fabricated MoTe2/Ge van der Waals heterojunction shows excellent photoresponse performances under the illumination of a 915 nm laser.The photoresponsivity and specific detectivity can reach to 12,460 A/W and 3.3×10^12 Jones,respectively.And the photoresponse time is 5 ms.However,the MoTe2/Ge heterojunction suffers from a large reverse current at dark due to the low barrier between MoTe2 and Ge.Therefore,to reduce the reverse current,an ultrathin GeO2 layer deposited by ozone oxidation has been introduced to the MoTe2/Ge heterojunction.The reverse current of the MoTe2/GeO2/Ge heterojunction at dark was suppressed from 0.44µA/µm^2 to 0.03 nA/µm^2,being reduced by more than four orders of magnitude.The MoTe2/Ge heterojunction with the GeO2 layer also exhibits good photoresponse performances,with a high responsivity of 15.6 A/W,short response time of 5 ms,and good specific detectivity of 4.86×10^11 Jones.These properties suggest that MoTe2/Ge heterostructure is one of the promising structures for the development of high performance near-infrared photodetectors.
基金supported by the National Key Research and Development Program of China(2016YFA0302300,016YFA0200400)the National Science and Technology Major Project of China(2016ZX02301001)+1 种基金the National Natural Science Foundation of China(61306105)the Tsinghua University Initiative Scientific Research Program
文摘Molybdenum ditelluride （MoTe2） has been demonstrated great potential in electronic and optoelectronic applications. However, the reported effective hole mobility remains far below its theoretical value. Herein, taking advantage of high-κ screening effect, we have fabricated back-gated MoTe2 transistors on an Al2O3 high-κ dielectric and systematically investigated the electronic and optoelectronic proper- ties. A high current on/off ratio exceeding 106 is achieved in the Al2O3-based MoTe2 transistors, and the hole mobility is demonstrated to be 150 cm2 V^-1 s^-1, compared to 0.2-20 cm^2 V^-1 s^-1 ever obtained from back-gated MoTe2 transistors in the literatures. Moreover, a considerable hole concentration of 1.2 × 10^13 cm 2 is attained in our Al2O3-based MoTe2 transistors owing to the strong gate control capa- bility, leading to a high on-state hole current of 6.1 μA μm^-1. After optimization, our Al2O3-based MoTe2 phototransistor exhibits outstanding photodetective performance, with a high responsivity of 543 AW^-1 and a high photogain of 1,662 at 405 nm light illumination, which are boosted around 419 times compared to the referential SiO2-based control devices. The mechanisms of photoconductivity in the Al2O3-based MoTe2 phototransistors have been analyzed in detail, and the photogating effect is considered to play an important role. This work may provide useful insight to improve carrier mobility in two-dimensional layered semiconductors and open opportunities to facilitate the development of high-performance photodetectors in the future.
基金This project was supported by the Research Grant Council of Hong Kong SAR(No.1620441)NSFC-RGC Joint Research Scheme(No.N_HKUST607/17)+4 种基金the Innovation and Technology Commission(No.ITC-CNERC14SC01)the Zhongshan Municipal Bureau of Science&Technology(No.ZSST19EG03)National Natural Science Foundation of China(NSFC)(Nos.11825203,51872100,21825103,21501060 and 51727809)National Basic Research Program of China(Nos.2015CB932600 and 2019kfyRCPY059)Foundation of Shenzhen Science and Technology Innovation Committee(No.JCYJ20180504170444967).
文摘Infrared(IR)light photodetection based on two dimensional(2D)materials of proper bandgap has attracted increasing attention.However,the weak IR absorption in 2D materials,due to their ultrathin attribute and indirect bandgap in multilayer structures,degrades their performance when used as IR photodetectors.In this work,we utilize the fact that few-layer MoTe2 flake has a near-IR(NIR)bandgap and demonstrate a^60-fold enhancement of NIR response by introducing a gold hollow nanorods on the surface.Such gold hollow nanorods have distinct absorption peak located also at the NIR regime,therefore induces strong resonance,benefitting NIR absorption in MoTe2,resulting in strong near-field enhancement.With the evidence from steady and transient state optical spectra,we confirm that the enhancement of NIR response originates only photon absorption,rather than electron transport at interfaces as observed in other heterostructures,therefore,precluding the requirement of high-quality interfaces for commercial applications.
基金We acknowledge the financial support from the National Natural Science Foundation of China(Nos.11874427,11874423).Dr.H an H uang acknowledges support from the Innovation-Driven project of Central South University(No.2017CX018)and from the Natural Science Foundation of H unan province(No.2016JJ1021).Mr.Xiaoming Zheng acknowledges the support from the Fundamental Research Funds for the Central Universities of Central South University(No.2017zzts066).
文摘Doping can improve the band alignment at the metal-semiconductor interface to modify the corresponding Schottky barrier,which is crucial for the realization of high-performance logic components.Here,we systematically investigated a convenient and effective method,ultraviolet ozone treatment,for p-type doping of MoTe2 field-effect transistors to enormously enhance the corresponding electrical performance.The resulted hole concentration and mobility are near 100 times enhanced to be〜1.0×10^13 cm^-2 and 101.4 cm^2/(V·s),respectively,and the conductivity is improved by 5 orders of magnitude.These values are comparable to the highest ones ever obtained via annealing doping or non-lithographic fabrication methods at room temperature.Compared with the pristine one,the photoresponsivity(522 mA/W)is enhanced approximately 100 times.Such excellent performances can be attributed to the sharply reduced Schottky barrier because of the surface charge transfer from MoTe2 to MoOx(x<3),as proved by photoemission spectroscopy.Additionally,the p-doped devices exhibit excellent stability in ambient air.Our findings show significant potential in future nanoelectronic and optoelectronic applications.
基金We acknowledge finandal support by National Natural Science Foundation of China （Nos. 51472008, 51290272, 51471004, and 51672307）, the National High-tech R＆D Program of China （No. 2016YFA0200103）, the National Basic Research Program of China （No. 2014CB921002）, the Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics （No. KF201601）, the Strategic Priority Research Program of Chinese Academy of Sciences （No. XDB07030200） and the Key Research Program of Frontier Sciences, CAS （No. QYZDB-SSW-JSC035）.
文摘Molybdenum ditelluride （MoTe2）, which is an important transition-metal dichalcogenide, has attracted considerable interest owing to its unique properties, such as its small bandgap and large Seebeck coefficient. However, the batch production of monolayer MoTe2 has been rarely reported. In this study, we demonstrate the synthesis of large-domain （edge length exceeding 30 μm）, monolayer MoTe2 from chemical vapor deposition-grown monolayer MoS2 using a chalcogen atom-exchange synthesis route. An in-depth investigation of the tellurization process reveals that the substitution of S atoms by Te is prevalently initiated at the edges and grain boundaries of the monolayer MoS2, which differs from the homogeneous selenization of MoS2 flakes with the formation of alloyed Mo-S-Se hybrids. Moreover, we detect a large compressive strain （approximately -10%） in the transformed MoTe2 lattice, which possibly drives the phase transition from 2H to 1T＇ at the reaction temperature of 500 ℃. This phase change is substantiated by experimental facts and first-principles calculations. This work introduces a novel route for the templated synthesis of two-dimensional layered materials through atom substitutional chemistry and provides a new pathway for engineering the strain and thus the intriguing physics and chemistry.
基金This work is supported by the National Natural Science Foundation of China(No.21405109)Seed Foundation of State Key Laboratory of Precision Measurement Technology and Instruments,China(No.Pilt1710).
文摘Flash memories and semiconductor p-n junctions are two elementary but incompatible building blocks of most electronic and optoelectronic devices.The pressing demand to efficiently transfer massive data between memories and logic circuits,as well as for high data storage capability and device integration density,has fueled the rapid growth of technique and material innovations.Two-dimensional(2D)materials are considered as one of the most promising candidates to solve this challenge.However,a key aspect for 2D materials to build functional devices requires effective and accurate control of the carrier polarity,concentration and spatial distribution in the atomically thin structures.Here,a non-volatile opto-electrical doping approach is demonstrated,which enables reversibly writing spatially resolved doping patterns in the MoTe2 conductance channel through a MoTe2/hexagonal boron nitride(h-BN)heterostructure.Based on the doping effect induced by the combination of electrostatic modulation and ultraviolet light illumination,a 3-bit flash memory and various homojunctions on the same MoTe2/BN heterostructure are successfully developed.The flash memory achieved 8 well distinguished memory states with a maximum on/off ratio over 10^4.Each state showed negligible decay during the retention time of 2,400 s.The heterostructure also allowed the formation of p-p,n-n,p-n,and n-p homojunctions and the free transition among these states.The MoTe2 p-n homojunction with a rectification ratio of 10^3 exhibited excellent photodetection and photovoltaic performance.Having the memory device and p-n junction built on the same structure makes it possible to bring memory and computational circuit on the same chip,one step further to realize near-memory computing.
基金supported by the National Natural Science Foundation of China(Grant Nos.11674036,11078022,and 61378040)the Beijing Youth Top-notch Talent Support Program(Grant No.2017000026833ZK08)the Fund of State Key Laboratory of Information Photonics and Optical Communications(Beijing University of Posts and Telecommunications,Grant Nos.IPOC2016ZT04 and IPOC2017ZZ05)
文摘Materials in the transition metal dichalcogenide family, including WS2, MoS2, WSe2, and MoSe2, etc., have captured a substantial amount of attention due to their remarkable nonlinearities and optoelectronic properties.Compared with WS2 and MoS2, the monolayered MoTe2 owns a smaller direct bandgap of 1.1 eV. It is beneficial for the applications in broadband absorption. In this letter, using the magnetron sputtering technique, MoTe2 is deposited on the surface of the tapered fiber to be assembled into the saturable absorber. We first implement the MoTe2-based Q-switched fiber laser operating at the wavelength of 1559 nm. The minimum pulse duration and signal-to-noise ratio are 677 ns and 63 dB, respectively. Moreover, the output power of 25 mW is impressive compared with previous work. We believe that MoTe2 is a promising 2D material for ultrafast photonic devices in the high-power Q-switched fiber lasers.
