MoTe2

/Tag: MoTe2

Generation of strain-induced pseudo-magnetic field in a doped type-II Weyl semimetal. (arXiv:1903.06224v1 [cond-mat.mes-hall])

2019-03-18T04:30:34+00:00March 18th, 2019|Categories: Publications|Tags: |

In Weyl semimetals, there is an intriguing possibility of realizing a pseudo-magnetic field in presence of small strain due to certain special cases of static deformations. This pseudo-magnetic field can be large enough to form quantized Landau levels and thus become observable in Weyl semimetals. In this paper, we experimentally show the emergence of a pseudo-magnetic field (~ 3 Tesla) by Scanning Tunneling Spectroscopy (STS) on the doped Weyl semimetal Re-MoTe2, where distinct Landau level oscillations in the tunneling conductance are clearly resolved. The crystal lattice is intrinsically strained where large area STM imaging of the surface reveals differently strained domains where atomic scale deformations exist forming topographic ripples with varying periodicity in the real space. The effect of pseudo-magnetic field is clearly resolved in areas under maximum strain.

Published : "arXiv Mesoscale and Nanoscale Physics".

Photodetectors: Ultrahigh‐Sensitive Broadband Photodetectors Based on Dielectric Shielded MoTe2/Graphene/SnS2 p–g–n Junctions (Adv. Mater. 6/2019)

2019-02-27T02:40:00+00:00February 27th, 2019|Categories: Publications|Tags: , , , |

In article number 1805656, Rui Chen, Liyuan Zhang, Youpin Gong, and co‐workers develop an h‐BN/MoTe2/graphene/SnS2/h‐BN van der Waals heterostructure to realize an ultrahigh‐sensitivity broadband (405–1550 nm) photodetector, due to its unique advantages for high‐efficiency light absorption and exciton dissociation. Graphene plays a key role in enhancing the sensitivity and broadening the spectral range, providing a viable approach toward future ultrahigh sensitivity and broadband photodetectors.

Published in: "Advanced Materials".

Ultrahigh‐Sensitive Broadband Photodetectors Based on Dielectric Shielded MoTe2/Graphene/SnS2 p–g–n Junctions

2019-02-27T02:39:49+00:00February 27th, 2019|Categories: Publications|Tags: , , , |

h‐BN/MoTe2/graphene/SnS2/h‐BN van der Waals heterostructure photodetectors present an extraordinary broadband responsivity exceeding 2.6 × 103 A W−1 and detectivity up to ≈1013 Jones in a wide spectrum, which is attributed to the enhanced light absorption and highly effective exciton dissociation originating from the vertical built‐in electric field and multiple photoactive layers in the unique heterostructures. Abstract 2D atomic sheets of transition metal dichalcogenides (TMDs) have a tremendous potential for next‐generation optoelectronics since they can be stacked layer‐by‐layer to form van der Waals (vdW) heterostructures. This allows not only bypassing difficulties in heteroepitaxy of lattice‐mismatched semiconductors of desired functionalities but also providing a scheme to design new optoelectronics that can surpass the fundamental limitations on their conventional semiconductor counterparts. Herein, a novel 2D h‐BN/p‐MoTe2/graphene/n‐SnS2/h‐BN p–g–n junction, fabricated by a layer‐by‐layer dry transfer, demonstrates high‐sensitivity, broadband photodetection at room temperature. The combination of the MoTe2 and SnS2 of complementary bandgaps, and the graphene interlayer provides a unique vdW heterostructure with a vertical built‐in electric field for high‐efficiency broadband light absorption, exciton dissociation, and carrier transfer. The graphene interlayer plays a critical role in enhancing sensitivity and broadening the spectral range. An optimized device containing 5−7‐layer graphene has been achieved and shows an extraordinary responsivity exceeding 2600 A W−1 with fast photoresponse and specific detectivity up to ≈1013 Jones in the ultraviolet–visible–near‐infrared spectrum. This result suggests that the vdW p–g–n junctions containing multiple photoactive TMDs can provide a viable approach toward future ultrahigh‐sensitivity and broadband photonic detectors.

Published in: "Advanced Materials".

Ohmic Contact in 2D Semiconductors via the Formation of a Benzyl Viologen Interlayer

2019-02-21T02:33:07+00:00February 21st, 2019|Categories: Publications|Tags: , , , |

Solution‐processed polymeric contacts used in 2D semiconductor devices are reported here. Predoping of the benzyl viologen alters the contact surface to obtain electron‐doped materials with high work functions. Ohmic contacts are induced by the polymer and the thus formed devices produce 3‐, 700‐, 3000‐, and 17‐fold increases in the mobilities for MoS2, WSe2, MoTe2, and black phosphorus devices, respectively. Abstract The fabrication of a polymeric Ohmic contact interlayer between a metal and a 2D material using solution‐processed benzyl viologen (BV) is reported here. Predoping of the polymer alters the contact surface to obtain electron‐doped materials with ultrahigh work functions that significantly enhance the current density across the contact and reduce the contact resistance and Schottky barrier height. The fabrication of solution‐processed polymeric contacts for the preparation of high mobility MoS2, WSe2, MoTe2, and BP (black phosphorous) FETs with significantly lowered contact resistance is demonstrated. Ohmic contacts are achieved and produce 3‐, 700‐, 3000‐, and 17‐fold increases in electron mobilities, respectively, when the bottom gate voltage is 10 V compared to those respective materials alone. Ambipolar and p‐type 2D material based FETs could, therefore, be transformed into n‐type FETs. Most importantly, the devices exhibit excellent stability in both ambient and vacuum.

Published in: "Advanced Functional Materials".

Photodetectors: Ultrahigh‐Sensitive Broadband Photodetectors Based on Dielectric Shielded MoTe2/Graphene/SnS2 p–g–n Junctions (Adv. Mater. 6/2019)

2019-02-16T22:37:25+00:00February 16th, 2019|Categories: Publications|Tags: , , , |

In article number 1805656, Rui Chen, Liyuan Zhang, Youpin Gong, and co‐workers develop an h‐BN/MoTe2/graphene/SnS2/h‐BN van der Waals heterostructure to realize an ultrahigh‐sensitivity broadband (405–1550 nm) photodetector, due to its unique advantages for high‐efficiency light absorption and exciton dissociation. Graphene plays a key role in enhancing the sensitivity and broadening the spectral range, providing a viable approach toward future ultrahigh sensitivity and broadband photodetectors.

Published in: "Advanced Materials".

Photodetectors: Ultrahigh‐Sensitive Broadband Photodetectors Based on Dielectric Shielded MoTe2/Graphene/SnS2 p–g–n Junctions (Adv. Mater. 6/2019)

2019-02-11T08:49:49+00:00February 11th, 2019|Categories: Publications|Tags: , , , |

In article number 1805656, Rui Chen, Liyuan Zhang, Youpin Gong, and co‐workers develop an h‐BN/MoTe2/graphene/SnS2/h‐BN van der Waals heterostructure to realize an ultrahigh‐sensitivity broadband (405–1550 nm) photodetector, due to its unique advantages for high‐efficiency light absorption and exciton dissociation. Graphene plays a key role in enhancing the sensitivity and broadening the spectral range, providing a viable approach toward future ultrahigh sensitivity and broadband photodetectors.

Published in: "Advanced Materials".

Electron–hole liquid in a van der Waals heterostructure photocell at room temperature

2019-02-04T16:42:26+00:00February 4th, 2019|Categories: Publications|Tags: , |

Electron–hole liquid in a van der Waals heterostructure photocell at room temperatureElectron–hole liquid in a van der Waals heterostructure photocell at room temperature, Published online: 04 February 2019; doi:10.1038/s41566-019-0349-yPhotoexcited charge carriers are typically approximated as a gas, but now it is shown that electrons and holes can behave as a liquid in MoTe2 photocells.

Published in: "Nature Photonics".

Van der Waals Heterostructure Devices with Dynamically Controlled Conduction Polarity and Multifunctionality

2019-01-21T20:32:49+00:00January 21st, 2019|Categories: Publications|Tags: , , |

A new application of vdWHs to dynamically control and optimize the electronic and optoelectronic properties of 2D materials is demonstrated. The semivertical MoTe2/MoS2 structure allows for a desirable multifunctional integration of field effect transistors with an on/off ratio >107 and diode with rectification ratio >106. Moreover, the devices exhibit strong capability of suppressing the widely observed trap states–related negative photoresponse effect. Abstract Controlling the conduction behavior of 2D materials is an important prerequisite to achieve their electronic and optoelectronic applications. However, most of the reported approaches are aware of the shortcomings of inflexibility and complexity, which limits the possibility of multifunctional integration. Here, taking advantage of van der Waals heterostructure engineering, a simple method to achieve a dynamically controlled binary channel in a semivertical MoTe2/MoS2 field effect transistor is proposed. It is enabled by the high switchability between tunneling and thermal transports through simply changing the sign of voltage bias. In addition, the proposed system allows for multifunctional integration of transistor with on/off ratio >107 and diode with rectification ratio >106. Moreover, the devices show screen capability to negative photoresponse effect that is widely observed in ambipolar materials, hence improving the photodetection reliability and sensitivity. This study broadens the functionalities of van der Waals heterostructures and opens up more possibilities to realize multifunctional devices.

Published in: "Advanced Functional Materials".

Van der Waals Heterostructure Devices with Dynamically Controlled Conduction Polarity and Multifunctionality

2019-01-21T20:32:48+00:00January 21st, 2019|Categories: Publications|Tags: , , |

A new application of vdWHs to dynamically control and optimize the electronic and optoelectronic properties of 2D materials is demonstrated. The semivertical MoTe2/MoS2 structure allows for a desirable multifunctional integration of field effect transistors with an on/off ratio >107 and diode with rectification ratio >106. Moreover, the devices exhibit strong capability of suppressing the widely observed trap states–related negative photoresponse effect. Abstract Controlling the conduction behavior of 2D materials is an important prerequisite to achieve their electronic and optoelectronic applications. However, most of the reported approaches are aware of the shortcomings of inflexibility and complexity, which limits the possibility of multifunctional integration. Here, taking advantage of van der Waals heterostructure engineering, a simple method to achieve a dynamically controlled binary channel in a semivertical MoTe2/MoS2 field effect transistor is proposed. It is enabled by the high switchability between tunneling and thermal transports through simply changing the sign of voltage bias. In addition, the proposed system allows for multifunctional integration of transistor with on/off ratio >107 and diode with rectification ratio >106. Moreover, the devices show screen capability to negative photoresponse effect that is widely observed in ambipolar materials, hence improving the photodetection reliability and sensitivity. This study broadens the functionalities of van der Waals heterostructures and opens up more possibilities to realize multifunctional devices.

Published in: "Advanced Functional Materials".

Ohmic Contact in 2D Semiconductors via the Formation of a Benzyl Viologen Interlayer

2019-01-05T22:32:40+00:00January 5th, 2019|Categories: Publications|Tags: , , , |

Solution‐processed polymeric contacts used in 2D semiconductor devices are reported here. Predoping of the benzyl viologen alters the contact surface to obtain electron‐doped materials with high work functions. Ohmic contacts are induced by the polymer and the thus formed devices produce 3‐, 700‐, 3000‐, and 17‐fold increases in the mobilities for MoS2, WSe2, MoTe2, and black phosphorus devices, respectively. Abstract The fabrication of a polymeric Ohmic contact interlayer between a metal and a 2D material using solution‐processed benzyl viologen (BV) is reported here. Predoping of the polymer alters the contact surface to obtain electron‐doped materials with ultrahigh work functions that significantly enhance the current density across the contact and reduce the contact resistance and Schottky barrier height. The fabrication of solution‐processed polymeric contacts for the preparation of high mobility MoS2, WSe2, MoTe2, and BP (black phosphorous) FETs with significantly lowered contact resistance is demonstrated. Ohmic contacts are achieved and produce 3‐, 700‐, 3000‐, and 17‐fold increases in electron mobilities, respectively, when the bottom gate voltage is 10 V compared to those respective materials alone. Ambipolar and p‐type 2D material based FETs could, therefore, be transformed into n‐type FETs. Most importantly, the devices exhibit excellent stability in both ambient and vacuum.

Published in: "Advanced Functional Materials".

Ohmic Contact in 2D Semiconductors via the Formation of a Benzyl Viologen Interlayer

2019-01-02T10:32:05+00:00January 2nd, 2019|Categories: Publications|Tags: , , , |

Solution‐processed polymeric contacts used in 2D semiconductor devices are reported here. Predoping of the benzyl viologen alters the contact surface to obtain electron‐doped materials with high work functions. Ohmic contacts are induced by the polymer and the thus formed devices produce 3‐, 700‐, 3000‐, and 17‐fold increases in the mobilities for MoS2, WSe2, MoTe2, and black phosphorus devices, respectively. Abstract The fabrication of a polymeric Ohmic contact interlayer between a metal and a 2D material using solution‐processed benzyl viologen (BV) is reported here. Predoping of the polymer alters the contact surface to obtain electron‐doped materials with ultrahigh work functions that significantly enhance the current density across the contact and reduce the contact resistance and Schottky barrier height. The fabrication of solution‐processed polymeric contacts for the preparation of high mobility MoS2, WSe2, MoTe2, and BP (black phosphorous) FETs with significantly lowered contact resistance is demonstrated. Ohmic contacts are achieved and produce 3‐, 700‐, 3000‐, and 17‐fold increases in electron mobilities, respectively, when the bottom gate voltage is 10 V compared to those respective materials alone. Ambipolar and p‐type 2D material based FETs could, therefore, be transformed into n‐type FETs. Most importantly, the devices exhibit excellent stability in both ambient and vacuum.

Published in: "Advanced Functional Materials".

Photodoping: Nonvolatile and Programmable Photodoping in MoTe2 for Photoresist‐Free Complementary Electronic Devices (Adv. Mater. 52/2018)

2019-01-01T22:35:04+00:00January 1st, 2019|Categories: Publications|Tags: , |

In article number 1804470, Du Xiang, Wei Chen, and co‐workers report photoinduced nonvolatile and programmable doping in MoTe2 based on a heterostructure of MoTe2 and h‐BN. By spatially controlling the photodoping region, high‐performance photoresist‐free p–n junctions and inverters in the MoTe2 homostructure are achieved, illustrating the great potential of applying this photodoping technique in 2D logic electronics.

Published in: "Advanced Materials".

Humidity‐Controlled Ultralow Power Layer‐by‐Layer Thinning, Nanopatterning and Bandgap Engineering of MoTe2

2018-12-30T20:32:19+00:00December 30th, 2018|Categories: Publications|Tags: |

A precision, laser‐assisted, humidity‐controlled, layer‐by‐layer thinning method in 2D MoTe2 films is presented. Field effect transistors fabricated from thinned layers exhibit an order of magnitude increase in on/off current, enhanced field‐effect mobility, and the fastest photoresponse for (visible) MoTe2 photodetectors reported to date. Localized band gap engineering is also performed, with sub‐200 nm spatial resolution, via the creation of lateral homojunctions. Abstract A highly effective laser thinning method is demonstrated to accurately control the thickness of MoTe2 layers. By utilizing the humidity present in the ambient atmosphere, multilayered MoTe2 films can be uniformly thinned all the way down to monolayer with layer‐by‐layer precision using an ultralow laser power density of 0.2 mW µm−2. Localized bandgap engineering is also performed in MoTe2, by creating regions with different bandgaps on the same film, enabling the formation of lateral homojunctions with sub‐200 nm spatial resolution. Field‐effect transistors fabricated from these thinned layers exhibit significantly improved electrical properties with an order of magnitude increase in on/off current ratios, along with enhancements in on‐current and field‐effect mobility values. Thinned devices also exhibit the fastest photoresponse (45 µs) for an MoTe2‐based visible photodetector reported to date, along with a high photoresponsivity. A highly sensitive monolayer MoTe2 photodetector is also reported. These results demonstrate the efficiency of the presented thinning approach in producing high‐quality MoTe2 films for electronic and optoelectronic applications.

Published in: "Advanced Functional Materials".

Photodoping: Nonvolatile and Programmable Photodoping in MoTe2 for Photoresist‐Free Complementary Electronic Devices (Adv. Mater. 52/2018)

2018-12-29T22:36:04+00:00December 29th, 2018|Categories: Publications|Tags: , |

In article number 1804470, Du Xiang, Wei Chen, and co‐workers report photoinduced nonvolatile and programmable doping in MoTe2 based on a heterostructure of MoTe2 and h‐BN. By spatially controlling the photodoping region, high‐performance photoresist‐free p–n junctions and inverters in the MoTe2 homostructure are achieved, illustrating the great potential of applying this photodoping technique in 2D logic electronics.

Published in: "Advanced Materials".

Spontanous breaking of time-reversal symmetry at the edges of 1T’ monolayer transition metal dichalcogenides. (arXiv:1812.09082v1 [cond-mat.mes-hall])

2018-12-24T02:29:29+00:00December 24th, 2018|Categories: Publications|Tags: , , |

Using density functional theory calculations and the Greens’s function formalism, we report the existence of magnetic edge states with a non-collinear spin texture present on different edges of the 1T’ phase of the three monolayer transition metal dichalcogenides (TMDs): MoS2, MoTe2 and WTe2. The magnetic states are gapless and accompanied by a spontaneous breaking of the time-reversal symmetry. This may have an impact on the prospects of utilizing WTe2 as a quantum spin Hall insulator. It has previously been suggested that the topologically protected edge states of the 1T’ TMDs could be switched off by applying a perpendicular electric field. We confirm with fully self-consistent DFT calculations, that the topological edge states can be switched off. The investigated magnetic edge states are seen to be robust and remains gapless when applying a field.

Published in: "arXiv Material Science".

Photodoping: Nonvolatile and Programmable Photodoping in MoTe2 for Photoresist‐Free Complementary Electronic Devices (Adv. Mater. 52/2018)

2018-12-22T10:33:54+00:00December 22nd, 2018|Categories: Publications|Tags: , |

In article number 1804470, Du Xiang, Wei Chen, and co‐workers report photoinduced nonvolatile and programmable doping in MoTe2 based on a heterostructure of MoTe2 and h‐BN. By spatially controlling the photodoping region, high‐performance photoresist‐free p–n junctions and inverters in the MoTe2 homostructure are achieved, illustrating the great potential of applying this photodoping technique in 2D logic electronics.

Published in: "Advanced Materials".

Intrinsic Spin Hall Conductivity of MoTe2 and WTe2 Semimetals. (arXiv:1812.06910v1 [cond-mat.mtrl-sci])

2018-12-18T02:29:22+00:00December 18th, 2018|Categories: Publications|Tags: , , |

We report a comprehensive study on the intrinsic spin Hall conductivity (SHC) of semimetals MoTe2 and WTe2 by ab initio calculation. Large SHC and desirable spin Hall angles have been discovered, due to the strong spin orbit coupling effect and low charge conductivity in semimetals. Diverse anisotropic SHC values, attributed to the unusual reduced-symmetry crystalline structure, have been revealed. We report an effective method on SHC optimization by electron doping, and exhibit the mechanism of SHC variation respect to the energy shifting by the spin Berry curvature. Our work provides insights into the realization of strong spin Hall effects in 2D systems.

Published in: "arXiv Material Science".

Ultrahigh‐Sensitive Broadband Photodetectors Based on Dielectric Shielded MoTe2/Graphene/SnS2 p–g–n Junctions

2018-12-15T22:33:56+00:00December 15th, 2018|Categories: Publications|Tags: , , , |

h‐BN/MoTe2/graphene/SnS2/h‐BN van der Waals heterostructure photodetectors present an extraordinary broadband responsivity exceeding 2.6 × 103 A W−1 and detectivity up to ≈1013 Jones in a wide spectrum, which is attributed to the enhanced light absorption and high‐effective exciton dissociation originated from the vertical built‐in electric field and multiple photoactive layers in the unique heterostructures. Abstract 2D atomic sheets of transition metal dichalcogenides (TMDs) have a tremendous potential for next‐generation optoelectronics since they can be stacked layer‐by‐layer to form van der Waals (vdW) heterostructures. This allows not only bypassing difficulties in heteroepitaxy of lattice‐mismatched semiconductors of desired functionalities but also providing a scheme to design new optoelectronics that can surpass the fundamental limitations on their conventional semiconductor counterparts. Herein, a novel 2D h‐BN/p‐MoTe2/graphene/n‐SnS2/h‐BN p–g–n junction, fabricated by a layer‐by‐layer dry transfer, demonstrates high‐sensitivity, broadband photodetection at room temperature. The combination of the MoTe2 and SnS2 of complementary bandgaps, and the graphene interlayer provides a unique vdW heterostructure with a vertical built‐in electric field for high‐efficiency broadband light absorption, exciton dissociation, and carrier transfer. The graphene interlayer plays a critical role in enhancing sensitivity and broadening the spectral range. An optimized device containing 5−7‐layer graphene has been achieved and shows an extraordinary responsivity exceeding 2600 A W−1 with fast photoresponse and specific detectivity up to ≈1013 Jones in the ultraviolet–visible–near‐infrared spectrum. This result suggests that the vdW p–g–n junctions containing multiple photoactive TMDs can provide a viable approach toward future ultrahigh‐sensitivity and broadband photonic detectors.

Published in: "Advanced Materials".

Ultrahigh‐Sensitive Broadband Photodetectors Based on Dielectric Shielded MoTe2/Graphene/SnS2 p–g–n Junctions

2018-12-15T10:34:09+00:00December 15th, 2018|Categories: Publications|Tags: , , , |

h‐BN/MoTe2/graphene/SnS2/h‐BN van der Waals heterostructure photodetectors present an extraordinary broadband responsivity exceeding 2.6 × 103 A W−1 and detectivity up to ≈1013 Jones in a wide spectrum, which is attributed to the enhanced light absorption and high‐effective exciton dissociation originated from the vertical built‐in electric field and multiple photoactive layers in the unique heterostructures. Abstract 2D atomic sheets of transition metal dichalcogenides (TMDs) have a tremendous potential for next‐generation optoelectronics since they can be stacked layer‐by‐layer to form van der Waals (vdW) heterostructures. This allows not only bypassing difficulties in heteroepitaxy of lattice‐mismatched semiconductors of desired functionalities but also providing a scheme to design new optoelectronics that can surpass the fundamental limitations on their conventional semiconductor counterparts. Herein, a novel 2D h‐BN/p‐MoTe2/graphene/n‐SnS2/h‐BN p–g–n junction, fabricated by a layer‐by‐layer dry transfer, demonstrates high‐sensitivity, broadband photodetection at room temperature. The combination of the MoTe2 and SnS2 of complementary bandgaps, and the graphene interlayer provides a unique vdW heterostructure with a vertical built‐in electric field for high‐efficiency broadband light absorption, exciton dissociation, and carrier transfer. The graphene interlayer plays a critical role in enhancing sensitivity and broadening the spectral range. An optimized device containing 5−7‐layer graphene has been achieved and shows an extraordinary responsivity exceeding 2600 A W−1 with fast photoresponse and specific detectivity up to ≈1013 Jones in the ultraviolet–visible–near‐infrared spectrum. This result suggests that the vdW p–g–n junctions containing multiple photoactive TMDs can provide a viable approach toward future ultrahigh‐sensitivity and broadband photonic detectors.

Published in: "Advanced Materials".

Excitonic Complexes and Optical Gain in Two-Dimensional Molybdenum Ditelluride Well below Mott Transition. (arXiv:1812.04296v1 [cond-mat.mes-hall])

2018-12-12T02:29:27+00:00December 12th, 2018|Categories: Publications|Tags: , |

Strong Coulomb interaction in 2D materials provides unprecedented opportunities for studying many key issues of condensed matter physics, such as co-existence and mutual conversions of excitonic complexes, fundamental optical processes associated with their conversions, and their roles in the celebrated Mott transition. Recent lasing demonstrations in 2D materials raise important questions about the existence and origin of optical gain and possible roles of excitonic complexes. While lasing occurred at extremely low densities dominated by various excitonic complexes, optical gain was observed in the only experiment at densities several orders of magnitude higher, exceeding the Mott density. Here, we report a new gain mechanism involving charged excitons or trions well below the Mott density in 2D molybdenum ditelluride. Our combined experimental and modeling study not only reveals the complex interplays of excitonic complexes well below the Mott transition, but also provides foundation for lasing at extremely low excitation levels, important for future energy efficient photonic devices.

Published in: "arXiv Material Science".

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