A prerequisite for widespread applications of atomically thin transition metal dichalcogenides in future electronics is to achieve reliable electrical contacts,which is of considerable challenge due to the difficultie...A prerequisite for widespread applications of atomically thin transition metal dichalcogenides in future electronics is to achieve reliable electrical contacts,which is of considerable challenge due to the difficulties in selectively doping and inevitable physical damages of these atomically thin materials during typical metal integration process.Here,we report the in situ growth of ultrathin metallic NiSe single crystals on WSe2 in which the metallic NiSe nanosheets function as the contact electrodes to WSe2,creating an interface that is essentially free from chemical disorder.The NiSe/WSe2 heterostructures also exhibit well-aligned lattice orientation between the two layers,forming a periodic Moire pattern.Electrical transport studies demonstrate that the NiSe nanosheets exhibit an excellent metallic feature,as evidenced by the extra-high electrical conductivity of up to 1.6×10^6 S-nf1.The WSe2 transistors with the NiSe contact show field-effect mobilities (/vFe) more than double that with Cr/Au electrodes.This study demonstrates an effective pathway to achieve reliable electrical contacts to the atomically thin 2D materials,and maybe readily extended for fabricating 2D/2D low-resistance contacts for a variety of transition metal dichalcogenides.展开更多
Since its discovery, the direct imaging and determination of the crystal structure of few-layer graphdiyne has proven difficult because it is too delicate under irradiation by an electron beam. In this work, the cryst...Since its discovery, the direct imaging and determination of the crystal structure of few-layer graphdiyne has proven difficult because it is too delicate under irradiation by an electron beam. In this work, the crystal structure of a six-layered graphdiyne nanosheet was directly observed by low-voltage transmission electron microscopy (TEM) using low current density. The combined use of high-resolution TEM (HRTEM) simulation, electron energy-loss spectroscopy, and electron diffraction revealed that the as-synthesized nanosheet was crystalline graphdiyne with a thickness of 2.19 nm (corresponding to a thickness of six layers) and showed ABC stacking. Thus, this work provides direct evidence for the existence and crystal structure of few-layer graphdiyne, which is a new type of two-dimensional carbon material complementary to graphene.展开更多
We report the first demonstration of group delay tuning with stimulated Raman scattering-induced dispersion in a hydrogen-filled hollow-core optical fiber.A pump laser induces a sharp refractive index change near the ...We report the first demonstration of group delay tuning with stimulated Raman scattering-induced dispersion in a hydrogen-filled hollow-core optical fiber.A pump laser induces a sharp refractive index change near the S0(0)Raman transition of hydrogen molecules,enabling the control of the group velocity of signal pulses around the Stokes wavelength.Experiments with an 80-m-long hollow-core fiber filled with 2.5 bar hydrogen achieved continuous tuning of the pulse delay up to 1.42 ns by varying the Raman amplification from 0 to 10 dB.The tunable pulse delay is realized by changing the pump power as well as the hydrogen pressure.This work provides a new technique for controlling the pulse propagation in optical fibers with high flexibility.展开更多
With micro-and nano-structured optical fibers,parts-per-million to parts-per-trillion level gas detection has been demonstrated for a range of gases such as methane,acetylene,ethane,carbon monoxide,hydrogen,and oxygen...With micro-and nano-structured optical fibers,parts-per-million to parts-per-trillion level gas detection has been demonstrated for a range of gases such as methane,acetylene,ethane,carbon monoxide,hydrogen,and oxygen.We review the recent development in optical fiber gas cells and gas detection systems based on direct absorption,photothermal,photoacoustic,and stimulated Raman spectroscopies.展开更多
基金the financial support from the Fundamental Research Funds of the Central Universities (No.531107051078)the Double First-Class University In让iative of Hunan University (No.531109100004)+2 种基金the 111 Project of China (No.D17003)the support from the National Natural Science Foundation of China (No.751214296,51802090,61874041,and 61804050)Hunan Key Laboratory of Two-Dimensional Materials (No.801200005).
文摘A prerequisite for widespread applications of atomically thin transition metal dichalcogenides in future electronics is to achieve reliable electrical contacts,which is of considerable challenge due to the difficulties in selectively doping and inevitable physical damages of these atomically thin materials during typical metal integration process.Here,we report the in situ growth of ultrathin metallic NiSe single crystals on WSe2 in which the metallic NiSe nanosheets function as the contact electrodes to WSe2,creating an interface that is essentially free from chemical disorder.The NiSe/WSe2 heterostructures also exhibit well-aligned lattice orientation between the two layers,forming a periodic Moire pattern.Electrical transport studies demonstrate that the NiSe nanosheets exhibit an excellent metallic feature,as evidenced by the extra-high electrical conductivity of up to 1.6×10^6 S-nf1.The WSe2 transistors with the NiSe contact show field-effect mobilities (/vFe) more than double that with Cr/Au electrodes.This study demonstrates an effective pathway to achieve reliable electrical contacts to the atomically thin 2D materials,and maybe readily extended for fabricating 2D/2D low-resistance contacts for a variety of transition metal dichalcogenides.
基金This work was financially supported by the National Natural Science Foundation of China (Nos. 11604241, 21790052 and 21331007), the National Program for Thousand Young Talents of China, the Postdoctoral Science Foundation of China (No. 2015M580209), the Tianjin Municipal Education Commission, the Tianjin Municipal Science and Technology Commission (No. 15JCYBJC52600), and the Fundamental Research Fund of Tianjin University of Technology.
文摘Since its discovery, the direct imaging and determination of the crystal structure of few-layer graphdiyne has proven difficult because it is too delicate under irradiation by an electron beam. In this work, the crystal structure of a six-layered graphdiyne nanosheet was directly observed by low-voltage transmission electron microscopy (TEM) using low current density. The combined use of high-resolution TEM (HRTEM) simulation, electron energy-loss spectroscopy, and electron diffraction revealed that the as-synthesized nanosheet was crystalline graphdiyne with a thickness of 2.19 nm (corresponding to a thickness of six layers) and showed ABC stacking. Thus, this work provides direct evidence for the existence and crystal structure of few-layer graphdiyne, which is a new type of two-dimensional carbon material complementary to graphene.
基金This work was supported by the Hong Kong SAR government(GRF grant PolyU 152210/18E)the National Natural Science Foundation of China(Nos.61827820 and 61535004)the Hong Kong Polytechnic University(Nos.1-ZVG4 and 4-BCD1).
文摘We report the first demonstration of group delay tuning with stimulated Raman scattering-induced dispersion in a hydrogen-filled hollow-core optical fiber.A pump laser induces a sharp refractive index change near the S0(0)Raman transition of hydrogen molecules,enabling the control of the group velocity of signal pulses around the Stokes wavelength.Experiments with an 80-m-long hollow-core fiber filled with 2.5 bar hydrogen achieved continuous tuning of the pulse delay up to 1.42 ns by varying the Raman amplification from 0 to 10 dB.The tunable pulse delay is realized by changing the pump power as well as the hydrogen pressure.This work provides a new technique for controlling the pulse propagation in optical fibers with high flexibility.
基金the support of NSF of China(Grant No.61827820)Hong Kong SAR Government GRF Grant(Grant No.PolyU 152603/16E)+1 种基金the Local Innovative and Research Teams Project of Guangdong Pear River Talents Program(Grant No.2019BT02X105)the Hong Kong Polytechnic University(Grant Nos.P0034330 and 1-9B65).
文摘With micro-and nano-structured optical fibers,parts-per-million to parts-per-trillion level gas detection has been demonstrated for a range of gases such as methane,acetylene,ethane,carbon monoxide,hydrogen,and oxygen.We review the recent development in optical fiber gas cells and gas detection systems based on direct absorption,photothermal,photoacoustic,and stimulated Raman spectroscopies.