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Controlled Micro/Nanodome Formation in Proton‐Irradiated Bulk Transition‐Metal Dichalcogenides
摘要： At the few-atom-thick limit, transition-metal dichalcogenides (TMDs) exhibit strongly interconnected structural and optoelectronic properties. The possibility to tailor the latter by controlling the former is expected to have a great impact on applied and fundamental research. As shown here, proton irradiation deeply affects the surface morphology of bulk TMD crystals. Protons penetrate the top layer, resulting in the production and progressive accumulation of molecular hydrogen in the first interlayer region. This leads to the blistering of one-monolayer thick domes, which stud the crystal surface and locally turn the dark bulk material into an efficient light emitter. The domes are stable (>2-year lifetime) and robust, and host strong, complex strain fields. Lithographic techniques provide a means to engineer the formation process so that the domes can be produced with well-ordered positions and sizes tunable from the nanometer to the micrometer scale, with important prospects for so far unattainable applications.
关键词： transition-metal dichalcogenides,hydrogen evolution reaction,strain,photoluminescence,2D materials,Raman
更新于2025-09-11 14:15:04
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Direct Synthesis of a Self‐Assembled WSe <sub/>2</sub> /MoS <sub/>2</sub> Heterostructure Array and its Optoelectrical Properties
摘要： Functional van der Waals heterojunctions of transition metal dichalcogenides are emerging as a potential candidate for the basis of next-generation logic devices and optoelectronics. However, the complexity of synthesis processes so far has delayed the successful integration of the heterostructure device array within a large scale, which is necessary for practical applications. Here, a direct synthesis method is introduced to fabricate an array of self-assembled WSe2/MoS2 heterostructures through facile solution-based directional precipitation. By manipulating the internal convection flow (i.e., Marangoni flow) of the solution, the WSe2 wires are selectively stacked over the MoS2 wires at a specific angle, which enables the formation of parallel- and cross-aligned heterostructures. The realized WSe2/MoS2-based p–n heterojunction shows not only high rectification (ideality factor: 1.18) but also promising optoelectrical properties with a high responsivity of 5.39 A W?1 and response speed of 16 μs. As a feasible application, a WSe2/MoS2-based photodiode array (10 × 10) is demonstrated, which proves that the photosensing system can detect the position and intensity of an external light source. The solution-based growth of hierarchical structures with various alignments could offer a method for the further development of large-area electronic and optoelectronic applications.
关键词： transition-metal dichalcogenides,p–n junctions,Marangoni flow,photodetectors,heterojunctions
更新于2025-09-11 14:15:04
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Rhenium Diselenide (ReSe <sub/>2</sub> ) Near‐Infrared Photodetector: Performance Enhancement by Selective p‐Doping Technique
摘要： In this study, a near-infrared photodetector featuring a high photoresponsivity and a short photoresponse time is demonstrated, which is fabricated on rhenium diselenide (ReSe2) with a relatively narrow bandgap (0.9–1.0 eV) compared to conventional transition-metal dichalcogenides (TMDs). The excellent photo and temporal responses, which generally show a trade-off relation, are achieved simultaneously by applying a p-doping technique based on hydrochloric acid (HCl) to a selected ReSe2 region. Because the p-doping of ReSe2 originates from the charge transfer from un-ionized Cl molecules in the HCl to the ReSe2 surface, by adjusting the concentration of the HCl solution from 0.1 to 10 m, the doping concentration of the ReSe2 is controlled between 3.64 × 1010 and 3.61 × 1011 cm?2. Especially, the application of the selective HCl doping technique to the ReSe2 photodetector increases the photoresponsivity from 79.99 to 1.93 × 103 A W?1, and it also enhances the rise and decay times from 10.5 to 1.4 ms and from 291 to 3.1 ms, respectively, compared with the undoped ReSe2 device. The proposed selective p-doping technique and its fundamental analysis will provide a scientific foundation for implementing high-performance TMD-based electronic and optoelectronic devices.
关键词： photodetector,transition-metal dichalcogenides (TMDs),p-doping,selective doping,HCl doping,ReSe2,transistor
更新于2025-09-11 14:15:04
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Laser‐Directed Assembly of Nanorods of 2D Materials
摘要： Herein, the previously unrealized ability to grow nanorods and nanotubes of 2D materials using femtosecond laser irradiation is demonstrated. In as short as 20 min, nanorods of tungsten disulfide, molybdenum disulfide, graphene, and boron nitride are grown in solutions. The technique fragments nanoparticles of the 2D materials from bulk flakes and leverages molecular scale alignment by nonresonant intense laser pulses to direct their assembly into nanorods up to several micrometers in length. The laser treatment process is found to induce phase transformations in some of the materials, and also results in the modification of the nanorods with functional groups from the solvent atoms. Notably, the WS2 nanoparticles, which are ablated from semiconducting 2H WS2 crystallographic phase flakes, reassemble into nanorods consisting of the 1T metallic phase. Due to this transition, and the 1D nature of the fabricated nanorods, the WS2 nanorods display substantial improvements in electrical conductivity and optical transparency when employed as transparent conductors.
关键词： laser assembly,graphene,nanorods,transition metal dichalcogenides
更新于2025-09-11 14:15:04
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Rashba splitting in bilayer transition metal dichalcogenides controlled by electronic ferroelectricity
摘要： Based on ?rst-principles calculations and k · p model analyses, we uncover the coexistence and coupling of Rashba spin splitting with electronic ferroelectricity in bilayer transition metal dichalcogenides MX2 (M = Mo,W; X = S,Se,Te) with certain stacking con?gurations. The reversible spontaneous ferroelectric polarization, along the out-of-plane direction (the preferred direction for applications), totally arises from the interlayer charge transfer, rather than being governed by the ionic displacement as found in conventional ferroelectrics. The spin texture related to the Rashba spin splitting can be reversed upon inversion of the ferroelectric polarization. In particular, by applying a small in-plane compressive strain, the magnitude of Rashba band splitting can be tuned to be as large as 100 meV. These results would open up possibilities for exploring two-dimensional multiferroic physics and developing electrically controlled nanoscale spintronic devices.
关键词： Rashba splitting,bilayer transition metal dichalcogenides,spintronic devices,electronic ferroelectricity
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Intravalley Spin-Flip Relaxation Dynamics in Single-Layer WS <sub/>2</sub>
摘要： Two-dimensional Transition Metal Dichalcogenides (TMDs) have been widely studied because of the peculiar electronic band structure and the strong excitonic effects. In these materials the large spin-orbit coupling lifts the spin degeneracy of the valence (VB) and the conduction band (CB) giving rise to the A and B interband excitonic transitions. In monolayer WS2, the spins of electrons in the lowest CB and in the highest VB at K/K’ point of the Brillouin zone are antiparallel resulting in an intravalley dark exciton state at a lower energy than the bright exciton. Here we use two-colour helicity-resolved pump-probe spectroscopy to directly resolve the intravalley spin-?ip process of the photoexcited electrons in the CB of single-layer WS2. We ?nd that at T=77 K this process occurs on a sub-ps time scale and it is signi?cantly dependent on the temperature, strongly pointing to a phonon assisted relaxation process. Our results shed light on the intravalley spin relaxation process in single-layer WS2, determining the formation of the intravalley dark exciton, which we measure to occur on a sub-ps timescale. The study of dark excitons formation dynamics is important for designing TMD-based electronic/photonic devices.
关键词： WS2,spin-?ip relaxation,exciton,pump-probe spectroscopy,Transition Metal Dichalcogenides
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Direct Laser Synthesis of Two-Dimensional Transition Metal Dichalcogenides
摘要： The emergence of nanomaterials with their often superior mechanical, electronic and optical properties compared with bulk form demands a robust technology that can synthesize, modify and pattern scalably and cost effectively. This can be fulfilled via laser processing protocols which produce such materials with both high precision and excellent spatial controllability [1]. Direct laser synthesis of nanomaterials such as graphene and nano-structured metal oxides have been explored thoroughly for a wide range of applications [2,3]. However, to date, there are only a few reports associated with the laser processing of two-dimensional transition metal dichalcogenides (2D-TMDCs) [4]. These mainly utilize laser radiation for thinning TMDC films through sublimation down to a single molecular thickness [1]. However, this top-down approach is not practical for large- area and scalable production. In addition, further processing steps such as lithographic patterning are then required for discrete device fabrication. Here we present a novel method for the local synthesis and patterning of two-dimensional MoS2 and WS2 layers. The synthesis of these materials is achieved by spatially selective, visible laser irradiation of suitable precursors coated on the surface of planar substrates under ambient, room temperature conditions. The non- exposed precursor regions are then completely removed in a single step, revealing the synthesised 2D-TMDCs. This method can produce micro-patterned films with lateral dimensions that approach the diffraction limit of the focused laser beam. An example of such laser synthesised MoS2 tracks can be seen in the optical microscopy image of Figure 1(a) where it clearly shows a well-defined micro-pattern without any precursor residue. Using this method, we have achieved local synthesis of of MoS2 and WS2 with thickness down to three molecular layers for MoS2 and monolayer WS2 on various glass and crystalline substrates. The quality and thickness of the resulting films can be tuned by modifying the precursor chemistry and laser parameters. Different microprobe and spectroscopic spectroscopy, photoluminescence spectroscopy (PL) and X-ray photoelectron spectroscopy (XPS) have been used to assess the quality and thickness of the deposited MoS2 and WS2 structures. Finally, we have demonstrated the electronic functionality of our films by fabricating a thin film transistor (TFT). The transfer characteristics (source-drain current vs gate voltage) of such a TFT using a laser-synthesised MoS2 channel is shown in Figure 1(b).
关键词： Two-Dimensional Transition Metal Dichalcogenides,WS2,MoS2,Direct Laser Synthesis,Thin Film Transistor
更新于2025-09-11 14:15:04
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Nonlinear photoresponse of metallic graphene-like VSe2 ultrathin nanosheets for pulse laser generation
摘要： Vanadium diselenide (VSe2), a typical metallic behaviour material among transition metal dichalcogenides (TMDCs) family, exhibits excellent photoelectric characteristics with a zero band gap, missing applicaiotn in pulse generation. In this work, a high-quality VSe2 saturable absorber (SA) was synthesized through a liquid-phase exfoliation method. The saturable absorption of obtained VSe2-SA was characterized systematically. The measured modulation depth was 9.9%, and the saturated intensity was 533.8 μJ/cm2. By incorporating this optical modulator into a ytterbium-doped ?ber laser cavity, a stable passively Q-switched laser could be achieved. The pulse had the central wavelength of 1064.03 nm. As the pump power was increased, the repetition rate increased from 24.3 kHz to 35.6 kHz, and the pulse duration decreased from 7.21 μs to 5.27 μs. The output power had the maximum value of 28.55 mW. These results indicated that VSe2 is an e?ective candidate to generate pulse laser due to its excellent nonlinear optical properties and universal photoelectric response, which may advance the applications of VSe2-based nonlinear optics and photoelectric devices.
关键词： VSe2,?ber laser,transition metal dichalcogenides,pulse laser,saturable absorber
更新于2025-09-11 14:15:04
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Recent progress in the controlled synthesis of 2D metallic transition metal dichalcogenides
摘要： Two-dimensional (2D) metallic transition metal dichalcogenides (MTMDCs), the complement of 2D semiconducting TMDCs, have attracted extensive attentions in recent years because of their versatile properties such as superconductivity, charge density wave, and magnetism. To promote the investigations of their fantastic properties and broad applications, the preparation of large-area, high-quality, and thickness-tunable 2D MTMDCs has become a very urgent topic and great efforts have been made. This topical review therefore focuses on the introduction of the recent achievements for the controllable syntheses of 2D MTMDCs (VS2, VSe2, TaS2, TaSe2, NbS2, NbSe2, etc.). To begin with, some earlier developed routes such as chemical vapor transport, mechanical/chemical exfoliation, as well as molecular beam epitaxy methods are briefly introduced. Secondly, the scalable chemical vapor deposition methods involved with two sorts of metal-based feedstocks, including transition metal chlorides and transition metal oxidations mixed with alkali halides, are discussed separately. Finally, challenges for the syntheses of high-quality 2D MTMDCs are discussed and the future research directions in the related fields are proposed.
关键词： chemical vapor deposition,metallic transition metal dichalcogenides,synthesis,two dimensional
更新于2025-09-11 14:15:04
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Mode-Locked Er-Doped Fiber Laser by Using MoS2/SiO2 Saturable Absorber
摘要： The two-dimensional (2D) layered material MoS2 has attracted numerous attentions for electronics and optoelectronics applications. In this work, a novel type of MoS2-doped sol-gel glass composite material is prepared. The nonlinear optical properties of prepared MoS2/SiO2 composite material are measured with modulation depth (ΔT) of 3.5% and saturable intensity (Isat) of 20.15 MW/cm2. The optical damage threshold is 3.46 J/cm2. Using the MoS2/SiO2 composite material as saturable absorber (SA), a passive mode-locked Er-doped fiber (EDF) laser is realized. Stable conventional soliton mode-locking pulses are successfully generated with a pulse width of 780 fs at the pump power of 90 mW. In the pump power range of 100–600 mW, another stable mode-locking operation is obtained. The pulse width is 1.21 ps and the maximum output power is 5.11 mW. The results indicate that MoS2/SiO2 composite materials could offer a new way for optical applications.
关键词： Nonlinear optical materials,Saturable absorbers,Transition metal dichalcogenides
更新于2025-09-11 14:15:04