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Quantitative Mapping of the Charge Density in a Monolayer of MoS <sub/>2</sub> at Atomic Resolution by Off-Axis Electron Holography
摘要： The electric potential, electric field and charge density of a monolayer of MoS2 has been quantitatively measured at atomic scale resolution. This has been performed by off-axis electron holography using a double aberration-corrected transmission electron microscope operated at 80 kV and a low electron beam current density. Using this low dose rate and acceleration voltage, the specimen damage is limited during imaging. In order to improve the sensitivity of the measurement, series of holograms have been acquired. Instabilities of the microscope such as the drifts of the specimen, biprism and optical aberrations during the acquisition have been corrected by data processing. Phase images of the MoS2 monolayer have been acquired with a sensitivity of 2π/698 rad associated to a spatial resolution of 2.4 ?. The improvement in the signal-to-noise ratio allows the charge density to be directly calculated from the phase images using Poisson’s equation. Density functional theory simulations of the potential and charge density of this MoS2 monolayer were performed for comparison to the experiment. The experimental measurements and simulations are consistent with each other and notably, the charge density in a sulphur mono-vacancy (VS) site is shown.
关键词： MoS2,high-resolution,charge density,electric potential,electric field,electron holography,sulphur vacancy
更新于2025-09-12 10:27:22
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Hydrothermal processed heterogeneous MoS2 assisted charge transport in dye sensitized solar cells
摘要： Photovoltaic performance in dye sensitized solar cells (DSSCs) was improved by incorporating hydrothermal processed molybdenum disulfide (MoS2) into the bulk of titanium dioxide (TiO2) nanoparticle film. MoS2 exhibits a heterogeneous morphology comprising randomly distributed clustered nanoparticles and one dimensional nano-needles. The heterogeneous MoS2 was examined by X-ray photoelectron spectroscopy to study Mo 3d and S 2p peaks. Transmission electron microscopic studies on the heterogeneous MoS2 assert the presence of multilayers which further confirmed by UV–visible optical absorption spectroscopy showed absence of band-edge excitonic peaks at 612 nm and 674 nm. DSSCs show 17% enhancement in performance for 0.09 wt% of heterogeneous MoS2 incorporated TiO2 nanoparticle film compared to reference DSSC fabricated using only TiO2. Further changes in performance was examined by varying the concentration of MoS2 in TiO2 and observed that there is an optimum value to facilitate photo-generated charge transport kinetics in TiO2. The heterogeneous nature of MoS2 effectively acquired photo-electrons from TiO2 due to the presence of conduction band edge few meV below than that of in TiO2 and helps improving the performance.
关键词： TiO2,MoS2,Charge transport,Hydrothermal processing,Dye sensitized solar cells
更新于2025-09-12 10:27:22
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Catalyst-Free Growth of MoS2 Nanorods Synthesized by Dual Pulsed Laser-Assisted Chemical Vapor Deposition and Their Structural, Optical and Electrical Properties
摘要： Molybdenum disulfide (MoS2) nanorods (NRs) were synthesized from bulk MoS2 using laser-assisted chemical vapor deposition. A q-switched Nd:YAG laser with combined beam wavelengths of 1064 nm and 532 nm was used to ablate a solid MoS2 target. A vapor–solid process at a furnace temperature of 1000°C was found to support the growth of MoS2 NRs without the need for any metal catalyst. Powder x-ray diffraction analysis (PXRD), field emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and ultraviolet–visible (UV–Vis) and photoluminescence (PL) spectroscopy were used to characterize the structural and optical properties of MoS2 NRs. The PXRD revealed the crystallinity and phase purity of the as-synthesized NRs, while electron microscopy showed that MoS2 NRs had lengths in the range of 0.5–1.2 μm and widths between 40 nm and 160 nm. UV–Vis absorption spectra exhibited broad absorption, and PL measurements showed a sharp emission peak at 379 nm. Tauc plot calculations determined that the MoS2 NRs showed a direct transition. The electrical conductivity of the NRs was found to be 317.95 S/cm. In comparison with the MoS2 nanoparticles, the MoS2 NRs showed higher conductivity due to the in-plane electron transport, which is higher in NRs.
关键词： optical studies,MoS2,conductivity,electron microscopy,nanorods,LACVD
更新于2025-09-12 10:27:22
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Enhanced electrocatalytic properties in MoS2/MoTe2 hybrid heterostructures for dye-sensitized solar cells
摘要： In this work, the hybrid bilayer of molybdenum disulfide (MoS2)/molybdenum telluride (MoTe2) was constructed on fluorine-doped tin oxide glass (FTO), and dye-sensitized solar cells (DSSCs) employing the material as counter electrode (CE) were implemented. The thickness of each layer of MoS2 and MoTe2 was tuned by changing the sputtering time to enhance DSSC performance. The DSSC with the MoS2/MoTe2 hybrid CE, exhibited a maximum power conversion efficiency (PCE) of 8.07% (6% for MoS2 and 7.25% for MoTe2 CE), and was comparable to one with Pt CE (8.33%). The observed good result of the MoS2/MoTe2 hybrid CE is ascribed to the synergistic properties between MoS2 and the metallic phase of MoTe2.
关键词： MoS2/MoTe2,DSSCs,Counter electrode,Hybrids
更新于2025-09-12 10:27:22
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Synthesis of MoS2–MoO2/MWCNTs counter electrode for high-efficient dye-sensitized solar cells
摘要： In this work, MoS2–MoO2 and MoS2–MoO2/MWCNTs counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) were prepared by sulfurization of a one-pot hydrothermally obtained MoO2 film and MoO2/MWCNTs composite film on fluorine-doped tin oxide glasses at 500?°C for 2?h in argon atmosphere. The promoted MoS2 particles on a surface of MoS2–MoO2 and MoS2–MoO2/MWCNTs films were identified by X-ray diffraction to have a hexagonal structure. Morphology of MoO2, MoO2/MWCNTs, MoS2–MoO2, and MoS2–MoO2/MWCNTs CEs was studied using field emission scanning electron microscope and transmission electron microscope. Functional groups in MoS2–MoO2/MWCNTs sample were identified by Raman spectroscopy. Results of cyclic voltammetry and electrochemical impedance spectroscopy displayed a high electrocatalytic activity performance and low charge transfer resistance of MoS2–MoO2/MWCNTs CE as compared to those of MoO2, MoO2/MWCNTs, and MoS2–MoO2 CEs. Interestingly, the DSSC based on MoS2–MoO2/MWCNTs CE could provide the higher power conversion efficiency of 7.79% compared to that of 7.26% for Pt-based DSSC.
关键词： electrocatalytic activity,dye-sensitized solar cells,counter electrode,MoS2–MoO2,MWCNTs
更新于2025-09-12 10:27:22
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Growth of CdSe/MoS2 vertical heterostructures for fast visible-wavelength photodetectors
摘要： Heterostructures composed of different semiconducting materials have aroused wide attentions due to their fascinating properties originated from the interfaces. Particularly, the recent two dimensional layered materials (2DLM) have provided novel platforms to flexibly design the heterostructures for diverse electronic and optoelectronic applications. In this work, we have reported the growth of CdSe nanoplates/MoS2 monolayer vertical heterostructures with efficient and fast visible-wavelength photodetections. Highly dense CdSe nanoplates were vertically assembled on monolayer MoS2 through a two-step chemical vapor deposition (CVD) process. The interfacial photoinduced charge behaviors were investigated in detail via the time resolution photoluminescence (TRPL) measurements, revealing the efficient charge transfer across the heterointerface. Benefiting from the large CdSe coverage and efficient charge transfer, superior photodetection performances of the CdSe/MoS2 heterostructures can be obtained with an enhanced photoresponsivity of 1.63 A/W, which can be further improved to be 12 A/W via applying the gate voltage. Besides, the heterostructure detectors also exhibit a very fast photoresponse speed of 370 μs, much faster than previous photodetectors based on CVD-grown 2D heterostructures. The as-synthesized CdSe/MoS2 heterostructures may find important applications in integrated optoelectronic systems.
关键词： Responsivity,Chemical vapor deposition,Photodetectors,Vertical heterostructures,CdSe/MoS2
更新于2025-09-12 10:27:22
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High-Power Large-Energy Raman Soliton Generations Within a Mode-Locked Yb-Doped Fiber Laser Based on High-Damage-Threshold CVD-MoS2 as Modulator
摘要： In our work, based on a high-damage-threshold MoS2 saturable absorber (SA), high-power intra-cavity Raman solitons within a passively mode-locked Yb-doped fiber laser were demonstrated successfully for the first time. The damage threshold of the MoS2 SA was as high as ~0.48 J/cm2. By adjusting the polarization states, stable single- or dual-pulse Raman soliton operations were obtained. The maximum average output power for single-pulse and dual-pulse Raman soliton operations was 80.11 and 89.33 mW, respectively. Our experiment results show significant enhancement in comparison with previous works, which provides fundamental guidance for future designs of high-power, large-energy, intra-cavity Raman soliton generations based on two-dimensional materials as SAs.
关键词： mode-locked Raman fiber laser,high-damage 2D MoS2 materials,ultra-fast optical modulation
更新于2025-09-12 10:27:22
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Controlled Plasma Thinning of Bulk MoS <sub/>2</sub> Flakes for Photodetector Fabrication
摘要： The electronic properties of layered materials are directly determined based on their thicknesses. Remarkable progress has been carried out on synthesis of wafer-scale atomically molybdenum disulfide (MoS2) layers as a two-dimensional material in the past few years in order to transform them into commercial products. Although chemical/mechanical exfoliation techniques are used to obtain a high-quality monolayer of MoS2, the lack of suitable control in the thickness and the lateral size of the flakes restrict their benefits. As a result, a straightforward, effective, and reliable approach is widely demanded to achieve a flake with control in its thickness for optoelectronic applications. In this study, thick MoS2 flakes are obtained by a short-time bath sonication in dimethylformamide solvent, which are thinned with the aid of a sequential plasma etching process using H2, O2, and SF6 plasma. A comprehensive study has been carried out on MoS2 flakes based on scanning electron microscopy, atomic force microscopy, Raman, transmission electron microscopy, and X-ray photoelectron microscopy measurements, which ultimately leads to a two-cycle plasma thinning method. In this approach, H2 is used in the passivation step in the first subcycle, and O2/SF6 plasma acts as an etching step for removing the MoS2 layers in the second subcycle. Finally, we show that this technique can be enthusiastically used to fabricate MoS2-based photodetectors with a considerable photoresponsivity of 1.39 A/W and a response time of 0.45 s under laser excitation of 532 nm.
关键词： photodetector,MoS2,optoelectronic applications,plasma thinning,two-dimensional materials
更新于2025-09-12 10:27:22
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Maskless Micro/Nanopatterning and Bipolar Electrical-Rectification of MoS2 Flakes Through Femtosecond Laser Direct Writing
摘要： MoS2 micro/nanostructures are desirable for tuning electronic properties, developing required functionality, and improving existing performance of multilayer MoS2 devices. This work presents a useful method to flexibly microprocess multilayer MoS2 flakes through femtosecond laser pulse direct writing, which can directly fabricate regular MoS2 nanoribbon arrays with ribbon widths of 179, 152, 116, 98, and 77 nm, and arbitrarily pattern MoS2 flakes to form micro/nanostructures such as single nanoribbon, labyrinth array, and cross structure. This method is mask-free and simple, and has high flexibility, strong controllability, and high precision. Moreover, numerous oxygen molecules are chemically and physically adsorbed on laser-processed MoS2, attributed to roughness defect-sites and edges of micro/nanostructures that contain numerous unsaturated edge-sites and highly active centres. In addition, electrical tests of the field effect transistor fabricated from prepared MoS2 nanoribbon arrays reveal new interesting features: output and transfer characteristics exhibit strong rectification (not going through zero and bipolar conduction) of drain?source current, which is supposedly attributed to the parallel structures with many edge-defects and p-type chemical doping of oxygen molecules on MoS2 nanoribbon arrays. This work demonstrates the ability of femtosecond laser pulses to directly induce micro/nanostructures, property changes, and new device-properties of two-dimension materials, which may future enable new applications at electronic devices based on MoS2 such as logic circuits, complementary circuits, chemical sensors, and p?n diodes.
关键词： micro/nanopatterning,MoS2 flakes,oxygen bonding,femtosecond laser direct writing,electrical rectification
更新于2025-09-12 10:27:22
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Site-selective Atomic Layer Precision Thinning of MoS2 via Laser-Assisted Anisotropic Chemical Etching
摘要： Various exotic optoelectronic properties of two-dimensional (2D) transition metal dichalcogenides (TMDCs) strongly depend on their number of layers, and typically manifest in ultra-thin few- or mono-layer formats. Thus, precise manipulation of thickness and shape is essential to fully access their potential in optoelectronic applications. Here, we demonstrate site-selective atomic layer precision thinning of exfoliated MoS2 flake by laser. The oxidation mediated anisotropic chemical etching initiated from edge defects and progressed by controlled scanning of the laser beam. Thereby, the top-most layer can be preferentially removed in designed patterns without damaging the bottom flake. In addition, we could monitor the deceleration of the thinning by in-situ reflectance measurement. The apparent slow-down of the thinning rate is attributed to the sharp reduction in the temperature of the flake due to thickness dependent optical properties. Fabrication of monolayer stripes by laser thinning suggests potential applications in non-linear optical gratings. The proposed thinning method would offer a unique and rather straightforward way to obtain arbitrary shape and thickness of TMDCs flake for various optoelectronic applications.
关键词： Laser Thinning,Single layer precision thinning,Non-linear optical grating,Anisotropic chemical etching,TMDCs,MoS2
更新于2025-09-12 10:27:22