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Ruthenium decorated tungsten disulfide quantum dots for CO2 gas sensor
摘要： In this work, a selective chemi-resistive gas sensor for carbon dioxide gas detection at room temperature (~ 25 °C) was successfully fabricated, where ruthenium decorated tungsten disulfide (Ru@WS2) quantum dots (QDs) have been used as the sensing material. A mixed solvent of lithium hydroxide (LiOH·H2O) and N-Methyl-2-pyrrolidone (NMP) were used to obtain the Ru decorated WS2 QD from the exfoliated WS2 nanoflakes. Then the prepared WS2 QD and Ru@WS2 QD were confirmed using different material characterisation techniques. The gas sensors were then exposed to various concentration of CO2 gas in dry air condition. Also, the effect of humidity of both the sensors in 5000 ppm CO2 gas has been studied. The Ru@WS2 QDs based sensor showed superior sensitivity and good selectivity to CO2 gas in comparison with isopropanol, acetone, ethanol, methanol and benzene at room temperature than WS2 QD. The sensor showed an increase in resistance when exposed to CO2 gas ranging from 500 to 5000 ppm, indicating p-type characteristics. Ru@WS2 QD shows less effect at different humid condition compares to WS2 QD as a CO2 gas sensor.
关键词： Ruthenium decorated tungsten disulfide (Ru@WS2),Transition metal dichalcogenides (TMDC),Quantum Dot (QD),Sensitivity,Selectivity,Gas sensor
更新于2025-09-11 14:15:04
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Flakes Size-Dependent Optical and Electrochemical Properties of MoS2
摘要： Background: Molybdenum disulfide (MoS2) is a transition metal dichalcogenides and has some interesting and promising properties. MoS2 has direct and indirect band gaps depending on its crystalline structure. In addition, its sheets morphology makes it a good candidate for supercapacitor applications. Objective: The aim of this work is to study the effect of MoS2 flakes size on its optical and electrochemical properties. Method: MoS2 with different flakes sizes were prepared by exfoliation method. The exfoliation was performed by sonication of MoS2 powder in N,N-Dimethylformamide followed by different centrifugation speeds. UV-Vis spectra illustrated the optical energy gap was inversely proportional to the MoS2 flakes size. Results: Absorption coefficient values indicated that the exfoliation reduced the number of layers. Symmetric supercapacitor was made from two MoS2 electrodes and tested in 6 M KOH electrolyte. The specific capacitance was found to be dramatically increased with decreasing flakes size (9.5 and 4.5 mF/cm2 for 0.26 and 0.98 μm flakes size, respectively). Conclusion: These findings recommend that MoS2 can be the excellent electrode material for supercapacitor.
关键词： nanoflakes,cyclic voltammetry,supercapacitors,Transition Metal Dichalcogenides (TMDs),optical band gap,Molybdenum disulfide
更新于2025-09-10 09:29:36
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crystals
摘要： Transition-metal dichalcogenides open novel opportunities for the exploration of exciting new physics and devices. As a representative system, 2H -MoS2 has been extensively investigated owing to its unique band structure with a large band gap, degenerate valleys, and nonzero Berry curvature. However, experimental studies of metastable 1T polytypes have been a challenge for a long time, and electronic properties are obscure due to the inaccessibility of single phase without the coexistence of 1T (cid:2), 1T (cid:2)(cid:2), and 1T (cid:2)(cid:2)(cid:2) lattice structures, which hinder the broad applications of MoS2 in future nanodevices and optoelectronic devices. Using Kx (H2O)yMoS2 as the precursor, we have successfully obtained high-quality layered crystals of the metastable 1T (cid:2)(cid:2)(cid:2)-MoS2 with √3a superstructure and metastable 1T (cid:2)-MoS2 with a × 2a superstructure, as evidenced by structural characterizations through scanning tunneling microscopy, Raman spectroscopy, and x-ray diffraction. It is found that the metastable 1T (cid:2)-MoS2 is a superconductor with onset transition temperature (Tc) of 4.2 K, while the metastable 1T (cid:2)(cid:2)(cid:2)-MoS2 shows either superconductivity with Tc of 5.3 K or insulating behavior, which strongly depends on the synthesis procedure. Both of the metastable polytypes of MoS2 crystals can be transformed to the stable 2H phase with mild annealing at about 70 °C in He atmosphere. These ?ndings provide pivotal information on the atomic con?gurations and physical properties of 1T polytypes of MoS2.
关键词： Transition-metal dichalcogenides,MoS2,metastable phases,superconductivity,structural characterization
更新于2025-09-10 09:29:36
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Gold/WS2 nanocomposites fabricated by in-situ ultrasonication and assembling for photoelectrochemical immunosensing of carcinoembryonic antigen
摘要： Tungsten disulfide (WS2) nanosheets were obtained by exfoliating WS2 bulk crystals in N-methylpyrrolidone by ultrasonication. Gold nanoparticles (GNPs) were synthesized by in-situ ultrasonication of sodium citrate and HAuCl4 while fabricating the WS2 nanosheets. In this way, the GNPs were self-assembled on WS2 nanosheets to form a GNPs/WS2 nanocomposite through interaction between sulfur and gold atoms. The photoelectrochemical response of WS2 nanosheets is significantly enhanced after integration of the GNPs. The GNPs/WS2 nanocomposite was coated onto a glassy carbon electrode (GCE) to construct a sensing interface which then was modified with an antibody against the carcinoembryonic antigen (CEA) to obtain a photoelectrochemical immunosensor for CEA. Under optimized conditions, the decline in relative photocurrent is linearly related to the logarithm of the CEA concentration in the range from 0.001 to 40 ng mL?1. The detection limit is 0.5 pg mL?1 (at S/N = 3). The assay is sensitive, selective, stable and reproducible. It was applied to the determination of CEA in clinical serum samples.
关键词： Gold nanoparticles,CEA,Photoelectrochemistry,Nanosheets,Transition metal dichalcogenides,Immunosensor
更新于2025-09-10 09:29:36
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Multidimensional Coherent Spectroscopy of Semiconductors
摘要： Optical multidimensional coherent spectroscopy (MDCS) is a nonlinear spectroscopy technique where a material is excited by a series of laser pulses to produce a spectrum as a function of multiple frequencies. The technique’s ability to elucidate excited-state structure and interactions has made MDCS a valuable tool in the study of excitons in semiconductors. This review introduces the method and describes progress it has fostered establishing a better understanding of dephasing rates, coherent coupling mechanisms, and many-body interactions pertaining to optically generated electronic excitations in a variety of semiconductor material systems. Emphasis is placed on nanostructured gallium arsenide quantum wells and quantum dots, on quantum dots in other III–V and II–VI semiconductors, and on atomically thin transition metal dichalcogenides. Recent technical advances and potential future directions in the ?eld are also discussed.
关键词： quantum dots,excitons,quantum wells,Fourier-transform spectroscopy,transition metal dichalcogenides
更新于2025-09-10 09:29:36
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Ultrafast formation and dynamics of interlayer exciton in a large-area CVD-grown WS <sub/>2</sub> /WSe <sub/>2</sub> heterostructure
摘要： A WS2/WSe2 heterostructure is constructed by stacking a WS2 monolayer on the top of WSe2 monolayer fabricated with chemical vapor deposition (CVD) method. Ultrafast transient spectroscopy is used to demonstrate the ultrafast charge transfer and interlayer exciton dynamics in the heterostructure. When the WS2/WSe2 heterostructure was photoexcitated at 617 nm (2.01 eV) to excite the A-exciton transition of WS2, an ultrafast photobleaching was observed around the WSe2 A-exciton transition at 749 nm. The bleaching signal lasts several nanoseconds, which is much longer than the A-exciton lifetime in both the WS2 and WSe2 monolayer film. Moreover, by selectively photoexciting the A-exciton of WSe2 at 749 nm in the heterostructure, an ultrafast photobleaching occurs around the WS2 A-exciton transition, the recovery of the bleaching shows a single exponential relaxation with typical time constant of ~1.8 ps. The very fast relaxation in the heterostructure probing around 620 nm is indicative that rich defect states exist below the conduction band in WS2, which can efficiently trap these electrons transferred from the WSe2 upon photoexcitation. Our spectroscopic results reveal that our CVD-grown WS2/WSe2 bilayer film has a type II heterostructure in nature at room temperature. With photoexcitation, electrons and holes can be separately confined in the WS2 and WSe2 layer, respectively; as a result, interlayer excitons are formed.
关键词： charge transfer,interlayer exciton,type-II heterostructure,transition metal dichalcogenides,transient spectroscopy
更新于2025-09-10 09:29:36
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European Microscopy Congress 2016: Proceedings || Is the electronic structure of few layer transition metal dichalcogenides always two dimensional ?
摘要： The electronic structure of the transition metal dichalcogenides (TMDs) is investigated using angle-resolved photoemission spectroscopy (ARPES). We observe a new class of layered materials that can be prepared in various thicknesses down to single layers. Compared with the more well-known graphene, the TMDs are semiconductors and can be more useful in applications where an energy gap is essential. Our results show that the electronic structure of the TMDs is highly dependent on the number of layers, with a transition from indirect to direct bandgap as the thickness is reduced to a single layer. This transition is accompanied by a significant enhancement in photoluminescence intensity, making monolayer TMDs promising candidates for optoelectronic applications.
关键词： Angle-resolved photoemission spectroscopy,Bandgap engineering,Electronic structure,Optoelectronic applications,Transition metal dichalcogenides
更新于2025-09-10 09:29:36
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Increased yield of MoS <sub/>2</sub> monolayer exfoliation through the bimetallic corrosion of aluminum
摘要： In this paper, we propose a corrosion assisted exfoliation method as an improvement to the traditional tape exfoliation to obtain transition-metal dichalcogenide monolayers. Our method primarily relies on the electrochemical potential difference between transition metals and aluminum. The assistance of bubbles resulting from the bimetallic corrosion increases the yield of the exfoliation process for monolayers by 30-fold while boosting the probability of obtaining isolated monolayers. We use Raman measurements and a statistical comparison of the improved method with tape exfoliation to lay the evidence for our findings.
关键词： transition-metal dichalcogenides,MoS2,bimetallic corrosion,monolayer exfoliation,aluminum
更新于2025-09-10 09:29:36
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Polyphenol-Assisted Exfoliation of Transition Metal Dichalcogenides into Nanosheets as Photothermal Nanocarriers for Enhanced Antibiofilm Activity
摘要： Transition metal dichalcogenides (TMDs) nanosheets have evoked enormous research enthusiasm and have shown increased potentials in biomedical field. However, a great challenge lies in high-throughput, large-scale and eco-friendly preparation of TMDs nanosheets dispersions with high quality. Herein, we report a universal polyphenol-assisted strategy to facilely exfoliate various TMDs into monolayer or few-layer nanosheets. By optimizing the exfoliation condition of molybdenum disulfide (MoS2), the yield and concentration of as-exfoliated nanosheets is up to 60.5% and 1.21 mg/mL, respectively. This is the most efficient aqueous exfoliation method at present and is versatile for the choices of polyphenols and TMDs nanomaterials. The as-exfoliated MoS2 nanosheets possess superior biomedical stability as nanocarriers to load antibiotic drug. They show high photothermal conversion effect and thus induce a synergetic effect of chemotherapy and photothermal therapy to harvest enhanced antibiofilm activity under near-infrared (NIR) light. All these results offer an appealing strategy toward the synthesis and application of ultrathin TMDs nanosheets, with great implications for their development.
关键词： monolayer nanosheets,aqueous exfoliation,photothermal nanocarrier,transition metal dichalcogenides (TMDs),antibiofilm activity
更新于2025-09-10 09:29:36
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Room Temperature Valley Polarization and Coherence in Transition Metal Dichalcogenide-Graphene van der Waals Heterostructures
摘要： Van der Waals heterostructures made of graphene and transition metal dichalcogenides (TMD) are an emerging platform for opto-electronic, -spintronic and -valleytronic devices that could benefit from (i) strong light-matter interactions and spin-valley locking in TMDs and (ii) exceptional electron and spin transport in graphene. The operation of such devices requires significant valley polarization and valley coherence, ideally up to room temperature. Here, using a comprehensive Mueller polarimetry analysis, we report artifact-free room temperature degrees of valley polarization up to 40 % and, remarkably, of valley coherence up to 20 % in monolayer tungsten disulfide (WS2)/graphene heterostructures. At a temperature of 20 K, we measure a record degree of valley coherence of 60 %, a value that exceeds the degree of valley polarization (50 %) and indicates that our samples are minimally affected by pure dephasing processes. Valley contrasts have been particularly elusive in molybdenum diselenide (MoSe2), even at cryogenic temperatures. Upon interfacing monolayer MoSe2 with graphene, the room temperature degrees of valley polarization and coherence are as high as 14 % and 20 %, respectively. Our results are discussed in light of recent reports of highly efficient interlayer exciton and carrier transfer in TMD/graphene heterostructures and hold promise for room temperature chiral light-matter interactions and opto-valleytronic devices.
关键词： Mueller polarimetry,spin-valley locking,Transition metal dichalcogenides,graphene,chiral optics,opto-valleytronics,excitons
更新于2025-09-10 09:29:36