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Graphene samples preparation and some possible uses in developing optical communication devices
摘要： Graphene is a two-dimensional material which has been attracting the attention of worldwide scientific community, motivated by their optical and electronic properties. There are different methods for obtaining grapheme; however, the micromechanical exfoliation process is the simplest and it allows samples with high quality to be obtained. In this paper, the preparation process of graphene flakes by exfoliation method and their characterization by Raman spectroscopy are shown. Moreover, some possible uses of graphene flakes applied to develop optical communication high speed devices are described.
关键词： exfoliation method,graphene,Raman spectroscopy,flakes
更新于2025-09-12 10:27:22
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Mechanistic insights into the phenomena of increasing capacity with cycle number: using pulsed-laser deposited MoO <sub/>2</sub> thin film electrodes
摘要： Lithium ion batteries typically lose capacity or energy storage density (i.e. capacity fading) over the course of extended cycling which can be problematic for applications and appears to be exaggerated when high current rates are used. However, in some cases fluctuations in capacity with cycle number and even increases in capacity with cycle number are noted with predominantly thin film based electrodes. Here we demonstrate the synthesis and in-depth characterisation of laser deposited MoO2 thin film anodes and its unconventional mechanism. A MoO2 electrode shows an initial capacity of 79 mA h g?1 which increases to capacities of 600 mA h g?1 at 15.8 A g?1 after 90 000 cycles. A maximum capacity of 1714 mA h g?1 was achieved in an electrode cycled at 1.5 A g?1 for over 3800 cycles, the highest recorded capacity in MoOx anodes to date. The most intriguing aspects of this work is the fact that capacity is shown to fluctuate and typically increase well above the theoretical capacity of MoO2. A combination of electrochemical cycling, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, focused ion beam milling and transmission electron microscopy at various states of cycling is used to illustrate a proposed mechanism. The mechanism illustrated is based on exfoliation of layers of MoO2 off the pulsed laser deposition (PLD) grown MoO2 electrodes during cycling that creates additional surface area and easier access for Li-ions to both adsorb to the surface and insert/react with the host material. Further features in the capacity evolution are rationalised by this mechanism and methods to control the capacity evolution are detailed. These results present a rational explanation for when an electrode undergoes a substantial increase in capacity over its extended cycling life.
关键词： pulsed laser deposition,MoO2 thin film anodes,exfoliation mechanism,Lithium ion batteries,capacity increase
更新于2025-09-12 10:27:22
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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) - Nonlinear Refraction and Nonlinear Absorption in Layered Transition Metals Dichalcogenides
摘要： The unique thickness- and composition-dependent properties of two-dimensional Transition Metal Dichalcogenides (TMDs) afford opportunities to a wide range of applications, as reviewed in [1]. Among the diverse methods to fabricate TMDs, redox exfoliation offers features critical to composite, coating and ink technologies, including low cost, low-energy, and a general framework for exfoliating TMDs from Groups IV, V, VI, and VII. Nonlinear (NL) optical absorption is a relevant effect in TMDs with potential applications in multiphoton microscopy, fluorescence imaging and optical limiting. For instance, two-photon absorption (TPA) saturation in MoS2 was reported in [2]. On the other hand, NL refraction may be exploited for all-optical switching and optical processing. In this communication, we describe the NL optical behavior of MoS2, WS2, NbS2 and ZrTe2 in the femtosecond regime. Details of the redox exfoliation and morphological characterization of the TMDs are given in [3]. For the experiments, the TMDs were suspended in acetonitrile with concentrations of (cid:26)(cid:19)(cid:3)(cid:541)(cid:74)(cid:18)(cid:80)(cid:79) (MoS2)(cid:15)(cid:3)(cid:23)(cid:19)(cid:3)(cid:541)(cid:74)(cid:18)(cid:80)(cid:79) (WS2), (cid:20)(cid:19)(cid:19)(cid:3) (cid:541)(cid:74)(cid:18)(cid:80)(cid:79)(cid:3) (NbS2) (cid:68)(cid:81)(cid:71)(cid:3) (cid:20)(cid:19)(cid:19)(cid:3) (cid:541)(cid:74)(cid:18)(cid:80)(cid:79) (ZrTe2). The mean lateral flakes’ sizes varied from 84 nm to 325 nm and thicknesses from 2.0±1.1 nm to 3.8±1.7 nm. Fig.1(a) shows the linear extinction spectra of the four samples. The effective NL refractive index (nNL) and effective NL absorption coefficient ((cid:68)NL) were measured. In principle, both parameters include contributions from NL susceptibilities and NL light scattering. The light source used was a Ti:Sapphire based regenerative amplifier (800 nm, 1 kHz, 100 fs). The beam was focused with a 15 cm focal length lens onto a 1 mm quartz cuvette. The peak intensity was varied up to (cid:1835) =120 GW/cm2. Z-scan measurements were also performed for pure acetonitrile which showed third-order refractive index equal to +1.9×10-17cm2/W. Fig.1(b) shows the ratio between the peak-to-valley Z-scan curve and the laser intensity (|(cid:959)(cid:1846)|/(cid:1835)) versus (cid:1835) that indicates an effective fifth-order nonlinearity of MoS2 - the values of the third- and fifth-order effective refractive indices are +(4.5±0.3)×10-16 cm2/W and - (7.1±0.2) × 10-25 cm4/W2, respectively. Fig. 1(c) shows that in the case of WS2 only the third-order nonlinearity is observed and nNL=+(3.4±0.2) ×10-16 cm2/W. Fig. 1(d), for NbS2, shows a change in the nNL sign from negative to positive as the intensity increases. Finally, Fig.1(e) for the novel ZrTe2 material shows third-order response with nNL=+(4.2±0.3)×10-16 cm2/W. NL absorption was only observed for NbS2 which presented the effective TPA changing to saturated absorption as the intensity is increased. The results were analyzed considering the sample’s characteristics and applying the Z-scan procedure as described in [4]. To fit the NL absorption curves of NbS2 we assumed homogeneous broadening relaxation and the saturation intensities obtained were 33 GW/cm2 for 1-photon and 39 GW/cm2 for 2-photon absorption. The effective TPA coefficient was 0.21 cm/GW for intensities below saturation.
关键词： Transition Metals Dichalcogenides,TMDs,redox exfoliation,Nonlinear Absorption,Nonlinear Refraction,femtosecond regime
更新于2025-09-12 10:27:22
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Surface Engineering of MoS <sub/>2</sub> via Laser‐Induced Exfoliation in Protic Solvents
摘要： With excellent performance in the hydrogen evolution reaction (HER), molybdenum disulfide (MoS2) is considered a promising nonprecious candidate to substitute Pt-based catalysts. Herein, pulsed laser irradiation in liquid is used to realize one-step exfoliation of bulk 2H-MoS2 to ultrastable few-layer MoS2 nanosheets. Such prepared MoS2 nanosheets are rich in S vacancies and metallic 1T phase, which significantly contribute to the boosted catalytic HER activity. Protic solvents play a pivotal role in the production of S vacancies and 2H-to-1T phase transition under laser irradiation. MoS2 exfoliated in an optimal solvent of formic acid exhibits outstanding HER activity with an overpotential of 180 mV at 10 mA cm?2 and Tafel slope of 54 mV dec?1.
关键词： molybdenum disulfide,sulfur vacancy,solvent effect,phase transition,laser exfoliation in liquid
更新于2025-09-11 14:15:04
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An Unexpected Transformation of Organic Solvents into 2D Fluorescent Quantum Dots During Ultrasonication Assisted Liquid Phase Exfoliation
摘要： Ultrasonication within organic solvents is widely used to exfoliate layered materials and produce two-dimensional (2D) nanostructures. Several 2D materials synthesized by such liquid phase exfoliation (LPE) approaches are reported to exhibit photoluminescence. In these approaches, it is presumed that while the 2D nanostructures are derived from the layered parent material undergoing delamination, the organic solvent serves as a dispersing medium. However, in this study, we show that the organic solvent also contributes towards formation of 2D nanostructures that are optically active. We show that that bare organic solvent, when exposed to ultrasonication, transforms into 2D photoluminescent carbon quantum dots (CQDs) that display blue, cyan, green, and yellow emissions depending upon the excitation wavelength. Although this finding is intuitive, it has remained unacknowledged in the design of experiments which require ultrasonication of layered materials in organic solvents. Our results suggest that optical properties of dispersions obtained by LPE embody a contribution not only from the 2D nanostructures derived from the layered material but also from the 2D CQDs that are formed as a natural result of the liquid medium being exposed to ultrasonication. We anticipate that this new physical insight would form an important addition to the guidelines for exfoliation and help in rightly inferring the optical properties of the 2D material dispersions produced by these methods.
关键词： 2D nanostructures,Carbon quantum dots,Organic solvents,Liquid phase exfoliation,Ultrasonication,Photoluminescence
更新于2025-09-11 14:15:04
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High-yield production of stable antimonene quantum sheets for highly efficient organic photovoltaics
摘要： High-performance organic photovoltaics (OPVs) are of great scientific and technological importance due to their potential large-scale industrial applications. Introducing semiconductor quantum dots has been proven to be an effective way to improve the power conversion efficiency (PCE) of OPVs. In this paper, we report a novel approach to fabricate atomically thin antimonene quantum sheets (AMQSs) possessing a uniform size (～2.2 nm) via imidazolium ionic liquid-assisted exfoliation. In this method, the yield of AMQSs (1.1 mg mL?1) has been increased by nearly two orders of magnitude compared with that of previously reported methods. Furthermore, upon adding AMQSs into the light absorber in OPVs, the optimal device with 1.0 mg mL?1 AMQSs shows the highest PCE of 9.75%, resulting in over 25% enhancement in PCE compared to that of the reference device. It also leads to a noticeable enhancement in the short-circuit current density (Jsc) of 16.7% and the fill factor (FF) of 8.4%. The increased PCE is mainly due to the two-dimensional electronic structure of AMQSs that can enhance the light absorption, assist exciton dissociation and reduce charge recombination of OPVs. This work provides a new avenue toward mass production of two-dimensional quantum sheets and points to a new strategy for highly efficient OPVs.
关键词： antimonene quantum sheets,organic photovoltaics,power conversion efficiency,ionic liquid-assisted exfoliation,two-dimensional materials
更新于2025-09-11 14:15:04
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Macroscopically aligned carbon nanotubes for flexible and high-temperature electronics, optoelectronics, and thermoelectrics
摘要： With excellent performance in the hydrogen evolution reaction (HER), molybdenum disulfide (MoS2) is considered a promising nonprecious candidate to substitute Pt-based catalysts. Herein, pulsed laser irradiation in liquid is used to realize one-step exfoliation of bulk 2H-MoS2 to ultrastable few-layer MoS2 nanosheets. Such prepared MoS2 nanosheets are rich in S vacancies and metallic 1T phase, which significantly contribute to the boosted catalytic HER activity. Protic solvents play a pivotal role in the production of S vacancies and 2H-to-1T phase transition under laser irradiation. MoS2 exfoliated in an optimal solvent of formic acid exhibits outstanding HER activity with an overpotential of 180 mV at 10 mA cm?2 and Tafel slope of 54 mV dec?1.
关键词： molybdenum disulfide,sulfur vacancy,solvent effect,phase transition,laser exfoliation in liquid
更新于2025-09-11 14:15:04
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Slot-Die-Printed Two-Dimensional ZrS <sub/>3</sub> Charge Transport Layer for Perovskite Light-Emitting Diodes
摘要： Liquid phase exfoliation of zirconium trisulfide (ZrS3) was used to produce stable and ready-to-use inks for solution processed semiconductor thin film deposition. Ribbon-like layered crystals of ZrS3 were produced by chemical vapor transport method and were then exfoliated in three different solvents: dimethyl formamide, ethanol and isopropyl alcohol. The resulting ZrS3 dispersions were compared for stability and the ability to form continuous films on top of perovskite layer in light-emitting diodes with ITO/PEDOT:PSS/MAPbBr3/2D-ZrS3/LiF/Al structure. Film deposition was performed by using either spray or slot-die coating methods. Slot-die coating route proved to produce better and more uniform films with respect to spray-coating. We found that 2D ZrS3 electron injection layer (EIL) stabilized the interface between the perovskite and LiF/Al cathode, reducing the turn-on voltage to 2.8 V and showing a luminance that does not degrade during voltage sweep. On the opposite, EIL-free devices show electroluminescence on the first voltage sweep that reduces almost to zero in the subsequent sweeps. Combining physical device simulation and Density Functional Theory calculation, we are able to explain these results in terms of lowering of electron injection barrier at the cathode.
关键词： perovskite light emitting diodes,slot-die printing,2D materials,exfoliation,transition metal trichalcogenides,ZrS3
更新于2025-09-11 14:15:04
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The Electrical Property of Large Few Layer Graphene Flakes Obtained by Microwaves Assisted Exfoliation of Expanded Graphite
摘要： Few layer graphene (FLG) was synthesized by (cid:2)-wave assisted exfoliation of expanded graphite in toluene with an overall yield from c.a. 7% to 20%. A significant difference in the absorption of (cid:2)-waves by the expanded graphite and toluene allowed a rapid heating of the medium. The number of FLG sheets varies from 3 to 12, while the lateral size of the sheets exceeds few (cid:2)ms. The obtained FLG exhibits very low resistance with average value of 1.6 k(cid:3) (500 (cid:3) minimum) which is comparable to that of high quality graphenes synthesized by CVD methods, and lower than numbers of exfoliated graphenes.
关键词： (cid:2)-waves,electrical properties,expanded graphite,few layer graphene,resistance.,liquid exfoliation
更新于2025-09-11 14:12:44
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Dewetting of monolayer water and isopropanol between MoS2 nanosheets
摘要： Understanding dewetting of solvent molecules confined to layered material (LM) interfaces is crucial to the synthesis of two-dimensional materials by liquid-phase exfoliation. Here, we examine dewetting behavior of water and isopropanol/water (IPA/H2O) mixtures between molybdenum disulfide (MoS2) membranes using molecular dynamics (MD) simulations. We find that a monolayer of water spontaneously ruptures into nanodroplets surrounded by dry regions. The average speed of receding dry patches is close to the speed of sound in air. In contrast, monolayer mixtures of IPA/H2O between MoS2 membranes slowly transform into percolating networks of nanoislands and nanochannels in which water molecules diffuse inside and IPA molecules stay at the periphery of islands and channels. These contrasting behaviors may explain why IPA/H2O mixtures are much more effective than H2O alone in weakening interlayer coupling and exfoliating MoS2 into atomically thin sheets.
关键词： molecular dynamics simulations,liquid-phase exfoliation,isopropanol/water mixtures,two-dimensional materials,layered material interfaces,dewetting,solvent molecules,MoS2 membranes
更新于2025-09-10 09:29:36