Strong two‐photon absorption (TPA) in monolayer MoS2 is demonstrated in contrast to saturable absorption (SA) in multilayer MoS2 under the excitation of femtosecond laser pulses in the near‐infrared region. MoS2 in the forms of monolayer single crystal and multilayer triangular islands are grown on either quartz or SiO2/Si by employing the seeding method through chemical vapor deposition. The nonlinear transmission measurements reveal that monolayer MoS2 possesses a nonsaturation TPA coefficient as high as ∼(7.62 ±0.15) ×103 cm/GW, larger than that of conventional semiconductors by a factor of 103. As a result of TPA, two‐photon pumped frequency upconverted luminescence is observed directly in the monolayer MoS2. For the multilayer MoS2, the SA response is demonstrated with the ratio of the excited‐state absorption cross section to ground‐state cross section of ∼0.18. In addition, the laser damage threshold of the monolayer MoS2 is ∼97 GW/cm2, larger than that of the multilayer MoS2 of ∼78 GW/cm2.
The electrocatalytic splitting of water via hydrogen evolution reaction (HER) is one of the most efficient technologies for hydrogen production, while the massive consumption of precious Pt‐based catalysts hinders its commercialization, bringing an urgent task to explore low‐cost and earth‐abundant alternatives. Herein, a cost‐efficient system composed of metal Pt/molybdenum disulphide (MoS2) nanosheets hybrids for the HER by auxiliary of solar light is reported. The uniformly Pt nanoparticle decorated MoS2 sheets can be easily obtained under hydrothermal condition using oleylamine as capping agent and N,N‐dimethylmethanamide (DMF) as intercalation molecule for MoS2 exfoliation. The Pt/MoS2 hybrid shows a significantly enhanced HER activity compared with bare MoS2 due to enhancing conductivity and reducing overpotential by electron transport between Pt and MoS2. As a result, a Tafel slope of 38 mV per decade is obtained, suggesting a highly efficient Volmer–Heyrovsky reaction of hydrogen evolution. 相似文献
Apart from unique properties of layered transition‐metal dichalcogenide nanosheets like MoS2, quantum dots (QDs) from these layered materials promise novel science and applications due to their quantum confinement effect. However, the reported fabrication techniques for such QDs all involve the use of liquid organic solvents and the final material extraction from such liquid dispersions. Here a novel and convenient dry method for the synthesis of MoS2 quantum dots interspersed on few‐layer MoS2 using soft hydrogen plasma treatment followed by post‐annealing is demonstrated. The size of MoS2 nanodots can be well controlled by adjusting the working pressure of hydrogen plasma and post‐thermal annealing. This method relies on the cumulative hydrogen ion bombardment effect which can destroy the hexagonal structure of the top MoS2 layer and disintegrate the top layer into MoS2 nanodots and even QDs. Post‐thermal annealing can further reduce the size. Such MoS2 quantum dots interspersed on few‐layer MoS2 exhibit two new photoluminescence peaks at around 575 nm because of the quantum confinement effect. This dry method is versatile, scalable, and compatible with the semiconductor manufacturing processes, and can be extended to other layered materials for applications in hydrogen evolution reaction, catalysis, and energy devices. 相似文献
The electronic structures of a MoS2 monolayer are investigated with the all-electron first principle calculations based on the density functional theory (DFT) and the spin-orbital couplings (SOCs). Our results show that the monolayer MoS2 is a direct band gap semiconductor with a band gap of 1.8 eV. The SOCs and d-electrons in Mo play a very significant role in deciding its electronic and optical properties. Moreover, electronic elementary excitations are studied theoretically within the diagrammatic self-consistent field theory. Under random phase approximation, it shows that two branches of plasmon modes can be achieved via the conduction-band transitions due to the SOCs, which are different from the plasmons in a two-dimensional electron gas and graphene owing to the quasi-linear energy dispersion in single-layer MoS2. Moreover, the strong optical absorption up to 105 cm-1 and two optical absorption edges I and II can be observed. This study is relevant to the applications of monolayer MoS2 as an advanced photoelectronic device. 相似文献
Mass production and commercial availability are prerequisites for the viability and wide application of MoS2. Here, we demonstrate enhanced grindstone chemistry for a one‐step synthesis of biofunctionalized MoS2. By adding a SiO2 auxiliary agent the exfoliation efficiency increases from 16.23% to 58.59% and a rapid and high‐yield exfoliation of MoS2 is seen. SiO2 exhibits a fragmentation effect, which reduces the lateral size and facilitates the exfoliation of MoS2, thus inducing a high‐efficient paradigm in the top‐down fabrication of biofunctionalized MoS2 nanosheets. The as‐prepared MoS2‐chitosan (MoS2‐CS) nanosheets display complete disaggregation and homogeneous dispersion, as well as a high content of chitosan (ca. 20 wt%). As a proof‐of‐concept application, the MoS2‐CS nanosheets act as a biosorbent for PbII removal, exhibiting a good adsorption capacity and recyclability. This green and facile enhanced grindstone chemistry with minimal use of organic solvents and high‐throughput efficiency can be extended to the fabrication of other biocompatible inorganic 2D analogues for a variety of applications. 相似文献
For decades, there has been extensive research on exploring fundamental physical mechanisms for strong and fast optical nonlinearities. One of the important nonlinear‐optical mechanisms is multiphoton absorption which has a wide range of photonic applications. Herein, a theoretical model is proposed for three‐photon absorption (3PA) in monolayer MoS2. The model shows that the 3PA coefficients are on the order of 0.1 cm3/GW2. As compared to bulk semiconductors, these coefficients are enhanced by several orders of magnitude due to excitonic effects. Such exciton‐enhanced 3PA is validated by light‐intensity‐dependent photocurrent measurements on a monolayer MoS2 photodetector with femtosecond laser pulses. These results lay both theoretical and experimental foundation for developing sensitive near‐infrared MoS2‐based three‐photon detectors. 相似文献
Two-dimensional MoS2 nanosheets were synthesized by using halloysite nanotubes (HNTs) as template under the hydrothermal synthesis. The structure and morphology of the as-synthesized MoS2 nanosheets were determined by a series of characterizations. The results showed that the as-synthesized MoS2 nanosheets were of the plate-like structure with about five layers, and the basal spacing was about 0.63 nm. It was demonstrated that HNTs played a crucial template role in the formation of the plate-like MoS2 nanosheets. The formation mechanism was proposed. Furthermore, the tribological performance of the as-prepared MoS2 nanosheets in oil was intensively examined on the ball-on-ball wear tester. The testing results verified that the as-prepared MoS2 nanosheets as additive could significantly improve the friction performance of oil, which exhibited the good antifriction, antiwear, and load-carrying properties. 相似文献
Molybdenum disulfide (MoS2) nanosheets are a promising lubricant additive for enhanced engine efficiency in cars. However, high-cost production methods and poor dispersion have limited their application in industry. In this study, the ball milling process is demonstrated as a low-cost and high-efficient method for fabrication of oil-dispersible MoS2 nanosheet, and the ball milling parameters are optimized. Moreover, the lubrication effectiveness of ball-milled MoS2 nanosheet was also evaluated. Results indicated that well-dispersed MoS2 nanosheets with a size of 250 nm can be manufactured with optimized surfactants of zinc dialkyldithiphosphates (ZDDP) and polyisobutylene succinimide (PIBS) after being ball milled for 36 h. Tribological results revealed that a friction coefficient of white oil with 0.25% MoS2 nanosheets reached 0.075, much lower than that of lubricant without nanosheets (0.16). The wear scar radius of 0.015% MoS2 nanosheets was similar with that of Hertz contact, and the wear scar radius reduction reached 20% compared with that of 1% ZDDP. In addition, EDS and XPS results indicated the formation of a MoS2 and FeS tribofilm on the wear surface. 相似文献
An analytic expression of the dielectric function of monolayer molybdenum disulfide (MoS2) ε?=?ε1 + iε2 is presented for energies from 1.4 to 6.0?eV and temperatures from 35 to 350?K. The dielectric function parametric model is used to express ε as a sum of polynomials, which naturally includes asymmetry of critical-point lineshapes. The temperature dependence is achieved by fitting model parameters. In this way, the dielectric function of MoS2 for arbitrary temperature can be calculated. We observed the fundamental absorption peak, which occurs at the K point of the Brillouin zone. These results are expected to be useful in designing and understanding applied-device technologies based on monolayer MoS2. 相似文献
Embedding alkali-metal in monolayer MoS2 has been investigated by using first principles with density functional theory. The calculation of the electronic and optical properties indicates that alkali-metal was embedded in monolayer MoS2 appearing almost metallic behavior, and the MoS2 layer shows clear p-type doping behavior. The covalent bonding appears between the alkali-metal atoms and defective MoS2. More importantly, embedding alkali-metal can increase the work function for monolayer MoS2. Furthermore, the absorption spectrum of monolayer MoS2 is red shifted because of alkali metal embedding. Accordingly, this study will provide the theoretical basis for producing the alkali-metal-doped monolayer MoS2 radiation shielding and photoelectric devices. 相似文献
In this work, the photocatalyst composed of ultrathin MoS2 nanosheets onto the surface of cubic CdS nanoparticles with an average diameter of 7~10 nm has been successfully fabricated through a facile and mild photodeposition route. The ultrathin MoS2 nanosheets as a cocatalyst were demonstrated to greatly boost photocatalytic H2 evolution over cubic CdS upon visible light irradiation. It was clearly revealed that both the cubic CdS substrate and structure of ultrathin MoS2 nanosheets play critical roles in the observed efficient H2 evolution. The cubic CdS offers a strong adherence for ultrathin MoS2 nanosheets to form a well contact interface, across which the photogenerated charge transfer and charge separation are achieved. The ultrathin MoS2 nanosheets introduce a high density of unsaturated active S atoms for H2 evolution. 相似文献
The electronic structure and optical properties of Mo, S vacancy and V doping in MoS2 monolayer will be investigated through first-principles calculations based on the density functional theory. The results indicate that the MoS2 with Mo, S vacancy and V doping (Mo14VS32, Mo15VS31 and Mo14VS31) will gain the property of magnetic semiconductor with the magnetic moment of 1 μB, 1 μB and 0.95 μB, respectively. The optical properties of these V-doped and vacancy defect structures all reflect the phenomenon of red shift. The absorption edge of pure monolayer molybdenum disulfide is 0.8 eV, whereas the absorption edges of Mo14VS32, Mo15VS31 and Mo14VS31 become 0 eV, 0.2 eV and 0.16 eV, respectively. As a potential material, MoS2 is widely used in many fields such as the production of optoelectronic devices, military devices and civil devices. 相似文献
Three‐dimensional (3D) multilayer molybdenum disulfide (MoS2)/reduced graphene oxide (RGO) nanocomposites are prepared by a solution‐processed self‐assembly based on the interaction using different sizes of MoS2 and GO nanosheets followed by in situ chemical reduction. 3D multilayer assemblies with MoS2 wrapped by large RGO nanosheets and good interface are observed by transmission electron microscopy. The interaction of Na+ ions with oxygen‐containing groups of GO is also investigated. The measurement of lithium ion batteries (LIBs) shows that MoS2/RGO anode nanocomposite with a weight ratio of MoS2 to GO of 3:1 exhibits an excellent rate performance of 750 mAh g?1 at 3 A g?1 outperforming many previous studies and a high reversible capacity up to ≈1180 mAh g?1 after 80 cycles at 100 mA g?1. Good rate performance and high capacity of MoS2/RGO with 3D unique layered‐structures are attributed to the combined effects of continuous conductive networks of RGO, good interface facilitating charge transfer, and strong RGO sheets preventing the volume expansion. Results indicate that 3D multilayer MoS2/RGO prepared by a facile solution‐processed assembly can be developed to be an excellent nanoarchitecture for high‐performance LIBs. 相似文献
Using first-principles methods, we systematically investigate the electronic properties and atomic mechanism of the monolayer MoS2/WS2 homo-junction structure, which contains different phase structures, either the semiconducting hexagonal (H) structure or metallic trigonal (T) structure. Through tuning the size of the lateral homo-junction structure of either MoS2 or WS2, it can produce different boundaries which induce different phase transferred styles. More interestingly, the electronic structures of homo-junction structures can also be tuned by changing the size of the armchair and zigzag shapes of nanoribbons. The homo-junction structure of either MoS2 or WS2 exhibits alterable band structure and band edge position with the changing of the size. The strong dependence of the band offset on the sizes of the homo-junction monolayer also implicates a possible way of patterning quantum structures with size engineering. 相似文献
A facile one‐pot synthetic route is reported to prepare algae‐like molybdenum disulfide/polypyrrole (MoS2/PPy) nanocomposite through a redox reaction between ammonium tetrathiomolybdate and pyrrole monomer under a hydrothermal condition without any other templates. The as‐prepared unique algae‐like MoS2/PPy nanocomposites are composed of few layer MoS2 nanosheets, which are covered with PPy. Structural and morphological characterizations of this unique nanocomposite are investigated by Fourier‐transform infrared spectra, Raman spectra, X‐ray diffraction pattern, X‐ray photoelectron spectra, energy‐dispersive X‐ray spectroscopy, and transmission electron microscopy. The as‐prepared MoS2/PPy nanocomposites exhibit an excellent peroxidase‐like catalytic activity toward the oxidation of 3,3,5,5‐tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2) in acetate buffer solution (pH 4.0), which provides a facile strategy for the colorimetric detection of H2O2 with a high sensitivity. 相似文献
We have demonstrated a simple near‐infrared (NIR) photodetector (PD) based on charge transfer complex (CTC) formed in molybdenum trioxide (MoO3) doped N,N′‐di(naphthalene‐1‐yl)‐N,N′‐diphenyl‐benzidine (NPB), which shows a photocurrent of about 0.35 A/cm2 at –3 V under 980 nm illumination. The existence of CTC formation promotes photocurrent generation which is investigated by comparison with MoO3 doped 2‐methyl‐9,10‐di(2‐naphthyl)anthracene (MADN) film which has no CTC absorption. It can be evolved that this kind of simple‐structure photodetector has potential application in the near‐infrared (NIR) detection area. It is shown in this Letter that although both MoO3 and NPB have larger energy gaps of about 3 eV and weak absorption in the NIR region, the charge transfer complexes formed by mixing the two materials show an extra absorption band and good photoelectric response in the NIR region.
Large-scale growth of mostly monolayer molybdenum disulfide (MoS2) on quartz, sapphire, SiO2/Si, and waveguide substrates is demonstrated by chemical vapor deposition with the same growth parameters. Centimeter-scale areas with large flakes and films of MoS2 on all the growth substrates are observed. The atomic force microscopy and Raman measurements indicate the synthesized MoS2 is monolayer with high quality and uniformity. The MoS2 field effect transistors based on the as-grown MoS2 exhibit carrier mobility of 1–2 cm2V?1s?1 and On/Off ratio of ~104 while showing large photoresponse. Our results provide a simple approach to realize MoS2 on various substrates for electronics and optoelectronics applications. 相似文献