Wintersweet Branch‐Like C/C@SnO2/MoS2 Nanofibers as High‐Performance Li and Na‐Ion Battery Anodes

Structure and morphology of molybdenum disulfide (MoS₂) play an important role in improving its reversible lithium storage and sodium storage as anodes. In this study, a facile method is developed to prepare C/C@SnO₂/MoS₂ nanofibers with MoS₂ nanoflakes anchoring on the core–shell C/C@SnO₂ nanofibers through hydrothermal reaction. By adjusting the concentration of MoS₂ precursors, the synthesized MoS₂ with different slabs dimensions, size, and morphologies are obtained, constituting budding and blooming wintersweet branch‐like composite structure, respectively. Owing to scattered MoS₂ nanoparticles and sporadic MoS₂ nanoflakes, the budding wintersweet branch‐like composite nanofibers processes less slabs of staking in number and large specific surface area. Benefiting from the exposed C@SnO₂ shell layer, the synergistic effect among SnO₂, carbon, and MoS₂ is strengthened, which maximizes the advantage of each material to exhibit stable specific capacities of 650 and 230 mAh g^?1 for Li‐ion batteries and Na‐ion batteries after 200 cycles.     

Three‐Dimensional Multilayer Assemblies of MoS2/Reduced Graphene Oxide for High‐Performance Lithium Ion Batteries

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.     

Superhydrophobic MoS2-based multifunctional sponge for recovery and detection of spilled oil

Oil spills are a major threat to the marine ecosystem, requiring immediate solutions to remove spilled oil from oceanic environments. In this study, we report a superhydrophobic molybdenum disulfide (MoS₂) coated polydimethylsiloxane (PDMS) sponge and demonstrate its high proficiency in spilled oil recovery and oil spill detection based on oil-water separation ability. This novel oil sorbent is fabricated by a simple dip-coating to incorporate MoS₂ flakes into PDMS sponge. The optimized MoS₂-sponge displays a water contact angle of >152°, demonstrating excellent superhydrophobicity and high oil absorption (>97 wt%) for a variety of oils, including vegetable oil and fuel waste. Moreover, the material retains excellent oil absorption capability upon repetitive compression cycles. The versatility of this novel sorbent has been extended for the real-time spontaneous detection of oils by taking advantage of electrically conductive MoS₂ layers.     

Characteristics of a type-II n-MoS2/p-Ge van der Waals heterojunction

A few-atomic-layer molybdenum disulfide (MoS₂) film on Si/SiO₂ substrates grown by metal-organic chemical vapor deposition was investigated. The few-atomic-layer MoS₂ film was subsequently transferred onto a (100) p-Ge substrate to build a van der Waals n-p heterojunction. The as-grown few-atomic-layer MoS₂ film and the MoS₂/Ge heterostructure were characterized atomic force microscopy, spectroscopic ellipsometry, high-resolution scanning transmission electron microscopy, Raman spectroscopy analyses, photoluminescence (PL) measurements at room temperature (RT, 300 K), and type-II band alignment of the heterostructure determined by ultraviolet photoelectron spectroscopy. The RT-PL measurements showed dominant peaks at 1.96 and 1.8 eV for the as-grown MoS₂ and red-shifted PL peaks for that transferred onto Ge. We examined the electrical characteristics of the few-atomic-layer MoS₂ by forming a type-II band alignment van der Waals heterojunction with a highly doped p-Ge. The heterojunction solar cell exhibited an open-circuit voltage of 0.15 V and a short-circuit current density of 45.26 μA/cm². The external quantum efficiency measurements showed a spectral response up to approximately 500 nm owing to the absorption by the few-atomic-layer MoS₂ film.     

The effect of carrier gas flow rate on the growth of MoS<Subscript>2</Subscript> nanoflakes prepared by thermal chemical vapor deposition

Molybdenum disulfide nanoflakes (MoS₂) are superior material for their semiconducting properties. For bulk and monolayer MoS₂ the band gap changes from indirect-to-direct, respectively. So, it exhibits promising prospects in the applications of optoelectronics and valleytronics, such as solar cells, transistors, photodetectors, etc. In this research, the influence of different Ar flow rates as the carrier gas, is investigated for growing MoS₂ nanoflakes on silicon substrates using one-step thermal chemical vapor deposition by simultaneously evaporating of solid sources like sulfur and molybdenum trioxide powders. The structural and optical properties of the obtained nanoflakes are assessed by using X-ray diffraction pattern, scanning electron microscopy, UV–visible absorption, photoluminescence and Raman spectroscopy. It is shown that, Ar gas flow rate is strongly affects on the final products as few-layer MoS₂ structures. Moreover, the abundance of MoS₂ in comparison to MoO₂ and MoO₃ structures, in the obtained nanoflakes, is influenced by the Ar flow rate.     

MoO2@MoS2 Nanoarchitectures for High‐Loading Advanced Lithium‐Ion Battery Anodes

The capacity loading per unit area is of importance as specific capacity while evaluating the lithium‐ion battery anode. However, the low conductivity of several advanced anode materials (such as molybdenum sulfide, MoS₂) prohibits the wide application of materials. Nanostructural engineering becomes a key to overcome the obstacles. A one‐step in situ conversion reaction is employed to synthesize molybdenum oxide (MoO₂)–MoS₂ core–shell nanoarchitectures (MoO₂@MoS₂) by partially sulfiding MoO₂ into MoS₂ using sulfur. The MoO₂@MoS₂ displays a 3D architecture constructed by hundreds of MoS₂ ultrathin sheets with several layers arranged and fixed to an MoO₂ particle vertically with the size in the range of 200–500 nm. MoO₂ acts as the molybdenum source for the synthesis of MoS₂, as well as the conductive substrate. The designed 3D architectures with empty space between MoS₂ layers can prevent the damage originated from volume change of MoS₂ undergoing charge/discharge process. The lithium storage capacities of the MoO₂@MoS₂ 3D architectures are higher and the stability has been significantly improved compared to pure MoS₂. 4 mAh cm^?2 capacity loading of MoO₂@MoS₂ has been achieved with a specific capacity of more than 1000 mAh g^?1.     

Temperature dependence of the dielectric function of monolayer MoS2

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.     

Controlled exfoliation of molybdenum disulfide for developing thin film humidity sensor

We report a facile, size-controllable exfoliation process using an ultrasound-assisted liquid method to fabricate few-layer molybdenum disulfide (MoS₂) nanosheets. The morphology, structure and size distribution of the nanosheets processed with different ultrasonic powers were examined by atomic force microscopy, Raman spectroscopy and dynamic light scattering. It was revealed that the size of nanosheets reduces and final yield increases with elevating ultrasonic power. Bulk and exfoliated MoS₂ based thin film sensors are fabricated by a simple drop casting method on alumina substrates. Our sensors exhibit excellent sensitivity with very quick response and recovery speed to humidity gas. Comparative studies are carried out to draw up the size or ultrasonic power dependent sensing behavior.     

Large-scale chemical vapor deposition growth of highly crystalline MoS2 thin films on various substrates and their optoelectronic properties

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.     

二维辉钼材料及器件研究进展

经过几十年的发展, 集成电路的特征尺寸将在10–15年内达到其物理极限, 替代材料的研究迫在眉睫. 石墨烯曾被寄予厚望, 但由于其缺乏带隙限制了在数字电路领域的应用. 近年来, 单层及多层辉钼材料由于具有优异的半导体性能, 有可能超过石墨烯成为硅的替代者而引起了微纳电子领域的广泛关注. 本文对近二年国际上辉钼半导体器件研制、辉钼半导体材料的性能 表征及制备方法研究等方面的进展进行了综述, 并对大面积单层材料的研制提出了值得关注的方向. 关键词： 2')" href="#">MoS₂ 辉钼材料 纳米材料 集成电路     

Fracture‐induced nanoscrolls from CVD‐grown monolayer molybdenum disulfide

We report a simple and effective way of fabricating molybdenum disulfide (MoS₂) nanoscrolls by self‐rolling up fractured monolayer CVD‐grown MoS₂ microflakes. Morphological results reveal that MoS₂ nanoscrolls are formed only at newly formed edges, owing to an orientation‐specific fracture behavior. Using Raman spectroscopy, we show that the E¹_2g Raman peak (A_1g peak) for MoS₂ nanoscrolls significantly red‐shifts (blue‐shifts), indicating structural change. The proposed mechanism is that the newly formed edges induced by fracture behavior self‐roll up to nanoscrolls to minimize the surface free energy, meanwhile, the serious lattice contradiction of upper sulfur plane controls the rolling directions. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Hall effect measurements using low ac magnetic fields and lock-in technique on field effect transistors with molybdenum disulfide channels

Hall effect measurements conventionally rely on the use of dc magnetic fields. For electronic devices made of ultrathin semiconducting materials, such as molybdenum disulfide (MoS₂), the dc Hall effect measurements have practical difficulties. Here, we report the results of the Hall effect measurements using ac magnetic fields and a lock-in detection of the Hall voltage for field effect transistors with ultrathin MoS₂ channels. The ac Hall effect measurements have some advantages over the dc measurements. The carrier concentration and the Hall mobility were estimated as a function of gate voltage from the results of the ac Hall effect measurements. They used a magnetic field strength that was lower by two orders of magnitude than those used in prior studies on MoS₂ devices, which relied on dc magnetic fields.     

Effects of V-shaped edge defect and H-saturation on spin-dependent electronic transport of zigzag MoS2 nanoribbons

Based on nonequilibrium Green's function in combination with density functional theory calculations, the spin-dependent electronic transport properties of one-dimensional zigzag molybdenum disulfide (MoS₂) nanoribbons with V-shaped defect and H-saturation on the edges have been studied. Our results show that the spin-polarized transport properties can be found in all the considered zigzag MoS₂ nanoribbons systems. The edge defects, especially the V-shaped defect on the Mo edge, and H-saturation on the edges can suppress the electronic transport of the systems. Also, the spin-filtering and negative differential resistance behaviors can be observed obviously. The mechanisms are proposed for these phenomena.     

Electrical stability of multilayer MoS2 field‐effect transistor under negative bias stress at various temperatures

The electrical stability of molybdenum disulfide (MoS₂) transistors is crucial for their use in various applications. However, it is tricky to evaluate the inherent stability of MoS₂ transistors because it is highly dependent on environmental conditions during measurement such as humidity, light, and electrical factors. We studied the threshold voltage instability under negative bias stress at a variety of temperatures in a vacuum and in the dark to eliminate any environmental effects. In particular, the measurement of transfer curves under stress is minimized in order to study the inherent instability of MoS₂ transistors, even though the measurement of transfer curves is normally indispensable to check for the evolution of electrical instability. MoS₂ transistors have high average effective energy when compared to conventional amorphous Si and oxide semiconductor transistors, which allows for adequate operation at high temperatures. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Structure of van der Waals bound hybrids of organic semiconductors and transition metal dichalcogenides: the case of acene films on MoS2

Transition metal dichalcogenides (TMDC) are important representatives in the emerging field of two‐dimensional materials. At present their combination with molecular films is discussed as it enables the realization of van der Waals bound organic/inorganic hybrids which are of interest in future device architectures. Here, we discuss the potential use of molybdenum disulfide (MoS₂) as supporting substrate for the growth of well‐defined, crystalline organic adlayers. By this means, hybrid systems between the TMDC surface and organic compounds can be prepared, allowing for the profound investigation of mutual optical and electronic coupling mechanisms. As model system, we choose pentacene and perfluoropentacene as prototypical organic semiconductors and analyze their film formation on MoS₂(001) surfaces. In both cases, we observe smooth, crystalline film growth in lying molecular configuration, hence enabling the preparation of well‐defined hybrid systems. By contrast, on defective MoS₂ surfaces both materials adopt an upright molecular orientation and exhibit distinctly different film morphologies. This emphasizes the importance of highly ordered TMDC surfaces with low defect density for the fabrication of well‐defined hybrid systems.     

Novel molybdenum disulfide nanosheets–decorated polyaniline: Preparation,characterization and enhanced electrocatalytic activity for hydrogen evolution reaction

Novel molybdenum disulfide nanosheets–decorated polyaniline (MoS₂/PANI) was synthesized and investigated as an efficient catalyst for hydrogen evolution reaction (HER). Compared with MoS₂, MoS₂/PANI nanocomposites exhibited higher catalytic activity and lower Tafel slope for HER in H₂SO₄ solution. The amount of 19 wt% PANI for coupling with MoS₂ resulted in a high current density of 80 mA cm⁻² at 400 mV (vs. RHE). In addition, the optimal MoS₂/PANI nanocomposite showed impressive long-term stability even after 500 cycles. The enhanced catalytic activity of MoS₂/PANI nanocomposites was primarily ascribed to the effective electron transport channels of PANI and the increase of electrochemically accessible surface area in composite materials, which was advantageous to facilitate the charge transfer at catalyst/electrolyte interface.     

One‐Pot Synthesis of Algae‐Like MoS2/PPy Nanocomposite: A Synergistic Catalyst with Superior Peroxidase‐Like Catalytic Activity for H2O2 Detection

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.     

Effect of substrate and temperature on the electronic properties of monolayer molybdenum disulfide field-effect transistors

The use of two-dimensional nanostructured molybdenum disulfide (MoS₂) films in field-effect transistors (FETs) in place of graphene was investigated. Monolayer MoS₂ films were fabricated by chemical vapor deposition. The output and transfer curves of supported and suspended MoS₂ FETs were measured. The mobility of the suspended device reached 364.2 cm²?V^?1?s^?1 at 150?°C. The hysteresis of the supported device in transfer curves was much larger than that of the suspended device, and it increased at higher temperatures. These results indicate that the device mobility was limited by Coulomb scattering at ambient temperature, and surface/interface phonon scattering at 150?°C, and the injection of electrons, via quantum tunneling through the Schottky barrier at the contact, was enhanced at higher temperatures and led to the increase of the hysteresis. The suspended MoS₂ films show potential for application as a channel material in electronic devices, and further understanding the causes of hysteresis in a material is important for its use in technologies, such as memory devices and sensing cells.     

High-performance nonenzymatic electrochemical glucose biosensor based on AgNP-decorated MoS2 microflowers

A facile hydrothermal route was used to synthesize silver nanoparticle (AgNP)-decorated microflower molybdenum disulfide (MoS₂-MF) for bio-electrochemical platform fabrication to detect nonenzymatic glucose concentration. The morphologies of the materials were studied by scanning electron microscopy, and their structural characteristics were analyzed by X-ray diffractometry and energy-dispersive X-ray spectroscopy. The electrochemical characteristics of the AgNPs/MoS₂-MF/PtE biosensor were studied by cyclic voltammetry. The obtained data indicated that the developed nonenzymatic glucose sensor has a large linear response between 1.0 and 15.0 mM, a limit of detection of as low as 1.0 mM, and a sensitivity of 46.5 μA nM⁻¹ cm⁻². The biosensor also displayed outstanding selectivity, stability, reproducibility, and repeatability. Additionally, the AgNPs/MoS₂-MF/PtE biosensor was utilized to detect glucose concentration in real sample and showed practical application potential for glucose detection.     

Electrochemical impedance spectroscopic study of the lithium storage mechanism in commercial molybdenum disulfide

The first lithiation and delithiation processes of commercial molybdenum disulfide (MoS₂) electrode as anode material for lithium-ion batteries were studied by electrochemical impedance spectroscopy (EIS). It is found that the typical EIS is composed of four parts, namely, high-frequency semicircle, middle-frequency semicircle, low-frequency short sloping line, and low-frequency arc in the Nyquist diagram, and they can be attributed to the solid electrolyte interphase (SEI) film and ionic resistance in pores, charge transfer step, solid state diffusion process, and phase transformation, respectively. An equivalent circuit that includes elements related to the SEI film and charge transfer process, in addition to phase transformation, is proposed to simulate the experimental EIS data. The change of kinetic parameters for lithiation and delithiation of MoS₂ electrode as a function of potential in the first charge–discharge cycle is analyzed, and the reason for the rapid degradation in capacity of the MoS₂ electrode when cycled between 3.00 and 0.01 V is discussed in detail.