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MoS2 is a two-dimensional layered transition metal dichalcogenide with unique electronic and optical properties. The fabrication of ultrathin MoS2 is vitally important, since interlayer interactions in its ultrathin varieties will become thickness-dependent, providing thickness-governed tunability and diverse applications of those properties. Unlike with a number of studies that have reported detailed information on direct bandgap emission from MoS2 monolayers, reliable experimental evidence for thickness-induced evolution or transformation of the indirect bandgap remains scarce. Here, the sulfurization of MoO3 thin films with nominal thicknesses of 30 nm, 5 nm and 3 nm was performed. All sulfurized samples were examined at room temperature with spectroscopic ellipsometry and photoluminescence spectroscopy to obtain information about their dielectric function and edge emission spectra. This investigation unveiled an indirect-to-indirect crossover between the transitions, associated with two different Λ and K valleys of the MoS2 conduction band, by thinning its thickness down to a few layers. [ABSTRACT FROM AUTHOR]

We report on the facile and scalable catalytic conversion of natural graphite and MoS2 minerals into α-MoO3 nanoribbons incorporated into hexagonal MoS2 and graphene nanosheets, and evaluate the structural, morphological and electrochemical performances of the hybrid nanostructured material obtained. Mechanochemical treatment of raw materials, followed by catalytic molten salt treatment leads to the formation of nanostructures with promising electrochemical performances. We examined the effect of processing temperature on the electrochemical performance of the products. At 1100 °C, an excellent Li-ion storage capacity of 773.5 mAh g−1 is obtained after 180 cycles, considerably greater than that of MoS2 (176.8 mAh g−1). The enhanced capacity and the rate performance of this electrode are attributed to the well-integrated components, characterized by the formation of interfacial molybdenum oxycarbide layer during the synthesis process, contributing to the reduced electrical/electrochemical resistance of the sample. This unique morphology promotes the charge and ions transfer through the reduction of the Li-ion diffusion coefficient (1.2 × 10−18 cm2 s−1), enhancing the pseudocapacitive performance of the electrode; 59.3% at the scan rate of 0.5 mV s−1. This article provides a green and low-cost route to convert highly available natural graphite and MoS2 minerals into nanostructured hybrid materials with promising Li-ion storage performance. [ABSTRACT FROM AUTHOR]

MoS2 is a two-dimensional layered transition metal dichalcogenide with unique electronic and optical properties. The fabrication of ultrathin MoS2 is vitally important, since interlayer interactions in its ultrathin varieties will become thickness-dependent, providing thickness-governed tunability and diverse applications of those properties. Unlike with a number of studies that have reported detailed information on direct bandgap emission from MoS2 monolayers, reliable experimental evidence for thickness-induced evolution or transformation of the indirect bandgap remains scarce. Here, the sulfurization of MoO3 thin films with nominal thicknesses of 30 nm, 5 nm and 3 nm was performed. All sulfurized samples were examined at room temperature with spectroscopic ellipsometry and photoluminescence spectroscopy to obtain information about their dielectric function and edge emission spectra. This investigation unveiled an indirect-to-indirect crossover between the transitions, associated with two different Λ and K valleys of the MoS2 conduction band, by thinning its thickness down to a few layers.

In this study, a comprehensive hydrometallurgical processing of molybdenite (MoS 2) concentrate was investigated. This investigation involved a novel approach combining mechanical activation, leaching, and polyelectrolyte extraction methods. The integrated method effectively addressed the challenge of low leaching rate of molybdenite, resulting in the successful production of high-purity molybdenum trioxide. Milled molybdenite samples were analyzed by different methods of X-ray diffraction, atomic force and electron microscopy, and BET. The increasing trend of the specific surface area during milling was determined by a model fitting which was useful for optimization of milling time. Several leaching reagents were studied to achieve high molybdenum dissolution. The most promising results were achieved through a two-hour process, yielding an impressive leaching efficiency of 80% and a resulting Mo concentration of 6700 mg/L. Molybdenum recovery was efficiently carried out through polyelectrolyte extraction, as confirmed by ICP and CHNS analyses, demonstrating selective precipitation of molybdenum from the solution. The subsequent calcination of the precipitated molybdenum(VI) compound resulted in the production of high-purity molybdenum trioxide. Furthermore, a conceptual hydrometallurgical treatment process for molybdenite concentrate was proposed, aiming to recover molybdenum, sulfuric acid, and copper. This proposed process presents a promising avenue for further exploration in pilot plant studies within the molybdenum industry. [Display omitted] • Finding solutions for scaling-up challenges of hydrometallurgical treatment of MoS 2. • Evaluation of synergistic effect of acids to stabilize molybdenum in solution. • A complete flowsheet for a low-emission process for Mo recovery. • An industrially feasible production of MoO 3 from MoS 2 without sulfur oxides emission. [ABSTRACT FROM AUTHOR]

Using radio frequency magnetron sputtering (RFMS), the undoped and Ti-doped vertical nanowall structured MoS 2 thin films were grown. In order to benefit from the chromic properties of the MoO 3 and inherited surface/volume ratio of the vertical nanowall structures of the MoS 2 , these films thermally oxidized to α-MoO 3 while retaining the morphology. Measurements of in-situ transmittance during the oxidation process revealed that the MoS 2 samples with a highTi content oxidized more quickly. On the other hand, the presence of Ti has led to denser nanowall formations. Optical modulation (OM) in the visible region improved with increasing Ti concentration within the coloring potential range of -0.2 to -0.45 V, which are relatively low working voltages that indicate energy efficient electrochromic materials. The highest Ti-doped MoO 3 (MTO40) and undoped (MBO) samples exhibit 52.2 % and 37.6 % OM at 700 nm (47.8 % and 25.7 %, respectively, at 550 nm) under -0.45 V applied potential. On the other hand, the coloring times for MBO, MTO20, MTO30, and MTO40 are 4.7, 4.1, 6.2, and 2.9 s, respectively, while the bleaching durations are 3.1, 1.4, 1.1, and 1.2 s for samples. These Ti-doped MoO 3 electrochemical characteristics demonstrate the suitability of the proposed technique for device applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Two-dimensional van der Waals crystals (2D vdW) are recognized as one of the potential materials to solve the physical limits caused by size scaling. Here, vdW metal oxide MoO3 is applied with the gate dielectric in a 2D field-effect transistor (FET). Due to its high dielectric constant and the good response of MoS2 to visible light, we obtained a field effect transistor for photodetection. In general, the device exhibits a threshold voltage near 0 V, Ion/Ioff ratio of 105, electron mobility about 85 cm2 V−1 s−1 and a good response to visible light, the responsivity is near 5 A/W at low laser power, which shows that MoO3 is a potential material as gate dielectric. [ABSTRACT FROM AUTHOR]

Abstract Molybdenum-based materials have been intensively investigated for high-performance gas sensor applications. Particularly, molybdenum oxides and dichalcogenides nanostructures have been widely examined due to their tunable structural and physicochemical properties that meet sensor requirements. These materials have good durability, are naturally abundant, low cost, and have facile preparation, allowing scalable fabrication to fulfill the growing demand of susceptible sensor devices. Significant advances have been made in recent decades to design and fabricate various molybdenum oxides- and dichalcogenides-based sensing materials, though it is still challenging to achieve high performances. Therefore, many experimental and theoretical investigations have been devoted to exploring suitable approaches which can significantly enhance their gas sensing properties. This review comprehensively examines recent advanced strategies to improve the nanostructured molybdenum-based material performance for detecting harmful pollutants, dangerous gases, or even exhaled breath monitoring. The summary and future challenges to advance their gas sensing performances will also be presented.

We explore a phase engineering strategy to improve the electrochemical performance of transition metal sulfides (TMSs) in anode materials for lithium-ion batteries (LIBs). A one-pot hydrothermal approach has been employed to synthesize MoS2 nanostructures. MoS2 and MoO3 phases can be readily controlled by straightforward calcination in the (200–300) °C temperature range. An optimized temperature of 250 °C yields a phase-engineered MoO3@MoS2 hybrid, while 200 and 300 °C produce single MoS2 and MoO3 phases. When tested in LIBs anode, the optimized MoO3@MoS2 hybrid outperforms the pristine MoS2 and MoO3 counterparts. With above 99% Coulombic efficiency (CE), the hybrid anode retains its capacity of 564 mAh g−1 after 100 cycles, and maintains a capacity of 278 mAh g−1 at 700 mA g−1 current density. These favorable characteristics are attributed to the formation of MoO3 passivation surface layer on MoS2 and reactive interfaces between the two phases, which facilitate the Li-ion insertion/extraction, successively improving MoO3@MoS2 anode performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Large-area and homogeneous MoS 2 films were prepared on sapphire using two-step process. It was experimentally verified that most of the MoO 3 reacts with sulfur in situ on the substrate surface during sulfidation, and a small portion of the MoO 3 sublimated before being sulfurized. • The phase transition occurs as the vulcanization temperature increases, from MoO 3 to S- doped MoO 3 at 500 ℃, mixture of MoO 3 and MoS 2 at 600 ℃, O- doped MoS 2 at 700 ℃, ideal stoichiometric ratio of MoS 2 at 800 ℃, and S- deficient MoS 2 at 900 ℃, respectively. And the work function of the samples is significantly modulated from 4.68 eV to 3.90 eV, and the band gap energy decreases from 3.08 eV to 1.00 eV gradually, which are fairly consistent with the theoretical predictions. • The contacts between Ti and S- doped MoO 3 , or the mixture of MoO 3 and MoS 2 , are ohmic- like contacts. While the contacts between Ti and O- doped MoS 2 , ideal stoichiometric ratio of MoS 2 , or S- deficient MoS 2 are Schottky contacts. The transformation of MoO 3 into MoS 2 is investigated by sulfurizing MoO 3 on sapphire at various temperatures. The amorphous MoO 3 are crystallized at 500 ℃ and then sulfurized from 500 ℃ to 900 ℃. The phase transition occurs as the temperature increases, from MoO 3 to S- doped MoO 3 at 500 ℃, mixture of MoO 3 and MoS 2 at 600 ℃, O- doped MoS 2 at 700 ℃, ideal stoichiometric ratio of MoS 2 at 800 ℃, and S- deficient MoS 2 at 900 ℃, respectively. Correspondingly, the work function is significantly modulated from 4.68 eV for MoO 3 to 3.90 eV for MoS 2 , and the band gap energy decreases from 3.08 eV to 1.00 eV gradually, which are fairly consistent with the theoretical predictions. The contacts between titanium and S- doped MoO 3 , or the mixture of MoO 3 and MoS 2 , are ohmic- like contacts with specific contact resistivities of 2.68 × 10-3 Ω•cm2 and 3.14 × 10-3 Ω•cm2. While the contacts between Ti and O- doped MoS 2 , ideal stoichiometric ratio of MoS 2 , or S- deficient MoS 2 are Schottky contacts with barrier heights of 0.22 eV, 0.43 eV and 0.45 eV, respectively. Those results demonstrate that temperature plays pivotal role in determining the phase of sulfurized MoO 3 and their properties. [ABSTRACT FROM AUTHOR]

We report on the facile and scalable catalytic conversion of natural graphite and MoS2 minerals into α-MoO3 nanoribbons incorporated into hexagonal MoS2 and graphene nanosheets, and evaluate the structural, morphological and electrochemical performances of the hybrid nanostructured material obtained. Mechanochemical treatment of raw materials, followed by catalytic molten salt treatment leads to the formation of nanostructures with promising electrochemical performances. We examined the effect of processing temperature on the electrochemical performance of the products. At 1100 °C, an excellent Li-ion storage capacity of 773.5 mAh g−1 is obtained after 180 cycles, considerably greater than that of MoS2 (176.8 mAh g−1). The enhanced capacity and the rate performance of this electrode are attributed to the well-integrated components, characterized by the formation of interfacial molybdenum oxycarbide layer during the synthesis process, contributing to the reduced electrical/electrochemical resistance of the sample. This unique morphology promotes the charge and ions transfer through the reduction of the Li-ion diffusion coefficient (1.2 × 10−18 cm2 s−1), enhancing the pseudocapacitive performance of the electrode; 59.3% at the scan rate of 0.5 mV s−1. This article provides a green and low-cost route to convert highly available natural graphite and MoS2 minerals into nanostructured hybrid materials with promising Li-ion storage performance.

Molybdenum disulfide (MoS 2) is a 2D layered structured material with a Mo:S of 1:2 and is a great attention seeker for hydrogen production through water-splitting. In the present work, we prepared nanostructured MoS x with different sulfur molar concentrations (x = 2, 1, 0.5) through a one-step hydrothermal method. The decrease in sulfur concentration resulted in a new phase that is MoO 3 with a Mo:S of 1:0.5. The structural, morphological, and optical properties of all the samples were studied through X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectroscopy (FTIR), and Ultraviolet–Visible (UV–Vis) spectroscopy, respectively. Moreover, the electrochemical behavior was studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and Tafel slope. Optimum properties were observed for Mo:S (1:1) with an onset potential of 96 mV, an overpotential of 130 mV for hydrogen evolution reaction (HER) coupled with a specific capacitance of 889 F/g and low charge transfer resistance of 43 Ω. Further, it was noted that the electrocatalytic activity of MoS 1 was better than that of the composite and bare MoO 3. It is proposed that the excellent electrochemical activity arises from sulfur vacancies which provide active sites for HER and a free path for ions to flow through the material. • MoS x (x = 2, 1, 0.5) nanostructures are prepared through a hydrothermal method. • A decrease in sulfur concentration resulted in a new phase i.e. MoO 3 for MoS 0.5. • Optimum properties are achieved for MoS 1 with the lowest overpotential and R ct. • Catalyst MoS 1 has the best HER activity due to the presence of sulfur vacancies. [ABSTRACT FROM AUTHOR]

Two-dimensional van der Waals crystals (2D vdW) are recognized as one of the potential materials to solve the physical limits caused by size scaling. Here, vdW metal oxide MoO3 is applied with the gate dielectric in a 2D field-effect transistor (FET). Due to its high dielectric constant and the good response of MoS2 to visible light, we obtained a field effect transistor for photodetection. In general, the device exhibits a threshold voltage near 0 V, Ion/Ioff ratio of 105, electron mobility about 85 cm2 V−1 s−1 and a good response to visible light, the responsivity is near 5 A/W at low laser power, which shows that MoO3 is a potential material as gate dielectric.

In this paper, molybdenum disulfide (MoS2) thin films were deposited using an initial solution of molybdenum trioxide (MoO3) and thiourea (SC(NH2)2) on glass substrate with various mole concentrations by spray pyrolysis. The films were deposited in two steps (a) [S/ Mo] mole concentration ratio (x) varied at values of 0, 1, 2, 3, 5 and 10 at substrate temperature of Ts = 400ºC and (b) under post sulfurization process in the presence of argon gas at an annealing temperature of Ta = 450ºC. We applied x-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet-visible (UV-Vis) spectra for characterization of the MoS2 thin films in terms of morphology, crystal structure and optical properties. The effect of [S/Mo] mole concentration ratio and post sulfurization processes on the structural conversion, morphology, x-ray diffraction and optical properties of these films have been studied. In non-sulfurization conditions it is found that the films are polycrystalline with a MoO3 single phase and in post sulfurization conditions have hexagonal crystal structure corresponding to MoS2 phase with preferred orientation along the (002) plane. The intensity of peaks increased with sulfurization and increase of mole concentration. The morphology of films obtained by scanning electron microscopy (SEM) appears as bar-shaped nano-grains. The average grain size increases with increasing mole concentration of S, in solution. Optical transparency of films changed in the range of 20% to 50% and 20% to 5%, in the visible region before and after sulfurization, respectively. The energy band gap (Eg) of films hardly depends to post sulfurization process, band gap decreased from 3.2 eV to 1.2 eV. [ABSTRACT FROM AUTHOR]

We explore a phase engineering strategy to improve the electrochemical performance of transition metal sulfides (TMSs) in anode materials for lithium-ion batteries (LIBs). A one-pot hydrothermal approach has been employed to synthesize MoS2 nanostructures. MoS2 and MoO3 phases can be readily controlled by straightforward calcination in the (200–300) °C temperature range. An optimized temperature of 250 °C yields a phase-engineered MoO3@MoS2 hybrid, while 200 and 300 °C produce single MoS2 and MoO3 phases. When tested in LIBs anode, the optimized MoO3@MoS2 hybrid outperforms the pristine MoS2 and MoO3 counterparts. With above 99% Coulombic efficiency (CE), the hybrid anode retains its capacity of 564 mAh g−1 after 100 cycles, and maintains a capacity of 278 mAh g−1 at 700 mA g−1 current density. These favorable characteristics are attributed to the formation of MoO3 passivation surface layer on MoS2 and reactive interfaces between the two phases, which facilitate the Li-ion insertion/extraction, successively improving MoO3@MoS2 anode performance.

Highlights: Various advanced strategies for improving gas sensing performances of molybdenum-based nanostructures are reviewed. The plausible mechanism of enhanced gas sensing properties from each strategy is discussed. The conclusive outlook, challenge, and suggestions for future development toward marked commercialization of molybdenum-based gas sensing devices are provided.Molybdenum-based materials have been intensively investigated for high-performance gas sensor applications. Particularly, molybdenum oxides and dichalcogenides nanostructures have been widely examined due to their tunable structural and physicochemical properties that meet sensor requirements. These materials have good durability, are naturally abundant, low cost, and have facile preparation, allowing scalable fabrication to fulfill the growing demand of susceptible sensor devices. Significant advances have been made in recent decades to design and fabricate various molybdenum oxides- and dichalcogenides-based sensing materials, though it is still challenging to achieve high performances. Therefore, many experimental and theoretical investigations have been devoted to exploring suitable approaches which can significantly enhance their gas sensing properties. This review comprehensively examines recent advanced strategies to improve the nanostructured molybdenum-based material performance for detecting harmful pollutants, dangerous gases, or even exhaled breath monitoring. The summary and future challenges to advance their gas sensing performances will also be presented. [ABSTRACT FROM AUTHOR]

Thermal oxidation in air of molybdenum disulfide (MoS 2) into layer structured molybdenum trioxide (α-MoO 3) is investigated using a combination of thermal analysis, electron microscopy, Raman, X-ray diffraction and photoelectron spectroscopy. The phase evolutions occurred during the thermal process is characterized by the surface oxidation of MoS 2 , followed by the bulk oxidation to form α-MoO 3 and the formation of Mo 17 O 47 at higher temperatures. The single-phase MoO 3 formed at optimum temperature condition is found to possess crystalline defects and considerably greater values of Li-ion storage cycling and rate performances in comparison with samples prepared at alternative temperatures and also the initial MoS 2. This sample (P-MoO 3 -820) exhibits a charge capacity of 628 mA h g−1 after 250 cycles (100 mA g−1) with a Li+ diffusion coefficient of 2.3 × 10-13 cm2 s−1, substantially greater than that of initial MoS 2 (8.1 × 10−16 cm2 s−1). The electrochemical performance of P-MoO 3 -820 in full-cell configuration against a commercial LiFePO 4 cathode is evaluated and a specific capacity of 100 mAh g−1 after 500 cycles is recorded. This article, for the first time, discusses the thermal oxidation in air of MoS 2 as a simple and relatively clean approach to fabricate defective crystalline MoO 3 with enhanced Li-ion storage kinetics. • Thermal oxidation of molybdenum disulfide; thermochemistry and phase evolution. • Thermal conversion of MoS 2 into layer structured α-MoO 3 with crystalline defects. • Enhanced Li-ion storage performance and electrochemical kinetics. [ABSTRACT FROM AUTHOR]

In this study, a novel MoO 3 @MoS 2 /TiO 2 photocatalyst with higher photocatalytic hydrogen production efficiency was prepared via a hydrothermal followed by quenching method. The prepared composites were characterized by X-ray diffraction (XRD), Raman spectroscopy, UV–Vis Spectrophotometers, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). The photocatalytic performance for hydrogen evolution was also investigated. The results show that MoS 2 -340 °C/TiO 2 exhibits excellent photocatalytic hydrogen production efficiency (4669 μmol g−1 h−1), which is 5.8 times higher than that of unquenched MoS 2 /TiO 2 under the same conditions. MoO 3 on the surface and edges of large layered MoS 2 creates more traps adjacent to the joint. More photogenerated electrons can be enriched during the photocatalytic reaction, which achieve the purpose of exposing more active sites. • Surface partially oxidized MoS2 nanosheets are synthesized via a hydrothermal followed by quenching method. • The novel MoO3@MoS2/TiO2 photocatalyst with higher photocatalytic hydrogen production efficiency was prepared. • The hydrogen production efficiency of MoS2-340˚C/TiO2 is enhanced by 5.8 times compared to the unmodified MoS2/TiO2. • The existence of many active sites of surface partially oxidized MoS2 leads to higher efficiency hydrogen evolution. [ABSTRACT FROM AUTHOR]

MoO3/MoS2 microspheres were successfully synthesized via one-step solvothermal method. The crystal structure, morphology, and composition of MoO3/MoS2 microspheres were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). And MoO3/MoS2 microspheres exhibited excellent photocatalytic performance in the degradation of methyl orange under visible light irradiation. The photocatalytic degradation rate of MoO3/MoS2 microsphere is 18.5 and 2.5 times of pure MoO3 and MoS2, respectively. The enhanced photocatalytic activity of MoO3/MoS2 should be attributed to the formation of heterojunctions between MoO3 and MoS2 nanosheets, resulting in the effective separation and utilization of the photo-generated charge carries. [ABSTRACT FROM AUTHOR]

Abstract Control over thickness, size, and area of chemical vapor deposition (CVD) grown molybdenum disulfide (MoS 2) flakes is crucial for device application. Herein, we report a quantitative comparison of CVD synthesis of MoS 2 on SiO 2 /Si substrate using three different precursors viz., molybdenum trioxide (MoO 3), ammonium heptamolybdate (AHM), and tellurium (Te). A three-step chemical reaction mechanism of evolution of MoS 2 from MoO 3 micro-crystals is proposed for MoO 3 precursor. Furthermore, a strategy based on growth temperature and ratio of amount of precursors is developed to systematically control thickness and area of MoS 2 flakes. Our findings show that for large-sized crystalline monolayer MoS 2 flakes, MoO 3 is a better choice than AHM and Te-assisted synthesis. Moreover, Te as growth promoter, can lower down growth temperature by ∼250 °C. This study can be further used to fabricate MoS 2 based high-performance electronic devices such as photodetectors, thin film transistors, and sensors. Graphical abstract Image 1 Highlights • MoO 3 is a better choice than AHM and Te-assisted synthesis for large-sized 1L-MoS 2. • Low-temperature CVD growth of MoS 2 can be achieved using Te powder. • Three-step chemical reaction of evolution of MoS 2 is proposed. [ABSTRACT FROM AUTHOR]

Graphical abstract A novel ternary nanocomposite containing MoS 2 /MoO 3 and PPy for use as supercapacitor electrode. The Intercalated a-C was found to improve the surface capacitive-controlled capacitance, MoO 3 to provide redox reactions, and PPy to improve the conductivity and also gives an additional of redox reaction. Synergistic effect between PPy and MoS 2 /MoO 3 results in significantly improvement of capacitance and cycle life of PPy. Highlights • Demonstrating synergetic effects of a novel ternary MoS 2 /MoO 3 /PPy nanocomposite. • Cycle life and capacitance of PPy are largely enhanced by the addition of MoS 2 /MoO 3. • Morphological change of MoS 2 made by a one-step oxidation/exfoliation process. • The discovery of unexpected amorphous carbon (a-C) films. • The a-C film enhances the capacitance performance. • The mechanism of the formation of a-C films reported. Abstract A novel ternary nanocomposite MoS 2 /MoO 3 /polypyrrole (PPy) has been fabricated. MoO 3 nanoparticle-decorated few-layered MoS 2 nanosheets were first prepared via the exfoliation of partially oxidized MoS 2. In situ oxidation polymerization was then used to fabricate the ternary nanocomposites. We show the synergetic effects provided by the ternary composites via investigating the electrochemical performance of supercapacitors using the nanocomposites as the electrodes. Furthermore, the morphology evolution during the synthesis of the MoO 3 nanoparticle-decorated MoS 2 nanosheets was also examined. This not only allows the understanding of the formation mechanism but also leads to the surprising discovery of unprecedented amorphous carbon (a-C) layers intercalated in between the MoS 2 nanosheets. We therefore propose a mechanism to explain the formation of such a-C layer and demonstrate that the a-C plays a critical role in the supercapacitor performance. Finally, we demonstrate that the cycle life and capacitance of PPy are enhanced via the addition of MoS 2 /MoO 3 with an excellent Csp of 352 F g−1 and electrochemical stability with Csp retention up to 105% after 2000 cycles. [ABSTRACT FROM AUTHOR]

Ternary MoS2/MoO3/C nanosheets were successfully synthesized via a chemical vapor deposition method. The hybrids were characterized by x-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy, raman and x-ray photoelectron spectroscopic methods. The as-obtained MoS2/MoO3/C nanosheets applied as an anode material for lithium-ion batteries, showed high initial discharge/charge capacities at current rates of 0.5C, 1640.9 mA h g−1 and 1393.8 mA h g−1 respectively, with initial coulombic efficiency of approximately 84.9%. The material exhibited superior rate capabilities, with specific discharge capacities of 1240.2 mA h g−1, 1048.5 mA h g−1, 917.2 mA h g−1, 742.3 mA h g−1, 663.6 mA h g−1, 601.8 mA h g−1 and 593.4 mA h g−1 at current rates of 0.2C, 0.4C, 1C, 4C, 8C, 12C and 15C, respectively. This superior electrochemical performance was mainly due to the uniformly-distributed MoS2 nanosheets and to highly graphitized carbon, which not only mitigated mechanical stress during repeated cycling, but also provided good conductivity. [ABSTRACT FROM AUTHOR]

Molybdenum oxide (MoO3) thin films have been deposited using plasma-enhanced atomic layer deposition with molybdenum hexacarbonyl (Mo(CO)6) and oxygen plasma. Self-limiting growth was verified at a deposition temperature of 162°C and the growth rate was determined to be 0.76 Å/cycle. It was found that the as-deposited amorphous thin films crystallized into β- or α-MoO3 during annealing temperatures from 300°C to 400°C in air. In addition, the optical bandgap (Eg) of the amorphous MoO3 was estimated to be 4 eV by transmittance spectral analysis. Moreover, metal-insulator-semiconductor capacitors based on p-type (100) silicon substrates were fabricated to investigate the electrical properties of MoO3. It was shown that the MoO3 thin films exhibit a good dielectric performance and that the dielectric constant of the amorphous MoO3 was determined to be about 17. Additionally, a low leakage current of 6.43 × 10−7 A/cm2 at 1 V was detected and the equivalent oxide thickness was calculated to be 10.5 nm. As a result, MoO3 thin films, as a new high-κ gate dielectrics system, might be a good candidate for metal-insulator-semiconductor field-effect transistors based on two-dimensional transition metal dichalcogenides, especially for metal oxide semiconductor field-effect transistors using molybdenum disulfide (MoS2) as channel material. [ABSTRACT FROM AUTHOR]

• A MoS 2 (n)/a-Si:H (i)/c-Si (p)/MoO 3 type heterojunction solar cell is studied using short diode approximation method. • The MoO 3 layer is introduced just below the c-Si (p) layer to reduce the barrier height due to the difference in work function (ɸ) between c-Si (p) and MoO 3 layers. • With proper tuning of the ɸ value, the efficiency could be further improved to 23.54% with a small increase in V oc (650 mV) and J sc (46.5 mA/cm2). • The principal novelty of this study concerns the inclusion of MoO 3 layer with tunable work function. C-Si based heterojunction solar cells with dopant-free electron and hole transport layers (ETL and HTL) have attracted the researcher's attention due to their high efficiency and relatively less complicated fabrication process. A number of materials have been proposed for their applications, as ETL and HTL. We have chosen n-type MoS 2 monolayer as ETL for c-Si based heterojunction solar cells and optimized the layer parameters, doping and thickness to achieve the efficiency of 21.05% with a V oc of 641 mV and J sc of 45.88 mA/cm2 when direct metallization of Ag is used at back contact using one sided short diode approximation. Further, with insertion of MoO 3 as HTL at the back before Ag electrode, the efficiency could be improved to 23.54% with proper tuning of work function of MoO 3. The increase in efficiency is accompanied with a small increase in V oc (650 mV) and J sc (46.5 mA/cm2). Our studies provide a pathway to fabricate dopant free c-Si based heterojunction solar cells with comparable efficiency as those for HIT solar cells. [ABSTRACT FROM AUTHOR]

We report on the MoO3 oxides and their derivatives on microscopic 2H MoS2 flakes oxidized in air and high relative humidity at a moderate temperature range below 410 °C. We combine XPS and AFM measurements such as topography, friction, creation of nanoscale ripples and scratches on the MoS2 flakes deposited on Si substrates. We detect MoO3 oxides mostly by measuring selected nanomechanical properties of the MoO3 layer, such as its compressive mechanical stress at the plastic yield. We discuss basal surface coverage of the single MoS2 flakes by the MoO3 oxides. We discuss conditions for appearance of all possible MoO3 oxide derivatives, such as molybdenum(VI) hydroxyoxides and MoO3 hydrates. Our findings agree with an expected mechanistic switch in thermal oxidation in water vapors vs. air.

The article describes the synthesis of nano-MoS 2 and its subsequent conversion to MoO 3 nanoplatelets in a household microwave oven. [Display omitted] • Synthesis of MoS 2 nanoparticles from Ammonium heptamolybdate and thiourea. • Use of household microwave oven eliminating the requirement of sophisticated setup. • Rapid energy and time saving synthesis. • Transformation of MoS 2 to MoO 3 via calcination. • Phase purity analysis by XRD and XPS. Few-layer nanosheets of MoS 2 were chemically synthesized in a household microwave oven using ammonium heptamolybdate, thiourea and hydrazine hydrate in ethylene glycol. The binding energies values of 226.1 (S 2s) and 229.16, 232.16 eV for Mo 3d confirmed the formation of MoS 2. The so-obtained MoS 2 nanosheets were converted to phase pure nanoplatelets of MoO 3 via sintering process with an average crystallite size of about 30–35 nm. [ABSTRACT FROM AUTHOR]

Abstract: The fast thermolysis of ammonium molybdate leads to a mixture of MoO3 and Mo5.3O14.5(OH)2.8(H2O)1.36 with spherical and rod-like morphologies. The oxide mixture can be converted in quantitative yield to inorganic fullerene-type (IF) MoS2 and MoS2 nanotubes (NT) by H2S reduction using a facile and quick procedure. The products were studied by X-Ray Diffraction (XRD) and by Transmission Electron Microscopy (TEM). TEM analysis reveals that the spherical and rod-like morphology of the oxide precursor is preserved during the H2S treatment. [Copyright &y& Elsevier]

The first part of this paper deals with the morphology of the MoS2 phase and its oxide precursor, the MoO3 phase, mainly from a geometrical point of view. After giving a brief review of the literature describing the structure of these compounds, Mo densities in both phases were calculated along various crystallographic planes. Further, using structural models recently proposed by others, Mo densities in MoS2 were also calculated in the case of an epitactic growth on γ-Al2O3 and TiO2 model surfaces. Then, the calculated Mo densities were compared with experimental results (Mo density when HDS activity is maximal) previously obtained for catalysts constituted of MoS2 supported on a low SSA TiO2, a high SSA TiO2 and a conventional γ-alumina. It was suggested that either on alumina or titania the MoS2 phase is growing as (100) MoS2 planes. However, while on the alumina the optimal MoS2 phase might be constituted of dispersed MoS2 slabs covering only a part of the alumina surface (2.9–3.9 Mo atoms/nm2), on titania the optimal MoS2 phase might be constituted of a uniform MoS2 monolayer (5.2 atoms/nm2 for the high SSA titania, which is equal to the Mo density of a perfect MoS2 (100) plane). This difference may originate in the creation of a 'TiMoS' phase enhancing the S atoms mobility over Mo/TiO2-sulfided catalysts. Indeed, while in the case of a γ-alumina carrier the active sites (labile S atoms) are located on the edge of MoS2 slabs making the ratio Moedge/Mototal a crucial parameter for the catalytic performances, in the case of a titania carrier the labile sulfur atoms might be statistically distributed all over the TiMoS active phase. Further, the higher Mo density observed over the high SSA titania (5.2 atoms/nm2) when compared to that over the low SSA titania (4.2 atoms/nm2) was supposedly due to the pH-swing method advantageously used to prepare the former carrier. Indeed, this method allows giving a solid with enhanced mechanical properties providing a good stability to the derived catalysts under experimental conditions. In addition, this TiO2 carrier exhibits a great homogeneity, with a surface structure substantially uniform, which might be adequate for a long-range growth of (100) MoS2 slabs. [ABSTRACT FROM AUTHOR]

• Sulfidation characteristics of amorphous MoO 3− x films evaporated from MoO 3 and MoO 2 are compared. • More largely-reduced MoO 3− x is appropriate for formation of a continuous MoS 2 film. • Thickness and sulfidation temperature are optimized to produce a MoS 2 monolayer. • Operation of bottom-gated transistors with a synthesized MoS 2 film is demonstrated. In this study, the thermal sulfidation characteristics of two amorphous nonstoichiometric Mo-oxide (MoO 3− x) films were investigated that were deposited using e-beam evaporation of MoO 3 and MoO 2 powders. It was observed that evaporation of MoO 2 produced an amorphous MoO 3− x film that exhibited a greater number of low oxidation states than that obtained by MoO 3 evaporation. Moreover, subsequent sulfidation allowed the formation of a continuous MoS 2 film; meanwhile, the MoO 3 -evaporated sample transformed into a discontinuous MoS 2 film. Both the initial thickness of the MoO 2 -evaporated film and the sulfidation temperature were varied to determine their effects on the final MoS 2 film quality. The sulfidation of an approximately 1-nm-thick MoO 2 -evaporated film at 780 °C produced a predominantly monolayer MoS 2 film. Further, an operation of the bottom-gated transistor arrays using the synthesized MoS 2 film was demonstrated along with a preliminary experimental result for potential application in three-dimensional device integration. [ABSTRACT FROM AUTHOR]

We report on the MoO3 oxides and their derivatives on microscopic 2H MoS2 flakes oxidized in air and high relative humidity at a moderate temperature range below 410 °C. We combine XPS and AFM measurements such as topography, friction, creation of nanoscale ripples and scratches on the MoS2 flakes deposited on Si substrates. We detect MoO3 oxides mostly by measuring selected nanomechanical properties of the MoO3 layer, such as its compressive mechanical stress at the plastic yield. We discuss basal surface coverage of the single MoS2 flakes by the MoO3 oxides. We discuss conditions for appearance of all possible MoO3 oxide derivatives, such as molybdenum(VI) hydroxyoxides and MoO3 hydrates. Our findings agree with an expected mechanistic switch in thermal oxidation in water vapors vs. air. [ABSTRACT FROM AUTHOR]

Environmental friendly supercritical fluid CO 2 technique has been used to synthesize MoS 2 /nanobelt MoO 3 and MoS 2 /nanowire Poly(3-hexylthiophene) (P3HT) nanocomposite using commercial MoS 2 and P3HT powders, and hydrothermally synthesized MoO 3 as the precursor materials. Two unique features are demonstrated. One is that the supercritical fluid CO 2 not only transforms the commercial 2H MoS 2 into 1T exfoliated MoS 2 but also partially oxidizes MoS 2 into MoO 3-x. The other is that not only nanowires are inserted into layered MoS 2 for the first time but also the resulting MoS 2 /P3HT nanocomposites exhibit a distinctive structure favoring ion transport. More importantly, the unique features lead to reduced electrical resistance due to improved ion and electron transfers. Both MoS 2 /MoO 3 and MoS 2 /P3HT exhibit significantly improved electrical conductivity with additional redox active sites such that excellent specific capacitance of 39 mF cm−2 and 55 mF cm−2 at 5 mV s−1 in 1 M KCl are obtained for MoS 2 /MoO 3 and MoS 2 /P3HT, respectively. The results show an enhancement of capacitance by 244% and 423% for MoS 2 /MoO 3 and MoS 2 /P3HT as compare to exfoliated MoS 2 , respectively. The MoS 2 /MoO 3 and MoS 2 /P3HT symmetric cell also show excellent cycle stability up to 114% and 722% after 2000 cycles, respectively. MoO 3 nanobelts and P3HT nanowires were inserted into MoS 2 layers for the formation of sandwich-like MoS 2 /MoO 3 or P3HT heterostructures. The resulting single or few layer 1T/2H MoS 2 , oxygen vacancies MoO 3-x , shorten ionic diffusion path between MoS 2 layers due to the existence of P3HT, and additional redox active sites from the MoO 3 and P3HT all contribute to increase the Csp by 244% and 423% for MoS 2 /MoO 3 and MoS 2 /P3HT, respectively, as compared to MoS 2. Image 1 • For the first time, nanowires are inserted in between 2 dimensional MoS 2 layers. • Supercritical fluid CO 2 partially oxidizes MoS 2 into MoO 3-x. • Synergistic effect of insertion of MoO 3 or P3HT into MoS 2 layers is demonstrated. • Unique structure of MoS 2 /P3HT significantly enhanced the electrical conductivity. • Excellent Csp of 39 mF cm−2 and 55 mF cm−2 for MoS 2 /MoO 3 and MoS 2 /P3HT, respectively. [ABSTRACT FROM AUTHOR]

3D networked polypyrrole (PPy) nanotube/N-doped graphene (NDG) has been fabricated through a facile two-step method, in-situ polymerization assisted by MoO 3 template and a microwave-assisted hydrothermal method at a short time. The MoO 3 template-assisted polymerization is demonstrated as an effective way to obtain PPy nanotubes with controlled thickness. It is found that the PPy nanotube formation and N doping of reduced graphene oxide occur simultaneously during the microwave process at short time. Due to the unique structure and excellent electrical conductivity, the PPy nanotube/NDG shows extremely small equivalent series resistance of 1.7 Ω, charge transfer resistance (Rc) of 0.1 Ω, pore resistance (Rd) of 0.1 Ω, and specific capacitance (Csp) of 292 F g−1 at 5 mV s−1. Also, a novel MoS 2 -decorated core-shelled MoO 3 /PPy has also been fabricated through a facile method. Owing to the unique structure and rich redox activities, MoS 2 -decorated core-shelled MoO 3 /PPy shows excellent performance with Csp of 527 F g−1 at 5 mV s−1 and low charge transfer resistance of 0.5 Ω. Furthermore, an aqueous asymmetric supercapacitor, consisting of MoS 2 /MoO 3 /PPy positive electrode and PPy nanotube/NDG negative electrode, has been constructed. The asymmetric supercapacitor shows an excellent energy density of 43.2 Wh kg−1 at power density of 674 W kg−1. The asymmetric supercapacitor also shows an excellent retention of 126% after 5000 cycles, possess high potential for application in the energy storage. • MoO 3 template as an effective way to obtain PPy nanotube with controlled PPy thickness. • PPy nanotube formation and N-doping graphene were simultaneously occurred. • Heterostructure MoS 2 /MoO 3 /PPy owing a unique structure and rich redox activity was demonstrated. • The ASC shows high energy density of 43.2 Wh kg−1 at power density 674 W kg−1. • The ASC shows an excellent capacitance retention up to 126% after 5000 cycles. [ABSTRACT FROM AUTHOR]