Molybdenum Precursor Research Articles

Influence of the Carrier Gas Flow in the CVD Synthesis of 2-Dimensional MoS2 Based on the Spin-Coating of Liquid Molybdenum Precursors.

Atomically thin molybdenum disulfide (MoS2) is a two-dimensional semiconductor with versatile applications. The recent adoption of liquid molybdenum precursors in chemical vapor deposition has contributed significantly to the reproducible wafer-scale synthesis of MoS2 monolayer and few-layer films. In this work, we study the effects of the carrier gas flow rate on the properties of two-dimensional molybdenum disulfide grown by liquid-precursor-intermediate chemical vapor deposition on SiO2/Si substrates. We characterized the samples using Optical Microscopy, Scanning Electron Microscopy, Raman spectroscopy, and Photoluminescence spectroscopy. We analyzed samples grown with different nitrogen carrier flows, ranging from 150 to 300 sccm, and discussed the effect of carrier gas flows on their properties. We found a correlation between MoS2 flake lateral size, shape, and number of layers, and we present a qualitative growth model based on changes in sulfur provision caused by different carrier flows. We show how the use of liquid precursors can allow for the synthesis of homogeneous, single-layer flakes up to 100 µm in lateral size by optimizing the gas flow rate. These results are essential for gaining a deeper understanding of the growth process of MoS2.

Construction of Mo/S/Ag Cluster Complexes from Dinuclear Molybdenum Precursors [R4N]2[(edt)2Mo2S2(μ‐S)2] (R = Et, nPr; edt = −SCH2CH2S−)

AbstractWe have demonstrated that complexes [(edt)2Mo2O2(μ‐S)2Ag2(dppm)2]·4CH3OH·DMF (2, edt = 1,2‐ethanedithiolate dianion, dppm = bis(diphenylphosphino)methane, DMF = N,N‐dimethylformamide) and [(μ‐Cl)2Ag4(μ3‐Cl)2(dppm)2]·4DMF (3), were generated by combining a dinuclear molybdenum precursor [Et4N]2[(edt)2Mo2S2(μ‐S)2] (1a) with two equimolar AgCl and dppm in a CH3OH‐DMF mixed solution. Treatment of complex 1a with one equimolar AgCl and DPEPhos in CH3OH and DMF mixed solutions, producing complex [Et4N][(edt)2Mo2S2(μ‐S)2Ag(DPEPhos)]·CH3OH (4, DPEPhos = bis(2‐diphenylphosphinophenyl)ether). Treatment of complex [nPr4N]2[(edt)2Mo2S2(μ‐S)2] (1b) with AgBr in acetonitrile followed by addition of (NH4)2S produced a dodecanuclear Mo–Ag–S cage cluster [nPr4N]2[{Mo2Ag2S2O2(edt)2}3(μ6‐S)]·1.5CH3CN (5). Complexes 2−5 have been characterized by infrared(IR), 1H NMR, UV‐vis, and fluorescence spectroscopies. Moreover, molecular structures of complexes 2−5 have been established by single‐crystal X‐ray crystallography.

To Split or Not to Split: [AsCCAs]-Coordinated Mo, W, and Re Complexes and Their Reactivity toward Molecular Dinitrogen.

Molybdenum, tungsten, and rhenium halides bearing a 2,2'-(iPr2As)2-substituted diphenylacetylene ([AsCCAs], 1-As) were prepared and reduced under an atmosphere of dinitrogen in order to activate the latter substrate. In the case of molybdenum, a diiodo (2-As) and a triiodo molybdenum precursor (5) were equally suited for reductive N2 splitting, which led to the isolation of [AsCCAs]Mo≡N(I) (3-As) in each case. For tungsten, [AsCCAs]WCl3 (6) was reduced under N2 to afford {[AsCCAs]WCl2}2(N2) (7), which is best described as a dinuclear π8δ4-configured μ-(η1: η1)-N2-bridged dimer. Attempts to reductively cleave the N2 unit in 7 did not lead to the expected tungsten nitride (8), which had to be prepared independently via the treatment of 7 with sodium azide. To arrive at a π10δ4-configured N2-bridged dimer in a tetragonally distorted ligand environment, [AsCCAs]ReCl3 (9) was reduced in the presence of N2. As expected, a μ-(η1: η1)-N2-bridged dirhenium species, namely, {[AsCCAs]ReCl2}2(N2) (10), was formed, but found to very quickly decompose (presumably via loss of N2), not only under reduced pressure, but also upon irradiation or heating. Hence, an alternative synthetic route to the originally envisioned nitride, [AsCCAs]Re≡N(Cl)2 (11), was developed. While all the aforementioned nitrides (3-As, 8, and 11) were found to be fairly robust, significantly different stabilities were noticed for {[AsCCAs]MCl2}2(N2) (7 for M = W, 10 for M = Re), which is ascribed to the electronically different MN2M cores (π8δ4 for 7 vs π10δ4 for 10) in these μ-(η1: η1)-N2-bridged dimers.

Promotion of a Mo-based ionic crystal precursor for MoS2 wafer growth

The influence of covalent/ionic molybdenum precursors on the quality of MoS2 is investigated. It is found that the reaction of Na2MoO4 as a typical ionic precursor is highly favourable for defect control and surface homogeneity in wafer growth.

Direct liquid injection pulsed-pressure MOCVD of large area MoS2 on Si/SiO2.

Large-scale, high-quality growth of transition metal dichalcogenides (TMD) of controlled thickness is paramount for many applications in opto- and microelectronics. This paper describes the direct growth of well-controlled large area molybdenum disulfide (MoS2) on Si/SiO2 substrates by direct liquid injection pulsed-pressure metal-organic chemical vapor deposition (DLI-PP-MOCVD) using low-toxicity precursors. It is shown that control of the deposited thickness can be achieved by carefully tuning the amount of molybdenum precursor evaporated and that continuous layers are routinely obtained. Homogeneity and reproducibility have also been examined, as well as the average size of the grains. When targeting monolayer thickness, the MoS2 showed near stoichiometry (S/Mo = 1.93-1.95), low roughness and high photoluminescence (PL) quantum yield, equivalent to exfoliated monolayers and CVD MoS2 grown on the same substrates.

Harnessing plasma-generated reactive species for the synthesis of different phases of molybdenum oxide to study adsorption and photocatalytic activity.

This study employs plasma-liquid interaction technique to synthesize different phases of molybdenum oxide using air and argon as plasma-forming gases. In situ plasma-generated nitrogen species primarily NO3-/NO2- and hydrogen species (H+) facilitate the reduction of the molybdenum precursor anion (Mo7O24-). The reduced Mo species subsequently reacts with reactive oxygen species, forming MoO6 octahedra, which is the building block of a molybdenum oxide crystal. Varied concentrations of NO3-/NO2- and H+ species in air and argon plasma treatment significantly influence the growth process. Air plasma synthesis yields hexagonal molybdenum oxide microrods, which upon calcination changes its phase to orthorhombic 2D layered structure. Moreover, the argon plasma synthesized sample exhibits a mixed phase of hexagonal and orthorhombic molybdenum oxide due to the heavy argon ion bombardment, inducing material porosity and surface oxygen vacancies. The mixed-phase material exhibits superior adsorption and photo-degradation towards cationic dye compared to the other two phases. The higher photocatalytic performance may be responsible for the extended lifetime of the photo-generated charge carriers possessed by the mixed-phase material. Radical scavenging tests have identified holes and hydroxyl radicals as the key reactive species that take part in the photo-degradation process.

Cross-domain growth and angle-dependent interlayer coupling of twisted bilayer MoS2

Twisted 2D transition metal dichalcogenides (TMDCs) play a significant role in the development of twistronics. However, it is still challenging to prepare high-quality twisted TMDCs by current stacking or folding techniques. Herein, we propose a cross-domain chemical vapor deposition method to synthesize twisted bilayer MoS2 through precisely controlling the supply of molybdenum precursor. It is found that the top layer of a bilayer MoS2 grain maintains its original orientation even when it crosses over to neighboring monolayer MoS2 grain. This suggests that the van der Waals epitaxy can be prevented with the assistance of covalent bonds. Furthermore, the interlayer coupling strength reaches a maximum value at the twisted angle (θ) of 0° or 60° and a minimum at θ = 30°. Moreover, the evolution of in-plane shear mode and out-of-plane breathing mode obtained from low-frequency Raman spectroscopy reveals atomic reconstructions of the moiré pattern. Meanwhile, the shift of the indirect bandgap exhibits an angle dependence consistent with the interlayer coupling strength, which likely comes from the mixing of pz orbitals. The change in A−/A intensity ratio is not mainly originated from the trion binding energy, but the excess electron concentration. Our results offer a feasible approach to prepare high-quality twisted TMDCs and provide a good platform for studying twistronics and related phenomena.

Molybdenum-Catalyzed Directed Activation of Aryl Chlorides and Fluorides

AbstractA low-valent molybdenum species generated by the reduction of a molybdenum precursor with phenylmagnesium bromide catalytically cleaves a C–Cl or C–F bond in an aromatic ketone under mild conditions, followed by cyclization to produce a hydroxyphthalan (1,3-dihydro-2-benzofuran-1-ol) derivative.

Efficiently catalyzing photo-oxidation of water by surface engineering of bismuth vanadate with nickel molybdenum oxide coverages

Bismuth vanadate with suitable band edges is one of the efficient photocatalysts for water oxidation. Establishing heterojunction can improve electron diffusion lengths and photocatalytic ability of BiVO4. In this work, nickel molybdenum oxide (Ni–Mo–O) and BiVO4 heterojunction is established by the hydrothermal process with different nickel to molybdenum precursor ratios. The Ni–Mo–O/BiVO4 electrode is applied as photoanodes for water oxidation. The growth mechanism of Ni–Mo–O on BiVO4 surface is proposed. The Ni–Mo–O deposition amount is optimized regarding to light absorbance and charger transportation. The largest photocurrent density of 1.72 mA/cm2 at 1.23 VRHE is obtained for the optimal NiMoO4/BiVO4 electrode (NM12) in the electrolyte without hole scavenger, while the pure BiVO4 electrode only shows a photocurrent density of 0.90 mA/cm2. The NM12 electrode even presented an impressive photocurrent density of 5.39 mA/cm2 at 1.23 VRHE in the electrolyte with the hole scavenger, owing to the abundant active sites and higher light absorbance as well as the favorable synergistic effects from its suitable Ni to Mo ratio. The NM12 electrode also shows excellent long-term stability with the photocurrent retention of 83% after illumination for 6500 s. This work opens a blueprint for establishing a novel heterojunction with the adjustable metal ratio and coverage on BiVO4.

Defect-rich 1T-MoS2 nanosheets towards efficient electrochemical hydrogen evolution by simultaneous phase and defect engineering

Molybdenum sulfide (MoS2) has been considered as a promising candidate to replace Pt for the electrochemical hydrogen evolution reaction (HER). However, the disadvantages of inert basal planes and low conductivity limit its application in HER. Herein, we report a facile strategy to achieve simultaneous phase transition and defect engineering in MoS2 by adjusting the ratio of sulfur precursor to molybdenum precursor in the synthesis process. The excess thiourea are adsorbed on the surface of as-formed MoS2 nanocrystallites, which hinders the further crystallization process and creates a large amount of defects on the basal planes. Besides, ammonia ions could in situ insert into the interlayers of MoS2 and induce a phase transition from 2H–MoS2 to 1T-MoS2. The optimized defect-rich 1T-MoS2 catalyst shows a small overpotential of 232 mV at 10 mA cm−2 and Tafel slope of 61 mV dec−1 in acidic media. The superior HER activity is attributed to the defect-rich and 1T-phase structure, which contributes significantly enhanced electronic conductivity and greatly exposed active sites.

Sisal-derived acid-char molybdenum catalyst for reductive deoxygenation of sulfoxides

The deoxygenation of sulfoxides is a rather important reaction from both synthetic and biological points of view, due to the potential of sulfides as intermediates in a variety of processes. Homogenous Mo-based catalysts successfully perform the reduction of diphenyl sulfoxide to diphenyl sulfide with high yields but present the well-known limitations regarding recovery and recycling. Thus, in the present work, two new supported catalysts were prepared through the immobilization of molybdenum precursor species (dichlorodioxodi(aquo)molybdenum(VI) and sodium molybdate), onto a sisal-derived acid-char (S13.5), obtained from rope industry wastes by acid-mediated carbonization. The heterogeneous Mo-based materials were characterized by IR spectroscopy, elemental analysis, ICP, solid state NMR, XPS, and SEM, and were evaluated as catalysts for the reduction of sulfoxides to sulfides in the presence of phenylsilane as reducing agent under different reaction conditions. The influence of various experimental parameters, including reducing agent type and amount, solvent type, and acid promoter were investigated. Catalytic studies revealed that both catalysts deoxygenate sulfoxides at 120 °C in toluene solution with high yields (up to 97%). The MoO2Cl2 derived catalyst shown to be highly efficient in the reduction of diaryl, alkylaryl, dibenzyl, and dialkyl sulfoxides to the corresponding sulfoxides using phenylsilane as reductant and no need of acid promoter.

High-Performance Bimetallic Mo/Ni-N-C Electrocatalyst for Efficient Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is a crucial process in a variety of energy-related technologies, including water splitting and electrochemical conversion. Despite significant progress in the development of OER catalysts, there is still a need for more efficient and cost-effective materials. M-N-C (metal-nitrogen-carbon) materials appear as efficient, low-cost, and sustainable alternatives for the oxygen evolution reaction (OER).In this work, we have synthesized bimetallic Mo/Ni-C catalysts using shungite carbon codoped with nitrogen, molybdenum, and nickel precursors and characterized their physical and chemical properties using a variety of techniques, including X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Due to their highly porous structure along with the high concentration of active sites these catalysts exhibit excellent activity and stability for the OER, with low overpotentials.Overall, our work highlights the potential of bimetallic Mo/Ni-N-C catalysts as efficient and cost-effective alternatives to noble-metal-based catalysts for the OER with significant implications in renewable energy technologies.

Role of density gradients in the growth dynamics of 2-dimensional MoS2 using liquid phase molybdenum precursor in chemical vapor deposition

The key objective of this work was the comparison of MoS2 2-dimensional monolayer flakes grown by Chemical Vapour Deposition with different density gradients in the liquid precursors solution. Structures grown using solutions with iodixanol or glycerol were characterized by Optical Microscopy, Atomic Force Microscopy, Raman spectroscopy and Photoluminescence. Furthermore, electrical properties of structures were studied by characterizing backgated Field-Effect Transistors fabricated on individual flakes.The fundamental outcome of this study is that there are relevant differences between the structures grown with the two different liquid solutions: MoS2 structures grown with glycerol present a large variability in the lateral size of the sharp-corner triangular structure with a good crystalline quality while the employment of iodixanol (the most used substance) causes a poorer crystalline quality, demonstrated by the presence of nanometric pores, with a more homogeneous sizing of the triangular structures.The poor crystalline quality of the iodixanol samples results in reduced light emission efficiency and lower mobility.

Low-Temperature Growth of 2D-MoS2 Thin Films by Plasma-Enhanced Atomic Layer Deposition Using a New Molybdenum Precursor and Applicability to Gas Sensors

Low-Temperature Growth of 2D-MoS₂ Thin Films by Plasma-Enhanced Atomic Layer Deposition Using a New Molybdenum Precursor and Applicability to Gas Sensors

Co3O4 Nanocube-Templated CoS2 and CoS2/MoS2 Heterostructures for Multifunctional Electrocatalysis

The design and development of efficient and low-cost electrocatalysts for both anodic (oxygen evolution reaction (OER)/hydrazine oxidation reaction (HzOR)) and cathodic (hydrogen evolution reaction (HER)) reactions are the major challenges for cleaner hydrogen production. Especially, the fabrication of electrocatalysts with abundant electrochemically active sites through simple synthetic routes is of great interest to draw excellent catalytic efficiency. This report provides a strategy to prepare CoS2–MoS2 heterostructures and spheroid-like CoS2 through the sulfurization reaction from the common Co3O4 nanocube precursor in the presence and absence of the molybdenum precursor, respectively. The as-prepared CoS2–MoS2 (25) heterostructure (prepared with 25 mg of Co3O4) shows excellent HER activity in 1 M KOH by delivering a current density of 10 mA/cmgeo2 at an overpotential of 92.5 ± 3.1 mV. The observed enhancement in the HER activity is attributed to the improved water dissociation kinetics at the abundant interfacial area shared between the two components of the heterostructure. Besides, spheroid-like CoS2 shows good OER and hydrazine oxidation reaction (HzOR) activity owing to the high electrochemically active surface area. In addition, the alkaline electrolyzer (HER//OER) constructed using the CoS2–MoS2 (25) heterostructure and spheroid-like CoS2 as the cathode and anode, respectively, delivers a current density of 10 mA/cmgeo2 at a cell potential of 1.67 V. Furthermore, the hydrazine-assisted electrolyzer (HER//HzOR) displays a low cell potential of 0.53 V to attain the same current density along with excellent durability up to 30 h.

Molybdenum Carbide/Ni Nanoparticles Embedded into Carbon Nanofibers as an Effective Non-Precious Catalyst for Green Hydrogen Production from Methanol Electrooxidation.

Molybdenum carbide co-catalyst and carbon nanofiber matrix are suggested to improve the nickel activity toward methanol electrooxidation process. The proposed electrocatalyst has been synthesized by calcination electrospun nanofiber mats composed of molybdenum chloride, nickel acetate, and poly (vinyl alcohol) under vacuum at elevated temperatures. The fabricated catalyst has been characterized using XRD, SEM, and TEM analysis. The electrochemical measurements demonstrated that the fabricated composite acquired specific activity for methanol electrooxidation when molybdenum content and calcination temperature were tuned. In terms of the current density, the highest performance is attributed to the nanofibers obtained from electrospun solution having 5% molybdenum precursor compared to nickel acetate as a current density of 107 mA/cm2 was generated. The process operating parameters have been optimized and expressed mathematically using the Taguchi robust design method. Experimental design has been employed in investigating the key operating parameters of methanol electrooxidation reaction to obtain the highest oxidation current density peak. The main effective operating parameters of the methanol oxidation reaction are Mo content in the electrocatalyst, methanol concentration, and reaction temperature. Employing Taguchi's robust design helped to capture the optimum conditions yielding the maximum current density. The calculations revealed that the optimum parameters are as follows: Mo content, 5 wt.%; methanol concentration, 2.65 M; and reaction temperature, 50 °C. A mathematical model has been statistically derived to describe the experimental data adequately with an R2 value of 0. 979. The optimization process indicated that the maximum current density can be identified statistically at 5% Mo, 2.0 M methanol concentration, and 45 °C operating temperature.

Synthesis and characterization of volatile liquid Mo precursors for vapor phase deposition of thin films containing molybdenum

Volatile molybdenum precursors in liquid phase for vapor phase deposition of thin films containing molybdenum have been successfully synthesized. Heteroleptic liquid molybdenum precursors were prepared by treating MoCl5 with bidentate β-ketonate ligands such as 2,2,6,6-Tetramethyl-3,5-heptanedione (thdH) at different stoichiometric ratios (1:1 and 1:2). Molybdenum precursors in liquid phases also have been obtained via simple ligand-exchange reactions of Mo(thd)xCl4-x (x = 1 or 2) with LiNR2 (R = Et(C2H5), iPr(C3H7), SiMe3(Si(CH3)3)). The newly synthesized molybdenum precursors are readily miscible (soluble) in most organic solvents, such as acetonitrile, diethyl ether, and hexane. The chemical composition of these precursors has been characterized using Fourier-transform infrared analysis and nuclear magnetic resonance spectroscopy. The volatility and thermal stability of precursor compounds have also been investigated using thermogravimetric analysis and vapor pressure measurement. The strategy used in this experiment, which introduces bidentate ligands to the coordination sphere of the central molybdenum atom in MoCl5, improves the volatility and transferability of molybdenum precursors in gas-phase deposition processes by making them in a liquid phase.

Molybdenum catalyzed deoxydehydration of aliphatic glycols under microwave irradiation

The effectiveness of microwave irradiation in promoting the deoxydehydration of aliphatic diols using dioxomolybdenum catalysts has been evaluated. The commercially available molybdenum precursor MoO2(acac)2 was found to be a superior catalyst as compared to dioxomolybdenum complexes stabilized by aminebisphenol ligands under these conditions. Octane-1,2-diol and decane-1,2-diol were converted to the corresponding olefins in 40−53% yields in 40 mins at 220−230 οC; this is a significant reduction in reaction time and higher activity when compared to reactions performed using conventional heating. More importantly, a similar yield (48%) of 1-decene could be achieved within 10 mins from a reaction carried out at 250 οC.

Plasma-Enhanced Atomic Layer Deposition of Molybdenum Oxide Thin Films at Low Temperatures for Hydrogen Gas Sensing.

Molybdenum oxide thin films are very appealing for gas sensing applications due to their tunable material characteristics. Particularly, the growing demand for developing hydrogen sensors has triggered the exploration of functional materials such as molybdenum oxides (MoOx). Strategies to enhance the performance of MoOx-based gas sensors include nanostructured growth accompanied by precise control of composition and crystallinity. These features can be delivered by using atomic layer deposition (ALD) processing of thin films, where precursor chemistry plays an important role. Herein, we report a new plasma-enhanced ALD process for molybdenum oxide employing the molybdenum precursor [Mo(NtBu)2(tBu2DAD)] (DAD = diazadienyl) and oxygen plasma. Analysis of the film thickness reveals typical ALD characteristics such as linearity and surface saturation with a growth rate of 0.75 Å/cycle in a broad temperature window between 100 and 240 °C. While the films are amorphous at 100 °C, crystalline β-MoO3 is obtained at 240 °C. Compositional analysis reveals nearly stoichiometric and pure MoO3 films with oxygen vacancies present at the surface. Subsequently, hydrogen gas sensitivity of the molybdenum oxide thin films is demonstrated in a laboratory-scale chemiresistive hydrogen sensor setup at an operation temperature of 120 °C. Sensitivities of up to 18% are achieved for the film deposited at 240 °C, showing a strong correlation between crystallinity, oxygen vacancies at the surface, and hydrogen gas sensitivity.

Electrochemical and X-ray structural evidence of multiple molybdenum precursor candidates from a reported non-aqueous electrodeposition of molybdenum disulfide.

A published report of electrodeposited molybdenum(iv) disulfide microflowers at 100 °C in the ionic liquid N-methyl-N-propylpiperidinium bis(trifluoromethane)sulfonimide (PP13-TFSI) from 1,4-butanedithiol and the concentrated filtrate from a reaction mixture of molybdenum(vi) trioxide and ethylene glycol could not be reproduced reliably, affording numerous uniquely coloured reaction mixtures that precipitated a variety of crystalline molybdenum coordination complexes. Further attempts to use the same two of these filtrates to electrodeposit molybdenum(iv) disulfide from 0.1 M PP13-TFSI in tetrahydrofuran with 1,4-butanedithiol at room temperature were unsuccessful. Various crude reaction mixtures grew crystals of different identity from eight attempts to synthesize the reported molybdenum-precursor. Single crystal X-ray diffraction (SC-XRD) offered insight into a wide range of structural features from four candidate paramagnetic precursor compounds, including a novel organomolybdenum cluster. Electrochemical studies of the various molybdenum-precursor filtrates, ethylene glycol, and 1,4-butanedithiol were conducted in 0.1 M PP13-TFSI in tetrahydrofuran, offering insight into differences between preparations of the molybdenum-precursor and interference between ethylene glycol and 1,4-butanedithiol on platinum working electrodes. Molybdenum(iv) disulfide electrodeposition attempts included cyclic voltammetry and chronoamperometry on platinum and glassy carbon working electrodes, which led to either no deposited material, or molybdenum, carbon, oxygen, and sulfur containing amorphous and non-homogenous deposits, as indicated by SEM-EDS analysis.