Deposition Of MoS2 Research Articles

Light and complex 3D MoS2/graphene heterostructures as efficient catalysts for the hydrogen evolution reaction.

Multi-component 3D porous structures are highly promising hierarchical materials for numerous applications. Herein we show that atomic-layer deposition (ALD) of MoS2 on graphene foams with variable pore size is a promising methodology to prepare complex 3D heterostructures to be used as electrocatalysts for the hydrogen evolution reaction (HER). The effect of MoS2 crystallinity is studied and a trade-off between the high density of defects naturally presented in amorphous MoS2 coatings and the highly crystalline phase obtained after annealing at 800 °C is established. Specifically, an optimal annealing at 500 °C is shown to yield improved catalytic performance with an overpotential of 180 mV, a low Tafel slope of 47 mV dec-1, and a high exchange current of 17 μA cm-2. The ALD deposition is highly conformal, and thus advantageous when coating 3D porous structures with small pore sizes, as required for real-world applications. This approach is enabled by conformal thin film deposition on porous structures with controlled crystallinity by tuning the annealing temperature. The results presented here therefore serve as an effective and general platform for the design of chemically and structurally tunable, binder-free, complex, lightweight, and highly efficient 3D porous heterostructures to be used for catalysis, energy storage, composite materials, sensors, water treatment, and more.

Morphology-controlled MoS2 by low-temperature atomic layer deposition.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) such as MoS2 are materials for multifarious applications such as sensing, catalysis, and energy storage. Due to their peculiar charge-transport properties, it is always desired to control their morphologies from vertical nanostructures to horizontal basal-plane oriented smooth layers. In this work, we established a low-temperature ALD process for MoS2 deposition using bis(t-butylimino)bis(dimethylamino)molybdenum(vi) and H2S precursors. The ALD reaction parameters, including reaction temperature and precursor pulse times, are systematically investigated and optimized. Polycrystalline MoS2 is conformally deposited on carbon nanotubes, Si-wafers, and glass substrates. Moreover, the morphologies of the deposited MoS2 films are tuned from smooth film to vertically grown flakes, and to nano-dots, by controlling the reaction parameters/conditions. It is noticed that our MoS2 nanostructures showed morphology-dependent optical and electrocatalytic properties, allowing us to choose the required morphology for a targeted application.

Few-layer flakes of Molybdenum Disulphide produced by anodic arc discharge in pulsed mode

Here, the synthesis of Molybdenum Disulphide (MoS2) flakes by means of anodic atmospheric arc discharge is reported for the first time. The vertical electrode configuration consisted of a compound anode (hollow graphite anode filled with MoS2 powder) and a solid graphite cathode placed just above of the compound anode. Arc processes were operated in pulsed mode to preferentially evaporate the powder component from the anode and to minimize Carbon ablation. Pulsed anodic arc discharges were conducted at 2 Hz and 10% duty cycle in 300 Torr of Helium with a peak current of 250–300 A and a peak voltage of 35 V. A probe made of Tungsten wire was placed in the vicinity of the arc column to collect the evaporated material. The measured thickness profile was correlated to the particle flux distribution and it was fitted by a simple model of plasma expansion. During pulse phase, electron density was estimated around 5 × 1022 m−3 or higher, and ion current density was of the order of 10 A mm−2. Morphology, structure and composition of the samples were characterized by Raman spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The study shows that pulsed arc discharge of the compound anode leads to moderate C deposition combined with MoS2 deposition in the form of fragmented nanocrystals and few atomic monolayers of MoS2. Such synthesis technique is promising to produce new 2D nanomaterials with tailored structure and functionality thanks to the flexibility of pulsed power.

Ligand-Assisted Volatilization and Thermal Stability of Bis(imido)dichloromolybdenum(VI) ([(t-BuN═)2MoCl2]2) and Its Adducts

Volatile molybdenum-containing compounds have successfully been utilized for the atomic layer deposition of MoNx, MoO3, MoS2, and MoCxNy. Most of the reported volatile molybdenum-containing compounds have been prepared via salt metathesis reactions of bis(tert-butylimido)dichloromolybdenum(VI) with anionic nitrogen-based ligands. Herein we describe the preparation of several adducts of [(t-BuN═)2MoCl2]2 (2) via ligand exchange reactions, which include the isolation and characterization of (t-BuN═)2MoCl2·2THF, (t-BuN═)2MoCl2·(tetramethylethylenediamine), (t-BuN═)2MoCl2·(2,2′-bipyridine), (t-BuN═)2MoCl2·(trimethylphosphine), (t-BuN═)2MoCl2·(1,2-bis(dimethylphosphino)ethane), and (t-BuN═)2MoCl2·(1,3-bis(tert-butyl)imidazolin-2-ylidene). These compounds have been characterized using NMR spectroscopy and elemental analysis, and the solid-state structures have been determined using single-crystal X-ray crystallography. The volatility and thermal stability of all compounds have been assessed using TGA and DSC, showing that the coordinated ligands can improve the volatility, but in many cases the gas-phase species reverts to 2. This highlights a strategy for using coordinative ligands that are easily thermolyzed during evaporation and delivery yet improve the volatility of a key precursor.

Electrodeposited MoS2 and WS2 Thin Films for Pseudocapacitance Studies

Cathodic electrodeposition of MoS2 (WS2) atop glassy carbon (ITO) was recently reported utilizing a single-source precursor MoS4 2- (WS4 2-) from an aqueous (acetonitrile) electrolyte. Since MoS2 and WS2 are hydrodesulfurization (HDS) catalysts for sulfur removal from hydrocarbons, they immediately react with and desulfurize the electrolytes from which they are deposited, yielding amorphous deposits that contain excess sulfur. However, the desired stoichiometry MX2 can be recovered by high temperature annealing, which removes excess sulfur and forms moderately crystallized and partially oriented thin films, as shown by x-ray diffraction (XRD) studies. This two-step process for deposition of MoS2 and WS2 thin films of controlled thickness facilitates scientific studies of the nature of pseudocapacitance in these materials. Most reports of MoS2 and WS2 pseudocapacitance study nanocomposites with carbon in order to maximize the specific capacitance, but fundamental electrochemical studies are challenging due to the complex topography and surface heterogeneity. The specific capacitance of MoS2 and WS2 thin films with a thickness ranging from 10 nm to 5μm were studied by cyclic voltammetry and galvanostatic charge discharge in several electrolytes, including 1.0 M aqueous Na2SO4, 1.0 M aqueous LiClO4, and 1.0 M LiClO4 in acetonitrile. For both MoS2 and WS2 thin films, the specific capacitance of stoichiometric films obtained by high temperature annealing is 1-2 orders of magnitude higher than the as-deposited amorphous films. The maximum specific capacitance of 1980 F/g is obtained for 10 nm thick WS2 films in 1.0 M aqueous LiClO4, although this is of course arises from the small mass in the denominator. The capacitance per unit area for WS2 films in 1.0 M aqueous Na2SO4 increases with increasing film thickness, and then reaches a plateau value at a thickness of 30-50 nm. This suggests that the active region thickness for charge storage in WS2 is 30-50 nm, which is close to values previously reported for charge storage in RuO2. Since the cation radius of Li+ (0.90 nm) is smaller than that of Na+ (1.16 nm), higher capacitance per unit area is obtained in LiClO4- than in Na2SO4-containing electrolytes. In addition, the capacitance per unit area in LiClO4-containing electrolytes does not reach a maximum plateau value until a much higher WS2 film thickness. Cathodic electrodeposition of Cu-doped MoS2 atop glassy carbon can also be accomplished from an aqueous electrolyte containing 10.0 mM (NH4)2MoS4, 5.0 mM CuSO4, 0.1 M KCl, and 0.50 M KSCN at pH 6.95. Without the presence of thiocyanate (SCN-) as a complexing agent, the cathodic potentials for electrodeposition of Cu and MoS2 are separated by ~700 mV. However, the addition of SCN- shifts the Cu deposition potential in the cathodic direction towards the deposition potential of MoS2. In addition, a cathodic shoulder is observed during cyclic voltammetry experiments that may indicate an induced co-deposition effect. Electrodeposition at the potential of this cathodic shoulder yields MoS2 thin films that contain 1-4 atom% Cu, as determined by energy dispersive x-ray spectroscopy (EDX) and Rutherford backscattering (RBS). As observed for un-doped MoS2 thin films, high temperature annealing is required to obtain moderately recrystallized and partially oriented films. Four-point probe measurements demonstrate that Cu doping reduces the MoS2 resistivity by 10.3x. The capacitance obtained by cyclic voltammetry and galvanostatic charge discharge for Cu-doped MoS2 thin films is 2.5-3.5x higher than that obtained for MoS2 films of the same thickness.

MoS2 coating on CoSx-embedded nitrogen-doped-carbon-nanosheets grown on carbon cloth for energy conversion

Designing low-cost and highly efficient electrocatalysts has become a critical aspect to achieve sustainable energy production. Herein, we report the preparation strategy of MoS2 on Co-oxide nanoparticles embedded nitrogen-doped carbon nanosheets (Co-NC) those derived by ZIF-L anchored on a carbon cloth as an electrode for hydrogen evolution reaction (HER). The hybrid electrode denoted as MoS2/Co-NC/CC was synthesized in sequence of the growth of the leaf-like zeolitic imidazolate framework (Co-ZIF-L) on a carbon cloth (CC), the carbonization of the Co-ZIF-L and deposition of MoS2 by metal organic chemical deposition (MOCVD). The hierarchical porous catalyst presented remarkable electrochemical activity towards the HER in acidic solution, exhibiting great stability and fast kinetics with a small Tafel slope of 51 mV dec−1. Moreover, to produce a current density of 10 mA cm−2 (η10), MoS2/Co-NC/CC required a low overpotential of 111 mV, which is comparable with Pt.

Highly sensitive and low detection limit of resistive NO2 gas sensor based on a MoS2/graphene two-dimensional heterostructures

The atomic-layer thickness of two-dimensional (2D) materials allows efficient interaction with gas molecules, promotes charge transfer inside these materials, and allows fast absorption/desorption of gas molecules on their surface. 2D materials such as graphene, transition metal dichalcogenides (e.g., MoS2), and phosphorene are promising gas sensor components, exhibiting the advantages of high surface-to-volume ratio, low noise levels, and sensitivity of electronic properties to changes in the surrounding environment. Herein, we performed large-scale thermal chemical vapor deposition (CVD) of MoS2 on graphene and used the prepared hybrid to construct a resistive NO2 gas sensor, which showed high sensitivity, good selectivity and a low detection limit (0.2 ppm), exhibiting the additional advantages of broad detection (0.2–100 ppm) and working temperature (25–200 °C) ranges. The excellent performance of the above sensor was ascribed to the synergistic effects of MoS2 and graphene, with the high active surface of MoS2 leading to the exposure of a large fraction of edge sites and thus achieving excellent activity.

Site-Selective Integration of MoS2 Flakes on Nanopores by Means of Electrophoretic Deposition.

Here, we propose an easy method for site-selective deposition of two-dimensional (2D) material flakes onto nanoholes by means of electrophoretic deposition. This method can be applied to both simple flat nanostructures and complex three-dimensional structures incorporating nanoholes. The deposition method is here used for the decoration of large ordered arrays of plasmonic structures with either a single or few layers of MoS2. In principle, the plasmonic field generated by the nanohole can significantly interact with the 2D layer leading to enhanced light–material interaction. This makes our platform an ideal system for hybrid 2D material/plasmonic investigations. The engineered deposition of 2D materials on plasmonic nanostructures is useful for several important applications such as enhanced light emission, strong coupling, hot-electron generation, and 2D material sensors.

High mobility solution processed MoS2 thin film transistors

A simple wet-chemical synthesis of layered MoS2 thin films on sapphire is reported. The gap in understanding solution processed MoS2 deposition needs to be closed to exploit all its excellent properties for low-cost applications. In this work, as deposited Mo-precursor thin films were prepared based on the solubility and coating properties of Molybdenum(V) chloride in 1-Methoxy-2-propanol. Subsequent annealing of the deposited amorphous Mo-precursor films in the presence of sulfur resulted in the formation of highly crystalline layered MoS2 films on sapphire. Improved crystallinity of the deposited films was achieved by increasing the process temperature and performing the post-annealing treatment. Post-annealing at temperatures above 900 °C increased the uniformity of multilayer films, together with the increase of MoS2 grain size. For charge transport analysis, top-gate top-contact thin film transistors (TFTs) based on these solution processed MoS2 films were fabricated. Ionic liquid gating of the TFT devices exhibited n-type semiconducting behaviour with field-effect mobility as high as 12.07 cm2/Vs and Ion/off ratio ∼ 106. X-ray photoelectron spectroscopy measurements revealed that the films annealed between 900 °C and 980 °C had an average chemical composition of S/Mo ∼ 1.84. This facile liquid phase synthesis method with centimeter-scale uniformity and controllable film thickness up to 1.2 ± 0.65 nm is suitable for low-cost preparation of other transition metal dichalcogenides thin films in next-generation electronics.

Pristine and Alkylated MoS2 Nanosheets for Enhancement of Tribological Performance of Paraffin Grease Under Boundary Lubrication Regime

In the present study, lubricating grease was developed with paraffin oil and 12-lithium hydroxy stearate metal soap as a thickening agent. MoS2 nanosheets were synthesized by hydrothermal method and functionalized with 1-octadecanethiol (i.e., MoS2-ODT). The MoS2 and MoS2-ODT nanosheets were dispersed in the grease with different concentrations to evaluate its tribological performance. Tribological results unveiled that the addition of MoS2 nanosheets in grease appreciably reduced the coefficient of friction and mean wear volume of tribo-interfaces as compared with pure grease. Energy dispersive spectroscopy (EDS) spectrum revealed the deposition of MoS2 on the worn surface and confirmed a thin tribo-film which protects steel tribo-pair against wear.

Electrochemical Activation of MoTe2 for the Hydrogen Evolution Reaction

Sunlight is widely distributed geographically and provides enough energy in one hour to supply the world’s energy demands for a full year. However, this form of renewable energy is intermittent; thus current renewable energy technologies must be fed in to the grid or the excess energy is otherwise wasted. Recent efforts have therefore been focused on the conversion of this excess energy into a fuel in the form of hydrogen via water electrolysis. Due to the diffuse nature of solar power, hydrogen evolution reaction (HER) electrocatalysts are typically compared at a current density of 10 mA cm- 2, which roughly equates to a 10% efficient solar-to-fuels device.1 This means electrocatalysts of extremely high surface areas are required, thus making the scarce and expensive platinum electrocatalyst an impractical choice. Layered transition metal dichalcogenides (TMDCs) can offer a viable alternative due to their high surface area of catalytically active edge and basal plane sites which offer a maximum energy output from the entire surface. Recently, semimetallic 1T’-MoTe2 has emerged as a promising electrocatalyst for the HER based on its ability to accommodate an excess of electrons, making it a prime candidate for investigating the effect of electrochemical activation of TMDCs towards the HER.2,3 With this in mind, we report a novel solid-state nanocrystalline 1T’-MoTe2 electrocatalyst which undergoes an in operando activation as the HER progresses. Continuous cyclic voltammetry under reducing potentials results in a dramatic improvement in electrocatalytic activity after only 100 cycles, thus resulting in a positive shift in overpotential from -320 mV to -178 mV at j = 10 mA cm- 2. Similarly, potentiostatic electrolysis shows a rapid increase in current density with time, while gas chromatography confirms the continuous increase in rate of hydrogen production. This catalytic enhancement is also corroborated by a substantial improvement in turnover frequency and charge transfer resistance, all the while maintaining the original particle morphology, surface area and composition. Previous speculations attribute this improved performance in similar TMDC materials to substantial changes in crystal structure, morphology and / or composition, but the true mechanism of activation remains unclear.4–6 In this context, we aim to understand the origin of this enhanced catalytic activity, and hence investigate the stability of the nanocrystalline 1T’-MoTe2 after electrochemical activation. Further, we rule out changes in crystal structure by Powder X-Ray Diffraction and Raman Spectroscopy, while HRTEM and ICP-OES exclude changes in morphology and composition as the reason for the improved catalytic activity. Finally, by proving the electrochemically active surface area remains constant after cycling, while at the same time the charge transfer resistance halves in value and turnover frequency increases, we propose that the in operando activation is a result of changes to the electronic structure upon cycling. Hence, this study offers a new perspective on the path of electrochemical activation of TMDCs towards the hydrogen evolution reaction. References Roger, I., Shipman, M. A. & Symes, M. D. Earth-abundant catalysts for electrochemical and photoelectrochemical water splitting. Nat. Rev. Chem. 1, 3 (2017).McGlynn, J. C. et al. Molybdenum Ditelluride Rendered into an Efficient and Stable Electrocatalyst for the Hydrogen Evolution Reaction by Polymorphic Control. Energy Technol. 6, 345–350 (2018).Seok, J. et al. Active hydrogen evolution through lattice distortion in metallic MoTe 2. 2D Mater. 4, 25061 (2017).Liu, Y. et al. Self-optimizing, highly surface-active layered metal dichalcogenide catalysts for hydrogen evolution. Nat. Energy (2017). doi:10.1038/nenergy.2017.127Voiry, D. et al. Conducting MoS2 Nanosheets as Catalysts for Hydrogen Evolution Reaction. Nano Lett. 13, 6222–6227 (2013).Roger, I. et al. The direct hydrothermal deposition of cobalt-doped MoS2 onto fluorine-doped SnO2 substrates for catalysis of the electrochemical hydrogen evolution reaction. J. Mater. Chem. A 5, 1472–1480 (2017). Figure 1

Formation of defects and impurities in MoSx and their effect on electronic properties

The authors investigate the thermodynamic and electronic properties of few- and monolayer MoS2 using density functional theory. They calculate the formation energies of S vacancies and the doping effect of C and O under various chemical environments which are commonly observed during MoS2 deposition. The results show that in the oxidizing condition, O readily gets incorporated into the MoS2 layer and assists in C doping. They analyze the bandgap and density of states of MoS2 at different concentrations of defect. They find that the bandgap decreases as the defect concentration increases, wherein the ordering of S vacancies has a more significant influence than that of the other two defects. The S vacancy and C dopants generate deep acceptor gap states within the bandgap of MoS2, while O dopant states are delocalized. They also observe that the carbon dopants form penetrative dimers, which lead to shallow acceptor states. This work contributes to the understanding of defect/impurity incorporation during deposition and prediction of electronic behavior of deposited low-quality MoS2 materials.

Chemical Vapor Deposition Growth of Large-Area Monolayer MoS2 and Fabrication of Relevant Back-Gated Transistor**Supported by the National Natural Science Foundation of China under Grant No 61774064.

A closed two-temperature-zone chemical vapor deposition (CVD) furnace was used to grow monolayer molybdenum disulfide (MoS2) by optimizing the temperature and thus the evaporation volume of the Mo precursor. The experimental results show that the Mo precursor temperature has a large effect on the size and shape transformation of the monolayer MoS2, and at a lower temperature of <760°C, the size of the triangular MoS2 increases with the elevating temperature, while at a higher temperature of >760°C, the shape starts to change from a triangle to a truncated triangle. A large-area triangular monolayer MoS2 with a side length of 145 μm is achieved at 760°C. Further, the as-grown monolayer MoS2 is used to fabricate back-gated transistors by means of electron beam lithography to evaluate the electrical properties of MoS2 thin films. The MoS2 transistors with monolayer MoS2 grown at 760°C exhibit a high on/off current ratio of 106, a mobility of 1.92 cm2/Vs and a subthreshold swing of 194.6 mV/dec, demonstrating the feasible approach of CVD deposition of monolayer MoS2 and the fabrication of transistors on it.

Enhanced photoelectrochemical activity of MoS2-decorated ZnO nanowires electrodeposited onto stainless steel mesh for hydrogen production

A novel MoS2-coated ZnO heterostructure grown onto stainless steel substrate was successfully realized via an original two-step electrodeposition process. The X-ray diffraction revealed the mixed wurtzite and hexagonal structures of both ZnO and MoS2 for 30 min as an optimized MoS2 deposition time. The optical properties studied through UV–visible diffuse reflectance and photoluminescence show that the incorporation of MoS2 to the ZnO nanowires further extends the light absorption. More importantly, from PEC measurements, the obtained heterostructure exhibits the highest photocurrent density at a bias of 0 V with improved stability and provides the highest value of solar-to-hydrogen energy efficiency η(%) compared to bare ZnO. As a result, the MoS2 acts as a cocatalyst to suppress the electron-hole pairs recombination and prevents the photocorrosion of ZnO as proposed in the possible transfer mechanism within the MoS2/ZnO heterostructure.These findings may provide more insights into the design of highly efficient MoS2-coated ZnO photoanodes for solar energy-to‑hydrogen generation.

Revealing the Role of Gold in the Growth of Two-Dimensional Molybdenum Disulfide by Surface Alloy Formation.

The formation of Mo/Au surface alloy during Au-assisted chemical vapor deposition (CVD) of MoS2 is confirmed by a series of control experiments. A metal-organic chemical vapor deposition (MOCVD) system is adapted to conduct two-dimensional MoS2 growth in a controlled environment. Sequential injection of Mo and S precursors, which does not yield any MoS2 on SiO2 /Si, grows atomically thin MoS2 on Au, indicating the formation of an alloy phase. Transmission electron microscopy of a cross-section of the specimen confirms the confinement of the alloy phase near the surface only. These results show that the reaction intermediate is the surface alloy, and that the role of Au in the Au-assisted CVD is the formation of an atomically thin reservoir of Mo near the surface. This mechanism is clearly distinguished from that of MOCVD, which does not involve the formation of any alloy phases.

Reprint of “Ion-mediated growth of ultra thin molybdenum disulfide layers on highly oriented pyrolytic graphite”

Van der Waals (vdW) heterostructures composed of different two-dimensional (2D) materials are at the center of many novel devices. To prepare vdW heterostructures which are of the highest quality and suitable for applications, chemical vapour deposition (CVD) can be used to grow the 2D materials directly on top of each other and thus build the vdW heterostructure in a bottom-up fashion. However, obtaining layers of uniform quality by precisely controlling their growth poses a severe challenge. The aim of our work is to understand the growth mechanisms and we have chosen MoS2 layers on highly oriented pyrolytic graphite (HOPG) as a model system for the MoS2-graphene interface. In our model system we observe, that MoS2 layers do not grow on the HOPG terraces but are more likely to grow at HOPG edges, one-dimensional defects, which obviously acts as growth seeds. In graphene however, step edges are absent and the ever-improving quality of commercially available CVD graphene yields less and less defects per unit area. While this is clearly an advantage for most devices, in the light of our findings it constitutes a major disadvantage for the bottom-up preparation of vdW heterostructures. To overcome this obstacle we artificially introduce defects into the HOPG surface by highly charged ion irradiation. In this way we induce an easily controllable number of quasi zero-dimensional defects before the chemical vapour deposition of MoS2 takes place. We show that this treatment results in MoS2 island growth on top HOPG terraces.

Rubbing-Induced Site-Selective Growth of MoS2 Device Patterns.

The superior electronic and mechanical properties of two-dimensional layered transition-metal dichalcogenides could be exploited to make a broad range of devices with attractive functionalities. However, the nanofabrication of such layered material-based devices still needs resist-based lithography and plasma etching processes for patterning layered materials into functional device features. Such patterning processes lead to unavoidable contaminations, to which the transport characteristics of atomically thin-layered materials are very sensitive. More seriously, such lithography-introduced contaminants cannot be safely eliminated by conventional semiconductor cleaning approaches. This challenge seriously retards the manufacturing of large arrays of layered material-based devices with consistent characteristics. Toward addressing this challenge, we introduce a rubbing-induced site-selective growth method capable of directly generating few-layer MoS2 device patterns without the need of any additional patterning processes. This method consists of two critical steps: (i) a damage-free mechanical rubbing process for generating microscale triboelectric charge patterns on a dielectric surface and (ii) site-selective deposition of MoS2 within rubbing-induced charge patterns. Our microscopy characterizations in combination with finite element analysis indicate that the field magnitude distribution within triboelectric charge patterns determines the morphologies of grown MoS2 patterns. In addition, the MoS2 line patterns produced by the presented method have been implemented for making arrays of working transistors and memristors. These devices exhibit a high yield and good uniformity in their electronic properties over large areas. The presented method could be further developed into a cost-efficient nanomanufacturing approach for producing functional device patterns based on various layered materials.

Strategies to facilitate the formation of free standing MoS2 nanolayers on SiO2 surface by atomic layer deposition: A DFT study

In this study, we employ density functional theory calculations to investigate the very initial formation of a buffer layer during atomic layer deposition of MoS2 at the SiO2 (001) surface. In our previous study, we described that the self-limiting atomic layer deposition (ALD) reactions using Mo(NMe2)2(NtBu)2 as precursor and H2S as co-reagent terminate in the formation of a so-called building block on the SiO2 (001) surface. This building block consists of Mo which shares bonds with the surface O of SiO2 (001) at the bottom and terminal S at the top. Electronic band structure calculations indicate that the subsequently deposited buffer-layer that is composed of these building blocks has (opto)-electrical properties that are far from the ideal situation. Based on our studies, we propose alternative ALD chemistries which lead to the formation of a so-called underpinned building block. In this cluster, the Mo atoms are underpinned by S atoms, suppressing the formation of a buffer layer. This ultimately facilitates the formation of a free standing conformal 2D-MoS2 nanolayer at the interface. Through the proposed chemistries, the opto-electrical properties of the deposited layers will be preserved.

Dopamine-Assisted Synthesis of MoS2 Nanosheets on Carbon Nanotube for Improved Lithium and Sodium Storage Properties

Hybrid materials with delicate composition and morphology usually promote advanced functions. We report a simple synthesis approach to coaxially grow MoS2 nanosheets on carbon nanotubes (CNTs), which were precoated with polydopamine (PDA), with the ability to readily control phase and morphology. It is found that the thin PDA layer on CNTs surface with abundant catechol base and chinone base can effectively attract both Mo4+ and S2– for subsequently in situ forming MoS2 shell and sheet-like morphology, and therefore, it is essential for the successful deposition of MoS2. The as-prepared MoS2 nanosheets/CNTs (MoS2@CNT) composite with a unique hierarchical hybrid nanostructure with large active surface and enhanced structural robustness has greatly promoted the charge-transfer process and enhanced the electrochemical properties when used as the electrode materials for lithium-ion batteries and sodium-ion batteries. As the anode materials for LIBs, the MoS2@CNTs electrode exhibited extremely stable cycling p...

Phototransistors with Negative or Ambipolar Photoresponse Based on As‐Grown Heterostructures of Single‐Walled Carbon Nanotube and MoS2

AbstractA facile synthesis method for the heterostructures of single‐walled carbon nanotubes (SWCNTs) and few‐layer MoS2 is reported. The heterostructures are realized by in situ chemical vapor deposition of MoS2 on individual SWCNTs. Field effect transistors based on the heterostructures display different transfer characteristics depending on the formation of MoS2 conduction channels along SWCNTs. Under light illumination, negative photoresponse originating from charge transfer from MoS2 to SWCNT is observed while positive photoresponse is observed in MoS2 conduction channels, leading to ambipolar photoresponse in devices with both SWCNT and MoS2 channels. The heterostructure phototransistor, for negative photoresponse, exhibits high responsivity (100–1000 AW−1) at low bias voltages (0.1 V) in the visible spectrum (500–700 nm) by combining high mobility conduction channel (SWCNT) with efficient light absorber (MoS2).