Graphene Molybdenum Disulfide Research Articles

Design of ultra-thick graphene-molybdenum disulfide electrodes to reduce volume expansion and capacity fading by first principles

The shuttling of polysulfide intermediates and volume distortion during cycling make it challenging for the applications of MoS2 at high current densities without capacity fading. In order to improve the cycle life and rate capability of lithium-ion batteries, introducing a porous matrix is a viable strategy. Here, MoS2 with 3D porous graphene prepared by low-temperature hydrothermal (160 °C) and low-energy ultrasound-assisted (40 W for 120 s) methods shows no impurities, large layer thickness (0.94 nm, 54 % increase) and no bare MoS2, resulting in smaller volume expansion (34 % in Li4MoS2), higher lithium stability (0.66 eV of adsorption energy) and more convenient ion transport channels. The first-principles calculations show that more lithium can be inserted without destroying the layered structure by forming a lithium metal layer between the MoS2 layers. The encapsulation of graphene not only hinders the shuttle effect of sulfur, but also improves the adsorption energy of lithium atoms in the electrode. In addition, electrochemical analysis shows that the clear drop in charge transfer resistance (Rct) in the first 300 cycles also indicates the improvement of the reaction pathway by graphene. As a result, the as-prepared rGO/MoS2 still maintains a specific capacity of 1008 mAh·g−1 with a very low capacity decay rate (0.03 % per cycle) at a current density of 1 A·g−1 after 500 cycles as an electrode material for lithium-ion batteries.

Unravelling the Phase Transition of 2h-Mos2 to 1t-Mos2 Induced by the Chemical Interaction of Pd with Molybdenum Disulfide–Graphene Hybrids

Unravelling the Phase Transition of 2h-Mos2 to 1t-Mos2 Induced by the Chemical Interaction of Pd with Molybdenum Disulfide–Graphene Hybrids

Two-dimensional nanocomposite-based electrochemical sensor for rapid determination of trans-resveratrol

A two-dimensional nanocomposite-based disposable electrochemical sensor was fabricated for the rapid analysis of trans-resveratrol (TRA) in red wine. The sensor was prepared by modifying graphene-molybdenum disulfide (Gr-MoS2) nanocomposite on the surface of screen-printed electrode (SPE). Results show that the Gr-MoS2 nanocomposite with sheet-on-sheet structure can accelerate the oxidation reaction kinetics of TRA due to its large effective electrochemical surface area and high electron transfer rate. As a result, the Gr-MoS2 nanocomposite appears the synergistic effects, making the highly sensitive detection of TRA come true. The prepared sensor showed a linear response in TRA concentration from 1.0 to 200 μmol L−1 (with a limit of detection of 0.45 μmol L−1). After validating the accuracy with high performance liquid chromatography (HPLC), this nanocomposite-based electrochemical sensor can be applied for the detection of TRA in real red wine samples.

Size-dependent dynamic characteristics of graphene based multi-layer nano hetero-structures

Carbon-based nano hetero-structures are receiving increasing attention due their ability in multi-synchronous modulation of a range of mechanical and other critically desirable properties. In this paper, the vibration characteristics of two different graphene based heterostructures, graphene-hexagonal boron nitride (hBN) and graphene-molybdenum disulfide (MoS2), are explored based on atomistic finite element approach. Such vibrational characteristics of nanostructures are of utmost importance in order to access their suitability as structural members for adoption in various nano-scale devices and systems. In the current analysis, the developed atomistic finite element model for nano-heterostructures is extensively validated first with the results available in literature considering elastic responses and natural frequencies. Thereafter a range of insightful new results are presented for the dynamic behaviour of various configurations of graphene-hBN and graphene-MoS2 heterostructures including their size, chirality and boundary dependence. The investigation of tunable vibrational properties along with simultaneous modulation of other mechanical, electronic, optical, thermal and chemical attributes of such nano-heterostructures would accelerate their application as prospective candidates for manufacturing nanosensors, electromechanical resonators, and a wide range of other devices and systems across the length-scales.

Ethanol concentration sensor based on TiO2-ZnO composite film enhanced surface plasmon resonance with a molybdenum disulfide-graphene oxide hybrid nano-sheet

A method of ethanol concentration detection based on surface plasmon resonance is proposed. Therefore, a novel prism coupling structure is designed for the ethanol concentration sensor by use of the unique feature of graphene oxide (GO) to act as a sieve for ethanol in water, and a TiO2-ZnO composite film is chosen to enhance the surface plasmon resonance with a molybdenum disulfide–graphene oxide hybrid nano-sheet. The thickness of each layer of the structure is analyzed by the finite element method to obtain the optimal value in order to improve the sensitivity greatly. The optimal thickness of each layer is given, and the sensitivity of the surface plasmon resonance ethanol concentration sensor can reach as high as 0.089°/% within the detection range of ethanol concentration (0%–80%). The relationship between the surface plasmon resonance angle and the ethanol concentration is obtained within the detection range of ethanol concentration.

Ultra-sensitive surface plasmon resonance biosensor based on MoS2–graphene hybrid nanostructure with silver metal layer

The optical biosensors based on the plasmonic technology are an important research item in the field of biophotonics. The graphene–molybdenum disulfide (MoS2) based hybrid structures are very effective in designing and fabricating of the sensitive optical biosensors. In this paper, we propose a nanostructure Ag/MoS2/graphene as an optical biosensor with high performance and sensitivity. The proposed configuration for this surface plasmon resonance (SPR) optical biosensor is Kretschmann. Herein, the enhancement of sensitivity for the proposed SPR optical biosensor is investigated in different states. By determining of the numbers of MoS2 layer and the thickness of the metal layer, we increased the sensitivity of the proposed biosensor. The maximum sensitivity ~ 190°/RIU is achieved. For this ultra-sensitive SPR biosensor with maximum sensitivity, the numbers of MoS2 and graphene layer is 2 and the resonance wavelength is determined 680 nm.

Sensitivity enhancement of SPR optical biosensor based on Graphene–MoS2 structure with nanocomposite layer

The optical plasmonic biosensors are an important research item in the field of bio-photonics. The graphene-molybdenum disulfide (MoS2) based hybrid structures are very useful in designing and fabrication of the high sensitive biosensors. In this paper, we designed hetero-structured Air/MoS2/Nanocomposite/MoS2/Graphene as an optical biosensor with high sensitivity. The proposed configuration for this Surface Plasmon Resonance (SPR) biosensor is Otto configuration. Herein, the enhancement sensitivity of this proposed SPR biosensor is investigated in different arrangement of layers. The influence of the refractive index of the coupling prism, the thickness of the nanocomposite layer, the constituent components of the nanocomposite layer and the number of the MoS2 layer is investigated and the optimal values is calculated for the biosensor with maximum sensitivity. The maximum sensitivity ∼200°/RIU is achieved with six layers of MoS2 layer and a nanocomposite layer containing the gold nanoparticles and TiO2 as host dielectric.

Solution-processed Graphene-MoS2 heterostructure for efficient hole extraction in organic solar cells

A major bottleneck exploiting the unique electronic properties of two-dimensional materials like graphene is the lack of mass production methods that are able to produce van der Waals heterostructures. Here, we prepare Graphene-molybdenum disulfide (MoS2) heterostructures via liquid-phase exfoliation followed by hydrothermal reaction, and employ Graphene-MoS2 hybrid thin films as the hole extraction layer in PTB7-Th:PC71BM organic solar cells. We demonstrate a maximum power conversion efficiency of 9.5% whilst retaining more than 93% of the initial efficiency over a storage period of 1000 h, surpassing current reported two-dimensional materials based devices. Our results represent the great potential of two-dimensional heterostructures as hole extraction materials for efficient and stable photovoltaics devices.

Broad-spectrum enhanced absorption of graphene-molybdenum disulfide photovoltaic cells in metal-mirror microcavity

The optical absorption of graphene-molybdenum disulfide photovoltaic cells (GM-PVc) in wedge-shaped metal-mirror microcavities (w-MMCs) combined with a spectrum-splitting structure was studied. Results showed that the combination of spectrum-splitting structure and w-MMC can enable the light absorption of GM-PVcs to reach about 65% in the broad spectrum. The influence of processing errors on the absorption of GM-PVcs in w-MMCs was 3–14 times lower than that of GM-PVcs in wedge photonic crystal microcavities. The light absorption of GM-PVcs reached 60% in the broad spectrum, even with the processing errors. The proposed structure is easy to implement and may have potentially important applications in the development of ultra-thin and high-efficiency solar cells and optoelectronic devices.

Strain-modulation-assisted enhanced broadband photodetector based on large-area, flexible, few-layered Gr/MoS2 on cellulose paper

Electronic structure and carrier behavior in semiconductor junctions can be effectively modulated on the application of strain. This work represents the first demonstration of a large-area, flexible, paper-based graphene-molybdenum disulfide (Gr/MoS2) broadband photodetector using a low-cost solution-processed hydrothermal method and enhancement in photodetection through strain modulation by assembling the device on polydimethylsiloxane. Optimization, in terms of process parameters, was carried out to obtain trilayer MoS2 over Gr-cellulose paper. Under strain, potential barrier variation and piezopotential induced in MoS2 leads to 79.41% enhancement in photodetection in the visible region. Piezopotential induced in MoS2 lowers the conduction-band energy thereby increasing the effective electric field favoring easy electron-hole separation. The advantage of vertically stacked Gr/MoS2 for the photodetector is the utilization of the entire area as a junction where effective separation of electron-hole pairs occurs. Detailed studies of the mechanism in terms of potential barrier variation in Gr/MoS2 and an energy-band diagram are presented to help understand the proposed phenomenon. The present work demonstrates the significance of few-layer MoS2 or Gr in relation to strain-modulated photosensing in comparison to their counterparts grown via chemical vapor deposition. The results provide an excellent approach for the fabrication of low-cost heterojunctions for improved optoelectronic performance, which can be further extended to similar 2D-material heterojunctions for analog, digital and optoelectronic applications.

MoS2-Graphene-Mycosporine-Like Amino Acid Nanocomposite as Photocatalyst

In the quest of extending isostructural hybridization approach to organic–inorganic nanocomposite-based photocatalytic systems, a unique strategy of replacing the traditional inorganic semiconductors with naturally produced mycosporine-like amino acids (MAA) is proposed. The main motivation of incorporating MAA in symbiotically configured nanocomposites is with regard to MAA green, nontoxic nature, UV absorption and photostability. Our facile one-pot solvothermal method is to facilitate the amalgamation of MAA and molybdenum disulfide-graphene (MG) composite at the molecular/nanoscale level to endow better photocatalytic functionality. It is observed that the rate of photocatalytic dye degradation of Rhodamine 6G (R6G) becomes consistently enhanced with an incremental increase in the concentration of MAA in MG. The combination of MG-MAA leads up to 81.2% quenching of the PL emission, as compared with MG. Noticeable decrease in PL lifetime from 280 ps (MG) to 77[Formula: see text]ps (MG-MAA) explicitly implies fast charge extraction and transport of the charge carriers.

Stacking sequence dependent photo-electrocatalytic performance of CVD grown MoS2/graphene van der Waals solids

New layered solids by the combinatorial stacking of different atomic layers are emanating as novel candidates for energy efficient devices. Here, sequentially stacked single layer graphene-molybdenum disulfide (MoS2) van der Waals (vdW) solids are demonstrated for their efficacy in the catalysis of hydrogen evolution reaction (HER), and importance of their stacking order in tuning the photo-electrocatalytic (PEC) efficiency is unraveled. Single layer graphene and a few layered MoS2 stacked vdW solids based transparent flexible electrodes were prepared, and a particular stacking sequence where top-graphene: bottom-MoS2/polydimethylsiloxane (PDMS) geometry (MSGR) exhibited the lowest onset and over potentials and a very high exchange current density (j0 ∼ 245 ± 1 μA cm−2) in acidic HER in comparison to the individual layers and other stacked configuration (MoS2 on top of graphene on PDMS, GRMS). The HER studies under dark and white light illuminations were conducted to explore the PEC responses of the devices. The augmented HER performance of MSGR is further confirmed from the charge transfer resistance measurements using electrochemical impedance spectroscopy. Role of graphene plasmonics and MoS2 to graphene electron transfer were studied, and this study unravels the importance of a new factor, stacking order of vdW layers, while designing novel devices from the layered solids.

A facile electrochemical sensor based on well-dispersed graphene-molybdenum disulfide modified electrode for highly sensitive detection of dopamine

A dopamine electrochemical sensor was easily fabricated by modifying the glassy carbon electrode with well-dispersed graphene and molybdenum disulfide hybrids. Graphene had the ability to enhance the electrochemical response intensity and molybdenum disulfide served as an amplification element when added to the graphene layer. The modification activity was investigated with the electrochemical impedance spectroscopy technique. A highly sensitive electrochemical method was developed to detect dopamine based on the strong enhancement effect of graphene-molybdenum disulfide. The oxidation peak currents varied linearly with the addition of dopamine over the range from 5.0×10−8 to 1.0×10−5molL−1, and the lower detection limit was 7.13×10−9molL−1 (S/N=3). This work demonstrated a simple, efficient design for a chemical sensor that employs graphene-molybdenum disulfide for dopamine detection.

Graphene-MoS2 Hybrid Structure Enhanced Fiber Optic Surface Plasmon Resonance Sensor

In this paper, a fiber optic surface plasmon resonance sensor based on graphene-MoS2 hybrid structure is presented. The wavelength interrogation method is employed to analyze the reflection spectra and the performance of the sensor. The theoretical analysis shows that the confined electric field generated at the interface between the sensor surface and the surrounding environment can be enhanced by introducing graphene-molybdenum disulfide (MoS2) hybrid structure as the sensing layers coated on the core of fiber. Such electric field enhancement significantly improves the sensitivity of the fiber optic surface plasmon resonance sensor. Furthermore, it is suggested that coating more number of graphene and MoS2 layers on thicker Au film is a good selection for the higher enhancement of the sensitivity. The sensitivity of the proposed sensor exhibits an enhancement of 20 % compared to that of the conventional fiber optic surface plasmon resonance sensing scheme without graphene-MoS2 hybrid structure. The proposed graphene-MoS2-Au fiber optic surface plasmon resonance sensor is simple in structure, has high sensitivity, and shows good potential in practical applications.

Broadband perfect light trapping in the thinnest monolayer graphene-MoS2 photovoltaic cell: the new application of spectrum-splitting structure.

The light absorption of a monolayer graphene-molybdenum disulfide photovoltaic (GM-PV) cell in a wedge-shaped microcavity with a spectrum-splitting structure is investigated theoretically. The GM-PV cell, which is three times thinner than the traditional photovoltaic cell, exhibits up to 98% light absorptance in a wide wavelength range. This rate exceeds the fundamental limit of nanophotonic light trapping in solar cells. The effects of defect layer thickness, GM-PV cell position in the microcavity, incident angle, and lens aberration on the light absorptance of the GM-PV cell are explored. Despite these effects, the GM-PV cell can still achieve at least 90% light absorptance with the current technology. Our proposal provides different methods to design light-trapping structures and apply spectrum-splitting systems.

A small-signal generator based on a multi-layer graphene/molybdenum disulfide heterojunction

In this work, we fabricate a heterojunction small-signal generator (HSSG) based on a graphene-molybdenum disulfide (MoS2) heterojunction. The HSSG is fundamentally different from any analog device developed previously. The HSSG is composed of two quasi-2D heterojunctions and has three terminals named injector (I), recombinator (R), and generator (G). MoS2 serves as I and G, and graphene works as R in the HSSG. The scale coefficient (β = IG/IR) of the HSSG is 1.14 × 10−4 (VIG, IR = 0.2 V) to 1.95 × 10−4 (VIG, IR = 1 V). The current generated from G could be as low as pA scale, which reveals the good performance of the HSSG.