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Covalently tethering photosensitizers to catalytically active 1T-MoS2 surfaces holds great promise for the solar-driven hydrogen evolution reaction (HER). Herein, we report the preparation of two new RuII -complex-functionalized MoS2 hybrids [RuII (bpy)2 (phen)]-MoS2 and [RuII (bpy)2 (py)Cl]-MoS2 . The influence of covalent functionalization of chemically exfoliated 1T-MoS2 with coordinating ligands and RuII complexes on the HER activity and photo-electrochemical performance of this dye-sensitized system was studied systematically. We find that the photo-electrochemical performance of this RuII -complex-sensitized MoS2 system is highly dependent on the surface extent of photosensitizers and the catalytic activity of functionalized MoS2 . The latter was strongly affected by the number and the kind of functional groups. Our results underline the tunability of the photovoltage generation in this dye-sensitized MoS2 system by manipulation of the surface functionalities, which provides a practical guidance for smart design of future dye-sensitized MoS2 hydrogen production devices towards improved the photofuel conversion efficiency.

Self-assembly of nanomaterials by wet chemistry methods is a suitable approach for the preparation of engineered structures with novel functionalities. In this work, we study the ability of long-chain amines to direct the growth of a layered nanomaterial, using [Re x Se y Cl z ] clusters as building blocks. The amines link to the clusters as ligands during the synthesis, directing the self-assembly due to their amphiphilic properties, which produces a platelet-shaped 2D material with sizes up to several μm in diameter and thicknesses in the range of 60–80 nm. This is, to the best of our knowledge, the first report on a one-step mild chemistry method for the preparation of 2D structures composed of alternate layers of self-assembled amines and sub-nm clusters of a rhenium chalcogenide. Furthermore, these materials can be used as a suitable source of clusters which then, conveniently released by a simple acid/base reaction, have been successfully incorporated to the surface of graphene. The simple clusters deposition method developed here offers a promising route towards the preparation of hybrid clusters/2D materials with outstanding properties arising from quantum confinement effects combined with high surface areas and the enormous compositional variety of 2D materials and clusters. These hybrids are expected to play a key role in the development of active materials for applications ranging from highly efficient energy storage systems, more active catalysts and upper-sensitivity gas sensors. Scaffolds made of chain-shaped molecules can be erected and dismantled to control the assembly of small atomic clusters. Andres Seral-Ascaso, Valeria Nicolosi and colleagues from Trinity College Dublin, Ireland, developed a method to let grains of few Rhenium and Selenium atoms assemble into flat, circular platelets in a liquid solution. Key to the process are the organic molecules composing the solution, having a head that attaches to the clusters and a chain-like tail that makes the molecules align like poles of a scaffold. The clusters are held together in stable platelets, until the addition of another liquid breaks the alignment and disperses the clusters again. Breaking the organic scaffold in a solution that contains graphene sheets makes the re-dispersed clusters deposit on such sheets, forming composite materials that may find use in batteries or sensors.

We report on 2H-2H′/1T phase conversion of MoS2 and MoSe2 polycrystalline films grown by thermally assisted conversion. The structural conversion of the transition metal dichalcogenides was successfully carried out by organolithium treatment on chip. As a result we obtained a new 2H-2H′/1T cophase system of the TMDs thin films which was verified by Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The conversion was successfully carried out on selected areas yielding a lateral heterostructure between the pristine 2H phase and the 2H′/1T cophase regions. Scanning electron microscopy and atomic force microscopy revealed changes in the surface morphology and work function of the cophase system in comparison to the pristine films, with a surprisingly sharp lateral interface region.

Two-dimensional layered transition metal dichalcogenides (TMDs) have attracted great interest owing to their unique properties and a wide array of potential applications. However, due to their inert nature, pristine TMDs are very challenging to functionalize. We demonstrate a general route to functionalize exfoliated 2H-MoS2 with cysteine. Critically, MoS2 was found to be facilitating the oxidation of the thiol cysteine to the disulfide cystine during functionalization. The resulting cystine was physisorbed on MoS2 rather than coordinated as a thiol (cysteine) filling S-vacancies in the 2H-MoS2 surface, as originally conceived. These observations were found to be true for other organic thiols and indeed other TMDs. Our findings suggest that functionalization of two-dimensional MoS2 using organic thiols may not yield covalently or datively tethered functionalities, rather, in this instance, they yield physisorbed disulfides that are easily removed.

This work describes silicon nanoparticle-based lithium-ion battery negative electrodes where multiple nonactive electrode additives (usually carbon black and an inert polymer binder) are replaced with a single conductive binder, in this case, the conducting polymerPSS. While enabling the production of well-mixed slurry-cast electrodes with high silicon content (up to 95 wt %), this combination eliminates the well-known occurrence of capacity losses due to physical separation of the silicon and traditional inorganic conductive additives during repeated lithiation/delithiation processes. Using an in situ secondary doping treatment of thePSS with small quantities of formic acid, electrodes containing 80 wt % SiNPs can be prepared with electrical conductivity as high as 4.2 S/cm. Even at the relatively high areal loading of 1 mg/cm(2), this system demonstrated a first cycle lithiation capacity of 3685 mA·h/g (based on the SiNP mass) and a first cycle efficiency of ∼78%. After 100 repeated cycles at 1 A/g this electrode was still able to store an impressive 1950 mA·h/g normalized to Si mass (∼75% capacity retention), corresponding to 1542 mA·h/g when the capacity is normalized by the total electrode mass. At the maximum electrode thickness studied (∼1.5 mg/cm(2)), a high areal capacity of 3 mA·h/cm(2) was achieved. Importantly, these electrodes are based on commercially available components and are produced by the standard slurry coating methods required for large-scale electrode production. Hence, the results presented here are highly relevant for the realization of commercial LiB negative electrodes that surpass the performance of current graphite-based negative electrode systems.

Here we demonstrate that liquid phase exfoliation can be used to convert layered crystals of nickel hydroxide into Ni(OH)2 nanosheets in relatively large quantities and without the need for ion intercalation. While other procedures require harsh synthesis conditions and multiple reaction steps, this method involves ultrasonication of commercially available powders in aqueous surfactant solutions and so is relatively mild and potentially scalable. Such mild exfoliation is possible because the surface energy of Ni(OH)2, as measured by inverse gas chromatography, is relatively low at ∼70 mJ m−2, similar to other layered materials. TEM, AFM, XPS and Raman spectroscopy show the exfoliated nanosheets to be relatively thin (mean ∼10 monolayers thick) and of good quality. Size selection by liquid cascade centrifugation allowed the production of samples with mean nanosheet lengths ranging from 55 to 195 nm. Optical measurements on dispersions showed the optical absorption coefficient spectra to be relatively invariant with nanosheet size while the scattering coefficient spectra varied strongly with size. The resultant size-dependence allows the extinction spectra to be used to estimate nanosheet size as well as concentration. We used the exfoliated nanosheets to prepare thin film electrodes for use in supercapacitors and as oxygen evolution catalysts. While the resultant capacitance was reasonably high at ∼1200 F cm−3 (20 mV s−1), the catalytic performance was exceptional with currents of 10 mA cm−2 observed at overpotentials as low as 297 mV, close to the state of the art.

Understanding the correlation between the physico-chemical properties of carbonaceous nanomaterials and how these properties impact on cells and subcellular mechanisms is critical to their risk assessment and safe translation into newly engineered devices. Here the toxicity, uptake and catabolic response of primary human macrophages to pristine graphene (PG) and pristine single walled carbon nanotubes (pSWCNT) are explored, compared and contrasted. The nanomaterial toxicity was assessed using three complementary techniques (live–dead assay, real time impedance technique and confocal microscopic analysis), all of which indicated no signs of acute cytotoxicity in response to PG or pSWCNT. Transmission electron microscopy (TEM) demonstrated that PG was phagocytosed by the cells into single membrane lysosomal vesicles, whereas the primary macrophages exposed to pSWCNT contained many double membrane vesicles indicative of an autophagic response. These distinct catabolic pathways were further verified by biochemical and microscopic techniques. Raman spectroscopic mapping was used to explore the nanomaterial uptake and distribution. Based on the G-band, significant uptake and accumulation of the PG in discrete vesicles was recorded, whereas the pSWCNT were not taken up to the same extent. Thermogravimetric analysis (TGA) of the cells treated with PG revealed that ∼20–30% of the remaining dry mass was made up of PG. No detectable amount of pSWCNT was recorded using TGA. TEM analysis confirmed that PG was still graphitic even after 24 hours of accumulation in the lysosomal compartments. In conclusion, these two nanomaterials, with similar surface chemistries but unique geometries, differ significantly in their uptake mechanisms and subsequently induced lysosomal and autophagic catabolic pathways in human primary macrophages.

A rigorous study of electrodeposited pure and mixed Ni/Fe oxides was performed in three different sodium hydroxide electrolytes with various Fe impurity concentrations (

The effect of adding chromium (Cr) to the copper catalyst for chemical vapour deposition growth of graphene is investigated. We observe a suppression of the formation of multilayer islands of graphene in the Cr-rich regions. This is shown with optical microscopy, scanning electron microscopy and scanning Raman spectroscopy. In addition, carbon isotope labelling is employed to elucidate the mechanism by which the formation of multilayer islands is minimised. The use of mixed catalysts is an important step in the optimisation of catalytic growth of graphene.

Although transition metal dichalcogenides such as MoS2 have been recognized as highly potent two-dimensional nanomaterials, general methods to chemically functionalize them are scarce. Herein, we demonstrate a functionalization route that results in organic groups bonded to the MoS2 surface via covalent C-S bonds. This is based on lithium intercalation, chemical exfoliation and subsequent quenching of the negative charges residing on the MoS2 by electrophiles such as diazonium salts. Typical degrees of functionalization are 10-20 atom % and are potentially tunable by the choice of intercalation conditions. Significantly, no further defects are introduced, and annealing at 350 °C restores the pristine 2H-MoS2. We show that, unlike both chemically exfoliated and pristine MoS2, the functionalized MoS2 is very well dispersible in anisole, confirming a significant modification of the surface properties by functionalization. DFT calculations show that the grafting of the functional group to the sulfur atoms of (charged) MoS2 is energetically favorable and that S-C bonds are formed.

Here, we demonstrate the production of large quantities of gallium sulfide (GaS) nanosheets by liquid exfoliation of layered GaS powder. The exfoliation was achieved by sonication of the powder in suitable solvents. The variation of dispersed concentration with solvent was consistent with classical solution thermodynamics and showed successful solvents to be those with Hildebrand solubility parameters close to 21.5 MPa1/2. In this way, nanosheets could be produced at concentrations of up to ∼0.2 mg/mL with lateral sizes and thicknesses of 50–1000 nm and 3–80 layers, respectively. The nanosheets appeared to be relatively defect-free although oxygen was observed in the vicinity of the edges. Using controlled centrifugation techniques, it was possible to prepare dispersions containing size-selected nanosheets. Spectroscopic measurements showed the optical properties of the dispersions to vary strongly with nanosheet size, allowing the elucidation of spectroscopic metrics for in situ estimation of nanosheet s...

Layered two-dimensional (2D) inorganic transition-metal dichalchogenides (TMDs) have attracted great interest as a result of their potential application in optoelectronics, catalysis, and medicine. However, methods to functionalize and process such 2D TMDs remain scarce. We have established a facile route towards functionalized layered MoS2 . We found that the reaction of liquid-exfoliated 2D MoS2 , with M(OAc)2 salts (M=Ni, Cu, Zn; OAc=acetate) yielded functionalized MoS2 -M(OAc)2 materials. Importantly, this method furnished the 2H-polytype of MoS2 which is a semiconductor. X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT-IR), and thermogravimetric analysis (TGA) provide strong evidence for the coordination of MoS2 surface sulfur atoms to the M(OAc)2 salt. Interestingly, functionalization of 2H-MoS2 allows for its dispersion/processing in more conventional laboratory solvents.

This commmunication presents a study of atomic layer deposition of Al2O3 on transition metal dichalcogenide (TMD) two-dimensional films which is crucial for use of these promising materials for electronic applications. Deposition of Al2O3 on pristine chemical vapour deposited MoS2 and WS2 crystals is demonstrated. This deposition is dependent on the number of TMD layers as there is no deposition on pristine monolayers. In addition, we show that it is possible to reliably seed the deposition, even on the monolayer, using non-covalent functionalisation with perylene derivatives as anchor unit.

In this work, lithium titanate nanoparticles (nLTO)/single wall carbon nanotubes (SWCNT) composite electrodes are prepared by the combination of an ultrasound irradiation and ultrasonic spray deposition methods. It was found that a mass fraction of 15% carbon nanotubes optimizes the electrochemical performance of nLTO electrodes. These present capacities as high as 173, 130, 110 and 70 mAh.g−1 at 0.1C, 1C, 10C and 100C, respectively. Moreover, after 1000 cycles at 1C, the nLTO/SWCNT composites present a capacity loss of just 9% and a Coulombic efficiency of 99.8%. Therefore, the presented methodology might be extended to other suitable active materials in order to manufacture binder free electrodes with optimal energy storage capabilities.

We report the plasma assisted synthesis of WS 2 thin films and demonstrate their suitability for sensing applications. This was achieved by using a H 2 S plasma to sulphurise WO 3 films at temperatures as low as 500 °C. This is a significant step towards semiconductor compatible growth of transition metal dichalcogenide (TMD) thin films without the need for highly elevated temperatures. We found that the electrical transport in thin films is highly sensitive to the presence of NH 3 . A sensitivity of 1.4 ppm NH 3 in nitrogen at room temperature has been achieved, demonstrating the potential of 2D TMD films for sensing applications.

Two dimensional transition metal dichalcogenides (TMDs) are exciting materials for future applications in nanoelectronics, nanophotonics and sensing. In particular, sulfides and selenides of molybdenum (Mo) and tungsten (W) have attracted interest as they possess a band gap, which is important for integration into electronic device structures. However, the low throughput synthesis of high quality TMD thin films has thus far hindered the development of devices, and so a scalable method is required to fully exploit their exceptional properties. Within this work a facile route to the manufacture of devices from MoS 2 and WS 2 , grown by vapour phase sulfurisation of pre-deposited metal layers, is presented. Highly homogenous TMD films are produced over large areas. Fine control over TMD film thickness, down to a few layers, is achieved by modifying the thickness of the pre-deposited metal layer. The films are characterised by Raman spectroscopy, electron microscopy and X-ray photoelectron spectroscopy. The thinnest films exhibit photoluminescence, as predicted for monolayer MoS 2 films, due to confinement in two dimensions. By using shadow mask lithography, films with well-defined geometries were produced and subsequently integrated with standard microprocessing process flows and electrically characterised. In this way, MoS 2 based sensors were produced, displaying sensitivity to NH 3 down to 400 ppb. Our device manufacture is versatile, and is adaptable for future nanoscale (opto-) electronic devices as it is reproducible, cost effective and scalable up to wafer scale.

In this work, inkjet printing methods are used to create graphene field effect transistors with mobilities up to 3000 cm 2 V −1 s −1 . A commercially-available chromium-based ink is used to define the device channel by inhibiting chemical vapour deposition of graphene in defined regions on a copper catalyst. We report on the patterned graphene growth using optical and electronic microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Silver nanoparticle ink is used to create electrical contacts to the defined graphene regions. The resulting devices were characterised by electrical transport measurements at room temperature. As a result we are able to fabricate high-performance graphene field effect transistors entirely defined by a commercial inkjet printer with channel lengths of 50 μm.

We report on 2H-2H'/1T phase conversion of MoS

Layered two-dimensional (2D) materials display great potential for a range of applications, particularly in electronics. We report the large-scale synthesis of thin films of platinum diselenide (PtSe

In this study, nickel oxide films were prepared through an electrodeposition technique. NiO films were fabricated on Indium Tin Oxide (ITO) supports by cycling the potential between two different sets of limits. The electrodeposition technique which involved using the shorter potential limits was denoted as deposition process 1 and the technique using the wider potential limits was called deposition process 2. Subsequently, the films fabricated by the two deposition process were evaluated as electrochromic materials. The results show that the Colouration Efficiency (CE) values achieved for the deposition process 1 and 2 were 49 cm2 C-1 and 10 cm2 C-1, respectively. The switching times of the film made by the first deposition process were also calculated, as this film showed improved electrochromic capabilities. The coloration and bleaching switching times for this NiO film are 5.7 and 7.4 seconds,respectively. The improved electrochromic results for the film fabricated by deposition process 1 maybe due to the smaller potential deposition window as it produced a thinner film with no traces of sulphate ions on the film’s surface compared to the other NiO film produced by the second electrodeposition technique. The films are characterized by SEM-EDX, Raman spectroscopy and XPS. The regeneration of the bleach state was shown to be hindered. This may be due to conductive pathways involved in the reduction of the coloured state being blocked. Raman spectroscopy was used to determine the presence of both the Ni(OH)2 and NiOOH after the reduction event.

Layered two-dimensional (2D) materials display great potential for a range of applications, particularly in electronics. We report the large-scale synthesis of thin films of platinum diselenide (PtSe2), a thus far scarcely investigated transition metal dichalcogenide. Importantly, the synthesis by thermal assisted conversion is performed at 400 {\deg}C, representing a breakthrough for the direct integration of this novel material with silicon (Si) technology. Besides the thorough characterization of this new 2D material, we demonstrate its promise for applications in high-performance gas sensing with extremely short response and recovery times observed due to the 2D nature of the films. Furthermore, we realized vertically-stacked heterostructures of PtSe2 on Si which act as both photodiodes and photovoltaic cells. Thus this study establishes PtSe2 as a potential candidate for next-generation sensors and (opto-)electronic devices, using fabrication protocols compatible with established Si technologies.

We describe the soft chemistry synthesis of amine-templated gallium chalcogenide nanotubes through the reaction of gallium(III) acetylacetonate and the chalcogen (sulfur, selenium) using a mixture of long-chain amines (hexadecylamine and dodecylamine) as a solvent. Beyond their role as solvent, the amines also act as a template, directing the growth of discrete units with a one-dimensional multilayer tubular nanostructure. These new materials, which broaden the family of amine-stabilized gallium chalcogenides, can be tentatively classified as direct large band gap semiconductors. Their preliminary performance as active material for electrodes in lithium ion batteries has also been tested, demonstrating great potential in energy storage field even without optimization.

While 2D transition metal dichalcogenides are known to be promising materials for electrocatalysis of hydrogen production, it is not clear which member of this family of materials is the most effective catalyst. Here we perform a comprehensive study, comparing the catalytic performance of electrodes consisting of porous arrays of liquid exfoliated MX2 nanosheets (M = Mo, W; X = S, Se, Te). We find a clear hierarchy with selenides > sulphides > tellurides with MoSe2 clearly out-performing the other materials. In all cases the performance, as characterised by current density at a given potential, can be improved by increasing the number of active sites (via control of the electrode thickness) and/or by adding carbon nanotubes to the electrode (i.e. increasing the electrode conductivity). While all materials formed reasonably stable electrodes, addition of nanotubes tended to improve mechanical cohesion. In an attempt to maximise performance, we prepared thick (∼15 μm), free standing MoSe2/SWNT composite electrodes which displayed Tafel slopes of ∼77 mV per decade and exchange current densities of ∼0.1 mA cm−2. These electrodes had low onset potentials, reaching −2 mA cm−2 at −41 mV (vs. RHE) and generated high current densities of −35 mA cm−2 at −200 mV (vs. RHE).

Platinum diselenide (PtSe2) is a newly discovered 2D material which is of great interest for applications in electronics and catalysis. PtSe2 films were synthesized by thermally assisted selenization of predeposited platinum films and scanning transmission electron microscopy revealed the crystal structure of these films to be 1T. Raman scattering of these films was studied as a function of film thickness, laser wavelength and laser polarization. Eg and A1g Raman active modes were identified using polarization measurements in the Raman setup. These modes were found to display a clear position and intensity dependence with film thickness, for multiple excitation wavelengths, and their peak positions agree with simulated phonon dispersion curves for PtSe2. These results highlight the practicality of using Raman spectroscopy as a prime characterization technique for newly synthesized 2D materials.

Few-layer black phosphorus (BP) is a new two-dimensional material which is of great interest for applications, mainly in electronics. However, its lack of environmental stability severely limits its synthesis and processing. Here we demonstrate that high-quality, few-layer BP nanosheets, with controllable size and observable photoluminescence, can be produced in large quantities by liquid phase exfoliation under ambient conditions in solvents such as N-cyclohexyl-2-pyrrolidone (CHP). Nanosheets are surprisingly stable in CHP, probably due to the solvation shell protecting the nanosheets from reacting with water or oxygen. Experiments, supported by simulations, show reactions to occur only at the nanosheet edge, with the rate and extent of the reaction dependent on the water/oxygen content. We demonstrate that liquid-exfoliated BP nanosheets are potentially useful in a range of applications from ultrafast saturable absorbers to gas sensors to fillers for composite reinforcement., While phosphorene is an exciting new 2D material, techniques to produce it in large quantities in a stable, processable form are lacking. Here, the authors achieve this using liquid phase exfoliation and demonstrate the resultant nanosheets to be useful in a number of applications.

The structure and chemistry of clean GaN surfaces and InGaN thin films and nanostructures grown by metal organic vapour pressure epitaxy (MOVPE) has been studied by means of X-ray photoemission spectroscopy, low-energy electron diffraction as well as scanning tunneling microscopy (STM) and transmission electron microscopy. Thermal annealing strongly improves the cleanliness of samples after dry nitrogen transfer and related exposure to residual oxygen. Nitrogen plasma assisted cleaning is shown to successfully further remove carbon contaminations, while Ga deposition with subsequent desorption to is shown to be superior for an enhanced reduction of surface oxygen. Using STM, the surface morphology has been studied in dependence on major growth parameters at various stages of InGaN MOVPE growth. The formation of nano-islands is reported for different growth conditions. By means of micro- photoluminescence measurements, we find samples to show strong photoluminescence from quantum-dot-like structures, however, the corresponding growth front is found to be rather flat throughout InGaN deposition. This leads to the conclusion that the formation of quantum dots does not proceed in a Stranski-Krastanov-like fashion but most likely during over- growth.

An efficient, high-throughput method for the formation of densely packed molecular films on graphene is reported. The films exhibit high stability and remain intact during a subsequent derivatisation reaction, offering a versatile route for the non-covalent functionalisation of graphene.

The optical nonlinearity of WS2 and MoS2 monolayer and few-layer films was investigated using the Z-scan technique with femtosecond pulses from the visible to the near-infrared range. The nonlinear absorption of few- and multilayer WS2 and MoS2 films and their dependences on excitation wavelength were studied. WS2 films with 1-3 layers exhibited a giant two-photon absorption (TPA) coefficient as high as (1.0 ± 0.8) × 10(4) cm/GW. TPA saturation was observed for the WS2 film with 1-3 layers and for the MoS2 film with 25-27 layers. The giant nonlinearity of WS2 and MoS2 films is attributed to a two-dimensional confinement, a giant exciton effect, and the band edge resonance of TPA.

A highly efficient surface plasmon resonance (SPR) immunosensor is described using a functionalized single graphene layer on a thin gold film. The aim of this approach was two-fold: first, to amplify the SPR signal by growing graphene through chemical vapor deposition and, second, to control the immobilization of biotinylated cholera toxin antigen on copper coordinated nitrilotriacetic acid (NTA) using graphene as an ultrathin layer. The NTA groups were attached to graphene via pyrene derivatives implying π-π interactions. With this setup, an immunosensor for the specific antibody anticholera toxin with a detection limit of 4 pg mL(-1) was obtained. In parallel, NTA polypyrrole films of different thicknesses were electrogenerated on the gold sensing platform where the optimal electropolymerization conditions were determined. For this optimized polypyrrole-NTA setup, the simple presence of a graphene layer between the gold and polymer film led to a significant increase of the SPR signal.

The non-covalent functionalisation of graphene is an attractive strategy to alter the surface chemistry of graphene without damaging its superior electrical and mechanical properties. Using the facile method of aqueous-phase functionalisation on large-scale CVD-grown graphene, we investigated the formation of different packing densities in self-assembled monolayers (SAMs) of perylene bisimide derivatives and related this to the amount of substrate contamination. We were able to directly observe wet-chemically deposited SAMs in scanning tunnelling microscopy (STM) on transferred CVD graphene and revealed that the densely packed perylene ad-layers adsorb with the conjugated {\pi}-system of the core perpendicular to the graphene substrate. This elucidation of the non-covalent functionalisation of graphene has major implications on controlling its surface chemistry and opens new pathways for adaptable functionalisation in ambient conditions and on the large scale., Comment: 27 pages (including SI), 10 figures

The reduction of dimensionality has revealed exciting properties in layered 2D materials such as graphene and transition metal dichalcogenides (TMDs). In order to use these materials in functional devices, processes for reliable large scale synthesis, functionalization and integration must be developed. Here we present the thermally assisted conversion of various TMD layers. The sulfides and selenides of Mo and W have been produced on silicon chips. These films have been characterized thoroughly and electrically addressed. Furthermore, we report on CVD growth of MoS 2 and WS 2 monolayers in a microreactor setup. Besides transistor applications, TMDs can be used for other electronic applications such as chemical sensors and photodiodes. Integrating novel 2D materials with silicon technology may lead to significant advances toward a wide range of novel devices.

Reliable chemical vapour deposition (CVD) of transition metal dichalcogenides (TMDs) is currently a highly pressing research field, as numerous potential applications rely on the production of high quality films on a macroscopic scale. Here, we show the use of liquid phase exfoliated nanosheets and patterned sputter deposited layers as solid precursors for chemical vapour deposition. TMD monolayers were realized using a close proximity precursor supply in a CVD microreactor setup. A model describing the growth mechanism, which is capable of producing TMD monolayers on arbitrary substrates, is presented. Raman spectroscopy, photoluminescence, X-ray photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy, scanning electron microscopy and electrical transport measurements reveal the high quality of the TMD samples produced. Furthermore, through patterning of the precursor supply, we achieve patterned growth of monolayer TMDs in defined locations, which could be adapted for the facile production of electronic device components.

International audience; 2D metal chalcogenide (MC) nanosheets (NS) have displayed high capacities as lithium‐ion battery (LiB) anodes. Nevertheless, their complicated synthesis routes coupled with low electronic conductivity greatly limit them as promising LiB electrode material. Here, this work reports a facile single‐walled carbon nanotube (SWCNT) percolating strategy for efficiently maximizing the electrochemical performances of gallium chalcogenide (GaX, X = S or Se). Multiscaled flexible GaX NS/SWCNT heterostructures with abundant voids for Li+ diffusion are fabricated by embedding the liquid‐exfoliated GaX NS matrix within a SWCNT‐percolated network; the latter improves the electron transport and ion diffusion kinetics as well as maintains the mechanical flexibility. Consequently, high capacities (i.e., 838 mAh g−1 per gallium (II) sulfide (GaS) NS/SWCNT mass and 1107 mAh g−1 per GaS mass; the latter is close to the theoretical value) and good rate capabilities are achieved, which can be majorly attributed to the alloying processes of disordered Ga formed after the first irreversible GaX conversion reaction, as monitored by in situ X‐ray diffraction. The presented approach, colloidal solution processing of SWCNT and liquid‐exfoliated MC NS to produce flexible paper‐based electrode, could be generalized for wearable energy storage devices with promising performances.

Here we demonstrate significant improvements in the performance of supercapacitor electrodes based on 2D MnO2 nanoplatelets by the addition of carbon nanotubes. Electrodes based on MnO2 nanoplatelets do not display high areal capacitance because the electrical properties of such films are poor, limiting the transport of charge between redox sites and the external circuit. In addition, the mechanical strength is low, limiting the achievable electrode thickness, even in the presence of binders. By adding carbon nanotubes to the MnO2-based electrodes, we have increased the conductivity by up to 8 orders of magnitude, in line with percolation theory. The nanotube network facilitates charge transport, resulting in large increases in capacitance, especially at high rates, around 1 V/s. The increase in MnO2 specific capacitance scaled with nanotube content in a manner fully consistent with percolation theory. Importantly, the mechanical robustness was significantly enhanced, allowing the fabrication of electrodes that were 10 times thicker than could be achieved in MnO2-only films. This resulted in composite films with areal capacitances up to 40 times higher than could be achieved with MnO2-only electrodes.

Two-dimensional nanomaterials such as MoS2 are of great interest both because of their novel physical properties and their applications potential. Liquid exfoliation, an important production method, is limited by our inability to quickly and easily measure nanosheet size, thickness or concentration. Here we demonstrate a method to simultaneously determine mean values of these properties from an optical extinction spectrum measured on a liquid dispersion of MoS2 nanosheets. The concentration measurement is based on the size-independence of the low-wavelength extinction coefficient, while the size and thickness measurements rely on the effect of edges and quantum confinement on the optical spectra. The resultant controllability of concentration, size and thickness facilitates the preparation of dispersions with pre-determined properties such as high monolayer-content, leading to first measurement of A-exciton MoS2 luminescence in liquid suspensions. These techniques are general and can be applied to a range of two-dimensional materials including WS2, MoSe2 and WSe2.

X-ray photoelectron spectroscopy has been used to study two different two-step cleaning methods of MOVPE grown GaN(0001). Carbon and oxygen were identified as the major contaminants, even though the samples were stored in a glove box after growth and transferred under nitrogen atmosphere. By thermal annealing of the samples a significant oxygen decrease and a complete removal of the carbon was achieved. To remove the residual oxygen, subsequently Ga deposition/re-desorption cycles and N-plasma treatment were performed (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Graphene has been long thought of as a perfect barrier material due to its impermeability to all gases as well as mechanical and chemical durability. Moreover, graphene layers are transparent and conductive, significantly widening the field of potential applications beyond simple barrier coatings. However, it is very challenging to realize such barriers on a macro­scopic scale as immaculate large area films are not available. In this work, a highly effective oxygen gas barrier made from multiple layers of chemical vapor deposited graphene is presented. The individual graphene layers are stacked using a modified polymer-assisted transfer method, avoiding polymer residue yielding an oxygen-tight arrangement. A stack of three layers of graphene transmitted 6.9 cm3 m−2 d−1 of O2 which corresponds to 1.10 × 10−17 cm3 cm/cm2 s (cm Hg) when normalized to thickness and pressure. This is several orders of magnitude better than any macroscale graphene coating reported to date and performs on a level that can compete with most modern coatings while being much thinner and conductive.

Graphene and other two-dimensional (2D) materials such as inorganic transition metal dichalchogenides (TMDs) represent key nanostructural materials for use in a range of functional devices including gas and biosensors. The functionalization of nanomaterials is a critical factor for tailoring their surface properties, enhancing their potential applicability in optoelectronics and catalysis to name but a few. Porphyrins can easily be used for the construction of π-extended systems using well-established synthetic chemistry methodologies. [1] These range from organometallic C-C bond forming reactions to introduce tailored substituents at the porphyrin periphery and the construction of porphyrin arrays connected conjugated linkers, to porphyrin tape-like oligomers through oxidative meso-meso and meso-β-fusing reactions. The selective functionalization of these heteroaromatic systems now opens the possibility to combine them with carbon-based aromatic systems to yield mixed π-extended systems with unique photophysical properties. Present studies reveal the emergence of a surface chemistry of such systems where specific reactions, e.g., metallation, remetallation and C-C–coupling can be induced on surfaces. [2] Surface/macrocycle interactions alter the chemical properties of porphyrins and the adsorption of tailored macrocycles onto 2D surfaces could generate novel platform systems for, e.g., the attachment of biomarkers for use as biosensors. Additionally, TMDs, e.g., MoS2, represent a growing area of research due to their fascinating electronic and optoelectronic properties. [3] Through chemical modification of these surfaces it is hoped that attachment of large heteroaromatic systems will further tailor these materials for functional use. References [1] A. A. Ryan, M. O. Senge Eur. J. Org. Chem. 3700 (2013). [2] S. Krasnikov, C. Doyle, N. Sergeeva, A. Preobrajenski, N. Vinogradov, Y. Sergeeva, A. Zakharov, M. Senge, A. Cafolla Nano Res. 4, 376 (2011). [3] G. S. Duesberg Nat. Mater. 13, 1075 (2014).

For many applications, in particular in electronics, where chemical vapor deposited (CVD) graphene is used, it needs to be transferred from the growth substrate to the device substrate, generally employing a polymer film as a support layer. This process step is crucial for the overall integrity and electronic performance of the graphene. In this work we will investigate the effects of the transfer using various polymers with atomic force, Raman spectroscopy and X-ray photoelectron spectroscopy combined with field dependent transport measurements to build up a complete picture regarding the morphology, structural integrity and electrical performance of CVD graphene. Further, we introduce nitrocellulose based polymer alternatives to the most commonly used poly(methyl methacrylate) resist, outperforming the latter in most respects.

The electrochemical generation of hydrogen fuel via the proton reduction in the Hydrogen Evolution Reaction (HER) in aqueous media is currently dependent on the use expensive noble metal catalysts for which alternatives must be sought. Molybdenum disulfide (MoS₂) has shown great promise as a suitable electrocatalyst in this regard. While many lab-scale experiments on the HER activity of this material have demonstrated its viability and explored some fundamental mechanistic features of HER at MoS₂, these experimental techniques are often ill-suited to large scale production of such electrodes. In this study we present work on the fabrication of MoS₂/pyrolytic carbon (PyC) electrodes via vapour phase sulfurization of Mo thin films. These hybrid electrodes combine the catalytic activity of MoS₂ with the conductivity and stability of PyC, whilst using industrially compatible processing techniques. Structural defects in the sulfur lattice were found to be key catalytically active sites for HER and thinner MoS₂ films displayed a higher quantity of these defects and, hence, an improved HER activity. The observed Tafel slope of 95 mV decade(-1) is comparable to previous literature works on MoS₂ HER performance.