Synthesis of bulk WS2 nanotube phases

Flatlands in the Holy Land: The Evolution of Layered Materials Research in Israel

The experimental identification of fullerenes in 1985, carbon nanotubes in 1991, inorganic nanotubes in 1992, and graphene in 2004 are cornerstone events that have marked the beginning of the layered nanostructures era of materials science. Nowadays, the synthesis of such low-dimensional systems is a routine practice allowing the controlled fabrication of 0-, 1-, and 2D layered structures of diverse chemical compositions. These systems possess unique physical properties that stem from their structural anisotropy characterized by strong intralayer covalent bonding and weaker interlayer dispersive interactions. This, in turn, results in promising functionality that attracts the attention of scientists from many disciplines including chemists, physicists, material scientists, engineers, as well as life scientists that are interested in both their basic and applied science aspects. Here, a short review of the contribution of the Israeli scientific community to this effort over the past 3 decades, is provided.

One-pot growth of two-dimensional lateral heterostructures via sequential edge-epitaxy

Two-dimensional heterojunctions of transition-metal dichalcogenides have great potential for application in low-power, high-performance and flexible electro-optical devices, such as tunnelling transistors, light-emitting diodes, photodetectors and photovoltaic cells. Although complex heterostructures have been fabricated via the van der Waals stacking of different two-dimensional materials, the in situ fabrication of high-quality lateral heterostructures with multiple junctions remains a challenge. Transition-metal-dichalcogenide lateral heterostructures have been synthesized via single-step, two-step or multi-step growth processes. However, these methods lack the flexibility to control, in situ, the growth of individual domains. In situ synthesis of multi-junction lateral heterostructures does not require multiple exchanges of sources or reactors, a limitation in previous approaches as it exposes the edges to ambient contamination, compromises the homogeneity of domain size in periodic structures, and results in long processing times. Here we report a one-pot synthetic approach, using a single heterogeneous solid source, for the continuous fabrication of lateral multi-junction heterostructures consisting of monolayers of transition-metal dichalcogenides. The sequential formation of heterojunctions is achieved solely by changing the composition of the reactive gas environment in the presence of water vapour. This enables selective control of the water-induced oxidation and volatilization of each transition-metal precursor, as well as its nucleation on the substrate, leading to sequential edge-epitaxy of distinct transition-metal dichalcogenides. Photoluminescence maps confirm the sequential spatial modulation of the bandgap, and atomic-resolution images reveal defect-free lateral connectivity between the different transition-metal-dichalcogenide domains within a single crystal structure. Electrical transport measurements revealed diode-like responses across the junctions. Our new approach offers greater flexibility and control than previous methods for continuous growth of transition-metal-dichalcogenide-based multi-junction lateral heterostructures. These findings could be extended to other families of two-dimensional materials, and establish a foundation for the development of complex and atomically thin in-plane superlattices, devices and integrated circuits.

Nanocomposites based on tubular and onion nanostructures of molybdenum and tungsten disulfides: inorganic design, functional properties and applications

The review concerns the development and the state-of-the-art in studies on the surface modification methods aimed at fabricating promising nanocomposites based on multilayer inorganic tubular and onion (fullerene-like) MoS2 and WS2 nanostructures. The synthetic details and structural features of these materials are considered. Considerable attention is paid to targeted functionalization of molybdenum and tungsten disulfide nanostructures and to fundamental principles that underlie their ability to chemical interactions. The functional properties and applications of the obtained materials are described.

The bibliography includes 183 references.

Structural Evolution of Sub-10 nm Octahedral Platinum-Nickel Bimetallic Nanocrystals

Octahedral Pt alloy nanocrystals (NCs) have shown excellent activities as electrocatalysts toward oxygen reduction reaction (ORR). As the activity and stability of NCs are highly dependent on their structure and the elemental distribution, it is of great importance to understand the formation mechanism of octahedral NCs and to rationally synthesize shape-controlled alloy catalysts with optimized ORR activity and stability. However, the factors controlling the structural and compositional evolution during the synthesis have not been well understood yet. Here, we systematically investigated the structure and composition evolution pathways of Pt-Ni octahedra synthesized with the assistance of W(CO)₆ and revealed a unique core-shell structure consisting of a Pt core and a Pt-Ni alloy shell. Below 140 °C, sphere-like pure Pt NCs with the diameter of 3-4 nm first nucleated, followed by the isotropic growth of Pt-Ni alloy on the seeds at temperatures between 170 and 230 °C forming Pt@Pt-Ni core-shell octahedra with {111} facets. Owing to its unique structure, the Pt@Pt-Ni octahedra show an unparalleled stability during potential cycling, that is, no activity drop after 10 000 cycles between 0.6 and 1.0 V. This work proposes the Pt@Pt-Ni octahedra as a high profile electrocatalyst for ORR and reveals the structural and composition evolution pathways of Pt-based bimetallic NCs.

In vitro cytocompatibility of one-dimensional and two-dimensional nanostructure-reinforced biodegradable polymeric nanocomposites

This study investigates the in vitro cytocompatibility of one-dimensional and two-dimensional (1D and 2D) carbon and inorganic nanomaterial reinforced polymeric nanocomposites fabricated using biodegradable polymer poly (propylene fumarate), crosslinking agent N-vinyl pyrrolidone (NVP) and following nanomaterials: single and multiwalled carbon nanotubes, single and multiwalled graphene oxide nanoribbons, graphene oxide nanoplatelets, molybdenum disulfide nanoplatelets, or tungsten disulfide nanotubes dispersed between 0.02 and 0.2 wt% concentrations in the polymer. The extraction media of unreacted components, crosslinked nanocomposites and their degradation products were examined for effects on viability and attachment using two cell lines: NIH3T3 fibroblasts and MC3T3 preosteoblasts. The extraction media of unreacted PPF/NVP elicited acute dose-dependent cytotoxicity attributed to leaching of unreacted components into cell culture media. However, extraction media of crosslinked nanocomposites showed no dose dependent adverse effects. Further, all crosslinked nanocomposites showed high viability (78-100%), high cellular attachment (40-55%), and spreading that was confirmed by confocal and scanning electron microscopy. Degradation products of nanocomposites showed a mild dose-dependent cytotoxicity possibly due to acidic degradation components of PPF. In general, compared to PPF control, none of the nanocomposites showed significant differences in cellular response to unreacted components, crosslinked nanocomposites and their degradation products. Initial minor cytotoxic response and lower cell attachment numbers were observed only for a few nanocomposite groups; these effects were absent at later time points for all PPF nanocomposites. The favorable cytocompatibility results for all the nanocomposites opens avenues for in vivo safety and efficacy studies for bone tissue engineering applications.

Fullerene-like WS(2) nanoparticles and nanotubes by the vapor-phase synthesis of WCl(n) and H(2)S

Inorganic fullerene-like (IF) nanoparticles and nanotubes of WS(2) were synthesized by a gas phase reaction starting from WCl(n) (n = 4, 5, 6) and H(2)S. The effect of the various metal chloride precursors on the formation of the products was investigated during the course of the study. Various parameters have been studied to understand the growth and formation of the IF-WS(2) nanoparticles and nanotubes. The parameters that have been studied include flow rates of the various carrier gases, heating of the precursor metal chlorides and the temperature at which the reactions were carried out. The best set of conditions wherein maximum yields of the high quality pure-phase IF-WS(2) nanoparticles and nanotubes are obtained have been identified. A detailed growth mechanism has been outlined to understand the course of formation of the various products of WS(2).

Coordinatively Induced Length Control and Photoluminescence of W18O49 Nanorods

A coordinatively induced length control of W18O49 nanorods has been developed using thermal decomposition of W(CO)6 in octyl ether solutions of single or mixed capping agents, oleic acid (OA), oleic acid/hexadecylamine (HDA), and oleic acid/trioctylphosphine oxide (TOPO). The order of length for nanorods synthesized with different capping agents was OA > OA/HDA > OA/TOPO, which was the opposite of order of their coordinating power. The order of crystalline size (diameter x length) from the TEM image was OA/HDA > OA > OA/TOPO and matched exactly with the order of crystallinity from the XRD pattern. The order of photoluminescence intensity was OA/HDA < OA < OA/TOPO and was the opposite of the order for the crystalline size or crystallinity. The strong coordinating power and steric bulkiness of TOPO is thought to interrupt the growth of the nanorods, the rearrangement of the end face atoms, and the fusion of the lateral faces and, thereby, increase the oxygen defects and the photoluminescence intensity.

Shock-wave resistance of WS2 nanotubes

The shock-wave resistance of WS(2) nanotubes has been studied and compared to that of carbon nanotubes. Detailed structural features of post-shock samples were investigated using HRTEM, XRD, and Raman spectroscopy. WS(2) nanotubes are capable of withstanding shear stress caused by shock waves of up to 21 GPa, although some nanotube tips and nanoparticles containing multiple structural defects in the bending regions are destroyed. Small WS(2) species, consisting of only a few layers, are extruded from the nanotubes. Well-crystallized tube bodies were found to exhibit significant stability under shock, indicating high tensile strength. XRD and Raman analyses have confirmed this structural stability. Under similar shock conditions, WS(2) tubes are more stable than carbon nanotubes, the latter being transformed into a diamond phase. WS(2) nanotubes containing small concentrations of defects possess significantly higher mechanical strength, and, as a consequence, hollow WS(2) nanoparticles are expected to act as excellent lubricants under much higher loading than was previously thought.