WS2 Nanotubes Research Articles

Mechanical Properties of WS2 Nanotubes

Their mesoscopic dimensions (including a nanometer scale diameter and a micrometer scale length) make nanotubes a unique and attractive object of study, including the study of their mechanical properties and fracture in particular. The investigation of the mechanical properties of individual WS2 nanotubes is a challenging task due to their small size. Hence, various microscopy based techniques were used to overcome this challenge. The Young’s modulus was studied by techniques like atomic force microscope (AFM) and scanning electron microscope (SEM); it was also calculated by using the density-functional-based tight-binding (DFTB) method. Tensile tests and bending tests of individual WS2 nanotubes were performed as well. Furthermore, the shock wave resistance of these nanotubes was tested. The Young’s modulus of WS2 nanotubes was found to be in the range of 150–170 GPa, which is in good agreement with DFTB calculations. WS2 nanotubes also showed tensile strength as high as 16 GPa and fracture strain of 14%. These results indicate the high quality of these nanotubes which reach their theoretical strength. The interlayer shear (sliding) modulus was found to be ca. 2 GPa, this value is in good agreement with DFTB calculations. Moreover, the nanotubes were able to withstand shock waves as high as 21 GPa.

Microscopic Investigation of Shear in Multiwalled Nanotube Deformation

The cylindrical geometry of nanotubes dictates a strong anisotropy of their physical properties. In practice, the difficulty in extracting individual components of the elastic tensor has limited the available information to only very partial and indirect experimental data. Here, the interlayer shear (sliding) modulus (C44) of single multiwalled WS2 nanotubes was studied by atomic force microscopy bending tests. The observed value of 2 GPa agrees well with the value of 4 GPa obtained for density functional tight binding calculations for 2H−MoS2. This value of the shear modulus represents a much higher degree of anisotropy than that obtained for carbon nanotubes and enables assignment of the mode of shear deformation.

Hierarchical Assembly of TiO2 Nanoparticles on WS2 Nanotubes Achieved Through Multifunctional Polymeric Ligands

Particles on the tube: Here, novel surface functionalization of WS2 nanotubes with polymeric ligands, by complexation with a combination of Ni2+ through a scorpionate-type nitrilotriacetic acid, and immobilization of TiO2 nanoparticles onto the surface of nanotubes is demonstrated (see schematic representation). The synthesis of the functional polymeric ligands was achieved through a reactive polymer precursor route.

Nanoscale Weibull Statistics for Nanofibers and Nanotubes

In this paper a modification of the classical Weibull statistics is applied to nanostructures. A comparison is presented of “nanoscale” versus classical Weibull statistics in treating recent experimental results on the fracture strength of C nanofibers and nanotubes, and WS2 nanotubes. “Nanoscale” Weibull moduli of 3.8 for electrospun and then heat-treated carbon nanofibers, 2.7 for arc-discharge synthesized multiwalled carbon nanotubes, 1.8 for chemical vapor deposited multiwalled carbon nanotubes, and 3.0 for multiwalled WS2 nanotubes, are deduced.

Investigation of Micro-Tribological Behavior of MS<sub>2</sub> Nanotubes

It is well known that metal dichalcogenides MS2 (M=Mo, W, Nb, Ta, TiS, Zr ,Hf, S=S, Se) have lamellar structure, the bonds of adjacent lamellae are weak van der Waals interactions and inter-lamellar are strong covalent interactions. The structures make adjacent lamellae easy to slip and it shows low friction coefficient during friction process. MS2 are often used as solid lubricants in high/low temperature, heave load and vacuum, in which oil is failure. WS2 has better high temperature properties than MoS2, although little natural WS2 mineral has been deposited, and people must synthesize it by chemical means, so its price is nearly 5 times expensive than that of MoS2. Until now little study is made comparing with MoS2. Furthermore the research papers about tribological behavior of NbS2, TaS2, TiS2, ZrS2, HfS2 are not seen. In this study the thermal decomposition method is used to produce fullerene-like MS2 nanotubes. The morphology, microstructure and tribological behavior of MS2 nanotubes are investigated by means of SEM, TEM, XRD and AFM. The results show that the diameter of MoS2, WS2 and NbS2 nanotube is less than 100nm, and the length is more than 2μm. The MoS2, WS2 nanotube has lower friction coefficient than MoS2 powder tested by AFM using Si3N4 probe. Similar results are also found for NbS2 nanotube. The macroscopic friction test for pin on disc tester shows nearly the same results. TEM image shows that MS2 nanotubes have rolling debris between two antagonist surfaces, and MoS2 powder only has flattened debris. It may be the fullerene structure brings the chemical stability and lead low friction.

Two-dimensional tungsten oxide nanowire networks

The authors report the synthesis and characterization of two-dimensional (2D) single crystalline nanonetworks consisting of tungsten oxide nanowires with diameters of ca. 20nm. The 2D networks are believed to result from the nanowire growth along the four crystallographic equivalent directions of ⟨110⟩ in the tetragonal WO2.9 structure. These 2D tungsten oxide networks may be potential precursors for creating 2D networks comprising WS2 nanotubes.

New quantized failure criteria: application to nanotubes and nanowires

In this paper new quantized failure criteria are proposed, also for nanoscale applications. The main theories in the context of the strength of solids, i.e., of brittle fracture, dynamic fracture, fatigue and Weibull Statistics are reconsidered according to the proposed “quantization rules”. The “corresponding principle” is verified and thus the classical theories are found to be the limit cases of the quantized counterparts. As an example, our treatment is applied to very recent experimental results on carbon or WS2 nanotubes and to futurist ultra-nanocrystalline diamond nanowires, for which the tensile, bending and ideal strength are estimated.

Novel Route to WOx Nanorods and WS2 Nanotubes from WS2 Inorganic Fullerenes

WO(x) (2 < x < 3) and WS(2) nanostructures have been widely praised due to applications as catalysts, solid lubricants, field emitters, and optical components. Many methods have been developed to fabricate these nanomaterials; however, most attention was focused on the same dimensional transformation from WO(x) nanoparticles or nanorods to WS(2) nanoparticles or nanotubes. In a solid-vapor reaction, by simply controlling the quantity of water vapor and reaction temperature, we have realized the transformation from quasi-zero-dimensional WS(2) nanoparticles to one-dimensional W(18)O(49) nanorods, and subsequent sulfuration reactions have further converted these W(18)O(49) nanorods into WS(2) nanotubes. The reaction temperature, quantity of water vapor, and pretreatment of the WS(2) nanoparticle precursors are important process parameters for long, thin, and homogeneous W(18)O(49) nanorods growth. The morphologies, crystal structures, and circling transformation mechanisms of sulfide-oxide-sulfide are discussed, and the photoluminescence properties of the resulting nanorods are investigated using a Xe lamp under an excitation of 270 nm.

From Single Molecules to Nanoscopically Structured Functional Materials

AbstractThe synthesis of MS2 (M = Mo, W) onion-like nanoparticles by means of a high temperature MOCVD process starting from W(CO)6 and elemental sulfur is reported. The reaction can also be carried out in two steps where the intermediate amorphous WS2 nanoparticles formed through the high temperature reaction of tungsten and sulfur in the initial phase of the reaction are isolated and converted in a separate annealing step to onion-type WS2 nanoparticles. Based on a study of the temperature dependence of the reaction a set of conditions could be derived where onion-like structures were formed in a one-step reaction. Onion-like structures obtained in the single-step process were filled, whereas the particles obtained by the two-step procedure were systematically hollow. A model could be devised to rationalize the different outcome of the reactions. The MOCVD approach therefore allows a selective synthesis of open and filled fullerene-like chalcogenide nanoparticles. Furthermore, we demonstrate the novel surface functionalization of WS2 nanotubes with polymeric ligands by complexation with a combination of Ni2+ via an scorpionate-type nitrilotriacetic acid (NTA) and immobilization of TiO2 nanoparticles onto the surface of nanotubes. Synthesis of such a functional polymeric ligand was achieved via a reactive polymer precursor route.

Direct Tensile Tests of Individual WS&lt;sub&gt;2&lt;/sub&gt; Nanotubes

The Young’s modulus of WS2 nanotubes is an important property for various applications. Measurements of the mechanical properties of individual nanotubes are challenging because of the small size of the tubes. Lately, measurements of the Young’s modulus by buckling of an individual nanotube using an atomic force microscope1 resulted in an average value of 171GPa. Tensile tests of individual WS2 nanotubes were performed experimentally using a scanning electron microscope and simulated tensile tests of MoS2 nanotubes were performed by means of a densityfunctional tight-binding (DFTB) based molecular dynamics (MD) scheme. Preliminary results for WS2 nanotubes show Young’s modulus value of ca.162GPa, tensile strength value of ca. 13GPa and average elongation of ca. 12%. MD simulations resulted in elongation of 19% for zigzag and 17% for armchair MoS2 single wall nanotubes. Since MoS2 and WS2 nanotubes have similar structures the same behavior is expected for both, hence there is a good agreement regarding the elongation of WS2 nanotubes between experiment and simulation.

Synthesis and Investigation of Micro-Tribological Behavior of WS&lt;sub&gt;2&lt;/sub&gt; Nanotube

MS2(M=Mo, W, S=S, Se) are often used as solid lubricants in high/low temperature, high load, vacuum, in which oil lubrication is failed. Although WS2 is much more expensive than MoS2, it has better high temperature properties than MoS2. Thermal decomposition method is used to produce fullerence-like WS2 nanotube on Al2O3 template using (NH4)2WS4. The fabricated WS2 nanotube’s diameter is about 100nm and its length is longer than 2µm.The morphology, microstructure and tribological behavior of WS2 nanotube are investigated by means of SEM, TEM, XRD and AFM. The friction force between Si3N4 probe of AFM with WS2 nanotube is lower than that with MoS2 powder. Similar results are also found in pin-disc tester by GCr15 pin and lubricants coating disc. The results of HETEM show that WS2 nanotube has rolling debris between the two antagonist surfaces, and MoS2 powder only has flattened debris. It may be the fullerence structure brings the chemical stability and leads to low friction.

WS2 Nanotubes Synthesized for Lithium Storage

WS₂ Nanotubes Synthesized for Lithium Storage

Electron Microscopy and Microanalysis Study of Conversion of WOx Nanowires into WS2 Nanotubes

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Mechanical behavior of individual WS2 nanotubes

The Young's modulus of WS2 nanotubes is an important property for various applications. Measurements of the mechanical properties of individual nanotubes are challenged by their small size. In the current work, atomic force microscopy was used to determine the Young's modulus of an individual multiwall WS2 nanotube, which was mounted on a silicon cantilever. The buckling force was measured by pushing the nanotube against a mica surface. The average Young's modulus of an individual WS2 nanotube, which was calculated by using Euler's equation, was found to be 171 GPa. First-principle calculations of the Young's modulus of MoS2 single-wall nanotubes using density-functional–based tight-binding method resulted in a value (230 GPa) that is close to that of the bulk material. Furthermore, the diameter dependence of the Young's modulus in both zigzag and armchair configuration was studied and was found to approach the bulk value for nanotubes with few-nanometer diameters. Similar behavior is expected for WS2 nanotubes. The mechanical behavior of the WS2 nanotubes as atomic force microscope imaging tips gave further support for the measured Young's modulus.

Mechanical behavior of individual WS2 nanotubes

Mechanical behavior of individual WS2 nanotubes

Study of the growth mechanism of WS2 nanotubes produced by a fluidized bed reactor

Metal dichalcogenide nanotubes and in particular those of WS2 were shown to exhibit some unique physical and chemical properties, which offer numerous applications for this kind of nanophase material. Using a fluidized bed reactor (FBR), WS2 nanotubes were obtained in substantial amounts recently, rendering a systematic study of their properties possible. The FBR synthesized nanotubes are multiwalled (5–7 layers); open-ended; long (<0.5 mm), and with diameters of 15–20 nm. They are therefore distinguishable from the previously reported WS2 nanotubes which were shorter, bulkier and with closed ends. Careful analysis by various electron microscopy techniques is used in the present study to shed some light on the growth mechanism of these newly synthesized nanotubes. The proposed growth mechanism model differs markedly from the previously reported mechanisms of formation of both fullerene-like WS2 nanostructures and inorganic nanotubes of WS2.

TEM and EFTEM characterization of WS2 Nanotubes

TEM and EFTEM characterization of WS₂ Nanotubes

Synthesis of NiCl2 nanotubes and fullerene-like structures by laser ablation: theoretical considerations and comparison with MoS2 nanotubes

Laser ablation has been extensively used for the synthesis of nanoparticles of various sorts, and in particular single wall carbon nanotubes and C60 molecules. NiCl2 nanotubes were recently also produced using this technique. While fullerene-like NiCl2 structures can be obtained through regular ablation, vapor phase enriched with CCl4 gas (reactive ablation) is necessary for the synthesis of the nanotubes. The experimental results indicate that the synthesis of such nanotubes is much more difficult than the synthesis of say MoS2 or WS2 nanotubes. Moreover, the NiCl2 nanotubes are of larger diameter and consist on the average of more layers than their MoS2 predecessors. First principle calculations show that single layer NiCl2 nanotubes of diameter smaller than 54 nm are unstable and lose their outer chlorine atoms. In contrast, MoS2 nanotubes with diameter of 2 nm and larger are found to be stable using the same kind of calculations. To gain better understanding of the differences between the materials, a review of the mechanical properties of layered metal dihalide and metal dichalcogenide compounds is undertaken. First principle calculations show that the Young's and bending moduli of NiCl2 are almost twice larger than those of MoS2. The large ionicity of NiCl2 entails much larger shear and stacking fault energies for this compound as compared to MoS2, which explains its smaller propensity to bend and fold. These observations are supported by analysis of the corresponding Raman modes.Furthermore, metal dihalide compounds are very hygroscopic making their handling, and especially their analysis more difficult. This analysis explains the greater difficulties to grow NiCl2 nanotubes or fullerene-like nanoparticles, as compared to their MoS2 analogues.

Synthesis and Characterization of WS2 Nanotubes

High-purity WS2 nanotubes were synthesized on a relatively large scale by thermal decomposition of amorphous/nano (NH4)2WS4 in a floating hydrogen and thiophene atmosphere at a heating temperature of 360−450 °C. Extensive investigations of WS2 nanotubes by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron microscopy, and Brunauer−Emmett−Teller measurements were reported. Our improved route yielded large quantities of open-ended WS2 nanotubes with an average length of 5 μm, an outer diameter of 25−50 nm, an inner diameter of up to 20 nm, and an interlayer spacing of 0.62 nm. The present study is also of interest because it provides a clue to better understanding the inside out growth mechanism of WS2 nanotubes, and this can be extended for the synthesis of other metal-sulfide nanostructural materials.

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.