Publications

The lifestyle of mankind has improved significantly since the start of the industrial revolution and the establishment of a science (engineering)-based society, some 250 years ago. Notwithstanding, the outcome of these advances, a major threat is looming on the future of humanity due to the greenhouse effect produced by fossil fuel effluents and the degradation of the environment on earth. Chemistry and chemical engineering are key players in confronting these challenges and establishing sustainable lifestyle on earth. In particular, the interplay between materials research; solid-state chemistry and nanoscience (nanotechnology) will be crucial for the future of sustainable life on earth. Education of the population-at-large to shift from a consumer-based society into sustainability-concerned lifestyle, is mandatory for realization of this paradigm shift. Harmonizing the interplay between entrepreneurs, financing bodies, public agencies, international organizations, legal bodies and research institutes should also play an integral part of this new equation.

Nanocomposite materials, integrating nanoscale additives into a polymer matrix, hold immense promise for their exceptional property amalgamation. This study delves into the fabrication and characterization of polyetherimide (PEI) nanocomposite strings fortified with multiwall WS₂ nanotubes. The manufacturing process capitalizes on the preferential alignment of WS₂ nanotubes along the string axis, corroborated by scanning electron microscopy (SEM). Mechanical measurements unveil a remarkable acceleration of strain hardening in the nanocomposite strings, chiefly attributed to the WS₂ nanotubes. Structural analyses via X-ray diffraction (XRD) and wide-angle X-ray scattering (WAXS) reveal intriguing structural alterations during tensile deformation. Notably a semi-crystalline framework ∼100 nm in diameter surrounding the WS₂ nanotubes emerges, which is stabilized by the π-π interactions between the PEI chains. The amorphous majority phase (97% by volume) undergoes also major structural changes upon strain becoming more compact and closing-up of the distance beweeetn the PEI chains. Dynamic mechanical analysis (DMA) demonstrates improved thermal stability of the evolved semi-crystalline π-π oriented PEI molecules, characterized by delayed thermal \u201cstructural melting\u201d, underscoring the pivotal role of the WS₂ nanotubes in reinforcing the nanocomposite. The insight gained in this study of WS₂ nanotube-reinforced PEI nanocomposite strings, could offer diverse applications for such tailor-made polymeric materials.

The inclusion of tungsten disulphide nanotubes (WS₂ NTs) in chitosan, plasticized with glycerol, facilitates the formation of a polyelectrolyte complex. The glycerol interrupts the intramolecular hydrogen bonding between chitosan chains allowing positively charged protonated amines of chitosan to form a complex with negatively charged oxygen ions chemisorbed to the tungsten atoms in defects. These interactions, with the unique mechanical and chemical properties of WS₂ NTs, result in a chitosan film with superior properties relative to unfilled chitosan. Even at low WS₂ NT loadings (≤1 wt%), the Young's modulus (E) increases by 59%, tensile strength (σ) by 40% and tensile toughness by 74%, compared to neat chitosan, without sacrificing ductility. Addition of highly dispersed WS₂ NTs significantly improves the gas barrier properties of chitosan, with a 50% reduction in oxygen permeability, while the addition of both glycerol and WS₂ NTs to chitosan effectively reduces the carbon dioxide permeability by 80% and the water vapor transmission rate by 90%. The intrinsic antimicrobial efficacy of chitosan against both Gram-positive and Gram-negative bacteria is enhanced on inclusion of WS₂ NTs. Polyelectrolyte complexation of WS₂ NTs and glycerol-plasticized chitosan provides a cost-effective, sustainable route to biodegradable films with desirable mechanical, gas barrier properties, and antimicrobial efficacy suitable for food packaging applications.

The synthesis of complex new nanostructures is challenging but also bears the potential for observing new physiochemical properties and offers unique applications in the long run. High-temperature synthesis of ternary WSe2xS2(1-x) (denoted as WSSe) nanotubes in a pure phase and in substantial quantities is particularly challenging, requiring a unique reactor design and control over several parameters, simultaneously. Here, the growth of WSSe nanotubes with the composition 0 ≤ x

The dimensional limit of ferroelectricity has been long explored. The critical contravention is that the downscaling of ferroelectricity leads to a loss of polarization. This work demonstrates a zero-dimensional ferroelectricity by the atomic sliding at the restrained van der Waals interface of crossed tungsten disufilde nanotubes. The developed zero-dimensional ferroelectric diode in this work presents not only non-volatile resistive memory, but also the programmable photovoltaic effect at the visible band. Benefiting from the intrinsic dimensional limitation, the zero-dimensional ferroelectric diode allows electrical operation at an ultra-low current. By breaking through the critical size of depolarization, this work demonstrates the ultimately downscaled interfacial ferroelectricity of zero-dimensional, and contributes to a branch of devices that integrates zero-dimensional ferroelectric memory, nano electro-mechanical system, and programmable photovoltaics in one.Down-scaled ferroelectricity normally diminishes due to the arising depolarization field. Here, the authors realize a 0D ferroelectric diode device taking advantage of the sliding at the van der Waals interface by the two crossed tungsten disulfide nanotubes.

Functionalisation of nanofillers is required for the promotion of strong interfacial interactions with polymers and is essential as a route for the preparation of (nano)composites with superior mechanical properties. Tungsten disulphide nanotubes (WS₂ NTs) were functionalized using (3-aminopropyl) triethoxysilane (APTES) for preparation of composites with poly(lactic acid) (PLA). The WS₂ NTs : APTES ratios used were 1 : 1, 1 : 2 and 1 : 4 WS₂ NTs : APTES. The APTES formed siloxane networks bound to the NTs via surface oxygen and carbon moieties adsorbed on the WS₂ NTs surface, detected by X-ray photoelectron spectroscopy (XPS) studies and chemical mapping using energy dispersive X-ray spectroscopy in the scanning transmission electron microscope (STEM-EDS). The successful silane modification of the WS2 NTs was clearly evident with both significant peak shifting by as much as 60 cm(-1) for Si-O-Si vibrations (FTIR) and peak broadening of the A(1g) band in the Raman spectra of the WS2 NTs. The evolution of new bands was also observed and are associated with Si-CH₂-CH₂ and, symmetric and assymetric -NH³⁺ deformation modes (FTIR). Further evidence for functionalization was obtained from zeta potential measurements as there was a change in surface charge from negative for pure WS₂ NTs to positive for APTES modified WS₂ NTs. Additionally, the thermal stability of APTES was shifted to much higher temperatures as it was bound to the WS₂ NTs. The APTES modified WS2 NTs were organophilic and readily dispersed in PLA, while presence of the pendant amine and hydroxyl groups resulted in strong interfacial interactions with the polymer matrix. The inclusion of as little as 0.5 wt% WS2 NTs modified with 2.0 wt% APTES resulted in an increase of 600% in both the elongation at break (a measure of ductility) and the tensile toughness relative to neat PLA, without impacting the stiffness or strength of the polymer.

The birth of nanoscience more than 50 years ago fueled the renaissance in layered materials research leading to many materials discoveries with unprecedented scientific and technological impacts. Following the early reports on carbon fullerenes and nanotubes, the discovery of inorganic one-dimensional (1D) nanotubes and zero-dimensional (0D) fullerenes created a major playground for new physicochemical observations. The meteoric rise of two-dimensional (2D) materials in concert set off outstanding advances in the synthesis and manipulation of layered materials with atomic precision. This review identifies new directions in materials science that emerge through integrating the two layered systems2D with inorganic 1D and 0D. Summarizing the key developments in the two distinct nanomaterials families, we highlight preliminary instances of integrating them into functional nanostructures. A few gedankenexperiments regarding prospective applications of the integrated system are then introduced to stimulate further experimental and theoretical investigations that can potentially result in unforeseen scientific observations. Graphical abstract: [Figure not available: see fulltext.]

The synthesis of fundamentally small MoS₂ nanotubes and nanocones(horns) that have proven elusive in prior studies has been achieved via ablation of a precursor mixture of crystallites of MoS₂ + MoO₃ by highly concentrated solar radiation. The special far-from-equilibrium conditions achieved in the solar furnace prove conducive to the generation of these singular nanostructures. Extensive electron microscopy and characterization results (transmission electron microscopy (TEM), electron diffraction (ED), X-ray diffraction (XRD), scanning TEM (STEM), and high angle annular dark field (HAADF)) reveal a range of nanoparticle shapes and sizes based on which reaction mechanisms are proposed. Molecular dynamics simulations indicate that the sizable thermal fluctuations intrinsically produced in the high-temperature solar reactor soften the MoS₂ nanostructures, yielding corrugated layers that favor nanostructures with only a few layers, in agreement with the experimental observations.

One-dimensional (1D) analogues of two-dimensional (2D) layered materials, especially nanotubes exhibit unique properties, which are distinct from the 2D flakes. The nanotubes and fullerene-like nanoparticles from layered transition metal dichalcogenides (TMDs) are one of the prime foci of this field in the last 30 years. In this concise review, we present the advancement made in the TMDs nanotubes and fullerene-like nanoparticles over the last few years. The synthesis and structure of TMDs nanotubes such as WS₂/MoS₂ are briefly described. The mechanical properties of single WS₂ nanotubes were examined by in-situ electron microscopy techniques and are briefly discussed. Their reinforcement effects in polymer composites are also presented, as well as their superior tribological behavior. The unique optoelectronic properties of WS₂ (MoS₂) nanotubes are presented. Thus, the bulk photovoltaic effect and superconductivity exhibited by WS₂ nanotubes, which are a manifestation of their 1D structure and low symmetry, are revisited briefly. The strong light-matter interaction of nanotubes resulting in polariton quasiparticles and their evolution as a function of nanotube diameter are explained. Last but not least, a new family of misfit layered nanotubes and their exceptional physical properties are briefly touched upon.

Multi-walled WS₂nanotubes (NTs) with lengths ranging from 2 to 65 μm and widths from 50 to 110 nm were synthesized in a horizontal quartz-made reactor by a process yielding NTs with aspect ratios (ARs) between ∼40 and >1000. The NTs obtained were thermally stable in air up to 400 °C but were oxidized within the temperature range 400-550 °C to produce yellow WO₃particles. Critically, 400 °C is well above the temperature used to mix additives with the majority of melt-processable polymers. The hydrophilic WS₂NTs were easily dispersed in poly(lactic) acid (PLA) using a twin-screw extruder, but the shear stresses applied during melt mixing resulted in chopping of the NTs such that the AR decreased by >95% and the tensile mechanical properties of the PLA were unchanged. Although the as-extruded unfilled PLA was >99% amorphous, the much-shortened WS₂NTs had a significant effect on the crystallization behavior of PLA, inducing heterogeneous nucleation, increasing the crystallization temperature (T_c) by ∼3 °C and the crystalline content by 15%, and significantly increasing the rate of PLA crystallization, producing smaller and more densely packed spherulites. The reduction in the AR and the nucleating effect of WS₂NTs for PLA are critical considerations in the preparation, by melt mixing, of composites of rigid 1D NTs and polymers, irrespective of the target application, including bone tissue engineering and bioresorbable vascular scaffolds.

Among the different methods for orienting liquid crystal (LC) molecules, adding nanoparticles into the matrix of the substrate material towards modifying its surface, is actively pursued. In this context, the influence of the nanoparticle content on the texture of the surface of polymer film used as the substrate for the LC orientation is of particular interest. Thus, in the current paper, WS₂ nanotubes were used to dope the polyimide (PI) substrate-film in order to modify and control its surface morphology/roughness and properties. The modified organic surface structure is applied in order to achieve a new means for controlling the orientation of the LC molecules. This tool adds to the classical methods for controlling the orientation of the LC molecules, such as the display technique.

Misfit layered compounds (MLCs) MX-TX2, where M, T = metal atoms and X = S, Se, or Te, and their nanotubes are of significant interest due to their rich chemistry and unique quasi-1D structure. In particular, LnX-TX2 (Ln = rare-earth atom) constitute a relatively large family of MLCs, from which nanotubes have been synthesized. The properties of MLCs can be tuned by the chemical and structural interplay between LnX and TX2 sublayers and alloying of each of the Ln, T, and X elements. In order to engineer them to gain desirable performance, a detailed understanding of their complex structure is indispensable. MLC nanotubes are a relative newcomer and offer new opportunities. In particular, like WS2 nanotubes before, the confinement of the free carriers in these quasi-1D nanostructures and their chiral nature offer intriguing physical behavior. High-resolution transmission electron microscopy in conjunction with a focused ion beam are engaged to study SmS-TaS2 nanotubes and their cross-sections at the atomic scale. The atomic resolution images distinctly reveal that Ta is in trigonal prismatic coordination with S atoms in a hexagonal structure. Furthermore, the position of the sulfur atoms in both the SmS and the TaS2 sublattices is revealed. X-ray photoelectron spectroscopy, electron energy loss spectroscopy, and X-ray absorption spectroscopy are carried out. These analyses conclude that charge transfer from the Sm to the Ta atoms leads to filling of the Ta 5d z 2 level, which is confirmed by density functional theory (DFT) calculations. Transport measurements show that the nanotubes are semimetallic with resistivities in the range of 104 Ω·cm at room temperature, and magnetic susceptibility measurements show a superconducting transition at 4 K.

Abstract: Tungsten disulfide polycrystalline microfibers were successfully synthesized by a process involving electrospinning, calcination, and sulfidation steps. We used an aqueous solution of silicotungstic acid (H₄SiW₁₂O₄₀) and polyvinyl alcohol as precursors for the synthesis of composite fibers by the needle-less electrospinning technique. The obtained green composite fibers (av. diam. 460 nm) were converted by calcination in air to tungsten oxide WO₃ fibers with traces of SiO₂ and a smaller diameter (av. diam. 335 nm). The heat treatment of the WO₃ fibers under flowing H₂/H₂S/N₂ stream led to conversion to tungsten disulfide WS₂ with retention of the fibrous morphology (av. diam. 196 nm). Characterization of the intermediate and final fibers was performed by the XRD, SEM, TEM, HAADF STEM EDS, elemental analyses ICP-OES, and IR spectroscopy methods. Graphical abstract: [Figure not available: see fulltext.]

Distinct from carbon nanotubes, transition-metal dichalcogenide (TMD) nanotubes are noncentrosymmetric and polar and can exhibit some intriguing phenomena such as nonreciprocal superconductivity, chiral shift current, bulk photovoltaic effect, and exciton-polaritons. However, basic characterizations of individual TMD nanotubes are still quite limited, and much remains unclear about their structural chirality and electronic properties. Here we report an optical second-harmonic generation (SHG) study on multiwalled WS2 nanotubes on a single-tube level. As it is highly sensitive to the crystallographic symmetry, SHG microscopy unveiled multiple structural domains within a single WS2 nanotube, which are otherwise hidden under conventional white-light optical microscopy. Moreover, the polarization-resolved SHG anisotropy patterns revealed that different domains on the same tube can be of different chirality. In addition, we observed the excitonic states of individual WS2 nanotubes via SHG excitation spectroscopy, which were otherwise difficult to acquire due to the indirect band gap of the material.

We present density functional theory calculations of the vibrational and electronic properties of the misfit-layer compound (MLC) LaS-CrS2 and its isolated sublayers to identify the vibrational modes of the compound. From the comparison of two model systems, (i) the fully relaxed misfit-layer compound supercell and (ii) its sublayers as isolated systems, we extract the charges, which are transferred between the two sublayers and the concomitant changes of the structural parameters upon formation of the supercell. The deformation within each sublayer indicates a strong influence of the charge transfer, confirming the important role of the interlayer interaction between the two sublayers. By comparing the vibrational properties of the two model systems, we assign several frequency regimes within the vibrations of the supercell to phonon branches of the sublayers. From polarized Raman spectra, we find that some of the Raman modes are directly inherited from the Δ-point phonons of the hypothetical isolated 1T-CrS2 layer; other Raman modes are backfolded from the A1g-associated phonon branch of the 1T-CrS2 onto the misfit-layer compound MLC Δ-point, which is a direct consequence of the supercell formation in LaS-CrS2.

The non-stoichiometric misfit layered compounds (MLC) of the general formula ((MX)(1+y))(m)(TX2)(n) (abbreviated herein as MX-TX2) have been investigated quite extensively over the last 30 years. Here MX is a atomic slab of a material with distorted rocksalt structure and TX2 is a layered compound with hexagonal (octahedral) coordination between the metal T atom and the chalcogen X atom. Recognizing the mismatch between the two (MX and TX2) sublattices, nanotubes from the MLC of different compositions were described in the past. In particular, semimetallic nanotubes belonging to the family LnX-TaX2 with Ln = rare earth atom and X = S, Se, Te have been studied in the past. While some of them, like LaS-TaS2 were obtained with moderately high yields, others like YbS-TaS2 were scarce. In the present study, a new strategy for promoting the yield of such MLC nanotubes by alloying the LaS sublattice with another Ln atom is proposed. Detailed transmission electron microscopy investigation of the (mixed) Ln(x)La((1-x))S-TaS2 (Ln = Pr, Sm, Ho, Yb) nanotubes show clearly that the substituting Ln atom resides in the rocksalt LaS sublattice of the nanotubes. Raman measurements show distinct differences between mixed tubes with open-shell (Pr, Sm, Ho) and close-shell (La, Yb) rare-earth atoms. Density functional calculations show that the interplay between two important factors determine the enhanced stability of the mixed nanotubes- the size and electronic structure of the substituting rare-earth atom. The smaller is the substituting rare-earth atom (larger Z number), the more dissimilar it is to the original La atom. This dissimilarity enhances the incommensurability between the Ln(x)La((1-x))5 and the TS2 subunits, promoting thereby the stability of the mixed MLC. However, the electronic structure of the Ln atom was found to play a more significant role. The MLC lattice of the LaS-TaS2 is electron-rich and consequently the 4d(z)(2) level of Ta is full. The unoccupied 4f levels of the substituent open-shell atoms (Pr, Sm, Ho), which are positioned below the Fermi level, serve as electron acceptors. Consequently, the Ln substitution is found to enhance the stability of the mixed lattice and nanotubes thereof. This strategy can be employed for enhancing the yield of these and other misfit nanotubes using different substituents of the right size and energy profile.

Misfit layered compounds (MLCs) have been studied in the literature for the last 40 years. They are generally made of an alternating sequence of two monolayers, a distorted rocksalt structure, and a hexagonal layered compound. In a typical MLC, the c-axis is common to the two monolayers and so is one of the axes in the layer plan. However, the two compounds are non-commensurate along at least one axis, and the ratio between the two axes is an irrational number making the MLC a non-stoichiometric compound. The two main families of MLC are those based on metal dichalcogenides and CoO2 as the hexagonal layered compound. Traditionally, ternary MLCs were prepared and studied, but some quaternary and multinary MLC minerals have been known for many years. Over the last few years, interest in MLCs with four and even larger number of atoms has grown. Doping or alloying of a ternary MLC permits precise control of the charge carrier density and hence the electrical, thermoelectric, catalytic, and optical properties of such compounds. In this short review, some of these developments will be discussed with the main emphasis put on quaternary MLC nanotubes belonging to the chalcogenide series. The synthesis, structural characterization, and some of their properties are considered. Some recent developments in quaternary cobaltite MLCs and recent studies on exfoliated MLCs are discussed as well.

We present the analysis of a family of nanotubes (NTs) based on the quaternary misfit layered compound (MLC) YxLa1-xS-TaS2. The NTs were successfully synthesized within the whole range of possible compositions via the chemical vapor transport technique. In-depth analysis of the NTs using electron microscopy and spectroscopy proves the in-phase (partial) substitution of La by Y in the (La,Y)S subsystem and reveals structural changes compared to the previously reported LaS-TaS2 MLC-NTs. The observed structure can be linked to the slightly different lattice parameters of LaS and YS. Raman spectroscopy and infrared transmission measurements reveal the tunability of the plasmonic and vibrational properties. Density-functional theory calculations showed that the YxLa1-xS-TaS2 MLCs are stable in all compositions. Moreover, the calculations indicated that substitution of La by Sc atoms is electronically not favorable, which explains our failed attempt to synthesize these MLC and NTs thereof.

Time parameters (reaction time and relaxation time of medium) of liquid crystal cell sensitized with WS2 nanoparticles and constructed taking into account the modification of the conductive ITO coating by carbon nanotubes are considered. Carbon nanotubes were vertically deposited on the surface of the conductive layer using the laser method and the orientation effect of an electric field with a strength of 600 V/cm. The use of two control functions, namely: the sensitization process of mesophase volume and nanostructuring of the solid - liquid crystal interface allowed increasing the mesophase switching performance and significantly reducing the resistance of the conductive layers acted as orientant and conductor.

Core-shell nanoparticles provide a unique morphology to exploit electronic interactions between dissimilar materials, conferring upon them new or improved functionalities. MoS2 is a layered transition-metal disulfide that has been studied extensively for the hydrogen evolution reaction (HER) but still suffers from low electrocatalytic activity due to its poor electronic conductivity. To understand the fundamental aspects of the MoS2-Au hybrids with regard to their electrocatalytic activity, a single to a few layers of MoS2 were deposited over Au nanoparticles via a versatile procedure that allows for complete encapsulation of Au nanoparticles of arbitrary geometries. High-resolution transmission electron microscopy of the Au@MoS2 nanoparticles provides direct evidence for the core-shell morphology and also reveals the presence of morphological defects and irregularities in the MoS2 shell that are known to be more active for HER than the pristine MoS2 basal plane. Electrochemical measurements show a significant improvement in the HER activity of AugMoS(2) nanoparticles relative to freestanding MoS2 or Au-decorated MoS2. The best electrochemical performance was demonstrated by the Au nanostars-the largest Au core employed here-encapsulated in a MoS2 shell. Density-functional theory calculations show that charge transfer occurs from the Au to the MoS2 layers, producing a more conductive catalyst layer and a better electrode for electrochemical HER The strategies to further improve the catalytic properties of such hybrid nanoparticles are discussed.

Advanced nanomaterials play a prominent role in nanoscience and nanotechnology developments, opening new frontiers in these areas. Among these nanomaterials, due to their unique characteristics and enhanced chemical and physical properties, inorganic nanotubes have been considered one of the most interesting nanostructures. In recent years, important progress has been achieved in the production and study of these nanomaterials, including boron nitride, transition metal dichalcogenide nanotubular structures, misfit-based nanotubes and other hybrid/doped nanotubular objects. This review is devoted to the in-depth analysis of recent studies on the synthesis, atomic structures, properties and applications of inorganic nanotubes and related nanostructures. Particular attention is paid to the growth mechanism of these nanomaterials. This is a crucial point for the challenges ahead related to the mass production of high-quality defect-free nanotubes for a variety of applications.

Composites of poly(l-lactic acid) (PLLA) reinforced by adding inorganic nanotubes of tungsten disulfide (INT-WS2) were prepared by solvent casting. In addition to the pristine nanotubes, PLLA nanocomposites containing surface modified nanotubes were studied as well. Several surface-active agents, including polyethylene imine (PEI), were studied in this context. In addition, other biocompatible polymers, like poly d,l-lactic acid (PDLLA) and others were considered in combination with the INT-WS2. The nanotubes were added to the polymer in different proportions up to 3 wt %. The dispersion of the nanotubes in the nanocomposites were analyzed by several techniques, including X-ray tomography microscopy (Micro-XCT). Moreover, high-temperature rheological measurements of the molten polymer were conducted. In contrast to other nanoparticles, which lead to a considerable increase of the viscosity of the molten polymer, the WS2 nanotubes did not affect the viscosity significantly. They did not affect the complex viscosity of the molten PLLA phase, either. The mechanical and tribological properties of the nanocomposites were found to improve considerably by adding the nanotubes. A direct correlation was observed between the dispersion of the nanotubes in the polymer matrix and its mechanical properties.

Self-lubricating films are of immense importance in various tribological applications. Nanoparticles are often used as the lubricating component in such films. Inorganic fullerene-like (IF) nanoparticles of WS2 have been used in the past for variety of tribological applications including for self-lubricating polymer and metallic films. IF nanoparticles from MoS2 with superior tribological behavior were reported in the past. However, such nanoparticles, which are available in minute amounts, were not applied for self-lubricating coatings in the past. In the current work, inorganic fullerene-like nanoparticles of MoS2 (IF-MoS2) were co-evaporated with titanium (cobalt) on metal substrates. The films were characterized by different techniques and were shown to have good adhesion to the underlying substrate. Furthermore, tribological tests indicated that such coatings exhibit improved friction coefficient (roughly 0.1) and very small wear under relatively high load.

The synthesis and characterization of nanotubes from misfit layered compounds (MLCs) of the type (LnS)(1+y)TaS2 (denoted here as LnS-TaS2; Ln=Pr, Sm, Gd, and Yb), not reported before, are described (the bulk compound YbS-LaS2 was not previously documented). Transmission electron microscopy and selected area electron diffraction showed that the interlayer spacing along the c axis decreased with an increase in the atomic number of the lanthanide atom, which suggested tighter interaction between the LnS layer and TaS2 for the late lanthanides. The Raman spectra of the tubules were studied and compared to those of the bulk MLC compounds. Similar to the bulk MLCs, the Raman spectra could be divided into the low-frequency modes (110-150cm(-1)) of the LnS lattice and the high-frequency modes (250-400cm(-1)) of the TaS2 lattice. The Raman spectra indicated that the vibrational lattice modes of the strained layers in the tubes were stiffer than those in the bulk compounds. Furthermore, the modes of the late lanthanides were higher in energy than those of the earlier lanthanides, which suggested larger charge transfer between the LnS and TaS2 layers for the late lanthanides. Polarized Raman measurements showed the expected binodal intensity profile (antenna effect). The intensity ratio of the Raman signal showed that the E-2g mode of TaS2 was more sensitive to the light-polarization effect than its A(1g) mode. These nanotubes are expected to reveal interesting low-temperature quasi-1D transport behavior.

First, the mechanisms leading to the formation of nanotubes from layered (2-D) materials are briefly discussed. Two main mechanisms are evoked: (1) The asymmetry of the layer along the c-axis, which leads to spontaneous folding, as revealed first by Pauling in 1930; (2) The seaming of the layer due to the abundance of dangling bonds in the rim atoms of the 2-D nanoclusters. This mechanism was discussed first in connection with carbon fullerenes and carbon nanotubes, some 30 years ago and was further extended to inorganic 2-D materials in 1992. In the second part of this work, the formation mechanism of nanotubes from misfit layered compounds (MLC) is deliberated. Here, the two forces are shown to work in synergy leading to facile formation of nanotubes from ternary misfit compounds. This synergy is demonstrated through the versatile chemistry, which has been employed to synthesize MLC nanotubes. Furthering in complexity, few recent examples of nanotubes from quaternary chalcogenide-based MLC are briefly discussed.

Due to their favourable and rich electronic and optical properties, group-VI-B transition-metal dichalcogenides (TMDs) have attracted considerable interest. They have earned their position in the materials portfolio of the spintronics and valleytronics communities. The electrical performance of TMDs is enhanced by rolling up the two-dimensional (2D) sheets to form quasi-one-dimensional (1D) tubular structures. The fabrication of p-n junctions out of these tubular TMDs would boost their potential for optoelectronic devices as such junctions represent a fundamental building block. Here, we report the realization of a p-n junction out of a single, isolated WS₂-nanotube (WS₂-NT). Light-emitting diode operation and photovoltaic behaviour were observed based on such p-n junctions. The emitted light as well as the photovoltaic effect exhibit strong linear polarization characteristics due to the quasi-1D nature. The external quantum efficiency for the photovoltaic effect reaches a value as high as 4.8%, exceeding by far that of 2D TMDs and even approaching the internal quantum efficiency of the 2D TMDs. This efficiency improvement indicates that TMD nanotubes are superior candidates over 2D TMDs for optoelectronic applications.

Films combining hydroxyapatite (HA) with minute amounts (ca. 1 weight %) of (rhenium doped) fullerene-like MoS2 (IF) nanoparticles were deposited onto porous titanium substrate through electrophoretic process (EPD). The films were analyzed by scanning electron microscopy (SEM), X-ray diffraction and Raman spectroscopy. The SEM analysis showed relatively uniform coatings of the HA + IF on the titanium substrate. Chemical composition analysis using energy dispersive X-ray spectroscopy (EDS) of the coatings revealed the presence of calcium phosphate minerals like hydroxyapatite, as a majority phase. Tribological tests were undertaken showing that the IF nanoparticles endow the HA film very low friction and wear characteristics. Such films could be of interest for various medical technologies. Means for improving the adhesion of the film to the underlying substrate and its fracture toughness, without compromising its biocompatibility are discussed at the end.

We report here a unique and efficient methodology for the surface functionalization of closed-cage inorganic fullerene-like (IF) nanoparticles and inorganic nanotubes (INTs) composed of two-dimensional nanomaterials of transition-metal chalcogenides (MS
₂; M = W or Mo). The first step is the physical coverage of these robust inorganic materials with monodispersed and dense monolayers of gold, silver, and palladium nanoparticles. The structural continuity at the interface between the IF/INT and the metallic nanoparticles is investigated. Lattice matching between these nanocrystalline materials and strong chemical affinity lead to efficient binding of the metallic nanoparticles onto the outer sulfide layer of the MS
₂-based structures. It is shown that this functionalization results in narrowing of the IF/INT optical band gap, increased work function, and improved surface-enhanced Raman scattering. In the second step, functionalization of the surface-bound nanoparticles is carried out by a ligand-exchange reaction. This ligand exchange involving the tetraoctylammonium bromide capping layer and an alkyl thiol enhances the solubility (∼10×) of the otherwise nearly insoluble materials in organic solvents. The scope of this method is further demonstrated by introducing a ruthenium(II) polypyridyl complex on the surface of the surface-bound AuNPs to generate fluorescent multicomponent materials.

This study conducted tensile and hardness tests to compare the mechanical properties of Mg alloys and metal matrix composites with and without WS₂ or multi-walled carbon nanotubes. We also examined the microscopic structures to investigate their failure characteristics. Our results indicate that AZ61 presented the best mechanical properties following the addition of WS₂ and solution heat treatment, and increasing the content of WS₂ improved the mechanical properties. This performance of this combination even outperformed that of metal matrix composites containing multi-walled carbon nanotubes. This study developed an image processing method, in which X-ray images of the metal matrix composite specimens undergo filtering, binarization, edge enhancement, and morphological calculations to determine the area of internal defects in Mg metal matrix composites. The results indicated reduced percentage of internal defect area values in AZ31-T4 and AZ61-T4 following the addition of 0.2% WS₂ inorganic nanotube (INT). X-ray diffraction results revealed that the solution heat treatment process causes the WS₂ to dissolve into the Mg base, thereby shifting the peak to the right. This improves solid solution strengthening and enhances the mechanical properties. Further observation of the microscopic structures indicated that the AZ61-T4 possesses finer grains than does the AZ31-T4, which is consistent with the existing literature.

We have synthesized quaternary chalcogenide-based misfit nanotubes LnS(Se)-TaS₂(Se) (Ln = La, Ce, Nd, and Ho). None of the compounds described here were reported in the literature as a bulk compound. The characterization of these nanotubes, at the atomic level, has been developed via different transmission electron microscopy techniques, including high-resolution scanning transmission electron microscopy, electron diffraction, and electron energy-loss spectroscopy. In particular, quantification at sub-nanometer scale was achieved by acquiring high-quality electron energy-loss spectra at high energy (∼between 1000 and 2500 eV). Remarkably, the sulfur was found to reside primarily in the distorted rocksalt LnS lattice, while the Se is associated with the hexagonal TaSe₂ site. Consequently, these quaternary misfit layered compounds in the form of nanostructures possess a double superstructure of La/Ta and S/Se with the same periodicity. In addition, the interlayer spacing between the layers and the interatomic distances within the layer vary systematically in the nanotubes, showing clear reduction when going from the lightest (La atom) to the heaviest (Ho) atom. Amorphous layers, of different nature, were observed at the surface of the nanotubes. For La-based NTs, the thin external amorphous layer (inferior to 10 nm) can be ascribed to a Se deficiency. Contrarily, for Ho-based NTs, the thick amorphous layer (between 10 and 20 nm) is clearly ascribed to oxidation. All of these findings helped us to understand the atomic structure of these new compounds and nanotubes thereof.

The study of inorganic nanometer-scale materials with hollow closed-cage structures, such as inorganic fullerene-like (IF) nanostructures and inorganic nanotubes (INTs), is a rapidly growing field. Numerous kinds of IF nanostructures and INTs were synthesized for a variety of applications, particularly for lubrication, functional coatings, and reinforcement of polymer matrices. To date, such nanostructures have been synthesized mostly by heating a transition metal or oxide thereof in the presence of precursor gases, which are however toxic and hazardous. In this context, one frontier of research in this field is the development of new avenues for the green synthesis of IF structures and INTs, directly from the bulk of layered compounds. In the present work, we demonstrate a simple roomerature and environmentally friendly approach for the synthesis of IF nanostructures and INTs via ultrashort-pulse laser ablation of a mixture of transition-metal dichalcogenides in bulk form mixed with Pb/PbO, in ambient air. The method can be considered as a synergy of photothermally and photochemically induced chemical transformations. The ultrafast-laser-induced excitation of the material, complemented with the formation of extended hot annealing regions in the presence of the metal catalyst, facilitates the formation of different nanostructures. Being fast, easy, and material-independent, our method offers new opportunities for the synthesis of IF nanostructures and INTs from different bulk metal chalcogenide compounds. On the basis of the capabilities of laser technology as well, this method could advantageously be further developed into a versatile tool for the simultaneous growth and patterning of such nanostructures in preselected positions for a variety of applications.

Multiwalled carbon (MWCNT) and tungsten disulfide (INTWS2) nanotubes are materials with excellent mechanical properties, high electrical and thermal conductivity. These special properties make them excellent candidates for high strength and electrically conductive polymer nanocomposite applications. In this work, the possibility of the improvement of mechanical, thermal and electrical properties of poly(trimethylene terephthalate) (PTT) by the introduction of MWCNT and INTWS2 nanotubes was investigated. The PTT nanocomposites with low loading of nanotubes were prepared by in situ polymerization method. Analysis of the nanocomposites' morphology carried out by SEM and TEM has confirmed that welldispersed nanotubes in the PTT matrix were obtained at low loading (

Nanoparticles, and more specifically gold nanoparticles (AuNPs), have attracted much scientific and technological interest in the last few decades. Their popularity is attributed to their unique optical, catalytic, electrical and magnetic properties when compared with the bulk. However, one of the main problems with AuNPs is their long-term stability. Two-dimensional materials like MoS₂ (WS₂) are semiconductors that exhibit a combination of properties which make them suitable for electronic, optical and (photo)catalytic devices. Few-layer MoS₂ (WS₂) nanoparticles (NPs), and in particular single-layer ones, show intriguing optical and electrical properties which are very different from those of the bulk compounds. Here we demonstrate the synthesis of AuNPs sheathed by a single layer of MoS₂ (WS₂), i.e. a core-shell nanostructure (AuNP@1L-MoS₂). The hybrid NPs exhibit optical properties that are different from those of either constituent and are amenable for modulation via their chemistry, offering a myriad of applications.

Owing to their outstanding variety of properties, nanoparticles attracted considerable interest for developing a new age of novel polymer nanocomposites and adhesives. Among them, inorganic nanotubes (INTs) of tungsten disulfide (WS₂) and carbon nanotubes (CNTs) have been identified as unique candidates for many industrial applications by virtue of their superior mechanical, thermal and tribological properties. In this work, a comparative study between INT-WS₂ and multi-walled carbon nanotubes (MWCNTs) regarding the properties of structural polyurethane (PU) adhesives is presented. Specifically, we evaluate the thermomechanical properties, chemical and micro-phase structure, bonded joints performance in lap shear and peel modes, and fracture mechanisms, with aiming to highlight some of the differences between these nanotubes. The added content spanned over the range of 0.3, 0.6, 0.9 and 1.2 wt% of INT-WS₂, while CNTs are incorporated at the same volumetric fractions (e.g., 0.1, 0.2, 0.3 and 0.4 wt%). According to the results of the tests, in all measured aspects, INT-WS₂ outperformed the carbon counterparts. With regards to the thermomechanical attributes, the hard segment Tg of the PU increased by 14 °C at 0.6 wt% INTs, whereas CNTs recorded only modest improvement of 8 °C at the nanocomposite loaded with 0.4 wt%. The structural bonding performance indicates an improvement of 117% and 38% in the shear and peel strengths at 0.9 and 1.2 wt% INTs, respectively, while CNTs show moderate changes. Interestingly, the changes are also reflected by the interplay between the hard and soft segments of the PU, and different fracture mechanisms operating within the nanocomposites. At any rate, the combined attributes of >20 MPa in the shear strength and approximately 2 N/mm in (average) peel strength, targets the PU/INT nanoadhesives as promising alternative for conventional epoxy systems which has similar shear strength with inferior peel strength.

Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity-unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures.

We study for the first time the resonant torsional behaviors of inorganic nanotubes, specifically tungsten disulfide (WS₂) and boron nitride (BN) nanotubes, and compare them to that of carbon nanotubes. We have found WS₂ nanotubes to have the highest quality factor (Q) and torsional resonance frequency, followed by BN nanotubes and carbon nanotubes. Dynamic and static torsional spring constants of the various nanotubes were found to be different, especially in the case of WS₂, possibly due to a velocity-dependent intershell friction. These results indicate that inorganic nanotubes are promising building blocks for high-Q nanoelectromechanical systems (NEMS).

In this report, a systematic study of the effects of p- and n-type doping of the inorganic fullerene (IF) MoS₂ on the efficiency of the hydrogen evolution reaction (HER) is described. Active edge site enriched IF-MoS₂, promoted by strategically introducing Nb (p-type) and Re (n-type) dopants (below 500 ppm), enables facile HER over a range of pH values. Experimental results suggest that although Nb-doping on IF-MoS₂ leads to better electrocatalytic HER activity in an alkaline medium with an onset potential difference of 80 mV, Re-doping gives excellent activity in an acidic medium. The present work presents a systematic study of HER activity by finely tuning the activity in different electrolyte media with varied pH values through deliberate doping of the parent catalyst with p- and n- type materials. The doped IF-MoS₂ catalysts exhibit excellent catalytic activity even with sea water as an electrolyte.

Various nanotubes from ternary misfit compounds have been reported in recent years. In the present work, the detailed atomic structure and chemical configuration of misfit-layered nanotubes based on the TbS-CrS₂ are reported. These analyses have been developed via different transmission electron microscopy techniques, including high-resolution scanning transmission electron microscopy, electron diffraction, and electron energy loss spectroscopy. These structural analyses show that two different kinds of nanotubes can be produced: a "regular" nanotube and a "wavy" one. Both kinds of nanotubes show the alternating arrangements of the TbS and CrS₂ subsystems; however, the wavy ones present a nearly periodically deficiency in terbium. In addition to the structural investigation, the chemical analyses have proved that the outer layer of both kinds of nanotubes is composed of the elements Cr and S. All these findings helped to understand the growth mechanism during the sulfurization reaction taking place in the synthesis process.

Misfit layered compounds (MLCs) have generated significant interest in recent years as potential thermoelectric materials. MLC nanotubes could reveal behavior that is entirely different from the bulk material. Recently, new chemical strategies were exploited for the synthesis of nanotubular forms of chalcogenide-based MLCs, which are promising candidates for thermoelectric materials. However, analogous synthesis of oxide-based MLC nanotubes has not been demonstrated until now. Here, we report a chemical strategy for synthesis of cobalt-oxide-based misfit nanotubes. A combination of high-resolution (scanning) transmission electron microscopy (including image simulations), spatially resolved electron energy-loss spectroscopy, electron diffraction, and density functional theory (DFT) calculations is used to discover the formation of a phase within these nanotubes that differs significantly from bulk calcium cobaltite MLCs. Furthermore, DFT calculations show that this phase is semiconducting with a band gap in excess of 1 eV, unlike bulk calcium cobaltite MLCs, which are known to be metallic. Through systematic experiments, we propose a formation mechanism for these nanotubes that could also apply more generally to realizing other oxide-based MLC nanotubes.

We bring together synchrotron-based infrared and Raman spectroscopies, diamond anvil cell techniques, and an analysis of frequency shifts and lattice dynamics to unveil the vibrational properties of multiwall WS₂ nanotubes under compression. While most of the vibrational modes display similar hardening trends, the Raman-active A_1g breathing mode is almost twice as responsive, suggesting that the nanotube breakdown pathway under strain proceeds through this displacement. At the same time, the previously unexplored high pressure infrared response provides unexpected insight into the electronic properties of the multiwall WS₂ tubes. The development of the localized absorption is fit to a percolation model, indicating that the nanotubes display a modest macroscopic conductivity due to hopping from tube to tube.

We have previously studied the micromechanics of graphene composites by using Raman spectroscopy to map the strain in model composite systems comprising of single graphene flakes. The design rules derived from these models have then been applied successfully to bulk composites. Herein, we have adapted our approach to understand the behaviour of transition metal transition metal dichalcogenide (TMDC) reinforcements such as tungsten disulphide (WS₂) and molybdenum disulphide (MoS₂). Few-layer nanoplatelets were produced by mechanical exfoliation, applied to a polymer substrate and then put under uniaxial strain. Small but significant Raman band shifts were observed upon deformation. These strain-induced bands shifts were modeled using density functional perturbation theory with good correlation between the experimental and predicted band shifts. The micromechanical behaviour of these experimental systems were modeled and compared to that of graphene, with the differences being correlated nature of the interfaces and microstructures. Finally, composites were produced using WS₂ nanotubes in order to assess the role of the dimensionality of the reinforcement in the mechanical performance.

Palladium nanoparticles were deposited on multiwall WS₂ nanotubes. The composite nanoparticles were characterized by a variety of techniques. The Pd nanoparticles were deposited uniformly on the surface of WS₂ nanotubes. An epitaxial relationship between the (111) plane of Pd and the (013) plane of WS₂ was mostly observed. The composite nanoparticles were found to perform efficiently as catalysts for cross-coupling (Heck and Suzuki) reactions. The role of the nanotubes support in the catalytic process is briefly discussed.

Thermoset adhesives such as epoxy exhibit high stiffness, strength and adhesion properties, but relatively poor toughness, elongation and conductivity. Nanofillers such as carbon (CNTs) and tungsten disulfide (WS₂) nanotubes (INTs) and fullerene-like (IF) nanoparticles (NPs) possess excellent mechanical properties and also high electrical (thermal) conductivity. The quality of dispersion of the nanofillers in the thermoset adhesives has a major effect on the final properties of the nanocomposite adhesive. Dispersion techniques such as solution mixing, ultrasonication, three-roll milling, etc. have been used. Significant enhancements in stiffness, tensile strength, shear and peel strengths, fracture toughness, glass transition temperature, CLTE (coefficient of linear thermal expansion) among others, can be achieved at low CNTs concentrations (less than 1 wt.%), while at higher content of the CNTs, agglomeration reduces the toughness. Also for the WS₂ nanoparticles, the lower concentrations (up to 1 wt.%) are preferable in order to improve the mechanical performance of the epoxy-based composites. Enhanced dispersion and interfacial interactions, resulting in improved mechanical performance of the nanocomposites containing CNTs, could be achieved by covalent and noncovalent modifications. The dispersion of WS₂ nanostructures in the polymer medium was obtained using simple techniques like shear mixing and sonication without surface modifications. Moreover, it was found that the IF-NPs could covalently interact with the epoxy, without any surface modifications. The toughening mechanism of polymer matrices by the tubular nanofillers is mainly attributed to pull-out and crack bridging of the nanotubes. At the same time, inorganic nanocomposite adhesives exhibit promising results. IF structures of WS₂ were found to exhibit crack deflection and bowing mechanisms. Electrically and thermally conductive adhesives have been obtained by adding CNTs, whereas conductive nanocomposites containing INT-WS₂ have not been reported. In the case of CNTs the percolation path could be realized already at low levels (0.25 -1 wt.%). Furthermore, as the CNTs content increases, so does the conductivity of the composite material. In addition, the thermal conductivity of CNTs was found to have insignificant effect on the thermal conductivity of the nanoadhesives. Furthermore, the electrical and thermal conductive properties of most surface treated and functionalized CNTs were found to decrease, compared to untreated CNTs. The resulting nanocomposite adhesives containing carbon and tungsten disulfide nanotubes and fullerenes exhibit promising results in various applications.

We report the synthesis and supporting density-functional-theory computations for a closed-cage, misfit layered-compound superstructure from PbS-SnS₂, generated by highly concentrated sunlight from a precursor mixture of Pb, SnS₂, and graphite. The unique reactor conditions created in our solar furnace are found to be particularly conducive to the formation of these nanomaterials. Detailed structural and chemical characterization revealed a spontaneous inside-out formation mechanism, with a broad range of nonhollow fullerene-like structures starting at a diameter of ∼20 nm and a wall thickness of ∼5 layers. The computations also reveal a counterintuitive charge transfer pathway from the SnS₂ layers to the PbS layers, which indicates that, in contrast to binary-layered compounds where it is principally van der Waals forces that hold the layers together, polar forces appear to be as important in stabilizing superstructures of misfit layered compounds. (Figure Presented).

Sodium ion batteries (SIBs) are considered as a promising alternative to threaten the reign of lithium ion batteries (LIBs) among various next-generation rechargeable energy storage systems, including magnesium ion, metalr, and metalsulfur batteries. Since both sodium and lithium are located in Group 1 of the periodic table, they share similar (electro)chemical properties with regard to ionization pattern, electronegativity, and electronic configuration; thus the vast number of compounds developed from LIBs can provide guidance to design electrode materials for SIBs. However, the larger ionic radius of the sodium cation and unique (de)sodiation processes may also lead to uncertainties in terms of thermodynamic or kinetic properties. Herein, we present the first construction of SIBs based on inorganic fullerene-like (IF) MoS₂ nanoparticles. Closed-shell-type structures, represented by C₆₀ fullerene, have largely been neglected for studies of alkali-metal hosting materials due to their inaccessibility for intercalating ions into the inner spaces. However, IF-MoS₂, with faceted surfaces, can diffuse sodium ions through the defective channels, thereby allowing reversible sodium ion intercalation/deintercalation. Interestingly, Re-doped MoS₂ showed good electrochemical performances with fast kinetics (ca. 74 mA h g^-1 at 20 C). N-type doping caused by Re substitution of Mo in IF-MoS₂ revealed enhanced electrical conductivity and an increased number of diffusion defect sites. Thus, chemical modification of fullerene-like structures through doping is proven to be a promising synthetic strategy to prepare improved electrodes.

In the present work, MoS2 nanoparticles with fullerene-like structure, and most particularly those doped with minute amounts of rhenium atoms, are used as additive to medical gels in order to facilitate their entry into constricted openings of soft material rings. This procedure is used to mimic the entry of endoscopes to constricted openings of the human body, like urethra, etc. It is shown that the Re-doped nanoparticles reduce the traction force used to retrieve the metallic lead of the endoscope from the soft ring by a factor close to three times with respect to the original gel. The mechanism of the mitigation of both friction and adhesion forces in these systems by the nanoparticles is discussed.

Recent studies have clearly indicated the favorable effect of lead as a growth promoter for MX₂ (M = Mo, W; X = S, Se) nanotubes using MX₂ powder as a precursor material. The experimental work indicated that the lead atoms are not stable in the molybdenum oxide lattice ion high concentration. The initial lead concentration in the oxide nanowhiskers (Pb:Mo ratio = 0.28) is reduced by one order of magnitude after one year in the drawer. The initial Pb concentration in the MoS₂ nanotubes lattice (produced by solar ablation) is appreciably smaller (Pb:Mo ratio for the primary samples is 0.12) and is further reduced with time and annealing at 810 °C, without consuming the nanotubes. In order to elucidate the composition of these nanotubes in greater detail; the Pb-"modified" MX₂ compounds were studied by means of DFT calculations and additional experimental work. The calculations indicate that Pb doping as well as Pb intercalation of MoS₂ lead to the destabilization of the system; and therefore a high Pb content within the MoS₂ lattice cannot be expected in the final products. Furthermore; substitutional doping (Pb_Mo) leads to p-type semiconducting character; while intercalation of MoS₂ by Pb atoms (Pb_y/MoS₂) should cause n-type semiconducting behavior. This study not only sheds light on the role of added lead to the growth of the nanotubes and their role as electron donors; but furthermore could pave the way to a large scale synthesis of the MoS₂ nanotubes.

Tubular structures of the MS-TaS₂ with (M = Pb, Sn, Sb, Bi) misfit layered compounds are reported. The lattice mismatch between the alternating MS and TaS₂ layers leads to a variety of chiral tubular structures. Such tubular structures are studied via scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). For the PbS-TaS₂ and SnS-TaS ₂ tubules, relative in-plane orientations as well as folding vectors of the two subsystems can be determined. However, almost ring-like SAED patterns are obtained for SbS-TaS₂ nanotubes precluding exact determination of the relative in plane orientation. Also, very complex diffraction patterns were obtained for BiS-TaS₂ nanotubes.

Ureteral stents and urethral catheters are commonly used medical devices for maintaining urinary flow. However, long-term placement (>30 days) of these devices in the urinary tracts is limited by the development of encrustation, a phenomenon that holds a prevalence of 50% within this patient population, resulting in a great deal of morbidity to the patients. Here we report the influence of surface coating of an all-silicone catheter with rhenium-doped fullerene-like molybdenum disulfide (Re:IF-MoS₂) nanoparticles on the growth and attachment of in vitro encrustation stones. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD) analyses indicated a remarkable attenuation in encrustation occupation on the Re:IF-MoS₂-coated catheter surfaces compared to neat catheters. The doped nanoparticles displayed a unique tendency to self-assemble into mosaic-like arrangements, modifying the surface to be encrustation-repellent. The mechanism of encrustation retardation on the surface coated catheters is discussed in some detail. The ramification of these results for the clogging of other body indwelling devices is briefly discussed. This journal is

The optical and electronic properties of suspensions of inorganic fullerene-like nanoparticles of MoS₂ are studied through light absorption and zeta-potential measurements and compared to those of the corresponding microscopic platelets. The total extinction measurements show that, in addition to excitonic peaks and the indirect band gap transition, a new peak is observed at 700-800 nm. This spectral peak has not been reported previously for MoS₂. Comparison of the total extinction and decoupled absorption spectrum indicates that this peak largely originates from scattering. Furthermore, the dependence of this peak on nanoparticle size, shape, and surface charge, as well as solvent refractive index, suggests that this transition arises from a plasmon resonance.

Thermoset-elastomer polyurethane (PU) nanocomposites were prepared using two types of tungsten disulphide (WS2) nanoparticles: inorganic fullerene-like (IF) and inorganic nanotubes (INT) through an in-situ polymerization process. The quality of dispersion was evaluated using scanning electron microscope (SEM) and the thermomechanical properties were analyzed using dynamic mechanical analysis (DMA). Addition of 1% and 3 wt.%. IFs resulted in enhancement in storage modulus of 45 and 100%, respectively, compared to the neat polymer. The enhancement using only 0.5% wt. INTs was more than 100% and then decreased with additional amount of nanotubes. While no significant change in the composites glass transition temperature (Tg) was observed with IF-WS2, 0.5% INT-WS2 showed a 20 °C increase of Tg. In both cases, analysis of the chemical structure using an attenuated total reflectance- Fourier transform infrared spectroscopy showed no effect of the nanoparticles on the chemical structure of the PU and wide-angle X-ray diffraction showed no change in morphology. In the case of IF-WS2 the highest peel strength was obtained with 1% wt. demonstrating a 44% improvement in peel strength. However, in the case of INT-WS2, incorporating 0.5% wt. improved the peel strength by more than 1000%. SEM analysis showed a unique development of a nodular morphology and a failure mechanism dominated by nanotube pull-out. It was concluded that the geometry of the nanoparticles (nanotubes or fullerene) has a dominant effect on the final PU nanocomposite properties.

In this paper the synthesis of inorganic nanotubes (INT) and to a lesser extent, inorganic fullerene-like nanoparticles (IF) of WS₂, which have been recently scaled-up, is discussed in some detail. Subsequently the mechanical properties of IF/INT are summarized, in reference to their remarkable possibility to reinforce polymer matrices and serve as superior solid lubricants. The effect of adding minute amounts of such nanoparticles to various polymer matrices is reviewed with reference to thermoplastic and thermosetting polymers. Possible different applications of such nanocomposites are also briefly discussed.

Recently large amounts of inorganic nanotubes (INT) and inorganic fullerene-like (IF) nanoparticles of WS₂ became available and methods for their dispersion in different media were developed. In the present work the tribological properties of epoxy composite compounded with tungsten disulfide particles of different sizes and morphologies, including quasi-spherical IF nanoparticles, one-dimensional INT as well as micron-size platelets (2H) were investigated. The coefficient of friction and wear loss were measured under dry contact conditions using different tribological rigs. Remarkable reduction in wear and also friction (under high load) was demonstrated for the IF/INT epoxy nanocomposite. The reduced wear is attributed in general to the reinforcement of the polymer matrix by nanoparticles and the simultaneous reduction of the epoxy brittleness. Contrarily, the friction of the neat epoxy sample and epoxy mixed with platelets was accompanied with strong wear and transfer of a polymer film onto the rubbed surfaces. These results are consistent with the recently reported improvements in the fracture toughness, peel and shear strength of the epoxy-nanoparticles (IF/INT) composites.

Polymer-inorganic nanoparticle composites are an area of great research interest. Inorganic fullerene-like (IF) structures and inorganic nanotubes (INT) are used for producing composite materials with specific goals of reinforcement of the polymer and ameliorating its thermal stability. Here, a composite material containing INT and conducting polymer (polyaniline (PANI)) is synthesized by an in situ oxidative polymerization of the monomer in the presence of WS₂ nanotubes. The structure and electrical behavior of PANI/INT composite is studied and compared with the results of pristine PANI (synthesized under the same conditions without INT). Most remarkably, INT-WS₂ are found to play the role of an active doping agent. The highest conductivity is obtained for 0.85 wt% (ca. 0.06 at%) nanotubes content, two orders of magnitude higher than that of pristine PANI. This work suggests a new approach to control the host-guest interaction in the polymer nanocomposite via (Lewis) acid-base equilibrium. A composite material containing WS ₂ nanotubes (INT-WS₂) and conducting polymer (polyaniline (PANI)) is obtained by an in situ oxidative polymerization of the monomer in the presence of the INT-WS₂. Electron transfer from PANI to the INT-WS₂ is shown to produce a peak in the conductivity at 0.85 wt% (0.2 at%) of the nanotubes.

WS₂ nanoribbons have been synthesized by chemical unzipping of WS₂ nanotubes. Lithium atoms are intercalated in WS₂ nanotubes by a solvothermal reaction with n-butyllithium in hexane. The lithiated WS₂ nanotubes are then reacted with various solvents - water, ethanol, and long chain thiols. While the tubes break into pieces when treated with water and ethanol, they unzip through longitudinal cutting along the axes to yield nanoribbons when treated with long chain thiols, 1-octanethiol and 1-dodecanethiol. The slow diffusion of the long chain thiols reduces the aggression of the reaction, leading to controlled opening of the tubes.

This study describes a new method for fabrication of thin composite films using physical vapor deposition (PVD). Titanium (Ti) and hybrid films of titanium containing tungsten disulphide nanoparticles with inorganic fullerene-like structure (Ti/IF-WS₂) were fabricated with a modified PVD machine. The evaporation process includes the pulsed deposition of IF-WS₂ by a sprayer head. This process results in IF-WS₂ nanoparticles embedded in a Ti matrix. The layers were characterized by various techniques, which confirm the composition and structure of the hybrid film. The Ti/IF-WS₂ shows better wear resistance and a lower friction coefficient when compared to the Ti layer or Ti substrate. The Ti/IF films show very good antireflective properties in the visible and near-IR region. Such films may find numerous applications, for example, in the aerospace and medical technology.

We investigated the infrared vibrational properties of pristine and Re-substituted MoS₂ nanoparticles and analyzed the extracted phonon lifetimes in terms of multiple scattering events. Our measurements reveal both size- and doping-dependent changes that we attribute to grain boundary scattering and charge and mass effects, respectively. By contrast, Born charge is affected only by size. These findings illustrate the utility of reaching beyond traditional bulk semiconductors and quantum dots to explore how doping and confinement impact carrier-phonon interactions in low-dimensional semiconducting nanomaterials.

Mechanical properties and fracture behaviors of multiwalled WS₂ nanotubes produced by large scale fluidized bed method were investigated under uniaxial tension using in situ transmission electron microscopy probing; these were directly correlated to the nanotube atomic structures. The tubes with the average outer diameter ∼40 nm sustained tensile force of ∼2949 nN and revealed fracture strength of ∼11.8 GPa. Surprisingly, these rather thick WS₂ nanotubes could bear much higher loadings than the thin WS ₂ nanotubes with almost "defect-free" structures studied previously. In addition, the fracture strength of the "thick" nanotubes did not show common size dependent degradation when the tube diameters increased from ∼20 to ∼60 nm. HRTEM characterizations and real time observations revealed that the anomalous tensile properties are related to the intershell cross-linking and geometric constraints from the inverted cone-shaped tube cap structures, which resulted in the multishell loading and fracturing.

Inorganic fullerene-like (IF) nanoparticles (NP) and inorganic nanotubes (INT) of layered compounds, such as WS₂, have been of particular interest due to their unique structural characteristics. Recently, the catalytic decomposition of thiophene using INT of WS₂ decorated with Co NP was demonstrated. This finding also suggests that these materials could be also suitable for the photocatalytic treatment of pollutants in wastewaters. In the present work, the photocatalytic decomposition of methyl orange (MO) in aqueous solution using Co-coated INT-WS₂ as well as other NP was investigated. The photocatalytic reactivity under visible light illumination of this photocatalyst was measured and compared with that of various IF and INT and TiO₂ (P25). The Co NP-coated INT-WS₂ exhibited the highest photodegradation of MO among the studied NP. The significant enhancement in the photoactivity of the hybrid nanostructure can be attributed to the combination of the metallic Co NP and the semiconducting WS₂ nanotubes. The hybrid nanostructure enables the efficient light absorption by the INT and the subsequent charge separation of the hybrid semiconductormetal NP under visible light illumination. In addition, Raman spectroscopy technique was used to verify that the MO was decomposed by Co-coated nanotubes and not adsorbed in large amounts on the hybrid NP surface.

The electrical properties of WS ₂ nanotubes (NTs) were studied through measuring 59 devices. Important electrical parameters, such as the carrier concentration, mobility, and effective barrier height at the contacts, were obtained through fitting experimental non-linear I-V curves using a metal-semiconductor-metal model. The carrier mobility was found to be several orders of magnitude higher than that have been reported previously for WS ₂ NTs. Water absorption was found to decrease the conductivity and carrier mobility of the NTs, and could be removed when the sample was dried. Oxygen absorption also slightly decreased the conductivity of WS ₂ NTs.

WS ₂ nanostructures hold structural characteristics which suggest they will be suitable for heterogeneous catalysis in the hydrodesulfurization (HDS) process. In this work, WS ₂ nanotubes (INT-WS ₂) were coated with cobalt nanoparticles using electroless plating method. Prior to cobalt deposition, the nanotubes surface was activated using palladium seeding process. The deposited cobalt nanoparticles had hcp crystal structure and formed non-uniform layer on the nanotubes surface. The catalytic reactivity of the produced cobalt coated nanotubes toward thiophene decomposition was characterized by an atmospheric flow reactor. The coated nanotubes revealed good catalytic reactivity toward thiophene mineralization. Further, the adsorption kinetics of thiophene on coated INT-WS ₂ was studied by thermal desorption spectroscopy (TDS). The cobalt coated system was found to be more catalytically active than the pristine INT-WS ₂ system. This result is promising since further optimization of the nanofabrication process of the catalyst should increase the conversion rates even further.

A synthetic route for preparation of inorganic WS ₂ nanotube (INT)-colloidal semiconductor quantum dot (QD) hybrid structures is developed, and transient carrier dynamics on these hybrids are studied via transient photoluminescence spectroscopy utilizing several different types of QDs. Measurements reveal efficient resonant energy transfer from the QDs to the INT upon photoexcitation, provided that the QD emission is at a higher energy than the INT direct gap. Charge transfer in the hybrid system, characterized using QDs with band gaps below the INT direct gap, is found to be absent. This is attributed to the presence of an organic barrier layer due to the relatively long-chain organic ligands of the QDs under study. This system, analogous to carbon nanotube-QD hybrids, holds potential for a variety of applications, including photovoltaics, luminescence tagging and optoelectronics. This journal is

Metallic films impregnated with fullerene-like-WS2 (MoS2) nanoparticles were fabricated on stainless steel and Ti-Ni substrates using galvanic and electroless deposition. The coatings were obtained from aqueous suspensions containing the metallic salts as well as the dispersed nanoparticles. Tribological tests showed that the films have low friction and wear. Such coatings could be useful for numerous civilian and defense-related applications.

Inorganic nanoparticles of layered [two-dimensional (2D)] compounds with hollow polyhedral structure, known as fullerenelike nanoparticles (IF), were found to have excellent lubricating properties. This behavior can be explained by superposition of three main mechanisms: rolling, sliding, and exfoliation-material transfer (third body). In order to elucidate the tribological mechanism of individual nanoparticles in different regimes, in situ axial nanocompression and shearing forces were applied to individual nanoparticles using a high resolution scanning electron microscope. Gold nanoparticles deposited onto the IF nanoparticles surface served as markers, delineating the motion of individual IF nanoparticle. It can be concluded from these experiments that rolling is an important lubrication mechanism for IF-WS ₂ in the relatively low range of normal stress (0.96±0.38 GPa). Sliding is shown to be relevant under slightly higher normal stress, where the spacing between the two mating surfaces does not permit free rolling of the nanoparticles. Exfoliation of the IF nanoparticles becomes the dominant mechanism at the high end of normal stress; above 1.2 GPa and (slow) shear; i.e., boundary lubrication conditions. It is argued that the modus operandi of the nanoparticles depends on their degree of crystallinity (defects); sizes; shape, and their mechanical characteristics. This study suggests that the rolling mechanism, which leads to low friction and wear, could be attained by improving the sphericity of the IF nanoparticle, the dispersion (deagglomeration) of the nanoparticles, and the smoothness of the mating surfaces.

Nanoparticles of layered compounds, like MoS₂ and WS ₂, having hollow closed-cage structures and known as fullerene-like (IF) and inorganic nanotubes (INT), are synthesized in macroscopic amounts. They were found to have superior tribological properties and can serve as solid-state additives to different lubrication fluids. More recently, metallic films incorporating the IF nanoparticles were prepared via wet deposition methods and also by physical vapor deposition techniques. The incorporation of the nanoparticles endows such coatings self-lubricating behavior, i.e. low friction and wear, which is highly desirable for variety of applications. The current feature article provides a short overview of the progress in the materials synthesis of IF and INT phases. Subsequently, a progress report of the various efforts to apply such coatings to medical devices and drug delivery is described.

Nickel-titanium (NiTi) alloys combine several remarkable characteristics, among them are shape-memory, superelasticity, great strain recovery, good biocompatibility, and corrosion resistance. These render them well suited to a wide range of medical applications, such as cardiovascular stents, laparoscopy, and dental applications such as NiTi endodontic files (EFs) used for root canal treatment, which are the focus of this work. Unfortunately, fatigue-induced and incidental failure of NiTi EFs is not uncommon, which may lead to severe medical consequences. Here we examine the effects of cobalt coatings with impregnated fullerene-like WS₂ nanoparticles on file fatigue and failure. Dynamic x-ray diffraction, nanoindentation and torque measurements all indicate a significant improvement in the fatigue resistance and time to breakage of the coated files, stemming from reduced friction between the file and the surrounding tissue. These methods are possibly applicable to a variety of NiTi-based medical devices where fatigue and consequent failure are of relevance.

Seamless transition: New hybrid fullerene-like nanostructures of MoS ₂ are comprised of a nanoscale octahedral core with a smooth transition to quasi-spherical outer shells. The particles were generated by ultra-high irradiance solar ablation and their structures confirmed by modeling studies.

The growth mechanism of WS₂ nanotubes is briefly discussed. Two distinct growth mechanisms can be delineated, leading to somewhat different products: 1) thick (50-150 nm) and very long (20-50 microns and above) nanotubes consisting of many (> 20) layers, and 2) slender (20-25 nm) nanotubes with 5-10 layers. The synthesis of large amounts of pure WS₂ nanotubes belonging to the first category in the large-scale fluidized-bed reactor is described. Characterization of the nanotubes, which grow catalyst-free by a number of analytical techniques, is reported. The nanotubes reveal highly crystalline order, suggesting very good mechanical behavior and numerous applications, especially in the field of nanocomposites.

A track record of generating novel fullerene-like and nanotubular inorganic nanostructures from Cs₂O, SiO_2-x, WS₂, and MoS₂ by photothermal ablation with highly concentrated sunlight and ultra-bright lamp light is reviewed, and augmented with new results for exfoliated MoS₂ and carbon as well as carbon nanotubes.

A nanostructure, being either an Inorganic Fullerene-like (IF) nanostructure or an Inorganic Nanotube (INT), A1-x-Bx-chalcogenide are described. A being a metal or transition metal or an alloy of metals and/or transition metals, B being a metal or transition metal B different from that of A and x being ≤0.3. A process for their manufacture and their use for modifying the electronic character of A-chalcogenide are described.

New materials and techniques pertaining to the synthesis of inorganic nanotubes have been ever increasing since the initiation of the field in 1992. Recently, WS2 nanotubes, which are produced now in large amounts, were filled with molten lead iodide salt by a capillary wetting process, resulting in PbI₂@WS₂ core-shell nanotubes. This work features progress in the synthesis of new core-shell nanotubes, including Bil₃@WS ₂ nanotubes produced in a similar same manner. In addition, two new techniques for obtaining core-shell nanotubes are presented. The first is via electron-beam irradiation, i.e., in situ synthesis within a transmission electron microscope. This synthesis results in SbI₃ nanotubes, observed either in a hollow core Of WS₂ ones (Sbl₃@WS ₂ nanotubes), or atop of them (WS₂@Sbl₃ nanotubes). The second technique involves a gaseous phase reaction, where the layered product employs WS₂ nanotubes as nucleation sites. In this case, the MoS₂ layers most often cover the WS₂ nanotube, resulting in WS₂@MoS₂ core-shell nanotubes. Notably, superstructures of the form MoS₂@WS₂ are occasionally obtained. Using a semi-empirical model, it is shown that the Pbl₂ nanotubes become stable within the core of MoS2 nanotubes only above a critical core diameter of the host (>12 nm); below this diameter the PbI₂ crystallizes as nanowires. These model calculations are in agreement with the current experimental observations, providing further support to the growth mechanism of such core-shell nanotubes.

In this work the effect of inorganic fullerene-like (closed cages) nanoparticles of tungsten disulfide (IF-WS₂) on the mechanical properties and especially on the toughness of epoxy resins, was studied. The epoxy resin used was the well-known DGEBA (di-glycidyl ether of bis-phenol A) cured with polyamidoamine. The epoxy/IF-WS₂ nanocomposites were prepared by applying a high shear mixing to obtain a uniform dispersion and homogeneous distribution of the IF nanoparticles in the epoxy matrix. Two mixing procedures were used - a low shear of short duration and high shear with a long mixing time. The resulting epoxy nanocomposites were first characterized for their shear and peel strength using appropriate bonded joints. The experimental results demonstrate that enhanced shear strengths and shear moduli were achieved, together with a significant increase in the peel strengths at low concentrations of the IF-WS₂ nanoparticles (more than 100% increase at 0.5 wt% IF-WS₂). Above the threshold value of 0.5% IF-WS ₂ the peel strength decreased sharply. The fractured surfaces of the bonded joints were examined by transmission and scanning electron microscopy in order to characterize the fracture mechanisms and analyze the dispersion level of the nanoparticles within the polymer. The electron micrographs indicated that the presence of the nanoparticles in the epoxy matrix induced fracture mechanisms which were different from those observed in the pristine epoxy phase. These mechanisms included: crack deflection; crack bowing; and crack pinning. Evidence for a chemical interaction between the nanoparticles and the epoxy were obtained by infrared measurements in the attenuated total transmittance mode. The data suggests the formation of new carbon-oxygen-sulfur bonds, which are most likely due to the reaction of the outermost sulfur layer of the IF nanoparticles with the reactive epoxy groups. The observed simultaneous increase in both shear and peel strengths at very low IF-WS₂ concentrations, found in this work, could lead to the development of high performance adhesives and to new types of structural and ballistic fiber nanocomposites.

WS₂ nanotubes have been filled and intercalated by molten phase caesium iodide. The presence of caesium iodide inside the WS₂ nanotubes has been determined using high-resolution transmission electron microscopy (HRTEM) coupled with electron energy-loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDS). Noticeably, a Moiré pattern was observed due to the interference between encapsulated CsI and WS₂ layers. The intercalation of CsI into the host concentric WS₂ lattices resulted in an increase in the interplanar spacing.

WS₂ inorganic nanotubes (INT) and inorganic fullerene-like nano-particles (IF) are well-known for their high mechanical strength and as superior solid lubricants. The outermost WS₂ layer is considered to be fully bonded; thus, it was suggested that the interactions of these WS₂ nanostructures with their surroundings are governed by purely van der Waals (vdW) interactions. However, in the case of IF-WS₂ nanoparticles, the faceted surface may contain sites with nonsaturated coordination, which, in turn, react with the surrounding media. Gold nanoparticles(GNP) wereusedas probesforthe IF-WS₂ surfacedefects,mapped by both scanning and transmission electron microscopy. The interaction between the GNP and the reactive surface was investigated using INT-WS₂ as a model and was characterized by atomic force microscopy (AFM).

The characterization of nanostructures to the atomic dimensions becomes more important, as devices based on a single particle are being produced. In particular, inorganic nanotubes were shown to host interesting properties making them excellent candidates for various devices. The WS₂ nanotubes outperform the bulk in their mechanical properties offering numerous applications especially as part of high strength nanocomposites. In contrast, their electrical properties are less remarkable. The structure-function relationship can be investigated by aberration-corrected high-resolution transmission electron microscopy (HRTEM), which enables the insight into their atomic structure as well as performing spectroscopic measurements down to the atomic scale. In the present work, the deciphering of atomic structure and the chiral angle of the different shells in a multiwall WS2 nanotube is demonstrated. In certain cases, the helicity of the structure can also be deduced. Finally, first electron energy loss spectra (EELS) of a single tube are presented, acquired by a new acquisition technique that allows for high spatial resolution (denoted StripeSTEM). The measured band gap values correspond with the values found in literature for thin films, obtained by spectroscopic techniques, and are higher than the values resulting from STM measurements.

Multiwall WS₂ nanotube templates were used as hosts to prepare core-shell Pbl₂@WS₂ nanotubes by a capillarywetting method. Conformal growth of Pbl₂ layers on the inner wall of the relatively wide WS₂ nanotubes (i.d. ca.10 nm) leads to nanotubular structures which were not previously observed in narrow carbon nanotube templates. Image simulation after structural modeling (see picture) showed good agreement with the experimental HRTEM image.

The growth mechanism of WS 2 nanotubes in the large-scale fluidized-bed reactor is studied in greater detail. This study and careful parameterization of the conditions within the reactor lead to the synthesis of large amounts (50-100 g/batch) of pure nanotubes, which appear as a fluffy powder, and (400-500 g/batch) of nanotubes/ nanoplatelets mixture (50:50), where nanotubes usually coming in bundles. The two products are obtained simultaneously in the same reaction but are collected in different zones of the reactor, in a reproducible fashion. The characterization of the nanotubes, which grow catalyst-free, by a number of analytical techniques is reported. The majority of the nanotubes range from 10 to 50 micron in length and 20-180 nm in diameter. The nanotubes reveal highly crystalline order, suggesting very good mechanical behavior with numerous applications.

In this article a comparison between inorganic nanoparticles with hollow closed structure and the carbon fullerenes and nanotubes is undertaken. First, the structural evolution of inorganic fullerene-like (IF) nanoparticles of MoS₂ as a function of their size is examined in some detail and compared to that of carbon and BN fullerenes. It is shown that hollow closed structures of MoS₂ are stable above 3 nm (app 103 atoms). In the range of 3-8 nm (103-105) nanooctahedra with metallic character are the most stable form of MoS₂ Semiconducting nanotubes and quasispherical IF nano-particles become the stable-most form beyond that size and the bulk (platelets) are stable above about 0.2 μm. The stability of inorganic nanotubes is also discussed. The scaling-up of the synthesis of IF-WS ₂ and the very recent successful synthesis of large, amounts of pure WS₂ nanotubes are briefly described. The stability of IF and INT of MoS₂ (WS₂) under pressure and that of carbon is also discussed. Applications of the IF-WS₂ as superior solid lubricants, which lead to their recent commercialization, is demonstrated.

We report on the first nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) investigation of inorganic fullerene-like MoS ₂ nanoparticles. Spectra of bulk 2H-MoS₂ samples have also been measured for comparison. The similarity between the measured quadrupole coupling constants and chemical shielding anisotropy parameters for bulk and fullerene-like MoS₂ reflects the nearly identical local crystalline environments of the Mo atoms in these two materials. EPR measurements show that fullerene-like MoS₂ exhibits a larger density of dangling bonds carrying unpaired electrons, indicative of them having a more defective structure than the bulk sample. The latter observation explains the increase in the spin-lattice relaxation rate observed in the NMR measurements for this sample in comparison with the bulk 2H- MoS₂ ones.

A new type of composite metal-nanoparticle coating that significantly reduces the friction force of various surfaces, particularly archwires in orthodontic applications, is demonstrated. The coating is based on electrodeposited Ni film impregnated with inorganic fullerene-like nanospheres of tungsten disulphide. The first encouraging tests have shown reduction of up to 60% of the friction force between coated rectangular archwires and self-ligating brackets in comparison with uncoated archwires. The coating not only significantly reduces friction of commercial archwires but also maintains this low value of friction for the duration of the tests in comparison to archwires coated with nickel film without the nanoparticles. The coated surfaces of the wires were examined by scanning electron microscopy equipped with energy dispersive analyzer and by x-ray powder diffraction methods before and after the friction tests. Using these analyses, it was possible to qualitatively estimate the state of the Ni+IF-WS₂ coating before and after the friction test compared to Ni coated wires without IF-WS₂.

The adsorption kinetics of thiophene on WS₂ nanoparticles with fullerene-like (onion-like) structure has been studied at ultra-high vacuum conditions by sample temperature ramping techniques. At low temperatures, thiophene adsorbs molecularly. The formation of H₂S and alkanes is evident at greater temperatures on fully sulfided as well as reduced and oxidized WS₂ nanoparticles.

Inorganic fullerene-like (IF) Mo_1-xRe_xS₂ and W_1-xRe_xS₂ nanoparticles have been synthesized by a gasphase reaction involving the respective metal halides with H₂S. The IF-Mo(W)_1-xRe_xS₂ nanoparticles, contain - ing up to 5% Re, were characterized by a variety of experimental techniques. Analyses of the X-ray powder diffraction and different electron microscopy techniques show that the Re is doped in the MoS₂ host lattice. Interestingly, Re-dop ed MoS₂ nanotubes are present as well, although in small quantities (∼5%). XPS results confirm the nanoparticles to be more n-type arising from the effect of Re doping. Additionally, density-functional tight-binding (DFTB) calculations support the observed n-type behavior.

The time dependent chemical changes occurring at the surface of inorganic fullerene-like (IF) nanoparticles of WS₂ were investigated using X-ray photoelectron spectroscopy (XPS) and compared to those of bulk powder, 2H-WS₂. It was possible to follow the long term surface oxidation and carbonization occurring at defects on the outermost surface (0001) molecular layers of the inorganic fullerene-like nanoparticles. Vacuum annealing was shown to remove most of these contaminants and bring the surface close to its pristine stoichiometric composition. In accordance with previous measurements, further evidence was obtained for the existence of water molecules, which were entrapped in the hollow core and interstitial defects of the fullerene-like nanoparticles during the synthesis. These water molecules were also shown to be removable by the vacuum annealing process. Chemically resolved electrical measurements (CREM) in the XPS showed that the IF samples had become less p-type after the vacuum annealing. Finally, tribological measurements showed that the vacuum annealed IF samples performed better as an oil additive than the non-annealed IF samples and the 2H-WS₂ powder.

WS₂ inorganic fullerene-like (IF) nanoparticles were subjected to intercalation with potassium, sodium, and rubidium atoms in heated sealed ampules. The product of the intercalation process was not pure and was composed of both intercalated and nonintercalated phases. X-ray diffraction measurements under inert conditions of the intercalated powders showed that the interlayer expansion was correlated with the alkali metal radius. Small increase of the a-axis was observed as well and was explained on the grounds of the WS₂ band structure. The XPS analysis of the rubidium intercalated material showed a rise in the Fermi energy as a result of the intercalation, endowing the originally p-type nanoparticles an n-type character.

Inorganic fullerene-like (IF) nanoparticles and nanotubes of WS₂ were synthesized by a gas phase reaction starting from WCl_n (n = 4, 5, 6) and H₂S. 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-WS₂ 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-WS₂ 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 WS₂.

This review summarizes recent work on the polymer-assisted fabrication of well-defined inorganic and organic nanoparticles with controlled shape, size, and functional properties. The discussion concentrates on the physical-chemical aspects of the problem. Special attention is paid to the preparation of nanocomposites with individual (non-aggregated) nanoparticles with narrow size distribution and versatile morphologies, including the design of nanoparticles and nanocomposites that can serve multifunctional purposes. We have focused also on the problem of the spatial arrangement of nanoparticles and elucidation of the role of polymers in this process because it is a key problem in nanotechnology industrialization. The potential applications of nanoparticles encapsulated in polymers and in nanocomposites are briefly discussed. We try also to emphasize the synergistic role of the ingredients on the performance of nanocomposites.

Back in 1992 it was proposed that nanoparticles of layered compounds will be unstable against folding and will close up into fullerene-like structures (IF) and nanotubes. In the years that followed nanotubes and fullerene-like structures were synthesized from numerous compounds with layered structure. More recently, crystalline and noncrystalline nanotubes of compounds with a 3D, i.e., quasi-isotropic lattice have been intensively investigated. In view of their eminent applications potential, much effort and substantial progress has been achieved in the scaling-up of the synthesis of inorganic nanotubes and fullerene-like nanoparticles of WS(2) and MoS(2) and also other compounds. Early on it was suggested that hollow nano-octahedra consisting of a few hundred MoS(2) moieties make the true analogs of C(60), etc. This notion has been advanced considerably in recent years through a combined experimental-theoretical effort. Substantial progress has been accomplished in the use of such nanoparticles for tribological applications and lately for impact resilient nanocomposites. These tests indicated that IF-MoS(2) and IF-WS(2) are heading for large-scale applications in the automotive, machining, aerospace, electronics, defense, medical and numerous other kinds of industries. A few products based on these nanoparticles have been recently commercialized by "ApNano Materials, Inc" ("NanoMaterials, Ltd.", see also www.apnano.com). Most recently, a manufacturing facility for the commercialization of these nanomaterials has been erected and sales of the product started. Novel applications of inorganic nanotubes and fullerene-like nanoparticles in the fields of catalysis; microelectronics; Li rechargeable batteries; medical and optoelectronics will be discussed.

Reactors driven by highly concentrated sunlight can create conditions well suited to the synthesis of inorganic nanomaterials. We report the experimental realization of a broad range of closed-cage (fullerene-like) nanostructures, nanotubes and/or nanowires for MoS₂, SiO₂ and Si, achieved via solar ablation. The solar technique generates the strong temperature and radiative gradients - in addition to the extensive high-temperature annealing environment - conducive to producing such nanostructures. The identity of the nanostructures was established with TEM, HRTEM and EDS. The fullerene-like and nanotube MoS₂ configurations achieved fundamentally minimum sizes predicted by molecular structural theory. Furthermore, our experiments represent the first time SiO₂ nanofibers and nanospheres have been produced purely from quartz. The solar route is far less energy intensive than laser ablation and other high-temperature chemical reactors, simpler and less costly.

In this paper, we report on the synthesis and applications of semiconducting nanostructures. Nanostructures of interest were zinc oxide (ZnO) nanowires and tungsten disulfide WS₂ nanotubes where transistors/phototransistors and photovoltaic (PV) energy conversion cells have been fabricated. ZnO nanowires were grown with both high- and low-temperature approaches, depending on the application. Individual ZnO nanowire side-gated transistors revealed excellent performance with a field-effect mobility of 928 cm² V·s. ZnO networks were proposed for large-area macroelectronic devices as a less lithographically intense alternative to individual nanowire transistors where mobility values in excess of 20 cm² /V·s have been achieved. Flexible PV devices utilizing ZnO nanowires as electron acceptors and for photoinduced charge separation and transport have been presented. Phototransistors were fabricated using individual WS₂ nanotubes, where clear sensitivity to visible light has been observed. The results presented here simply reveal the potential use of inorganic nanowires/tubes for various optoelectronic devices.

Fullerene-like WS ₂ (MoS ₂) nanoparticles (IF) have been studied in the past as solid lubricants. Using the tribological ball-on-flat experiments, it was shown that the size of the aggregates and their distribution determine the penetration and entrapping of the IF nanoparticles at the interface. It is expected that the wedge clearance at the inlet of the contact, i.e., the oblique-angle entrance to the contact zone between the two mating tribological surfaces, as well as the average surface roughness, can limit the supply of the lubricant into the interface in, e.g., the block-on-ring experiment. In the present series of experiments, the Stribeck curve was designed first using a linear loading scheme and pure oil. It was concluded that a wedge clearance (oblique-angle) in the inlet of the contact zone leads to entrapment of the IF nanoparticles and their compaction, which hamper the supply of the fluid lubricant into the interface. A ball-on-flat and flat block-on-ring friction devices with wedge clearance in the inlet of the contact can distort the efficacy of IF. Procedures for improving the supply of the IF nanoparticles to the contact zone and improving thereby their efficacy are considered.

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.

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.

Inorganic fullerene-like (IF) solid lubricant nanoparticles and nanotubes with extremely useful mechanical and tribological characteristics have been realized, offering a plethora of new applications for these nanomaterials. The IF nanoparticles were found to be in the aggregated state. It is expected that the size of the aggregates and their distribution determine the penetration and entrapping of IF nanopowder into the interface. The main goal of the present work is to elucidate the effect of the mixing time of IF-WS₂ nanomaterial in the oil on the size of the IF aggregates and their influence on the friction and wear. The fraction of small aggregates increases and that of the large aggregates decreases with longer mixing time. Consequently, the spread of the tribological results diminishes with the lengthening of the mixing time. The reproducibility of the friction results for the pairs lubricated with oil +IF nanoparticles is determined by distribution of the IF aggregates in the lubricant and the size of the solid lubricant aggregates.

A simple, inexpensive, and reproducible photothermal procedure for synthesizing IF-Cs₂O nanoparticles with immensely concentrated sunlight was demonstrated. The solar-driven synthesis of IF-Cs₂O was performed in evacuated quartz ampoules that contained 3R-Cs₂-O crystallites under continuous irradiation with a concentrated solar power of 2.0-7.7 W, and periods ranging from 30 to 840 s. Samples were collected from the deposit that gathered on the quartz ampoule during the solar irradiation for TEM analysis. The interaction of the beam with the materials led to thermal motion, charging, desorption of trace quantities, or possible chemical changes. The results of the electron energy loss spectroscopy and imaging with a Gatan imaging filters proved that only cesium and oxygen were present in the nanoparticles.

We have proposed in 1992 that nanoparticles of layered compounds will be unstable against folding and close into fullerene-like structures and nanotubes (IF). Nanotubes and fullerene-like structures were prepared from numerous compounds with layered and recently also non-layered structure by various groups. Much progress has been achieved in the synthesis of inorganic nanotubes and fullerene-like nanoparticles of WS₂ and MoS₂ and many other metal dichalcogenides over the last few years. Substantial progress has been accomplished in the use of such nanoparticles for tribological applications and lately for impact resilient nanocomposites. These tests indicated that IF-MoS₂ and IF-WS₂ are heading for large scale applications in the automotive, machining, aerospace, electronics, defense, medical and numerous other kinds of industries. A few products based on these nanoparticles have been recently commercialized by "ApNano Materials, Inc". Novel applications of inorganic nanotubes and fullerene-like nanoparticles in the fields of catalysis; microelectronics; Li rechargeable batteries; medical and opto-electronics will be discussed.

It is well accepted by now that nanoparticles of inorganic layered compounds form closed-cage structures (IF). In particular closed-cage nanoparticles of metal dihalides, like NiCl₂, CdCl₂ and CdI₂ were shown to produce such structures in the past. In the present report IF-NiBr₂ polyhedra and quasi-spherical structures were obtained by the evaporation/recrystallization technique as well as by laser ablation. When the nanoclusters were formed in humid atmosphere, nickel perbromate hydrate [Ni(BrO₄)₂(H₂O)₆] polyhedra and short tubules were produced, as a result of a reaction with water. Nanooctahedra of NiBr₂ were found occasionally in the irradiated soot. The reoccurrence of this structure in the IF family suggests that it is a generic one. Consistent with previous observations, this study showed that formation of the IF materials stabilized the material under the electron-beam irradiation. The growth mechanism of these nanostructures is briefly discussed.

Inorganic fullerene-like nanoparticles of WS ₂ (IF-WS ₂), are synthesized by a reaction of tungsten oxide with molecular hydrogen and hydrogen sulfide. The synthesized nanoparticles appear as large agglomerates (>40 microns), each one counting thousands of IF nanoparticles. ¹H nuclear magnetic resonance study of these nanoparticles is reported. The measurements show that the prepared product contains water (and possibly some hydrogen) molecules that occupy the voids in the central part of the fullerene-like nanoparticles and the nanopores between the adhering IF-WS ₂ particles. Defects in the IF-WS ₂ structure, arising due to the strain release during the folding of the layers, may result in additional sites for the absorbed water. Vacuum annealing of the powder leads to substantial reduction in the amount of absorbed water molecules.

Electrical resistivity and Hall effect measurements of pellets compacted from fullerene-like WS2 nanoparticles (IF-WS2) and bulk 2H-WS2 powder were carried out using the van der Pauw method over a wide temperature range. In addition IF-WS2 pellets were annealed at elevated temperatures under vacuum in a specially designed system. Arrhenius plots for the conductivities of the WS2 samples (2H, IF and IF+annealing) exhibit marked uprise of partial derivative In (sigma T-1)/partial derivative T-1 with temperature. The resistivity of the non-annealed IF-WS2 pellets is higher by 2-8 orders of magnitude than that of 2H-WS2 pellets, whereas the resistivity of the annealed IF pellets is higher than that of the non-annealed ones. Hall Effect measurements at 300 K show p-type conductivity and similar carrier concentration for both types of materials. The carrier mobility of 2H-WS2 platelets is found to be in the range of the reported values. However, IF-WS2 pellets have shown an unusually low mobility for a semiconducting material. The experimental data was found to be in a good agreement with a model used for analyzing the conductivity of polycrystalline semiconductors, which takes into consideration fluctuations of the barrier heights among the different nanoparticles as well as within a single nanoparticle boundary. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bi₂Se₃ nanorods have been synthesized through a simple hydrothermal reduction approach. The nanorods formed were ≈10nm in diameter and 100-200nm in length. XRD characterization suggested that the product consisted of the hexagonal phase of pure Bi₂Se₃. EDX and XPS studies further confirmed the composition and purity of the product. A possible mechanism for the reaction is proposed, where Bi₂Se ₃ microsheets are presumed to be the intermediate for the formation of the nanorods. The effect of solvent on the morphology of the final product is discussed, where, in the presence of aprotic solvent DMF, nanoparticle formation is observed. A bandgap of 2.25eV is observed from the UV-visible absorption spectra.

Fullerene-like WS₂ (MoS₂) nanoparticles (IF) have been studied in the past. Their efficacy as additives for lubrication fluids has been demonstrated. It was shown that the IF nanoparticles are usually delaminated in the inlet of the smooth contact. Thin sheets of broken IF nanoparticles can be entrapped between the rubbed surfaces and thus favorably affect the friction and the wear. Friction pairs at real mechanical macrosystems are often subjected to friction-induced vibrations. It was shown that the mechanical excitations can improve the supplying and preservation of fluid lubricant film in the interface. It can be hypothesized that under vibrations in a definite range of frequencies and amplitudes, the probability for small IF aggregates to be entrapped into the interface is increased. The main goal of this work was to study the effect of artificial mechanical excitations on the friction and wear of contact pairs rubbed with nanoparticles. In order to avoid friction-induced excitations, a new ball-on-flat friction device was developed. The frequency and the amplitude of the ball were varied using a motion of miniature micromotor attached to the ball holder. The behavior of IF nanoparticles in friction tests with and without external mechanical excitations was compared with the tribological behavior of the contact pair lubricated with pure paraffin oil. It was found that the external mechanical excitation of the mechanical parts rubbed with nanoparticles allows a penetration of these nanoparticles into interface. This effect leads to a remarkable shortening of the run-in period and improves the tribological properties of contact pairs. From the present results it may be anticipated that the accidental friction-induced vibrations, which are determined by the stiffness and damping force of the device, lead to preferential penetration of the IF nanoparticles into the contact area, affecting thereby the tribological behavior of the interface.

A new class of inorganic nanostructures with a closed cage structure has been discovered. These inorganic fullerenes are multi-walled (i.e. onion-like) spherical particles which can also be wrapped to form nanotubes. They are extremely effective as solid lubricants, particularly under extreme conditions. The development and initial applications of these materials are reviewed.

We obtained a Raman signal from an individual WS2 nanotube mounted on an atomic force microscopy cantilever tip. We discuss the implications for simultaneous investigations of the mechanical properties of WS2 nanotubes by combining different experimental methods. From the orientation dependence of this nanotube's resonant Raman intensity, we estimate the ratio of the perpendicular to parallel polarizabilities αXXαZZ0.16. We compare the WS2 nanotube with single-walled carbon nanotubes and expect a similarly strong depolarization effect for multiwalled carbon nanotubes.

TiS2 nanoparticles with nested fullerene-like structure (IF) 60-120 nm in size consisting of up to 100 concentric molecular layers and having quite a perfectly spherical shape were obtained by reacting TiCl4 and H2S using first a horizontal and subsequently a vertical reactor. The proposed growth mechanism of these nanoparticles, i.e. nucleation and growth, is radically different from the one proposed for the growth of the fullerene-like WS2 from the respective oxide nanoparticles. It was found that adding 1-2% IF-TiS2 improves the behavior of lubricating oil substantially. The improved performance of the additive was attributed to the nearly spherical shape of the nanoparticles which promotes rolling friction.

Inorganic closed-cage nanoparticles of TiS₂ were synthesized using gas-phase synthesis. The reported nanoparticles are perfectly spherical with diameters centered between 60 and 80 nm, consisting from up to 80-100 concentric layers. The nucleation and growth mechanism was proposed for the formation of these nanoparticles. Tribological experiments emphasized the important role played by the spherical shape of the nanoparticles in providing rolling friction with a reduced friction coefficient and wear.

Fullerene-like WS₂ (MoS₂) nanoparticles (IF) have been studied in the past. It was shown that the IF nanopaticles appear to form a protective film allowing increased load capacity of the rubbed pairs under mixed lubrication. The main objective of the present work is to evaluate the behavior of the IF nanoparticles under severe contact conditions - the transition to seizure. The effect of the IF nanoparticles burnished to porous alumina matrix on friction and wear of alumina-Si₃N₄ pair under high contact pressure is also considered. It was shown that when the gap between the contact surfaces is smaller than the size of the IF nanoparticles, there is no effect of the nanopaprticles on the friction force. With load increasing, the IF nanoparticles penetrate into the interface, protecting the rubbed surfaces from a direct contact and thus increase the critical point of transition to seizure. Burnishing of the porous alumina surfaces by the IF solid lubricant nanoparticles provides very low friction coefficient and wear loss under high contact pressure. The IF-WS₂ nanoparticles are found to be preserved in the rough summits, fill the valleys, and the pores of the sintered alumina and thus limit the straight contact between the ceramic surfaces. Although the external sheets of the outermost layers of the IF-WS₂ nanoparticles were peeled-off, the pristine IF nanoparticles remain in the valleys and pores of the alumina supplying the solid lubricant sheets to the contact area during a long-term test.

Recently, the behavior of inorganic fullerene-like (IF) WS₂ nanoparticles in the interface of steel-on-steel pair has been analyzed. It was shown that originally when the gap between the contact surfaces is smaller than the size of the IF nanoparticles, there is no effect of the nanoparticles on the friction force. During the test stiff IF nanoparticles can plough the surface of hard steel samples and penetrate into the interface under friction. Molecular sheets of WS₂ from the delaminated IF nanoparticles, which reside in the valleys of the rough surfaces cover the contact spots and thus decrease the number of adhered spots at the transition to seizure. The goal of the present work was to study the behavior of IF nanoparticles in the interface of ceramic surfaces. The friction tests were performed using a ball-on-flat device. A silicon nitride ball was slid against an alumina flat with maximum contact pressure close to 2 GPa. SEM, TEM and AFM techniques have been used in order to assess the behavior of IF nanoparticles in the interface. The behavior of IF nanoparticles in the much harder ceramic interfaces was found to be appreciably different from the steel pair. The pristine IF nanoparticles are damaged in the inlet of the contact during the first few cycles and thin shells of broken nanoparticles gradually cover the middle range of the contact surface. Different modes of deformation and destruction of the IF nanoparticles are exhibited when going from the middle to edge area of the contact. While aggregates of the pristine nanoparticles are formed at the edge of the contact, thin shells of broken IF nanoparticles are observed in the middle area where contact pressure is maximum. Mechanical stability and damage of IF nanoparticles in the ceramic interface are discussed.

Oxides of cesium play a key role in ameliorating the photoelectron emission of various opto-electronic devices. However, due to their extreme reactivity, their electronic and optical properties have hardly been touched upon. With the objective of better understanding the electronic and optical properties of Cs₂O in relationship to its structure, an experimental and theoretical study of this compound was undertaken. First-principles density functional theory calculations were performed. The preferred structural motif for this compound was found to be anti-CdCl₂. Here three Cs-O-Cs molecular layers are stacked together through relatively weak van-der-Waals forces. The energy bands were also calculated. The lowest transition at 1.45 eV, was found to be between the K point in the valence band to the Γ point in the conduction band. A direct transition at 2 eV was found in the center (Γ) of the Brillouin zone. X-ray powder diffraction, transmission electron microscopy and selected area electron diffraction were used to analyze the synthesized material. These measurements showed good agreement with the calculated structure of this compound. Absorption measurements at 4.2 K indicated two optical transitions with somewhat higher energy (indirect one at 1.65 and a direct transition at 2.2 eV, respectively). Photoluminescence measurements also showed similar transitions, suggesting that the lower indirect transition is enhanced by three nearby minima at 1.5 eV in the Brillouin zone.

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 microscope(1) 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 density-functional 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.

We have proposed in 1992 that nanoparticles of layered compounds will be unstable against folding and close into fullerene-like structures and nanotubes (IF). Initially this hypothesis was realized in WS2, MoS2 and the respective diselenides. Subsequently, nanotubes and fullerene-like structures were prepared from numerous compounds with layered and recently also non-layered structure by various groups. Much progress has been achieved in the synthesis of inorganic nanotubes and fullerene-like nanoparticles of WS2 and MoS2 and many other metal dichalcogenides over the last few years. Synthetic methods for the production of multiwall WS2 nanotubes by sulfidizing WO3 nanoparticles have been described and further progress is underway. A fluidized-bed reactor for the synthesis of up to half a kg/day of fullerene-like WS2 nanoparticles has been established in our lab, and the scaling-up of the synthesis to 100 kg/day is under way. The detailed mechanisms for the synthesis of fullerene-like WS2 and MoS2 nanoparticles and nanotubes of these compounds have been elucidated. Substantial progress has been accomplished in the use of such nanoparticles for tribological applications and lately for nanocomposites, e.g. for impact resilient materials for self-protection. Few testing programs have been undertaken together with major industrial partners and have clearly indicated the usefulness of the fullerene-like WS2 (MoS2) as solid lubricants in various products. These tests indicated that IF-MoS2 and IF-WS2 are heading for large scale applications in the automotive, machining, aerospace, electronics, medical and numerous other kinds of industries. This technology was licensed to "NanoMaterials", which is currently involved in many collaborative development programs. Orders for about 1000 tons/year have been secured and further orders from major industrial partners are expected shortly. Novel applications of inorganic nanotubes in the fields of microelectronics; Li rechargeable batteries; medical and opto-electronic will be presented.

Two-dimensional compounds (like graphite or MoS₂) are capable of bending their layers and forming a closed cage structure, which is denoted the inorganic-fullerene-like (IF) phase in the case of inorganic materials. Simultaneous thermal analysis (TG-DTA) of a number of nanomaterials (IF-MoS ₂, IF-NbS₂, and IF-WS₂) and their bulk counterparts was carried out in inert and oxidizing environments at various heating rates. Oxidation occurred at 295°C for the smallest particle size (100 nm) but the oxidation temperature increased to 440°C for the largest particle size (3 μm). At low heating rates, the oxidation occurred through sulfates and lower oxides, while at high heating rates mostly one-step oxidation to the highest oxide was observed. The stability in N₂ atmosphere depended on the criterion of stability chosen: Choosing the onset temperatures of the decomposition step (between 1200°C and 1390°C), the stability decreased in the order WS₂ ≈ MoS₂ > NbS₂; and the bulk material reacted mostly at higher temperatures compared to the IF-phase. Choosing the extent of decomposition as a measure of stability, no specific trend could be found. Surprisingly, a single IF-WS₂ sample was found to be most stable by both methods. This study shows that IF nanoparticles are comparably (though somewhat less) stable against oxidation as well as decomposition than the bulk material exhibiting the usual plate-like structure.

A study of the tribological behavior of nested inorganic fullerene-like (IF) nanoparticles of WS₂, as a potential additive to base oils is presented. Friction measurement results obtained from three different test rigs over a wide range of normal loads and sliding velocities are shown. Stribeck curves are used to reveal the lubrication regimes where the IF are most effective. It is found that the addition of IF-WS₂ nanoparticles to the base oils results in up to 50% reduction in friction coefficient in the mixed lubrication regime. The mechanism of improved friction and wear behavior with the IF additive is discussed.

Inorganic fullerene-like structures (IF) of the layered hafnium sulfide, Hf₂S, have been synthesized by the laser ablation of HfS₃ in tert-butyl disulfide medium. Apart from the Hf₂S IFs exhibiting quasi-spherical as well as faceted nested-shell geometries, quasi-spherical nanoparticles of HfS were observed by this means. Whereas Hf₂S has anti-NbS₂ structure with S layers sandwiched between two Hf layers, HfS has the nonlayered WC-type structure. The nanoparticles of HfS show excess sulfur in the core, and they do not possess closed-shell geometry. The mechanism of formation of these nanoparticles has also been discussed.

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 WS ₂ nanotubes. The mechanical behavior of the WS₂ nanotubes as atomic force microscope imaging tips gave further support for the measured Young's modulus.

The development of inorganic and fullerene-like nanoparticles from layered compounds is discussed. It is found that most of the inorganic layered materials comprise more than one atomic layer with strong chemical bonds interconnecting between the atoms of the different layers. The Young's modulus of WS₂ nanotubes is also elaborated.

Tin disulfide pellets were laser ablated in an inert gas atmosphere, and closed cage fullerene-like (IF) nanoparticles were produced. The nanoparticles had various polyhedra and short tubular structures. Some of these forms contained a periodic pattern of fringes resulting in a superstructure. These patterns could be assigned to a superlattice created by periodic stacking of layered SnS₂ and SnS. Such superlattices are reminiscent of misfit layer compounds, which are known to form tubular morphologies. This mechanism adds up to the established mechanism for IF formation, namely, the annihilation of reactive dangling bonds at the periphery of the nanoparticles. Additionally, it suggests that one of the driving forces to form tubules in misfit compounds is the annihilation of dangling bonds at the rim of the layered structure.

Nanoparticles of various layered compounds were shown to form closed cage or nanotubular structures, which were designated as inorganic fullerene-like (IF) materials. In particular, closed cage structures and nanotubes were synthesized from NiCl₂ and CdCl₂ in the past. In the present work IF-CdI₂ nanoparticles were synthesized by electron-beam irradiation of the source powder leading to evaporation and subsequent recrystallization into closed nanoparticles with a non-hollow core. This process created polyhedral nanoparticles with hexagonal or elongated rectangular characters. Consistent with previous observations, this study shows that the seamless structure of the IF materials can stabilize phases, which are otherwise unstable under the electron-beam irradiation.

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.

Multiwall WS₂ nanotubes of 40-50 nm diameter were functionalized with n-octadecyl phosphonic acid by sonication in toluene and blended with mixtures of polystyrene (PS) and polymethylmethacrylate (PMMA) to form new nanocomposite (NC) materials. The surface and domain structures were studied by atomic force microscopy (AFM), scanning transmission X-ray microscopy (STXM) and transmission electron microscopy (TEM) for various levels of loading of nanotubes up to 20 wt%. Phase-separated domain size and surface roughness of the nanocomposite films were found to be dramatically reduced relative to the pure homopolymer blend and good dispersal of the nanotubes in the blend matrix was attained.

Recently, it has been established that WS₂ and MoS₂ nanoparticles (inorganic fullerene-like, IF) mixed with oil, and impregnated into porous matrix of powdered materials appear to enhance the tribological properties of mating surfaces in definite loading range in comparison to typical metal dichalcogenide solid lubricants. The main results have been obtained under relatively low pressures. It is important to evaluate the tribological properties of IF when the concentrated contact is obtained. The effect of the IF in oil was studied using pin-on-disk tester in the regime of mixed lubrication. The interaction between the full film and the asperity contact fractions has been considered and the time evolution of the friction force was evaluated. The states of the mating surfaces and the nanoparticles before and after the friction test were studied by transmission electron microscopy (TEM), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). It was established that the IF nanoparticles mixed with oil allow to decrease the fraction of straight asperity contact under mixed lubrication regime and thus improve their tribological properties. TEM analysis showed that the shape of the IF nanoparticles is preserved under low loads. It was found that some of the IF nanoparticles were damaged after the friction at the maximal load of 420 N. The IF nanopaticles appear to form a protective film allowing increased load capacity of the rubbed pairs. The role of the IF solid lubricants as a part of a third body is discussed in this work. The mechanism of friction and wear of the IF nanoparticles are discussed.

Recently it has been established that WS₂ and MoS₂ nanoparticles (IF) mixed in oil, and impregnated into porous matrix of powdered materials appear to enhance the tribological properties in definite loading range in comparison to typical metal dichalcogenides particles. Modification of the contact surface by IF-WS₂ nanoparticles from oil, grease and from pores of densified powdered samples is considered in this work. The role of the IF solid lubricants as a part of a third body is discussed also in this work. The effect of the IF in oil was studied using a pin-on-disk tester. The study of IF in greases and impregnated into the pores of densified matrices was performed using a ring-block tester. The state of the mating surfaces and the nanoparticles before and after the friction test has been studied by TEM, SEM and XPS. It was established that the IF nanoparticles form a protective film allowing an increase in the load capacity of rubbed pairs. The tribological behavior of lithium grease with IF was found to be appreciably better than that of a commercially available grease incorporating MoS₂ platelets (2H). It is found that the IF nanoparticles lead to improved tribological behavior of greases with the IF nanoparticles under very high loads. Impregnation of the IF-WS₂ into the pores of densified powdered materials provides a reduced friction coefficient and wear rate over a wide load range in comparison to 2H solid lubricant. The main advantages of the IF nanoparticles is ascribed to the release and furnishing of the nanoparticles from the open pores onto the metal surface and their confinement at the interface, which is not possible with dense flat surfaces. It is expected that the spherical shape of IF nanoparticles facilitate their sliding/rolling between the rubbed surfaces.

Inorganic Fullerene-like (IF)-MoS2 nanoparticles were tested under boundary lubrication and ultra-high vacuum (UHV) and were found to give an ultra-low friction coefficient in both cases compared to hexagonal (h)-MoS2 material. Previous works made by Rapoport et al. with IF-WS2 revealed that the benefit effect of the inorganic fullerene-like materials decreases at high loads and sliding velocities. Nevertheless, under the conditions used in our experiments using high contact pressure (maximum pressure above 1.1 GPa in oil and 400 MPa in high vacuum) and slow sliding velocities (1.7 mm/s in oil test and 1 mm/s in hi-h vacuum), friction always decreases and stabilizes at about 0.04 for 800 cycles in both cases. Therefore, IF-MoS2 material appears to be a good candidate for use in various environments in regard to other MoS2 crystal structures. Wear mechanisms were investigated using both High Resolution TEM and surface analyses (XPS) on the wear tracks. Wear particles collected from the flat wear scar show several morphologies, suggesting at least two lubricating mechanisms. As spherical particles are found in the wear debris, rolling may be a possible event. However, flattened and unwrapped IF-MoS2 particles are often observed after friction. In this case, low friction is thought to be due either to sliding between IF-MoS2 external flattened planes or to slip between individual unwrapped MoS2 sheets. (C) 2002 Elsevier Science B.V. All rights reserved.

It was shown that nanoclusters of layered compounds, like MoS₂ fold into hollow cage structures of various shapes (IF), including spherical and polyhedral structures, nanotubes of a μm length, etc. Following this discovery a few methodologies for the systematic synthesis of large amounts of MoS₂ and WS₂ nanotubes were pursued. Recently, nanotubes from various other layered compounds were synthesized. The structural, optical and electrochemical properties of MoS₂ (WS₂) and other nanotubes were investigated in some detail. It was found that MoS₂ nanotubes are semiconductors with a tunable bandgap, which decreases, as the diameter of the nanoparticle decreases. The fullerene-like WS₂ and MoS₂ nanparticles were found to have interesting tribological properties, which makes them suitable as both additives to lubricating fluids and as dry lubricants, suggesting numerous applications for these nanomaterials.

One of the main advantages of powder metallurgy technology is controlled porosity for self-lubrication. To decrease friction and wear of contact pairs, solid lubricants such as WS₂ and MoS₂ are used. Recently, inorganic fullerene-like supramolecules of WS₂ and MoS₂ with structures closely related to carbon fullerenes and nanotubes have been synthesized. Experiments showed that the supramolecules possess lubricating properties superior to those of layered materials, in which each unit cell contains two layers with a hexagonal arrangement. It is expected that the fabrication of densified powders containing solid lubricant nanoparticles will lead to the development of a new class of composites with improved mechanical properties. The main goal of the present work was to study material and process parameters for the formation of a porous matrix and the impregnation of nanoparticles. Self-lubricating sintered bronze, iron and iron-nickel base composites were produced. Friction and wear results for the powder materials impregnated with layered materials and supramolecules as solid lubricants are presented.

The impregnation of inorganic fullerene-like nanoparticles of WS₂ (IF) allows to improve effectively the tribological properties of powdered materials in comparison to the impregnation of oil or commercially available layered WS₂ (2H) particles. The main goal of this work was to determine the dominant lubrication regimes under friction of the bronze, iron, and iron-nickel porous matrixes impregnated with 2H and IF solid lubricants. The tribological tests were performed at laboratory atmosphere (humidity Ο50%) using a ring-on-block tester at the sliding speed of V = 1 m/s, and the loads of 150-1000 N. The wear of the metal bodies was measured by an eddy current probe system and by weighting of the samples before and after the test. In order to evaluate the radial clearance, the profiles of wear blocks were analyzed by profile projector. Than these data were used in the calculation of the Sommerfeld reciprocal values. Friction and wear results were presented as the Stribeck curves. The critical Sommerfeld reciprocals were evaluated from these curves. The Stribeck curves were compared with the Morgan's curves for different ranges of non-dimensional permeability, ψ. These results are used then in calculation of the permeability, Φ. Three lubrication regimes as: quasi-hydrodynamic, boundary or mixed, and dry friction were revealed under friction of porous samples in the load-range studied. It was found that the impregnation of IF nanoparticles provides the regime of quasi-hydrodynamic lubrication in the widest range of loads in comparison to the reference sample and the sample impregnated with 2H-WS₂. Fe-Ni samples exhibited the highest wear resistance and provided the widest range of quasi-hydrodynamic lubrication in comparison to bronze and iron powdered composites. The effect of IF on the regimes of lubrication is explained on the base of the third-body model. It is expected that the sliding/rolling of the IF nanoparticles in the boundary of the first bodies and in between the wear particles (third-body) facilitate the shear of the lubrication film and thus provide the quasi-hydrodynamic regime of friction. It is supposed that the roll shape of IF nanoparticles allows to release the IF from the pores to contact surfaces.

The synthesis of multigram portions of WS₂ nanotubes and large foils consisting of aligned nanotubes was presented. Nanotubes and fullerene-like nanoparticles of WS₂ were observed by annealing very thin films of tungsten in a H₂S atmosphere. It is found that a slow in-diffusion of the sulfur and out-diffusion of the oxygen leads to a conversion of the oxide core into a multilayer WS₂ nanotube.

NbS₂ nanoparticles with a closed cage structure (inorganic fullerene-like phase - IF) were synthesized by reaction between NbCl₅ vapor and H₂S gas in a reducing atmosphere at 400°C, and subsequent annealing under a H₂S/H₂ atmosphere at 550°C. Following the synthesis, the nanoparticles were found to have a large excess of Nb; they were agglomerated; highly dislocated and enfolded by amorphous material. After annealing, most of the amorphous material crystallized into closed NbS₂ shells, and the nanoparticles appeared to be much more faceted. Transmission electron microscopy revealed that the interlayer spacing (c/n) of the annealed particles had decreased. They were also agglomerated, being connected to neighboring nanoparticles through their outer NbS₂ layers after annealing. In related experiments Nb₂O₃ nanofibers, which organize into a nanoflower superstructure, and also NbS₂ nanofibers were synthesized under somewhat different growth conditions.