Recently, milligram quantities of MoS2 fullerene-like nanotubes and negative curvature polyhedra (generically called inorganic fullerene-like material, IF), were reproducibly obtained by a gas phase reaction from an oxide precursor (Feldman, Y.; Wasserman, E.; Srolovitz, D. J.; Tenne, R. Science 1995, 267, 222. Srolovitz, D. J.; Safran, S. A.; Homyonfer, M.; Tenne, R. Phys. Rev. Lett. 1995, 74, 1778). The present work focuses on the mechanism of the synthesis of IF-MS2 (M = W, Mo). The IF material is obtained from oxide particles smaller than ca. 0.2 μm, while larger oxide particles result in 2H-MS2 platelets. The key step in the reaction mechanism is the formation of a closed layer of MS2, which isolates the nanoparticle from its surroundings and prevents its fusion into larger particles. Subsequently, the oxide core of the nanoparticle is progressively converted into a sulfide nanoparticle with an empty core (IF). Taking advantage of this process, we report here a routine for the fabrication of macroscopic quantities of a pure IF-WS2 phase with a very high yield. As anticipated, the size distribution of the IF material is determined by the size distribution of the oxide precursor. The present synthesis paves the way for a systematic study of these materials which are promising candidates for, e.g., solid lubrication.

Using the paradigm of carbon fullerenes, it is shown that nanoparticles of inorganic compounds with a layered structure, like MoS 2 , are unstable against bending and form hollow closed clusters, designated inorganic fullerene-like structures (IF). The analogy can be extended to similar nanostructures, like nanotubes (NT), nested fullerenes, fullerenes with negative curvature (Schwartzites), etc. Various synthetic routes are described to obtain isolated phases of IF. Pentagons and heptagons are expected to play a primordial role in the folding of these nanostructures but no direct evidence for their presence or their detailed structure exists so far. Depending on the structure of the unit cell of the layered compound, apexes of a different topology, like triangles or rectangles, are believed to be stable elements in IF. Applications of such nanoparticles as solid lubricants in mixtures with lubricating fluids are described. ContentsI. Introduction 3225 II. Typical IF Structures of Metal Dichalcogenides 3229 III. Synthesis of IF Structures 3229 IV. The Structure of MoS 2 (WS 2 ) Nanotubes 3235 V. Applications 3237 VI. Conclusion 3237

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The kinetics of point‐defect association/dissociation reactions in Ce0.8Gd0.2O1.9 and their influence on the crystal lattice parameter are investigated by monitoring thermally induced stress and strain in substrate‐ and self‐supported thin films. It is found that, in the temperature range of 100–180 °C, the lattice parameter of the substrate‐supported films and the lateral dimensions of annealed, self‐supported films both exhibit a hysteretic behavior consistent with dissociation/association of oxygen vacancy–aliovalent dopant complexes. This leads to strong deviation from linear elastic behavior, denoted in the authors' previous work as the “chemical strain” effect. At room temperature, the equilibrium state of the point defects is reached within a few months. During this period, the lattice parameter of the substrate‐supported films spontaneously increases, while the self‐supported films are observed to transform from the flat to the buckled state, indicating that formation of the dopant–vacancy complex is associated with a volume increase. The unexpectedly slow kinetics of establishing the defect equilibrium at room temperature can explain the fact that, depending on the sample history, the “observable” lattice parameters of Ce0.8Gd0.2O1.9, as reported in the literature, may differ from one another by a few tenths of a percent. These findings strongly suggest that the lattice parameter of the materials with a large concentration of interacting point defects is a strong function of time and material preparation route.

Oxidation and corrosion reactions have a major effect on the application of non-noble metals. Kinetic information and simple theoretical models are often insufficient for describing such processes in metals at the nanoscale, particularly in cases involving formation of internal voids (nano Kirkendall effect, NKE) during oxidation. Here we study the kinetics of solid-state oxidation of chemically-grown copper nanoparticles (NPs) by in situ localized surface plasmon resonance (LSPR) spectroscopy during isothermal annealing in the range 110-170 °C. We show that LSPR spectroscopy is highly effective in kinetic studies of such systems, enabling convenient in situ real-time measurements during oxidation. Change of the LSPR spectra throughout the oxidation follows a common pattern, observed for different temperatures, NP sizes and substrates. The well-defined initial Cu NP surface plasmon (SP) band red-shifts continuously with oxidation, while the extinction intensity initially increases to reach a maximum value at a characteristic oxidation time τ, after which the SP intensity continuously drops. The characteristic time τ is used as a scaling parameter for the kinetic analysis. Evolution of the SP wavelength and extinction intensity during oxidation at different temperatures follows the same kinetics when the oxidation time is normalized to τ, thus pointing to a general oxidation mechanism. The characteristic time τ is used to estimate the activation energy of the process, determined to be 144 ± 6 kJ mol, similar to previously reported values for high-temperature Cu thermal oxidation. The central role of the NKE in the solid-state oxidation process is revealed by electron microscopy, while formation of CuO as the major oxidation product is established by X-ray diffraction, XPS, and electrochemical measurements. The results indicate a transition of the oxidation mechanism from a Valensi-Carter (VC) to NKE mechanism with the degree of oxidation. To interpret the optical evolution during oxidation, Mie scattering solutions for metal core-oxide shell spherical particles are computed, considering formation of Kirkendall voids. The model calculations are in agreement with the experimental results, showing that the large red-shift of the LSPR band during oxidation is the result of Kirkendall voiding, thus establishing the major role of the NKE in determining the optical behavior of such systems.

While experiments did not confirm earlier speculations on exceptional lubrication behavior of carbon-based fullerenes, inorganic fullerene-like nested nanostructures (IFs) were recently reported to show improved tribological behavior when added to lubricant fluids. [1] In this report, we confirm the tribological advantages of WS 2 IFs as additives to tetradecane between two shearing mica surfaces, and show that the lower friction in this system is associated with friction-induced material transfer of WS 2 from the IFs to the mica surfaces. While the material transfer occurs via delamination and structural degradation of the IFs, their addition to conventional lubricant fluids provides an effective route for in situ deposition of an ultrathin solid lubricant coating on the shearing surfaces.Spherical molecules such as C 60 and C 70 were speculated to have tribological advantages due to their high frequency rotation in the solid lattice, which would allow them to act as molecular ball bearings at shearing interfaces. Nevertheless, despite the large number of experimental studies, this issue remains controversial. Addition of C 60 to fluid lubricants has been shown to dramatically reduce the viscous drag at the solid±liquid interface, [2±5] and other earlier studies reported encouraging results. [6,7] On the other hand, organic fullerene-based solid lubricant films were reported to show disappointing friction and wear properties, [8±10] failed to produce coatings of commercial value, [11] and fullerene additives were reported to offer no advantage over conventional additives. [12] Coatings of Mo and W chalcogenides were reported to be effective solid lubricants [13] which exhibit a prolonged wear life. [14] The tribological properties were shown to be highly sensitive to the atmosphere due to chemical reactions with oxygen and water under shearing conditions. [15±18] While the low friction of metal chalcogenide solid lubricants is often explained by the facile shear of the c-planes of the 2H lattice, this mechanism cannot explain their unusually long

The dark‐field diffraction contrast of helical nanotubes (NTs) is shown to be asymmetric when an NT is tilted at appropriate angle with respect to the incident electron beam. This phenomenon was used for the chirality determination of multi‐shell NTs observed in MoS2 layered compound. Both kinds of NT — helical and non‐helical — were found. In the case of helical NTs only right‐hand chirality was observed.

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