The mechanical properties of materials and particularly the strength are greatly affected by the presence of defects; therefore, the theoretical strength (Ϸ10% of the Young's modulus) is not generally achievable for macroscopic objects. On the contrary, nanotubes, which are almost defect-free, should achieve the theoretical strength that would be reflected in superior mechanical properties. In this study, both tensile tests and buckling experiments of individual WS2 nanotubes were carried out in a highresolution scanning electron microscope. Tensile tests of MoS2 nanotubes were simulated by means of a density-functional tightbinding-based molecular dynamics scheme as well. The combination of these studies provides a microscopic picture of the nature of the fracture process, giving insight to the strength and flexibility of the WS2 nanotubes (tensile strength of Ϸ16 GPa). Fracture analysis with recently proposed models indicates that the strength of such nanotubes is governed by a small number of defects. A fraction of the nanotubes attained the theoretical strength indicating absence of defects.inorganic ͉ mechanical properties T he strength of macroscopic objects is determined by the intrinsic (crystalline) properties of the material as well as by such extrinsic factors as grain boundaries, dislocations, vacancies, and other defects (1, 2). These extrinsic factors are affected by the manufacturing processes used for the preparation of a specific specimen. Thus, the strength of macroscopic objects is generally much smaller than the theoretical value of 10% of Young's modulus. This apparent discrepancy highlights the fact that the strength of materials is only partially determined by their intrinsic mechanical properties (1, 2), i.e., the strength of their chemical bonds.In general, the strength of macroscopic materials increases as the scale decreases. In reinforcing fibers for example, this is true whether the scale is taken as the diameter of the fiber or its length. It is also true for the characteristic (or average) dimension of a reinforcing particle or a platelet. This phenomenon is usually called the size effect and can be understood by two distinct arguments, based either on probability or fracture mechanics. From a probabilistic viewpoint, Weibull (3, 4) and Freudenthal (5) proposed a formal link between the probability of occurrence of a critical defect in a solid of (dimensionless) volume, the concentration of defects, and the size (length, area, and volume) of the solid specimen.

Inorganic fullerene-like WS 2 and MoS 2 nanoparticles have been synthesized using exclusively solid precursors, by reaction of the corresponding metal oxide nanopowder, sulfur and a hydrogen-releasing agent (NaBH 4 or LiAlH 4 ), achieved either by conventional furnace heating up to ~900 °C or by photothermal ablation at far higher temperatures driven by highly concentrated white light. In contrast to the established syntheses that require toxic and hazardous gases, working solely with solid precursors permits relatively safer reactor conditions conducive to industrial scale-up.

Inorganic fullerene-like (IF) nanoparticles of MoS 2 were synthesized using gas-phase reaction starting from MoCl 5 and H 2 S . The IF- MoS 2 nanoparticles are spherical and in some cases faceted with diameters in general ranging between 20 and 80 nm. The IF- MoS 2 nanoparticles have large hollow cores, filled in some cases with amorphous material. Various parameters have been investigated to understand the growth and formation of the IF- MoS 2 nanoparticles. The parameters that have been studied include flow rates of the various carrier gases, temperature at which the reaction was carried out, time of the reaction and heating of the precursor material. The best set of conditions wherein maximum yields of the IF- MoS 2 nanoparticles are obtained have been identified. Additionally, annealing the as-obtained samples or heating them in a mixture of H 2 along with H 2 S improves the crystallinity and reduces the amorphous material filling in the core. Apart from the fullerene-like nanoparticles under certain experimental conditions nanotubes of MoS 2 have also been obtained nonetheless in small yields.

Mo(2)C nanoparticles encapsulated within MoS(2) inorganic fullerene-like nanoparticles and nanotubes were produced by carbothermal reaction at 1200-1300 °C inside a vertical induction furnace. The particles were analyzed using various electron microscopy techniques and complementary methods.