On the mechanical behavior of WS ₂ nanotubes under axial tension and compression

Abstract

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.

Atom by atom: HRTEM insights into inorganic nanotubes and fullerene-like structures

“…This insight is of great importance, because it confirms the fact that the outer shells are most likely either armchair or zigzag and not chiral. Therefore, theoretical calculations can be used to understand various measurements [e.g., mechanical measurements of a tensile stress-strain test on individual nanotubes (17)]. These calculations are facilitated using a nonchiral tube because of the computation time and complexity.…”

“…WS 2 nanotubes were discovered in the early 1990s, and since then they have been the subject of intensive study (2,(17)(18)(19)(20). This structure is fascinating, because it also exhibits properties that differ from the bulk 2H material.…”

“…This contrasts with carbon nanotubes and QDs (23), where the bandgap increases with the shrinking size of the nanoparticles because of quantum confinement of the electron (hole). Furthermore, the mechanical behavior of the nanotubes considerably outweighs that of the bulk material (17).…”

Structure and Stability of Molybdenum Sulfide Fullerenes

“…[1][2][3] Theoretical investigations provided a basic understanding of the electronic and mechanical properties of the INTs. [4][5][6][7] These materials are currently being contemplated for numerous applications, in particular, as superior solid lubricants and as impact-resistant nanocomposites. [8] Bulk synthesis of the IFs normally yields quasispherical nanoparticles with at least 20 molecular layers and outer diameters of greater than 30 nm.…”

“…[4][5][6][7] The value of e vdW was taken as twice the measured surface energy of MoS 2 . [17] The difference between the numbers of atoms N j and N jÀ1 for two shells of a multilayer nanooctahedron can be determined from the lattice constants a and c of bulk…”