Mechanical behavior of individual WS 2 nanotubes
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Mechanical behavior of individual WS2 nanotubes I. Kaplan-Ashiri Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, 76100 Israel
S.R. Cohen and K. Gartsman Chemical Research Support, Weizmann Institute of Science, Rehovot, 76100 Israel
R. Rosentsveig Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, 76100 Israel
G. Seifert Institut fur Physikalische Chemie, Technical University, Dresden, 01062 Germany
R. Tennea) Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, 76100 Israel (Received 31 July 2003; accepted 23 September 2003)
The Young’s modulus of WS2 nanotubes is an important property for various applications. Measurements of the mechanical properties of individual nanotubes are challenged by their small size. In the current work, atomic force microscopy was used to determine the Young’s modulus of an individual multiwall WS2 nanotube, which was mounted on a silicon cantilever. The buckling force was measured by pushing the nanotube against a mica surface. The average Young’s modulus of an individual WS2 nanotube, which was calculated by using Euler’s equation, was found to be 171 GPa. First-principle calculations of the Young’s modulus of MoS2 single-wall nanotubes using density-functional–based tight-binding method resulted in a value (230 GPa) that is close to that of the bulk material. Furthermore, the diameter dependence of the Young’s modulus in both zigzag and armchair configuration was studied and was found to approach the bulk value for nanotubes with few-nanometer diameters. Similar behavior is expected for WS2 nanotubes. The mechanical behavior of the WS2 nanotubes as atomic force microscope imaging tips gave further support for the measured Young’s modulus.
I. INTRODUCTION
The synthesis of inorganic fullerene (IF)-like nanoparticles and nanotubes was first reported in 1992.1 A number of methods have been developed for the synthesis of WS2 (MoS2) multiwall nanotubes.2 At present, by using the fluidized bed reactor (FBR) with somewhat modified conditions, WS2 nanoparticles with fullerene-like structure enriched by 5% WS2 chiral multiwall nanotubes are obtained.3 The length of the nanotubes varied from several hundred nanometers to several micrometers. Along with these, much longer (up to 0.3 mm) nanotubes were observed. The nanotubes are also quite uniform in shape and are open-ended. Their outer diameter varies from 10 to 30 nm, with the main size distribution centered between 15 and 20 nm. The typical number of layers in a nanotube varies, being 5–8. Thus, the hollow core of the
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J. Mater. Res., Vol. 19, No. 2, Feb 2004
nanotubes occupies up to 70% of their total volume. The nanotubes were found to be quite perfectly crystalline and almost defect free. These nanotubes exhibit
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