| AVS 56th International Symposium & Exhibition | |
| Tribology Focus Topic | Tuesday Sessions |
| Session TR+SS-TuA |
| Session: | Surface Science for Tribology |
| Presenter: | I. Kaplan-Ashiri, Weizmann Institute of Science, Israel |
| Authors: | I. Kaplan-Ashiri, Weizmann Institute of Science, Israel S.R. Cohen, Weizmann Institute of Science, Israel K. Gartsman, Weizmann Institute of Science, Israel G. Seifert, Technische Universität, Germany H.D. Wagner, Weizmann Institute of Science, Israel R. Tenne, Weizmann Institute of Science, Israel |
| Correspondent: | Click to Email |
WS2 forms multiwalled nanotubes which seem to be almost defect free and their structure can be precisely defined. Hence they can serve as good candidates for the study of nanomechanics.
Various mechanical tests were applied on individual WS2 nanotubes to reveal their mechanical properties and behavior. First, nanotubes were axially compressed in atomic force microscope, and their Young's modulus was observed according to Euler's buckling point. An average value of 170GPa was obtained. A similar test which was conducted in the scanning electron microscope resulted in large elastic deformation of the nanotube. Here the Young's modulus was obtained from the post buckling equations, and found to be 150GPa. In a third experiment, the nanotubes were axially strained until fracture occurred. The Young's modulus was then observed according to Hooke's law and found to be 152GPa. These moduli values are in good agreement between themselves and also with density functional tight-binding (DFTB) calculations and the bulk material (150GPa).
Tensile strengths and strain values as high as 16GPa and 14% were observed as well. These values reveal that WS2 nanotubes reached their theoretical strength, hence they are suspected to be defect free. The high strain value is unique to the tubular nanophase of WS2 and is also in good agreement with molecular dynamics simulation of MoS2 nanotubes. The nanotubes were deformed elastically until failure, in "sword in a sheath" mechanism and probably fractured in a brittle mode.
Clamped nanotubes were bent and the shear (sliding) modulus was obtained according to Timoshenko's bending equation and found to be 2GPa. This value is in good agreement with DFTB calculations (4GPa) for sliding of two adjacent layers of MoS2.
Furthermore, a unique nonlinear elastic deformation was observed both in post buckling and in bending tests. This mode of deformation is associated with the tubular structure.