"These materials can be strained to over 12% of their initial length and at the same time yield under tensile stress of about 20 GPa," Reshef Tenne of the Weizmann Institute told nanotechweb.org. "The mechanical properties of macroscopic materials are dictated by their composition and the occurrence of ubiquitous grain boundaries and defects such as vacancies, dislocations etc. Nanotubes like ours are perfect."
Tenne and colleagues tested the mechanical properties of the nanotubes in a high resolution scanning electron microscope. They attached the nanotubes to two atomic force microscope cantilevers, applying the force through the upper cantilever. The researchers believe that this technique applied force only to the outer shell of the nanotube.
The nanotubes exhibited a Young's modulus of 152 GP (±68), a strength of 3.7–16.3 GPa (±11%) and an elongation of 5–14% (±0.1%). The strongest nanotubes had a strength that was around 11% of the Young's modulus. This roughly corresponds to the material's theoretical strength, indicating that the nanotubes were largely free of critical defects.
Theoretical modelling of the behaviour of defect-free single-wall molybdenum sulphide nanotubes, which have the same structure as the tungsten sulphide tubes, gave results that agreed well with these values. The model suggested that fracture began at atomistic defects.
The tungsten sulphide nanotubes could have applications in nanocomposites, solid state lubrication and nanomachines.
Now the team plans to synthesize macroscopic amounts of the material. "We are well on our way to achieve this goal," said Tenne. "Second is to look into their electronic and optical properties in detail, and understand the structure-properties relationship."
The researchers reported their work in PNAS.