Improvement of the mechanical properties of single-walled carbon nanotube networks by carbon plasma coatings

Carbon vacuum arc was used to deposit 5–25 nm thick carbon coatings on single-walled carbon nanotube (SWCNT) networks. The SWCNT bundles thus embedded in conformal coatings maintained their optical transparency and electrical conductivity. Sheet resistances of the networks were measured during the vacuum arc deposition, revealing initially a 100-fold increase, followed by significant recovery after exposing the samples to an ambient atmosphere. Nanoindentation measurements revealed improved elasticity of the network after applying the carbon coating. Pristine SWCNT networks were easily deformed permanently, but a 20 nm carbon coating strengthened the nanostructure, resulting in a fully elastic recovery from a 20 μN load applied with a Berkovich tip. In nano-wear tests on selected areas, the coated SWCNT maintained its networking integrity after two passes raster scan at loads up to 25 μN. On the other hand, the pristine networks were badly damaged under a 10 μN scan load and completely displaced under 25 μN. Raman and electron energy loss spectroscopies indicated the carbon coating on bundles to be mainly sp2 bonded. Finite element modeling suggests that the low content of sp3 bonds may be due to heating by the intense ion flux during the plasma pulse.