Atomic layer deposition on gram quantities of multi-walled carbon nanotubes

Atomic layer deposition (ALD) was employed to grow coaxial thin films of Al2O3 and Al2O3 /W bilayers on multi-walled carbon nanotubes (MWCNTs). Although the MWCNTs have an extremely high surface area, a rotary ALD reactor was successfully employed to perform ALD on gram quantities of MWCNTs. The uncoated and ALD-coated MWCNTs were characterized with transmission electron microscopy and x-ray photoelectron spectroscopy. Al2O3 ALD on untreated MWCNTs was characterized by nucleation difficulties that resulted in the growth of isolated Al2O3 nanospheres on the MWCNT surface. The formation of a physisorbed NO2 monolayer provided an adhesion layer for the nucleation and growth of Al2O3 ALD films. The NO2 monolayer facilitated the growth of extremely conformal coaxial Al2O3 ALD coatings on the MWCNTs. Cracks were also observed in the coaxial Al2O3 ALD films on the MWCNTs. After cracking, the coaxial Al2O3 ALD films were observed to slide on the surface of the MWCNTs and expose regions of bare MWCNTs. The Al2O3 ALD film also served as a seed layer for the growth of W ALD on the MWCNTs. The W ALD films can significantly reduce the resistance of the W/Al2O3/MWCNT wire. The results demonstrate the potential for ALD films to tune the properties of gram quantities of very high surface area MWCNTs.