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

Abstract

Atomic layer deposition (ALD) was employed to grow coaxial thin films ofAl2O3 andAl2O3 /W bilayers on multi-walled carbon nanotubes (MWCNTs). Although the MWCNTs havean extremely high surface area, a rotary ALD reactor was successfully employed to performALD on gram quantities of MWCNTs. The uncoated and ALD-coated MWCNTs werecharacterized with transmission electron microscopy and x-ray photoelectron spectroscopy.Al2O3 ALDon untreated MWCNTs was characterized by nucleation difficulties that resulted in the growth ofisolated Al2O3 nanospheres on the MWCNT surface. The formation of a physisorbedNO2 monolayer provided an adhesion layer for the nucleation and growth ofAl2O3 ALDfilms. The NO2 monolayer facilitated the growth of extremely conformal coaxialAl2O3 ALD coatings on the MWCNTs. Cracks were also observed in the coaxialAl2O3 ALD films on the MWCNTs. After cracking, the coaxialAl2O3 ALDfilms 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 theMWCNTs. The W ALD films can significantly reduce the resistance of theW/Al2O3/MWCNT wire. The results demonstrate the potential for ALD films to tune the properties of gramquantities of very high surface area MWCNTs.