Conformal Coating of Carbon Nanotubes

There is great interest in the growth, functionalisation and application of carbon nanotubes. Growth and coating can be combined in a single tool.

Here we show that the growth and functionalisation of carbon nanotubes can be performed in a vacuum environment using OIPT’s Nanofab800Agile and FlexAL tools. Carbon nanotubes were grown through thermal chemical vapour deposition (CVD) and plasma-enhanced chemical vapour deposition (PECVD) processes to give the dense carbon nanotubes and vertical carbon nanotubes respectively.

Atomic Layer Deposition (ALD) processes were then employed to coat the carbon nanotubes. Both the dense and vertical carbon nanotube samples survive the oxygen plasma steps of the ALD processes. After the ALD deposition of Al2O3, there is no obvious change on the morphology of the carbon nanotubes, also no lump materials of Al2O3 can be observed through scanning electron microscope (SEM). The presence of Al2O3 on the treated carbon nanotube samples is verified though energy dispersive X-ray analysis (EDX). Fig.1 and Fig.2 show the SEM images and EDX spectrum from Al2O3 coated vertical carbon nanotubes and dense carbon nanotubes. These implied that the coating of Al2O3 was conformal.

Control of the coating thickness may provide a non-destructive approach to functionalise carbon nanotubes, moreover the growth and coating step can in principle be performed in vacuum in a single tool, which is attractive to the semiconductor industry.

Fig 1. The SEM image and EDX spectrum of Al2O3 coated vertical carbon nanotubes (a) SEM image of Al2O3 –coated vertical carbon nanotubes (b) EDX spectrum shows the presence of Al and O (Co is the catalyst at the tip of carbon nanotubes, Si is from the substrate). 

Fig 2. The SEM image and EDX spectrum of Al2O3 coated dense carbon nanotubes (a) SEM image of Al2O3 –coated dense carbon nanotubes (b) EDX spectrum shows the presence of Al and O (C is not indicated).