Controlled growth of CNT in mesoporous AAO through optimized conditions formembrane preparation and CVD operation

Abstract

Anodic aluminium oxide (RAAO) membranes with a mesoporous structure were preparedunder strictly controlling experimental process conditions, and physically and chemicallycharacterized by a wide range of experimental techniques. Commercial anodicaluminium oxide (CAAO) membranes were also investigated for comparison.We demonstrated that RAAO membranes have lower content of both water andphosphorus and showed better porosity shape than CAAO. The RAAO membraneswere used for template growth of carbon nanotubes (CNT) inside its pores byethylene chemical vapour deposition (CVD) in the absence of a catalyst. A compositematerial, containing one nanotube for each channel, having the same length as themembrane thickness and an external diameter close to the diameter of the membraneholes, was obtained. Yield, selectivity and quality of CNTs in terms of diameter,length and arrangement (i.e. number of tubes for each channel) were optimized byinvestigating the effect of changing the experimental conditions for the CVDprocess. We showed that upon thermal treatment RAAO membranes were madeup of crystallized allotropic alumina phases, which govern the subsequent CNTgrowth, because of their catalytic activity, likely due to their Lewis acidity. Thestrict control of experimental conditions for membrane preparation and CNTgrowth allowed us to enhance the carbon structural order, which is a criticalrequisite for CNT application as a substitute for copper in novel nano-interconnects.