Super growth of vertically aligned carbon nanotubes on pulsed laser deposited catalytic thin films

Abstract

Efficient and reproducible growth of vertically aligned carbon nanotube (CNT) forests by catalytic chemical vapor deposition (CVD) requires precise setting of the properties of the catalyst thin films and CVD conditions. In this work, super growth of vertically aligned CNTs onto Al2O3 support and Fe–Co catalyst layer system is presented. The layers were grown by pulsed laser deposition (PLD) onto silicon wafer pieces. Their thickness and optical properties were controlled by spectroscopic ellipsometry. The effect of heat treatment at 750 °C in nitrogen and in hydrogen of these PLD layers was compared. High-resolution electron microscopic images showed that treatment of catalyst layers in H2 resulted in finer and denser catalytic particles. As a result, well-aligned, dense and few-walled CNT forests with 1–1.5 mm height were deposited by water-vapor-assisted CVD on the hydrogen-treated films, while without hydrogen treatment defected CNT structures were grown. According to these observations, Raman spectroscopy showed a higher degree of crystallinity in case of CNT-s, where reduction by hydrogen influenced the oxidation state of the metallic catalytic particles in a beneficial way.