Controlled Syntheses of Aligned Multi-Walled Carbon Nanotubes: Catalyst Particle Size and Density Control via Layer-by-Layer Assembling

Using the layer-by-layer assembly method, we have fabricated catalyst particles of a controlled size distribution and packing density for aligned carbon nanotube growth. In particular, poly(sodium-4-styrenesulfonate), PSS, and iron hydroxide colloid were layer-by-layer assembled via the electrostatic interaction onto an acetic-acid-plasma treated quartz plate. This multilayer catalyst precursor film was then calcined in Ar/H 2 at 750 °C to produce iron nanoparticles for the subsequent growth of carbon nanotubes at 750 °C under a combined flow of Ar/H 2 and C 2 H 2 . UV−vis absorption and X-ray photoelectron spectroscopic (XPS) measurements confirm the consecutive formation of the iron hydroxide colloid/PSS multilayer films. Atomic force and electron microscopic (AFM, SEM, TEM) imaging shows that the catalyst particles thus prepared possess a layer-number-dependent size distribution and packing density after calcination. Aligned multi-walled carbon nanotubes with a controlled structure and morphology were produced from judiciously designed layer-by-layer assembled multilayer catalyst precursor films with a desirable layer number and composition.