Carbon nanotubes grown by chemical vapor deposition have revealed differences in growth rate and characteristics depending on the underlying buffer layer. As determined by in situ photoelectron spectroscopy, iron catalyst deposited onto Si substrates covered with Al 2 O 3, TiN, or TiO 2 underwent different chemical changes during annealing and exposure to C 2 H 2 as function of buffer layer. Formation of thin tubes (2−4 walls) and fast growth rate were associated with conversion of Fe onto FeO particles on Al 2 O 3 layers. On the other hand, thick multiwalled tubes (more than 20 walls) grew from pure Fe particles formed onto TiN and TiO 2 layers. The influence of different buffer layers is attributed to a combination of chemical and morphological changes induced in the catalyst due to catalyst-substrate interaction.
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Arcos et al. (2004) studied this question.