The influence of the temperature and precursor pressure upon the defect density of single-walled carbon nanotubes grown by catalytic chemical vapor deposition was studied for several catalyst-precursor couples. The single-walled carbon nanotube defect density was assessed by studying the Raman D-band. In situ Raman monitoring was used to determine experimental conditions allowing the preparation of samples free of pyrolytic carbon and not altered by air exposure. The most striking feature was that the Arrhenius plots of the IG/ID ratio had a convex shape. That is, the apparent activation energy decreased with increasing temperature. From high-resolution transmission electron microscope observations and oxidation experiments, this evolution of the D-band features was attributed to the catalytic growth of long single-walled carbon nanotubes with few defects at high temperatures, and of short and defective single-walled carbon nanotubes and carbon structures at low temperatures. The convex Arrhenius behavior was well accounted by two kinetic models. One was a model which considered a change in intermediate states as a function of the temperature (for instance due to a phase transition of the catalyst particle or a change of intermediate carbon species). The other model considered a high-temperature process of defect creation (for instance, by reaction with reactive gas species).

Influence of the Growth Conditions on the Defect Density of Single-Walled Carbon Nanotubes. M.Picher, H.Navas, R.Arenal, E.Quesnel, E.Anglaret, V.Jourdain: Carbon, 2012, 50[7], 2407-16