Existence and kinetics of graphitic carbonaceous impurities in carbon nanotube forests to assess the absolute purity.

We present an approach that can identify and assess carbonaceous impurities in carbon nanotube (CNT) forests. First, the kinetics of the impurity accumulation was elucidated by investigating the time evolution of both the height and weight of the forests. Second, the kinetics was used to extract a power scaling law revealing the carbonaceous impurity level to solely depend on the total volume of carbon exposure. Third, the power scaling law allowed for a quantitative model describing both the growth of CNTs and accumulation of the carbonaceous impurities. Lastly, from the model the absolute purities of the SWNT forests were evaluated as above 95% with a high of 99.5%.