To address this question, we deposited 0.3 nm of Co on TEM windows. We annealed the windows in our tube furnace under isothermal and non-isothermal conditions without any hydrocarbon present. The annealing was performed in the presence of argon and hydrogen to induce film dewetting and particle formation. Subsequently, scanning (S)TEM images were collected and particle sizes from several images were extracted manually to build particle size distribution histograms. The results of the STEM analyses are shown in Figure for the nonisothermal (Figure ) and isothermal (Figure and 6c) cases. The differences in particle size are clear -the particle sizes are larger in the 850 ºC anneal compared to the 750 ºC anneal. The corresponding size distribution histograms are shown in Figure . Interestingly, the particle sizes in the sample annealed using non-isothermal conditions are very similar to those for the sample annealed at 750 ºC; the mean size is, in fact, a little smaller (4.5 nm compared to 4.8 nm). This corroborates our earlier observation of RBM frequencies being higher (corresponding to smaller CNT diameters) in the non-isothermal growth compared to isothermal growth at 750ºC (Figure ). We note that the overall particle sizes shown in Figure are larger than expected for catalysts producing single-walled CNTs (experiments have found the catalyst particle size to be between 1 to 1.6 times the tube diameter ). This is because we performed our annealing experiments on bare SiO2 windows, whereas the CVD and ARES growth substrates contained an alumina barrier between the SiO2 and the catalyst films. These bare SiO2 windows were purposely chosen for improved image resolution and ease of analysis. And while the particle sizes are on average a factor of 2 larger, the trends in the sizes between the isothermal and non-isothermal anneals are the same as what we observed for the CNT diameters in all of the CVD growth experiments.