One of the reasons for the increase in particle density in the non-isothermal case could be due to incomplete dewetting of the catalyst film under isothermal conditions (Figure ). As mentioned above, film dewetting typically proceeds by hole formation, which can occur at defect sites; this is followed by nucleation and growth of particles. In the non-isothermal case, continuous cooling could destabilize the film, resulting in spinodal dewetting of the metal oxide film into metallic nanoparticles. This implies that, during the non-isothermal growth phase, new particles are continuously formed and can nucleate CNTs before they coarsen or become inactive, which could explain our observation of high growth rates and long lifetimes in the in situ experiments.