In a typical growth experiment, the samples (regardless of catalyst type) were loaded into the quartz reactor tube in horizontal tube furnace (Lindberg Blue/M Mini Mite) and held outside the hot zone under a continuous flow of hydrogen (100 sccm) and argon (500 sccm). The furnace was heated to the desired temperature (e.g. 750-850°C) and upon reaching it, the samples were introduced into the hot zone and exposed to 15 sccm of ethylene for a duration of 5 min (this step was done without ethylene for STEM studies). The rapid annealing of the films guaranteed that particle formation did not proceed below the target temperature (Ti) was reached. At this point, the samples were either exposed to a fixed temperature to achieve isothermal growth, or continuously cooled to a final temperature (Tf) below the initial temperature (Ti) to achieve nonisothermal growth. For the non-isothermal growths, the Tf was set immediately after introduction of the samples into the hot zone. The PID control of the furnace automatically lowered the temperature over a duration of approximately 3 minutes for a temperature difference (ΔT) of 50 or 100°C.