The tube furnace CVD growth experiments were performed on Fe and Co catalysts at atmospheric pressure under argon, hydrogen and ethylene flow (details in the Experimental methods section). Figure shows the results of growth experiments from 1 nm Co films, where Ti and Tf were set to 850 and 750 ºC, respectively, for a total growth duration of 5 minutes. As mentioned above, we performed isothermal growth at 750 and 850 ºC for comparison. These experimental conditions typically produce bundled mats (also referred to as spaghetti-like) of CNTs from 1 nm catalyst films. Optical images of the silicon substrates after growth clearly show the high density of nanotubes in the non-isothermal growth (Figure ) compared to the two isothermal growths (Figure and). SEM images from these substrates reveal bundled mats in the two isothermal growths (Figure and 4f), as expected. On the other hand, the nonisothermal growth produced a vertically aligned array with a height around 5 µm (Figure ).