Figure 5
Experimental and theoretical investigations of the effect of catalyst pretreatment on SWNTs growth: Axial growth state. (a–d) Optimized structures from the first-principles calculations for (a) Co55 and Co33O22 clusters as well as (b) (6,4) and (6,5) SWNTs. (c,d) Binding structure between (c) Co55 and SWNTs and (d) Co33O22 and SWNTs. (e) The γ –x plot of Co and CoOx obtained by first-principles calculations. (f) Normalized growth yield A as a function of x for Co (red) and CoOx (blue) calculated by the theoretical equation (3). Solid and dashed line in (e) correspond to d = 0.757 nm and 0.692 nm, respectively. (g) Schematic illustration of the chirality shift from (6,5) to (6,4) achieved after pretreatment by considering the independent shift in d and x. (h) Experimental PL intensity ratio of (7,3)/(6,4) (red), (7,3)/(6,5) (black), and (6,4)/(6,5) (blue) as a function of H2/N2 flow ratio employed during the pretreatment process. Higher and lower ratio of H2/N2 result in stronger and weaker reduction of oxidized Co catalyst, resulting in pure and oxidized Co surface, respectively.
