(a) Like in a battleship game with the position shaped like hexagons rather than boxes, CNTs are defined by two indices. These two numbers indicate different structures. Among all the possible CNTs that can be formed, that is, one for each combination of the two numbers, only the ones in blue fit the symmetry of the underlying solid catalyst (WC, shown as gray balls). They are the ones whose two indices can be divided by 4. (b) Then, according to the growth rate, scientists slimmed down to only two CNTs structures which could grow quickly: the (8, 4) and the (12, 4). Some CNTs, such as (12, 0) were eliminated because their flat edge does not allow the fast incorporation of carbon atoms. (c) Finally, the scientists controlled the size of the catalyst and found that (8, 4) CNT is the one that fits the small catalyst. By controlling the size of the catalyst, only one type of CNTs can be synthesized, so that the purity of the resulting array improves. (d) In this study, scientists managed to obtain 80-90% of (8, 4) CNTs with a small fraction of other types. Theoretically, IBS scientists predict that, in the optimal conditions, the purity of the (8, 4) CNTs could reach 99.9% or higher.