Fig. 13

a Diameter and chirality distributions of the FeW-catalysed SWCNTs under a water vapor concentration of 522 ppm. About 90% of the as-prepared SWCNTs were reported to be in the diameter range of 2.0–3.2 nm adapted from [140]. b Schematic illustration of the diameter-dependent and electronic-type-dependent etching mechanisms during growth. High selectivity of s-SWNTs could be obtained by controlling the diameter via the Fe-W catalysts. Adapted from [140]