https://phys.org/news/2018-07-theorists-mechanism-pure-nanotubes-unusual.html

Instead, they found the catalyst in question starts nanotubes with a variety of chiral angles but redirects almost all of them toward a fast-growing variant known as (12,6). The cause appears to be a Janus-like interface that is composed of armchair and zigzag segments—and ultimately changes how nanotubes grow.

Because chirality determines a nanotube's electrical properties, the ability to grow chiral-specific batches is a nanotechnology holy grail. It could lead to wires that, unlike copper or aluminum, transmit energy without loss. Nanotubes generally grow in random chiralities.