Janus Segregation at the Carbon Nanotube-Catalyst Interface.

The contact between a carbon nanotube (CNT) edge and a catalyst is a curvilinear interface of fundamental and practical importance. Here, the first-principles evidence shows that on a rigid/solid catalyst the faceted CNT edge is significantly lower in energy compared to the minimal-length circle, with the interface energy difference decreasing on more compliant surfaces. This universal trend, found for typical monometallic (Ni, Co), bimetallic (Co7W6), and metal carbide (WC) catalysts, results in a peculiar edge segregation into one-dimensional Janus (armchair-zigzag) interface. Its lowered energy greatly enhances the nucleation probability of chiral tubes, dramatically affecting their growth kinetics. This offers a richer basis for understanding, modeling, and control of catalytic CNT synthesis.