▎ 摘　　要

Although fullerenes can be efficiently generated from graphite in high yield, the route to the formation of these symmetrical and aesthetically pleasing carbon cages from a flat graphene sheet remains a mystery. The most widely accepted mechanisms postulate that the graphene structure dissociates to very small clusters of carbon atoms such as C(2), which subsequently coalesce to form fullerene cages through a series of intermediates. In this Article, aberration-corrected transmission electron microscopy directly visualizes, in real time, a process of fullerene formation from a graphene sheet. Quantum chemical modelling explains four critical steps in a top-down mechanism of fullerene formation: (i) loss of carbon atoms at the edge of graphene, leading to (ii) the formation of pentagons, which (iii) triggers the curving of graphene into a bowl-shaped structure and which (iv) subsequently zips up its open edges to form a closed fullerene structure.