▎ 摘　　要

We demonstrate a new synthesis route for the growth of organometallic sandwich molecular nanowires, taking the example of Eu-cyclooctatetraene (EuCot), a predicted ferromagnetic semiconductor. We employ simultaneous exposure of Cot molecules and Eu vapor in ultrahigh vacuum to an inert substrate, such as graphene. Using a Cot excess under temperature conditions of a finite residence time of the molecule, the reactand diffusion confined to two dimensions results in a clean product of ultralong wires. In situ scanning tunneling microscopy reveals not only their molecular structure but also a rich and intriguing growth morphology. The new on-surface synthesis permits experimental access to a largely unexplored class of one-dimensional organometallic systems with potential for exciting electronic and magnetic properties.