Assembly of Ferrocene Molecules on Metal Surfaces Revisited

Metallocene (MCp2) wires
have recently attracted considerable
interest in relation to molecular spintronics due to predictions concerning
their half-metallic nature. This exciting prospect is however hampered
by the little and often-contradictory knowledge we have concerning
the metallocene self-assembly and interaction with a metal. Here,
we elucidate these aspects by focusing on the adsorption of ferrocene
on Cu(111) and Cu(100). Combining low-temperature scanning tunneling
microscopy and density functional theory calculations, we demonstrate
that the two-dimensional molecular arrangement consists of vertical-
and horizontal-lying molecules. The noncovalent T-shaped interactions
between Cp rings of vertical and horizontal molecules are essential
for the stability of the physisorbed molecular layer. These results
provide a fresh insight into ferrocene adsorption on surfaces and
may serve as an archetypal reference for future work with this important
variety of organometallic molecules.