Controlling the Electronic and Structural Coupling of C Nano Films on Fe(001) through Oxygen Adsorption at the Interface.

C molecules coupled to metals form hybrid systems exploited in a broad range of emerging fields, such as nanoelectronics, spintronics, and photovoltaic solar cells. The electronic coupling at the C/metal interface plays a crucial role in determining the charge and spin transport in C-based devices; therefore, a detailed understanding of the interface electronic structure is a prerequisite to engineering the device functionalities. Here, we compare the electronic and structural properties of C monolayers interfaced with Fe(001) and oxygen-passivated Fe(001)-p(1 × 1)O substrates. By combining scanning tunneling microscopy and spectroscopy, Auger electron spectroscopy, photoemission and inverse photoemission spectroscopies, we are able to elucidate the striking effect of oxygen on the interaction between Fe(001) and C. Upon C deposition on the oxygen-passivated surface, the oxygen layer remains buried at the C/Fe(001)-p(1 × 1)O interface, efficiently decoupling the fullerene film from the metallic substrate. Tunneling and photoemission spectroscopies reveal the presence of well-defined molecular resonances for the C/Fe(001)-p(1 × 1)O system, with a large HOMO-LUMO gap of about 3.4 eV. On the other hand, for the C/Fe(001) interface, a strong hybridization between the substrate states and the C orbitals occurs, resulting in broader molecular resonances.