Field emission angular distribution from single molecules

Abstract

We demonstrate that the field emission from a single molecule at the apex of a metallic tip exhibits a well-defined angular distribution pattern (field emission angular distribution, FAD) with a spherical harmonics shape, regardless of the species of the molecule. From carefully controlled simultaneous measurements of the emission pattern, the emission current and emission energy, we deduced the formation mechanism of the FAD pattern in which the electron from the metallic tip resonantly tunnels into vacuum via a molecule-induced state situated at the Fermi level of the tip. The characteristic FAD patterns were consistent with the Fourier transform of the superatom molecular orbitals (SAMOs). Thus, the present method is unique for real-time imaging of the SAMOs, or the low-lying Rydberg states, of single molecules.