Rocking motion induced charging of C60 on h-BN/Ni(111)

TL;DR

This study reveals that molecular rocking motion in C60 on h-BN/Ni(111) induces significant charge transfer involving electron-phonon interactions, affecting work function and orbital occupancy.

Contribution

It demonstrates that molecular rocking motion causes charge redistribution in C60 monolayers via electron-phonon coupling, a novel insight into molecular motion and charge transfer mechanisms.

Findings

Work function decreases between 150-250 K

HOMO binding energy increases by approx. 100 meV

LUMO occupancy changes by 0.4 electrons

Abstract

One monolayer of C60 on one monolayer of hexagonal boron nitride on nickel is investigated by photoemission. Between 150 and 250 K the work function decreases and the binding energy of the highest occupied molecular orbital (HOMO) increases by approx. 100 meV. In parallel, the occupancy of the, in the cold state almost empty, lowest unoccupied molecular orbital (LUMO) changes by 0.4 electrons. This charge redistribution is triggered by onset of molecular rocking motion, i.e. by orientation dependent tunneling between the LUMO of C60 and the substrate. The magnitude of the charge transfer is large and cannot be explained within a single particle picture. It is proposed to involve electron-phonon coupling where C60- polaron formation leads to electron self-trapping.