Fingerprinting weak electronic interaction at a van der Waals interface: Fano signatures in a pentacene monolayer on graphite

We investigated the influence of van der Waals interactions on the electronic structure at the interface between a pentacene monolayer and a graphite surface. Upon cooling below 130 K, the pentacene molecules form a densely packed monolayer characterized by newly developed dispersive bands. These bands, observed using low-energy angle-resolved photoelectron spectroscopy with photon energy varying from 7.2 to 8.5 eV, exhibit constant final-state characteristics that overlap with nondispersive molecular-orbital states. This overlap results in variations in photoemission intensity—both enhancement and suppressions—indicative of Fano resonance. Such resonance arises from the interaction between a discrete molecular state and a continuum state. The Fano profile analysis of spectral fine features reveals the wave-function connection by the broader spread in unoccupied states at the physisorbed interface.