Covalent bonding and hole–electron Coulomb interactionUin C₆₀on Be(0001) surfaces

Abstract

We have investigated the bonding nature and hole-electron Coulomb interaction U in thin C(60) films on Be(0001) surfaces using valence-band and core-level photoemission, inverse photoemission, and near-edge x-ray absorption spectroscopies. The C(60) monolayer had strong covalent bonding with the Be substrate, producing a nearly insulating film, in contrast to a metallic overlayer due to charge transfer observed on many other metallic surfaces. The effect of polarization of surrounding molecules and the image potential decreases the energy gap and U, but the bonding-antibonding contribution increases the gap at the interface. The measured U in thin solid films agrees well with a model calculation using gas-phase values. The deduced hole-electron attraction on the surface is about 0.7 eV larger than the reported hole-hole repulsion determined by Auger spectroscopy. On the basis of the surface-solid difference, the newly estimated value of U for hole-hole correlation places doped C(60) compounds nearer the metallic side of a Mott transition.

Direct observation of photocarrier electron dynamics in C60 films on graphite by time-resolved two-photon photoemission

“…It is known that ΔE for a C 60 monolayer on a metal substrate is small compared to that in the bulk C 60 , because the on-site charge is more effectively screened by the substrate than by a C 60 film, resulting in a reduction of U 49 50 51 . As mentioned above, the energy positions are almost identical regardless of the C 60 coverage on HOPG ( Supplementary Figs S1 and S4 ), which shows that the screening effect from HOPG is much smaller than that from a metal substrate, due to its low density of states near E F .…”

Optimal Electron Doping of aC60Monolayer on Cu(111) via Interface Reconstruction

“…Since C 60 films on metallic surfaces typically involve substrate-to-C 60 electron transfer that partially populates the C 60 lowest unoccupied molecular orbital (LUMO), it has been of great interest to pursue optimally doped C 60 films. Earlier studies show that the electron transfer amount does not simply depend on the substrate work function [2]. This raises the question of the role of the C 60 =metal interface structure.…”

Monolayer and Bilayer Perfluoropentacene on Cu(111)

“…Following an earlier analysis of Pn/Cu(111), we suggest that the first layer of PFP molecules participates in charge transfer with the substrate. This behavior arises when the LUMO of the molecular overlayer is broadened through adsorption, including the Fermi energy of the substrate. , This results in partial filling of the LUMO and charge transfer between the substrate and the ML, leading to a Fermi surface in the molecular layer and a degree of metallic conduction. − …”

“…15,39 This results in partial filling of the LUMO and charge transfer between the substrate and the ML, leading to a Fermi surface in the molecular layer and a degree of metallic conduction. [40][41][42] Adsorption site lattice determination…”