Superatom orbitals of C60on Ag(111): Two-photon photoemission and scanning tunneling spectroscopy

Abstract

The unoccupied electronic structure of C 60 layers on Ag(111) was investigated with two-photon photoemission (2PPE) and scanning tunneling spectroscopy (STS). The focus, in addition to providing unoccupied level assignments for C 60 monolayers, is on identifying signatures of C 60 superatom molecular orbitals (SAMOs), diffuse unoccupied levels weakly bound by the spherical potential of the fullerene shell, in the two complementary techniques. The s-SAMO is identified 3.3 eV above the Fermi level in 2PPE and at a bias of 3.5 eV in STS. Possible contributions from p-SAMO levels are also discussed for both measurement techniques. The results are compared with recent low-temperature scanning tunneling microscopy (LT-STM) work that investigated C 60 SAMOs on Cu(111) and oxygen-covered Cu(110) surfaces and with previous 2PPE measurements for C 60 monolayers on Au(111) and Cu (111).

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

“…S3 ). The result suggests that F0–F2 are assignable to a series of higher-lying superatomic molecular orbitals (SAMOs) 36 37 38 39 40 41 ; the wavefunctions of SAMOs generally diffuse outside the molecular framework, which would form highly dispersive band structures in a molecular film with a periodic surface structure. As shown in Fig.…”

“…S3 ), suggesting that the observation of SAMOs in 2PPE requires an initial or intermediate electronic state to allow the resonance. It is known that the lowest (1s-) SAMO is experimentally observed at around E F + 3.3–3.8 eV in a C 60 monolayer on noble metal substrates with a strongly delocalized nature 36 38 39 40 . The absence of the 1s-SAMO in our study is attributable to the 2D electronic structure of the HOPG substrate; since the electronic structures of graphene below and above E F are governed by sp 2 hybridized orbitals oriented parallel to the graphene plane, the chemical interaction with the overlayer material is very weak compared to metallic materials 8 .…”

Quantum beats at the metal/organic interface

“…graphene[4] and 2D topological insulators [5]), and the electron dynamics 10 of semiconductor surfaces [6] have been successfully studied using TPPE (to only name a few). Recently, a significant focus of study has been on the metal/organic [7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 15 31,32,33,34,35,36,37,38,39,40,41,42] and organic/organic [43,44,45,46,47,48,49] interfaces in an effort to understand charge generation and transport in organic electronic materials.…”

Electronic states of titanyl phthalocyanine films on alkanethiolate self-assembled monolayers probed by two-photon photoemission

“…In other words, the transition dipole moment of 2PPE is unambiguously directed normally to the surface. No polarization dependence has been observed for photons that excite molecular derived occupied and unoccupied states (e.g., HOMO and the lowest unoccupied molecular orbital (LUMO)) of molecules deposited on a surface [16,33]. In fact, as shown in Fig.…”