Abstract

Time-resolved two-photon photoemission (TR-2PPE) spectroscopy is employed to probe the electronic states of a C60 fullerene film formed on highly oriented pyrolytic graphite (HOPG), acting as a model two-dimensional (2D) material for multi-layered graphene. Owing to the in-plane sp2-hybridized nature of the HOPG, the TR-2PPE spectra reveal the energetics and dynamics of photocarriers in the C60 film: after hot excitons are nascently formed in C60 via intramolecular excitation by a pump photon, they dissociate into photocarriers of free electrons and the corresponding holes, and the electrons are subsequently detected by a probe photon as photoelectrons. The decay rate of photocarriers from the C60 film into the HOPG is evaluated to be 1.31 × 1012 s−1, suggesting a weak van der Waals interaction at the interface, where the photocarriers tentatively occupy the lowest unoccupied molecular orbital (LUMO) of C60. The photocarrier electron dynamics following the hot exciton dissociation in the organic thin films has not been realized for any metallic substrates exhibiting strong interactions with the overlayer. Furthermore, the thickness dependence of the electron lifetime in the LUMO reveals that the electron hopping rate in C60 layers is 3.3 ± 1.2 × 1013 s−1.

Highlights

  • We present a spectroscopic study of photocarrier electron dynamics of C60 deposited on a highly-oriented pyrolytic graphite (HOPG) as a model for multi-layered graphene by means of time-resolved two-photon photoemission (TR-2PPE) spectroscopy

  • Six spectral features labeled as L0, L2, F0, F1, F2, and H appear by the formation of C60 film

  • In addition to the rise and decay processes of lowest unoccupied molecular orbital (LUMO) electrons, the second term of the AC component is taken into account, because photoelectrons at the corresponding energy may include two components of (i) coherent 2PPE from occupied states of highly oriented pyrolytic graphite (HOPG) and HOMO−​1 of C60 and (ii) short-lived hot electrons in the HOPG and C60 film, both of which are not regarded as the photocarrier electrons in the LUMO

Read more

Summary

Introduction

Time-resolved two-photon photoemission (TR-2PPE) spectroscopy is employed to probe the electronic states of a C60 fullerene film formed on highly oriented pyrolytic graphite (HOPG), acting as a model two-dimensional (2D) material for multi-layered graphene. We present a spectroscopic study of photocarrier electron dynamics of C60 deposited on a highly-oriented pyrolytic graphite (HOPG) as a model for multi-layered graphene by means of time-resolved two-photon photoemission (TR-2PPE) spectroscopy.

Results
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call