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

Masahiro Shibuta, Kazuo Yamamoto, Tsutomu Ohta, Masato Nakaya, Toyoaki Eguchi, Atsushi Nakajima

Research output: Contribution to journalArticle

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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 sp 2-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.

Original languageEnglish
Article number35853
JournalScientific Reports
Volume6
DOIs
Publication statusPublished - 2016 Oct 24

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pyrolytic graphite
photoelectric emission
graphite
photons
molecular orbitals
electrons
excitons
probes
two dimensional models
free electrons
decay rates
fullerenes
graphene
photoelectrons
dissociation
pumps
life (durability)
thin films
electronics
spectroscopy

ASJC Scopus subject areas

  • General

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Direct observation of photocarrier electron dynamics in C60 films on graphite by time-resolved two-photon photoemission. / Shibuta, Masahiro; Yamamoto, Kazuo; Ohta, Tsutomu; Nakaya, Masato; Eguchi, Toyoaki; Nakajima, Atsushi.

In: Scientific Reports, Vol. 6, 35853, 24.10.2016.

Research output: Contribution to journalArticle

Shibuta, Masahiro ; Yamamoto, Kazuo ; Ohta, Tsutomu ; Nakaya, Masato ; Eguchi, Toyoaki ; Nakajima, Atsushi. / Direct observation of photocarrier electron dynamics in C60 films on graphite by time-resolved two-photon photoemission. In: Scientific Reports. 2016 ; Vol. 6.
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