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

Munehisa Ogura, Masahiro Shibuta, Toyoaki Eguchi, Atsushi Nakajima

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Abstract

We studied both occupied and unoccupied states of titanyl phthalocyanine (TiOPc) films formed on an octanethiolate self-assembled monolayer (SAM) on an Au(1 1 1) surface fabricated in a wet chemical process using two-photon photoemission (2PPE) spectroscopy. A 1.90-nm-thick layer of TiOPc formed an unoccupied state at 2.9 eV above the Fermi level. This state was resonantly enhanced at 4.3-4.4 eV photon energy, suggesting that electrons were excited from the highest occupied molecular orbital of TiOPc. The 2PPE measurements of photon energy dependence and light polarization selectivity revealed that the unoccupied state originates from a charge transfer exciton not observed in organic thin films deposited on bare metallic substrates. The formation of a charge transfer exciton implies that the SAM strongly insulates the molecular monolayer.

Original languageEnglish
Pages (from-to)272-277
Number of pages6
JournalJournal of Electron Spectroscopy and Related Phenomena
Volume195
DOIs
Publication statusPublished - 2014

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Keywords

  • Charge transfer exciton
  • Self-assembled monolayer
  • Titanyl phthalocyanine
  • Two-photon photoemission spectroscopy

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Radiation
  • Atomic and Molecular Physics, and Optics
  • Condensed Matter Physics
  • Spectroscopy
  • Physical and Theoretical Chemistry

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