Photoemission spectroscopy of tethered CdSe nanocrystals: Shifts in ionization potential and local vacuum level as a function of nanocrystal capping ligand

Andrea M. Munro, Brian Zacher, Amy Graham, Neal R. Armstrong

Research output: Contribution to journalArticle

62 Scopus citations

Abstract

We report the characterization of the frontier orbital energies and interface dipole effects for bare and ligand-capped 3.6 and 6.0 nm diameter CdSe nanocrystals (NC) tethered to smooth gold substrates, using He(I) and He(II) UV photoemission spectroscopy. Changes in the ionization potential (IP) of the NCs and local effective work function of the films were explored as a function of the dipolar nature of the NC capping ligands. The addition of thiol-capping ligands 1-hexanethiol, 1-benzenethiol, and 4-fluorothiophenol to both sizes of NCs produces negligible shifts in energy offset between the high kinetic energy edge of the CdSe NCs and the gold substrate Fermi energy. However, the local vacuum level and IP of the nanocrystal layer are altered by as much as 0.3 eV. We demonstrate the importance of determining both the local vacuum level and the high kinetic energy edge of a tethered NC sample. These studies demonstrate a method that can be used in the future to characterize the frontier orbital energy offsets for modified or unmodified nanocrystalline films, in which the NCs are incorporated into host materials, for applications ranging from photovoltaics to light-emitting diodes.

Original languageEnglish (US)
Pages (from-to)863-869
Number of pages7
JournalACS Applied Materials and Interfaces
Volume2
Issue number3
DOIs
StatePublished - Mar 24 2010

Keywords

  • Dipole moment
  • Self-assembled monolayer
  • Semiconductor nanocrystal
  • UV-photoelectron spectroscopy ionization potential
  • Vacuum level shift

ASJC Scopus subject areas

  • Materials Science(all)

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