AVS 50th International Symposium
    Organic Films and Devices Wednesday Sessions
       Session OF+NS-WeM

Paper OF+NS-WeM8
Two-Photon Photoemission Studies of Molecular Affinity Levels in Oligo-Phenylene Ethynylene Self-Assembled Monolayers

Wednesday, November 5, 2003, 10:40 am, Room 318/319

Session: Molecular Electronics
Presenter: C. Zangmeister, National Institute of Standards and Technology
Authors: C. Zangmeister, National Institute of Standards and Technology
S.W. Robey, National Institute of Standards and Technology
R.D. van Zee, National Institute of Standards and Technology
Correspondent: Click to Email
Two-photon photoemission has been used to study unoccupied electronic levels for a family of thiolated oligiomeric phenylene-ethynylene self-assembled monolayers. Self-assembled monolayers of a three phenyl ring oligomer (OPE) and the same oligomer with a nitro group substituted for one hydrogen on the center ring (NO@sub2@-OPE) were formed on polycrystalline Au/Si substrates as well as [111] oriented Au on mica. This class of compounds has received attention because of measured conduction characteristics and the reported negative-differential resistance behavior of these compounds in nanometer-sized pore structures. Single-color, two photon photoelectron spectroscopy measurements were performed in the ultraviolet using frequency-doubled, subpicosecond pulses from a Ti:Sapphire-pumped optical parametric amplifier. For the OPE monolayers we have, based on the excitation energy dependence, identified an unoccupied level ca. 1 eV above the vacuum level. Using previous two-photon photoemission and inverse photoemission of condensed benzene layers as a guide we tentatively identify this as the remnant of the e@sub2u@ unoccupied level for benzene localized on the carbon atoms of the phenyl ring. Results of studies on NO@sub2@-OPE layers will also be discussed.