AVS 51st International Symposium
    Organic Films and Devices Thursday Sessions
       Session OF+EM-ThA

Paper OF+EM-ThA8
Electronic Structure and Molecular Orientation of Conducting Polymer Films Produced via Surface Polymerization by Ion Assisted Deposition

Thursday, November 18, 2004, 4:20 pm, Room 304C

Session: Molecular and Organic Films and Devices - Optoelectronic
Presenter: S. Tepavcevic, University of Illinois at Chicago
Authors: S. Tepavcevic, University of Illinois at Chicago
Y. Choi, University of Illinois at Chicago
M. Bissen, University of Wisconsin-Madison
D. Wallace, University of Wisconsin-Madison
L. Hanley, University of Illinois at Chicago
Correspondent: Click to Email
Conducting polymer films are grown by mass-selected, hyperthermal organic cations coincident on a surface with a thermal beam of organic monomers, in a process termed surface polymerization by ion assisted deposition (SPIAD).@footnote 1,2@ SPIAD is applied here to create polymer films from thiophene ions and either @alpha@-terthiophene neutrals (3T SPIAD) or p-terphenyl neutrals (3P SPIAD). Mass spectrometry and x-ray photoelectron spectroscopy (XPS) verify the polymerization of both 3T and 3P SPIAD films. The electronic structure and molecular orientation of these films are probed by valence band XPS, ultraviolet photoelectron spectroscopy (UPS) and polarized near-edge x-ray absorption fine structure spectroscopy (NEXAFS). Valence band XPS and UPS of the 3T SPIAD films produced with 200 eV ions and an ion/neutral ratio 1/150 display similar spectral features as polythiophene films prepared electrochemically. A new state is observed 1 - 3 eV below the Fermi level in the 3T SPIAD film spectra which is not observed in films prepared by evaporation of 3T. This new state is attributed to an extended @pi@* bonding band along the conjugated aromatic chain of the polymerized 3T. Carbon K-edge NEXAFS probes the unoccupied @pi@* and @sigma@* bands of 3T SPIAD films which appear similar to those of the evaporated 3T film. Polarized NEXAFS show that the 3T SPIAD film is at least partially oriented with their molecular axes close to the normal of the substrate surface. The 3P SPIAD film prepared at 200 eV with an ion/neutral ratio 1/100 display more electron delocalization over the @pi@* bonding band compared with the 3P evaporated film. Polarized NEXAFS shows that as little or no orientation in the 3P SPIAD film, in contrast to the highly oriented 3P film. @FootnoteText@ @footnote 1@S. Tepavcevic, Y. Choi, and L. Hanley, J. Amer. Chem. Soc. 125 (2003) 2396. @footnote 2@Y. Choi, S. Tepavcevic, Z. Xu, and L. Hanley, Chem. Mater. (2004) in press.