Condensed Matter Physics Seminar
2 p.m., Thursday, September 21, 2006
Room 1201, Physics Building
Local Tunneling Spectroscopy of Molecule-Modified Image Potential
States: Benzene on Cu(111) and Cu(110)
Abstract: The use of organic materials in electronic devices is
attractive as an approach to expanding current device applications and
capabilities. Commercial use of organic materials can already be found in the
form of organic-based LED displays . Device structures invariably contain
interfaces between an organic material and a conducting electrode. Therefore it
is necessary to develop a detailed understanding of electronic structure at the
metal-organic interface. I will describe tunneling spectroscopy experiments that
measure electronic structure variations at the nanometer-length scale for
benzene adsorbed on both Cu(111) and Cu(110). By tracking the energetic position
of a type of surface state called an image potential state , it is possible
to monitor the details of local surface potential in this adsorption system.
Image potential states are normally unoccupied bound states that result from the
attraction between an electron just outside of a surface and the induced
polarization in the near-surface region. These states are pinned to the vacuum
level of the surface and therefore provide a sensitive probe of surface
electrostatic potential. Using an STM tip to measure local constant-current,
distance-voltage characteristics , we have studied image potential states as
a function of benzene surface coverage from isolated benzene molecules to
bilayer films on Cu(111) and Cu(110). Results to be discussed include 1) the
influence of a single molecule on local surface potential; 2) the variation in
surface potential across structural domain boundaries; and 3) layer-dependent
electric field effects due to the STM tip.
 S.R. Forrest, Nature 428, 911 (2004).
 P. Szymanski, S. Garret-Roe, and C.B. Harris, Prog. Surf. Sci. 78,
 P. Wahl, M.A. Schneider, L. Diekhöner, R. Vogelgesang, and K. Kern, Phys.
Rev. Lett. 91, 106802 (2003).
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