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)

Dan Dougherty

(NIST Gaithersburg)

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 [1]. 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 [2], 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 [3], 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.

[1] S.R. Forrest, Nature 428, 911 (2004).

[2] P. Szymanski, S. Garret-Roe, and C.B. Harris, Prog. Surf. Sci. 78, 1 (2005).

[3] P. Wahl, M.A. Schneider, L. Diekhöner, R. Vogelgesang, and K. Kern, Phys. Rev. Lett. 91, 106802 (2003).

Host:  Reutt-Robey
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