Regensburg 2004 – scientific programme
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O: Oberflächenphysik
O 33: Organische Dünnschichten II
O 33.5: Talk
Thursday, March 11, 2004, 12:15–12:30, H39
Effects of the molecular electric dipole on the HOMO-band fine structure: metal-phthalocyanine on graphite — •Satoshi Kera1,2, Hiroyuki Yamane3, and Nobuo Ueno3 — 1Exp. Phys. II, Univ. Würzburg, Am Hubland, 97074 Würzburg — 2Institute for Molecular Science, Okazaki 444-8585, Japan — 3Chiba Univ., Inage-ku, Chiba 263-8522, Japan
Photoelectron fine structures were observed for metal-phthalocyanine (Pb-, and OTiPc) ultrathin films on HOPG. They have an electric dipole perpendicular to the π-conjugated plane, hence a well-defined dipole layer could be intentionally produced by preparing an oriented monolayer. For the OTiPc film with asgrown island, in which staggered doublelayers are formed, we observed two prominent peaks for the HOMO band (single π state) originating from different molecular orientations in the islands. Upon annealing, they form a uniform monolayer with the O atom protruding into the vacuum, and give an unusually sharp HOMO band [1]. The EB difference of the HOMO bands between the staggered doublelayer and the oriented monolayer was found to agree with the Evac shift, leading to the conclusion that the relative position of the molecular energy level with respect to the substrate EF can be changed due to the dipole layer. These results suggest that we can tailor device interface properties by controlling the direction and/or the magnitude of the molecular electric dipole. Moreover it is also interesting to discuss the origins of the HOMO-bandwidth at the organic/inorganic interfaces. [1] S. Kera et al, Chem. Phys. Lett. 364, 93 (2002).