Orientation of Fluorophenols on Si(111)

Oriented adsorption of switchable organic molecules at surfaces is an important prerequisite for single molecular electronics [1, 2]. As model systems we select polar fluorophenols with tailored dipole moments and investigate their adsorption on the Si(111)7$\times $7 surface by near edge x-ray absorption fine structure spectroscopy (NEXAFS). A strong polarization dependence of the $\pi $* transitions is observed in fluorinated phenols, while phenol itself is isotropic. A quantitative model is developed to convert polarization-dependent NEXAFS data into orientational information. The model includes three angular degrees of freedom, two of them fixed and the other with a Gaussian distribution. Such a situation is encountered in a variety of self-assembled monolayers (SAMs) with tailored end groups [3]. [1] T. A. Jung, R. R. Schlittler, J. K. Gimzewski, Nature \textbf{386}, 696, (1997) [2] A. J. Mayne, M. Lastapis, G. Baffou, L. Soukiassian, G. Comtet, L. Hellener and G. Dujardin, Phys. Rev. B \textbf{69}, 045409 (2004) [3] Y.Y. Luk, N. L. Abbott, J. N. Crain and F. J. Himpsel, J. Chem. Phys. \textbf{120,} 10792 (2004)