Dresden 2009 – scientific programme
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O: Fachverband Oberflächenphysik
O 18: Metal substrates: Adsorption of organic / bio molecules III
O 18.3: Talk
Tuesday, March 24, 2009, 11:00–11:15, SCH A118
Embedded dipoles in monomolecular films: physical and electronic structure effects — •Michael Zharnikov1, Orlando M. Cabarcos2, Tobias Weidner1, Sundararajan Uppili2, Linda S. Dake3, and David L. Allara2 — 1Angewandte Physikalische Chemie, Universtät Heidelberg, Im Neuenheimer Feld 253, D-69120 Heidelberg, Germany — 2Department of Chemistry and the Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA — 3Department of Physics, Utica College, Utica, NY 13502, USA
Ester moiety was imbedded into the molecular chain of alkanethiolate self-assembled monolayers (SAMs) on Au(111), with the length of the segments below and above the ester moiety being varied. The bottom segments of the alkyl chain were found to be better ordered than the upper ones. The presence of the ester moiety leads to the formation of a strong electric dipole layer with a component of 1.05 Debye normal to the surface. This dipole layer exhibits a strong electrostatic effect on the XPS spectra in which the C 1s photoelectron kinetic energies are consistently shifted by 0.85 eV between the top and bottom alkyl chain segments, regardless of relative lengths. This shift correlates, within error, with the value of 0.81 eV predicted via classical electrostatics due to the presence of the ester dipole layer. Overall, these data show that SAMs assembled from molecules with appropriately selected internal groups can be used to prepare internally layered structures with highly controlled electrical characteristics and further demonstrate that simple XPS shifts in core level energies can be used to derived accurate molecular dipole values in structured thin films.