Dresden 2006 – wissenschaftliches Programm
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O: Oberflächenphysik
O 9: Organic films I
O 9.6: Vortrag
Montag, 27. März 2006, 16:15–16:30, TRE Phys
Two step adsorption of phenyl-functionalized tripod ligands on gold — •Tobias Weidner1, Andreas Krämer2, Tigran Vartanyan3, Ulrich Siemeling2, and Frank Träger1 — 1Institut für Physik, Universität Kassel, Kassel — 2Institut für Chemie, Universität Kassel, Kassel — 3Vavilov State Optical Institute, St Petersburg, Russia
Further progress in organic monolayer preparation depends on the thorough understanding of thin film formation processes. In this contribution in situ optical second harmonic generation (SHG) measurements have been employed to study the adsorption kinetics of the new tripodal thioether ligands PhSi(CH2SMe)3 and Ph-p-C6H4-Si(CH2SMe)3 on gold substrate from solution. Previous characterization by in situ ellipsometry and a number of ex situ methods, viz. high-resolution XPS, FTIRRAS, and STM indicated dense packing of the tripodal anchor groups on the surface with a substantially lower density of the biphenyl moieties. To characterize the adsorbate-substrate interaction quantitatively a new method based on SHG measurements at different temperatures was developed. The rate of adsorption was found to decrease from 2.4· 10−3 s−1 to 3.4· 10−4 s−1 when the solution temperature was raised from 2.5 to 49 degrees centigrade (at constant concentration). This contra intuitive behavior is explained by a two-step adsorption model assuming that stable chemical bonds are formed subsequent to a weakly bound precursor state. The theoretical description of such a model allows us to obtain an estimate of the enthalpy of the physisorbed state, a parameter difficult or impossible to determine by other techniques.