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CPP: Chemische Physik und Polymerphysik
CPP 23: POSTER Functional Organic Thin Films
CPP 23.7: Poster
Donnerstag, 30. März 2006, 17:00–19:00, P2
Effect of the Spacer Chain length on the Molecular Orientation and Packing Density of Terphenylalkanethiols on Au(111): Combined STM and FTIR Characterization: — •Asif Bashir1, Waleed Azzam1, Andreas Terfort2, Thomas Strunskus1, and Christof Wöll1 — 1Lehrstuhl für Physikalische Chemie I, Ruhr Universität Bochum — 2Institut für Anorganische und Angewandte Chemie, Universität Hamburg
Recently, the charge transport properties of aromatic thiolate, have received extensive attention because of their relative stability to other potential molecular electronic materials. Here, we report studies on Self-assembled monolayers (SAMs) of 4,4*-terphenyl-substituted alkanethiols C6H5(C6H4)2(CH2)n-SH (TPn, n = 1-6) adsorbed on Au (111) substrates using scanning tunneling microscopy (STM) and reflection absorption infrared spectroscopy (RAIRS). At 298 K, the structure and molecular orientation of TPn films (except TP2) exhibit a pronounced odd-even effect regarding both, the molecular orientation and packing density. Odd-numbered SAMs adopt a highly ordered (2√3 × √3)R30∘ structure. SAMs made from even-numbered TPn thiols, on the other hand exhibit a very different structure with a reduced packing density. At 298 K, a (5√3 × 3) rectangular unit cell was found for TP4 and TP6 SAMs. Whereas the structure of the odd numbered TPn SAMs is retained at a temperature of 333 K, the even-numbered SAMs undergo phase transitions to phases having a lower packing density. We will also report first results obtained for the geometric structures using ab-initio (DFT) electronic structure calculation.