Dresden 2011 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 54: Joint Session: Organic Semiconductors IV: Excitations and Charges
HL 54.9: Vortrag
Mittwoch, 16. März 2011, 16:30–16:45, ZEU 222
The impact of polar bonds on electron transport through self-assembled monolayers — •David A. Egger1, Ferdinand Rissner1, Egbert Zojer1, and Georg Heimel2 — 1Institute of Solid State Physics, Graz University of Technology, Austria — 2Institut für Physik, Humboldt-Universität zu Berlin, Germany
Density functional theory based surface- and transport-calculations are performed to elucidate the role of intra-molecular polar bonds built into self-assembled monolayers (SAMs) sandwiched between two metal electrodes. Conjugated (oligo)phenylene-ethynylenethiols (also known as ’Tour wires’) on gold are chosen due to their frequent appearance in past experimental and theoretical studies. Here, we substitute carbon by nitrogen atoms in a systematic way to realize two different molecules with zero dipole moment and virtually identical frontier molecular orbital energies. Despite this similarity in the electronic structure of the isolated species, the charge-transport characteristics of the corresponding SAMs are vastly different. We give a sound explanation for our observations based on an intuitive electrostatic rationale and conclude that the actual orientation of polar bonds in monolayers of preferentially oriented molecules crucially impacts characteristic parameters of molecular electronic devices, such as conductance gap or threshold voltage.