Polythiophene Adsorption on Noble Metal Surfaces via Electrospray Deposition

S. Förster,1 A. Sander,1 R. Hammer,1 K. Duncker,1 E. Kohl,1 and Wolf Widdra,1,2

1 Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany
2 Max Planck Institute of Microstructure Physics, Halle, Germany

Poly(3-hexylthiophene) (P3HT) adsorption on an atomically well-ordered Au(001) surface via electrospray deposition is reported [1]. In-situ scanning tunneling microscopy reveals a complex adsorption behavior of P3HT. Weakly adsorbed polymer chains exhibit a truly 2D random coil like chain configuration. Their end-to-end distance and their radius of gyration is reported as function of the polymer length. Additionally, a fraction of the P3HT molecules is constraint into a fully stretched configuration along the high-symmetry [110] crystal direction indicating a strong molecule-substrate interaction. This adsorption is accompanied by local lifting of the Au(001) surface reconstruction [2] underneath the polymer chains.

The adsorption of P3HT will be compared with direct surface polymerization of alpha-sexithiophene (6T). The thermally-induced polymerization on Ag(001) and Au(001) gives rise to long unbranched polymer chains or branched polymer networks depending on the annealing parameters [3]. There, the onset temperature for polymerization depends on the strength of interaction with the underlying substrate. Similar polymerization processes are also induced by ultraviolet radiation with photon energies between 3.0 and 4.2 eV. Radical formation by an electronic excitation in the 6T molecule is proposed as the driving mechanism that necessitates the interplay with the metallic substrate.

[1] S. Förster and W. Widdra, Journal Chemical Physics, 2014, 141, 054713.
[2] R. Hammer, A. Sander, S. Förster, M. Kiel, K. Meinel, and W. Widdra, Physical Review B, 2014, 90, 035446.
[3] A. Sander, R. Hammer, K. Duncker, S. Förster, and W. Widdra, Journal Chemical Physics, 2014, 141, 104704.