Polythiophene Adsorption and Restructuring on Gold Surfaces

E. Schreck1, T. Simon1, S. Förster1, R. Hammer1, and W. Widdra1,2

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

Scanning tunneling microscopy is used to study the complex adsorption behavior of poly-3-hexyl-thiophene (P3HT) on Au(001) [1] and Au(011). Upon electrospray deposition under ultrahigh vacuum conditions, weakly adsorbed polymer chains are found on Au(001), which exhibit a truly 2D random-coil-like chain backbone structure. Their end-to-end distance and their radius of gyration are 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 stronger molecule-substrate interaction. This adsorption is accompanied by local lifting of the Au(001) surface reconstruction [2] underneath the polymer chains [3].
For the more open Au(011) surface that exhibits a missing-row (2×1) reconstruction, we find a stronger interaction between P3HT and the gold surface. Polymer chains align predominantly along the missing rows by changing their conformation into an all-trans state. The presence of the polymer is inducing a local reorganization process changing the surface reconstruction from 2×1 to a 3×1 reconstruction. These results will be compared with similar findings for smaller thiophene oligomers (sexithiophene, 6T) on both substrates [4,5].

[1] S. Förster, E. Kohl, M. Ivanov, J. Gross, W. Widdra, and W. Janke, J. Chem. Phys. 141, 164701 (2014). (link)
[2] R. Hammer, A. Sander, S. Förster, M. Kiel, K. Meinel, and W. Widdra, Physical Review B, 2014, 90, 035446. (link)
[3] S. Förster and W. Widdra, J. Chem. Phys. 141, 054713 (2014). (link)
[4] K. Duncker, M. Kiel, A. Höfer, and W. Widdra, Phys. Rev. B 77, 155423 (2008). (link)
[5] M. Kiel, K. Duncker, C. Hagendorf, and W. Widdra, Phys. Rev. B 75, 195439 (2007). (link)