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)  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  crystal direction, indicating a stronger molecule-substrate interaction. This adsorption is accompanied by local lifting of the Au(001) surface reconstruction  underneath the polymer chains .
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].
 S. Förster, E. Kohl, M. Ivanov, J. Gross, W. Widdra, and W. Janke, J. Chem. Phys. 141, 164701 (2014). (link)
 R. Hammer, A. Sander, S. Förster, M. Kiel, K. Meinel, and W. Widdra, Physical Review B, 2014, 90, 035446. (link)
 S. Förster and W. Widdra, J. Chem. Phys. 141, 054713 (2014). (link)
 K. Duncker, M. Kiel, A. Höfer, and W. Widdra, Phys. Rev. B 77, 155423 (2008). (link)
 M. Kiel, K. Duncker, C. Hagendorf, and W. Widdra, Phys. Rev. B 75, 195439 (2007). (link)