Vertical bonding distances of PTCDA on Au(1 1 1) and Ag(1 1 1): Relation to the bonding type

• Published in: Surface science 2007-03, Vol.601 (6), p.1566-1573
• Main Authors: Henze, S.K.M., Bauer, O., Lee, T.-L., Sokolowski, M., Tautz, F.S.
• Format: Article
• Language: English
• Subjects: Chemisorption; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Metal–organic interface; Normal incidence X-ray standing wave (NIXSW); Physics; Physisorption; PTCDA; Surface structure
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2007.01.020

The vertical bonding distance of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) above the Au(1 1 1) surface has been measured by the normal incidence X-ray standing wave (NIXSW) technique. The carbon skeleton of PTCDA has a vertical distance of D = (3.27 ± 0.02) Å to the Au(1 1 1) substrate. This distance corresponds very nearly to the sum of the van der Waals radii of carbon and gold, suggesting the adsorption to be a physisorptive one. In contrast, the PTCDA/Ag(1 1 1) interface which according to spectroscopic data follows the standard model of chemisorption very closely, shows a considerably smaller bonding distance of D = (2.86 ± 0.01) Å [A. Hauschild, K. Karki, B.C.C. Cowie, M. Rohlfing, F.S. Tautz, M. Sokolowski, Phys. Rev. Lett. 94 (2005) 036106, comment: Rurali et al., Phys. Lett. 95 (2005) 209205, reply: Phys. Rev. Lett. 95 (2005) 209206]. The different vertical adsorption heights of PTCDA on gold and silver are discussed in relation to the different bonding mechanisms on both noble metal surfaces.