A refined structural analysis of the PTCDA monolayer on the reconstructed Au(111) surface - Rigid or distorted carpet?

The superstructures (H1 and H2) of peryienetetracarboxylicacid-dianhydride (PTCDA) monolayers on the (22 x root 3) reconstructed Au(111) surface reported by Mannsfeld et al. [S. Mannsfeld, M. Toerker, T. Schmitz-Hiibsch, F. Sellam, T. Fritz, K. Leo, Org. Electron. 2 (2001) 121] are reinvestigated by high resolution low energy electron diffraction (SPALEED). The purpose of this investigation is to elucidate in detail the point-on-line (p-o-l) structural relation of the homogeneous adsorbate layer with respect to the three reconstruction domains of the Au(111) surface. For the H2 (non-equilibrium) structure, diffraction patterns without a spot splitting are found, indicating an almost perfect undisturbed overgrowth of the domain boundaries of the (22 x root 3) reconstruction. As a consequence, the superstructure does not follow strictly the p-o-l relation, but only in an averaged manner. Contrary for the H1 phase (equilibrium structure), a spot splitting is observed, which indicates that superstructure domains on different Au(111) reconstruction domains exhibit slightly different angular orientations, thus adopting p-o-l relations on all Au(111) reconstruction domains. The PTCDA layer on Au(111) may be thus considered as a rigid or distorted carpet, depending on the preparation conditions. (c) 2006 Elsevier B.V. All rights reserved.