Combined LEED and STM study of PTCDA growth on reconstructed Au(111) and Au(100) single crystals

Abstract

The growth of perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) thin films on the reconstructed surfaces of Au(1 1 1) and Au(1 0 0) single crystals was investigated with low energy electron diffraction and scanning tunneling microscopy under ultrahigh vacuum conditions. The samples were prepared by means of the organic molecular beam epitaxy (OMBE) technique. Two phases with molecular arrangements resembling the (1 0 2) plane herringbone structure of the PTCDA bulk crystal are found on Au(1 1 1); one of them is observed at higher deposition rates only. Both herringbone phases grow homogeneously in large domains on top of the alternating domains of the well known (22×3) Au(1 1 1) surface reconstruction. We show that this surprising growth behavior can be explained using the point-on-line coincidence concept. On the reconstructed Au(1 0 0) surface, we observe various orientations of a herringbone phase. Again the different orientations of this phase are point-on-line coincident, this time with the almost hexagonal Au(1 0 0)hex surface reconstruction. Besides the herringbone phases we regularly observe a square phase of PTCDA on both substrate surfaces.