Organic semiconducting thin film growth on an organic substrate: 3,4,9,10-perylenetetracarboxylic dianhydride on a monolayer of decanethiol self-assembled on Au(111)

We use surface x-ray diffraction to study the structure of organic-organic heterojunctions grown by organic molecular-beam deposition. In particular, we study films of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) grow n on a decanethiol self-assembled monolayer (SAM) on a Au(lll) surface. The deposition of several (approximate to 16) monolayers of PTCDA results in u nstrained crystalline films whose (012) lattice planes are rotated 21.6 deg rees with respect to the(11 (2) over bar) Au azimuthal direction. This alig nment, which is different from that of PTCDA on the bare Au(lll) surface, i s most likely caused by the corrugation of the SAM surface [with the c(4 X 2) superlattice of the root 3 X root 3R30 degrees unit cell]. The SAM struc ture was found to be unaltered by the presence of the PTCDA overlayer. In a ddition, the heterogeneous PTCDA/SAM/Au structure, acting as an x-ray inter ferometer with the SAM as a spacer, allows for the precise determination of the SAM thickness.