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) grown on a decanethiol self-assembled monolayer (SAM) on a Au(111) surface. The deposition of several $\left(\approx 16\right)$ monolayers of PTCDA results in unstrained crystalline films whose (012) lattice planes are rotated $21.6°$ with respect to the $〈112¯〉$ Au azimuthal direction. This alignment, which is different from that of PTCDA on the bare Au(111) surface, is most likely caused by the corrugation of the SAM surface [with the $c(4\mathrm{}\times 2)$ superlattice of the $\sqrt{3}\times \sqrt{3}\mathrm{R}30°$ unit cell]. The SAM structure was found to be unaltered by the presence of the PTCDA overlayer. In addition, the heterogeneous PTCDA/SAM/Au structure, acting as an x-ray interferometer with the SAM as a spacer, allows for the precise determination of the SAM thickness.