“In situ” STM studies of the ordering process of a nonplanar derivative of PTCDI on Ag(1 1 0)

The formation of ordered structures of large, nonplanar perylene derivative DPP-PTCDI/perylene-3,4,9,10-tetra-carboxylic-diimide-di(2,6-isopropylphenyl)/on Ag(1 1 0) has been studied “in situ” by means of variable temperature STM. The observations of the molecule diffusion and resulting growth behaviour were performed within a wide temperature interval, 100–190 K. The results indicate that below 160 K the ordering process occurs within existing adsorbate islands. Under these conditions the tilting angle of the nonplanar molecules versus the substrate plane is optimised. Above 160 K the ordering process occurs in a larger scale, leading to the reorganisation of the adsorbate islands. The newly formed islands exhibit an elongated shape which is a consequence of differences in the diffusion coefficient of molecules in perpendicular directions with respect to the Ag(1 1 0) surface structure: parallel and perpendicular to the rows. This difference results from the specific site of adsorbate–substrate interaction. Heating of the substrate with pre-deposited molecules leads to the substrate reorganisation caused by the adsorbate molecules. This phenomenon is explained by the simultaneous diffusion of adsorbate molecules and substrate atoms.