Nanoconfinement effects in the self-assembly of diindenoperylene (DIP) on Cu(111) surfaces

The structure of monolayer films of diindenoperylene (DIP) on Cu(111) single crystals has been studied by means of scanning tunneling microscopy (STM). Pronounced film confinement effects are observed, resulting in distinctly different film structures depending upon the substrate terrace width. On wide terraces (exceeding approximately 15 nm in width) a short range ordered structure forms with the DIP molecules aligned along three discrete directions related by 60 degrees rotations. On the contrary, on narrow terraces (<15 nm), the confinement enhances the role of the step edges and leads to the formation of a long range ordered structure with co-directionally oriented molecules, tentatively ascribed to an energy minimization by optimization of the surface coverage.