4.5 Conclusions

In summary, by using STM and LEED it has been demonstrated that the self-assembly of NiDPP molecules at room temperature depends greatly on the choice of substrate.

If deposited on the relatively-inert Ag(111) surface, molecule–molecule interactions dominate and the NiDPP molecules form a close-packed, single-domain monolayer, which starts to grow from the substrate step edges.

In contrast, on the more-reactive Ag/Si(111)-√ --
  3 ×√ --
  3 R30 substrate, the molecule–substrate interaction is stronger than in former case, leading the deposited molecules to adopt one of three equivalent orientations on the surface. These initial orientations act as nucleation sites for the three equivalent molecular domains distributed randomly over the substrate terraces.

By studying the self-assembly of a simple molecule such as NiDPP on a wide range of substrates, it becomes possible to make predictions as to the probable supramolecular ordering of more complex molecules on those surfaces. This kind of work is fundamental to our understanding of molecule-substrate interactions, and will form the basis of molecular electronics in the future.