2D organic layers on surfaces: self-assembly and electronic structure*

Understanding the basic mechanisms leading to the formation of 2D organic layers on surfaces, either via Van der Waals, ionic or covalent interactions, is a necessary step toward the development of controlled and ordered organic layers, for technological applications such as homogeneous doping of graphene or 2D organic topological insulators. Using a combination of scanning tunnel microscopy, various electron spectroscopies techniques and ab-initio calculations, we have studied several aspects of the self-assembly and reactivity of particularly interesting model systems: Zinc tetraphenylporphyrins (ZnTPP) on single crystal surfaces.

First, we have explored the delicate balance of forces during the self-assembly process of ZnTPPs on metal single crystal surfaces. It is shown that molecule/molecule and molecule/surface interactions, as well as accumulated surface stress, all play an important role in determining self-assembly. In particular, it is shown that self-assembly can be kinetically trapped into metastable phases different from typical equilibrium outcomes. Furthermore, it is possible to generate under certain conditions on self-assembled ZnTPP arrays, surface mediated chemistry that leads, to site-selective dehydrogenation and intramolecular covalent bond creation. Intermolecular dehydrogenation is also possible, and if directed properly could lead to tunable highly ordered 2D covalent structure.