On-surface synthesis of nitrogen-doped graphene-based nanoarchitectures0D nanographenes, 1D nanoribbons and 2D nanoporous graphene

Abstract

Monolayer graphene has shown to possess distinguished physical properties, which make it one of the starring nanomaterials of the present and of the future. However, some missing properties in graphene limit its applications, such as the lack of band gap, relevant for electronics and optics; the selective reactivity, crucial for sensing, or the permeability, critical for sieving. The modification of its structure has seemed to become the best and most simple strategy to make it suitable for the implementation in nanodevices. Among the structural engineering strategies, the most straightforward approaches imply both scaling down and doping, which have been achieved for years with the top-down method. Nonetheless, with the incoming demand of smaller and more efficient devices, the atomic precision of the novel materials is imperative, something not feasible with the aforementioned technique. It has been demonstrated that the bottom-up protocol is the most appropriate method to achieve the desired functionalities of the nanostructure with atomic precision. By using bottom-up strategies, graphene nanostructures can be synthesized either in solution or on a suitable catalytic surface. Even though the synthesis in solution has bestowed a huge variability of different nanostructures, it makes challenging having monodisperse solution of large aromatic nanostructures and characterize them with the same atomic precision that they are synthesize. The surface-assisted synthesis is an alternative to overcome this issues. Furthermore, with the development of the Scanning Tunneling Microscope, the access to the observation and manipulation of single atoms, molecules or bigger nanostructures became possible, enabling the study of their local properties. In this regard, there have been remarkable works related to the on-surface synthesis of 0D nanographenes, 1D graphene nanoribbons, and 2D nanoporous graphenes. In this thesis dissertation, we address the growth of the three of them, focusing on the introduction of dopants and synthesis of hybrid components. In particular, we put emphasis in the synthesis of 2D nanoporous structures, which has been challenging due to the irreversibility of the reactions on the surface, impeding its extension in the long range order. The first part of this thesis dissertation starts by the description of the synthetic route to grow the material, facing the challenges related to the thermal instability of the precursors and intermediate steps. In the second part of the thesis the aforementioned challenges are overcome by proposing a novel strategy that we presume to be extendable to different kinds of hybrid nanoarchitectures. In particular, our N-doped nanoporous graphene, made by the intercalation of two types of graphene nanoribbons, can also be recognized as a nanometer scale superlattice of type-II heterojunctions. In the third part of this thesis dissertation we study a kinetically driven route to grow 0D N-doped nanographene chains, which feature zig-zag edges. We also test the concept of going beyond the synthesis of GNRs, by inducing further interribbon transformations to create new complex structures. We demonstrate this with two examples, AGNRs with topologically-induced superlattice bands, and AGNRs with fused nanopores, in particular annulene groups. Overall, the results of this thesis provide a deep insight and systematic analysis into the on-surface synthesis of graphene nanoarchitectures, in particular 0D nannographenes, 1D graphene nanoribbons, and 2D nanoporous graphene, which have been intrinsically doped with nitrogen heteroatoms. We proved the different reaction pathways originated from the same or very similar molecular precusor depending on the growth conditions. Specially, we provide a very important landmark in the synthesis of 2D lateral superlattice heterostructures that feature sharp discontinuities down to the single carbon-carbon bond limit, and which can be extended to other nanoarchitectures.