Electronic and magnetic properties of two dimensional on-surface organic systems

Abstract

The field of molecule-based technology has developed in parallel with nanotechnology over the past decades. However, these systems can offer their own unique functional properties for prospective applications, compared to more traditional, hard condensed matter-based nanotechnologies. This is due to the small size, low cost, and structural perfection that molecules have to offer. The essence of their properties goes beyond classical physics, due to their quantum nature. This fact makes molecule systems as equally fascinating from a physics perspective as they are for their potential use in new device industries. Surface and interface science is an active, interdisciplinary field with applications in chemistry and physics such as heterogeneous catalysis, energy conversion semiconductor and molecular electronics, organic spintronics and quantum magnetism, in particular at the organic-inorganic interface. In these nanoscale systems chemical bonding, electronic charge transfer and magnetic interactions at the interfaces play a fundamental role, and many of these effects are intimately coupled to the atomic structure. Thus knowledge of their structures on atomic scale is essential for the understanding of the underlying physics and for the development and performance of theoretical calculations. Complex self-assembled molecular layers on substrates with engineered architectures and tailored properties, are expected to play an important role in the miniaturization and development of future devices at the nanoscale. The work presented in this thesis addresses the electronic properties of self-assembled metal-organic on-surface networks confining the surface electrons, and a deeper understanding of the tuning of the electronic and magnetic properties of molecular adsorbates across those networks. The research is aimed at studying the interaction between the molecular adsorbates and the quantum confinement. This knowledge is essential e.g. for the development of organic molecule-based devices. In summary, the strength of this thesis lies in the provision of a systematic and comprehensive investigation of the interaction and surface-driven modifications of supported metal-organic complexes on noble metal surfaces, new insight into site-specific electronic and magnetic properties of confined and delocalized surface states with specifically chosen molecular adsorbates. By varying the metal center of organic adsorbates, one can change the density and distribution of the valence electrons in the metal center of the molecule. In other words, the original properties of the complex and the electronic and magnetic properties of the adsorbates are modified due to the presence or absence of the quantum confinement. The realization that the electronic and magnetic properties of the transition metal organic compound can be tailored selectively has created a large diversity of possible applications for these complexes. This includes the creation of exploratory single molecular data storage devices, the replacement of traditional semiconductor electronics by molecular electronics in supramolecular architectures, in magnetochemical sensors or as a means to control and fine tune the magnetic properties of complex architectures in spintronic devices, as well as other applications. The ultimate achievement of this thesis is its contribution to the understanding of the precise mechanisms of confinement-adsorbate interaction. The work presented here provides a solid foundation towards improvement in the development of smart design of structures consisting of just few individual molecules and directly visualizing electron scattering and confinement.