M. Corso

Charge Redistribution and Transport in Molecular Contacts

The forces between two single molecules brought into contact, and their connection with charge transport through the molecular junction, are studied here using non contact AFM, STM, and density functional theory simulations. A carbon monoxide molecule approaching an acetylene molecule (C_{2}H_{2}) initially feels weak attractive electrostatic forces, partly arising from charge reorganization in the presence of molecular . We find that the molecular contact is chemically passive, and protects the electron tunneling barrier from collapsing, even in the limit of repulsive forces. However, we find subtle conductance and force variations at different contacting sites along the C_{2}H_{2} molecule attributed to a weak overlap of their respective frontier orbitals.

Bottom-Up Fabrication of Atomically Precise Graphene Nanoribbons

Graphene nanoribbons (GNRs) make up an extremely interesting class of materials. On the one hand GNRs share many of the superlative properties of graphene, while on the other hand they display an exceptional degree of tunability of their optoelectronic properties. The presence or absence of correlated low-dimensional magnetism, or of a widely tunable band gap, is determined by the boundary conditions imposed by the width, crystallographic symmetry and edge structure of the nanoribbons. In combination with additional controllable parameters like the presence of heteroatoms, tailored strain, or the formation of heterostructures, the possibilities to shape the electronic properties of GNRs according to our needs are fantastic. However, to really benefit from that tunability and harness the opportunities offered by GNRs, atomic precision is strictly required in their synthesis. This can be achieved through an on-surface synthesis approach, in which one lets appropriately designed precursor molecules to react in a selective way that ends up forming GNRs. In this chapter we review the structure-property relations inherent to GNRs, the synthesis approach and the ways in which the varied properties of the resulting ribbons have been probed, finalizing with selected examples of demonstrated GNR applications.

Survival of spin state in magnetic porphyrins contacted by graphene nanoribbons

A magnetic porphyrin connected to graphene nanoribbons remains magnetic. We report on the construction and magnetic characterization of a fully functional hybrid molecular system composed of a single magnetic porphyrin molecule bonded to graphene nanoribbons with atomically precise contacts. We use on-surface synthesis to direct the hybrid creation by combining two molecular precursors on a gold surface. High-resolution imaging with a scanning tunneling microscope finds that the porphyrin core fuses into the graphene nanoribbons through the formation of new carbon rings at chemically predefined positions. These ensure the stability of the hybrid and the extension of the conjugated character of the ribbon into the molecule. By means of inelastic tunneling spectroscopy, we prove the survival of the magnetic functionality of the contacted porphyrin. The molecular spin appears unaffected by the graphenoid electrodes, and we simply observe that the magnetic anisotropy appears modified depending on the precise structure of the contacts.

Electronic Properties of Substitutionally Boron-Doped Graphene Nanoribbons on a Au(111) Surface

High-quality graphene nanoribbons (GNRs) grown by on-surface synthesis strategies with atomic precision can be controllably doped by inserting heteroatoms or chemical groups in the molecular precursors. Here, we study the electronic structure of armchair GNRs substitutionally doped with di-boron moieties at the center, through a combination of scanning tunneling spectroscopy, angle-resolved photoemission, and density functional theory simulations. Boron atoms appear with a small displacement toward the surface, signaling their stronger interactions with the metal. We find two boron-rich flat bands emerging as impurity states inside the GNR band gap, one of them particularly broadened after its hybridization with the gold surface states. In addition, the boron atoms shift the conduction and valence bands of the pristine GNR away from the gap edge and leave unaffected the bands above and below, which become the new frontier bands and have a negligible boron character. This is due to the selective mixing of ...