Molecular spin excitation by electron injection through a single graphene nanoribbon

Abstract

Graphene nanoribbons (GNRs) can be synthesized on metal surfaces with atomic precision using on surface synthesis techniques. Their precise size and shape can be tuned finely by selecting appropriate precursor molecules. The incorporation of additional functional molecules during the on-surface synthesis allows the creation of hybrid systems. Using these strategies, we aim at the creation of a magnetic system in which the GNRs act as leads contacting a functional unit. In earlier work, we demonstrated the creation of such hybrid systems by contacting magnetic porphyrin molecules with chiral (3,1)-GNRs on Au(111), and characterizing the porphyrin's magnetic properties using inelastic tunneling spectroscopy. These experiments showed that the spin of the porphyrin survived upon contacting it with up to 4 GNRs. As a further step towards fully functional molecular devices, now, we characterize the magnetic transport properties of essentially one-dimensional GNR-porphyrin-GNR hybrid systems. The linearity of the system is obtained by a small modification of the used precursor molecules. We contact the system at one GNR with the STM tip and lift the molecular complex partially from the surface, in order to create a transport junction. We investigate the porphyrin's spin state via inelastic tunneling spectroscopy in transport configuration, injecting electrons through the semiconducting GNRs into the magnetic porphyrin. The magnetic anisotropy energy is observed to be unaffected by the length of the GNRs. However, we observe an interaction between the porphyrin's d-orbital and the spin excitation.