In-situ fabricated epitaxial organic/ferromagnetic contacts for the combination of single-molecule interface characterization and device-level transport measurements

The field of molecular spintronics is an auspicious route to future concepts of data storage and processing. The hybridization of the electronic structure of non-magnetic organic molecules and ferromagnetic transition-metal surfaces can form hybrid molecular magnets, with distinct magnetic properties, which promise molecular spintronic devices with extremely high information density and low energy consumption. The investigation of these device concepts requires clean and epitaxial interfaces between the surface of a bottom electrode and molecular thin films which can only be realized under ultra-high vacuum (UHV) conditions. The electrodes must be grown on an insulating substrate to electrically separate the top and bottom electrodes of each device. To this end an entirely in-situ preparation of mesoscopic test devices with structurally and chemically well-defined interfaces have been investigated. Au(111)-buffered Co(0001) electrodes are deposited by MBE onto sapphire and mica substrates using shadow-masks. The surface quality is characterized by scanning tunneling microscopy (STM) and other surface science analysis tools. BNTCDI, which serves as an exemplary molecule, is sublimed and the interface formation in the monolayer regime is studied by STM. To bridge the gap between the understanding of microscopic effects and mesoscopic devices, BNTCDI/Co(0001)/Au(111) has been studied in the sub monolayer regime with both STM and STS, in order to determine the exact adsorption position and the electronic interaction. BNTCDI was imaged with sub-molecular resolution by means of STM. For further analysis of the adsorption position, the intramolecular N-H bonds which are very prominent in STM images were used as marker points and their conductance was investigated by means of STS. An intramolecular asymmetry was confirmed in a spatially resolved and energy dependent manner by dI/dV-maps. The asymmetry was attributed to different adsorption sites of the N-H bonds and an adsorption model was developed. A non magnetic Cu top electrode and a capping layer of MgO have been deposited on top of the BNTCDI layers to complete a mesoscopic (200x200 µm²) test device, which reveals in ex-situ transport measurements for the Co/BNTCDI/Cu junction non-metallic behavior and a resistance-area product of 24MΩ∙µm² at 10K