Oleksii Ivashenko: Fundamentals and applications of molecular nanotechnology: in situ spectroscopic study of operating molecular junctions

Molecular junctions are composed of a molecular film in between of two electrodes. In the circuit, electron transport takes place from one electrode through the molecular film to the other electrode via different mechanisms: tunneling, Schottky emission or field ionization, redox exchange, hopping, etc. Control electron transport in such a nanodevices faces several challenges: metal electromigration, temperature and life-time instability, device to device (batch to batch) variation, irreproducibility, and independence from the molecular structure. Several successful strategies for overcoming these challenges and utilizing such molecular junctions in nanotechnology R&D will be discussed. I shall focus on a molecular junction platform based on covalently bonded molecular layers on carbon shows good temperature tolerance (5-600 K), lifetime, and stability at extreme bias conditions, which are necessary for studying numerous interesting phenomena at the nanoscale, including transition of electron transport from tunneling to hopping, existence of hot carriers, light emission, etc. The model junction was prepared using gold/carbon electrodes containing molecular film composed of several aromatic molecules (nitroazobenzene, azobenzene, antraquinone, bisthienylbenzene, naphthalene di ‐ imide derivative) with thickness range 3-30 nm. In situ Raman and absorption spectroscopy, I-V measurements, performed in air and UHV (77-350K), probe the functionality of the junctions in variety of conditions. Remarkably, light emission, observed for the first time in molecular junctions, shows how electron transport can be studied in situ using electron energy loss spectroscopy.