(Invited) Electronic Structure and Raman Fingerprint of Atomically Precise Graphene Nanoribbons – a Key for Integration in Devices.

Abstract

Graphene nanoribbons (GNRs) are a novel tunable material that combines the best attributes of graphene and carbon nanotube worlds. We present our recent results on the electronic, optical and vibrational properties of atomically precise GNRs, particularly, pristine and boron-doped armchair graphene nanoribbons of N = 7 carbon atoms width (7-AGNRs and B-7AGNRs). Spatially aligned GNRs are synthesized by bottom-up approach on stepped Au surface. Using angle-resolved photoemission spectroscopy (ARPES) we reveal energy band dispersion of these systems. ARPES data allow us to determine the energies of one-dimensional sub-bands and the effective masses of charge carriers, which are important for charge transport characterization. Using ultra-high vacuum Raman spectroscopy we probe phonons of air-sensitive B-7AGNRs in situ and reveal the existence of characteristic splittings and red-shifts of vibration modes due to the presence of boron atoms. We perform transfer of 7-AGNRs on to the insulating substrate, which allows tuning and probing their optical response. Particularly, bright photoluminescence in 7-AGNRs is controllably induced by defect-engineering. Finally, we partially transform N=7 to narrow-gap N=14 AGNRs via lateral edge fusion on large-area surface. The band structure of 14-AGNRs is visualized by ARPES. Raman fingerprint allows easy identification of type and orientation of GNRs on both metallic and insulating substrates. The fused GNRs are also integrated in the field-effect transistor.