Excitonic Photoluminescence of Ultra-Narrow 7-Armchair Graphene Nanoribbons Grown by a New Bottom-Up Approach on a Ni Substrate under Low Vacuum

Compared to well-studied single-wall carbon nanotubes, narrow graphene nanoribbons (GNRs) are in shadow due to difficulties in their synthesis (necessity of ultra-high vacuum, noble-metal substrates, and tiny output yield). Here, we report a new approach to the bottom-up technique based on chemical vapor deposition to facilitate the synthesis of 7-armchair GNRs on a large scale under low vacuum on common Ni foil. The structure and high quality of produced GNRs are confirmed by multi-wavelength Raman. We demonstrate the characteristic optical absorption features of produced graphene nanoribbons at 2.05 and 2.22 eV associated with the E-11 and E-22 excitonic transitions of 7-armchair GNRs. The produced GNRs demonstrate bright photoluminescence (PL) in the red spectral range with the main characteristic feature at 2.04 eV associated with E-11 exciton transition. We also measured the PL excitation spectral map that contains a diversity of spectrum features associated with 7-armchair GNRs. The presented results can be beneficial for further study of atomically precise GNRs, especially in nonlinear optics, and can be promising for applications of GNRs.