Electronic structure evolution at DBBA/Au(111) interface W/O Bismuth insertion layer

Abstract

Atomically precise graphene nanoribbons (GNRs) can be on-surface synthesized from halogen containing molecular precursors. Here, we investigated the electronic structure evolution of 10,10′-dibromo-9,9′-bianthracene (DBBA), a famous precursor to 7-AGNRs, on both Au(111) and Bi-3×3-Au(111) as a function of film thickness and post-annealing temperature using photoemission spectroscopy, low temperature scanning tunneling microscopy and density functional theories. No obvious changes in electronic structure of DBBA in three STM-observed configurations can be detected, indicating that nonplanar π -conjugated DBBA is physisorbed on both surfaces. The energy level alignments at the DBBA-substrate interfaces are demonstrated. Bismuth(Bi) insertion layer makes molecular−substrate interaction weaker, and makes the energy levels of DBBA thin film rigidly shift by ˜0.70 eV away from Fermi level, which enlarges the hole injection barrier and results in DBBA desorption at ˜470 K before dehalogenation occuring. The surface work function reduction can be explained by the push back effect and charge transfer induced interface dipole. Our findings explain why 7-GNRs could not be formed on Bi-3×3-Au(111).