Effects of monolayer Bi on the self-assembly of DBBA on Au(111)

Abstract

The initial growth behaviors of nonplanar 10,10′-dibromo-9,9′-bianthryl (DBBA) molecules on the Au(111) substrates, which is either pristine or Bi-3 × √3-Au(111), at low deposition rates have been systematically investigated using low temperature scanning tunneling microscopy (LT-STM) and density functional theories (DFT) calculations. The effects of such substrates on the subsequent graphene nanoribbons (GNRs) formation are addressed. On clean Au(111), DBBA molecules self-assemble into highly ordered commensurate single-molecule chains along <112¯>Au at a coverage of 0.8 monolayer (ML), and collectively transit into long-range ordered commensurate double-molecule chains along <11¯0>Au but with many single-molecule vacancies at a coverage of 1.2 ML, revealing the delicate competing between intermolecular interactions and molecule-substrate interfacial interactions. The interfacial interactions are further tuned by introducing bismuth to form a Bi-3 × √3-Au(111)surface, where DBBA molecules self-assemble into an unique hexamer phase due to the enhanced intermolecular interactions via CH…π and halogen bonds. DFT calculations confirm the proposed molecular configuration change of single DBBA molecule when adsorbed on different substrates. The calculated difference in CBr bond gives further insight into why no GNRs formed on Bi-3 × √3-Au(111).