Top-down reorganization of self-assembled monolayers on Au(111).

Bottom-up synthesis of graphene nanoribbons (GNRs) from aryl halide precursors is often performed thermally or in-solution, without detailing the local molecular assembly or the precursor's response to electromechanics perturbation. This synthetic approach forms nanoribbons with well-defined widths and atomically precise edges, which are necessary for ensuring bandgap uniformity. However, neither on-surface nor solution-based GNR synthesis techniques adequately address the problem of positional control, which is crucial to the fabrication of GNR transistors. To better understand this issue, we investigate the on-surface ordering of 10, 10'-dibromo-9, 9'-bianthracene (DBBA), the 7A-GNR monomer precursor. Scanning tunneling microscopy imaging shows that DBBA molecules spontaneously assemble on Au(111) into non-covalent two-dimensional islands. By varying sample temperature during and after deposition, we observe three different adsorbate arrangements. These two-dimensional packing structures demonstrate differing responses to localized excitations. The difference in packing structures and their respective responses to electro-mechanical perturbations can give us insight into how to best optimize conditions for locally controlled and large-scale thermal GNR polymer growth.