Bottom-up
fabrication techniques enable atomically precise integration
of dopant atoms into the structure of graphene nanoribbons (GNRs).
Such dopants exhibit perfect alignment within GNRs and behave differently
from bulk semiconductor dopants. The effect of dopant concentration
on the electronic structure of GNRs, however, remains unclear despite
its importance in future electronics applications. Here we use scanning
tunneling microscopy and first-principles calculations to investigate
the electronic structure of bottom-up synthesized <i>N</i> = 7 armchair GNRs featuring varying concentrations of boron dopants.
First-principles calculations of freestanding GNRs predict that the
inclusion of boron atoms into a GNR backbone should induce two sharp
dopant states whose energy splitting varies with dopant concentration.
Scanning tunneling spectroscopy experiments, however, reveal two broad
dopant states with an energy splitting greater than expected. This
anomalous behavior results from an unusual hybridization between the
dopant states and the Au(111) surface, with the dopant–surface
interaction strength dictated by the dopant orbital symmetry
