(439d) Tuning the Bandgap of Graphene Nanoribbons through Defect-Interaction-Driven Edge Patterning

Graphene nanoribbons (GNRs) with widths narrower than 10 nm have outstanding electronic, thermal, and mechanical properties and are considered as very promising two-dimensional material structures for both front-end and back-end technologies in future generations of high-performance and low-power-consumption electronics. The electronic band structure of the GNRs can be modified and their bandgap can be tuned by controlling the GNR width and the type, i.e., the orientation, of its edges.

In this presentation, we report a defect engineering strategy for tuning the bandgap of GNRs based on patterning of the GNR edges. The defects of interest are nanopores, or vacancy clusters, which can be introduced into GNRs in regular arrangements by ion etching or electron irradiation. We have conducted a systematic analysis of pore-edge interactions in GNRs using molecular-statics computations based on reliable interatomic potentials, which have revealed strongly attractive interactions for nanopores in the vicinity of GNR edges. These attractive interactions provide the thermodynamic driving force for nanopore migration toward the GNR edge, leading to its coalescence with the GNR edge through a sequence of carbon ring reconstructions. We have studied nanopore dynamics near GNR edges in detail through molecular-dynamics (MD) simulations at high temperature. We have constructed the optimal kinetic pathways of the mechanisms mediating the coalescence of the nanopore and the GNR edge, as identified by the MD simulations, using climbing-image nudged elastic band calculations. We have found that the post-coalescence morphological evolution of an armchair GNR edge leads to the formation of a V-shaped edge pattern consisting of zigzag linear segments (facets). First-principles calculations of the electronic band structure of such patterned GNRs based on density functional theory show that the zigzag segments formed at the armchair edges can be used to tune the bandgap of the GNR. We find a linear dependence of the bandgap of the patterned GNRs on the linear density of the zigzag edge atoms, which is controlled by the size and concentration of the pores introduced in the defect-engineered GNR.