Tuning the electronic and magnetic properties of germanium-substituted armchair and zigzag graphene nanoribbons: A comprehensive DFT investigation

Substitution is among the effective methods to modify essential properties of graphene nanoribbons (GNRs) allowing them to be adaptive to a wide range of applications. In this study, the spin-polarized DFT calculations were performed to discover the structural, electronic, and magnetic properties of 7AGNR and 6ZGNR systems under different germanium substitutions. The critical concentrations and positions of Ge adatoms are considered by investigating different configurations. The systematic calculations and subsequent analysis provided a comprehensive framework for establishing the structure-property relationship. Importantly, the mechanisms responsible for this relationship were also determined, where Ge adatoms play important roles in the orbital hybridization, charge transfer, and new chemical bonding formation. The properties of 7AGNR and 6ZGNR were significantly altered by germanium substitution. The pristine 7AGNR has a bandgap of 1.57 eV, which can vary from 0.58 to 1.96 eV depending on the concentration and distribution of Ge adatom. Meanwhile, its nonmagnetic character is preserved. The 6ZGNR system, on the other hand, displays spin-splitting bandgap of 0.53 eV making it be a unique antiferromagnetic semiconductor. A single germanium atom substitution in 6ZGNR induces a ferromagnetic semi-metallic state with a magnetic moment ranging from −0.02 to −0.21 μ_B, whereas complete (100 %) germanium substitution yields a ferromagnetic semiconducting state with a magnetic moment of −0.03 μ_B. The mechanisms by which Ge adatoms modify the fundamental properties of 1D GNR systems can serve as a reference for investigating and tailoring the properties of other 1D systems for advanced applications.