Unlocking feature-rich properties of carbon-substituted germanene nanoribbons

Using density functional theory (DFT) calculations with both PBE and HSE06 functionals, we have systematically investigated the diverse structural, electronic, and magnetic properties of various carbon-substituted 7AGeNR and 6ZGeNR systems. This includes the evaluation of substitution energies, optimal lattice parameters, one-dimensional (1D) electronic band structures, partial density of states, and spatial charge and spin density distributions. These DFT-derived quantities are analyzed for orbital, atomic, and spin contributions to elucidate complex orbital hybridization and critical magnetic mechanisms. The 7AGeNR and 6ZGeNR systems, substituted with single, double, and full carbon atoms, exhibit notable stability as indicated by their significant substitution energies. The pristine 7AGeNR system displays non-magnetic semiconducting behavior, characterized by a bandgap of 0.57 eV. With the introduction of different carbon substitutions, this non-magnetic behavior persists. Simultaneously, significant alterations in the 1D electronic band structures are observed, resulting in band gaps that expand from 1.04 eV to 4.14 eV. In contrast, the pristine 6ZGeNR demonstrates antiferromagnetic semiconducting characteristics that transition to ferromagnetic semimetal properties in both single C configurations. The full carbon-substituted 6ZGeNR configuration manifests an unusual ferromagnetic 1D semiconductor behavior. From a chemical perspective, the carbon-substituted systems are formed with stable quasi σ and quasi π bonds in carbon-germanium bonding. On the magnetic front, their spin density distributions explain the variations in magnetic behavior. It has been determined that the hybridization of the carbon 2p_z and 2p_xy orbitals with germanium 4p_z and 4p_xy orbitals significantly influences the overall spin density of the 6ZGeNR systems. Our thorough computational results unveil the intricate electronic and magnetic properties inherent to the 7AGeNR and 6ZGeNR systems with different carbon substitutions. They also highlight their potential as candidates for a wide range of practical applications in one-dimensional materials.