Electronic transport modulation in C-57: A path toward carbon-based logic and switching devices

We report a comprehensive theoretical investigation of the two-dimensional carbon allotrope C-57, comprised of fused pentagonal and heptagonal rings, focusing on its electronic structure and transport properties. Using density functional theory (DFT) with SIESTA and non-equilibrium Green's function (NEGF) transport simulations via TranSIESTA, we demonstrate that pristine C-57 is intrinsically metallic, with multiple bands crossing the Fermi level and room-temperature carrier mobilities of 10³–10⁴ cm²V⁻¹s⁻¹. Edge hydrogenation opens a direct band gap of 0.437 eV, yielding semiconducting nanoribbons that exhibit negligible current below |V| ≃ 0.45 V and a sharp turn-on above threshold. Two- and three-dimensional maps of the density of states and transmission coefficients elucidate bias-tunable resonances governing conductance modulation. Comparison with other 2D carbon allotropes – such as graphdiyne and penta-graphene – highlights C-57's intermediate gap and reversible metal-to-semiconductor transition via chemical functionalization. These features position C-57 as a versatile all-carbon platform for low-voltage field-effect transistors, reconfigurable logic elements, and nanoscale sensors.