Tuning the electronic properties of graphene via embedding diborane molecules

Tuning the gapless and isotropic Dirac electron behavior in graphene remains an active research pursuit. Recently, a study revealed that the on-surface synthesis of zigzag graphene nanoribbons embedded with porphyrins laterally fused along the ribbon backbone opens exciting opportunities for creating hybrid graphene nanostructures in which the electronic properties can be precisely tuned [Xiang et al., Nat. Chem. 17, 1356 (2025)]. Inspired by this progress, herein, we propose a band engineering scheme involving the fusion of exotic molecules, rather than pure atoms or carbon-based molecules, into the graphene lattice, as exemplified by embedding diborane molecules along the armchair or zigzag direction in graphene (named diBEG-AN or diBEG-ZN). First-principles calculations reveal that diBEG-A1 is a direct bandgap semiconductor. Additionally, a bandgap oscillation emerges in other diBEG-ANs, following the rule N = 3,5,7 + 6n (where n is an integer). The combination of a broad intrinsic and strain-tunable direct bandgap window, light charge carriers, optical dichroism, and dipole-allowed optical transitions makes diBEG-ANs highly promising for optoelectronic and direction-dependent device applications. Strained diBEG-A5/A7 and diBEG-ZNs (N > 1) are Dirac semimetals (DSs) that exhibit tunable anisotropic phases, including the highly tilted type-I, type-II, and semi-DS states. Tight-binding analysis suggests that the diverse electronic properties of diBEGs primarily originate from the reformulation of orbital interactions near the diborane units. The engineering strategy proposed herein and the outcomes demonstrated hereby are poised to provide an alternative angle for graphene-related applications and the underlying physics.