Design of Low-Coverage Diamane C4X (X = H, F, OH, NH2) with Tunable Electronic and Mechanical Properties

Diamane, a fully sp3-hybridized two-dimensional carbon allotrope, has attracted attention due to its exceptional mechanical strength, tunable electronic properties, and potential for nanoelectronic and nanomechanical applications. While most studies focus on semi-functionalized (50% surface functionalization) C4X2 diamane, the stability and properties of configurations with lower functional group coverage remain unexplored. Here, we propose a novel diamane structure with 25% surface functionalization, denoted as C4X (X = H, F, OH, NH2), crystallizing in the P6/mmm space group. Using first-principles calculations, we systematically investigate the effects of different functional groups on the electronic and mechanical properties. Our results show that the bandgap can be effectively tuned from 2.97 to 3.42 eV, with C4F and C4OH exhibiting wider gaps due to strong C-p and O(F)-p orbital hybridization. C4H and C4NH2 possess high electron mobilities on the magnitude order of of 103 cm2 V−1 s−1. Mechanically, C4H demonstrates a Young’s modulus up to 614 GPa and a shear modulus of 274 GPa, underscoring its exceptional mechanical robustness. This work uncovers a previously unexplored low-coverage diamane configuration, highlighting the crucial role of surface chemistry in modulating electronic and mechanical behavior, and provides a promising design strategy for high-performance carbon-based nanoelectronic and nanomechanical devices.