Tuning the Electronic and Mechanical Properties of Two-Dimensional Diamond through N and B Doping

This paper examines the structural, thermodynamic, dynamic, elastic, and electronic properties of doped 2D diamond C4X2 (X = B or N) nanosheets in both AA ' A '' and ABC stacking configurations, by first-principles calculations. Those systems consist of three diamond-like graphene sheets with an undoped graphene layer between two 50% doped ones. Our results, based on the analysis of ab initio molecular dynamics simulations, phonon dispersion spectra, and Born's criteria for mechanical stability, revealed that all four structures are stable. Additionally, their standard enthalpy of formation values are similar to that of pristine 2D diamonds, recently synthesized by compressing three graphene layers together. The C4X2 (X = B or N) systems exhibit high elastic constant values and stiffness comparable to that of bulk diamond. The C4N2 nanosheets present wide indirect band gaps that could be advantageous for applications similar to those of the hexagonal boron nitride (h-BN), such as a substrate for high-mobility 2D devices. On the other hand, the C4B2 systems are semiconductors with direct band gaps, in the 1.6-2.0 eV range, and small effective masses, which are favorable characteristics to high carrier mobility and optoelectronics applications.