Twisted two-dimensional materials have emerged as a topic of high current interest in condensed-matter physics since the breakthrough of the twisted bilayer graphene. In this work, the structural and electronic properties, including the out-of-plane polarization of large (336 atoms) twisted hexagonal boron nitride flakes on graphene are investigated on the basis of density-functional theory calculations. Eleven different twist angles are examined, ranging from $0^{\text{o}}$ to ${60}^{\text{o}}$. The variation in the binding energies as a function of rotation angles is insignificant, suggesting a weak barrier for hBN-flake rotation. Additionally, the results demonstrate that the presence of the large hBN-flake breaks the symmetry of pristine graphene and opens a band gap. The largest value of the band gap is found to be 14.3 meV for $0^{\text{o}}$ twist angle. By investigating the vertical distance of the individual atoms in the flake to graphene, we find that it is laterally modulated where shorter distances exhibit an associated charge accumulation. Bader charge values show that the electron charge moves from graphene to the hBN flake, giving rise to a negative out-of-plane polarization that points downward from the hBN flake to graphene, where there is a 0.20 pC/m difference between twisted and nontwisted ($0^{\text{o}}$) configurations. The highest occupied and lowest unoccupied molecular orbitals are delocalized on graphene, but show a striking difference in shape and symmetry that reflects their interaction with the flake, where the former are of bonding character and the latter antibonding. The present results show that the twist angle can be used as an additional degree of freedom to tune the electronic properties of hBN flakes on graphene, which may be utilized in future electronic devices.

Close

PrevNext

View figure in article

• Electronic structure
• First-principles calculations
• Twistronics
• Two-dimensional electron system
• Polarization