Theoretical reproduction of superstructures revealed by STM on bilayer graphene

Abstract

In this work we performed density functional theory calculations for a twisted bilayer graphene (BLG). Several conmensurable rotation angles were analyzed and for each one a constant height mode STM image was obtained. These STM images, calculated under the Tersoff-Hamman theory, reproduce the main features experimentally observed, paticularly superstructures and giant corrugations. In this way we confirm that STM characterization of twisted BLG can produce superstructures whose tunneling current intensity maxima occur over regions with AA stacking. Additionally we give new evidence in favour of an electronic origin for the superstructures instead another physical grounds.

Moiré patterns on STM images of graphite induced by rotations of surface and subsurface layers

“…, which reproduce quite well the experimental observations: moiré patterns and giant corrugation [19]. Besides, these theoretical results point that: (a) current intensity maxima are over AA stacking regions, as previously reported [10,20]; and (b) giant corrugation has a strong electronic origin, as also was quoted recently [21].…”

“…Again only the 2p z orbital contributes near the Fermi Level, although the band structure suffers an important modification respect the TLG-NR case: near the M point and for energies range −1.0 < E − E F < −0.5 eV, four saddle points appear in the band structure. Four Van Hove Singularities (VHS) then appear in the density of states, which explain the current density maxima detected by the STM tip [19,29,30]. • .…”

“…This particular angle produces a commensurable superstructure composed of 222 carbon atoms, which is tractable from the computational point of view, while the periodicity (D = 1.5 nm) is representative of experimental data [19]. For this model we have performed Density Functional Theory calculations using the SIESTA ab initio package [22] which employ norm-conserving pseudo-potentials and localized atomic orbitals as basis set.…”

Electronic properties of graphene-based bilayer systems

“…Such structures have been observed in many experiments using scanning microscopy [6,348,349,351,352,365,366] and dark-field transmission electron microscopy [353,354] (DF-TEM). For different values of the twist angle θ, the STM images of the Moiré patterns are shown in Fig.…”

Periodic arrays of intercalated atoms in twisted bilayer graphene: Anab initioinvestigation

“…However, the interlayer distance in AA region increases to ∆z AA = 3.765Å, while in the AB region we find practically the same distance (∆z AB = 3.650Å). These small changes in the interlayer distances suggest that the origin of the STM images is mainly electronic rather than geometrical 40 . We found pertinent to investigate whether this behavior facilitates the creation of periodic arrays of intercalated atoms between twisted graphene layers.…”