TEM Dark Field Analysis on the Atomic Scale Reconstruction in Twisted Trilayer Graphene

Interfaces formed by joining two van der Waals (vdW) crystals has offered a new route to access exotic electronic behaviors. The interplay between twist-tunable length scale of moire superlattice and underlying atomic scale reconstruction has been key to understand such unconventional electronic behaviors. In the twisted bilayer graphene, for instance, periodic rearrangement of atoms with the moire length scale was reported to be responsible for many exotic phenomena including anomalous electronic transport in small twist angle (θ&lt;1°) and the strongly correlated behavior in magic angle (θ~1.1°). On the other hand, atomic configuration in twisted trilayer graphene and its correlation with the recently reported unconventional superconductivity has yet to be investigated. Although robust superconductivity in the twisted trilayer graphene has been reported by multiple groups, their insight onto the atomic and moire structure remains elusive due to the complicated nature of the interlayer interaction in trilayer system. The reconstruction between the top and bottom layers through the middle layer in addition to that between the two adjacent layers should be considered to understand the atomistic details of twisted trilayer graphene.<br/>In this study, we utilized the transmission electron microscopy (TEM) dark field (DF) imaging technique to investigate the reconstructed moiré lattice in twisted trilayer graphene. Assuming only a single event of electron scattering with the thin specimen, the intensity of TEM DF image can be interpreted as kinematical diffraction intensity variation in real space. Moreover, by obtaining the tilt-series DF images, one can monitor the change in such diffraction intensity as a function of the deviation from the exact Laue condition. We found that the atomic rearrangement occurs in all three layers, resulting in an array of commensurate domains of Bernal and rhombohedral stacking orders competing with each other.