Rotational stability of twisted bilayer graphene

Abstract

Moiré superlattices form in twisted graphene bilayers due to periodic regions of commensurability, but truncation of the moiré patterns affects the rotational stability of finitesized sheets. Here, we report the stepwise untwisting of nanometer-sized bilayer graphene flakes at elevated temperatures, each step corresponding to a potential energy barrier formed by changes to the commensurability between the moiré superlattice and flake size with twist angle. The number of locally-stable energy states and their barrier energies scale with the flake size, allowing twisted graphene flakes of several tens of nanometers to remain thermally stable even at chemical vapor deposition temperatures.

Origin of the vortex displacement field in twisted bilayer graphene

“…A similar multiple stacking domain structure was recently discussed in Ref. 22 in the framework of a model employing a network of partial dislocation. However, the relation between these two descriptions, in terms of vortices and in terms of dislocations, is currently unclear.…”

“…The splitting of the dislocation on hexagonal lattice results in formation of stacking fault which is accompanied also by the appearance of an edge components of partial dislocations 22 , b = (b/2 + b e ) + (b/2 − b e ). In this case, the edge component of displacement field can be written as…”

“…According to Ref. 22 the structure of conjugation of bilayer graphene can be described in terms of network of partial dislocations a/3<1 100> separating the regions of AB and BA stacking. The picture presented in Fig.…”

Imaging moiré deformation and dynamics in twisted bilayer graphene

“…However, no direct observation of untwisting has been presented in the literature, apart from the relaxation observed above 800 °C in ref. 17 , and theoretical work indicates untwisting of large flakes would be unlikely 46 . Indeed, we see no sign of untwisting.…”

An effective curved space-time geometric theory of generic twist angle graphene with application to a rotating bilayer configuration

“…Another motivation is that although Floquet engineering of TBG has been systematically studied [18,19,69,70], most of them have focued on light frequency driven regime or sliding TBG as a 2d Thouless pump [20,71]. The non-adiabatic structurally rotating driving TBG is still in need of investigation [72]. The nonadiabatic Thouless pump has only been reported in waveguide array [73].…”