Burgers vector analysis
This protocol is extracted from research article:
In situ manipulation and switching of dislocations in bilayer graphene
Sci Adv, Aug 10, 2018; DOI: 10.1126/sciadv.aat4712

Embedded Image DF-TEM was used for Burgers vector evaluation. The Embedded Image invisibility criterion was applied to extract the direction of the Burgers vector for the respective dislocation (10). While the invisibility criterion can be used to identify the direction of the Burgers vector, its absolute sign cannot be derived. To determine the sign of the Burgers vector, we studied the change in DF-TEM contrast of the dislocation upon tilting the bilayer graphene membrane. The tilting axis was chosen perpendicular to the Embedded Image diffraction vector so that the excitation error continuously changes during tilting (rocking curve scan). By tilting a few degrees away from the [0001] zone axis, the strain and (in the presence of an edge component) buckling of the membrane led to an asymmetric bright-dark contrast of the dislocation, as revealed in fig. S7. From the orientation of the bright-dark contrast, the absolute sign of the Burgers vector can be unambiguously derived. In the case of an edge dislocation, the sign of the Burgers vector determined whether an additional row of atoms was “inserted” in the top or bottom graphene layer. To interpret the sign of the Burgers vector, in this manner, the convention for the definition of the Burgers vector was fixed throughout the analysis. Here (in figs. S4 and S7), the so-called finish-to-start/right-hand convention (32) for the definition of the Burgers vector was used.

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