Fig. 4
From: Mosaic pattern formation in exfoliated graphene by mechanical deformation
Proposed mechanism of mosaic formation of a simply supported graphene flake by mechanical deformation. a–d Schematic of simply supported graphene under uniaxial tension experiencing compression in the lateral direction due to Poisson’s contraction of the substrate (indicated by the dotted arrows) (a). Upon loading—at the critical strain \(\varepsilon _{{\rm{cr}}}^{{\rm{tens}}}\)—the lateral strain exerted by the Poisson’s contraction of the underlying polymer induces graphene to buckle giving rise to lateral wrinkles (b). As strain increases, the amplitude of these wrinkles increases. The wrinkles stick up above the PMMA substrate, leaving a hollowed region between graphene and the underlying substrate resulting in a local absence/lack of the interface (c). Due to interface slippage, when the sample is subjected to unloading (d), graphene tends to buckle in the perpendicular direction (as indicated by white arrows) at \(\varepsilon _{{\rm{onset}}}^{{\rm{mosaic}}}\). The previously formed lateral wrinkles cannot be fully recovered and the intersection between the two families of wrinkles forms different junctions. The direction of the blue arrows indicates the loading/unloading of the substrate and graphene. e–f Representative loading-unloading cycle (e); 2D band Raman shift and graphene strain versus the applied strain for simply supported graphene on PMMA subjected to mechanical loading (f)
