Wrinkle networks in exfoliated multilayer graphene and other layered materials

We describe a method to obtain networks of wrinkles in multilayer graphene flakes (and other layered materials) by thermal contraction of the underlying PDMS substrate they are deposited on. The exfoliated flakes on PDMS are dipped into liquid nitrogen and after removal networks of wrinkles are found. The density of wrinkles can be controlled to some degree by sequential dipping into liquid nitrogen. Atomic force microscopy shows that wrinkles form preferentially along the armchair direction of the graphene lattice in such multilayer graphene platelets. Raman spectra show that the interlayer coupling at a wrinkle in multilayer graphene differs from, and is weaker than, that in undeformed regions. High resolution transmission electron microscopy measurements show that the interlayer distance increases in strained regions, which results in the interlayer coupling being decreased in particular regions of the wrinkles in these multilayer graphenes.