Wrinkled, rippled and crumpled graphene: an overview of formation mechanism, electronic properties, and applications

Distinctive from their 1D and 0D counterparts, 2D nanomaterials (2DNs) exhibit surface corrugations (wrinkles and ripples) and crumples. Thermal vibrations, edge instabilities, thermodynamically unstable (interatomic) interactions, strain in 2D crystals, thermal contraction, dislocations, solvent trapping, pre-strained substrate-relaxation, surface anchorage and high solvent surface tension during transfer cause wrinkles or ripples to form on graphene. These corrugations on graphene can modify its electronic structure, create polarized carrier puddles, induce pseudomagnetic field in bilayers and alter surface properties. This review outlines the different mechanisms of wrinkle, ripple and crumple formation, and the interplay between wrinkles' and ripples' attributes (wavelength/width, amplitude/height, length/size, and bending radius) and graphene's electronic properties and other mechanical, optical, surface, and chemical properties. Also included are brief discussions on corrugation-induced reversible wettability and transmittance in graphene, modulation of its chemical potential, enhanced energy storage and strain sensing via relaxation of corrugations. Finally, the review summarizes the future areas of research for 2D corrugations and crumples.