Pinning of graphene for conformal wrinkling over a soft corrugated substrate through prestretch-release process

Abstract

The adhesion of a 2D material to a substrate is facilitated by the van der Waals (vdW) interactions, which is significantly influenced by the roughness and wettability of the substrate. It is challenging to achieve good as well as conformal adhesion of mechanically exfoliated 2D materials to a hydrophobic soft substrate like polydimethylsiloxane (PDMS). In addition, the mechanical folding instabilities are inevitably observed in 2D elastic nanosheets over a smooth PDMS substrate under higher compressions in a prestretch-release process. However, the manipulation of the soft substrate’s surface roughness may provide an essential degree of freedom for tailoring the conformation level and topography of the 2D elastic nanosheets. Herein, we propose a technique to improve the interfacial adhesion of the graphene membrane to a periodically trenched PDMS substrate by suppressing the mechanical folding instabilities in a prestretch-release process. The conformal wrinkling of the graphene membrane, as confirmed through atomic force microscopy (AFM) imaging, is found to result from its pinning into the trenches via snap-through transition. We also show the impact of the substrate’s topography on the buckling behavior of the graphene membrane under the stress loading-unloading cycle by surface-engineering of the PDMS substrate using ion beam irradiation. This study offers fundamental as well as practical insights into the adhesion mechanics of the 2D elastic nanosheets over the corrugated soft substrates under the prestretch-release process. The wrinkled topography of the membrane could be harnessed for flexible, conformal, and tunable electronic devices.