Strain engineering of graphene with polymeric actuators

Monolayer graphene is a two-dimensional honeycomb lattice of carbon atoms. It exhibits exceptional mechanical and electronic properties which have catalysed the attention of the scientific community since 2004. The electronic properties of graphene can be tuned by deforming its honeycomb structure in order to promote the formation of strain-induced Landau levels, electronic band-gaps, hydrogen adsorption/desorption or to tailor its optical properties. However, this tuning strategy is poorly explored since it is challenging to find a reliable and flexible method to deform the crystal structure of graphene indeed, while pioneering results were obtained using pre-patterned substrate or complex micro-mechanical systems scalable and tunable methods to control the strain remain elusive. In this Thesis, I present the potential and current applications of polymeric micro-actuators based on poly-methyl-methacrylate (PMMA) as a mean to deform graphene and change its morphology. First, I discuss the perspectives of this technology to create periodic strain patterns and describe the results of numerical simulations. I show how periodic arrangements of polymeric actuators can be used to tune the electronic confinement and band-gap appearance in graphene and study how graphene orientation affects these phenomena. Then, after a preliminary characterization of the mechanical properties of PMMA, I report how polymeric micro-actuators can be used to induce deterministic and reproducible patterns of wrinkles on graphene deposited on top of hexagonal boron-nitride. Different actuation geometries are explored, and experimental results are successfully compared with theoretical predictions on the direction and magnitude of the induced wrinkles. Perspectives for the creation of novel devices based on the local control of strain in two-dimensional materials are finally discussed.