Modification of the Interlayer Coupling and Chemical Reactivity of Multilayer Graphene through Wrinkle Engineering

Wrinkles are special surface corrugations in two-dimensional materials, which can be used to tune their electronic, optical, and chemical properties. There have been many studies focusing on the wrinkle of monolayers and few layers, while studies on wrinkle-induced effects of multilayer materials are rarely reported. In this work, we present a highly efficient fast-cooling method to create wrinkle networks in layered materials, such as multilayer graphene (MLG), MoS2, etc. Due to the highly ordered stacking mode, the wrinkles fabricated on exfoliated graphene show high anisotropy. The wrinkles prefer to generate along armchair or zigzag alignments, which are demonstrated by hydrogen plasma-etched hexagonal pits. Theoretical analysis further proved that the preferential alignments of wrinkles are driven by minimization of the strain energy of the wrinkles and the van der Waals interactions between adjacent graphene layers. Our classical molecular dynamics simulation clearly reproduces the formation of wrinkles in multilayer graphene and reveals the alignment-dependent formation processes. Raman spectra measurements show that the intensity ratio of 2D-/2D+ on MLG wrinkles is higher than that of the flat area. High-resolution transmission electron microscopy (HRTEM) images show that the interlayer distance increases from 3.34 Å on a flat area to 3.83 Å on wrinkled multilayer graphene. Hydrogen plasma etching results reveal that the chemical reactivity of carbon atoms on wrinkles is significantly higher than that on flat areas, especially at the junction of wrinkles. All of the experimental results indicate that the interlayer coupling becomes weak and chemical reactivity increases on MLG wrinkles. This work proposes a new wrinkle engineering method for tuning the physical and chemical properties of MLG, which has important implications for unveiling novel phenomena of many other layered materials under strain, such as layered metal chalcogenides, black phosphorus, etc.