"Mechanical Properties of Bilayer Graphene" 

Soumya Sourav Sarangi, MSE PhD Candidate 

Advisor: Professor Gary J Cheng

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ABSTRACT

Bilayer graphene (BLG) structures are gaining popularity in recent times due to their exceptional optical and electrical properties. BLG is fabricated by stacking or growing single-layer graphene on top of another single-layer graphene or through mechanical exfoliation from the bulk graphite phase. BLG are useful as semiconductor materials in modern electronic devices due to existence of a tunable bandgap arising from the strong coupling between the graphene layers. The mechanical properties of the constituent materials in a device could determine its durability and stability, therefore it is extremely important to understand mechanical behavior of BLGs. In this context numerous experimental and simulation studies have reported that the strain to failure, intrinsic stress, and Young's modulus of BLG is comparable to those in single-layer graphene. The mechanical properties of BLGs are influenced by interlayer shearing and stacking sequences of the graphene layers, where interlayer interactions determine out-of-plane strength for the BLG, intralayer interactions affect in-plane strength, and the stress accumulation at edges cause interfacial dislocations and debonding between layers resulting in failure. Further, BLG with misorientation between the graphene layers caused by a relative twist in layers is called twisted bilayer graphene (tBLG). The tBLG structures are also attracting significant research interest in recent years due to their unique band gap structures at specific angles known as “magic angles”. Twisted bilayer graphene can be designed to become insulators or superconductors with only slight variation in twist angles, which opens exciting possibilities for technological applications. Despite these excellent properties and uses, very few studies have reported on tBLG’s mechanical behavior, highlighting the need for more in-depth research.