Anisotropic Strain Observation in Naturally Occurring Buckling on Twisted Bilayer Graphene: A Nano-Raman Study

Twisted bilayer graphene (tBG) is an exuberant electronic system, exhibiting a wide variety of electronic behaviors intricately influenced by both the twist angle and internal built-in strain. In our study, we explore how naturally occurring variations in the mismatch angle in the bilayer graphene result in localized strain gradients. These gradients are sufficient to store elastic energy, promoting deterministic buckling phenomena. Utilizing tip-enhanced Raman spectroscopy, we conducted nanometer-scale mapping of twist angle, strain distribution, and elastic energy across tBG, identifying pronounced and deterministic fluctuations in Raman peak shifts, particularly within the 2D band on wrinkled areas. This analysis enabled us to distinguish between uniaxial and biaxial strain effects and to evaluate the elastic energy that remains within these structures. Supported by finite element modeling, our results elucidate the relationship between anisotropic strain dynamics and buckling behavior, enhancing our understanding of tBG’s mechanical properties. Our findings contribute to the field of strain engineering in tBG and suggest new possibilities for tailoring the electronic and structural characteristics of these materials at the nanoscale.