Materials Research Lecture
Mechanical deformations, such as buckling, crumpling, wrinkling, collapsing, and delamination, are usually considered threats to mechanical integrity which are to be avoided in the design of materials and structures. However, if material systems and applied stresses are carefully controlled, such mechanical instabilities can be tailored to deterministically create functional morphologies that enable new and 'reconfigurable' functions. In particular, in atomically-thin material systems with ultralow bending stiffness, such as graphene, mechanical deformations enable new structural properties and device-level functionalities which surpass the limits of bulk material systems. In this talk, I will present our work on controlled deformation and straining of atomically-thin materials, and the emergent materials properties and applications of such deformed and strained atomically-thin materials. First, I will introduce two unique fabrication approaches to enable controlled deformation of atomically-thin materials: (1) a rapid and scalable method of creating crumpled atomically-thin surfaces by soft-matter transformation of shape-memory polymers, and (2) swelling/shrinking-induced crumpling process. Second, I will introduce a new class of 'architectured atomically-thin materials' that are fabricated using these novel approaches, which exhibit a wide range of new material properties. I will present the surface plasmonics enabled by crumpled topographies of graphene and will further discuss shape reconfigurability which opens the door to tunable plasmonic resonance of crumpled graphene. In addition, I will share our ongoing research efforts on strained superlattice for the modulation of electronic properties as well as strain gradient-induced flexoelectricity of crumpled transition metal dichalcogenide (TMDC) materials. Third and last, I will present our work on adaptive/conformal and multifunctional electronics based on mechanically deformed atomically-thin materials. Our optoelectronic sensor is based exclusively on graphene and transforms the two dimensional material into three dimensional (3D) crumpled structures. This added dimensionality enhances the photoabsorption of graphene by increasing its areal density with a buckled 3D structure, which simultaneously improves device stretchability to a 200% strain. Furthermore, we demonstrate a new concept of strain-tunable photoresponsivity where a 200% applied tensile strain results in 100% modulation in photoresponsivity. Our approach to forming architectured atomically-thin materials offers a unique avenue for enabling new materials properties and engineering of advanced device functions.