Experimental nanomechanics of 2D materials for strain engineering

The past 2 decades have witnessed the explosion of research on two-dimensional (2D) materials, where notable efforts have been made in the synthesis and design of a wide spectrum of applications. To understand their mechanical properties and responses triggered by deformation, the prerequisites for reliable applications under realistic service conditions, novel experimental methods have to be developed due to the limitations of traditional bulk mechanical testing for atomically-thin structures. Besides, the nearly-ideal 2D crystalline structures of many 2D materials endow them the great capability of deformation, showing promising potentials in "strain engineering" and "interface engineering" applications. This review summaries several representative approaches in experimental nanomechanics and corresponding progresses in the characterization of structural and mechanical properties of 2D materials, with the aim to provide insights into the instrumental design for nanomechanical tests. In addition, examples of strain-tuned material behaviors and changes in their performance are also discussed to demonstrate the significance of the nanomechanical approach for functional device design and applications.