Two-dimensional (2D) materials have attracted increasing attention recently due to their extraordinarily different material properties compared with conventional bulk materials. The 2D materials possess ultralow weight, high Young’s modulus, high strength, outstanding carrier mobility, as well as high anisotropy between the in-plane and out-of-plane mechanical properties. The nearby atoms in the same plane of layered 2D materials are connected via covalent bonding, while the interlayers are stacked together via weak van der Waals interactions. In this article, we review the in-plane mechanical properties (including the in-plane Young’s modulus, pretension, breaking strength/strain) and out-of-plane mechanical properties (including the perpendicular-to-plane Young’s modulus, shear force constant, and shear strength) of different 2D materials, varying from conductors, semiconductors, to insulators. The different fabrication methods for suspended 2D material structures are presented. The experimental methods and principles for mechanical properties characterization are reviewed. A comparison of the mechanical properties among different 2D materials is summarized. Furthermore, electrical output change as a result of mechanical deformation (piezoresistive and piezoelectric effects) is introduced briefly. By exploiting the unique mechanical and mechanoelectric transduction properties, 2D materials can be used in wide-ranging applications, including flexible electronics, strain sensors, nanogenerators, and innovative nanoelectromechanical systems (NEMS).
Part of the book: Two-dimensional Materials