**1. Introduction**

Since the first successful preparation of graphene by mechanical exfoliation from graphite crystals in 2004 [1], two-dimensional (2D) materials have attracted dramatic attention due to their extraordinary physical properties (ultralow weight, high Young's modulus, and high strength) [2–7] and outstanding electrical properties [1] compared with conventional bulk materials. In the past few years, graphene, with the highest measured Young's modulus (~1 TPa) [3], is the most widely studied 2D material. Studies have shown that graphene filled into the polymer matrices can reinforce the mechanical properties of the composites significantly [8]. However, pristine graphene does not have a bandgap [9], which limits its applications in certain fields requiring a semiconducting material. As a potential substitute material of graphene, the transition metal dichalcogenides (TMDCs, e.g., MoS2 and WSe2) and black phosphorus (BP) with an intrinsic bandgap [10, 11] possess the potential for electronics and optoelectronics applications [12–15] and open a new field for 2D materials study. Moreover, the existence of piezoelectricity and the more sensitive piezoresistive effect in TMDCs compared with graphene under mechanical deformation make them more interesting for innovative applications including tactile strain sensors [16], nanogenerators [17], and advanced nanoelectromechanical systems (NEMS).

In this review, first, we introduce the common approaches used for fabricating suspended 2D material structures. Then, characterization methods for extracting the in-plane and out-ofplane mechanical properties of 2D materials are presented. A summary of the experimental results is given. In the last section, we introduce the electrical output change of 2D materials induced by mechanical deformation—piezoresistive and piezoelectric effects. In addition, we provide some example applications of 2D materials that make use of their extraordinary mechanical as well as mechanoelectric transduction properties.
