  Anisotropic two-dimensional layered materials with low-symmetric lattices
have attracted increasing attention due to their unique orientation-dependent
mechanical properties. Black arsenic (b-As), with the puckered structure,
exhibits extreme in-plane anisotropy in optical, electrical and thermal
properties. However, experimental research on mechanical properties of b-As is
very rare, although theoretical calculations predicted the exotic elastic
properties of b-As, such as anisotropic Young's modulus and negative Poisson's
ratio. Herein, experimental observations on highly anisotropic elastic
properties of b-As were demonstrated using our developed in situ tensile
straining setup based on the effective microelectromechanical system. The
cyclic and repeatable load-displacement curves proved that Young's modulus
along zigzag direction was ~1.6 times greater than that along armchair
direction, while the anisotropic ratio of ultimate strain reached ~2.5,
attributed to hinge structure in armchair direction. This study could provide
significant insights to design novel anisotropic materials and explore their
potential applications in nanomechanics and nanodevices.
