  The family of emerging low-symmetry and structural in-plane anisotropic 2D
materials have been expanding rapidly in recent years. As an important emerging
anisotropic 2D material, the black phosphorene (BP) analog group IVA-VI metal
monochalcogenides (MMCs) have been surged recently due to their distinctive
crystalline symmetries, exotic in-plane anisotropic electronic and optical
response, earth abundant and environmentally friendly characteristics. In this
article, we review the recent research advancements in the field of anisotropic
2D MMCs. At first, the unique wavy crystal structures together with the optical
and electronic properties of such materials are discussed. The review continues
with the various methods adopted for the synthesis of layered MMCs including
micromechanical and liquid phase exfoliation as well as physical vapor
deposition. The last part of the article focuses on the application of the
structural anisotropic response of 2D MMCs in field effect transistors,
photovoltaic cells nonlinear optics and valleytronic devices. Besides
presenting the significant research in the field of this emerging class of 2D
materials, this review also delineates the existing limitations and discusses
emerging possibilities and future prospects.
