Abstract
The family of emerging low‐symmetry and structural in‐plane anisotropic two‐dimensional (2D) materials has been expanding rapidly in recent years. As an important emerging anisotropic 2D material, the black phosphorene 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 abundance, and environmentally friendly characteristics. In this article, the recent research advancements in the field of anisotropic 2D MMCs are reviewed. 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.
Highlights
Since the successful isolation of graphene,[1] research in atomically thin two dimensional (2D) materials has gained intensive interest. Beyond graphene materials such as hexagonal boron nitride (h-BN),[2,3,4] transition metal dichalcogenides (TMDs),[2, 4,5,6] multinary layered chalcogenides,[7] perovskites,[8,9,10] and MXenes[11,12,13] have opened up a new horizon in 2D material research
As a result the chalcogen captures two atoms from Sn, which leads to a change in its electronic configuration from 4d105s25p2 to 4d105s25p0; the same is true for Se-based metal monochalcogenides (MMCs), where, the electronic configuration of Se changes to 4s24p6.[54, 61] As a consequence, the buckled crystal layer structure is distorted (Figure 1)
The top-down approach relies on the exfoliation of thin 2D crystals from their parent layered bulk crystals and the most important are based on mechanical (ME), liquid phase (LPE) and electrochemical exfoliation (EE).[4, 5, 91,92,93]
Summary
Since the successful isolation of graphene,[1] research in atomically thin two dimensional (2D) materials has gained intensive interest. Beyond graphene materials such as hexagonal boron nitride (h-BN),[2,3,4] transition metal dichalcogenides (TMDs),[2, 4,5,6] multinary layered chalcogenides,[7] perovskites,[8,9,10] and MXenes[11,12,13] have opened up a new horizon in 2D material research These 2D materials possess intriguing optical, electronic, mechanical and optoelectronic properties, and are being explored for rich physics and many emerging scientific applications.[1, 3,4,5, 9, 12, 14, 15] completing the intensive research on semimetal graphene and beyond graphene semiconducting 2D materials, group V element black phosphorene (BP) discovered as a 2D material in 2014,[16] leading to many discoveries of novel physical phenomena.[16,17,18,19,20] The puckered or wavy lattice structure with reduced crystal symmetry (D2h) than graphene (D6h) and TMDs make it more interesting for exhibiting the novel physical phenomena. Besides presenting the potential and significance of 2D MMCs in various electronic applications it will delineate the existing limitations and discuss emerging possibilities and future prospects
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