Experimental formation of monolayer group-IV monochalcogenides

TL;DR

This paper reviews recent experimental methods for synthesizing monolayer group-IV monochalcogenides, highlighting challenges and comparing techniques like molecular beam epitaxy, etching, and exfoliation for potential applications in advanced 2D material devices.

Contribution

It provides a comprehensive overview of experimental routes for creating monolayer MX materials, including recent advances and a comparative analysis of different synthesis methods.

Findings

Molecular beam epitaxy enables controlled monolayer growth.

Two-step etching effectively produces monolayer MX.

Liquid phase exfoliation offers a scalable synthesis route.

Abstract

Monolayer group-IV monochalcogenides (MX, M = Ge, Sn, Pb; X = S, Se, Te) are a family of novel two-dimensional (2D) materials that have atomic structures closely related to that of the staggered black phosphorus lattice. The structure of most monolayer MX materials exhibits a broken inversion symmetry, and many of them exhibit ferroelectricity with a reversible in-plane electric polarization. A further consequence of the noncentrosymmetric structure is that when coupled with strong spin-orbit coupling, many MX materials are promising for the future applications in non-linear optics, photovoltaics, spintronics and valleytronics. Nevertheless, because of the relatively large exfoliation energy, the creation of monolayer MX materials is not easy, which hinders the integration of these materials into the fast-developing field of 2D material heterostructures. In this Perspective, we review recent developments in experimental routes to the creation of monolayer MX, including molecular beam epitaxy and two-step etching methods. Other approaches that could be used to prepare monolayer MX are also discussed, such as liquid phase exfoliation and solution phase synthesis. A quantitative comparison between these different methods is also presented.