Liquid state of post-transition metals for interfacial synthesis of two-dimensional materials

The nascent field of liquid metals, metals, and alloys of low melting points has provided opportunities for synthesizing low-dimensional materials. Located between transition- and non-metals in the periodic table, post-transition elements exhibit unique properties in particular low melting points. Taking on a liquid form at low temperature, post-transition liquid metals can be used as solvents for metallic solutes. The enigmatic surface of liquid metals is also ultra-active and smooth, offering opportunities for fabricating and templating two-dimensional (2D) films. So far, various 2D materials have been harvested from the surface of liquid metals including 2D metal compounds and nonmetallic materials. Utilizing different extraction and transfer techniques, the produced 2D films can be uniformly deposited on desired substrates at large lateral dimensions. Here, we present a comprehensive overview of the fundamentals underlying post-transition-elements-based liquid metals and alloys and explain the effect of atomic level electron configurations on their characteristics. We discuss the key physical properties of liquid metals including the origin of their low melting points and their high thermal and electrical conductivities. We illustrate their boundary-induced layering and oxidation as essential traits for creating 2D films. Afterward, the interfacial synthesis of 2D materials is depicted with the discussion of surface oxidation, reduction and exfoliation. We present different types of devices using liquid metal-induced 2D synthesis processes, including field-effect transistors, optoelectronic devices, systems that use 2D dielectric and conductive layers, and piezoelectric devices. Eventually, we discuss future prospects and outline how liquid metals can contribute to exciting future applications.