Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals

Abstract

A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (∼1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes.

Liquid Metal Phagocytosis: Intermetallic Wetting Induced Particle Internalization

“…Up to now, the search for safe‐handling room‐temperature LMs only narrows down to gallium‐based LMs, a group of alloys consisting gallium and other metals like indium, tin, etc. Recently, self‐powered motor,11 jumper,12 oscillator,13 soft actuators,14, 15, 16 and 2D semiconductor skin17 demonstrated with this class of material shed light on their new possibilities toward more diverse applications. Here, we report a particle‐eating phenomenon of gallium‐based LMs, which mimics the biological phagocytosis process (also known as cellular‐eating, a basic cell behavior referring to the transportation of external particles into cells from across the membranes18, 19, 20, 21), and thus we call it LM‐Phagocytosis.…”

Recent progress on liquid metals and their applications

“…This technique can be extended to make other 2D metal materials. Because many metallic elements can be alloyed with gallium, this means that gallium can provide a reaction environment to make 2D metal compounds [70].…”

“…There are many methods to fabricate 2D materials, such as the exfoliation technique, atomic layer deposition [75] and chemical vapour deposition [76,77], but finding a method to make high-quality, large-area and large-scale 2D sheets remains a great challenge. Carey et al introduced an approach to transform the native surface metal oxide layer of low melting point metal precursors to fabricate 2D metal chalcogenide compounds [70]. This novel method can synthesise large-area 2D semiconducting GaS through changing the oxide skin of the interfacial metal, and the metal is in the liquid state at room temperature.…”

“…For Ga-based liquid metal alloys which melting point less than room temperature, their surface show higher chemical activities owning to the diffusing metal atoms without lattice binding. Due to these specific features, Ga and its alloys provide an ideal reaction environment for the fabrication of nanomaterials [70].…”

“…(d) Firstly, hcl vapour is used to form a Gacl 3 layer. Then, this layer is exposed to s vapour to form Gas [70].…”