Self-limiting Growth Mechanisms for Stable Monolayer Films of Non-van-der-Waals Oxides

Progress and breakthroughs in high-tech applications, ranging from ICT, lighting to energy storage/generation and catalysis, builds on material deposition technology, which over the last decades has moved from bulk, to thin films to nanotechnology. A monolayer of a material represents the ultimate thinnest film possible, and the isolation and bottom-up growth of atomically-thin monolayer from layered van-der-Waals (vdW) materials highlight the huge impact both on fundamental research and applications that material design at the monolayer level can have.

While the catalogue of such experimentally isolated 2D layers has been expanding, the focus has been almost exclusively on vdW solids for which the natural phase is layered. There remain large gaps in accessible properties and functionalities, such as the lack of electronic band gaps between 2.3-6 eV.

The motivation for this proposal is to explore new science and approaches how to achieve selective nucleation and anisotropic crystal growth that is truly self-limiting to a monolayer for non-vdW materials, and thus open a new horizon of possibilities for materials design and tailoring of properties at the atomic level that hitherto have been limited to vdW materials. Reported approaches for this to date generally fall into two categories: (1) forcing a 2D phase of the material by strong interaction with the substrate (epitaxy) or with two interfaces (confined growth), (2) achieving a 2D layering by selective etching of planes in a specific crystal structure, followed by liquid exfoliation (e.g.

MAXene to MXene). A number of surface science studies have explored approach (1) with the state-of-the-art being the formation of small (