Abstract
We here present a planarized solid-state chemical reaction that can produce transition metal monochalcogenide (TMMC) 2D crystals with large lateral extent and finely controllable thickness down to individual layers. The enhanced lateral diffusion of a gaseous reactant at the interface between a solid precursor and graphene was found to provide a universal route towards layered TMMCs of different compositions. A unique layer-by-layer growth mechanism yields atomically abrupt crystal interfaces and kinetically controllable thickness down to a single TMMC layer. Our approach stabilizes 2D crystals with commonly unattainable thermodynamic phases, such as β-Cu2S and γ-CuSe, and spectroscopic characterization reveals ultra-large phase transition depression and interesting electronic properties. The presented ability to produce large-scale 2D crystals with high environmental stability was applied to highly sensitive and fast optoelectronic sensors. Our approach extends the morphological, compositional, and thermodynamic complexity of 2D materials.
Highlights
The fundamental effect of dimensional confinement on electrons is exemplified in 2D materials, which restrict their wave functions to atomic dimensions
The most common approach to producing 2D crystals with controllable thickness is the thinning of bulk crystals[9]
To estimate the achievable lateral 2D crystal size at such thicknesses, we introduce a planarization ratio (δ) that represents the preference towards lateral growth compared to out-of-plane growth
Summary
The fundamental effect of dimensional confinement on electrons is exemplified in 2D materials, which restrict their wave functions to atomic dimensions. The gained insight into elementary structure-property relations[5] and the prospect of applications in future optoelectronic devices[6] has attracted significant interest in the realization of 2D materials multi-layers and van-der-Waals crystals[7,8] Such structures represent specific examples of a class of nanostructures-2D crystals, which are laterally extended and span the thickness range between atomic-scale 2D materials and mesoscopic crystals of a few nanometers thickness. We here present a reaction process that produces 2D crystals with controllable thickness, high quality, and unique compositional, electronic, and thermodynamic properties This advance is achieved by conducting solid-state chemical reactions where one reagent exhibits an enhanced lateral diffusion compared to vertical interdiffusion (Fig. 1a) leading to a ‘planarized reaction’ that favors two-dimensional growth. Our realization of high-performance optoelectronic devices highlights the potential of 2D crystals for future applications
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