Chin H.-T. et al.Mario Hofmann2021-07-282021-07-28202123977132https://www.scopus.com/inward/record.uri?eid=2-s2.0-85102170590&doi=10.1038%2fs41699-021-00207-2&partnerID=40&md5=8269f2af79a96ca80ff5b3a0edbac576https://scholars.lib.ntu.edu.tw/handle/123456789/573715We 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. ? 2021, The Author(s).Crystals; Electronic properties; Transition metals; Crystal interfaces; Environmental stability; Lateral diffusion; Layer-by-layer growth; Opto-electronic sensors; Solid state chemical reactions; Spectroscopic characterization; Thermodynamic phasis; Phase transitionsjournal article10.1038/s41699-021-00207-22-s2.0-85102170590