Chemically exfoliated inorganic nanosheets for nanoelectronics

Two-dimensional (2D) nanomaterials constitute one of the most advanced research targets in materials science and engineering in this century. Among various methods for the synthesis of 2D nanomaterials, including top-down exfoliation and bottom-up crystal growth, chemical exfoliation has been widely used to yield monolayers of various layered compounds, such as clay minerals, transition metal chalcogenides (TMDCs), and oxides, long before the discovery of graphene. Soft chemical exfoliation is a technique to weaken the layer-to-layer interaction in layered compounds by chemical modification of interlayer galleries, which promotes monolayer exfoliation. The chemical exfoliation process using organic substances, typically amines, has been applied to a range of layered metal oxides and hydroxides for two decades, establishing high-yield exfoliation into their highly crystalline monolayers and colloidal integration processes have been developed to assemble the resultant 2D nanomaterials into well-organized nanoscale devices. Recently, such a strategy was found to be effective for TMDC and MXene nanosheets, expanding the lineup of functionalities of solution-processed 2D nanomaterial devices from dielectrics, optics, magnetics, and semiconductors to superconductors. Throughout this review, we share the historical research flow, recent progress, and prospects in the development of soft-chemical exfoliation, colloidal integration, and thin film applications of oxides, TMDC, and MXene nanosheets.