Writing in Nature Materials, Jing Li and co-workers 6 present an electrochemical exfoliation method that delivers the best attributes of these different production approaches, and expansively demonstrate both its effectiveness in producing high-quality 2D superconductor monolayers, and its versatility for use in different processing technologies. But while these liquid-dispersed samples have flooded the marketplace, liquid phase exfoliation (LPE) typically requires chemically or physically aggressive methods, yielding materials that are not only too small and defective for devices, but only a few per cent of which are monolayers, compromising the treasured properties of 2D materials. On the other hand, exfoliating layered crystals in liquids is cheaper, more scalable and has the built-in bonus that the resulting dispersions can be used to manipulate the nanosheets at high volume and low cost, for example, by inkjet printing 5. Methods that produce large, high-quality monolayers, such as mechanical exfoliation (the ‘Scotch tape method’) or chemical vapour deposition, are relatively painstaking and must typically be followed by intricate transfer methods for device fabrication. The discovery of graphene opened a door for manufacturing and investigating two-dimensional (2D) materials. However, for producing 2D materials a frustrating dichotomy exists. Such experiments require large-area, single-crystal samples with a low density of defects and clean interfaces between adjacent layers that can be readily manipulated into devices. Excitingly, the interplay between such exotic effects (and those that arise due to interfacial interactions) can be explored and controlled by creating devices from interleaved 2D sheets 2, 3, 4.

This is notably true for transition metal dichalcogenides (TMDs) where single layers can break inversion symmetry, resulting in the valley degree of freedom and unconventional superconductivity 1, 2.

Many of the most exquisite properties of two-dimensional (2D) materials only occur in their monolayer form.

Jing xiang 2d materials