Monolayer atomic crystal molecular superlattices

Superlattices consisting of alternating monolayer atomic crystals and molecular layers allow access to stable phosphorene monolayers with competitive transistor performance and to bulk monolayer materials with tunable optoelectronic properties. Molecules and 2D crystals layer up This paper reports the formation of superlattices of two-dimensional materials with layers of quaternary ammonium molecules introduced between the two-dimensional (2D) crystals via electrochemical intercalation. The team created a range of superlattices using different molecules that varied in size and symmetry and different two-dimensional crystals such as tungsten diselenide and molybdenum disulfide. Intercalation decoupled the 2D interlayer interactions, whereas varying the molecules adjusted the electronic and optical properties of the 2D layers. Importantly, the approach allowed the stable isolation of phosphorene monolayers (albeit within a superlattice), which has previously been challenging to achieve. They authors showed that field-effect transistor devices made with the phosphorene superlattices performed competitively compared to recently reported phosphorene-based devices. Artificial superlattices, based on van der Waals heterostructures of two-dimensional atomic crystals such as graphene or molybdenum disulfide, offer technological opportunities beyond the reach of existing materials 1 , 2 , 3 . Typical strategies for creating such artificial superlattices rely on arduous layer-by-layer exfoliation and restacking, with limited yield and reproducibility 4 , 5 , 6 , 7 , 8 . The bottom-up approach of using chemical-vapour deposition produces high-quality heterostructures 9 , 10 , 11 but becomes increasingly difficult for high-order superlattices. The intercalation of selected two-dimensional atomic crystals with alkali metal ions offers an alternative way to superlattice structures 12 , 13 , 14 , but these usually have poor stability and seriously altered electronic properties. Here we report an electrochemical molecular intercalation approach to a new class of stable superlattices in which monolayer atomic crystals alternate with molecular layers. Using black phosphorus as a model system, we show that intercalation with cetyl-trimethylammonium bromide produces monolayer phosphorene molecular superlattices in which the interlayer distance is more than double that in black phosphorus, effectively isolating the phosphorene monolayers. Electrical transport studies of transis