Tiled Monolayer Films of 2D Molybdenum Disulphide Nanoflakes Assembled at Liquid/Liquid Interfaces

Thin films of MoS2 bilayer nanoflakes, which are predominantly a single flake thick and in edge-to-edge contact, have been produced via self-assembled tiling at the planar interface between two immiscible liquids. Films of several square centimeters extent can be produced with total covered area approaching 90 % and over 70 % of the film covered by single flakes without overlap. Films produced through liquid/liquid assembly are shown to produce a lower uncovered area fraction and more uniform thickness when compared with films of similar areal coverage produced by the “top-down” techniques of spin coating and spray coating. Statistical analysis of flake coverage data, measured by AFM, shows that liquid/liquid assembly produces a distinctly different variation in film thickness than conventional “top-down” deposition. This supports the hypothesis that the 2D confinement of liquid/liquid assembly produces more uniform films. Demonstrator field-effect transistors (FETs) manufactured from the films exhibit mobility and on/off current ratios of 0.73 cm2 V-1 s-1 and 105 respectively; comparable to FETs of similar layout and CVD-grown or mechanically cleaved single crystal MoS2 channel material. This work demonstrates the use of liquid/liquid interfaces as a useful tool for self-assembly of high performance thin film devices made from dispersions of 2D materials.