Guidelines for Arranging 2D Nanosheets into Neatly Tiled Monolayer Films by a Spin-Coating Process

Neat (dense and non-overlapped) monolayer tiling of 2D nanosheets on a substrate surface is very important because we can conduct artificial lattice-engineering by repeating the tiling process in a designed sequence to tailor various hierarchical nanostructures, leading to a range of sophisticated functions. It is recently reported that a facile spin-coating technique realizes the neat monolayer tiling of various 2D nanosheets. Establishing universal guidelines to neatly tile 2D nanosheets on substrates of various materials and size/shape is of essential importance to fully apply this technique, but the mechanism how the nanosheets are tiled has not been clarified yet. In the present study, we have systematically examined the nanosheet deposition process at various rotation speeds by microscopic observations and found that the neat monolayer tiling of nanosheets is attained on the solvent surface during the spin-coating, and then the monolayer film is deposited onto the substrate surface from its center toward the edges upon evaporation of the solvent. Furthermore, we have clarified how the rotation speed and the nanosheet concentration govern the deposition behaviors in terms of neat tiling, overlap, or non-coverage in a such process. On the basis of the guidelines, we can predict the optimum spin-coating conditions for attaining the neat monolayer tiling of various nanosheets over an entire surface of the substrate.