Patterning and assembling nanomaterials by dip coating

Assembly is a fundamental issue for materials science and engineering at small scales as it can create structures with novel collective properties and arrange the nano- or micro-scale building blocks in desired patterns for practical scale device fabrication. Since the synthesis and processing of nanomaterials usually involve the use of solvents, a dewetting step is inevitable when the nanomaterials are transferred to a substrate. Therefore, it is of both scientific curiosity as well as technological importance to investigate dewetting induced assembly of nanomaterials. One can find inspiration from natural dewetting phenomena, such as coffee ring stains and wine tears, to design strategies for the assembly of colloidal particles. Here we show that dip coating is a simple but powerful technique to pattern and assemble nanomaterials through regulating the dewetting process of their dispersions. A few examples of wafer scale nanomaterials assemblies made by dip coating are given including linear nanoparticles arrays with widths ranging from tens of micrometers to tens of nanometers, aligned nanowire arrays with programmable wire density and array spacing, and 2D assembly of flat graphene oxide monolayers with continuously tunable tiling densities.