Automation of the Marangoni Effect for Making Well-Ordered and Transferable Colloidal Monolayers at the Air–Water Interface

The ability to efficiently create ordered colloidal monolayers on solid surfaces is critical for nanosphere lithography and related applications. We describe here a simple automated method for growing well-ordered 2D crystals of polystyrene spheres at an air-water interface and transferring them to silicon substrates on the wafer scale. The method exploits the Marangoni effect and is enhanced by surface treatment of both the basin for monolayer formation and the intended substrate for transfer. Quantitative image analysis of the sphere monolayers shows that the monolayer packing is improved by automation. Dual-droplet automation is shown to be useful for controlling 2D crystal growth and forming phase-separated monolayers from two different colloidal particle sizes.