Figure 1. Soap-film coating method.

(a) The principle of soap-film coating (SFC) and (b) bubble soap-film coating (bSFC). The single film and the foam are contained within a frame constructed from nylon wires. A “control wire” was added to increase the lifetime of the soap film by allowing a continuous refilling of liquid. (c) Comparison between some liquid coating methods. Several high-speed roll-to-roll techniques exist, such as doctor-blade coating and curtain coating; however, the thicknesses of the films are usually limited downwards. Wet chemical methods that can be used for the thinnest films include the molecular precision Langmuir–Blodgett (LB) technique⁷, dip⁸ and spin⁹ coating; however, these methods usually have a low deposition speed. The area that lacks high-speed and nano-thin deposition is addressed in this study using the soap-film coating method.