STTR Phase I: Ultrasonic Nanocoining for Creating Large, Low-Cost Arrays of Sub-Wavelength Features

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The broader impact/commercial potential of this Small Business Technology Transfer (STTR) Phase 1 project is to drastically reduce the cost of creating large surfaces coated with functional nano-scale features. One example is the moth-eye structure, consisting of a continuous pattern of 200 nm wide by 200 nm tall features, that gives surface anti-reflective properties. An anti-reflective surface can increase efficiency of solar cells, conceal aircraft or ships, or prevent glare on windshield glass or computer screens. Nano-features can also be used to create surfaces with superior durability and cleanliness through self-wetting and anti-fouling characteristics, as well as anti-fogging or de-icing properties. The low-cost scale-up is done through "roll-to-roll" processing, where a drum-shaped metal cylinder coated with nano-features is used as the mold for rolling miles of thin film, replicating the functional coating. The intellectual merit of this project is focused on accurately and inexpensively creating nano-scale features on the metal drum mold that is used in the roll-to-roll replication process. This is done using the recently-developed nanocoining process, whereby nano-features are indented into a metal surface using a diamond die indent features into the surface 40,000 times per second. Current machining methods rely on scraping material away with a sharp tool and cannot create features on nano-scale. This is because any tool sharp enough to create such a small feature will be prohibitively fragile and susceptible to rapid wear. Indenting is fundamentally different, and has been used for millennia to create coins. No material is removed; it is simply pushed aside, leaving behind the pattern on the die. The reduction of rubbing drastically reduces wear and the absence of a chip of removed material enables the process to work on the nano-scale. The objective of the initial phase of research is to indent a small test drum and replicate a plastic film coated with the features from the diamond die. The film will then be tested for anti-reflective and wetting properties, and scale-up will follow in later phases.