A novel, facile, and reproducible method of fabricating nanocells in thin films (see Figure) has been developed using a fluorinated block copolymer with a supercritical carbon dioxide (scCO₂) soluble block as a template. The nanocells have an average spacing of 34 nm and a number density of 9 X 10(10) cm^-2. The size of nanocellular structures is readily tunable by changing the saturation pressure of scCO₂.