In summary, we report the formation of self-assembled films presenting square arrays with unit cell sizes from 13 to 23 nm. The array represents the (100) surface of the 𝑄 𝐼𝐼 𝑃 phase, with the orientation representing the lowest-energy thermodynamic arrangement. Our findings suggest a robust route to periodic 2D and 3D nanostructured films with a hitherto unobtainable symmetry and periodicity; the straight channels and square array surface suggest applications ranging from lithography and templating to biomolecule delivery.