Dewetting Front Instabilities for Micro-patterning*

It has long been known that fluid instabilities can be harnessed for low-effort self-assembly of ordered structures on the nano- and micro- scales. Here, we demonstrate how a known thin film instability resulting from Van der Waals forces in an evaporating film can generate a number of extraordinarily ordered nano- and micro-structures. The patterns that can arise include hexagonal lattices, lines, branches, and triangular sawtooth structures. We find that the patterning mechanism is driven by fluid dynamics and Ostwald ripening of crystallizing salts at the fluid dewetting front. Controllability of these patterns can be further enhanced by application of flow-control strategies. We present a phase diagram of substrate properties that result in patterning, and perform stability analysis to predict the wavelength of the instability. Such patterns may have potential applications in sensor arrays, photonics, dielectric materials, and materials of controlled porosity.