MicroAngelo Technique: 3D Sculpting of Nanofilms by Spatiotemporal Modulation of Thermocapillary Forces

At age 17 with only a hammer and chisel, Michelangelo sculpted one of the most beautiful marble reliefs ever known, the Madonna of the Steps (1492), where millimeter variations in thickness imbue the surface with a sublime ethereal quality. Modern day sculpting tools such as extreme UV lithography are also a true marvel, patterning features below 10 nm though tool costs are prohibitive. In rapid development between these extremes are numerous inexpensive microscale techniques which, though increasingly popular, are still based on planar forms and surfaces with considerable roughness. Here we explore the foundations of MicroAngelo ©, a new one-step, non-contact technique capable of curved shapes and ultra-smooth surfaces. Film patterning is based on 3D sculpting of molten nanofilms by spatiotemporal modulation of thermocapillary forces where desired fluid shapes are rapidly affixed in-situ by electronic thermal control. We’ll first review interesting aspects of the governing thin film equation bearing on linear and nonlinear stability, parametric resonance, self-similar cusp formation from self-focusing, pattern resolution limits and proximity correction for quenching undesirable nonlinear wave interactions. We’ll then review efforts spanning two decades to elicit the cause of spontaneous nanopillar arrays in polymer nanofilms and discuss why the phenomenon is likely triggered by a long wavelength thermocapillary instability. We conclude with our own experimental efforts to measure the wavelength and growth rate of the fastest unstable mode as well as recent success in bypassing the instability to fabricate complex and hierarchical micro-optical arrays. Altogether, we hope these findings help usher development of a new class of lithographic tools based on programmable forces at liquid interfaces in order to enable next generation fabrication of 3D micro-optical and microfluidic circuits.