Rational Micro/Nanostructuring for Thin-Film Evaporation

Heat management in electronics and photonics devices is a critical challenge impeding accelerated breakthrough in these fields. Among approaches for heat dissipation, thin-film evaporation with micro/nanostructures has been one of the most promising approaches that can address future technological demand. The geometry and dimension of these micro/nanostructures directly govern the interfacial heat flux. Here, through theoretical and experimental analysis, we find that there is an optimal dimension of micro/nanostructures that maximizes the interfacial heat flux by thin-film evaporation. This optimal criterion is a consequence of two opposing phenomena: nonuniform evaporation flux across a liquid meniscus (divergent mass flux near the three-phase contact line) and the total liquid area exposed for evaporation. In vertical micro/nanostructures, the optimal width-to-spacing ratio is 1.27 for square pillars and 1.5 for wires (e.g., nanowires). This general criterion is independent of the solid material and the thermophysical properties of the cooling liquid. At the optimal width-to-spacing ratio, as the density of the pillars increases (i.e., smaller pillar's dimension), the interfacial heat flux increases. This study provides a direction for rational development of micro/nanostructures for thin-film evaporation and paves the path for development of high-performance thermal management systems.