Precise control of elastocapillary densification of nanostructures via low-pressure condensation

Capillary self-assembly of nanoscale filaments is an emerging means of fabricating complex and hierarchical surface textures. However, via conventional processing methods such as immersion in liquid and atmospheric pressure condensation of liquid onto the substrate, it is challenging to achieve uniform results over large areas and to adapt the process to structures with different dimensions and spacing. Here we study elastocapillary densification of carbon nanotube (CNT) microstructures via controlled low-pressure condensation of liquid and subsequent evaporation, with the structures placed on a temperature controlled substrate. We study the dynamics of liquid infiltration into the microstructures and achieve control over the liquid condensation rate within >1 μm s^-1. We find that the extent of densification depends on the amount of liquid delivered to the substrate as well as the size and spacing of the microstructures. We also show that the low-pressure condensation method can be used to form large arrays of anisotropic CNT microstructures, including thin-walled slanted microwells and tilted microposts.