Building 3D Circular Nanotubes Using In Situ Monitored Self-Assembly Process

Tubes with a circular cross-section can be noticed everywhere in daily life, from large ventilation pipes to a human’s small capillaries. Circular cross-sections also play an important role in fluidic channels, as it can eliminate the corner flow effect, undermine nonuniform pressure build up, and minimize shear stress in the channel. Moreover, it can largely simplify the fluidic theory model built for corners and improve its accuracy. However, in nanofluidics, fabrication of circular nanotubes (10-1000 nm) remains challenging, especially the curved one remains unsolved. In this work, both straight and curved circular nanotubes are fabricated via electron beam induced in-situ monitored self-assembly. This in-situ monitored ability provides real time images with a nanoscale resolution, leading to extreme fabrication precision for the realization of three-dimensional (3D) nanostructures (circular nanotubes). Two-dimensional (2D) nanopatterns defined on a planar substrate are firstly defined by electron beam lithography, followed by a deposition process and Si etching underneath. An electron beam is used to transform each 2D pattern into segmented 3D cylinder structures. Gaps on the top and between each cylinder are sealed by atomic layer deposition and the diameter of the tube can be precisely controlled from hundreds of nm down to ~10 nm with the resolution of 0.1 nm. To verify its capability for fluidic transportation, through the nanotubes with radius of ~100 nm, liquid flow/evaporation was in-situ monitored using a darkfield microscope via optical scattering effect. From the observations of fluidic flow in the curved circular nanocylinders, the dynamic behavior of the fluid was characterized, and novel counter-intuitive physical effect was discovered: nano pumping through evaporation in a nanocylinder.