Ion Beam Induced Directional Flow of Ionic Liquid at Nanoscale

The branched flow pattern is ubiquitous in nature such as neuron structures, blood vessels and alluvial fans with the spatial scale ranges from micrometer to kilometer.Recently, we discover that such character still exists at nanometer scale and can be harnessed for the directional flow control of ionic liquids.At the proper irradiation of Helium Focused Ion Beam (HFIB), ionic liquid (IL) flows through local protrusions at contact line then branches off into secondary rivulets and forms hierarchical flow patterns.Such phenomenon is attributed to the field induced ion emission and nano meter scale precursor film.Molecular dynamics simulation results verify the important roles played by surface charges and precursor films in the directional propagation of ionic liquids.Moreover, the evolutions of the precursor films from MD simulations well reproduces the experimental results quantitatively.Such features endow programmable control of liquid flow and long endurance of fabricated liquid film patterns.We expect such mechanism can open a new avenue for microfluidic instruments and liquid nano circuit fabrications.