In a recent study published in the journal Nanotechnology, researchers in the US and Singapore have developed a tunable nanostructured lithography mask composed of self-assembled nanoparticles. The group was able to use magnetic fields to control the nanoparticle assembly, and therefore the shape of the "lithography mask," to pattern different geometries. This new technique could pave the way for more versatile, scalable and cost-effective nanomanufacturing tools.

In this new approach, called self-assembled ferrofluid lithography (SAFLi), the team used iron oxide nanoparticles (diameter ~10 nm) in a liquid solution, referred to as a "ferrofluid," as a dynamic lithography mask. The particles, typically randomly dispersed in the solution, assemble to form ordered structures when external magnetic fields are applied.

In the system proposed by the team, microfluidic channels confine the ferrofluid over photosensitive film, which is then exposed by ultraviolet light. The assembled nanoparticles have higher optical absorption than the liquid and function as a lithography mask by replicating the assembly pattern in the polymer film. The assembly pattern can be actively controlled by tuning the external field, which allows various geometries to be patterned.

Using this technique the team has demonstrated a microdot array with controllable dot spacing and microring pattern with 250 nm feature sizes. Going forward, the group will try to use this technique to pattern more complex patterns with smaller feature sizes.