To address this challenge, in a recent paper published in Nanotechnology, researchers at Princeton University applied a novel technology that they developed earlier – self-perfection by liquefaction (SPEL) (Nature Nanotechnology 3 295–300), to fabricate the moulds with near-perfect structures that are unachievable with conventional methods. SPEL can “remove” the defects that are generated initially by a conventional lithography.

figure 1

Schematic of our process to make cylindrical pillar moulds with smooth sidewalls.

In Princeton’s work, they fabricated pillar moulds with a pillar diameter of 25 nm or smaller. At such small dimensions, a designed-to-be-circular disk made by a conventional lithography such as electron or ion beam has a non-circular shape and significant edge roughness. Indeed, the initial Cr patterns were more square-shaped with rough edges. But after SPEL, which selectively melts the Cr structures for a very short period of time (hundreds of nanoseconds by an ultrafast laser pulse), the Cr squares were turned into perfect semi-spheres with a reduced edge roughness.

Another advantage of SPEL was a further reduction of the pillar diameter by 43%. With the perfected Cr mask, pillar moulds were made by reactive ion etching. The high-quality moulds will have wide applications in plamoniscs, nanobiotechnology and patterned magnetic media.