"Until now, the areal density of commercially produced data storage media is less than 0.3 Tb/in2 at best. Our technique would be a breakthrough in the data-storage industry if it is commercialised," team leader Jin Kon Kim told nanotechweb.org.

In current AFM-based lithography, nanosized patterns are created on a polymer surface with the AFM tip. In IBM's Millipede system, for example, nanopatterns are drawn on PMMA with the tip heated to above the polymer's glass transition temperature (around 350 °C). This melts the polymer to create stable nanopatterns.

However, the problem is that heated AFM tips are difficult to fabricate. They also consume large amounts of power since less than 1% of the heat produced by the tip transfers to the polymer.

Kim's team has now developed a technique to create nanopatterns on a polymer film using an AFM tip that remains at room temperature. The researchers used polystyrene-block-poly(n-pentyl methacrylate) copolymer (PS-b-PnPMA) because it is “baroplastic” – that is, it undergoes a phase transition when pressure is applied. Thus, no heat is needed, and the nanopatterns produced are also stable.

"By simply pressing the AFM tip on the block copolymer surface, we fabricated nanoscopic indentations that have a density of 1 Tb/in2,” explained Kim. “Each of the nanopatterns is easily converted to '1' or '0' type binary digits, similar to a punched card system."

The density could be further increased if a sharper AFM tip is used.

To show that their storage medium could have practical applications, the scientists demonstrated that they could repeatedly erase and rewrite to the film (over 10 cycles) without damage.

"We believe that our technique is a milestone for developing high-density data storage media,” said Kim. “Furthermore, it could be used to easily fabricate nanostructures with very complex geometries."

The team now plans to test whether the fabricated indentations are stable over long periods of time. And next on the to-do list: further increase the areal density.

The work was published in Nature Nanotechnology.