To fabricate the three-dimensional, hollow nanostructures, the researchers have combined sidewall deposition through plasma sputtering with an ion milling process. The technique overcomes the pattern resolution limitation of moulds and shows high reproducibility. Also, the sputtering method can be replaced by other dry deposition techniques such as pulsed laser deposition (PLD) to create more complex functional materials. Furthermore, it can be adapted to produce various shapes at low-cost, over a large-area, and with high-reproducibility by using a NIL (nanoimprint lithograph) process.

The image above shows a typical Au box array with a sidewall thickness of 53 nm, an inner square dimension of 400 nm, and a height of 300 nm. By simply changing the deposition time, the researchers were able to fabricate various sidewall thicknesses from 12 to 61 nm. Integrated nanobox arrays featuring an inner square dimension of 160 nm and nanopillar arrays with an inner pore size of 65 nm were fabricated under the same process conditions by using smaller moulds.

The fabrication process can deliver unique high-aspect-ratio structures on any substrate with no-limitation on the deposited materials. Applications include spintronics, for example, ring-shaped MRAM (magnetoresistive random access memory), 3D fuel cells featuring complex metal-oxide materials, or catalyst imbedded high-performance batteries. In addition, the arrays could be used to contain special chemicals or particles by applying a SAM (self-assembled monolayer) coating to control the surface properties inside and outside of the nanoboxes. Individual boxes can be rendered controllable by using an appropriate substrate etching strategy.

The researchers presented their work in Nanotechnology.

About the authors
The work was performed at the ISIR (Institute of Scientific and Industrial Research), Osaka University, Japan. Nam-Goo Cha, PhD is a Research Professor in Hidekazu Tanaka’s group. The team is exploring new physics and device applications based on nanostructured functional oxides.