Nanolithography Techniques Produce Freestanding Components

Daniel S. Burgess

A research team at the Korea Research Institute of Standards and Science in Taejon and at Sogang University in Seoul, both in South Korea, has developed nanolithographic techniques that yield tiny freestanding gold components that can be moved and assembled into nanoscale machines. In a demonstration of the processes, the team fabricated gears, wheels, squares, dumbbells and letters, and moved a component without damaging it.

TOP: The nanocomponents are lithographically produced from 25- to 60-nm-thick gold plates that are synthesized in a chemical reaction and dripped in an aqueous solution onto a silicon substrate. Images courtesy of Dong Han Ha, Korea Research Institute of Standards and Science. BOTTOM: The freestanding plates are machined into various shapes using focused-ion-beam or electron-beam nanolithography. They can be picked up, moved and placed back on the substrate without being damaged, suggesting that the approach could be used to produce components for assembly into nanomachines.

The processes differ in whether they employ focused-ion-beam or electron-beam nanolithography for machining. In both, an aqueous solution of 25- to 60-nm-thick chemically synthesized gold plates — triangular or hexagonal in shape and 400 nm on a side — is dripped onto a substrate and allowed to evaporate, leaving behind the freestanding plates. The shape and size of the plates are determined by the synthesis conditions.

A 30-nm-thick layer of aluminum is deposited over the plates and silicon substrate by thermal evaporation to prevent damage or contamination. For milling by electron-beam lithography, an additional layer of resist is spin-coated onto the substrate. Machining takes approximately 2 minutes in each process.

Pick and place

To demonstrate the resolution of the techniques, the researchers produced a gear with a 55-nm-diameter center hole and six 100 × 80-nm teeth. They further verified that they could manipulate the nanocomponents, using a micromanipulator from Kleindiek Nanotechnik GmbH of Reutlingen, Germany, to pick up and move a tiny wheel over a distance of 4 µm and place it back on the substrate.

Applied Physics Letters, Dec. 5, 2005, 233110.