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Low-cost lithography yields 3D nanostructures

Posted: 24 Dec 2014 ?? ?Print Version ?Bookmark and Share

Keywords:North Carolina State University? 3D nanostructure? lithography? nanosphere?

North Carolina State University researchers have come up with a novel lithography technique that uses nanoscale spheres to create 3D structures with biomedical, electronic and photonic applications. According to them, the technique is significantly more cost efficient than conventional methods and does not rely on stacking 2D patterns to create 3D structures.

"Our approach reduces the cost of nanolithography to the point where it could be done in your garage," said Chih-Hao Chang, an assistant professor of mechanical and aerospace engineering at NC State and senior author of a paper on the work.

Hollow-core 3D nanostructures

A variety of asymmetric hollow-core 3D nanostructures fabricated by illuminating light on nanoparticles. Image credit: Xu Zhang

Most conventional lithography uses a variety of techniques to focus light on a photosensitive film to create 2D patterns. These techniques rely on specialised lenses, electron beams or lasers, all of which are extremely expensive. Other conventional techniques use mechanical probes, which are also costly. To create 3D structures, the 2D patterns are essentially printed on top of each other.

The researchers took a different approach, placing nanoscale polystyrene spheres on the surface of the photosensitive film.

The nanospheres are transparent, but bend and scatter the light that passes through them in predictable ways according to the angle that the light takes when it hits the nanosphere. The researchers control the nanolithography by altering the size of the nanosphere, the duration of light exposures and the angle, wavelength and polarisation of light. The researchers can also use one beam of light, or multiple beams of light, allowing them to create a wide variety of nanostructure designs.

"We are using the nanosphere to shape the pattern of light, which gives us the ability to shape the resulting nanostructure in three dimensions without using the expensive equipment required by conventional techniques," Chang noted. "And it allows us to create 3D structures all at once, without having to make layer after layer of 2D patterns."

The researchers have also shown that they can get the nanospheres to self-assemble in a regularly-spaced array, which in turn can be used to create a uniform pattern of 3D nanostructures.

"This could be used to create an array of nanoneedles for use in drug delivery or other applications," indicated Xu Zhang, a Ph.D. student in Chang's lab and lead author of the paper.

The technique could also be used to create nanoscale "inkjet printers" for printing electronics or biological cells, or to create antennas or photonic components.

"For this work, we focused on creating nanostructures using photosensitive polymers, which are commonly used in lithography," stated Zhang. "But the technique could also be used to create templates for 3D structures using other materials."

The researchers are looking at several additional ways to manipulate the technique to control the shape of resulting structures.

"We're exploring the use of nanosphere materials other than polystyrene, as well as nanoparticle shapes other than spheres," Chang added. "And ultimately we want to look at ways of controlling the placement of particles on the photosensitive film in patterns other than uniform arrays."

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