I imagine developing a new lithography technique that uses nanoscale spheres to create three-dimensional (3D) structures with biomedical, electronic and photonic applications while lowering the cost is not an easy thing to do. NC State researchers have reportedly developed a new technique that is significantly less expensive than conventional methods and does not rely on stacking two-dimensional (2D) patterns to create 3D structures.
“Our approach reduces the cost of nanolithography to the point where it could be done in your garage,” says Dr. Chih-Hao Chang, an assistant professor of mechanical and aerospace engineering at NC State and senior author of a paper on the work.
Conventional lithography generally uses a variety of techniques to focus light on a photosensitive film to create 2D patterns. These techniques rely on extremely expensive equipment. Specialized lenses, electron beams or lasers can all cost a small fortune. Other conventional techniques use mechanical probes, which can be prohibitively expensive.
3D structures are generally 2D patterns printed on top of one another in successive layers. The NC State researchers decided that placing nanoscale polystyrene spheres on the surface of the photosensitive film would be a good idea.
Why take this approach?
Well, the nanospheres are transparent, but they 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. By altering the size of the nanosphere, the duration of light exposures, and the angle, wavelength and polarization of light, the researchers were able to maintain higher levels of control. 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 says. “And it allows us to create 3-D structures all at once, without having to make layer after layer of 2D patterns.”
Amazingly, researchers have also shown that they can get the nanospheres to self-assemble in a regularly-spaced array, which can then 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,” says Xu Zhang, a Ph.D. student in Chang’s lab and lead author of the paper.
The new 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,” Zhang says. “But the technique could also be used to create templates for 3-D structures using other materials.”
By exploring new ways to manipulate the technique to control the shape of resulting structures, researchers hope that they will find and open unseen doors for new applications.
“We’re exploring the use of nanosphere materials other than polystyrene, as well as nanoparticle shapes other than spheres,” Chang says. “And ultimately we want to look at ways of controlling the placement of particles on the photosensitive film in patterns other than uniform arrays.”
If you would like more information, the paper “Sculpting Asymmetric Hollow-Core Three-Dimensional Nanostructures Using Colloidal Particles,” was published online Dec. 8 in the journal Small. It was co-authored by undergraduates Bin Dai and Zhiyuan Xu, who worked on the project at NC State as part of the Global Training Initiative (GTI) program with Jiangsu University and was supported by a NASA Early Career Faculty Grant, and by the Nanosystems Engineering Research Center for Advanced Self-Powered Systems of Integrated Sensors and Technologies at NC State under a National Science Foundation Grant.