- 3 October 2005 -

Natural concepts for nanofabrication

Graphics: http://hjs.geol.uib.no/diatoms/ & www.microscopy.fsu.edu/

Inspired by the intricacy of the shapes formed by micro-organisms - and by those organisms' ability to reproduce rapidly - a group of researchers at Georgia Institute of Technology have found an efficient way to create nanoscale parts for next-generation electronics.

Chemical engineer Kenneth Sandhage of the Georgia Institute of Technology and a team of biologists, geneticists, and electronic engineers have published details in the International Journal of Applied Ceramic Technology of a new process for converting the finely-detailed silica skeletons of diatoms, a type of single-celled algae, into synthetic replicas made of materials such as titanium dioxide, which conducts electricity and could be used in electronic devices.

The new techniques exploit the diatom's own ability to reproduce, and can be used to mass-produce intricate three-dimensional structures.

Sandhage got the idea after sitting next to a marine biologist who showed him the elaborate, ornamental- structures that are diatoms. Sandhage decided to try growing the organisms as templates for potential nanodevices. Diatoms reproduce through cell fission, creating two exact copies of their silica shells.
After 40 generations, a single diatom will have multiplied itself into a trillion times.

Sandhage uses a handful of methods to either coat the diatom shells with metallic substances or completely replace them with materials such as titanium dioxide that are better conductors and can withstand thermal stress, important features of materials to be used in electronics.

The resulting structures have features measured in tens of nanometers and complex 3D shapes can be produced much more quickly using Sandhage's approach. Conventional photolitho can be used to build three-dimensional structures by adding and etching one layer of silicon at a time, but is a frustratingly slow.

Sandhage's project isn't the first time researchers have used organic templates to produce nanoscale devices and materials. Angela Belcher, a professor in MIT's Department of Materials Science and Engineering, has used viral proteins to assemble a variety of materials, and a startup called Cambrios is pursuing commercial applications of her work.

Daniel Solis, a graduate student in Belcher's lab, is working on viruses that can attach themselves to gold electrodes and coat themselves with semiconductor material; eventually he hopes to use the viruses to make working transistors.
Diatoms could provide templates for many other types of structures.

Sandhage hopes that the hundreds of thousands of examples of uniquely-shaped diatoms in nature will inspire engineers to consider new design possibilities for processors and memory chips.

Sandhage's colleagues are already learning about how diatoms' genes determine their shape, with the hope of allowing engineers to design diatoms to their own specifications.

The genome of one diatom species has been completely sequenced, and another is on the way. Mark Hildebrand, a molecular biologist at the Scripps Institution of Oceanography and partners with Sandhage, believes that the diversity of natural diatom shapes suggests, though counter-intuitively, that there are just a few core genes that control these shapes.

If there are only a few key genes, he says, then relatively few mutations would be required to cause the huge variety of existing shapes. Hildebrand hopes that identifying these genes and manipulating both the genes and the environments in which the diatoms grow up will allow researchers to create novel structures.

That's a hope seconded by Lucent Technologies' Joanna Aizenberg, who has produced tiny lenses inspired by the structure of sponges, but Sandhage cautions that engineering the diatoms and arranging them into useful structures for electronic devices is "not a trivial challenge."

Source: Kevin Bullis. Web:http://www.technologyreview.com