A Sponge's Guide to Nano-Assembly

A new way to create complex nanostructures will improve batteries and solar panels.

One of the ongoing goals of nanotechnology is to easily and inexpensively create high-performance materials structured at the nanoscale. And one of the most promising strategies is to attempt to mimic nature's remarkable ability to self-assemble complex shapes with nanoscale precision. Now researchers at the University of California, Santa Barbara (UCSB), using clues gleaned from marine sponges, have developed a method of synthesizing semiconducting materials with useful structures and novel electronic properties. The first applications could be ways to make materials for more powerful batteries and highly efficient solar cells at a lower price.

This glass structure, formed by a species of marine sponge, helped inspire scientists to study such organisms to learn how to easily assemble complex, nanoscale structures. (Courtesy of James Weaver and Daniel E. Morse, University of California, Santa Barbara.)

"We are accessing structures that in some cases had never been achieved before. And in some cases we're discovering electronic properties that had never been known before for that class of materials," says Daniel Morse, professor of molecular genetics and biochemistry at UCSB, who led the project. The method works with a wide variety of materials. So far, he says, the group has made "30 different kinds of oxides, hydroxides, and phosphates."

[Click here for images of nature-based, nanoscale materials.] 

Today's solar cells and batteries are held back, in part, by their limited ability to transport electrical charge carriers, such as electrons and positive ions, in and out of active materials. One advance that could help is increasing the surface area of a material, while at the same time maintaining a thin-film structure that can easily be incorporated as an electrode layer in a device.

Morse and his colleagues began their research by studying the methods used by marine sponges to make intricate glass skeletons called spicules (see illustration). One type of sponge produces a cylinder that looks as if it were made of woven glass fibers, although it isn't woven at all, but assembled molecule by molecule to make the structure.

In particular, the researchers studied a type of sponge that makes tiny needles of glass. They found that the genes responsible for the glass structures encode for enzymes that serve as both a physical template for the structure and a catalyst for assembling molecular precursors into the desired material.

The scientists developed a synthesis method that uses the basic principles behind the natural assembly method: slow catalysis and the use of a physical template. They found they were able to assemble not only glass, but also a variety of semiconducting materials that could be useful in devices.

The method begins with a solution of molecular precursors. The researchers then expose the solution to ammonia vapor, which, as it slowly diffuses into the solution, acts as a catalyst. The physical template for the material is the surface of the solution. At this surface, where the vapor concentration is greatest, the material forms a thin film.