Pushing the Boundaries of Nano Innovation

zayd-lesemanZayd Leseman blends mechanical engineering and chemistry to create nanomaterials

A “pinch” of material. A “dash” of powder. “Stir” in together. Pour into a “mold.” When Zayd Leseman, assistant professor of mechanical engineering, talks about his research, he borrows many terms from the culinary arts. What he’s really doing is mixing mechanical engineering, chemistry, and industrial manufacturing processes to cook up the amazing materials of the future.

An interdisciplinary collaboration with Jonathan Phillips, a UNM/Los Alamos National Laboratory research professor of chemical and nuclear engineering, sparked Leseman’s focus on creating nanocarbon materials. “They have unique mechanical, thermal, and electrical properties so hey’re very interesting,” says Leseman.

Fiber Foams
With funding from NASA, Leseman is researching carbon nanofibers, which have varying diameters, lengths, and surface textures, as well as important thermal, electrical, and mechanical properties that are appealing to the space agency. The challenge has been how to rapidly grow a large volume of carbon nanofibers.

Leseman and Phillips are resolving that problem by using complimentary chemistry and a simple industrial process. By literally mixing specific catalysts together and then flowing a mixture of gases over them, they’ve been able to grow nanofibers at a rate more than 140 times faster than previously possible. “We’re speeding growth rates up to levels no one has seen before,” says Leseman. By accelerating fiber growth rates, the UNM team is making mass production of carbon nanofibers possible and more commercially viable.

Nanofibers are the basis for the team’s newest invention: carbon nanofoam. By combining a pinch of catalyst and putting the mixture into a furnace for an hour while flowing a mixture of gases, Leseman, Phillips, and graduate student Mark Atwater have created a block of tangled carbon nanofibers that is extremely strong — – but is more than 95% air. When dropped, the carbon nanofoam gently floats to the ground. The next step for the group of researchers is to convert the nanofoams into composite materials that are even stronger than the nanofoam itself.

Experimenting with Nano Origami

With help from Ron Salesky, a doctoral student in the Nanoscience and Microsystems Program, Leseman is developing a new method for assembling carbon nanotubes (CNTs) into three-dimensional shapes; a process that results in what he calls “nano origami.” Generally, whenresearchers grow CNTs, they can’t control the chirality or position of the carbon nanotubes. Their positioning drastically affects the density of CNTs, and the chirality determines whether they’re semi-metals or semi-conductors.

So Leseman and Salesky developed a novel self-assembly method that uses nanosurface chemistry to determine CNT chirality. By coating CNTs with a protein and mixing them in a solution of DNA strands with known sequences, they are able to select CNTs of known chiralities. Thus by using the DNA strands, Leseman and Salesky are capable of selectively picking the semimetal and semiconducting CNTs. The researchers filter out the CNTs they don’t want, leaving behind a volume of tubes with specific properties that can be arranged and attached into nano 2-D and 3-D structures, thus the term “nano origami.”

Leseman notes that by achieving such density, they’re upholding Moore’s Law. “Right now you can only pack so many transistors into a certain area. We can place these nanoelectronics just a nanometer apart so the density goes up drastically,” he says.

They plan to pack and stack CNTs tightly on to surfaces to create nano electronic circuits. Currently, the researchers are addressing the issue of bonding at the junctions between the CNTs in order to realize fully functional nanoelectronics created using these techniques. Beyond the size and power advantages, nanoelectronics made with CNTs have excellent thermal properties which help keep machines cool and improve performance speeds.

Whether it’s tubes, fibers, or foams, Leseman is combining disciplines to accelerate the development of nanomaterials while creating new types of materials. “Interdisciplinary research opens up new avenues of study that have yet to be explored,” says Leseman. “The people you work with have one set of knowledge and you have another set. When you combine the two, you end up with a new understanding or new way of making things.”