Nanowires with Aesthetic Appeal Utilized in a Range of Technologies

There are exam­ples of art imi­tating nature all around us—whether it’s Monet’s pastel Water Lilies or Chihuly’s glass­blown Seaforms, the human con­cep­tion of nat­ural phe­nomena daz­zles but does not often surprise.

Yet when asso­ciate pro­fessor of physics Latika Menon peered under the elec­tron micro­scope last fall, she dis­cov­ered the exact oppo­site. Instead of art imi­tating nature, she found nature imi­tating art.

Menon grew up in the eastern region of India and was vaguely familiar with a cul­tural dance from the western state of Rajasthan known as the Bhavai pot dance. Nimble dancers sway their hips as a tall stack of wide-​​bellied pots bal­ances gin­gerly atop their heads. Back in the lab at North­eastern, Menon’s team recently cre­ated gal­lium nitride nanowires, which bore a striking resem­blance to that stack of pots.

What’s more, a post­doc­toral research asso­ciate in Menon’s lab, Eugen Panaitescu, jumped on the band­wagon with a cul­tural art ref­er­ence of his own. Panaitescu, who hails from Romania, also saw his country’s famous End­less Column reflected in the nanowires. Ded­i­cated to the fallen Romanian heroes of World War I, Con­stantin Brancusi’s 96-​​foot-​​tall mono­lith is con­structed of 17 three-​​dimensional rhom­buses, peri­od­i­cally wavering from a wider cir­cum­fer­ence to a nar­rower one.

But the North­eastern researchers’ nanowires aren’t just notable for their aes­thetic appeal. Gal­lium nitride is used across a range of tech­nolo­gies, including most ubiq­ui­tously in light emit­ting diodes. The mate­rial also holds great poten­tial for solar cell arrays, mag­netic semi­con­duc­tors, high-​​frequency com­mu­ni­ca­tion devices, and many other things. But these advanced appli­ca­tions are restricted by our lim­ited ability to con­trol the material’s growth on the nanoscale.

The very thing that makes Menon’s nanowires beau­tiful rep­re­sents a break­through in her ability to process them for these novel uses. She deposited onto a sil­icon sub­strate small droplets of liquid gold metal, which act as cat­a­lysts to grab gaseous gal­lium nitride from the atmos­phere of the exper­i­mental system. The net forces between the tiny gold droplet, the solid sub­strate, and the gas cause the nanowire to grow in a par­tic­ular direc­tion, she explained. Depending on the size of the gold cat­a­lyst, she can create wires that exhibit peri­odic serrations.

“It first tries to grow out­ward, but that gives the gold a larger sur­face area,” she said. “So now the wire gets pulled in the inward direc­tion, and then the gold gets a smaller sur­face area, so it grows out­ward again.” This inward and out­ward growth repeated itself again and again to create a peri­odic struc­ture nearly 6 mil­lion times smaller than the end­less column and is sig­nif­i­cantly more promising for its use in advanced devices.

“That there is very little imple­men­ta­tion of nanowire tech­nology in elec­tronics or optical devices is due to the fact that it’s very hard to con­trol their shape and dimen­sions,” said Menon. But now that she has a very simple way of con­trol­ling growth, the next step is to con­trol the size of the cat­alytic droplet with which she starts.

Another advan­tage of Menon’s approach is using what Panaitescu called “macro­scopic tech­niques” to create nanoscale mate­rials, thus making it scal­able and inex­pen­sive. “We just con­trol a few para­me­ters and then leave it, let it do it’s nat­ural thing,” explained Menon.

Source: http://www.northeastern.edu/