WESA: Paul Leu runs a lab at the university where students work with the tiny particles called nanotubes. By Mark Nootbaar
'“Just to give you the idea of the scale of things, if you take one of these nanotubes and you were to enlarge it to the typical circumference of a pillar in a building, and then you take that column and enlarge it by the same scale, that original column would be the size of the diameter of the entire Earth,” Leu said. “So these things are incredibly, incredibly small.” They're smaller than the wavelength of visible light.
First-year graduate student Brad Pafchek is trying to create a product that will absorb as much light as possible. He works with a standard silicon disc that looks like a mirror and then exposes it to a plasma or ionized gas.
'“This plasma has a bunch of ions and radicals that are flying around at high energy and they etch into the surface,” Pafcheck said. That etching creates a surface that, to the eye, has a flat black appearance but, under an electron microscope, resembles conical structures. “So these bed of needles create kind of like a buffer region that allows light to get absorbed into the silicon itself, which is fantastic for solar cell applications, because that is the whole point to absorb light and create energy,” Pafcheck said. Pafchek creates this by changing a slew of variables, including the flow rate of the multiple gases used to make the plasma and the power at which they are introduced.
'Those tiny advances might have applications beyond solar energy. Third-year Ph.D. student Imrul Kayes is creating an antibacterial surface spiked with nanocones. According to Kayes, nearly 300 million structures fill just one square inch of material. Viewed under an electron microscope, it looks like a bed of nails, but those nails are just 60 nanometers at the tip. By comparison, a red blood cell is about 8,000 nanometers in diameter -- the wavelength of red light is 700 nanometers. Kayes coats the silicon spikes with a few nanometers of silver, then exposes it to a common bacteria known to cause serious infections among hospital patients.'