August 12, 2011 –
A UC Irvine materials scientist saved the day for a SURF-IT lunchtime-seminar audience.
Chemical engineering and materials science professor Albert Yee, who also happens to be CALIT2’s former director, was planning to listen to this week’s scheduled talk about nano- and micro-patterning of carbon. When the scheduled speaker cancelled unexpectedly, Yee offered to step in.
The noted researcher discussed the science of and applications for nanoimprinting, a method of building nanometer-sized structures on a variety of surfaces.
Nanoimprint lithography involves creating a mold that has a certain pattern with feature size as small as 10 nanometers, which is then brought into contact with a substrate made of polymers. The mold and substrate are pressed together, and using heat, the pattern is transferred to the substrate. The resulting nanostructure can then be built up, layer by layer, to form a three-dimensional structure.
These multiple layers allow very high density of materials, such as polymers, as well as semiconductor, conductor, and other electronic elements. This increases the speed of the electronic circuit because “the smaller the circuit elements, the faster the information gets transmitted,” Yee explained. “”That’s the ultimate goal – to get the highest density of elements possible so we can speed up the transmission of information.”
Until recently, the smallest nanostructures were approximately one-tenth of a micron, which is 100 nanometers. (The width of one strand of human hair is 100,000 nanometers.) But chipmakers announced recently that now they are making structures as small as 33 nanometers, which translates to roughly the size of a DNA molecule.
“The technology becomes very intricate,” Yee said. “It becomes even more intricate when you have to get this down to a smaller and smaller scale.” In his lab, he added, researchers have built structures as small as 25 nanometers – about one-fourth the size of the polymer molecule that these structures are made of. This is possible because the normally random coil molecules become aligned and ordered in these structures.
Electronic circuits are just one application for these nanostructures. They also can be used for sensing toxins and pollutants, for medical diagnosis and delivery of therapeutics, and even to prolong the life of stem cells, a discovery Yee and one of his graduate students stumbled upon accidentally.
They were trying to develop a pattern that would cause stem cells to elongate into specific types of cells, but the cells weren’t cooperating. “We were very disappointed at first,” Yee said, until he and his student noticed that the cells in the nanopatterned surface were more active than they were when in the “nutrient broth” they were usually kept alive in. “A cell biologist told us, ‘you hit the jackpot,’” Yee said.
Scientists don’t know exactly why the cells in these patterned nanostructures live longer, but Yee thinks it might have something to do with how busy they are. He compared the stem cells to humans, who need exercise to stay healthy. “When we look at the cells under a microscope, we find that when you have the right nanopattern the cells are constantly moving around. When we don’t have the right pattern the cells get very lazy and just sit there, eventually dying,” he said.
The audience gave Yee a hearty round of applause at the end of his impromptu – and very informative – lecture.
— Anna Lynn Spitzer
