To image the hybrid material as it was sensing, he and physics professor Marija Gajdardziska used a high-resolution transmission electron microscope (HRTEM). But to explain what was happening, the pair needed to know which molecules were attaching to the nanotube surface, which were attaching to the tin oxide surface, and how they changed upon attachment.
So the pair turned to physics professor Carol Hirschmugl, who recently pioneered a method of infrared imaging (IR) that not only offers high-definition images of samples, but also renders a chemical "signature" that identifies which atoms are interacting as sensing occurs.
Chen and Gajdardziska knew they would need to look at more attachment sites than are available on the surface of a carbon nanotube. So they "unrolled" the nanotube into a sheet of graphene to achieve a larger area.
That prompted them to search for ways to make graphene from its cousin, graphene oxide (GO), an insulator that can be scaled up inexpensively. GO consists of layers of graphene stacked on top of one another in an unaligned orientation. It is the subject of much research as scientists look for cheaper ways to replicate graphene's superior properties.
In one experiment, they heated the GO in a vacuum to reduce oxygen. Instead of being destroyed, however, the carbon and oxygen atoms in the layers of GO became aligned, transforming themselves into the "ordered," semiconducting GMO a carbon oxide that does not exist in nature.
It was not the result they expected.
"We thought the oxygen would go away and leave multilayered graphene, so the observation of something other than that was a surprise," says Eric Mattson, a doctoral student of Hir
|Contact: Junhong Chen|
University of Wisconsin - Milwaukee