MRI Faculty Spotlight
Peter Eklund's office occupies a historic piece of real estate: the lab space where Erwin Mueller, the inventor of the field ion microscope and the first man to "see" atoms, developed the atom-probe field ion microscope, which allowed scientists to identify single atoms and distinguish the isotopes of elements.
Next to his office, Prof. Eklund's group of graduate students and post doctoral researchers work to measure and predict the physical properties of nanomaterials as they cross from the large scale - at around 20 nm - to 2 or 3 nm, approaching the size of DNA. "I'm very hands-on with my students," Eklund says. "They're really capable, it;s hard to guess what results they're going to get. I don't just give them a topic and wait for their Ph. D. theses to arrive on my desk." Evaluating the results of that many talented researchers takes a great deal of time and some hard thought. Eklund explains that "Sometimes we hold off on publishing our research for several months. We don't want to publish just the data; we like to publish explanations."
The major focus of Prof. Eklund's research involves the growth and study of nanowires and carbon nanotubes, hollow single sheets of carbon atoms rolled into tubes with a shape like a soda straw. "We work on fundamental science issues as well as applications, such as chemical sensors, using nanowires as transistors, and trying to solve the hydrogen fuel storage problem for automobiles," he says. The posters lining the walls outside his second floor office and the lab one floor above illustrate the wide range of research he is engaged in, both with his students and across departments. In one poster outside his lab, the scattering effect of confined phonons in silicon nanowires is described, in a collaboration between Eklund and Kofi Adu, a postdoctoral researcher in his group. Confined quantum structures can have unusual optical, electrical, and thermal characteristics, which could be used to develop novel thermoelectric and optical electronic devices. "This is a scientific gut check," Eklund says about their research into basic properties of nanoscale materials. "Will phonon confinement increase or decrease scattering? Do we know how phonons work?"
In a paper published in the journal Science in January 2005, Eklund and collaborators Hugo Romero, Kim Bolton, and Arnie Rosen describe the changes in the electron transport capability of single-walled carbon nanotubes that have collided with inert gas atoms. The resulting dent in the side of the nanotube affects the resistance of the tube, a previously unknown effect that has implications for the use of nanotubes in electronic applications.
"Nanotubes are attractive because they are strong and because of their almost ballistic transport of electrons, which means that the electrical charge is transported without scattering," Eklund explains. "The holy grail of physics is to have electrons transported ballistically and be able to cut the current off without electric power loss."
That is a goal within sight, he believes, both with nanotubes and with nanowires, the solid version of the nanotube. Nanowires can be grown from a variety of semiconductor elements besides carbon or silicon, with interesting properties at the quantum level, such as enhanced photo-optical ability for sensors, enhanced electron mobility for electrical uses, as well as piezoelectric and pyroelectric properties useful in a variety of possible applications. "A challenge that we face with nanowires is packing them tightly, a billion nanowires on a single silicon chip platform, and orienting them in the correct direction." This is a problem of assembly at a very high density. However, he contends that even without an early resolution to the issue of high density assembly, other startling applications will nevertheless be produced from nanotubes and nanowires.
Other research interests include luminescent molecules, an area he is working on with Jim Adair, Penn State professor of Materials Science and Engineering. Luminescent molecules have interesting uses as markers for drug delivery. Their research involves placing luminescent molecules inside nanoparticles. They wish to understand the change in the luminescent properties upon incorporation into the host nanoparticles; that is, how to keep their dye markers from fading or losing their "optical punch" through photobleaching.
"We work on a lot of different aspects of nanomaterial. Right now we're playing with positive and negative curvatures in nanophase carbon materials (for the Department of Energy's Hydrogen Center of Excellence Program)." Hydrogen storage is a crucial element in the effort to move from an economy based on dwindling hydrocarbons that emit greenhouse gases to one that is based on clean and abundant hydrogen. The DOE estimates that within 15 years fossil fuel burning in the atmosphere will have reached an unsustainable level, and a cleaner fuel source must be in place by that time. "We are trying to develop a low-mass-density high-surface-area carbon material for storing hydrogen that will solve the problem of hydrogen fuel storage for automobiles," Eklund says.
His group is also developing different types of nanowires for use as medical sensors. "We've got two out of three problems solved. The only thing left is the functionalization of the chemical surface. Now we need to hook up with a biologist and a good chemist at Penn State and put together a team. That's one of my objectives for next year.
"Basically, you could say that we're experimenters with a passion for understanding theory and application," Professor Eklund concludes.
