Engineers to take a close look at how electrons flow between nanorods

Using a unique honeycomb-like structure, an engineer at Washington University in St. Louis plans to study how electrons can transfer by quantum tunneling from one nanoparticle to another while being illuminated.

This honeycomb-like structure serves as a template from which to grow gold nanorods, which Parag Banerjee's lab will use to study electron flow between nanorods.

Parag Banerjee, assistant professor of materials science in the School of Engineering & Applied Science, is co-principal investigator for a three-year, $400,000 grant from the Army Research Office with collaborators from the University of Dayton. With the funding, they will create simple nanostructures to determine the physical mechanisms for quantum electron transport through the structure when light shines on the electrons.

Banerjee's lab has created a "nano" honeycomb structure to test this activity by taking a foil of aluminum and applying voltage in a chemical bath. Using metallic nickel as the base of the honeycomb structure, a template forms through which he can grow a dense forest of gold nanorods that are only a few nanometers apart.

"We will determine what happens when we excite these gold nanorods with light," Banerjee says. "We are interested in probing the fate of electrons — do they move? Do they talk to each other across the nanorods?"

In particular, his lab will study how the electrons "tunnel" through neighboring nanoparticles.

"What quantum mechanics tells us is that if two pieces of metal are brought in close proximity to one another and a voltage is applied, a few lucky electrons inside the first metal will be transported through a barrier into the other piece of metal," Banerjee says. "Can a similar phenomenon occur with light-excited electrons as well?"

Some applications for the outcome of this study are radiation-based energy harvesting or antennas, which absorb different wavelengths of light and convert them to electricity using gold nanoparticles.

Banerjee and his team plan to sandwich a thin insulator between the gold nanoparticles so they can control the flow of charge and the distance between the particles.

"We hope that in three years, we'll have a proof-of-concept device for what it means to tunnel electrons through neighboring nanoparticles," he says.

The School of Engineering & Applied Science at Washington University in St. Louis focuses intellectual efforts through a new convergence paradigm and builds on strengths, particularly as applied to medicine and health, energy and environment, entrepreneurship and security. With 88 tenured/tenure-track and 40 additional full-time faculty, 1,300 undergraduate students, more than 900 graduate students and more than 23,000 alumni, we are working to leverage our partnerships with academic and industry partners — across disciplines and across the world — to contribute to solving the greatest global challenges of the 21st century.