GOING BOLDLY INTO THE TINIEST FRONTIER

At approximately 1/3000th the diameter of a human hair, the light-emitting diodes Dr. Chung Hoon Lee has created in his lab on the third floor of Haggerty Hall are among the smallest LED light sources in the world. What are the possible uses of such a microscopic light source? Certainly not lighting football fields or parking lots. In fact, it would take nearly 1 billion of these devices to generate as much light as a typical children’s nightlight.

By Stephen Filmanowicz

Not a problem. As light sources get smaller and less bright, their potential as transmitters of computer signals grows. In fact, if Lee, an assistant professor of electrical and computer engineering, can just get his nanodevice to emit even less light — by pulsing on so briefly that it emits as little as one photon at a time — it could begin generating serious interest as a quantum-computing alternative to the transistors on the highest-powered chips from Intel and other manufacturers. The LEDs are just one application of the work that is the main focus of Lee’s research, the creation of nanostructures featuring metal-coated silicon arms that form a tiny gap (between two and 10 nanometers wide) through which he can pass an electric current. When electroflourescent zinc oxide molecules bridge the gap, Lee has his tiny light source. The gaps in his nanostructure are small enough to hold a single DNA molecule or a single ball-shaped cluster of carbon molecules known as C60. And because DNA and C60 are among the most closely studied materials these days, interest will be high when Lee runs an electrical charge through the gap and studies the conductivity of these materials in their most basic form. He’s currently working with research partners at North Carolina State University and Cornell to acquire those materials and prepare for the tests. Though Lee isn’t the first scientist to create such nanoplatforms, his have decided advantages over predecessors. Because the nanostructure arms are suspended, whatever happens in the gap between them is free from interference from the base layer, or substrate, below. They can be created with everyday optical lithography machinery, compared with the $5 million electron beam lithography equipment used to create many previous nanogaps. And perhaps best of all, Lee’s platforms can be created — and located — with great predictability. That removes one of the more vexing aspects of conducting research at the nanoscale — the tendency of a tiny particle or structure being sought to be as elusive as a stray meteor in a vast galaxy. With the progress he and his research partners are making, Lee says such challenges are more than manageable. And the potential payoff in knowledge gained looks huge. “Think of the human body, for example. You can try to understand it as a single object or you can look closer and see individual organs and cells. You see how liver cells differ from heart cells and how they function differently,” he explains. “The same principle applies with nanotechnology. If you want to understand something, it really helps to understand it as a molecule. That’s the single building block.”

“ ” You learn more about something as you look at it in its smallest form.

Typical human hair

Nanogap

500 nm

November 2011 // 12