News | November 16, 2000

Self-assembly route to quantum dots said to be simpler, cheaper than others

Quantum dots are nanoscale structures that have the potential for use as superdense computer data storage media, highly tunable lasers and nonlinear optical devices. But making them has always been difficult and expensive. At the University of Nebraska, Lincoln (UNL), however, researchers are working on a self-assembling dot production method they say is far simpler and potentially cheaper than standard methods.

The conventional process for making quantum dot structures involves film growth (such as by atomic layer epitaxy or chemical vapor deposition), some type of lithographic patterning, and finally etching, such as by reactive ions. This is a complex series of steps. Now, UNL electrical engineering professor Supriyo Bandyopadhyay believes he's got a better way to make quantum dot structures.

The new procedure involves first creating a patterned array of nanoscale pits in an aluminum substrate using a process called electropolishing. The substrate is then anodized in an acid bath. The resulting electrochemical reactions cause a thin aluminum oxide layer to be deposited on the substrate. This oxide layer contains pores, which form over the underlying pits. Pore diameters and separation between pores can be controlled by the temperature, anodizing current, pH and the specific acid solution used.

The matrix of pores in the oxide film then act as a template for hosting either quantum dots (for small pore depths) or quantum wires (for large pore depths). The dots are formed by electrodepositing various metals or semiconductors within the pores from acid solutions. The net result is a regimented array of quantum dots or wires embedded in a surrounding insulator and dielectric (the aluminum oxide).

Bandyopadhyay's Quantum Device Laboratory at UNL is one of a handful of labs in the United States in the final round of two US government funding competitions to develop quantum dot-based electronics. The new deposition process is described in detail in US patent 5,747,180 (1998).

According to a UNL press release, Bandyopadhyay and five fellow UNL electrical engineers studying nanotechnology, Rod Dillon, Ned Ianno, Latika Menon, Paul Snyder and Frazer Williams, have been working on quantum computer research for about three years and have succeeded in demonstrating new types of computer memory. But Bandyopadhyay said his team is probably five years away from being able to demonstrate a small-scale quantum computer in the lab, while commercial versions probably won't be available for 20 to 25 years.

For more information, contact Supriyo Bandyopadhyay, University of Nebraska, at 402-472-0294, or

Edited by Gordon Graff
Managing Editor, Laboratory