University of Michigan physicists create first atomic-scale map of quantum dots

Physicists at the University of Michigan (Ann Arbor, MI) have created the first atomic-scale maps of quantum dots, a major step toward the goal of producing "designer dots" that can be tailored for specific applications.¹

Semiconductor quantum dots have potential applications in photovoltaic cells, lasers, LEDs, optical sensors, computers, and other technologies. Each dot is a well-ordered cluster of atoms 10 to 50 atoms in diameter.

Engineers are gaining the ability to manipulate the atoms in quantum dots to control their properties and behavior, through a process called directed assembly. But progress has been slowed until now by the lack of atomic-scale information about the structure and chemical makeup of quantum dots.

The new atomic-scale maps will help fill that knowledge gap, clearing the path to more rapid progress in the field of quantum-dot directed assembly, said Roy Clarke, University of Michigan professor of physics. Lead author of the paper is Divine Kumah of the university's Applied Physics Program, who conducted the research for his doctoral dissertation.

"Researchers have been able to chart the outline of these quantum dots for quite a while," said Clarke. "But this is the first time that anybody has been able to map them at the atomic level, to go in and see where the atoms are positioned, as well as their chemical composition. It's a very significant breakthrough."

X-ray mapping

To create the maps, Clarke's team illuminated the dots with an x-ray beam produced by the Advanced Photon Source at the Argonne National Laboratory (Argonne, IL). "We're measuring the position and the chemical makeup of individual pieces of a quantum dot at a resolution of one-hundredth of a nanometer," Clarke said.

The availability of atomic-scale maps will quicken progress in the field of directed assembly. That, in turn, will lead to new technologies based on quantum dots. "Atomic-scale mapping provides information that is essential if you're going to have controlled fabrication of quantum dots," Clarke said. "To make dots with a specific set of characteristics or a certain behavior, you have to know where everything is, so that you can place the atoms optimally."

The research was sponsored by a grant from the National Science Foundation. The U.S. Department of Energy supported work at Argonne National Laboratory's Advanced Photon Source.

REFERENCE

1. Divine P. Kumah et al., "Atomic-scale mapping of quantum dots formed by droplet epitaxy," Nature Nanotechnology, Published online: 27 September 2009 | doi:10.1038/nnano.2009.271.