Electronics Could Take A Quantum Leap

INEEL physicist Art Denison is presenting his research on quantum dots at the American Physical Society's centennial meeting being held in Atlanta on March 20-26.

Denison, who is collaborating with physicist Kelvin Lynn and other researchers from Washington State University, is trying to understand the unpredictable behavior of particles of such a small size. At this subatomic level, the physical laws we live with everyday are not easily predicted-this is the basis of quantum physics.

"The benefits of basic studies such as these are not always immediately apparent," Denison said. "However, history has shown that technological advantages and applications often follow." The results of this research could lead to vastly improved satellite dishes, CD players, TV screens, computer monitors, solar cells, and microchips.

Electrons within a quantum dot can absorb energy such as electricity or sunlight and emit energy as light or a current. Researchers are trying to tap quantum dots to make tiny, efficient semiconductors for computer chips.

"If we understand the properties of a single dot, we can hook several dots together to make a circuit," Denison said. "We could make molecular size computer chips. This research may lead to quantum computing."

Quantum dots could also be used in light-emitting applications. The wavelength of light emitted from a dot is related to its size. Larger dots generate red light, while smaller dots generate blue light. Color-emitting dots could be used for computer monitors, TV screens and in place of LED displays.

Interestingly, the smaller the quantum dot is, the greater energy it can potentially emit. Denison and other scientists are trying to understand this inverse relationship between the size of the dot and its energy potential. They are also looking at how quantum dots literally "squeeze" their electrons into smaller spaces than the electrons would normally like to occupy.

The researchers are using positrons to investigate the properties of quantum dots. Positrons are the antimatter equivalent of electrons. They have the same mass and spin as electrons; however, they have a positive charge equal in magnitude but opposite to electrons' negative charge.

"The advantage of using a single positron is that it removes the confusion brought about by electron-electron interactions," Denison said. "The positron, being alone, is immune to the harmonious interactions of the background electrons."

When an electron and positron collide, they annihilate one another in accordance with the equation E=mc2. In this case, all the energy present in the colliding electrons and positrons is converted into gamma rays. If a "squeezed" electron can emit more energy than a typical electron, the extra energy shows up as extra energy in the gamma rays emitted after annihilation. By studying the gamma rays, scientists can characterize or describe the size and electronic potential energy of a quantum dot.

Denison and Lynn have been probing quantum dots with positrons for a year. They have studied dots of cadmium selenide and silicon and germanium. They plan to publish research results within the next few months. Their dots were produced by laboratories at the University of California at Berkeley and at Davis. This research is being funded by the DOE's Basic Energy Sciences office.