News update

New, safe T-ray source

A group of Argonne researchers led by physicist Ulrich Welp has developed a new, compact source of terahertz radiation, or T-rays. This new technology could be used to create T-ray scanners that can detect dangerous or contraband materials at airports or create new imaging devices for skin and breast cancers.

Previously, T-rays could only be created by using a large table of expensive equipment. The Argonne T-ray source is only a few millimeters in size, small enough for engineers to potentially use it to make a portable scanner.

The new source comprises a stack of semiconducting crystals known as Josephson junctions. Researchers can induce alternating currents of various frequencies in these junctions by applying different amounts of voltage.

T-rays present an additional advantage over their more energetic cousins, X-rays: Because they lack sufficient energy to ionize atoms, T-rays are perfectly safe for human exposure. T-rays can penetrate skin, leather, fabric, cardboard and paper but do not pass through water or metal.

Quantum dots flicker quicker

Quantum dots—tiny, colorful light- emitting particles that blink like strobe lights—have become all the rage among nanoscientists who seek to understand one of their unusual but frustrating properties.

These semiconducting nanoparticles may represent the future of light-emitting materials because the color of light that they give off can be changed by merely altering the size of the particles. This unique behavior has made quantum dots the subject of intensive investigation for potential use in medical research, as well as for new forms of lighting, lasers and solar cells.

All of these applications, though, may be compromised by the annoying tendency of single dots to flicker on and off randomly like fireflies. This “blinking” behavior has been widely observed but remains poorly understood. Argonne scientist Matthew Pelton and collaborators from the California Institute of Technology and The University of Chicago recently discovered a previously unobserved change in the blinking of a single quantum dot viewed under a micro scope during periods shorter than a few microseconds.

This result confirms a theory that the fluctuations of energy levels in the quantum dot relative to its environment cause the dot to blink. This new insight may point the way to a better way to control blinking, brightening the prospects for real-world applications of quantum dots.

Argonne helps China sprint to clean air before Olympics

Beijing will play host to the 2008 Summer Olympics come this August. But the city has recently garnered a less favorable distinction for high levels of air pollution.

Argonne has played a leading role in helping China's scientists and policymakers improve air quality in advance of the Olympics. Since 2003, Argonne and the U.S. Department of Energy have been working with the China Automotive Technology and Research Center to promote the adoption of energy-efficient vehicles and cleaner fuels.

Scientists at Argonne have also helped to create models of Beijing air quality that have gotten the
attention of Beijing's mayor, who requested that the Chinese government implement unprecedented regional control programs to ensure that the city meets its 2008 air-quality goals.

For more information, please contact Dave Baurac (630/252-5584 or media@anl.gov) at Argonne.