Terahertz frequencies are 1000 times higher than microwave frequencies and 100 to 1000 lower than visible light. Because terahertz frequencies are easily absorbed by moisture in the atmosphere, they don't travel long distances; for that reason they haven't garnered the study given microwave frequencies used in cellphones and ovens. For years, researchers thought terahertz frequencies had no modern-day use. But Kolodzey, an electrical and computer engineering professor realized terahertz could be of great value for close-range applications.

"The region we call terahertz interacts with molecules and chemicals and biological agents in the air; there are interesting resonances and dispersions," Kolodzey said. "That makes them ideal for sensing the chemical composition of the environment. In this day and age, that's practical for analyzing and measuring."

James Kolodzey and the team that made a major breakthrough in terahertz nanotechnology. © University of Delaware.

Now Kolodzey and his team of graduate and post-doctoral students have discovered a way to harness terahertz frequencies via a palm-sized device with semiconductor nanostructures. Research is preliminary, but Kolodzey says the palm device might one day detect cancers in the body, determine from a distance the chemicals in a hazardous waste spill, or find victims trapped under rubble.

Unlike radio waves, which travel through objects, terazhertz frequencies are partially absorbed by objects or by the human body. Kolodzey and his team realized a dentist could use terahertz-powered technology, for example, to take a picture of the inside of the teeth the way an X-ray does. But terahertz isn't harmful to humans the way X-rays are because they emit at lower energy levels.

"Humans and animals have been evolving for many years while being bombarded with these frequencies that originate from any warm object in the environment," Kolodzey said.

But how do you harness the terahertz frequencies in a practical way so they could be used for applications like these?

Boron emits at terahertz frequenices

Kolodzey's team started by using nanotechnology to make semiconductor devices that could emit at terahertz frequencies. They wanted their semiconductor device to be handheld and small, like a laser pointer, so it could be easily used. They were stymied at first.

"We spent a few years on that and it wasn't easy," Kolodzey admitted. "This past year we had an unexpected breakthrough. We put small amounts of chemical additives in a silicon wafer and it emitted terahertz at a high level.

"We were stunned. Blown away," he said. "We didn't understand where it was coming from, but we weren't complaining."

The miracle chemical additive? Boron. In exploring scientific literature, the team discovered that about 36 years ago, scientists found boron absorbed at terahertz frequencies. To the Delaware team's delight, boron emitted at terahertz frequencies too.

"We look at our emitted signals and found it was at exactly the same energy level as the absorption level they'd seen years ago," Kolodzey said. "The agreement was uncanny."

James Kolodzey. © University of Delaware.

The researchers are now improving the structure of the device so it emits terahertz at even higher levels and uses less energy. The present machine is based on a silicon–germanium semiconductor and is the size of a cellphone. The semiconductor is used to select specific terahertz energy bands. It might, if marketed, use a side pack for cooling. Presently, a waveguide corrals and distributes the signal in the manner of a laser pointer.

"Our goal is to make the device usable and affordable," Kolodzey said.

Everyday applications for emitter

The skin of a patient who is ill with cancer seems to have very strong resonances in the terahertz region, Kolodzey has realized. This suggests medical applications using terahertz to highlight cancerous areas of the skin. In the future, a doctor might run a handheld device over the patient's skin and take readings to test for cancer.

"In terahertz there's no word for different colors, but certain wavelengths can distinguish cancers," Kolodzey said. "If your tooth has tooth decay or if there's a chemical spill in the ground, wavelengths show that. You could maybe even find the chemical composition of the spill from 30 feet away."

Chemicals have different terahertz resonances and responses. The emitter illuminates those resonances and a detector can essentially tell the user the chemical makeup of the area over which the emitter is passed. A terahertz device might be used to determine different types of pollutants in the environment and it may be possible to test surrounding air for bacteria like anthrax.

Research is preliminary and the terahertz device is still being tested, but its possibilities are endless.

Source: http://www.chemweb.com/alchem/articles/1052327194413.html

The Alchamist, in chemweb.com