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A close-up of beakers of lighted silicon nanocrystals.

The color emitted by silicon nanocrystals is determined by their size, with red-orange resulting from larger nanocrystals, and green from smaller nanocrystals that have not been exposed to oxygen.

Shining a new light on silicon

Nanotechnology may transform common element into uncommonly long-lasting lightbulb

By Rick Moore

Published on March 16, 2005

University scientist Uwe Kortshagen's research may have a big impact on society, but that's the only thing "big" about his work. Kortshagen's efforts in the broad field of nanotechnology focus on particles measured in namometers, which are a billionth of a meter in size, and require the strongest of microscopes to view.

How small, in everyday terms, is a nanometer? Picture holding a human hair between your fingers. Take the diameter of that hair, divide by about 100,000, and you have a nanometer. Another analogy is that a 1-nanometer crystal is to a soccer ball as a soccer ball is to the earth. We're talking teeny-tiny here.

Governor announces contest for "breakthrough ideas"

Last week (on March 9), during the same press conference in which InnovaLight announced its move to the Twin Cities, Governor Tim Pawlenty announced a new statewide contest to support breakthrough ideas by inventors and entrepreneurs.

The winner of the competition, called the Minnesota Cup, will receive $25,000 in seed capital, along with free public relations, and legal, research, and management support services. Second and third place will be worth $5,000 and $2,500, respectively. The Minnesota Cup award will be presented by David and Carolyn Cleveland, and is sponsored by the University of Minnesota.

"The ongoing vitality of our state's economy depends upon the constant discovery and commercialization of innovative, entrepreneurial ideas," says Pawlenty. "It's these 'breakthrough ideas' that have the powerful potential to grow and become the next Medtronic, Cargill, or 3M of our state."

Entrants will participate in two rounds of competition before judges select five finalists, who will present to a panel of executives, investors, entrepreneurs, and top officials at the U. Entries will be judged on originality, viability, and the quality of presentation. The competition will conclude with an awards ceremony in the fall.

For more information, and to submit your business ideas online, see breakthroughideas.umn.edu.

Kortshagen, a professor of mechanical engineering and physics, works with silicon, the second most abundant element on earth and a substance well-known for its electronic properties. And when it's small enough--here comes the need for nanotechnology--silicon assumes the ability to emit visible light when subjected to an electrical charge.

Kortshagen has developed an efficient way to make silicon nanocrystals. The process involves putting a gas that contains silicon and hydrogen (silane) into a reactor. When an electrical charge is applied to the gas, the hydrogen is stripped off from the silane, and the silicon atoms recombine to form silicon nanoparticles.

"Depending on how long we subject the particles to this process, we can adjust the size of the particles," says Kortshagen. "By adjusting the size, we can adjust the color at which the particles will emit light. The bigger particles will tend to emit light at longer wavelengths, meaning the red part of the spectrum, and the smaller particles will emit light in the green or blue part of the spectrum."

While all this may still sound a bit abstract, it has drawn the interest of business people and venture capitalists. The work of Kortshagen and other scientists has spawned a start-up company, InnovaLight, which is attempting to commercialize solid-state lighting from silicon. Since silicon nanocrystals can emit light in a range of colors--including white--when hooked up to an electrical source, and since silicon atoms are inherently stable, InnovaLight is hoping to develop a so-called "100-year lightbulb."

This new generation of lightbulbs, in addition to lasting 100 times longer than current incandescent light bulbs, would be 10 times more efficient, says InnovaLight CEO Paul Thurk. "It's truly an innovative and revolutionary technology," he says.

Last week, InnovaLight announced that it had completed a move from Austin, Texas, to a location on University Avenue in the "biosciences zone" of St. Paul. A number of factors drove the company's move to the Twin Cities, including the prominence of the area in materials science and a desire, Thurk says, "to better collaborate with the University of Minnesota."

There are still a few hurdles to clear before InnovaLight is able to capitalize on Kortshagen's work and market a lightbulb that outlasts any of us. So don't throw away your spare light bulbs just yet.

"One of the big problems with silicon is that it likes to react with oxygen," Kortshagen notes. "That is a big problem if you want to make--like InnovaLight wants to--white light sources. Oxygen, when it bonds to the silicon surface, basically limits the emission to the red-orange range. So in order to achieve blue and green emission (moving toward white light)--the next technical challenge that we have to overcome--we have to coat the particles with a coating that is impermeable to oxygen and which will remain so for a very long time."

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