Toward plastic spin transistors

But study hints efficient organic LEDS will be tough to make

University of Utah physicists John Lupton and Christoph Boehme use green and blue laser beams to "excite " a small piece of an organic or "plastic " polymer (glowing orange near Boehme's... Click here for more information.

SALT LAKE CITY – University of Utah physicists successfully controlled an electrical current using the "spin" within electrons – a step toward building an organic "spin transistor": a plastic semiconductor switch for future ultrafast computers and electronics.

The study also suggests it will be more difficult than thought to make highly efficient light-emitting diodes (LEDs) using organic materials. The findings hint such LEDs would convert no more than 25 percent of electricity into light rather than heat, contrary to earlier estimates of up to 63 percent.

Organic semiconductor or "plastic" LEDs are much cheaper and easier to fabricate than existing inorganic LEDs now used in traffic signals, some building lighting and as indicator lights on computers, TVs, cell phones, DVD players, modems, game consoles and other electronics.

The study – published online Sunday, Aug. 17 in the journal Nature Materials – was led by Christoph Boehme and John Lupton, assistant and associate professors of physics, respectively, at the University of Utah.

The promising news about spin transistors and sobering news about organic LEDs (OLEDs) both stem from an experiment that merged organic semiconductor electronics and spin electronics, or spintronics, which is part of quantum mechanics – the branch of physics that describes the behavior of molecules, atoms and subatomic particles.

"This is the first time anyone has done really fundamental, hands-on quantum mechanics with an organic LED," Lupton says. "This is tough stuff."

Lupton and Boehme conducted the study with postdoctoral researcher Dane McCamey and four University of Utah physics doctoral students: Heather Seipel, Seo-Young Paik, Manfred Walter and Nick Borys.

The Spin on Spintronics

An atom includes a nucleus of protons and neutrons, and a shell of orbiting electrons. In addition to an electrical charge, some nuclei and all electrons have a property known as "spin," which is like a particle's intrinsic angular momentum. An electron's spin often is described as a bar magnet that points up or down.