Toward plastic spin transistors

Computers and other electronics work because negatively charged electrons flow as electrical current. Computerized information is reduced by transistors to a binary code of ones or zeroes represented by the presence or absence of electrons in semiconductors.

Researchers also hope to develop even smaller, faster computers by using electrons' spin as well as their electrical charge to store and transmit information; the up and down spins of electrons also can represent ones and zeroes in computing.

Lupton says that physicists already have shown that spins can carry information in nonorganic materials. In 2004, other Utah physicists reported building the first organic "spin valve" to control electrical current.

In the new study, the researchers showed that information can be carried by spins in an organic polymer, and that a spin transistor is possible because "we can convert the spin information into a current, and manipulate it and change it," says Lupton. "We are manipulating this information and reading it out again. We are writing it and reading it."

Boehme says spin transistors and other spin electronics could make possible much smaller computer chips, and computers that are orders of magnitude faster than today's.

"Even the smallest transistor today consists of hundreds of thousands of atoms," says Boehme. "The ultimate goal of miniaturization is to implement electronics on the scale of atoms and electrons."

Shedding Light on Organic LEDs

LED semiconductors using compounds of gallium, arsenic, indium and other inorganic materials have made their way into traffic signals, vehicle brake lights and home electronics in recent years. Some inorganic LEDs can convert 47 percent to 64 percent of incoming electricity into white light rather than waste heat. But efforts to replace incandescent and even compact fluorescent light bulbs with LEDs have been hindered by costs exceeding $100 per LED bulb.

LEDs made of electrically conducting organic materials are cheaper and easier to manufacture, but their efficiency long was thought to have an upper limit of 25 percent.

A 2001 Nature paper by other University of Utah physicists suggested it might be possible to make organic LEDs that converted 41 percent to 63 percent of incoming electricity into light. But the new study suggests 25 percent efficiency may be correct – at least for the organic polymer studied – pure MEH-PPV – and possibly for others.

"Doping" organic semiconductors with other chemicals someday might lead to organic LED efficiencies above 25 percent, but Boehme says he is skeptical.

Even if organic LEDs are less efficient and have a shorter lifespan than inorganic LEDs, they still may be more economical because their cost is so much less, he adds.