Computer memory gets a new charge.

These days, machines need memories. To store information, they typically use a magnetic signal (e.g., on a cassette tape), an electric charge (e.g., in computer memory), or an optical pattern (e.g., on a compact disk).

Now comes a new memory system onto the scene. Chongyang Liu and his colleagues at the University of Texas at Austin report a new material they've developed, which uses electrical charges and light to store information. This new memory system traps and stores charges in a thin film of photoconductive material, called ZnODEP, and does so densely and rapidly. The result: a better way to store and retrieve data. "Information, as trapped charge, can be written, read, and erased by simultaneous application of an electric field and a light pulse," the researchers, all chemists, report in the Aug. 13 SCIENCE.

Photosensitive materials generally cannot store information, Liu explains. Video cameras and copy machines, for instance, must store pictures in other forms (magnetically or digitally), since photoconductivity stops when the light stops shining.

"Photoconductivity has not been useful for memory devices," Liu says. "But this system, using an electric field plus irradiation, has advantages of an ordinary computer memory and an optical disk. Our photosensitive material is interesting because it stores charge. It has a memory that lasts."

The electro-optical memory, says Liu, may benefit computers' backup and dynamic random access memories (RAM), as well as video cameras and navigation systems.