UCR scientists report a new organic bistable material

May 23, 2002

Scientists at the Center for Nanoscale Science and Engineering at the University of California, Riverside report in the 24 May 2002 issue of the journal Science a new bistable material that is likely to be of enormous interest and benefit to the electronic industry as well as to the computer storage industry. The material, as yet without a popular name, simultaneously exhibits bistability in three properties (or physical channels): optical, electrical, and magnetic.

"We fabricated the material thinking it should have novel conductivity properties," said Robert Haddon, professor of organic materials chemistry and engineering at UCR and co-author of the Science paper. "But when we measured the properties we discovered the bistability."

A bistable material is one that can exist in either one of two different states. The ability of a material to switch between two states is the basic requirement for a device such as a transistor, the ultimate building block of computers. Properties of a bistable material can change dramatically when the material switches between states, much like the changes a schizophrenic person might undergo when shifting from one personality to another.

When two different physical channels of a material are simultaneously involved in the switching, new applications and new fields of research can emerge. For example, the field of optoelectronics involves the optical and electrical channels; spintronics involves the magnetic and electrical channels.

"When our material switches between states," said Haddon, "it switches the conductivity, the amount of light transmitted, and the magnetism. Engineers are always trying to develop materials that switch between two states in such a way that the switching is manifested in more than one physical channel."

Haddon explained that in a transistor, switching occurs between two states in which the conductivity is different. In a computer storage device, switching occurs between two states, which have different magnetic properties. Photonic devices switch the amount of light allowed to pass through a material.

"Ultimately, to develop very sophisticated devices and new technologies," he said, "we need materials that combine one or two of three channels: optical, electrical and magnetic channels. Our material, as far as we know, is the first organic compound that combines all three."

Haddon mentioned that his team's multifunctional material has the potential to be used as the basis for new types of electronic devices, where multiple physical channels are utilized for writing, reading, and transferring information.

In their Science paper, the scientists discuss how the new material, which they call a 'neutral radical organic conductor,' exhibits bistability just above room temperature. One state, they note, is paramagnetic (attracted to a magnetic field), insulating, and infrared transparent. These properties reverse in the other state, producing a material that is diamagnetic (repelled by both poles of a magnet), conducting, and infrared opaque.
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University of California - Riverside

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