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Posted: May 07, 2014
Scientists find x-rays can cause reversible resistance changes
(Nanowerk News) Usually, when we think of a device that has defects, it means it’s time to throw it out. However, for several types of materials, imperfections are what actually make them function in the first place. Finding ways to control defects in a material without irrevocably damaging it could yield new information in the quest for an array of improved devices.
Synchrotron X-rays are frequently used to image a wide range of different materials, but they can also cause chemical changes as well. In a new study, researchers at the U.S. Department of Energy’s Argonne National Laboratory looked at how a material’s electrical resistance changes when it is irradiated with these high-energy X-rays.
In the experiment ("X-ray Irradiation Induced Reversible Resistance Change in Pt/TiO2/Pt Cells"), the researchers looked at titanium dioxide, a material known for exhibiting multiple resistive states induced by defect movement. This behavior, known as resistive switching, could offer scientists a mechanism that may hold the key to potential new computer memories and even artificial neurons, according to Argonne materials scientist Seungbum Hong, who led the study along with Argonne physicist Jung Ho Kim.
“It’s not easy to make a nanoscale device that switches reliably between resistive states,” Hong said. “In order to design reliable resistive switching materials, you need to understand and control the defect at the nanoscale.”
When the titanium dioxide cell was exposed to the X-rays generated by Argonne’s Advanced Photon Source, the scientists found the existence of a photovoltaic-like effect, which changes the resistance by orders of magnitude, depending on the intensity of the oncoming X-rays. This effect, combined with an X-ray irradiation-induced phase transition, triggers a non-volatile reversible resistance change – that is, the change in resistance can be observed even after the X-rays are turned off.
“This result was somewhat serendipitous, in that people had known that X-rays could damage these materials, but they hadn’t been looking for this kind of reversible change,” Kim said.