Scientists find X-rays can cause reversible resistance changes

By Jared SagoffMay 6, 2014

ARGONNE, Ill. – 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, 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.

An article based on the research, titled "X-ray Irradiation Induced Reversible Resistance Change in Pt/TiO2/Pt Cells", appeared in the January 13 edition of ACS Nano. Two other Argonne physicists, Jeff Eastman and John Freeland, also contributed to the study.

This research was funded by the U.S. Department of Energy’s Office of Science.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science. For more visit www.anl.gov.

The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.