US researchers find 7-volt pulse can alter sapphire's internal structure

US researchers recently discovered that applying a 7-volt pulse to an ultrathin electronic film can induce structural changes in the sapphire beneath it. Scientists at the US Department of Energy's Argonne National Laboratory found that this effect extends tens of micrometers into the sapphire, far deeper than the film's own thickness. Dr. Zahir Islam, a physicist at Argonne National Laboratory and co-author of the study, said the discovery challenges a common assumption in microelectronics: that the substrate beneath a film serves merely as passive support. Instead, the sapphire responds during device operation and influences the behavior of the film above it.

He emphasized: "This is a potential paradigm-shift observation. One cannot simply assume that the substrate is unrelated to the device's properties or behavior."

Sapphire substrate's unexpected response

In this study, researchers examined a vanadium dioxide (VO2) film grown on sapphire, which can transition from an electrical insulator to a conductor when voltage is applied. Vanadium dioxide is commonly used in electronic switches, wireless devices, tunable optical systems, and smart windows. The material is also being explored for memristors — electronic components that can retain data from previous electrical signals, making them attractive for neuromorphic computing. In the device the scientists studied, applying voltage triggered a localized insulator-to-conductor transition, creating a narrow conductive filament within the insulating film.

The scientists used Argonne's Advanced Photon Source to investigate deep structural changes. The method allowed them to examine structural changes inside the device and beneath its surface. They found that as voltage increased, the conductive filament expanded while generating non-uniform strain in the underlying sapphire — a deformation that penetrated tens of micrometers into the rigid substrate, far beyond what they would have expected from heating alone.

Dr. Elliot Kisiel, a Maria Goeppert Mayer Fellow at Argonne National Laboratory and lead author of the study, said the team initially suspected the sapphire substrate's unexpected response might be an experimental artifact — an error or misleading result caused by the experiment itself rather than the phenomenon under study. Kisiel explained in a news release: "Because the results were so surprising, we tested multiple devices, samples, film thicknesses, and even different substrates repeatedly. The effect persisted throughout." Kisiel is confident that as electronic devices shrink and components pack closer together, this discovery will become increasingly important.

Potential neuromorphic computing applications

For example, activity in one device could cause mechanical changes in a shared substrate that then affect nearby devices. While this could create problems, it could also be harnessed for neuromorphic computing, letting interconnected devices mimic the way the brain processes information.

Islam concluded: "The exceptional performance of Argonne's Advanced Photon Source allowed us to study more devices in less beam time and capture rich structural information with high fidelity." The research has been published in the journal Science.

Sapphire's new role in electronic devices

This research shows that the sapphire substrate is no longer a passive support but can actively influence film behavior, a finding that challenges traditional assumptions in microelectronics. As electronic devices continue to shrink, mutual influence between components will become increasingly pronounced, which could have profound implications for the design and function of future electronic components. Particularly in neuromorphic computing, such substrate mechanical changes could be used to mimic the brain's information processing, opening new application prospects.