University of Arizona Provost Postdoctoral Fellow Ali Habiboglu uses a molecular beam epitaxy system to synthesize graphene nanoribbons – a material Zafer Mutlu and collaborators are investigating for use in next-generation radiation-sensing devices and electronics.
Photo Credit: Leslie Hawthorne Klingler, Office of Research and Partnerships
Scientific Frontline: Extended "At a Glance" Summary: Graphene Nanoribbons in Extreme Environments
The Core Concept: Graphene nanoribbons (GNRs) are highly durable, nanoscale semiconductor materials designed to withstand extreme radiation and function as ultra-sensitive environmental sensors.
Key Distinction/Mechanism: Unlike standard silicon-based sensors that quickly degrade under intense radiation, GNRs maintain their structural integrity when exposed to gamma rays. Instead of physically degrading, the radiation subtly alters the ribbon edges, triggering a quantum phenomenon known as Anderson localization. This effect traps charge-carrying electrons in place and sharply reduces the electrical current, creating a clear, measurable signal of radiation exposure.
Major Frameworks/Components:
- Graphene Nanoribbons (GNRs): Ultra-thin semiconductor strips that operate according to the principles of quantum physics rather than classical mechanics.
- Anderson Localization: A quantum effect in which structural irregularities trap electrons, causing a significant and detectable drop in electrical current.
- Molecular Beam Epitaxy: The advanced, atomic-level fabrication technique utilized to synthesize and customize the nanoribbons.
Branch of Science: Materials Science, Quantum Physics, and Electrical Engineering.
Future Application: GNRs are being developed as real-time condition monitors for the innermost barriers (the first wall) of fusion reactors, as well as state-of-health sensors for deep-space probes, Earth-observation satellites, and advanced artificial intelligence hardware.
Why It Matters: Because GNRs can survive much closer to a fusion reactor's core than current electronics, they allow for real-time internal monitoring. This capability could drastically reduce costly shutdowns for manual inspection, thereby accelerating the commercial viability and reliability of near-limitless, clean fusion energy.
University of Arizona researchers have demonstrated a promising new application for graphene nanoribbons, a nanoscale semiconductor material with the potential to withstand extreme environments. The team's findings could help clear a key hurdle to bringing fusion energy to the electric grid.
For the proof-of-concept study, published in the journal ACS Applied Materials & Interfaces, the researchers integrated the nanoribbons, known as GNRs, into semiconductor devices and exposed them to gamma radiation. Their results suggest that the ribbons could serve as radiation sensors for fusion reactors and in deep space, where intense radiation challenges existing technologies and close monitoring of material degradation could help keep critical systems operating reliably.
"The devices survive the exposure and still respond, but their electrical performance changes dramatically," said principal investigator Zafer Mutlu, University of Arizona assistant professor of materials science and engineering in the College of Engineering. "That's exactly the behavior we want from a sensor."
GNR-based sensors could help unlock fusion energy as a clean, near-limitless power source by improving how engineers monitor the condition of a reactor's first wall. This innermost barrier separates the superheated fuel from the reactor structure and gradually degrades under intense radiation, requiring periodic inspection and replacement. Engineers track that damage, but today's silicon-based sensors cannot survive inside the first wall. Instead, they must be placed outside the barrier, forcing reliance on indirect measurements during operation and physical inspection after shutdown.
Because the gamma exposure left the ribbons' atomic framework intact while producing a strong, measurable electrical response, the researchers suggest GNR-based sensors could eventually be engineered to operate closer to the reactor core than today's electronics can survive—potentially reducing costly shutdowns for inspection and maintenance and increasing the amount of time fusion power plants can remain in operation.
"Real-time monitoring is our vision for this project," Mutlu said.
Inside the Discovery
While this is the first study of GNRs' response to gamma radiation, they are widely studied as leading candidates for pushing chip technology beyond the limits of silicon. Their microscopic size and durability could improve the speed and energy efficiency of chips used in everything from artificial intelligence systems to smartphones.
Mutlu and eight additional study authors, all from the University of Arizona, synthesized the ribbons from the molecular level before embedding them in common semiconductor devices. They used emerging fabrication techniques Mutlu helped develop to make the ribbons exactly nine atoms wide, one atom thick, and about 45 nanometers long on average—tens of thousands of times thinner than a human hair.
The minuscule ribbons behave according to the rules of quantum physics rather than classical physics, Mutlu said. In the absence of radiation, current flows in a well-defined way through GNRs, like the ones used in the study. The researchers' measurements indicate that gamma radiation passing through the surrounding air produces reactive molecules that subtly alter the ribbon edges without changing their overall structure. At this scale, quantum effects amplify the impact of small changes on electrical signal transport through the material.
The researchers propose that the changes trigger a quantum effect called Anderson localization, which traps charge-carrying electrons in place and sharply reduces current, producing the signal of radiation exposure that could provide more precise data for reactor maintenance planning.
Long considered a promising source of large-scale, carbon-free electricity, fusion has reached key laboratory milestones—including experiments since 2022 that have produced more energy than the lasers delivered to the fuel they consumed—but still faces major engineering barriers. University of Arizona researchers are collaborating with industry on efforts to scale enabling technologies and deliver fusion power to the grid.
Similar to this fusion application, GNR sensors could provide state-of-health data for space systems—including communications satellites, Earth-observation satellites, and deep-space probes—and identify early signs of radiation-related wear before failures occur.
Pushing Materials Design at the Nanoscale
The next step for Mutlu and his collaborators is to test the same device under different radiation doses. They also plan to explore GNRs of different sizes. After those investigations, Mutlu is confident the synthesis method used in the study will allow researchers to customize new forms of ribbons.
"You can design the material atom by atom, molecule by molecule. You can make it less sensitive, more sensitive, nonsensitive," said Mutlu, whose research has focused on quantum materials and semiconductor devices for more than a decade.
That level of control is important for future space systems, where both electronic components and monitoring devices must operate for long periods under continuous radiation exposure. The same ability to tailor the material at the atomic level could support radiation-resistant semiconductor chips as well as sensors that track system performance over time.
Funding: This research was supported by funding from the Semiconductor Research Corporation and the National Science Foundation.
Published in journal: ACS Applied Materials & Interfaces
Authors: Kentaro Yumigeta, Muhammed Yusufoglu, John G. Federice, Elena T. Hughes, Ahmet Mert Degirmenci, Jon T. Njardarson, Kelly Simmons-Potter, Barrett G. Potter, and Zafer Mutlu
Source/Credit: University of Arizona | Katy Smith
Edited by: Scientific Frontline
Reference Number: ms071626_01
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