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Two microscopic grains collide and produce a tiny spark. This phenomenon may have provided the energy to kick off life on Earth. But if these solid particles have the same composition, what factor causes the charge to flow in a given direction? In a new study published in Nature, physicists from the Institute of Science and Technology Austria (ISTA) identify the key factor as environmental carbon-based molecules that adhere to the materials’ surface.
What do Saharan dust storms, volcanic lightning, and accretion disks of matter orbiting around a star have in common? A tiny spark that transfers charge is at the core of these phenomena.
As far back as the 1950s, scientists suggested that energy from volcanic lightning may have helped convert primordial molecules into the first amino acids—the building blocks of proteins. In a recent study, scientists suggested that NASA’s Perseverance rover may have detected evidence of lightning amid dust storms on Mars.
Such interactions are commonplace in nature. And yet, scientists have not been able to pinpoint what causes the charge exchange to flow in a given direction between insulating solids. Now, researchers from the group of Scott Waitukaitis, assistant professor at the Institute of Science and Technology Austria (ISTA), have found the missing puzzle piece: environmental carbon-based molecules on material surfaces.
A single grain of quartz glass
To tackle the problem, former ISTA postdoc Galien Grosjean, the study’s first author, chose silica, one of the most common solid materials in the Universe. However, his measurements turned out more complicated than expected: charge would exchange at the slightest contact with any surface, including standard laboratory tools such as tweezers. How could he study contact and charge transfer without even touching the materials?
The solution was to develop an experimental system based on acoustic levitation to control a single grain without physical contact. By bouncing the grain on a plate made of the same material, Grosjean could precisely measure the charge transfer before and after this controlled contact. Doing this repeatedly with each sample, he found that some samples consistently charged positively, whereas others charged negatively.
But what caused the charge to flow in a given direction between two identical materials? And can the trend be reversed?
‘Leading theories took us off track’
The ISTA scientists explored various approaches to explain their findings and reverse the samples’ natural trend. Prior models suggested that the materials’ surfaces would be covered with a mosaic of random surface properties.
“Essentially, scientists imagined a ‘dairy cow pattern’ model,” says Grosjean.
“Initially, I thought that we would validate this model and move forward. We expected random fluctuations averaging out to zero as the grains rotated and made contacts on different tiny patches,” adds Waitukaitis.
However, the samples showed a clear, consistent pattern of charging. In parallel, the team explored the potential role of humidity and water molecules that adhere (adsorb) to the materials’ surface based on other leading models.
“We focused myopically on water for a long time, which led us down so many wrong turns,” says Waitukaitis. “We took those leading theories in the field for granted, and they took us off track. We needed time to build up the confidence to recognize that the reality was different.”
The culprit: a widespread environmental factor
The team continued to test new conditions until Grosjean decided to subject some samples to heat treatment. These ‘baked’ samples immediately showed a clear effect, consistently charging negatively post-contact.
“Since quartz glass is highly resistant to thermal changes, heat does not affect the material itself. As a result, we thought that any alteration must be due to molecules adsorbed to the material’s surface,” he says.
A parallel experiment, stripping the samples’ surface using plasma, showed the same effect.
“At this point, we started contacting other groups that study material surfaces and can precisely measure surface compositions to compare the samples before and after baking," says Grosjean. "That’s when we found that subjecting the materials to such treatment stripped them of their natural coating of environmental carbon species."
In fact, plasma treatment to remove carbon is a standard procedure in surface science.
“Here, we knew that carbon mattered, but it was not quite the smoking gun yet,” he says.
Next, the researchers examined how the charge effect evolved after baking or plasma treatment, observing that it diminished over the course of a day.
“In parallel, our collaborators showed that the carbon species also returned to the materials’ surface over the same period, making the correlation much stronger,” Grosjean notes.
In comparison, water molecules returned much faster to the materials’ surfaces. These experiments confirmed that environmental carbon was the culprit.
Overcoming natural tendencies
The ISTA scientists then sought to examine whether the effect of environmental carbon on charge applied to insulating oxides other than silica, including alumina, spinel, and zirconia. After standard cleaning, done without stripping their surfaces of adsorbed carbon species, these materials naturally fall into a series known as a triboelectric series, ranging from the most positively charged to the most negatively charged following contact. While this suggests that the materials have intrinsic tendencies, the team suspected that the carbon coating also contributed.
By examining each pair of materials and stripping the surface of the one that naturally charges more positively while keeping the other one intact, they could invert the entire series. Therefore, introducing this clear imbalance in the carbon coating helped the researchers demonstrate that the carbon effect can outweigh the materials’ inherent tendencies.
The origin of life, and beyond?
Waitukaitis underlines the challenges the team faced.
"These experiments are really hard," he says. "The carbon coating is never at equilibrium; a single monolayer of carbon already makes a difference, and the materials are sensitive to the slightest touch. That's why the phenomenon remained unexplained for so long.”
Using an experimental setup based on acoustic levitation, the ISTA team not only solved the problem of unwanted contact but also accessed extremely precise measurements at a resolution of 500 electrons.
In another recent study, the Waitukaitis group found that the contact history between materials made of soft, silicon-based polymers determined the direction of charge exchange. While both projects initially sought to validate the older models, the polymers and insulating oxides ended up showing distinct results.
“It is tempting to think that any finding must apply to all materials,” says Grosjean. “But we stopped making this mistake.”
Beyond microscopic grains, static electricity between insulating oxides is so widespread in nature that it could be at the origin of life, and perhaps even planetary formation.
“Most of these materials in nature are little particles smaller than one millimeter. They charge by colliding, rubbing, and rolling all over each other. That’s why desert sand, volcanic ash clouds, and dust particles get charged,” says Waitukaitis.
With these findings, scientists can now address bigger questions, such as whether this phenomenon occurs in protoplanetary disks—the birthplaces for planetary systems.
“Some current models of planetary formation rely on a predominant effect of charge,” Waitukaitis concludes. “As such, our research might have just shed light on the mechanism underlying the sparks of creation.”
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Funding information
This project has received support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 949120) and from the Marie Skłodowska-Curie programme (grant agreement no. 754411). The authors acknowledge the state of Lower Austria and the European Regional Development Fund under grant no. WST3-F-542638/004-2021, Fondecyt grant 1221597, and a Serra Húnter fellowship. This research was supported by the Scientific Service Units of the Institute of Science and Technology Austria through resources provided by the Miba Machine Shop, Nanofabrication Facility, Scientific Computing facility, and Lab Support Facility.
Galien Grosjean, Markus Ostermann, Markus Sauer, Michael Hahn, Christian M. Pichler, Florian Fahrnberger, Felix Pertl, Daniel M. Balazs, Mason M. Link, Seong H. Kim, Devin L. Schrader, Adriana Blanco, Francisco Gracia, Nicolás Mujica & Scott R. Waitukaitis. 2026. Adventitious carbon breaks symmetry in oxide contact electrification. Nature. DOI: 10.1038/s41586-025-10088-w / https://doi.org/10.1038/s41586-025-10088-w
https://ist.ac.at/en/research/waitukaitis-group/ Research group "Soft Electrified Materials" at ISTA
Levitating matter with sound. Experimental setup with an acoustically levitated particle of silica.
Source: © Thomas Zauner/ISTA
Copyright: © Thomas Zauner/ISTA
The trace of a bouncing particle. Temporal reslice of a high-speed video of a silica particle bounci ...
Source: © Galien Grosjean
Copyright: © Galien Grosjean
The trace of a bouncing particle. Temporal reslice of a high-speed video of a silica particle bouncing on the plate in the acoustic levitation experimental setup.
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