The Challenge to Find True Topography

Anyone who has slipped on a polished floor or felt their tires spinning in the snow knows instinctively the importance of surfaces. Certainly those in manufacturing—be it of robots, running shoes, or semiconductors—understand that they are vital. Yet for all the importance of surfaces, attempts to accurately measure and describe their topography vary wildly.

The University of Freiburg’s Lars Pastewka and the University of Pittsburgh’s Tevis Jacobs have teamed up with Saarland University’s Martin Müser and Jacobs’ graduate student Arushi Pradhan to conduct a worldwide challenge to increase awareness of how surface topography is measured and described. The results of their research are published in the article “The Surface-Topography Challenge: A multi-laboratory benchmark study to advance the characterization of topography” (DOI: 10.1007/s11249-025-02014-y).

Jacobs, William Kepler Whiteford Professor in mechanical engineering and materials science, studies surface performance, particularly adhesion, friction, and wear with applications from slip-and-fall accidents, to the function of medical devices, to the manufacturing of computer chips. These applications depend on the roughness of surfaces, or their topography, and variations in topography profoundly impact how objects interact with the world.

“Roughness matters down to the nanometer scale,” Jacobs said. In robotics, for example, the ability of a gripper to retrieve fragile items in a warehouse depends on topography across many different size scales. However, as he noted, “any individual measurement can’t fully describe a surface.”

“The industry-standard methods for measuring and characterizing roughness work well in certain cases, but they are limited in the information they contain and the predictive power they can provide,” added Pastewka, a professor in the Department of Microsystems Engineering and a long-time collaborator with Jacobs.

When scientific researchers measure surfaces, they often don’t use the industry-standard metrics, in favor of more precise measurements and more complex surface descriptors. But the problem is that there are a wide array of tools, techniques, and mathematical models that can be applied by different researchers.

“You might think of it like the parable of the blind men and the elephant,” said Jacobs. “To try to understand the large animal, each blind man puts a hand on a different part of its body and reaches a completely different conclusion about it. 

“Each scientific researcher measures an aspect of the surface, but different techniques and different size scales create remarkably different pictures of a single object.”

Challenging the scientific community to get a more complete picture

In 2015, Martin Müser, a professor of materials solutions, launched his Contact-Mechanics Challenge by creating a computer-based topographical surface, which he sent out to researchers. These scholars applied whatever theories, calculations, and models they wanted to compute its properties and solve an adhesion-related problem. Their methods were compared and assessed for their efficacy.

Müser’s challenge represented a high point in modeling roughness, and Jacobs and Pastewka were impressed. They wondered: what if we did that with a real-world surface?

At a 2022 Gordon Research Conference, Jacobs, Pastewka, Müser, and University of Pittsburgh postdoctoral scholar Nathaniel Miller announced the Surface-Topography Challenge. Using the same technology used to create microchips, the team created two different surfaces, one smooth, the other rougher, both coated in chromium nitride. Samples were mass produced for uniformity.

The team then sent samples of both surfaces to anyone who requested to participate. Participants were asked to measure the surfaces using whichever tools and techniques they preferred, and then to upload their raw data to a central repository.

Although the team worried that only a few researchers would participate, they were surprised and grateful that more than 150 people participated, from universities, national labs, and companies. Altogether, there were participants from 64 groups across 20 countries; participants submitted a total of 2,088 individual measurements.

Said Müser, “Seeing such a large number of participants in the Surface-Topography Challenge reflects the widespread interest in advancing our understanding of topography and how we can best measure it.”

“The simulation community has made tremendous advances in predicting the performance of rough surfaces, but these advances have had limited applicability because of a lack of comprehensive measurement of topography for real-world surfaces,” said Pastewka. “Now to get so many measurements of these two surfaces, we are gaining practical insights about how best to apply the theory in real-world manufacturing. The community participation has been inspiring.”

Finding a truer topography

Essential to the project, as Jacobs said, was his graduate student Arushi Pradhan. “She processed all the data in ways that illuminated the insights that came from this project. When the four of us met, she contributed vital analysis of the results. We couldn’t have completed this research without her.”

The data reflected the dramatic difference in results across the techniques scientists employed. Indeed, by one measure of roughness (the root mean square [RMS] height) the different measurements across different groups varied by a factor of 1,000,000!

As Pradhan said, “The data revealed just how difficult it is to reach consensus about a surface topography. We had to correct for inconsistencies, artifacts, and resolution limits as well as determine which techniques to include or exclude in describing the surfaces. But with all these measurements, we could reach a truer topography.”   

While Jacobs understands that it is impractical for manufacturers to employ the many techniques used during the challenge, he does hope they will consider a central conclusion: measuring the same surface with different scales and techniques, even just two or three, produces more accurate results.

“This surface-topography challenge wasn’t just for a few researchers; it’s for anyone who cares about surface performance,” said Jacobs. “Our ultimate goal is to find the right topography metrics—which can be used across research, product development, and quality assurance—to measure, control, and improve surface performance.”

Although the challenge has closed, the team continues to send samples to interested researchers https://contact.engineering/challenge with researchers interested in surface topography, including the shipping of samples https://contact.engineering/challenge. These samples can act like a benchmark for anyone who measures surfaces in their work.

“We don’t see this as the end,” said Jacobs. “Surface topography is critical to performance, but it’s not solved yet. This challenge is just the beginning.”

ACKNOWLEDGMENTS

The creation and organization of the Challenge was supported by the National Science Foundation (CAREER-1844739 and CMMI-2400999), the Deutsche Forschungsgemeinschaft (DFG grant EXC-2193/1-390951807) and the European Research Council (StG 747343). 

Contact:

Prof. Dr.-Ing. Lars Pastwka
University of Freiburg
Department of Microsystems Engineering (IMTEK)
Simulation
E-Mail: lars.pastewka@imtek.uni-freiburg.de

Kerstin Steiger-Merx
Referentin PR/Marketing
Technische Fakultät
Albert-Ludwigs-Universität Freiburg
Tel.: 0761/203-8056
E-Mail: steiger-merx@tf.uni-freiburg.de

28.07.2025