Samuel Jarman, SciencePOD

Laser-based surface micromachining is a powerful technique, capable of producing materials with periodic, nanoscale surface structures. Researchers are now hopeful that this technology could lead to new developments in fields ranging from medicine to manufacturing, but so far, its progress has been held back by the debris that inevitably accumulates on laser-induced nanostructures, and which has proven extremely difficult to remove.

In new research published in Applied Surface Science, researchers led by Alexander Breul, formerly the CTO of Intelligent Fluids GmbH, Leipzig, Germany, show how this debris can be removed using a gentle ‘wet chemical processing’ technique, which causes minimal damage to intricate laser-induced surface structures.

“The ability to remove unwanted debris from these precise nanostructures can greatly enhance the functionality and reliability of surfaces used in advanced technologies, such as optics, sensors, and bioengineering,” Breul says. “This improves practical applications and offers new insights into surface cleaning methods, contributing to more refined industrial processes.”

Laser-induced periodic surface structures (LIPSS) can be generated on a wide array of surfaces by powerful, ultra-short laser pulses, which interfere with the light being scattered by the surface. This generates periodic interference patterns which modulate the amount of laser energy absorbed by the surface – creating periodic patterns of extreme but highly localised heating. This heated material then ablates, leaving behind a periodic nanostructure on the surface.

In the process, however, some of the ablated material can react with molecules in the surrounding atmosphere, creating microscopic particles of debris that accumulate in the newly generated nanostructure. Unless these particles are removed, they can severely diminish the material’s performance in practical applications – especially when high levels of precision are required.

“As industries increasingly adopt these nanoscale technologies, optimising surface cleanliness without compromising structural integrity is crucial,” Breul says. “The ability to control debris is now more important than ever due to expanding applications for these materials in sustainability and advanced manufacturing.”

To address the challenge, Breul’s team explored how LIPSS could be cleaned using a ‘wet chemical’ process, where the surface is immersed in a chemical solution that detaches any unwanted debris from the surface. Since a wide array of liquids can be used in wet-chemical processing, they would need to carry out exhaustive tests to determine which of them would be best suited to cleaning LIPSS.

After fabricating LIPSS on copper, the researchers first used a combination of electron microscopy and atomic force microscopy to carefully map out the topography of the surfaces, as well as the sizes and distributions of any accumulated debris particles. They also used a combination of spectroscopy techniques to determine the chemical compositions of the surfaces and debris.

Afterwards, the team treated the surfaces with a variety of different liquids: including organic solvents and micro-emulsions. Finally, they repeated their analysis of the LIPSS topographies and compositions, allowing them to determine how effectively the debris had been removed from the copper.

“We tested various cleaning liquids to remove these contaminants without damaging the delicate structures,” Breul explains. “We found at least two solutions that successfully cleared particles, allowing for cleaner surfaces and improved performance without significant alteration of the original pattern.”

Based on these promising results, the team are now hopeful that the wet chemical processing techniques they have identified could pave the way for the more widespread use of LIPSS across a diverse array of applications.

“By finding effective ways to clean these surfaces without damaging them, the research could lead to more efficient solar panels, better medical implants, and improved manufacturing techniques,” Breul says. “It highlights how small improvements in materials science can have a big impact on everyday technologies.”