Diamond shown to wear down atom by atom

Despite being the hardest material on Earth, even diamond wears down eventually. Together with scientists from University of Bologna, Cyrian Leriche and colleagues at ARCNL have characterized this wear at the nano scale by looking at the footprints diamond leaves on a silicon nitride surface as it slides. Published in the journal ACS Applied Materials & Interfaces, their results suggest that synthetic diamond wears down atom by atom, and that the wear rate is highly influenced by environmental conditions.

Diamonds are a drill’s best friend 

Because of its supreme hardness, synthetic diamond is increasingly used in manufacturing applications to protect tools from wear. Think of, for example, electric saw blades or drill bits, which experience constant friction with whatever they cut or drill into.  

However, diamonds aren’t indestructible, either. Like any material, they wear down from friction, too. Understanding the way that diamond wears down at the nano scale (on the scale of tens of atoms) is useful for predicting the lifetime of diamond-coated parts.  

Chip-ped coatings 

Nanoscale wear can affect nanoscale precision positioning. As the latter is a requirement in computer chip production, understanding and controlling nanoscale wear are paramount to the semiconductor industry. 

Inspired by this challenge, Cyrian Leriche and colleagues in the Contact Dynamics group at ARCNL studied the wear of synthetic diamond coatings when they slide against silicon nitride surfaces. The group collaborated with researchers at University of Bologna in Italy to fit their experimental results to computer simulations of molecular interactions. “It was exciting to work on this,” shared University of Bologna PhD student Enrico Pedretti. “Our collaboration to find a correlation between the simulations and experimental measurements gave us a really nice result.” 

Footprints from diamond shoes 

For the experiments, they set up diamond-coated spheres and moved them in a series of parallel lines across a silicon nitride surface, similar to those used to make computer chips. The setup maintains a constant, extreme pressure between the diamond and silicon. “A billion kilograms on a square meter: that’s 100 times more pressure than at the deepest trenches in the ocean,” explains group leader Bart Weber.

They then looked at the scratches left behind to determine the volume of the diamond sample as it wears, sort of like measuring someone’s footprints to figure out their shoe size. Based on this, they calculated a wear rate of about one Angstrom (atom width) for every 20 micrometers (1/4 the width of a human hair) across the silicon nitride. Their results suggest that when experiencing friction, the diamond coating wears down one atom at a time. “I find it fascinating that, despite the gigantic pressures to which we experimentally expose the diamond, it only wears at a scale that is so small that it is hardly measurable,” says Bart. 

Environmental influences 

The researchers also studied the effects of the environment on the wear rate of the diamond coating. Their computer simulations suggested that in an open atmosphere, the water in the air sticks to surfaces, which makes the diamond and silicon surfaces have a harder time bonding together. This reduces the friction and thus the wear rate. By contrast, when the setup is isolated in a dry nitrogen-only environment, the wear rate is higher. This is a bit as if high humidity in the air made your shoes slip more easily on the ground.  

This was confirmed by their experiments: the wear rate of the diamond was twice as high in the nitrogen environment than in air. This strong influence of the external environment on the wear of diamond coatings is very useful in designing computer chip machines – it shows that careful control of the machine environment is an important factor in the lifetime of the machine components. 

Outlook 

The group’s results provide useful information about how diamond wears down at the nano scale, which can be applied to the design of diamond coatings to extend their lifetime. Now, the researchers are working on follow-up studies to explore how the wear rates change in different environments. Enrico is doing his PhD in M. Clelia Righi’s group at University of Bologna, but he is visiting ARCNL for the next six months to conduct these experiments with the team.

They are also doing experiments using different materials. “Some materials, like diamond, are so wear-resistant that you can’t see debris coming off,” explains PhD student Ozan Sahin. “You have to look at the chemical processes happening between the surfaces. Then you can see the wear atom by atom.”  

Nanoscale wear behavior in different materials is useful information for precision manufacturing in the semiconductor industry, as well as development of nanotechnology applications such as solar cells and targeted drug delivery technology. “These results are interesting for any high-precision applications,” shares Ozan. “If you need a sharp cut, or a thin coating, or anywhere you need really tiny diamond, this behavior is relevant.” 

Learn more 

To read the scientific publication, visit ACS Applied Materials & Interfaces. 

If you have questions about this study, please contact Bart Weber (email: B.Weber@arcnl.nl) or Enrico Pedretti (email: E.Pedretti@arcnl.nl).  

Reference

C. Leriche, E. Pedretti, O. Sahin, D. Kang, M. C. Righi, and B. Weber (2025). Passivation Species Suppress Atom-by-Atom Wear of Microcrystalline Diamond. ACS Applied Materials & Interfaces, Article ASAP. DOI: 10.1021/acsami.5c08647