Friction is difficult to predict and control, especially since nanoscale surfaces are never completely flat. Controlling friction is important for predicting earthquakes and miniaturising semiconductor devices, among other things. A group of researchers at the University of Amsterdam has now shown that the friction between two silicon surfaces depends mainly on the chemical bonds that the two surfaces form with each other. This information can be used to control the amount of friction.

The Amsterdam researchers show experimentally that the friction between a silicon sphere and a silicon surface depends mainly on the siloxane bonds (Si-O-Si) that form between the two surfaces. They thus establish a direct link between what happens at the nanoscale and how the material behaves at the macroscopic level. The link was revealed when they allowed the surfaces to dry in nitrogen. Surface contaminants settled on the surfaces and blocked the Si-OH groups, allowing fewer siloxane bonds to form. As a result, friction decreased.

First author Liang Peng, who is in the final stages of his PhD, looked at dynamic friction for this research, but now wants to see how the bonds between silicon surfaces affect the transition from static to dynamic friction. He foresees applications in lithography. ‘Friction is quite important for an alignment system. It can really affect the accuracy, so I hope engineers can use this to improve the performance of such systems.’

Liang Peng et al. (2023) Physical Review Letters, DOI: 10.1103/PhysRevLett.131.226201