Nanoscale friction of manganite superlattice films controlled by layer thickness and fluorine content

We investigate nanoscale friction in [LaMnO3]m/[SrMnO3]n superlattice films using lateral force microscopy, focusing on the effects of fluorine doping and top-layer thickness. For all samples, friction forces scale linearly with the sum of the applied normal and adhesion forces. While friction forces vary spatially due to local adhesion fluctuations, the friction coefficient remains position independent for each specimen. It is, however, systematically influenced by fluorine concentration and top-layer thickness. Our data indicates that frictional energy dissipation extends up to 5 nm beneath the surface, demonstrating a clear dependence on subsurface structure. We attribute this to viscoelastic dissipation within the stress field and evanescent waves generated by the sliding tip, which can quantitatively account for the observed friction coefficients. These results show that, once adhesion is properly accounted for, the friction coefficient is a reproducible material property that can be tuned via controlled modifications to surface and subsurface layers.