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

TL;DR

This study explores how nanoscale friction in manganite superlattice films is affected by layer thickness and fluorine doping, revealing that friction can be tuned by modifying subsurface structures and surface chemistry.

Contribution

It demonstrates that the friction coefficient in manganite superlattices is a reproducible material property influenced by subsurface and surface modifications, with a detailed analysis of energy dissipation mechanisms.

Findings

Friction forces scale linearly with normal and adhesion forces.

Friction coefficient depends systematically on fluorine content and layer thickness.

Frictional energy dissipation extends up to 5 nm beneath the surface.

Abstract

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.