AFM-based tribological study of nanopatterned surfaces: the influence of contact area instabilities

Abstract

Although the importance of morphology on the tribological properties of surfaces has long been proved, an exhaustive understanding of nanopatterning effects is still lacking due to the difficulty in both fabricating 'really nano-' structures and detecting their tribological properties. In the present work we show how the probe-surface contact area can be a critical parameter due to its remarkable local variability, making a correct interpretation of the data very difficult in the case of extremely small nanofeatures. Regular arrays of parallel 1D straight nanoprotrusions were fabricated by means of a low-dose focused ion beam, taking advantage of the amorphization-related swelling effect. The tribological properties of the patterns were detected in the presence of air and in vacuum (dry ambient) by atomic force microscopy. We have introduced a novel procedure and data analysis to reduce the uncertainties related to contact instabilities. The real time estimation of the radius of curvature of the contacting asperity enables us to study the dependence of the tribological properties of the patterns from their geometrical characteristics. The effect of the patterns on both adhesion and the coefficient of friction strongly depends on the contact area, which is linked to the local radius of curvature of the probe. However, a detectable hydrophobic character induced on the hydrophilic native SiO2 has been observed as well. The results suggest a scenario for capillary formation on the patterns.

Laterally-resolved mechanical and tribological properties of laser-structured polymer nanocomposites

“…In this work, authors observed that relative humidity played a key role on the measurements, as also reported by Feiler et al [51]. In our experiments, we cannot rule out the possible formation of a thin water layer between the nanostructures patterns, which might interact during LFM scanning, as recently proposed as a hypothesis by Rota and collaborators for LFM measurements in nanostructured inorganic surfaces [52]. However, in this latter work, LFM was carried out using probes with a curvature radius higher than the mean size of the nanostructures, not allowing a local characterization of the material and making hard to conclude about the role of water within the nanostructured channels.…”

Friction-Induced Nanofabrication: A Review

“…In addition, when the normal load increased, more silicon matrix was amorphized and thereby higher friction-induced hillocks were produced. The localized amorphous structure was expected to present lower density than crystal silicon, and hence piled up to form a hillock [58]. Similarly, the amorphization-dominated interaction may be the main contributor for the formation of friction-induced hillocks on other materials, such as glass and quartz [25,47,48].…”

Theoretical and computational studies on nanofriction: A review

“…Besides the AFM, there are other experimental techniques to determine the force of friction at nanoscale, such as WENDELSTEIN 7-X, a test rig that allows the determination of sliding friction, 120 FFM, which is a modified form of AFM used specifically for friction measurements by lateral displacement, [121][122][123][124][125] etc.…”