A comparative nanotribological investigation on amorphous and polycrystalline forms of MoS2

TL;DR

This study compares the wear resistance and frictional behavior of amorphous and polycrystalline MoS2 thin films, revealing that amorphous MoS2 exhibits significantly higher wear resistance and reduced friction, providing new insights into nanotribology of these materials.

Contribution

It provides a comparative nanotribological analysis of amorphous and polycrystalline MoS2, highlighting the superior wear resistance of the amorphous form at the nanoscale.

Findings

Amorphous MoS2 has about four times higher wear resistance than polycrystalline MoS2.

Both forms follow the Archard wear equation under certain conditions.

Friction is reduced after scratching due to surface smoothing.

Abstract

The wear behavior of two amorphous and polycrystalline forms of MoS2 prepared by magnetron sputtering has been characterized in a combined nanoindentation and atomic force microscopy study. From the analysis of the depth and width of wear tracks estimated after scratching the surfaces with a Berkovich indenter and a loading force up to 2 mN, we conclude that both forms follow the Archard wear equation, and the wear resistance is about four times higher on the amorphous MoS2. Moreover, a comparison of lateral force maps on pristine and worn areas shows a considerable reduction of friction on both forms, which is possibly due to the significant smoothing of the surfaces caused by scratching. With normal forces in the micro N range, the analysis is made difficult by the fact that the linear dimensions of the wear tracks are comparable to those of the granular structures forming the surfaces. Even if the Archard equation could not be tested in this case, the wear resistance is considerably larger on amorphous MoS2 also on the nanoscale. In this way, our results disclose information on the nanotribology of MoS2 thin films in forms different from the layered structures commonly discussed in the literature. The amorphous form outperforms the polycrystalline one.