Microstructure Dependent Mitigation of AFM Plowing Wear in WSe2 by Water Immersion

We have investigated the influence of microstructure and environment on the scratch response of WSe2. Using diamond-coated AFM probes with normal force values ranging from 2 to 10 µN, we scratched low- polycrystalline, high-polycrystalline, and mineral WSe2 in both air and water. In all cases, scratch depth and width increased with applied load. In air, polycrystalline WSe2 sustained substantially greater damage than mineral WSe2. When submerged in water, however, the extent and nature of scratching damage changed markedly. Both polycrystalline samples exhibited significantly lower wear, with low-polycrystalline WSe2 showing the most pronounced decrease. These reductions were accompanied by smaller fluctuations of the friction force recorded while scratching, indicating reduced plowing and more stable sliding under equivalent loads. We attribute this microstructure-dependent behavior to localized hydration at grain boundaries and near-surface disordered regions. This hydration forms a lubricant-like interfacial layer that lowers shear resistance and inhibits plowing-induced material removal. In contrast, mineral WSe2 offers fewer sites for interfacial modification via hydration; its scratch response therefore shows minimal environmental dependence and remains largely unaffected by water. Our findings demonstrate that water is a selective, structure-dependent mitigator of nanoscale scratch damage in WSe2 .