Capillary grip-induced stick-slip motion

We present capillary grip-induced stick-slip motion, a nanoscale tribological effect, where the role of a nanoscale confined water meniscus formed between a buckled sharp tip and a glass or mica surface is addressed by shear dynamic force measurement. We obtained the effective elasticity, viscosity, conservative (elastic) and non-conservative (viscous) forces, energy dissipation, and lateral force using small oscillation, amplitude-modulation, and shear-mode quartz tuning fork-atomic force microscopy (QTF-AFM). We distinguished the conservative and non-conservative forces by investigating the dependence of normal load and relative humidity, slip length, and stick-slip frequency. We found that the confined nanoscale water enhances the lateral forces via capillary grip-induced stick-slip on a rough surface, resulting in an increase of static lateral force (3-fold for both substrates) and kinetic lateral force (6-fold for glass, 3-fold for mica). This work provides quantitative and systematic understanding of nanoscale tribology properties in humid ambient conditions and is thus useful for control of friction as well as characterization of tribology in nanomaterials and nanodevices.