Material-related contact time dependence of adhesion force revealed by an AFM cantilever in a humid environment

Abstract

Contact time dependence of adhesion force in the literature is conflicting and needed to be clarified. The adhesion forces between silicon cantilevers and samples with different materials and hydrophilicity were measured to investigate the dependence on an atomic force microscope (AFM) in a humid environment. Results show that the dependence is related to surface materials. On the samples of silicon, glass, and sapphire, the adhesion force increases with dwell time logarithmically, and then reaches saturation. This was attributed to the large viscosity of thin liquid film on the surfaces, which hampers the growth of a liquid bridge, resulting in the long saturation time. For other samples (mica, silica, Au film, highly oriented pyrolytic graphite (HOPG), polymethyl methacrylate (PMMA), diamond-like carbon (DLC) film, and graphene-coated silica), the force does not depend on the dwell time. This was attributed to a very short saturated time due to the low viscosity of a film. However, some abnormal behaviors due to repeated contacts were observed on these samples during the measurements, and the possible reasons behind them were also related to the evolution of a liquid bridge in the contact zone. The results may facilitate the anti-adhesion design for small-scale structures and devices.