ABSTRACT
Abstract As the size of the contact decreases from the macro-scale to the nano-scale, the measured contact forces become more sensitive to the molecular adsorption from gaseous environments. This paper discusses the effects of water adsorption on the adhesion force measured with atomic force microscopy (AFM) for the single-asperity contact between silicon oxide surfaces. As relative humidity (RH) increases, the adhesion force measured with AFM initially increases, reaches a maximum, and then decreases at high RH. Traditionally, this RH dependence has been attributed to the capillary force caused by the liquid water condensation at the AFM tip-surface contact. However, the capillary force based on the liquid water property alone does not seem to be enough to explain the observed magnitude of the RH dependence. In this paper, experimental evidences are described to show correlations between the solid-like structured water layer on the silicon oxide surface observed with vibrational spectroscopy and the large RH dependence of the nano-asperity silicon oxide adhesion measured with AFM.
