Nanomechanical analysis of the adsorption and desorption of water vapor on porous surfaces

We fabricated nanoporous microcantilevers using anodic aluminum oxide (AAO) and measured the variations in the resonance frequency and deflection of the cantilever during the adsorption and desorption of water vapor. The high surface area and low modulus of the AAO cantilever, due to the presence of the nanopores, permitted the simultaneous measurement of both the changes in mass and surface stress with high sensitivity. The cantilever deflection at the resonance frequency revealed a large deflection change during the early stages of water adsorption and a small deflection change during the later stages. These effects were attributed to the transition from a sub-monolayer water film to a multilayer water film.