Qualitative adsorption measurements with an atomic force microscope

A simple method for the qualitative measurement of adsorption of solution species onto silicon nitride atomic force microscope cantilevers is presented. In this method, the change in resonant frequency of the cantilever, resulting from the added mass of the adsorbate, is measured as a function of time during the adsorption process. Results from the adsorption of copper (II) species and CTAB from aqueous solutions are presented. Cu(II) was seen to attain maximum coverage in a matter of minutes, while the adsorption of CTAB was beyond the resolution of the technique. Force measurements taken between the cantilever tip and a glass substrate during the adsorption process provide evidence that the change in cantilever frequency is a result of the adsorbate mass and is not just the result of any small viscosity differences.