Sensitivity measurement of a cantilever-based surface stress sensor

A detailed analysis of the temporal surface stress evolution for potential-driven adsorption of ions is discussed. A gold-coated cantilever is used to simultaneously measure the change in surface stress as well as the current response during an applied potential step. In this electrochemical configuration, the cantilever acts as the working electrode, a platinum wire as the counter electrode, and the Ag/AgCl (sat. KCl) electrode as the reference electrode. To study the time-dependent signal and the sensitivity of the cantilever response, the frequency of the potential step applied to the cantilever is varied from 1 s to 0.1 ms. First, a comparison between a strong adsorbing (chloride Cl⁻) and a weak adsorbing ion (perchlorate ClO$4 −$⁠) in a 1 mM solution is presented. Next, the linear relationship between surface stress and charge density is measured for these fast potential steps. The slope of this fit is defined as the sensitivity of the system and is shown to increase for shorter potential pulses. Finally, the behaviour of the surface stress and current for consecutive applied potential steps is studied.