| Abstract: | An electrochemical quartz crystal microbalance (EQCM) is described, which measures the shifts of frequency and bandwidth on multiple harmonics with a time‐resolution of 10 milliseconds. The technique requires the process under study to be repetitive. Examples are square wave amperometry and cyclovoltammetry. Data acquisition is fast because the raw data consist of traces of the electrical admittance at fixed frequencies . A few (∼10) such time traces are acquired sequentially at a set of frequencies evenly spaced around the crystal's resonance. Since all time‐traces are triggered by the same repetitive process, plots of the conductance G (ωi , t ) and the susceptance B (ωi , t ) from constant time delays, t , versus frequency can be produced a posteriori. The shifts, ΔG (ωi ) and ΔB (ωi ) quantify a difference between two resonance curves, pertaining to the sample's reference state and the state at time t . Fitting a difference of two resonance curves to these data, one obtains shifts of frequency, Δf (t ) and shifts of bandwidth, ΔΓ(t ), versus time. This procedure is repeated for the different overtones. Given the repetitive nature of the process, one may accumulate and average, which lowers the noise down to a few tens of mHz. The capabilities of this instrument are demonstrated with two examples, which are copper deposition/dissolution and electro‐responsivity of a polymer film containing weakly acidic side groups. |
