Regensburg 2019 – wissenschaftliches Programm
CPP 25.57: Poster
Dienstag, 2. April 2019, 14:00–16:00, Poster B1
A fast quartz crystal microbalance (QCM) with millisecond time resolution operating on multiple overtones at the same time — •Arne Langhoff, Frederick Meyer, Astrid Peschel, Judith Petri, and Diethelm Johannsmann — Institut für Physikalische Chemie, TU Clausthal, Germany
Second-generation QCMs (which include the QCM-D) rely on readings of the resonance frequency as well as bandwidth on multiple overtones. The added information gives access to the sample’s softness and other properties. Currently, most QCMs need about a second per frequency reading and they access different overtones sequentially. Using a multi-frequency lockin amplifier (MLA, supplied by Intermodulation Products AB, Stockholm), this limitation can be overcome. The MLA excites the resonator at 40 frequencies simultaneously. The channels are distributed over four "combs" (10 frequencies each), where each comb covers one overtone. The time resolution can be close to the inverse resonance bandwidth, which - for high-fundamental-frequency (HFF) resonators - is well below one millisecond. The technique is particularly powerful when applied to repetitive processes because accumulation can then lower the noise in frequency shift of 5-MHz resonators well into the mHz range. Applications chosen for demonstration are the impact of droplets onto the QCM surface (the kinetics of which is in ms range) and electrochemical measurements (in which case accumulation and averaging can be exploited). In the latter case, the fast dynamics after voltage reversal is monitored. The response is governed by changes of viscosity in the double layer.