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A Fast Electrochemical Quartz Crystal Microbalance,which Acquires Frequency and Bandwidth on Multiple Overtones
Author(s) -
Petri Judith,
Hochstädt Sebastian,
Nentwig Tristan,
Pausch Ansgar,
Langhoff Arne,
Johannsmann Diethelm
Publication year - 2017
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/elan.201600580
Subject(s) - quartz crystal microbalance , susceptance , analytical chemistry (journal) , bandwidth (computing) , chemistry , crystal (programming language) , time constant , materials science , voltage , physics , electrical engineering , adsorption , telecommunications , computer science , organic chemistry , quantum mechanics , chromatography , programming language , engineering
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 (ω i , t ) and the susceptance B (ω i , t ) from constant time delays, t , versus frequency can be produced a posteriori. The shifts, Δ G (ω i ) and Δ B (ω i ) 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, Δ f ( 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.