CHEMICAL-SENSITIVITY OF THE THICKNESS-SHEAR-MODE QUARTZ-RESONATOR NANOBALANCE

The thickness-shear-mode quartz resonator, known as an electrochemical quartz-crystal nanobalance (EQCN), is widely used as a mass-sensitive detector in microgravimetry electrochemical experiments. Using the ac oustic-wave model, we show that in experiments where the load film is involved in some chemical reaction, the resonance-frequency shifts are due not only to thickness-related mass changes in the load film, but also to changes in the film density or acoustic properties. Such effec ts may take place during electrochemical experiments such as corrosion , ion intercalation, oxidation-reduction, phosphatation, or any other chemical modification of the film. In such eases, the resonance-freque ncy shifts are due to the change both of mass and of resonator-film ac oustic coupling. The Sauerbrey relation does not take into account the effect of acoustic coupling; the use of this relation in electrochemi cal gravimetry may lead to erroneous conclusions. The change in resona nce frequency due to changes in density or acoustic properties may, un der some circumstances, provide information concerning the chemical na ture of the load film.