Signal oscillations of a piezoelectric quartz crystal in liquids caused by compressional waves

Impedance analysis of an electrode-separated piezoelectric sensor as a surface-monitoring technique for gelatin adsorption on quartz surface

The early events pertaining to gelatin adsorption and desorption onto quartz surfaces were studied, employing an electrode-separated piezoelectric sensor (ESPS). The adsorption of gelatin on a quartz crystal surface corresponds to a mass increase, which can be monitored in real time by the changes in the impedance parameters of the ESPS. It was shown that the adsorption of gelatin on a quartz surface is partly irreversible with respect to the dilution of the bulk phase. The observed adsorption kinetics is compatible with a mechanism that involves adsorption, desorption, and transformation from a reversible adsorption state to irreversible one. A progressive approach method was established to simulate the adsorption process. The adsorption densities and kinetic parameters in the early adsorption process were obtained from the responses of the ESPS in the adsorption process. The influence of pH and ionic strength was tested. A comparison with the Langmuir adsorption model was made.

Roughness-induced acoustic second-harmonic generation during electrochemical metal deposition on the quartz-crystal microbalance

This paper reports on the relation between the surface roughness and emission of compressional waves from the surface of an electrochemical quartz-crystal microbalance. The detection of the compressional waves took place with an ultrasonic microphone and the quartz crystal itself. As a model process, the electrochemical deposition of copper from an acidic copper sulfate solution has been chosen. For this system, the roughness of the layer can be tuned via the current density. Roughness may be a source of the longitudinal waves at twice the frequency of the exciting shear wave (acoustic second-harmonic generation, ASHG) if the flow profile above the quartz-crystal surface is not entirely laminar. Slight deviations from the laminar flow can be reached at high amplitudes of oscillation. Comparing the ASHG efficiency of a rough and smooth surface, we find that the rough surface is more efficient in generating second-harmonic waves. This suggests that ASHG can be used to obtain a roughness parameter independent from the resonance frequency or bandwidth (damping) of a quartz-crystal resonator. Such an independent determination of roughness should be very interesting in practical applications.