Authors: A. Arnau, Y. Jiménez, R. Torres
Event: 5th edition of Acoustic Wave Based Sensors: Fundamentals, Concepts, New Applications. Physikzentrum Bad Honnef, Germany (2005)
An Electrochemical Quartz Crystal Microbalance is used for a continuous monitoring of the growth of the polymer poly(3,4-ethylenedioxy) thiopene tetrabutyammonium perchlorate (PEDT-TBAP), which is electro-polymerized in acetonitrile of a gold electrode of a 10 MHz quartz crystal resonator. The surface acoustic impedance of the resonator is analyzed starting from the electrical admittance continuously measured by means of a network analyzer. Changes in the acoustic impedance suggest that a mechanical resonance phenomenon occurs during the electro-deposition of the coating. In order to determine the origin of this effect, the evolution of the physical properties of the coating is analyzed. The extraction of the physical properties of the coating is carried out by means of an algorithm recently developed by the authors. Four sets of coating properties are obtained with the algorithm in four different conditions. In one of them an additional technique, ellipsometry, is used to have an alternative measurement of the coating thickness, no additional techniques are necessary in the rest of the cases. All the cases show a significant change in the viscoelastic properties of the coating during the time-interval of the suspected mechanical resonance. Changes in the surface roughness of the coating during the experiment are confirmed by scanning electron microscopy (SEM). The analysis of the surface roughness of the coating and its effect on the effective values of the coating properties, seem to indicate that the changes in the viscoelastic properties are due to the changes in the surface roughness of the coating, and that these changes are responsible for the mechanical resonance effect. This analysis is carried out by means of the same algorithm which is used, in this case, as a simulation tool.