Microbalance, Electrochemical Quartz Crystal
Published Online: 15 SEP 2006
Copyright © 2000 John Wiley & Sons, Ltd. All rights reserved.
Encyclopedia of Analytical Chemistry
How to Cite
Ward, M. D. 2006. Microbalance, Electrochemical Quartz Crystal. Encyclopedia of Analytical Chemistry. .
- Published Online: 15 SEP 2006
The need for direct measurement of interfacial events at solid surfaces under ambient conditions has provoked surface scientists and electrochemists to develop direct in situ methods. Such processes include electroless or electrochemical metal deposition, insertion of ions into polymer ion-exchange films, growth of oxide films on metals, or the loss of material from corrosion processes. An increasing interest in molecular films has prompted development of methods for measuring adsorption of molecules from vapor or liquid phases. Many of these processes share a common feature, namely they are accompanied by changes in mass at the solid surface.
During the 1990s a new analytical method for the in situ examination of interfacial electrode processes, the electrochemical quartz crystal microbalance (EQCM), has emerged that has substantially influenced electrochemical science. This method relies on a single crystal of quartz that has been cut into a thin wafer and coated with gold electrodes on both sides. These electrodes are used to provide an alternating electric field so that the crystal is vibrated at a specific resonant frequency, while one of the electrodes is simultaneously used as a working electrode in an electrochemical cell. The resonant frequency shifts upon changes in mass that occur on the working electrode during an electrochemical process, with sensitivity as high as 100 pg cm−2 of electrode area. Recent developments also have illustrated that the quartz crystal microbalance (QCM) is capable of measuring the viscosity and density of liquids near the QCM surface. The purpose of this article is to provide the reader with a fundamental understanding of the EQCM and several illustrative examples of applications that demonstrate its unique capabilities, as well as the technical details required to build this apparatus.