Quartz Crystal Microbalance (QCM) Applications to Tribology

Scientific Fundamentals The quartz crystal microbalance (QCM) has been used as a nanoweighing device for many decades due to the high sensitivity of its resonant frequency, enabling measurements of as little as a tenth of a monolayer of adsorption (Sauerbrey 1959).When a voltage is applied to a piezoelectric, like quartz, it will mechanically deform according to the crystal’s orientation respective to the applied voltage. Since the focus here is on transverse (shear) deformation, the most commonly cut crystal for these purposes is AT-cut, which is oriented at angles of y = 35 150 from normal. When an alternating voltage is applied to the metal electrodes of an AT-cut QCM, it will mechanically oscillate at its fundamental frequency in transverse shear mode at a very high quality factor (Q) of around 10. An ATcut QCM is optimized for frequency stability and low temperature coefficient at room temperature. Figure 1 shows a diagram of a QCM and a side view of the oscillation. The resonant frequency depends on the thickness of the quartz and can typically range from 5 to 10 MHz. This technique assumes a thin, uniformly covered layer that is rigidly attached for a direct proportionality between the negative change in resonant