SENSITIVE MASS MEASUREMENT AT THE METAL/LIQUID INTERFACE.

Abstract

An analysis is presented which is based directly on the physics of the quartz/liquid interface, and provides both a quantitative relation between the changes in resonant frequency with the liquid properties and an intuitive understanding of why the mass sensitivity remains unchanged upon immersion into liquids. From the differential equations describing each medium, expressions are obtained for the shear waves in each. In the quartz, there is an undamped standing wave while in the liquid, a transmitted shear wave propagates away from the interface and is strongly damped. At the interface, the shear velocity of the quartz is matched to that of the liquid. It is found that the frequency changes of an AT cut quartz oscillator in liquid result from the mass of the liquid coupled to its surface as well as the mass of specific deposits. The independence of these two effects is verified by comparing the frequency change observed upon the electrodeposition of copper to that predicted by the theory developed for use in vacuum.