<title>Tests of the sensitivity and mass range of a 50-MHz quartz crystal microbalance (QCM)</title>

Abstract

When used on a spacecraft to measure outgassing/erosion rates, a 50 MHz QCM is twenty-five times more sensitive than a 10 MHz QCM, according to theoretical considerations. In a continuation of extending the sensitivity of the QCMs, the frequency range, which is a measurement of mass flux, has increased from 15 MHz to 25 MHz to a now reported 50 MHz crystal sensor. As reported in the previous investigation of the 25 MHz crystal by Wallace, et. al., we again used a thin film interference technique to determine the mass sensitivity of the crystal. Water ice was used as the deposition film and, from known density, interference properties of the resulting film gave the resulting film thickness. Thus the sensitivity of the crystal and also the mass range of operation, with the driving electronics, could be determined. Theoretical sensitivity of the 50 MHz crystal would be 5.657 X 10<SUP>9</SUP> Hz/g/cm<SUP>2</SUP> or 0.176 ng/cm<SUP>2</SUP>-Hz.