High mass sensitivity miniaturized quartz crystal microbalances (QCMs) for space applications

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High mass sensitivity miniaturized quartz crystal microbalances (QCMs) for space applications

Wallace, D.A. / Wallace, S.A.

The use of piezoelectric QCMs (quartz crystal microbalances) for the measurement of mass flux that is deposited on a surface for space applications has historically been limited to the use of crystals having a resonant frequency of, at most, 15 MHz, because of the difficulty of working with the small dimensions in thickness that are associated with such crystals. A new series of QCMs and TQCMs (thermoelectrically-cooled QCMs) with crystal frequencies upward to 25 MHz, has recently been developed. These are not only physically much smaller than earlier models, but also extend the mass senstivity range upward by a factor of 3.33 over the 15 MHz theoretical value of 5.102x10⁸ Hz cm²/g to about 1.7x10⁹ Hz cm²/g, lowering the limit of discernible condensate thickness measurement to approximately 0.06 angstrom/Hz. In this paper, the experiments on the comparative measurements of the mass sensitivity of the crystals at 25 MHz and the mass range that is available with these highly sensitive crystals were discussed. Also the profiles of the miniature crystals and the mass sensitivity of the plano-plano crystals versus the curved profile crystals were addressed.