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By Gerardo A. Brucker, Product Design Manager,
Stanford Research Systems, Sunnyvale, CA
his is the first of two articles on the use of quartz crystal microbalances (QCM).You will be impressed
on what these instruments can accomplish and their applications.This first installment focuses on basics
and measurement capabilities.The following article will address new applications.

WHAT ELSE CAN A QCM DO? surface of QCM electrodes. The results (1) Rm (resistor) corresponds to the
of his work are embodied in the dissipation of the oscillation ener-
The first practical application of
Sauerbrey equation, which relates the gy from mounting structures and
Quartz Crystal Microbalance (QCM)
mass change per unit area at the QCM from the medium in contact with
sensors was as thickness and deposition-
electrode surface to the observed change the crystal (i.e. losses induced by a
rate monitors for gas phase, thin-film
in oscillation frequency of the crystal: viscous solution or film)
processing in the vacuum coating indus-
(2) Cm (capacitor) corresponds to the
try. f = - Cf . m
6 6 (equation 1)
stored energy in the oscillation and
For many years, QCMs were regard-
where, is related to the elasticity of the
ed exclusively as gas-phase mass detec-
f - the observed frequency change, in
6 quartz and the surrounding medi-
tors; however, more recently their appli-
Hz, um
cation has been extended since scientists
m - the change in mass per unit area, in
6 (3) Lm (inductor) corresponds to the
realized that they can be operated in
g/cm2, and inertial component of the oscilla-
contact with liquids and viscoelastic
Cf - the sensitivity factor for the crystal tion, which is related to the mass
deposits. In this case, both frequency
used (i.e. 56.6 Hz