While several in-situ methods are available to CVD , few are as readily available for installation in almost any deposition chamber as the quartz crystal microbalance (QCM) sensor, which has a long history in studies of the surface chemistry in CVD processes. The QCM setup consists of a quartz crystal (a piezoelectric material), coated with metallic electrodes on the back-and front side of the quartz crystal. By applying an AC voltage to the metallic electrodes, a shear deformation of the quartz is induced, making it oscillate back and forth in an anti-parallel fashion at its resonant frequency. The resonant frequency shifts when mass adsorb to or desorb from the front electrode. Thus, the QCM can monitor instantaneous changes in adsorbed/desorbed mass by probing the shift in resonant frequency of the quartz crystal, according to Sauerbrey's equation: