VISCOELASTIC PROPERTIES OF THIN-FILMS PROBED WITH A QUARTZ CRYSTAL RESONATOR

We report on the application of quartz crystal resonators to the characterization of visco-elastic thin organic layers. A passive measurement of the quartz crystal's electrical impedance allows the measurement of its resonant frequencies as well as its damping in a number of vibration modes ranging in frequency from about 4 MHz to about 100 MHz. A parallel ellipsometer setup is used for simultaneous optical characterization. When one side of the quartz resonator is coated with a sufficiently soft material, the change in frequency and damping of the quartz is modified by the visco-elastic shear compliance of the layer. The visco-elastic constants can be derived. The method, therefore. has the unique capability to visco-elastically characterize thin films in the frequency range of f = 4-100 MHz. Results are presented on the first-order phase-transition of a polymerizable phospholipid and on UV-induced softening of a LB film of a hairy-rod molecule.