Role of mass accumulation and viscoelastic film properties for the response of acoustic-wave based chemical sensors

The sensitivity of acoustic-wave microsensors coated with a viscoelastic fi lm to mass changes and film modulus (changes) is examined. The study analyz es the acoustic load at the interface between the acoustic device and the c oating. The acoustic load carries information about surface mass and film m odulus; its determination has no restrictions in film thickness. Two regime s of film behavior can be distinguished: the gravimetric regime, where the sensor response is mainly mass sensitive, and the non-gravimetric regime, w here viscoelasticity gains influence on the sensor response. We develop a m ethod, which allows the assignment of the sensor signal to a gravimetric or a nongravimetric response. The critical value can be determined from oscil lator measurements. The related limits for the coating thickness are not th e same for the coating procedure and mass accumulation during chemical sens ing. As an example, we present results from a 10 MHz quartz crystal resonat or.