Influence of surface roughness on quartz crystal microbalance measurements in liquids

The influence of nanometer scale surface roughness on the frequency and dissipation responses of a quartz crystal microbalance operating in a liquid environment has been investigated by exposing quartz crystals, with a rough tantalum coating, to water solutions with varying concentrations of sucrose. A clear correlation between the measured surface roughness and the frequency shift is observed, while the shift in the dissipation factor is nearly unaffected by an increase in surface roughness. The experimental results are compared to published theoretical models for the frequency shift and shift in dissipation factor which incorporate roughness effects. For a high surface roughness the data cannot be satisfactorily explained by a model where the only effect of roughness is rigidly coupled liquid. A more advanced model, taking pressure gradients into account, provides a better description of the data.