Quartz crystal microbalance study of the interfacial nanobubbles.

The applications of quartz crystal microbalance (QCM) to the study of surface and interfacial science such as adsorption have become progressively common and popular these days. In this work, QCM with dissipation monitoring was used to study the formation of nanobubbles on bare and thiol-coated gold surfaces. The nanobubbles were produced using one of the established solvent exchange protocols and the formation was first confirmed by the tapping mode atomic force microscopy (AFM). By QCM measurements, we found that the formation of nanobubbles on the hydrophobic crystal surfaces can yield easily detectable shifts of frequency and dissipation from those measured directly in water without the presence of nanobubbles. The direction of the shifts is consistent with the depletion of water by gases of lower density. We also found that the formation of nanobubbles is a fast process and can be finished in less than a minute. The response of QCM at several overtones showed that nanobubbles cannot be used to explain why the shift in the half bandwidth is sometimes smaller than the negative frequency shift at higher overtones when the QCM crystal is operated in liquids.