Vibration amplitude of a tip-loaded quartz tuning fork during shear force microscopy scanning

This Note reports on experimental results obtained with a recently published vision method for in-plane vibration measurement [Sandoz et al., Rev. Sci. Instrum. 78, 023706 (2007)]. The latter is applied to a tip-loaded quartz tuning fork frequently used in scanning probe microscopy for shear-force monitoring of the tip-sample distance. The vibration amplitude of the tip-loaded prong is compared to that of the free one and the damping induced by tip-surface interactions is measured. The tuning-fork behavior is characterized during approaches from free space to surface contact. Tip-surface contact is clearly identified by a drastic reduction in the prong vibration amplitude. However, no differences were observed between hydrophilic and hydrophobic surfaces. Experiments reported here show that the vibration amplitude of the quartz tuning fork in free space is a good estimate of the vibration amplitude of the tip interacting with the sample surface during shear force sample-tip feedback. The experimental setup for measuring the amplitude is easily integrated in an inverted microscope setup on which the shear force microscope is installed for simultaneous scanning probe and optical microscopy analysis of the sample.